Acta physiologica latino americana最新文献

The effects of simulated altitude induced by a decompression chamber upon the blood levels of thyrotropin (TSH), thyroxine (T4) and triiodothyronine (T3), measured by radioimmunoassay, were studied in male Wistar rats. When blood was extracted during the first 15 minutes after the rats were removed from the chamber and analysed, it was found that TSH levels decreased at 380 mmHg during 24 hours and sometimes at 440 mmHg during 24 hours, but this did not happen when the exposure lasted a week. Likewise, serum levels of T4 and T3 decreased at 440 mmHg during 24 hours, but they did not decrease using the same exposure during a week. When the blood was extracted 1 hour after the rats were removed from the chamber and analysed, TSH levels markedly increased at 380 mmHg and at 440 mmHg, during 1 day and during a week. Serum T4 and T3 levels were found to be normal. These results show that severe hypobaric hypoxia is needed in order to depress serum TSH levels. When the rats are removed from the decompression chamber, however, a rebound effect with marked increase in serum TSH levels can be seen before 1 hour elapses.

Somatotropic cells from three months old male mice, made hypoxic by either bleeding or exposure to 0.5 atm. barometric pressure in a decompression chamber, showed important ultrastructural changes when compared with normoxic controls, during the 36 hours that follow initiation of hypoxia. These changes were found to be similar for both types of hypoxic animals. An equivalent number of dark cells, cells with a swollen rough endoplasmic reticulum (RER), extremely granulated and degranulated, were successively--and in this order--seen along the experiment. Most of the observed differences between experimental and control animals appears as a magnification of the normal circadian rhythms. The degranulation rate, which probably reflects growth hormone (GH) secretion rate, was found to be about three times greater in hypoxic than in control mice. These findings indicate that a decrease in the red cell mass or its consequence (hypoxia), induce important ultrastructural variations in somatotropic (STH) cells, which may or not be specific.

The antitoxic potency of crude Crotalus durissus terrificus serum against crotalic venom is similar to that of a standard horse anticrotalic serum in protecting mice against 4 LD50, while the potency of Bothrops neuwiedii serum is 20% of the latter. Failure to form precipitin lines in immunodiffusion tests suggests that the antitoxic factors present in the sera from both species are not immunoglobulins. It is, therefore, probable that crotoxin is not neutralized by an antigen-antibody reaction, but rather by formation of inactive complexes with specific serum components. Resistance to the venom is not reciprocal, since specimens of C. d. terrificus die after the injection of similar amounts of B. neuwiedii venom, which are tolerated by the homologous species.

Experiments were designed to study the cardiovascular effects of Bromocriptine (2-Br-alpha-ergocriptine) in the normotensive anesthetized rats. The intravenous administration of bromocriptine (20 micrograms/kg and 200 micrograms/kg) produced a long-lasting and not dose-dependent fall in the mean blood pressure and heart rate. The pressor response to phenylephrine, an alpha adrenergic agonist, was antagonized by bromocriptine in a dose-dependent manner. At a dose of 20 micrograms/kg bromocriptine behaved as a competitive antagonist, whereas at the dose of 200 micrograms/kg produced an insurmountable blockade of the response to phenylephrine. Previous administration of phentolamine (5 mg/kg) prevented the insurmountable blockade of alpha adrenoceptors by bromocriptine. This observation suggests that both drugs compete for the same receptor. It is concluded that blockade of peripheral alpha-adrenoceptors may contribute to cardiovascular effects of bromocriptine.

Estradiol benzoate (EB) or EB plus progesterone (P) were administered to chronic ovariectomized rats in doses which are known to induce sexual receptivity. P was injected 48 hr after EB and the animals were decapitated 54 hr after E.B. The ventromedial hypothalamus (VMH) (excluding the arcuate-median eminence region) was dissected out and used to determine 3H-noradrenaline (3H-NA) and 3H-serotonin (3H-5-HT) uptake and release induced by high potassium concentration. Animals injected with oil were used as controls. VMH from EB (10 micrograms/kg) plus P (2 mg/kg) primed animals had higher release of 3H-NE than controls; uptake and release of 3H-5-HT was also augmented in these animals. EB (100 micrograms/kg) priming alone did not induce significant variations. The increase in 3H-NA release is interpreted as evidence of incremented activity in a 3H-NA system, facilitating sexual receptivity. The change in 3H-5-HT uptake and release is discussed in respect to the existence of an inhibitory serotonergic system modulating sexual behavior.

Three lipoproteins were separated from the haemolymph of adult males of Triatoma infestans fed on hen blood. The densities were similar to the high density lipoprotein (HDL) and to two very high density lipoproteins (VHDL) isolated from a pool of adult male and female insects fasted during twelve days. The relative distribution and composition of the three lipoproteins were studied. The fatty acids were mainly carried by the 1.3 and 1.2 diacylglycerols of high density lipoprotein. Triacylglycerols were minor components. Similarly to fasted insects, the main fatty acids were oleic and palmitic. Linoleic was also present. Very high density lipoproteins (VHDL-II) (d 1.25-1.26) were found in the haemolymph of male insects. The relative distribution of HDL and VHDL on fed and fasted insects was different.