Effect of GABA and benzodiazepines on testicular androgen production

We have evaluated the effect of Ro5-4864, a selective probe to label peripheral type benzodiazepine receptor, on "in vitro" testicular androgen production. Decapsulated testes from adult rats showed a significant increase in the basal and hCG-stimulated testosterone secretion into the medium in response to 10(-5) M, 10(-6) M, and 10(-7) M Ro5-4864. In addition, we have studied the changes in testicular GABA content at three different ages and we found its highest concentration at 31 days of age. When we evaluated the effect of GABA on "in vitro" androgen production at different stages of gonadal maturation we observed that the highest concentration of GABA (10(-6) M) was able to modify the basal and hCG-stimulated androgen production from adult (60 days) and pubertal (45 days) testes. In addition, when prepubertal testes (31 days) were incubated under basal conditions, 10(-6) M GABA induced a significant increment of androstanediol production, while the stimulatory effect of hCG was reduced in the presence of the same GABA concentration. The present results suggest that GABA plays a physiological role in the regulation of rat testicular androgen production depending on the stage of sexual maturation.     

Bull sperm acrosome reaction induced by gamma-aminobutyric acid (GABA) is mediated by GABAergic receptors type A

The effect of gamma-aminobutyric acid (GABA) on the bull sperm acrosome reaction was evaluated, and the interaction of progesterone, a physiologic inducer of the acrosome reaction, with the GABA receptor was explored. The acrosome reaction was stimulated by GABA in a dose-dependent manner. This effect was inhibited completely by bicuculline, a GABA A receptor antagonist, but GABA B and C receptor antagonists had no effect. Accordingly, muscimol, a GABA A receptor agonist, stimulated the acrosome reaction to the same extent as GABA, whereas baclofen (GABA B receptor agonist) and CACA (GABA C receptor agonist), had no effect. Preincubation with progesterone followed by the addition of GABA resulted in a significant increase in the percentage of acrosome reacted spermatozoa compared with progesterone or GABA alone. Taking into account that this increase was less than a simple addition of effects, it might be suggested that GABA and progesterone act through the same receptor and/or use the same mechanism of action. To test this hypothesis, the abilities of GABA and progesterone to induce acrosome reaction were tested in the presence of bicuculline, which suppressed both stimulatory effects. Given that the GABA A receptor is linked to the Cl(-) channel, we tested whether picrotoxin, a blocker of this channel, could modulate the effects of progesterone or GABA. Cl(-) channel blocker picrotoxin dramatically reduced the GABA and progesterone-initiated AR. In conclusion: GABA and progesterone stimulate the acrosome reaction in bull spermatozoa acting through a classical GABA A receptor. The mechanism of action requires the functional integrity of the Ca(2+) Cl(-) channel.     

Sternomastoid, rib cage, and expiratory muscle activity during weaning failure.

We hypothesized that patients who fail weaning from mechanical ventilation recruit their inspiratory rib cage muscles sooner than they recruit their expiratory muscles, and that rib cage muscle recruitment is accompanied by recruitment of sternomastoid muscles. Accordingly, we measured sternomastoid electrical activity and changes in esophageal (DeltaPes) and gastric pressure (DeltaPga) in 11 weaning-failure and 8 weaning-success patients. At the start of trial, failure patients exhibited a higher DeltaPga-to-DeltaPes ratio than did success patients (P = 0.05), whereas expiratory rise in Pga was equivalent in the two groups. Between the start and end of the trial, failure patients developed additional increases in DeltaPga-to-DeltaPes ratio (P < 0.0014) and the expiratory rise in Pga also increased (P < 0.004). At the start of trial, sternomastoid activity was present in 8 of 11 failure patients contrasted with 1 of 8 success patients. Over the course of the trial, sternomastoid activity increased by 53.0 +/- 9.3% in the failure patients (P = 0.0005), whereas it did not change in the success patients. Failure patients recruited their respiratory muscles in a sequential manner. The sequence began with activity of diaphragm and greater-than-normal activity of inspiratory rib cage muscles; recruitment of sternomastoids and rib cage muscles approached near maximum within 4 min of trial commencement; expiratory muscles were recruited slowest of all. In conclusion, not only is activity of the inspiratory rib cage muscles increased during a failed weaning trial, but respiratory centers also recruit sternomastoid and expiratory muscles. Extradiaphragmatic muscle recruitment may be a mechanism for offsetting the effects of increased load on a weak diaphragm.     

Coenzyme a-synthesizing protein complex of Saccharomyces cerevisiae

The coenzyme A-synthesizing protein complex (CoA-SPC) is a multienzyme complex of Saccharomyces cerevisiae (Bakers' yeast), which has a molecular weight in excess of 200,000 as determined by Sephadex G-200 column chromatography. This multienzyme complex, which is insoluble in the crude yeast cell lysate, has been purified 229-fold. A cellular component of the yeast cell lysate, referred to as t-Factor, with a molecular weight of 400-1000 and chloride ion are involved in the solubilization of CoA-SPC. The CoA-SPC requires L-cysteine, D-pantothenic acid and ATP as substrates. The terminal CoA-SPC-bound intermediate is dephospho-CoA, which is subsequently phosphorylated and released from the complex as CoA. The sequence of reactions for the synthesis of CoA by the CoA-SPC differs significantly from those previously proposed for other systems. It could be that the reaction sequence is unique for the yeast cell.     

Reversal of endotoxin-mediated shock by NG-methyl-L-arginine, an inhibitor of nitric oxide synthesis

Septic shock is a life-threatening condition that results from exposure to bacterial endotoxin. It is manifested by cardiovascular collapse and mediated by the release of cytokines such as tumor necrosis factor. Some of these cytokines cause the release of vasoactive substances. In the present study, administration of 40 microgram/kg of bacterial endotoxin to dogs caused a 33% decrease in peripheral vascular resistance and a 54% fall in mean arterial blood pressure within 30 to 90 minutes. Vascular resistance and systemic arterial pressure returned to normal within 1.5 minutes after intravenous administration of NG-methyl-L-arginine (20 mg/kg), a potent and selective inhibitor of nitric oxide synthesis. L-Arginine reversed the effect of L-NMA and restored the endotoxin-induced hypotension. Although NG-methyl-L-arginine injection increased blood pressure in control dogs, the hypertensive effect was much greater in endotoxemic dogs (24.8 +/- 2.7 mmHg vs 47.8 +/- 6.8 mmHg, p = 0.01, n = 4). NG-Methyl-L-arginine caused only a modest increase in blood pressure in dogs made hypotensive by continuous intravenous infusion of nitroglycerin (17.1 +/- 5.0 mm Hg, n = 3). These findings suggest that nitric oxide overproduction is an important contributor to endotoxic shock. Moreover, our findings demonstrate for the first time, the utility of nitric oxide synthesis inhibitors in endotoxic shock and suggest that such inhibitors may be of therapeutic value in the treatment of septic shock.     

The distribution of proteoglycans of high electrophoretic mobility in cartilages from different species and of different ages

The distribution of small proteoglycans of high relative electrophoretic mobility in cartilage of various species and of different ages was studied. Proteoglycans extracted by 4 M guanidinium chloride were purified by ion-exchange chromatography and assessed by gel electrophoresis. Proteoglycans fractionated by equilibrium density gradient centrifugation under ‘dissociative’ conditions were similarly purified and assessed. A rapid migrating population was found in articular cartilages of young humans, baboons, calfs, pigs, rabbits, rats, chickens and in mandibular and vertebral cartilages of dog-fish. It was not detected in unfractionated proteoglycans extracted from fetal rat, pig, calf, baboon and human cartilages. In baboon and human fetal cartilages of advanced gestational age, however, small amounts of the rapid population were present being detected in the low density fractions of dissociative gradients. The rapid migrating population was not found either in unfractionated or in fractionated proteoglycans obtained from articular cartilages of humans aged over 40. It was absent from human osteoarthritic cartilages but was detected even at advanced age in cartilages covering osteophytes.