Acta physiologica latino americana最新文献

The role of the sympathetic nervous system in the control of the goitrogenic response was examined in adult male rats subjected to unilateral superior cervical ganglionectomy 12-30 days earlier. A spontaneous goiter as well as an increased thyroid growth after the administration of the goitrogenic agents methylmercaptoimidazole and thyrotropic stimulating hormone (TSH) were found in the ipsilateral lobe. Norepinephrine and epinephrine content decreased significantly by 80 and 31%, and thyroxine (T4) and triiodothyronine (T3) content by 24 and 15%, in the ipsilateral lobe. After the injection of a tracer dose of 125I, percent radioactivity incorporation to diiodotyrosine (DIT) was higher, and that to monoiodotyrosine (MIT) lower, in the ipsilateral lobe; additionally a lower ratio "labeled T3 + T4/labeled DIT" was found in the denervated thyroid lobe. These results suggest that the sympathetic nerve terminals in the thyroid gland modulate the organ's response to circulating TSH.

Adrenalectomized rats were injected twice with either 2 micrograms aldosterone or 6 micrograms 18-hydroxycorticosterone (18-OH-B) and were then kept either under normal, or high-CO2 respiratory conditions. Arterial blood samples were withdrawn sequentially from T1 (i.e., 70 minutes after the first injection) on, and were then submitted to determinations of pH and PCO2. Bicarbonate levels were calculated from these data. 18-OH-B: 1) increased pH under both conditions; 2) had a tendency to decrease PCO2 in both conditions; the decrease was significant at 130 minutes after injection, under normal conditions; 3) increased CO3H levels at T1 under high-CO2 atmospheres. Aldosterone did not produce changes in pH values, even if injected in doses equimolar to those of 18-OH-B, but showed a tendency--at these higher doses--to decrease PCO2 values.

The following parameters, RNA and protein content, gland weight and nuclear size were studied in pineal glands of adult male vizcachas, maintained in captivity under permanent light (Lot I) and darkness (Lot II). The same determinations were performed in pineals of vizcachas shot at night in their normal habitat (Lot III, Control lot). A significant rise of gland weight and RNA content was observed in Lot I (with respect to the Control lot), while nuclear size and protein content were unchanged. The only significative differences between Lots I and II were also found in the pineal weight and RNA content. These results indicate that exposure of vizcachas to permanent light for 10 days does not produce inhibition of the parameters under study as occurs in other species. Apparently, the light acts as a stressor in these nocturnal mammals.

The effects of grafting one extra pituitary gland beneath the kidney capsule of prepubertal male and female rats on plasma levels and pituitary content of gonadotropins and prolactin (PRL) in the adult age were studied. Further treatments with dopamine agonistic or antagonistic drugs have been performed in grafted and sham operated controls. PRL and gonadotropin values were measured by specific RIA methods using materials provided by NIAMDD. Plasma prolactin levels showed increased values 48 hr after the grafting, and maintained this elevation throughout the whole studied period. These high PRL levels in grafted rats resulted in a significant decrease of plasma LH values over the whole studied period compared with sham operated controls. Surprisingly an elevation of plasma FSH levels was detected in grafted animals, being the increase only significant in the first 3 months after the grafting. No differences could be detected from control values beyond this period. Female rats showed a constant diestrous anovulatory syndrome. Both male and female grafted rats showed diminished plasma LH and FSH responses to the i.p. LHRH administration. After EB administration control female rats showed a pulsatile response of plasma prolactin, FSH and LH with higher levels found in the afternoon. This pulsatility was abolished for PRL, diminished for LH and exaggerated for FSH in grafted animals. Male grafted rats presented a delay in the EB response pattern compared to control rats. Lisuride treatment (DA agonist) eight months after the grafting resulted in a significant reduction to plasma PRL levels. Acutely Lisuride administration restored LH response to LHRH together with a significant increase in the number of estrus in female rats. Chronic administration of the drug resulted in decreased plasma LH values not only in controls but also in grafted animals, together with an impaired response to LHRH and a significant increase in the number of diestrus in control and experimental rats. On the other hand, both acute or chronic Metoclopramide administration (DA antagonist drug) significantly increased plasma prolactin levels in control and grafted rats. This increase was accompanied by an elevation in the number of estrus in grafted female rats together with a restored LH response to LHRH higher to those observed in control female rats. These data suggest that prolactin influence on gonadotropin secretion and fertility could be mediated by a modification on dopamine secretion.

The effects of nitroglycerin and SIN-1 on atrial rate and intracellular levels of cGMP were studied in the isolated spontaneously beating rat atria. Basal atrial rate was 254 +/- 5 beats X min-1 in the group of experiments performed with SIN-1 and 276 +/- 8 beats X min-1 in that performed with nitroglycerin. No chronotropic effect was detected when nitroglycerin or SIN-1 were added in concentrations ranging from 10(-11)M to 10(-4)M. Measurements of cGMP levels showed that the nucleotide content of atrial tissue increased from a control value of 46.98 +/- 12.1 fmol X mg-1 (w.w.) to 86.4 +/- 3.2 fmol X mg-1 with 10(-5)M SIN-1 and to 107.6 +/- 12.2 fmol X mg-1 with 10(-5)M nitroglycerin (P less than 0.05). The data show no alteration in the chronotropic activity despite the increments in cGMP levels, probably due to an uncoupling between the guanylate cyclase sensitive to SIN-1 and nitroglycerin and the cGMP dependent protein kinase.

The localization of the outermost barrier to chloride influx in the abdominal skin of Leptodactylus ocellatus was investigated by a technique developed by Kidder et al. The method analyses the transient changes in transepithelial electrical potential differences produced when an impermeable anion (SO4(2) or gluconate) is rapidly replaced by Cl in the external bathing solution. The experimental results indicate that the Cl barrier is at the same level as the external Na barrier, that is, at the outward facing membrane of the cells of the stratum granulosum. Further experiments demonstrate that Br behaves like Cl, whereas I seems to behave as an impermeable anion, and that Na is needed for activating the anion permeation mechanism at the external barrier of the epithelium.

The release of 3H-catecholamines evoked by Black Widow spider venom gland extract (BW-GE) has been studied in the isolated rat hypothalamus (HT), occipital cortex (OC), preloaded with 3H-noradrenaline, and isolated caudate nucleus (CN) preloaded with 3H-dopamine. The BWGE at a concentration of 0.04 gland/ml increased significantly 3H-output in isolated slices of rat HT, OC and CN. This effect was markedly depressed when control calcium concentration in the medium (1.68 mM) was reduced (0-0.56 mM) or enhanced (3 mM), as well as in the presence of an organic Ca2+ antagonist, verapamil (10 microM), or ionophore A 23187 (40 microM), a substance that increases the influx of calcium into the cell. Morphine (up to 0.4 mM) evoked no effect upon 3H-noradrenaline release induced by BWGE. Morphine (10 microM), but not ionophore A 23187 or high Ca2+ (3 mM), reduced 3H-noradrenaline release induced by 20 mM K+. Low Ca2+ and verapamil produced similar effects than those observed for BWGE. Our results demonstrate differences between BWGE and potassium stimuli, and indicate that BWGE releases 3H-catecholamines by a calcium dependent process.

Several alterations of thyroid function parameters have been reported in animals treated with indomethacin, and we have studied the effect of this drug on the intrathyroidal iodine metabolism in Wistar rats. Indomethacin was administered by an esophagic tube in two doses (total = 6 mg) given at 0 and 5 hours in experiment I and three doses (total = 9 mg) given at 0, 10 and 23 hours in experiment II. No significant differences in thyroid weight, thyroidal 131I uptake and (131I) iodoaminoacids distribution was observed between the controls and indomethacin treated rats in experiments I and II. In experiment II the intrathyroidal protein bound 131I was not affected by indomethacin, but the extrathyroidal protein bound 131I was markedly affected by the drug, with 72% inhibition. Thyroid peroxidase activity was scarcely affected by the action of the drug. In experiment I indomethacin produced a reduction in serum total thyroxine (T4) of 52%, with a significant elevation in serum total triiodothyronine (T3) of 37%. In experiment II the serum total T4 and T3 levels in indomethacin treated rats were significantly reduced when compared to those of the control rats (77% and 56%, respectively). Serum thyrotropin (TSH) levels did not change in any of the two experiments. In summary, we have found that administration of indomethacin to rats causes an inhibition of thyroid function, measured by decreased thyroid hormone blood levels, without any change in the iodine organification process in these glands.

Weanling male rats weighing 48.5 +/- 1.4 g were divided into two groups, hypoxic and normoxic. The former was placed into an altitude chamber and maintained at a pressure equivalent to 0.45 atm. (6 100 m) over a period of 23 days. The normoxic group was maintained at sea level conditions. Food intake, body weight, body length and tail length were recorded every day. Body weight gain in hypoxic rats was 35% of that seen in normoxic controls at the end of the experimental period. Body length gain was 55% and tail length gain was 59% of normal at the same time. The amount of food eaten by the hypoxic animals during the entire exposure period was 55% of that consumed by normoxic ones. The average daily caloric intake related to metabolic body weight (appetite quotient) of hypoxic rats was 60% of the normoxic control value. Efficiency of protein utilization was not significantly different between both groups of rats. These results indicate that exposure to hypobaric hypoxia induces growth retardation in the rat, which appears to be the result of a diminution in food intake because of a decreased appetite.