Showing papers in "Experimental Biology and Medicine in 1991"

Prolactin and growth hormone in the regulation of the immune system.

Abstract: Evidence implicating prolactin (PRL) and growth hormone (GH) in the regulation of the immune system has been reviewed. Hypophysectomized animals have deficiencies in both cell-mediated and humoral immunological functions and either PRL or GH corrects these deficiencies. Animals administered bromocryptine, a drug that specifically blocks PRL release, have impaired immune responses similar to hypophysectomized animals, and again both PRL and GH correct these deficiencies. Genetically dwarf animals, which lack both PRL and GH, are also immunocompromised, and once again PRL and GH can correct the deficiencies. In dwarf animals, however, fewer studies have examined PRL actions. In growth-deficient children, immune function is not dramatically altered and basal secretion of GH has been reported. Very few clinical studies have examined whether PRL secretion is also deficient, and this may explain why a clear loss in immune function is not evident in growth-deficient children. In a number of species, including man, both PRL and GH stimulate thymic function and increase the secretion of thymulin, a thymic hormone. No studies, however, have reported on the effects of PRL and GH on other thymic hormones. A number of studies have reported in vitro effects of PRL and GH on cells involved with immunity, and the presence of high-affinity PRL and GH receptors have been observed on a number of these cells. The action of GH on the proliferative response of cells involved with immunity in vitro appears to be mediated by the production of insulin-like growth factor I. The effect of PRL on insulin-like growth factor I production by these cells has not been examined. One of the most consistent findings from in vitro studies is that prolactin antisera blocked a number of immune reactions. This led to the discovery that cells involved with immunity appear capable of producing PRL and GH, but the physiological significance of these observations have not been explored. There is a great need to identify the cell types responding to PRL and GH and this should be a goal of future investigations. There is also a need for investigators to be aware that both PRL and GH are involved in the regulation of the immune system and to design experiments to elucidate where each functions in the maturation cascade of cells involved with immunity. From the evidence available, it is apparent that PRL and GH have an important function in the immune system and future investigations should be directed toward elucidating their site(s) of action.

Membrane cholesterol dynamics: cholesterol domains and kinetic pools.

Abstract: Nonreceptor mediated cholesterol uptake and reverse cholesterol transport in cells occur through cellular membranes. Thus, elucidation of cholesterol dynamics in membranes is essential to understanding cellular cholesterol accumulation and loss. To this end, it has become increasingly evident that cholesterol is not randomly distributed in either model or biologic membranes. Instead, membrane cholesterol appears to be organized into structural and kinetic domains or pools. Cholesterol-rich and poor domains can even be observed histochemically and physically isolated from epithelial cell surface membranes. The physiologic importance of these domains is 2-fold: (i) Select membrane proteins (receptors, transporters, etc.) are localized in either cholesterol-rich or cholesterol-poor domains. Consequently, the structure and properties of the domains rather than of the bulk lipid may selectively affect the function of proteins residing therein. (ii) Kinetic evidence suggests that cholesterol transport through and between membranes may occur through specific domains or pools. Regulation of the size and properties of such domains may be controlling factors of cholesterol transport or accumulation in cells. Recent technologic advances in the use of fluorescent sterols have allowed examination of cholesterol domain structure in model and biologic membranes. These techniques have been applied to examine the role of high-density lipoprotein, cholesterol lowering drugs, and intracellular lipid transfer proteins in membrane sterol domain structure and sterol movement between membranes.

Nonenzymatic glycation of collagen in aging and diabetes

Abstract: Considerable progress has been made in our understanding of nonenzymatic glycation of collagen, and the relationship between glycation of collagen and changes in connective tissue associated with aging and diabetes. Recent studies surveyed in this review suggest the following conclusions: 1. Collagen content of early glycation products does not appear to increase throughout the life span in normal human subjects, although small increases may occur that are linked to glycemic changes. These products are increased, relative to age-matched controls, in experimental diabetes and in diabetes mellitus in collagen from virtually all tissues analyzed. 2. Collagen content of browning products increases with aging and appears to be higher in diabetic subjects than in age-matched controls. Rates of accumulation may be accelerated in subpopulations of diabetic subjects at high risk for developing complications. 3. Increases in early glycation products do not appear to be associated with alterations in collagen solubility, thermal rupture time, or mechanical strength, nor is there an association with most diabetic complications. Alterations in these products may, however, affect conformation, ligand binding, lysyl oxidase-mediated cross-linking, and interactions between collagen and other macromolecules in the extracellular matrix. 4. Increased content of browning products is associated with many physicochemical changes in collagen as well as with long-term complications in diabetes mellitus. 5. Regulatory mechanisms have been identified in vivo that may serve to control or limit the formation of glycation products. 7. Pharmacologic agents have been identified that may be able to reduce collagen content of late glycation products. Despite the progress that has been made in this field, many areas of uncertainty and controversy exist. For example, there is not yet a consensus that the browning products associated with collagen exclusively comprise advanced Maillard products derived from nonenzymatically glycated residues. There is evidence that oxidative reactions involving lipids also play a role in generating fluorophores and chromophores that may alter properties of collagen. Thus, in the extracellular matrix collagen may be continuously modified by at least three very different processes: Maillard reactions, interactions with oxidizing lipids, and enzymatically mediated cross-linking. The interrelationships between these and possibly other posttranslational modifications remain a poorly understood area of great complexity.

Follistatin and activin: a potential intrinsic regulatory system within diverse tissues.

Abstract: Until the 1920s, it was assumed that the sole gonadal hormones modulating anterior pituitary glandular secretions were lipid-soluble entities called steroids. Experimental evidence then surfaced during the ensuing decade that demonstrated that the testis also contained a hydrophilic material that might also influence pituitary secretory activity (1, 2). The name “inhibin” was given to this novel substance in view of its ability to inhibit hypertrophy of pituitary cells in castrated rats (2). Work in later years evoked the concept that inhibin could be an important regulator of follicle-stimulating hormone (FSH) secretion (3, 4). Thus, as a consequence of these landmark studies, investigators began a search to elucidate the chemical nature of the inhibins.Although inhibin was discovered as a potential secretory product of the testis, it was almost 45 years later that a nonsteroidal FSH suppressor was demonstrated in the ovarian follicular fluid of cows (5). Ironically, it was the ovarian follicular fluid f...

Oxygen radicals and reactive oxygen species in reproduction.

Abstract: Free radicals and reactive oxygen species play a number of significant and diverse roles in reproductive biology. In common with other biological systems, mechanisms have evolved to minimize the damaging effects that these highly reactive molecules can have on reproductive integrity. Conversely, however, recent findings illustrate the constructive roles that oxygen radicals and reactive oxygen species play in a number of important junctures in the development of germ cells and the obligate endocrine support they receive for the successful propagation of the species. Specifically addressed in this review are some aspects of sperm development and action, the uterine environment, oocyte maturation and ovulation, and corpus luteum function and regression.

Oxygen-Reactive Species and Antioxidant Responses during Development: The Metabolic Paradox of Cellular Differentiation:

Abstract: Metabolic gradients are established during early phases of development and their existence influences subsequent developmental events. Variations in oxygen supply and oxygen metabolism associated with the gradation of metabolic rate in embryos appear to form one basis for the influence of metabolic gradients on development. The rate of oxygen metabolism affects the rate of oxidant generation by various cellular biochemical pathways. Cells contain antioxidant defenses that respond to variations in cellular oxidant production. Large changes in the activity of the antioxidant enzyme superoxide dismutase and changes in cellular redox state occur during the differentiation of many types of cells. These changes correspond to an increased rate of oxidant production; the cellular environment becomes more prooxidizing during differentiation. Evidence is presented that implicates oxidants as a factor that can stimulate alterations in gene expression. Possible mechanisms by which oxidants influence gene expr...

Platelet factor 4: production, structure, and physiologic and immunologic action.

Abstract: Platelet factor 4 (PF4) is a protein found in megakaryocytes and platelet α-granules (1, 2). Immunocytochemical studies show that it is present as well in mast cell granules (3) and on the endothelium of human umbilical veins, but not arteries (4). Early work on PF4 has been reviewed elsewhere (5–7). Human platelets contain about 18 ± 4 μg of PF4/109 (8).Thrombospondin, platelet-derived growth factor, and compounds derived from platelet basic protein such as β-thromboglobulin (β-TG) are found in platelet α-granules in addition to PF4. All are secreted when platelets are appropriately stimulated; for example, since thrombin is a strong stimulus, these compounds are present in much higher concentrations in serum than in plasma (e.g., 5334 vs 1.8 ng/ml for PF4 [9]). They are also secreted after contact of platelets with collagen in damaged blood vessels, for example.Production and StructurePF4 is synthesized by megakaryocytes (10), an ability that correlates with cytoplasmic maturity (2, 11). The PF4 is firs...

Copper transport: an overview.

Abstract: ConclusionsCopper transport continues to show unexpected and, in some cases, surprising departures from traditional mechanisms. Although both iron and copper bind to plasma proteins, the recent data suggest that each works through separate and distinct mechanisms for gaining access to cells. Ceruloplasmin and albumin as postulated transport carriers have withstood the test of time. One must concede, however, that there may be other serum proteins that perform a copper transport function. One thought not to be forgotten is that in postulating specific transport proteins for copper, one is showing an “animal bias.”Plants and some microorganisms also require copper, but there have yet to be found specific proteins that perform copper transport functions in these organisms. There is an immediate and pressing need to clarify the nature of the component(s) that conveys copper ions through the cell membrane. We stand to learn how copper is shielded from doing harm to membrane components and perhaps apply this in...

Nicotine inhibits collagen synthesis and alkaline phosphatase activity, but stimulates DNA synthesis in osteoblast-like cells.

Abstract: Use of smokeless tobacco is associated with various oral lesions including periodontal damage and alveolar bone loss. This study was performed to test the effects of nicotine on bone-forming cells at concentrations that occur in the saliva of smokeless tobacco users. Confluent cultures of osteoblast-like cells isolated from chick embryo calvariae were incubated for 2 days with nicotine added to the culture medium (25-600 micrograms/ml). Nicotine inhibited alkaline phosphatase in the cell layer and released to the medium, whereas glycolysis (as indexed by lactate production) was unaffected or slightly elevated. The effects on medium and cell layer alkaline phosphatase were concentration dependent with maximal inhibition occurring at 600 micrograms nicotine/ml. Nicotine essentially did not affect the noncollagenous protein content of the cell layer, but did inhibit collagen synthesis (hydroxylation of [3H]proline and collagenase-digestible protein) at 100, 300, and 600 micrograms/ml. Release of [3H]hydroxyproline to the medium was also decreased in a dose-dependent manner, as was the collagenase-digestible protein for both the medium and cell layer. In contrast, DNA synthesis (incorporation of [3H]thymidine) was more than doubled by the alkaloid, whereas total DNA content was slightly inhibited at 600 micrograms/ml, suggesting stimulated cell turnover. Morphologic changes occurred in nicotine-treated cells including rounding up, detachment, and the occurrence of numerous large vacuoles. These results suggest that steps to reduce the salivary concentration of nicotine in smokeless tobacco users might diminish damaging effects of this product on alveolar bone.

Dehydroandrographolide succinic acid monoester as an inhibitor against the human immunodeficiency virus.

Abstract: Dehydroandrographolide succinic acid monoester (DASM) is the dehydroandrographolyl ester of succinic acid; and andrographolide, from which DASM is made, is the major diterpenoid lactone found in the Chinese medicinal herb, Andrographis paniculata. DASM has been found to be an inhibitor against the human immunodeficiency virus (HIV) in vitro. It was nontoxic to the H9 cell at the concentrations of 50-200 (average, 108) micrograms/ml and was inhibitory to the HIV-1 (IIIB) at the minimal concentration of 1.6-3.1 (average 2.0) micrograms/ml. It was also inhibitory to two other strains of HIV-1 and a strain of HIV-2. This inhibitory effect could also be demonstrated in cultures of activated human blood mononuclear cells; the 50% toxic dose and the 50% HIV inhibitory dose were about 200-greater than or equal to 400 and 0.8-2 micrograms/ml, respectively. At the subtoxic concentration, DASM partially interfered with HIV-induced cell fusion and with the binding of HIV to the H9 cell. Presumably, it also interfered with HIV replication at another unidentified step(s).

The role of endogenous opioids and their receptors in the immune system.

Abstract: Opioid peptides appear to be dynamic signaling molecules that are produced within the immune system and are active regulators of an immune response. Furthermore, the receptors for these peptides occurring on immunocyte membranes share characteristics with neuronal opioid receptors, including molecular size, immunogenicity, and the use of specific intracellular signaling pathways. Recent studies of the interaction of opioids with cytokines have indicated that opioid peptides are intimately involved within the immune system. Specifically, opioids, including 2-n-pentyloxy-2-phenyl-4-methyl-morpholine, naloxone, and beta-endorphin, have been shown to interact with IL-2 receptors (134) and regulate production of IL-1 and IL-2 (48-50, 135). Conversely, IL-1 has been shown to up-regulate opioid peptide binding in brain tissue (136). Furthermore, the induction of IL-1 by opioids has also been identified in the invertebrate Mytilus, indicating the evolutionary conservation of this relationship (137). These results seem to typify the intricate association between the immune and neuroendocrine systems through opioid pathways. It is predicted that future endeavors will use this relationship to diagnose and treat specific diseases that have at their basis neuroendocrine and immunologic imbalances.

Oxygen free radicals as pathogenic molecules in viral diseases.

Abstract: Oxygen free radicals such as superoxide anion (O2-) were generated markedly in influenza virus-infected mouse lung, and these molecular species were identified as the potent pathogenic agents. This finding has many important implications for understanding viral pathogenesis: namely, the direct viral cytotoxicity (referred cytopathic effect) is only a fraction of several types of events induced by virus infection. The toxicity and reactivity of oxygen radicals, which are presumably generated in excessive amounts by the overreaction of the host's immune response against the organs or tissues in which viruses are replicating, may explain the mechanism of tissue injuries observed not only in influenza virus infection in mice, but also in other types of viral diseases in which immunological interactions are usually involved.ConclusionIt has become clear that O2- is the prime toxic molecule generated in the viral infection. The generation of O2- is sustained by an enhanced supply of catabolic products o...

The antiobesity effect of dehydroepiandrosterone in rats

Abstract: Initial studies showed that dehydroepiandrosterone (DHEA) treatment in mice resulted in lower body weight gain. Subsequent studies have shown that DHEA treatment in rats has a similar effect. In adult rodents, weight loss is a consequence of DHEA treatment. In general, these effects are independent of changes in food intake and are accompanied by lower body fat. DHEA treatment has been shown in some circumstances to alter a number of serum factors including glucose, insulin, cholesterol, and triacylglycerol. Recent studies have focused on the effects of DHEA on liver metabolism. Studies have been undertaken to determine whether the antiobesity effect of DHEA is mediated by the previously described inhibition of glucose-6-phosphate dehydrogenase by this steroid. It appears that inhibition of glucose-6-phosphate dehydrogenase in liver is not the initial metabolic response to DHEA but may play a contributing role. Inhibition of glucose-6-phosphate dehydrogenase in adipose tissue may affect differentiation of fat cells. A number of other enzymes involved in lipid and carbohydrate metabolism have also been shown to be altered by DHEA treatment, and several futile cycles involving some of these enzymes have been proposed to play a role in DHEA's antiobesity action. In addition, mitochondrial protein content is elevated by DHEA treatment. There appear to be time-dependent changes due to DHEA treatment on hepatic mitochondrial state three rates of respiration. Studies continue to evaluate the role of alterations in mitochondrial metabolism in DHEA's antiobesity action.

Estradiol Down-Regulation of the Rat Uterine Estrogen Receptor:

Abstract: We have previously shown that neonatal exposure of rats to pharmacologic doses of diethylstilbestrol via daily injections resulted in a significant decrease in the estrogen-binding capacity of the uterine estrogen receptor (ER). In this study, we examined the effects of physiologic and pharmacologic doses of estradiol (E2) administered to adult ovariectomized rats via Silastic implants. Two days after implantation, uteri were removed, weighted, and homogenized, and ER levels were determined in the supernatant (hydroxylapatite assay) and low-speed pellet (nuclear exchange assay). Implants containing E2 concentrations of 0.005 or 0.05 mg/ml increased cytosolic but not total ER-binding capacity, whereas 0.5 or 5.0 mg of E2/ml implants decreased the binding capacity of cytosol ER to 40% and total ER to 50% of control values. The 0.005-mg/ml dose increased cytosol ER without increasing uterine weight; all higher doses significantly increased uterine weight. Determination of ER protein by an ER radioimmunoassay showed the same extent of reduction of ER concentration as the binding assays, demonstrating that the loss in E2 binding capacity is homologous down-regulation. The down-regulation of ER was maximal at 24 hr and was completely reversible after implant removal, although the time required to recover from down-regulation was dose dependent. Uterine weight also returned to control levels slowly after implant removal. Neither the sedimentation rate of the down-regulated ER nor the Kd of the cytosolic ER changed following long-term implantation; however, the Kd of the nuclear ER decreased significantly. This is the first demonstration of in vivo homologous down-regulation of uterine ER. ER down-regulation may play a role in several biologic processes.

The role of cell proliferation in multistage carcinogenesis.

Abstract: Carcinogenesis is a complex process in which it is believed that normal cellular growth control genes are altered by sequential mutational events, with subsequent clonal growth of the resulting precancerous or cancerous cells (1, 2). The induction of mutations and the preferential clonal growth of the resulting premalignant or malignant cells, thus, become critical events in the stages of initiation, promotion, and progression in chemical carcinogenesis (Fig. 1). One class of chemical carcinogens are the genotoxicants. These compounds or their metabolites are DNA reactive and directly induce mutations or clastogenic changes. The observation that most mutagens are also carcinogenic is the basis for many current predictive assays and risk assessment models. However, there are also different classes of nongenotoxic carcinogens that do not interact with the DNA. The class designated as mitogens directly induces cell proliferation in the target tissue. Another class, the cytotoxicants, produces cell death foll...

Active oxygen species as factors in multistage carcinogenesis.

Abstract: Oxygen, a necessary element for the life of a cell, is also the source of active states of oxygen including radicals, which can disrupt cell structure and alter cell function. Increasing evidence indicates that active oxygen species are formed in response to tumor promoters and that the cellular consequences of their actions may play a role in the process of tumor promotion. This report summarizes work from our laboratory that implicates active oxygen species derived in part from phagocytic cells in the tumor promotion process by phorbol esters and other promoters in mouse skin. Work from other laboratories indicates that phorbol ester promoters stimulate the production of active states of oxygen in mouse skin epidermal cells in vivo and in vitro. Oxidative DNA damage in epidermal cells from mice treated topically with the potent promoter phorbol myristate acetate has also been reported. The production of active states of oxygen including free radicals is discussed in relation to the mode of actio...

Angiotensin-converting enzyme inhibition reduces neuroblastoma cell growth rate.

Abstract: Because of the known capacity of angiotensin II to serve as a growth factor in multiple tissues, we elected to study the effects of renin-angiotensin system inhibition on the growth of human SH-SY5Y neuroblastoma cells. Cells were treated with captopril (0.05-5 mg/ml), enalapril, or enalaprilat (0.02-5 mg/ml) or saralasin (0.1-0.25 mg/ml). In all cases, statistically significant reductions in cell growth were seen over 5 days of culture. In additional experiments, captopril and enalaprilat significantly decreased thymidine incorporation into DNA in these cells. The administration of angiotensin II in the presence of captopril partially offset these suppressive effects.

Homing of Hemopoietic Progenitor Cells to the Marrow

Abstract: The recognition of hemopoietic stem cell after intravenous transplantation of marrow cells occurs initially by a lectin moiety on the surface of marrow sinus endothelium. The cell is then transported across the endothelial cytoplasm much in the way that a soluble ligand, such as transferrin, is transported. In the extravascular compartment, the cell binds to lineage-specific stromal cells. This mechanism, known as homing, is mediated by a lectin-glycoconjugate interaction, the lectin being on the surface of progenitor cell with specificity for galactosyl and mannosyl residues. The binding is subsequently stabilized by membrane-bound proteoglycans, integrin-like receptors, and fibronectin.

Reduction of enhanced mammary carcinogenesis in LA/N-cp (Corpulent) rats by energy restriction

Abstract: Restriction of energy intake significantly reduces mammary tumorigenesis in normal rats exposed to carcinogens. Genetically obese LA/N-cp (corpulent) female rats were given 7,12-dimethylbenz[a]anthracene and fed purified diets ad libitum or restricted to 60% of the ad libitum caloric intake. Phenotypically lean littermates were also fed ad libitum. Obese animals developed large mammary tumors more rapidly than genetically normal rats so that 100% of the animals had tumors in less than 16 weeks. Only 21% of the lean animals developed tumors; the energy restricted obese animals had a tumor incidence of 27%. Although obese rats fed the restricted diet weighed significantly less than those fed ad libitum, percent body fat was not reduced, indicating that lean tissue was affected more. Obese animals were markedly hyperinsulinemic (1003 +/- 193 microunits/ml) and energy restriction reduced this to 328 +/- 41; the lean animals had insulin levels of 12 +/- 2. Tumor-bearing rats had higher insulin levels than rats without tumors. These data suggest that body fatness is not directly associated with risk of carcinogenesis. Lean body mass, adipose tissue mass, and their interaction with insulin in its capacity as a growth factor rather than body fatness per se may be determinants of tumor promotion.

Genetic obesity: is the defect in the sympathetic nervous system? A review through developmental studies in the preobese Zucker rat.

Abstract: ConclusionThe chronological analysis of anomalies that emerge within the first postnatal week in fa/fa rats strongly suggests that increased lipid storage leading to obesity in Zucker rats is a consequence of a defect in energy expenditure. In the search for an unifying hypothesis that might explain the etiology of this genetic obesity, an alteration in the nervous system appears the most likely to agree with the monogenic transmittance of the syndrome. Such an alteration could cause a general defect in the peripheral organs, which are sympathetically innervated, and explain the decreased thermogenesis in BAT of fa/fa rats and in other organs like skeletal muscles (via decreased futile cycles activity; 150). It may also explain the decrease in the peripheral utilization of triglycerides and glucose, principally by skeletal muscles and BAT, which results in excess circulating levels of these substrates that could then be shunted for storage in WAT.The hyperinsulinemia, which progressively develops in preob...

Effects of hypertension on aortic antioxidant status in human abdominal aneurysmal and occlusive disease.

Abstract: The biochemical mechanisms by which hypertension accelerates atherosclerosis and increases the risk of aortic aneurysm rupture are poorly understood. This study evaluates the effects of hypertension on aortic trace element concentrations and antioxidant status in tissue removed from 26 normotensive (NT) and 20 hypertensive (HT) patients. Twenty-seven of 46 patients (59%) had aneurysmal (AA), and 19 of 46 (41%) had occlusive disease (OD). Aortic iron concentrations were markedly higher in both OD and AA tissue compared with controls. A similar trend was observed with copper concentrations, with the highest elevations observed in HT AA tissues. No significant differences were observed in zinc concentrations, except that HT AA aorta had significantly lower zinc levels than either OD or control tissue. Aortic ascorbic acid concentrations in diseased aorta were lower than those of controls, but independent of blood pressure. Copper-zinc-superoxide dismutase activity was similarly reduced, with the lowest activity observed in diseased aorta from HT patients. Only HT AA aorta had significantly higher manganese-superoxide dismutase activity than controls. The aortas of patients with AA had significantly lower amounts of elastin and greater elastase activity than either controls or those with OD. However, the differences were independent of blood pressure. Hypertensive patients with OD and AA had 31% more and 27% less aortic collagen, respectively, than their NT counterparts (P less than 0.05). These data suggest that the reduction in aortic collagen and elastin in HT patients with AA compared with their NT counterparts may explain the larger size of aneurysms and predispose to their eventual rupture. Furthermore, the diminished antioxidant status associated with HT predisposes to lipid peroxidation, which contributes to the acceleration of these processes. Our studies were conducted in patients with established aortic aneurysmal and occlusive disease. Whether these observations are pertinent to the pathogenesis of AA and OD remains unclear and merits further study.

Bile acid accumulation in gastric mucosal cells.

Abstract: Bile acids are one of the components of the gastric contents capable of disrupting the mucosal barrier to diffusion. The mechanism by which bile acids can damage the gastric epithelium is not completely understood. Several studies have emphasized mucosal lipid solubilization by bile acids in the pathogenesis of mucosal injury. Bile acid entry into gastric mucosal cells may be a critical and early step in the genesis of mucosal injury, but this possibility has not yet been investigated. The present study was designed to explore the interaction of bile acids with dispersed gastric mucosal cells isolated from the rabbit and guinea pig stomach. Results showed that both glycocholic and deoxycholic acid rapidly associated with the gastric cells and reached a steady state concentration by 30 min. Glycocholic acid accumulated in the cells to a concentration approximately eight times greater than that in the surrounding medium. The amount of bile acid associated with the cells was greater at an acidic than...

Oxysterols, cholesterol biosynthesis, and vascular endothelial cell monolayer barrier function.

Abstract: A spectrum of cholesterol oxidation derivatives (oxysterols) is generated in food products exposed to heat or radiation in the presence of oxygen. One of these derivatives (cholestan-3 beta,5 alpha,6 beta-triol) was shown to compromise the selective barrier function of cultured vascular endothelial cell monolayers, an action that may initiate atherosclerotic lesion formation. This study sought to investigate the relationship of cholesterol synthesis inhibition by several naturally occurring oxysterols to depression of vascular endothelial cell monolayer barrier function, determined as an increase in albumin transfer across cultured endothelial monolayers. All oxysterols tested caused a variable time- and dose-dependent elevation in trans-endothelial albumin transfer, and they were also able to inhibit cholesterol biosynthesis to varying degrees. Pure cholesterol was without effect on both counts. The correlation between the increase in albumin transfer related to oxysterol exposure and the ability of oxysterols to suppress cholesterol biosynthesis was, however, poor. Moreover, mevinolin, a water-soluble competitive inhibitor of cholesterol synthesis, reduced the rate of cholesterol synthesis to 0.9% of control but did not significantly increase albumin transfer. Cholestan-3 beta,5 alpha,6 beta-triol caused a 660% elevation in albumin transfer while cholesterol synthesis remained at 11% of control. We conclude that changes in endothelial barrier function caused by exposure to the oxysterols examined, but not pure cholesterol, are probably related to factors other than the well-known action of cholesterol biosynthesis inhibition. These findings may have implications in the development of atherosclerosis.

Tumor Necrosis Factor-α Affects Growth Hormone Secretion by a Direct Pituitary Interaction

Abstract: Administration of 50, 250, and 1,250 ng/kg iv of recombinant bovine tumor necrosis factor-alpha (RBTNF) did not affect basal plasma concentrations of growth hormone (GH) or thyroid-stimulating hormone in male calves. However, when administered 30 min before challenge with 1 microgram/kg iv of thyrotropin-releasing hormone (TRH), 250 ng/kg of RBTNF increased the subsequent incremental GH response. At 1,250 ng/kg of RBTNF, GH response to TRH was significantly blunted. For each dose of RBTNF administered, the incremental change in plasma thyroid-stimulating hormone following TRH was not significantly different from control. To examine direct effects of RBTNF on pituitary function, fresh bovine pituitaries were sliced into 1-mm cubes and incubated with 0 or 10(-8), 10(-9), or 10(-10) M RBTNF. Additional cultures were treated with 10(-8) or 10(-9) M GH-releasing factor or 10(-8) M TRH and 0 or 10(-8) M RBTNF. Media GH increased in cultures with 10(-10) M RBTNF and declined linearly as RBTNF concentration increased. RBTNF blocked GH release from GH-releasing factor- and TRH-challenged pituitary slices. Membranes prepared from homogenized bovine pituitaries had specific saturable binding characteristics for monomeric 125I-RBTNF. Membranes treated with 4 M MgCl2 for 10 min and washed free of Mg2+ produced Scatchard plots fit to a two-site model (high affinity site Kd = 6.6 nM), while Scatchards of non-Mg(2+)-treated membranes fit a single site (Kd = 8.9 nM). Polyacrylamide gel electrophoresis separation of 125I-RBTNF cross-linked pituitary membranes showed specific binding of monomeric 125I-RBTNF to protein components ranging in molecular weight from 19,000 to 77,000. The data suggest that RBTNF has modulatory effects on the regulation of GH secretion acting directly at the pituitary through specific receptors.

High and moderate affinity pathways for alpha-thrombin-induced platelet activation.

Abstract: .The interpretive review represents evidence for two pathways of α-thrombin-induced activation in human platelets and evaluates the possible roles of a functional thrombin receptor recently identified by expression cloning. [P.S.E.B.M. 1991, Vol 198]

Relationship of liver and skeletal muscle IGF-1 mRNA to plasma GH profile, production of IGF-1 by liver, plasma IGF-1 concentrations, and growth rates of cattle.

Abstract: Growth hormone (GH), insulin-like growth factor-1 (IGF-1), and thyroid hormone (T3 and T4) concentrations in blood plasma of 18 crossbred cattle (six bulls, six steers, and six heifers) were measured over an 8-hr period. One week later at slaughter, IGF-1 production by liver slices and IGF-1 mRNA concentrations in skeletal muscle and liver were measured. Bulls had higher (P < 0.05) mean plasma GH and GH peak amplitudes (P c 0.01) than heifers, and values for steers were intermediate between bulls and heifers. Baseline GH concentrations and number of GH peaks were not significantly different for the three groups. Bulls had 1.6-fold (P c 0.01) and 3.0-fold (P C 0.01) greater liver IGF-1 mRNA concentrations than steers or heifers, respectively, whereas the steers had 1.8-fold (P c 0.05) greater IGF-1 mRNA in liver than heifers. Production of IGF-1 by liver slices was greater (P c 0.05) in bulls than steers or heifers. Bulls had 1.3-fold greater plasma IGF-1 than steers (P c 0.01), whereas steers had 1.8-fold greater plasma IGF-1 than heifers (P c 0.01). There were no significant differences in concen- trations of skeletal muscle IGF-1 mRNA between the three groups of animals. Liver IGF- 1 mRNA, liver IGF-1 production, and plasma IGF-1 were all significantly correlated with gain and mean GH peak amplitude, but not with GH baseline, GH peak frequency, or concentrations of T3 and T4. Concentrations of IGF-1 mRNA in skeletal muscle were not correlated to gain or any parameter of the GH profile. Plasma concentrations of T3 were significantly (P c 0.05) negatively correlated to plasma GH baseline concentrations. Muscle IGF-1 mRNA concentration was negatively related to plasma T4 and T3. The results of this study suggest that the cascade of events starting with secretion of GH from the pituitary, expression of liver IGF-1 mRNA, and secretion of IGF-1 by the liver are important phenomena for growth of cattle. (P.S.E.B.M. 1991, VoI 1961

Enhancement of antibody production by lysophosphatidylcholine and alkylglycerol

Abstract: Inflammation products of normal and cancerous tissues, lysophosphatidylcholine and dodecylglycerol, were tested for their adjuvant effect on the antibody response. Mice treated with these agents and immunized with sheep erythrocytes simultaneously or at 3 days posttreatment developed a greatly enhanced antibody production as demonstrated by the Jerne plaque assay. Mice immunized at 3 days postadministration of agents did not significantly produce enhanced antibody-secreting cells as compared with those of mice simultaneously immunized. Since the mechanism of macrophage activation by lysophospholipids requires contribution of B and T cells, BALB/c-nu/nu mice treated with these agents and subsequently immunized with sheep erythrocytes did not produce antibodies. However, conditioned medium of in vitro-treated BALB/c-nu/nu B cells efficiently transmitted a signal to untreated BALB/c +/+ T cells for enhanced macrophage ingestion activity. This observation suggests that lysophospholipid-activated macrophages and T cells efficiently transmitted antigenic signal to the antibody-producing B cell population. Therefore, we conclude that these lipid metabolites have dual beneficial effects for the host by enhancing phagocytosis and antibody production. Thus, lysophosphatidylcholine and dodecylglycerol have potential practical application as adjuvants that could be administered separately or in combination with antigens.

Physiologic importance of pyrroloquinoline quinone.

Abstract: 0-quinone cofactors derived from tyrosine and tryptophan are involved in biological reactions that range from oxidative deaminations to free-radical-related redox reactions. Among these cofactors, pyrroloquinoline quinone (PQQ) has excited interest because of its presence in foods, unusual chemical properties and role as a growth-promoting factor in animals. Oral supplementation of PQQ in the nmol/g-diet range has been shown to improve B- and T-cell responsiveness to mitogens, mitochondrial function and reproductive outcome in mice. PQQ is easily absorbed and efficiently taken up by cultured cells. Consequently, a case can be made that PQQ may have physiological importance in animals.

Sex hormones and tumor promotion in liver.

Abstract: Epidemiological and experimental data strongly support a causal relationship between exposure to excessive levels of estrogens and the development of cancer in various tissues. In this paper, we have presented background information that shows a correlation between the prolonged use of oral contraceptives and the development of liver cancer. The clinical data supported the hypothesis that the estrogenic components of oral contraceptives were promoters of hepatocarcinogenesis, and the experimental evidence in support of this hypothesis and bearing on the mechanisms involved are also reviewed. The effects of estrogens on liver neoplasia and growth are: (i) synthetic steroidal estrogens are potent promoters of hepatocarcinogenesis in female rats; (ii) these estrogens stimulate liver growth at doses that are not hepatotoxic; (iii) the mechanisms by which the estrogens stimulate liver growth are indirect and include the enhancement of a serum/plasma growth factor, co-mitogenic effects which result in enhanced responsiveness of cultured hepatocytes to epidermal growth factor and decreased sensitivity of hepatocytes to growth inhibition by transforming growth factor-beta; (iv) the co-mitogenic effects of synthetic estrogens extend to endogenous estrogens and natural product estrogens; and (v) the co-mitogenic effects of estrogens for epidermal growth factor are associated with increased epidermal growth factor receptor protein levels caused by an increase in the half-life of the receptor protein. The synthetic estrogens also have weak "complete" carcinogenic activity in rat liver and strong complete carcinogenic activity in Syrian hamster kidney and Armenian hamster liver. Evidence from the literature is presented in support of a hypothesis that this process may involve indirect genotoxicity mediated through redox cycling and the formation of hydroxylated DNA bases. This process, together with the potent promoting activity of these estrogenic chemicals, may account for their complete carcinogenicity.

Detection of growth hormone and growth hormone-releasing hormone-related messenger RNA in rat leukocytes by the polymerase chain reaction.

Abstract: To validate that growth hormone (GH) and growth hormone-releasing hormone (GHRH) can be produced by leukocytes, we have assessed the presence of GH and GHRH-related mRNA in leukocyte cultures by reverse transcription and the polymerase chain reaction. A sample of the polymerase chain reactions were size-fractionated by electrophoresis in a 0.8% agarose gel and examined with ultraviolet light after ethidium bromide staining. Single major DNA bands corresponding in length to the distance between the 5' ends of the two GH and GHRH specific primers, 603 base pairs and 260 base pairs, respectively, were obtained. The DNA bands hybridized specifically to GH- and GHRH-specific probes after Southern transfer to nitrocellulose. The identity of the GH polymerase chain reaction material was confirmed by restriction enzyme analysis. The results showed that GH and GHRH gene expression occurs in mononuclear leukocytes and support the idea that these neuroendocrine hormones may be common signal molecules between the immune and neuroendocrine systems.