Showing papers by "University of Texas Southwestern Medical Center published in 1980"

The scavenger cell pathway for lipoprotein degradation: specificity of the binding site that mediates the uptake of negatively-charged LDL by macrophages.

Abstract: Macrophages isolated from a variety of organs in several animal species exhibit high affinity binding sites that recognize chemically modified proteins. One of these binding sites recognizes human plasma low density lipoprotein (LDL) in which the positive charges on the epsilon-amino groups of lysine have been removed or neutralized by chemical modification, thus giving the protein an enhanced negative charge. Effective treatments include reaction of LDL with organic acid anhydrides (acetylation or maleylation) and reaction with aldehydes, such as treatment with malondialdehyde. After the negatively-charged LDL binds to the surface receptor sites, it is rapidly internalized by the macrophages by endocytosis and hydrolyzed in lysosomes. The liberated cholesterol is reesterified in the cytoplasm, producing massive cholesteryl ester deposition. The binding sites for negatively-charged LDL has been demonstrated so far only on macrophages and other scavenger cells. It is not expressed in cultured fibroblasts, smooth muscle cells, lymphocytes, or adrenal cells. In addition to its affinity for acetylated LDL and malondialdehyde-treated LDL, the macrophage site binds a variety of polyanions. It exhibits a particularly high affinity for certain sulfated polysaccharides (dextran sulfate and fucoidin), certain polynucleotides (polyinosinic acid and polyguanylic acid), polyvinyl sulfate, and maleylated albumin. It is possible that the site that binds negatively-charged LDL may be responsible for the massive accumulation of cholesteryl esters that occurs in vivo in macrophages and other scavenger cells in patients with high levels of circulating plasma LDL.

Activation of skeletal muscle myosin light chain kinase by calcium(2+) and calmodulin.

Abstract: Many biological processes are now known to be regulated by Ca2+ via calmodulin (CM). Although a general mechanistic model by which Ca2+ and calmodulin modulate many of these activities has been proposed, an accurate quantitative model is not available. A detailed analysis of skeletal muscle myosin light chain kinase activation was undertaken in order to determine the stoichiometries and equilibrium constants of Ca2+, calmodulin, and enzyme catalytic subunit in the activation process. The analysis indicates that activation is a sequential, fully reversible process requiring both Ca2+ and calmodulin. The first step of the activation process appears to require binding of Ca2+ to all four divalent metal binding sites on calmodulin for form the complex, Ca42+-calmodulin. This complex then interacts with the inactive catalytic subunit of the enzyme to form the active holoenzyme complex, Ca42+-calmodulin-enzyme. Formation of the holoenzyme follows simply hyperbolic kinetics, indicating 1:1 stoichiometry of Ca42+-calmodulin to catalytic subunit. The rate equation derived from the mechanistic model was used to determine the values of KCa2+ and KCM, the intrinsic activation constants for each step of the activation process. KCa2+ and KCM were found to have values of 10 microM and 0.86 nM, respectively, at 10 mM Mg2+. The rate equation using these equilibrium constants accurately predicts the extent of enzyme activation over a wide range of Ca2+ and calmodulin concentrations. The kinetic model and analytical techniques employed herein may be generally applicable to other enzymes with similar regulatory schemes.

Feedback Regulation of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase in Livers of Mice Treated with Mevinolin, a Competitive Inhibitor of the Reductase

Abstract: Compactin (ML-236B) and the related compound, mevinolin, are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase), the rate-controlling enzyme in cholesterol synthesis. Previous studies have shown that administration of compactin to cultured cells elicits a compensatory increase in the amount of HMG CoA reductase in the cells. A similar increase in HMG CoA reductase has been reported in livers of rats and mice that have been treated with compactin. In this study, we explore the mechanism for the mevinolin-mediated increase in hepatic HMG CoA reductase in mice that have been fed a control diet and a 2% cholesterol diet. Administration of mevinolin to mice on a control diet produced a 6- to 10-fold increase in the amount of HMG CoA reductase in liver microsomes. When mice were fed the cholesterol-enriched diet, cholesterol accumulated in the liver and HMG CoA reductase declined by 90%. The administration of mevinolin to cholesterol-fed mice produced a three to eightfold increase in HMG CoA reductase. Despite the abundant amount of cholesterol that was already present in the livers of the mevinolin-treated, cholesterol-fed animals, their elevated HMG CoA reductase could be rapidly suppressed by the subcutaneous injection of small amounts of mevalonate, the product of HMG CoA reductase. These data are compatible with the existence in mouse liver of a multivalent feedback regulatory mechanism for HMG CoA reductase in which suppression of the enzyme requires both a sterol and a nonsterol substance derived from mevalonate. By blocking mevalonate synthesis, mevinolin activates this regulatory mechanism, and this in turn causes an increase in hepatic HMG CoA reductase. The ability to suppress the elevated HMG CoA reductase with mevalonate may prove useful in potentiating the effectiveness of mevinolin as a hypocholesterolemic agent.

Initial characterization of monoclonal antibodies against human monocytes

Abstract: Three monoclonal antibodies against human monocytes have been produced by somatic cell fusion. Extensive specificity analysis suggests that these antibodies react with most if not all human peripheral blood monocytes and not with highly purified T or B cells. Initial chemical characterization of the monocyte antigen recognized by two of these antibodies is presented. The molecule is a single polypeptide chain with an apparent molecular weight of 200,000. These reagents should prove useful in the clinical definition of disorders of monocyte differentiation, in studies of monocyte function, and in the elucidation of the genetics and structure of monocyte cell surface antigens.

Nongeometric determination of left ventricular volumes from equilibrium blood pool scans

Abstract: This study assesses the utility of a scintigraphic, nongeometric technique for the determination of left ventricular volumes. Accordingly, gated blood pool scintigraphy and cineangiography were performed within a 24 hour period in 22 patients. Scintigraphic volume measurements were calculated from individual frames of a modified 35 degrees left anterior oblique projection using an algorithm designed to consider (1) the background-corrected left ventricular activity normalized for activity per milliliter of peripheral venous blood; (2) total study time; (3) number of frames acquired per cardiac cycle; and (4) percent of the cardiac cycle acquired. Angiographic volumes were calculated by the area-length method and the Kennedy regression equation. There was an excellent correlation between scintigraphic and angiographic methods for all volume measurements grouped together (r = 0.985, standard error of the estimate [SEE] = 14.6 ml) as well as for segregated end-diastolic volumes (r = 0.985, SEE = 16.2 ml) and end-systolic volumes (r = 0.988, SEE = 14.7 ml). Prospective testing of the independent ability of scintigraphy to estimate ventricular volumes was provided for by studying an additional 13 patients, and good agreement was found between scintigraphic and angiographic determinations of left ventricular end-systolic and end-diastolic volumes. Thus, radionuclide techniques, which are independent of geometric assumptions, may be utilized for the quantitation of left ventricular volumes.

The use and misuse of androgens

Abstract: Because testosterone is rapidly metabolized by the liver, it is necessary either to administer androgens by injection in the form of testosterone esters that are absorbed slowly into the circulation or to administer by mouth derivatives that are slowly metabolized by the liver. The later derivatives, however, have deleterious side effects that limit their usefulness. Long-acting parenteral androgen esters are the treatment of choice in the replacement therapy of male hypogonadism. Because these esters must be hydrolyzed to the free hormone prior to exerting their cellular actions the effectiveness of therapy can be monitored by following plasma testosterone levels. All known effects of the endogenous hormone can be duplicated except for the induction and maintenance of normal spermatogenesis. Androgens have been tried in a variety of clinical situations other than male hypogonadism in the hopes that the nonvirilizing actions would outweigh any detectable side effects. The only disorders in which a salutary effect has been documented are hereditary angioneurotic edema and some patients with anemia due to failure off the bone marrow.

Evidence Justifying a High Fluid Intake in Treatment of Nephrolithiasis

Abstract: We quantitatively assessed the effect of urinary dilution on the crystallization of calcium salts. Urinary dilution was achieved in vitro (1 to 2 L/d) by addition of water to urine from six patients with renal stones and two normal subjects, and in vivo (1.023 to 2.383 L/d) by an increased ingestion of distilled water in four patients with nephrolithiasis and three normal subjects. Both forms of urinary dilution significantly reduced the urinary activity product ratio (state of saturation) of calcium phosphate (brushite), calcium oxalate, and monosodium urate. Moreover, the formation product ratio (limit of metastability or minimum supersaturation needed to elicit spontaneous nucleation) of calcium oxalate significantly increased, although that for brushite did not change significantly. Thus, there was a reduced propensity for crystallization of calcium salts. The results provide objective evidence for the beneficial role of an increased fluid intake in the management of nephrolithiasis.

Release of dopamine from tuberoinfundibular neurons into pituitary stalk blood after prolactin or haloperidol administration

Abstract: The effects of PRL or haloperidol on the release of dopamine from tuberoinfundibular neurons were assessed by measuring the concentrations of dopamine in hypophysial portal plasma. The mean concentration of dopamine in portal plasma of male rats which had received an intracerebroventricular injection of PRL or a sc injection of haloperidol on the day before the collection of pituitary stalk blood was approximately 5 times that in stalk plasma of vehicle-treated control rats. The haloperidol- induced increase in the concentration of dopamine in pituitary stalk plasma appeared to be PRL mediated, since this effect of haloperidol was significantly attenuated in rats which had been pretreated with antiserum to PRL. These observations are consistent with the view that the mechanisms involved in the release of dopamine from tuberoinfundibular neurons are regulated, in part, by PRL. Moreover, in view of the inhibitory effect of dopamine on PRL secretion, a PRL-induced increase in the release of dopamine from tub...

Lysosomal alterations in hypoxic and reoxygenated hearts. I. Ultrastructural and cytochemical changes.

Abstract: Rabbit hearts perfused under hypoxic conditions underwent progressive subcellular damage, which becomes irreversible by one hour. During the first 20 minutes of perfusion, minor dilation of mitochondria and condensation of nuclear chromatin were the only salient features of cell injury. By 40 minutes moderate mitochondrial swelling was evident in hypoxic myocytes. Moreover, an increase in degenerating mitochondria and autophagic vacuoles was apparent. Reperfusion after either 20 or 40 minutes of hypoxia restored contractility, and injured myocytes underwent a cellular repair process that involved a dramatic increase in lysosomal autoplagy. One hour of hypoxia yielded irreversibly injured myocytes. Upon reoxygenation, some of these cells displayed typical changes of necrosis, but others apparently underwent an abortive repair process involving the formation of large, probably nonfunctional lysosomes. These observations suggest that lysosomal autophagy is important in the efforts at repair that cardiac cells initiate during and after hypoxia.

Selective killing of normal or neoplastic B cells by antibodies coupled to the A chain of ricin

Abstract: Highly specific antibodies (affinity-purified or hybridoma) directed against cell surface immunoglobulins on normal or neoplastic murine B lymphocytes were covalently coupled to the A chain of the plant toxin ricin. Such conjugates containing antibodies specific for IgM, for either of the two allotypes of IgD, or for the idiotype of the B cell tumor BCL1 rapidly bound in vitro to cells expressing the corresponding surface antigen and inhibited protein synthesis in such cells. The results demonstrate that A chain-coupled anti-idiotype antibody may be useful as a tumor-specific cytotoxic agent.

Echocardiographic left ventricular masses in distance runners and weight lifters

Abstract: Sixty individuals including 17 competitive weight lifters (CWL), 12 competitive long-distance runners (LDR), 7 amateus (noncompetitive) weight lifters (AWL), 14 heavy controls (HC), and 10 light controls (LC) were studied at supine rest with echocardiographic determination of the left venticular mass (LVM) by the Penn convention. Lean body mass (LBM) was estimated by the Wilmore-Behnke method. The absolute LVM (mean +/- SE) was increased in the two competitive athlete groups compared to controls (LDR: 195 +/- 12; CWL: 190 +/- 10 vs. LC: 122 +/- 10; HC: 151 +/- 9 g). The AWL had a mass (174 +/- 20 g) intermediate between the LDR-CWL and the HC-LC groups. A significant (P = 0.033) correlation of LVM was found with LBM although the correlation coefficient was low (r = 0.276). Normalizing LVM by LBM revealed a significantly higher mass for LDR compared to all other groups but equalized CWL and HC (LDR: 3.2 +/- 0.2; CWL: 2.5 +/- 0.1; AWL: 2.5 +/- 0.2; HC: 2.3 +/- 0.2; LC: 2.0 +/- 0.2 g). These data suggest that training for competitive long-distance running (dynamic training) elevates LVM compared to nonathletic controls and CWL. On the other hand, training for weight lifting (static training) increases absolute LVM but only to the extent that LBM is increased.

Systemic immune unresponsiveness induced in adult mice by anterior chamber presentation of minor histocompatibility antigens.

Abstract: The ability to introduce carefully controlled numbers of viable cells into the anterior chamber of mouse eyes made it possible to examine the interrelationship between presentation of antigens into the anteior chamber and into conventional body sites and their synergistic/antagonistic effects on the immune system. P815 mastocytoma (DBA/2; H-2d) cells are syngeneic with BALB/c hosts at the major histocompatibility locus, but differ at multiple minor histocompatibility loci. When P815 cells were injected subcutaneously, they were rejected by BALB/c recipients who became specifically immune. By contrast, when P815 cells were injected intracamerally, they grew progressively into massive intraocular tumors; moreover, these BALB/c hosts proved subsequently unable to reject subcutaneously injected P815 cells, and, more impressively, failed to reject DBA/2 skin allografts placed orthotopically. Minor histocompatibility antigens, presented first through the anterior chamber of mouse eyes, elicit a suppressive rather than an aggressive host immune response that protects cells that bear these antigens from a destructive alloimmune reaction at both intracameral and systemic sites.

Splanchnic somatostatin: a hormonal regulator of nutrient homeostasis.

Abstract: Free (approximately 1600 daltons) somatostatin-like immunoreactivity was identified in arterial plasma of dogs that had received a test meal. Neutralization of circulating somatostatin while the dogs were consuming a fatty meal increased the plasma concentrations of triglycerides, gastrin, pancreatic polypeptide, and insulin after the meal. It is concluded that, in the dog, somatostatin is a true hormone that regulates the movement of nutrients from the gut to the internal environment.

Regulation of cholesterol and progesterone synthesis in human placental cells in culture by serum lipoproteins.

Abstract: Employing dispersed human trophoblastic cells in primary culture, the role of serum lipoproteins in regulating the synthesis of cholesterol and progesterone by the human placenta was investigated. The rate of secretion of progesterone by trophoblastic cells maintained in medium containing lipoprotein- poor serum was 100—190 ng mg−1 cell protein, whereas progesterone secretion by cells maintained in medium containing low density lipoprotein (LDL) increased as a function of LDL concentration, reaching a rate of 390 ng mg−1 cell protein 24 h−1 at an LDL concentration of 420 μg protein/ml. The rate of progesterone secretion by trophoblastic cells maintained in media containing high density lipoprotein in various concentrations (0—1000 /xg protein/ml) was also investigated. At high density lipoprotein concentrations of 1000 ng/ml, the rate of progesterone secretion by the trophoblastic cells was half that attained by cells maintained in medium containing LDL. The rate of incorporation of [14C]acetate into chol...

Changes in Nerve Conduction Velocity After Six Weeks of Glucoregulation With Portable Insulin Infusion Pumps

Abstract: Near normal glucoregulation was maintained in 10 patients with insulin-dependent (type I) diabetes mellitus for 6 wk with preprogrammed continuous subcutaneous insulin infusion using a portable battery-powered infusion pump (CSII). This form of therapy resulted in a statistically significant increase in motor nerve conduction velocity in the median and peroneal nerves compared with baseline values. There was no significant change in the motor nerve conduction velocity in the ulnar nerve or in the sensory nerve conduction studies. No changes occurred in five additional patients studied in similar fashion while on a conventional insulin regimen. These results suggest that the prevention of sustained hyperglycemia with CSII could theoretically result in the prevention of diabetic neuropathy. However, only long-term studies of CSII will provide the information necessary to determine the clinical relevance of the findings.