Acta physiologica latino americana最新文献

Glucose-induced insulin secretion by the perfused sodium pentobarbital-anesthetized-rat pancreases was studied under different extracellular pH ranging from 7.4 to 7.8. Under our experimental conditions the amount of insulin released was inversely correlated to the pH increase. Besides, metabolic (CO2H- excess) or gaseous (low pCO2) type of alkalosis, were equally effective inhibiting insulin secretion. During a 16.6 mM glucose stimulus, sequential modifications of extracellular pH (7.4-7.8-7.4) caused a dramatic decrease in insulin secretion during alkalosis and an enhancement of its release during the second 7.4 period. The installment and remotion of the inhibition followed almost immediately the changes in the pH of the perfusates. These findings indicate that extracellular diminution of H+ concentration produces a gradual and quickly reversible decrease upon glucose-induced insulin secretion. These characteristics suggest that the inhibitory effect may be mediated through changes in intracellular and/or transmembrane ion fluxes coupled to the variations in H+ concentration.

The effect of several beta-blockers on the vasoactive effect of several substances was studied on the perfused isolated rat mesenteric vessels. The agonists were tested while the beta-blocker was infused; the effects were compared in the same experiment with those observed in a control period in which the agonists were injected without simultaneous infusion of beta-blocker. l-propranolol, infused at three different doses, did not modify the vascular effect of either angiotensin II (AII) or vasopressin (VP). On the other hand, the constrictor effect of epinephrine (E) and norepinephrine (NE) was significantly reduced. Timolol, but not sotalol, showed the same results. d-propranolol produced the same effect as l-propranolol. A high dose of l-propranolol did not protect alpha adrenoceptors of blockade induced by phentolamine.

The suppressor activity induced by Concanavalin A (Con A) was evaluated in peripheral lymphocytes from 20 patients with solid malignant tumors of different origin, that is: 9 lung epidermoid carcinomas; 6 breast adenocarcinomas and 5 melanomas. Simultaneously 10 normal control subjects were studied. No significant differences in the percentage of suppression were found in patients bearing breast adenocarcinoma and lung epidermoid carcinoma as compared to normal subjects. Melanoma patients, on the contrary, showed significant differences on the same test. On the other hand, the Con A lymphoproliferative response was found to be only significantly increased in the melanoma patients compared to normal controls. No differences were found in the percentage of peripheral blood lymphocytes between patients and controls.

In order to determine if the inability of thyroxine to induce cellular effects at low temperature is mediated through a temperature-sensitive system for the translocation of T4 into the nucleus, the effect of temperature on the uptake of T4 by body tissues and sub-cellular fractions of carp liver and muscle was studied in vivo. A single injection of 125I-T4 (1 micro C/10 g body weight) was given intraperitoneally to juvenile carp maintained at 15 and 25 C. Uptake from the peritoneal cavity was rapid. All the tissues exhibited maximum radioactivity at 2 hour after the injection. Fish kept at 25 C showed another peak at 8 hour and those at 15 C at 48 hour after the single injection. Transfer of T4 from the cytoplasm to nuclei was not blocked at lower temperatures. For example, in liver at 8 hour, nuclei from fish tissues kept at lower or higher temperatures had equal amounts of radioactivity. Muscle nuclei had 15% more radioactivity than liver nuclei when expressed as radioactivity/g tissue. Since there are comparable amounts of activity in the nuclei at both temperatures, some other mechanism/s than a simple block in transport from cytoplasm to nuclei is operating. There are some indications that nutritional status of fish may be playing some role in this respect.

The effect of zinc deficiency on the lipid composition, fluorescence anisotropy of the membrane labeled with diphenyl hexatriene and delta 9, delta 6, and delta 5 fatty acid desaturation activity of liver and testes microsomal membranes was studied. Sixty days of zinc deficiency in weanling rats evoked a loss of hair and scaled and ridged tail. The activities of delta 6 and delta 5 desaturases, that are relevant enzymes involved in linoleic acid conversion into arachidonic acid, were decreased in both liver and testes. However, the delta 9 desaturase of liver was increased by the zinc deficiency. The arachidonic acid concentration of liver and testes microsomes was decreased. The microsomal phospholipid/cholesterol ratio was markedly decreased, and this change was correlative to an increase of the fluorescence anisotropy of membranes labeled with diphenyl hexatriene, that indicated an increase of the order parameter for diphenyl hexatriene and considering the criterium of Van Blitterswijk et al., an increase of the molecular packing of the bilayer. Zinc deficiency evoked an essential fatty acid deficiency status with low eicosa-5,8,11-trienoic acid, and decrease of delta 6 and, specially, delta 5 desaturase activity, that aggravates the symptoms and avoids compensatory biosynthesis of the polyunsaturated acids of oleic family.

Right atria from rats were analyzed for chronotropic responses to phenylephrine in face of various drugs and procedures. Propranolol, 10(-8) M, produced a competitive antagonism against the agonist which concentration-effect curve was closely similar to that obtained from reserpinized animals. Prazosin, but not phentolamine (both 10(-6) M) showed inhibition of the phenylephrine-induced changes in heart rate, as judged by their -log EC50. Either of the alpha-adrenoceptor antagonists exhibited a greater steepness in the curve slope with respect to control. The simultaneous exposure of tissues to phentolamine and propranolol proved to effectively antagonize the chronotropic effect of the agonist. This held true for phentolamine assayed in atria from reserpine-pretreated rats. Previous incubation of tissues with papaverine, 10(-5) M, brought about supersensitivity to phenylephrine which was thoroughly inhibited by either phentolamine or propranolol. These results strongly suggest that beta-adrenoceptor stimulation of heart rate by phenylephrine takes place indirectly via norepinephrine release. There is also alpha 1-adrenoceptor stimulation (blocked by prazosin). Finally, it is hypothesized that supersensitivity develops by papaverine-enhanced Ca2+ influx, since numerous evidences are against a phosphodiesterase inhibition-dependent cAMP accumulation mechanism triggered by papaverine in the presence of phenylephrine.

A microcomputer system was implemented for reliable, fast and accurate study of in vitro myometrial activity. By the analog-to-digital conversion, uterine contractions are captured, digitized, stored in magnetic disks and subsequently recalled for its mathematical analysis. The system allows to calculate area under the curve, dose-response curves and other parameters, including complex analysis of myometrial activity. Precision and saving time are the main advantages of the system, and it can be used to study any kind of biological waves. Because its low cost and simplicity, this system seems to be suitable for laboratories of physiology, pharmacology or biophysics.

Platelets aggregate with thrombin-free activated protein C in concentrations higher than physiological levels. Aggregation was dependent on an intact release mechanism since inhibition of aggregation occurred with adenosine or EDTA. However, activated protein C reduced the sensitivity of platelets to aggregate in the presence of thrombin. Probably, activated protein C competes for membrane sites sensitive to thrombin.

RNA rich preparations from lymphoid tissues of appropriate immunized donors, namely immune RNA (I-RNA), can transfer specific immune reactivity to normal recipients or to their cells. Because of this ability, I-RNA was considered as a good candidate for the immunoprophylaxis and immunotherapy of different diseases. Its use in neoplasic processes is reviewed here. The regression of small tumors, as well as the effective prevention of metastasis appearance after primary tumor surgery has been obtained in animal models. The results from human cancer therapy with I-RNA are still very confuse; however the data suggest that I-RNA has altered the natural history of the studied tumor. An intensification of better planned immunotherapy in animals and humans tumor models will lead to a deeper knowledge of the usefulness of this therapy.