Showing papers by "Baylor College of Medicine published in 1987"

A G protein directly regulates mammalian cardiac calcium channels.

Abstract: A possible direct effect of guanine nucleotide binding (G) proteins on calcium channels was examined in membrane patches excised from guinea pig cardiac myocytes and bovine cardiac sarcolemmal vesicles incorporated into planar lipid bilayers. The guanosine triphosphate analog, GTP gamma S, prolonged the survival of excised calcium channels independently of the presence of adenosine 39,59-monophosphate (cAMP), adenosine triphosphate, cAMP-activated protein kinase, and the protein kinase C activator tetradecanoyl phorbol acetate. A specific G protein, activated Gs, or its alpha subunit, purified from the plasma membranes of human erythrocytes, prolonged the survival of excised channels and stimulated the activity of incorporated channels. Thus, in addition to regulating calcium channels indirectly through activation of cytoplasmic kinases, G proteins can regulate calcium channels directly. Since they also directly regulate a subset of potassium channels, G proteins are now known to directly gate two classes of membrane ion channels.

Molecular cloning of complementary DNA encoding the avian receptor for vitamin D.

Abstract: Vitamin D3 receptors are intracellular proteins that mediate the nuclear action of the active metabolite 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Two receptor-specific monoclonal antibodies were used to recover the complementary DNA (cDNA) of this regulatory protein from a chicken intestinal lambda gt11 cDNA expression library. The amino acid sequences that were deduced from this cDNA revealed a highly conserved cysteine-rich region that displayed homology with a domain characteristic of other steroid receptors and with the gag-erbA oncogene product of avian erythroblastosis virus. RNA selected via hybridization with this DNA sequence directed the cell-free synthesis of immunoprecipitable vitamin D3 receptor. Northern blot analysis of polyadenylated RNA with these cDNA probes revealed two vitamin D receptor messenger RNAs (mRNAs) of 2.6 and 3.2 kilobases in receptor-containing chicken tissues and a major cross-hybridizing receptor mRNA species of 4.2 kilobases in mouse 3T6 fibroblasts. The 4.2-kilobase species was substantially increased by prior exposure of 3T6 cells to 1,25(OH)2D3. This cDNA represents perhaps the rarest mRNA cloned to date in eukaryotes, as well as the first receptor sequence described for an authentic vitamin.

Ameboid microglia as effectors of inflammation in the central nervous system

Abstract: Techniques for selective isolation, labeling, stimulation, and destruction of ameboid microglia allow study of some fundamental questions in neuroimmunology. Examination of surface morphology, proliferative capacity, and cytochemistry suggests that microglia are a class of brain mononuclear phagocytes distinct from blood monocytes, spleen macrophages, or resident peritoneal macrophages. Moreover, cultured ameboid microglia isolated from newborn brain can be induced to grow thin cytoplasmic projections several hundred microns in length; these process-bearing cells resemble a differentiated form of microglia found in adult brain. Ameboid microglia may contribute to brain inflammation by engulfing debris, by releasing cytotoxins, by killing neighboring cells, and by secreting astroglial growth factors. Importantly, ameboid microglia are closely tied to a network of immunomodulators that include colony-stimulating factors and Interleukin-1. The presence of activated microglia during normal embryogenesis and at sites of penetrating brain injury suggests that these cells serve as important effectors linking the immune system with growth and repair of the CNS.

Direct activation of mammalian atrial muscarinic potassium channels by GTP regulatory protein Gk

Abstract: The mammalian heart rate is regulated by the vagus nerve, which acts via muscarinic acetylcholine receptors to cause hyperpolarization of atrial pacemaker cells. The hyperpolarization is produced by the opening of potassium channels and involves an intermediary guanosine triphosphate-binding regulatory (G) protein. Potassium channels in isolated, inside-out patches of membranes from atrial cells now are shown to be activated by a purified pertussis toxin-sensitive G protein of subunit composition alpha beta gamma, with an alpha subunit of 40,000 daltons. Thus, mammalian atrial muscarinic potassium channels are activated directly by a G protein, not indirectly through a cascade of intermediary events. The G protein regulating these channels is identified as a potent Gk; it is active at 0.2 to 1 pM. Thus, proteins other than enzymes can be under control of receptor coupling G proteins.

A linked genetic marker for multiple endocrine neoplasia type 2A on chromosome 10.

Abstract: Multiple endocrine neoplasia type 2A (MEN2A) is an autosomal dominantly inherited cancer syndrome characterized by medullary carcinoma of the thyroid, phaeochromocytoma and hyperparathyroidism. Almost all gene carriers can be detected by screening tests before the age of 40 (ref. 1), but the nature and location of the predisposing gene are unknown. Simpson et al.2 recently reported preliminary evidence for linkage between the DNA probe p9-12A on chromosome 10 and MEN2A. We now report linkage between the MEN2A locus and the interstitial retinol-binding protein gene, which is located on chromosome 10p11.2-q11.2 (ref. 3).

Characterization and classification of neonatal seizures

Abstract: To characterize and classify neonatal seizures, we studied 349 neonates, using a portable, cribside EEG/polygraphic/video monitoring system. We recorded 415 clinical seizures in 71 infants; 11 other infants had electrical seizure activity without clinical accompaniments. Each seizure was analyzed in terms of its clinical character and its relationship to the presence of EEG seizure activity. Focal clonic seizures, some forms of myoclonic seizures, and focal tonic seizures were consistently associated with electrical seizure activity. Most "subtle" seizures, all generalized tonic seizures, and some forms of myoclonic seizures were either not associated with EEG seizure activity or had an inconsistent relationship with such activity. Seizures that were consistently and coherently related to focal EEG seizure activity had a high correlation with focal brain lesions and a favorable short-term outcome. Seizures with no relationship or an inconsistent relationship to EEG seizure activity were correlated with diffuse processes such as hypoxic-ischemic encephalopathy and a poor short-term outcome. The clinical and background EEG features of infants whose seizures were not accompanied by EEG seizure activity suggest that these seizures may not be epileptic in character.

Treatment of symptomatic hyponatremia and its relation to brain damage. A prospective study.

Abstract: We studied the effects of replacement therapy in two groups of patients with symptomatic hyponatremia. Thirty-three patients, who were studied prospectively, had no evidence of cerebral demyelinating lesions. Their hyponatremia (mean serum sodium concentration [+/- SE], 108 +/- 1 mmol per liter) was increased to 126 +/- 1 mmol per liter with hypertonic saline (856 mM) delivered at a rate of 1.3 +/- 0.2 mmol per liter per hour. The serum sodium concentration did not rise to normal or hypernatremic levels in the first 48 hours of therapy, and none of these patients had a respiratory arrest or other hypoxic episode. Twelve patients, evaluated retrospectively, had evidence of cerebral demyelinating lesions at autopsy or on computerized axial tomography. The rate of correction of hyponatremia (1 +/- 0.2 mmol per liter per hour) was similar to the rate in the patients in Group I. However, at least one of four characteristics was present: an increase in serum sodium to normal or hypernatremic levels in the first 48 hours, a change in the serum sodium concentration of more than 25 mmol per liter in the first 48 hours, a hypoxic-anoxic episode, and an elevation of serum sodium to hypernatremic levels in patients with hepatic encephalopathy. Although these four features were associated with demyelination, our observations suggest that this complication does not depend on the rate of correction of hyponatremia.

High density lipoprotein2. Relationship of the plasma levels of this lipoprotein species to its composition, to the magnitude of postprandial lipemia, and to the activities of lipoprotein lipase and hepatic lipase.

Abstract: Lipoprotein lipase (LPL) activity in postheparin plasma of 38 normolipidemic volunteers was related to the magnitude of postprandial lipemia after a fat meal, to triglyceride content of high density lipoprotein2 (HDL2), to hepatic lipase (HL) activity, and to HDL2 levels. LPL activity correlated indirectly with lipemia, triglyceride content of HDL2, HL activity, and levels of HDL2 but not of HDL3. HL activity correlated directly with lipemia and indirectly with HDL2 levels. Triglyceride content of HDL2 correlated directly with lipemia and indirectly with HDL2 levels. In HDL2, abundance of apolipoprotein (apo) A-II and the apoA-I/apoA-II ratio varied widely. The latter correlated positively with LPL activity and HDL2 levels, and, inversely, with HL activity, lipemia, and triglyceride content of HDL2. The study suggests that HDL-cholesterol is not an independent parameter of lipid transport, but is strongly affected by triglyceride metabolism through lipolytic enzymes, as exemplified by postprandial lipemia that affect both composition and plasma levels of HDL2.

Potential involvement of free radical reactions in ultraviolet light‐mediated cutaneous damage*

Abstract: Free radicals are chemical species characterized by an odd number of orbital electrons or by pairs of electrons of similar directional spin isolated singly in separate orbitals. Consequently most of these agents are highly reactive and usually exhibit an extremely short half-life, although due to steric and resonance effects some exceptions occur. Some radicals and their precursors, such as the diradical O2 which exists in the triplet state, represent a critical and essential element of normal metabolism of aerobic organisms where, under normal circumstances, controlled reduction of reactive oxygen species occurs via the cytochrome oxidase or cytochrome P-450 mixed function monooxygenase systems. In addition to reactive oxygen species, organisms may be subjected to a wide-range of other free radicals or their precursors, including those of both exogenous and endogenous origin. Elaborate defense mechanisms have evolved to avoid cellular damage from these highly reactive species. Enzymes, such as the superoxide dismutase, the glutathione peroxidase/reductase system, and catalase; interactions with conjugated diene systems such as those found in melanins, carotenoids, and tocopherols; and direct reduction by sulphydryl compounds, phenols, and purines represent but a few of these natural defense systems. Despite a strong rationale for considering free radicals as pathologic agents, progress in implicating these agents, or their reactions, in pathologic processes has been arduous. The fore-most hurdle to providing definitive evidence for free radical involvement rests with the highly transient nature of these species, hardly reaching measurable levels in vivo and thereby making rigorous testing of the hypothesis extremely difficult. Indeed, free radical damage has been studied, for the most part, by indirect means–usually by measurement of known free radical reaction intermediates and products from which free radical involvement is implied. Nevertheless, free radical formation has been shown to occur in UV-irradiated skin and a considerable body of circumstantial evidence has been amassed that strongly infers that these agents, or reactions initiated by them, are responsible for at least some of the deleterious effects of UV upon skin.

Urinary catecholamines before and after tracheostomy in patients with obstructive sleep apnea and hypertension.

Abstract: Obstructive apnea (asphyxia) is accompanied by acute elevation of systemic blood pressure. The usual nocturnal fall in blood pressure seen during sleep in normals may be absent in patients with repetitive apneas, and daytime systemic hypertension is reported to occur in up to 90% of such patients. Increased sympathetic activity in response to repetitive nocturnal episodes of asphyxia could explain the reversal of the diurnal pressure variation but not the daytime systemic hypertension in this setting. We examined diurnal variation in urinary catecholamines in eight subjects with severe apnea before and after tracheostomy. Five obese hypertensive subjects without apnea served as controls. Three urine specimens, two awake (7 a.m. to 3 p.m. and 3 p.m. to 11 p.m.) and one asleep (11 p.m. to 7 a.m.) were collected preoperatively and again 10-14 days postoperatively when the patient was free of pain and signs of stoma infection. All specimens were analyzed for epinephrine, norepineprine, metanephrine, and normetanephrine by liquid chromatography with electrochemical detection. Urinary epinephrine and metanephrine were not different between subjects and controls. Norepinephrine and normetanephrine were significantly higher in apneic subjects pretracheostomy as compared either with controls or with their own values posttracheostomy. Diurnal variation was not seen before or after tracheostomy. Only two of the controls showed significant diurnal variation in norepinephrine. We conclude that the absence of diurnal variation in catecholamines prior to tracheostomy reflects increased nocturnal sympathetic activity. Elevation of daytime norepinephrine and normetanephrine with return to control levels following tracheostomy implies increased sympathetic activity throughout the day.

The alpha subunit of the GTP binding protein Gk opens atrial potassium channels.

Abstract: Guanine nucleotide binding (G) proteins (subunit composition alpha beta gamma) dissociate on activation with guanosine triphosphate (GTP) analogs and magnesium to give alpha-guanine nucleotide complexes and free beta gamma subunits. Whether the opening of potassium channels by the recently described Gk in isolated membrane patches from mammalian atrial myocytes was mediated by the alpha k subunit or beta gamma dimer was tested. The alpha k subunit was found to be active, while the beta gamma dimer was inactive in stimulating potassium channel activity. Thus, Gk resembles Gs, the stimulatory regulatory component of adenylyl cyclase, and transducin, the regulatory component of the visual system, in that it regulates its effector function--the activity of the ligand-gated potassium channel--through its guanine nucleotide binding subunit.

Bradykinin-induced increases in cytosolic calcium and ionic currents in cultured bovine aortic endothelial cells.

Abstract: The goal of the present study was to determine if voltage-sensitive calcium channels are present in bovine aortic endothelial cell plasmalemma and if they contribute to the rise in cytosolic calcium produced by bradykinin. After bradykinin (100 nM) exposure, endothelial cell associated fura-2 fluorescence peaked within 10-20 seconds and then declined to a steady level 2- to 3-fold above resting values. Pretreatment with lanthanum (20 microM) abolished the steady level produced by bradykinin but had little effect on the initial, transient rise in cytosolic calcium. Chelation of extracellular calcium with EGTA before addition of bradykinin resulted in a substantial decrease in the fura-2 transient and elimination of the long-lasting component. Nimodipine (3 microM) and nitrendipine (1 microM) were without effect on either phase of the bradykinin-induced response. Moreover, elevation of extracellular potassium failed to produce a rise in intracellular calcium. With the use of the tight seal technique to voltage clamp the cells, inwardly rectifying and calcium-activated potassium currents were found to exist in the endothelial cells. Addition of bradykinin (100 nM) elicited a calcium-activated potassium current that was eliminated in the absence of intracellular potassium. No voltage-sensitive calcium currents were activated when the cells were exposed to 10 mM or 110 mM calcium chloride in the presence or absence of bradykinin. The binding of [3H](+)PN200-110 to endothelial cell membrane preparations was 1-3 orders of magnitude lower than that observed in PC-12, GH3, or BC3H1 cell membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular basis of the sparse fur mouse mutation

Abstract: The ornithine transcarbamylase-deficient sparse fur mouse is an excellent model to study the most common human urea cycle disorder. The mutation has been well characterized by both biochemical and enzymological methods, but its exact nature has not been revealed. A single base substitution in the complementary DNA for ornithine transcarbamylase from the sparse fur mouse has been identified by means of a combination of two recently described techniques for rapid mutational analysis. This strategy is simpler than conventional complementary DNA library construction, screening, and sequencing, which has often been used to find a new mutation. The ornithine transcarbamylase gene in the sparse fur mouse contains a C to A transversion that alters a histidine residue to an asparagine residue at amino acid 117.

Noradrenaline and β-adrenoceptor agonists increase activity of voltage-dependent calcium channels in hippocampal neurons

Abstract: The predominance of unconventional transmitter release sites at noradrenaline-containing synapses and the diffuse projections of noradrenaline-containing fibres originating in locus coeruleus have led to speculation that noradrenaline may act as a neuromodulator in the central nervous system. Evidence suggests that it has a modulatory function in the plasticity of the developing nervous system, in controlling behavioural states of an organism, and in learning and memory. Recently, Hopkins and Johnston demonstrated that noradrenaline enhances the magnitude, duration and probability of induction of long-term potentiation (LTP) at mossy fibre synapses in the hippocampal formation, and LTP is widely believed to be a cellular substrate for aspects of memory. To investigate the membrane effects of noradrenaline on central neurons, we used a newly developed preparation in which patch-clamp techniques can be applied to exposed adult cortical neurons. We report here that noradrenaline produces an enhancement in the activity of voltage-dependent calcium channels in granule cells of the hippocampal dentate gyrus. This action appears to be mediated by beta-adrenoceptors and can be mimicked by cyclic AMP.

4-Aminopyridine produces epileptiform activity in hippocampus and enhances synaptic excitation and inhibition.

Abstract: Using extra- and intracellular recording techniques, we investigated the epileptiform activity induced by low concentrations (5 and 10 microM) of bath-applied 4-aminopyridine (4-AP) in the CA3 subfield of rat hippocampal slices. We also studied the effects of 4-AP on the excitatory and inhibitory synaptic conductance changes in CA3 neurons produced by mossy fiber stimulation. Low concentrations of 4-AP induced spontaneously occurring epileptiform discharges at extracellular potassium concentrations between 1 and 10 mM. In contrast, picrotoxin and bicuculline produced spontaneous epileptiform discharges at extracellular potassium concentrations between 5 and 10 mM. The paroxysmal depolarizing shift (PDS) induced by 4-AP was also investigated. At potentials between -40 and -10 mV, the waveform of the PDS consisted of a depolarizing component enveloped by a hyperpolarizing component. The amplitude of the depolarizing component of the PDS was a monotonic function of the membrane potential, and the mean measured reversal potential was -25.7 mV. Under voltage-clamp conditions, the measured conductance associated with the depolarizing component of the PDS averaged 110 nS, with a reversal potential of -14.1 mV. Application of 5 microM 4-AP produced an increase in the inhibitory synaptic conductance change calculated from currents measured 15 ms following mossy fiber stimulation. The mean value increased from 35.2 to 58.1 nS (P less than 0.05) without a significant change in reversal potential. A concentration of 10 microM 4-AP also produced an increase in this inhibitory synaptic conductance change (from 53.3 to 66.3 nS, P less than 0.05) but caused a significant depolarization of the reversal potential (from -66.5 to -61.6 mV, P less than 0.05). This change in reversal potential may reflect a prolongation of the excitatory synaptic currents produced by 4-AP that contributes to the current measured 15 ms from the stimulus. Following application of either 5 or 10 microM 4-AP, there were no significant changes in the resting potential or input resistance of the neurons studied. Application of 5 microM 4-AP also significantly increased the amplitude of the measured excitatory synaptic conductance change produced by mossy fiber stimulation (from 27.9 to 44.1 nS, P less than 0.05) without producing a change in the reversal potential. In 5 of 21 neurons studied, a long-lasting outward synaptic current was present at holding potentials near rest following mossy fiber stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantification of atrial contribution to left ventricular filling by pulsed Doppler echocardiography and the effect of age in normal and diseased hearts.

Abstract: Atrial filling fraction, or the fraction of stroke volume resulting from atrial contraction, was measured by Doppler echocardiography from the time-velocity integral of mitral anulus inflow with a method that allows separation of conduit or passive flow from flow resulting from the atrial contraction. The method was validated in 17 patients with externally programmable ventricular demand pacemakers by showing that the time-velocity integral of passive flow (excluding the A wave) during sinus or sequential atrioventricular pacing was almost identical to the time-velocity integral during ventricular pacing. Atrial filling fractions were then measured in 41 normal subjects, aged 20 to 80 years; 28 patients with echocardiographic evidence of concentric left ventricular hypertrophy; 24 with dilated cardiomyopathy (13 of whom had an ischemic origin); and 19 with acute myocardial infarction. Atrial filling fraction increased significantly with age in normal subjects (r = 0.77; p less than 0.001) and ranged from 12% in a 20-year-old man to 46% in a normal 80-year-old woman. In the hypertrophy group, atrial filling fraction had a weak relation with age (r = 0.47; p = 0.006), and the values were significantly higher than in normal subjects. In patients with cardiomyopathy or infarction, atrial filling fraction varied over a wide range and showed no relation to age. Thus, atrial filling fraction as determined by Doppler echocardiography is significantly altered by both age and left ventricular disease. Age-corrected nomograms are essential when assessing atrial filling fraction in individual patients.

Monoclonal autoantibody from a (New Zealand black x New Zealand white)F1 mouse and some human scleroderma sera target an Mr 34,000 nucleolar protein of the U3 RNP particle.

Abstract: A monoclonal IgG2a antinucleolar autoantibody (72B9) was obtained by fusion of spleen cells from a (New Zealand black x New Zealand white)F1 mouse with myeloma cells (P3x63Ag8.653). Antibody 72B9 recognized a highly conserved nucleolar antigen present in both animal and plant cells. The staining pattern produced by antibody 72B9 in different cell substrates was identical with those obtained by scleroderma antibodies reactive with a basic (pI 8.5) nucleolar protein of Mr 34,000, which is associated with the U3 RNP particle. Western blotting further confirmed its reactivity with this scleroderma-related U3 RNP protein.

Selective disruption of gap junctional communication interferes with a patterning process in hydra

Abstract: The cells that make up the body column of hydra are extensively joined by gap junctions, capable of mediating the rapid exchange of small hydrophilic molecules between the cytoplasms of neighboring cells. Both the rate of transfer of small molecules through the gap junctions and the rate of return of gap junction coupling after grafting experiments are sufficiently rapid to mediate events in the patterning of hydra tissue. Antibodies to the major rat liver gap junction protein (27,000 daltons) recognize a gap junction antigen in hydra and are effective in eliminating junctional communication between hydra cells. The antibodies perturb the head inhibition gradient in grafting operations, suggesting that cell-cell communication via gap junctions is important in this defined tissue patterning process.

Histochemical staining of clonal mammalian cell lines expressing E. coli beta galactosidase indicates heterogeneous expression of the bacterial gene.

Abstract: An evaluation has been made of the E. coli beta-galactosidase (beta-gal) gene for use as a reporter gene in mammalian cells in culture. We have adopted a histochemical procedure which enables identification of those cells within a population that express the introduced bacterial gene. Data is presented concerning the sensitivity of the histochemical method relative to an immunological method of detection. It has been found that several clonal cell lines generated after transfection of human 293 cells with a Rous sarcoma virus (RSV) long terminal repeat (LTR) promoter-beta-gal construction are mosaic for expression of the introduced mini-gene. Furthermore, after treatment of these clonal cell lines with the nucleoside analog 5-aza-cytidine (5-aza-C), an increase in production of beta-gal under control of this promoter element was observed.

A novel calcium binding site in the galactose-binding protein of bacterial transport and chemotaxis

Abstract: The refined 1.9-A resolution structure of the periplasmic D-galac-tose-binding protein (GBP) reveals a calcium ion surrounded by seven ligands, all protein oxygen atoms. A nine-residue loop (amino-acid positions 134–142), which is preceded by a /β-turn and followed by a β-strand, provides five ligands from every second residue. The last two ligands are supplied by the carboxylate group of Glu 205. The entire GBP Ca2+-binding site adopts a conformation very similar to the site in the 'helix-loop-helix' or 'EF-hand' unit commonly found in intracellular calcium-binding proteins1, but without the two helices. Structural analyses have also uncovered the sugar-binding site some 30 A from the calcium and a site for interacting with the membrane-bound trg chemotactic signal transducer ∼45 A from the calcium. Our results show that a common tight calcium binding site of ancient origin can be tethered to different secondary structures. They also provide the first demonstration of a metal-binding site in a protein which is involved in bacterial active transport and chemotaxis.

A rating scale for amyotrophic lateral sclerosis: Description and preliminary experience

Abstract: A rating scale has been developed to provide a quantitative estimate of clinical status and disease progression in amyotrophic lateral sclerosis (ALS). This scale includes assessment of swallowing, speech, and respiratory function, and both strength and function of upper and lower extremity musculature. The evaluation is relatively simple to perform and yields reproducible data for both a total ALS score and a score for each group of functions tested. A score of 30 points is normal; 164 points indicates maximal dysfunction. The total ALS score increased in a linear fashion in each of 74 patients followed for at least one year. Among patients, the rate of disease progression varied twenty-fold, with a continuous distribution from the slowest to most rapid course. Thirty-four percent of patients exhibited a rapid change of greater than 48 points in the year, predicting progression to a terminal stage in less than two years; 19% of patients exhibited a slow change of less than 13 points in one year, predicting progression to a terminal stage over at least five years. This ALS scoring system should permit more accurate assessment of drug efficacy in clinical trials and correlation of rates of progression with clinical variables.

Ovarian follicular development: from physiology to molecular biology.

Abstract: Publisher Summary Theca cell differentiation and the synthesis of aromatizable androgens are obligatory for follicular estradiol production and the differentiation of granulosa cells. Previous studies indicated that theca cell differentiation was dependent on subtle increases in serum luteinizing hormone (LH) concentrations. To determine whether the effects of LH on theca cell 17 α-hydroxylase in vivo were mediated by cAMP, a theca cell culture system using theca explants from small antral (SA), preovulatory (PO), and luteinizing follicles was developed. SA theca produces only low amounts of androstenedione when cultured in medium alone. However, either when LH was added at the beginning of culture or when forskolin was added on day 4 of culture androstenedione, production was increased to 5–10 ng ml/theca and was maintained for 20 days of culture. PO theca initially produced more androstenedione than SA theca but failed to maintain steroid synthesis unless either LH or forskolin was added to the cultures.

Attenuation of dysfunction in the postischemic 'stunned' myocardium by dimethylthiourea.

Abstract: The mechanism for the prolonged contractile dysfunction observed in myocardium reperfused after reversible regional ischemia ("stunned" myocardium) is unclear. Recent studies suggest that myocardial stunning may be mediated by oxygen-derived free radicals, but the precise molecular species involved remain unknown. Thus we explored the role of the highly cytotoxic hydroxyl radical in regional postischemic dysfunction by using dimethylthiourea (DMTU), an effective and highly permeable hydroxyl radical scavenger. Open-chest dogs undergoing a 15 min occlusion of the left anterior descending coronary artery followed by 4 hr of reperfusion received either DMTU (0.5 g/kg iv over 45 min starting 30 min before occlusion, n = 14) or saline (n = 15). Control and treated dogs were comparable with respect to variables that may affect postischemic dysfunction, including heart rate, aortic pressure, left atrial pressure, arterial blood gases and hemoglobin concentration, size of the occluded bed (determined by postmortem perfusion), and collateral blood flow (determined by radioactive microspheres). Regional myocardial function was assessed by measuring wall thickening with an epicardial Doppler probe. The two groups exhibited comparable systolic thickening under baseline conditions and similar degrees of dyskinesis during ischemia. After reperfusion, however, wall thickening (expressed as percent of baseline) was considerably greater in treated as compared with control dogs: 53 +/- 9% (mean +/- SEM) vs 9 +/- 14% (p less than .03) at 1 hr, 55 +/- 9% vs 23 +/- 13% (p less than .05) at 2 hr, 60 +/- 9% vs 28 +/- 14% (p less than .05) at 3 hr, and 67 +/- 5% vs 36 +/- 13% (p less than .05) at 4 hr. Thus DMTU produced a significant and sustained improvement in recovery of contractile function. In concentrations greater than the plasma levels attained in vivo, DMTU did not scavenge either hydrogen peroxide or superoxide anion in vitro. These results suggest that the myocardial dysfunction occurring after a brief episode of regional ischemia is mediated in part by the hydroxyl radical.