Effect of testosterone on the pressor response to common carotid occlusion in gonadectomized conscious male rats with lesion of the median eminence

The influence of testosterone on the development of the pressor response to common carotid occlusion was investigated in control and median eminence-lesioned male rats. In control rats (N-9), gonadectomy performed 21 days before the experiments reduced by 22% (from 51 ñ 2 to 40 ñ 2 mmHg) and treatment with testosterone (330 µg for 4 days before the measurements) increased the initial peak pressor response (from 51 ñ 2 to 57 ñ 2 mmHg) which depends on carotid innervation. The maintained response which is of central origin (propably ischemic was less affected. In non gonadectomized rats (N=6), lesions of the median eminence (6 days) decreased the initial peak by 19% (from 52 ñ 2 to 42 ñ 3 mmHg) and the maintained response by 56% (from 32 ñ 2 to 14 ñ 1 mmHg). Sham-operated rats served as controls. In gonadectomized animals (N=6) the lesion reduced only the maintained response (from 23 ñ 2 to 11 ñ 1 mmHg). Testosterone supplementation restored the maintained response but did not alter the initial peak. These results indicate that the pressor response to common carotid occlusion in male rats is modulated by testosterone and that the depresiin in the maintained response caused by median eminence lesion can be reversed by steroid supplentation

The role of opioids in the analgesic response of rats during the estrous cycle

The analgesic response was evaluated by the tail immersion test in female rats during each phase of rhe estrous cycle. The reaction time (mean ñ SEM) for tail witdrawal from the hot water bath was faster during proestrus (5.78 ñ 0,28s) and decreased significantly during estrus (5.31 ñ 0.30s) and diestrus 1 (5.40 ñ 0.21s). Blockade of opiate receptors with naloxone (2mg/Kg, ip) invreased the sensitivity to the noxious stimulus only during proestrus (6.46 ñ 0.42 vs 5.02 ñ 0.41 s). These results suggest that the effects of gonadal steroids on nociception may involve an opioid pathway

Involvement of beta-adrenergic receptors in the differential release of gonadotropins in acutely orchidectomized rats

To determine the diferential release fo gonadotropins in acutely orchidectomized rats, a single injection of the beta-adrenergic blocker Bornaprolol (FM 24) was administered to the animals and plasma FSH levels weredetermined. FM 24 produced low plasma FSH levels only when injected 16 h before starting the blood collection and had no effect on FSH levels at 0,30 and 46 h after its administration. However, it produced low LH plasma levels at 0,16 and 30 h after administration. These findings confirm that pituitary beta-adrenergic receptors are involved in plasma LH release and suggest that they could also be involved in the differential release of FSH/LH

The efffect of age on the presssor reponse produced by common carotid artery occlusion in conscious rats

The pressor responses to s of common carotid artery occlusion were studied in conscious male rats of different ages. Compared to rats at the age of 2 months, the initial peak and the maintained response in 6-12 and 18 month old rats were well preserved. In 1-onth old rats, both components were significantly depressed but in 24-month old rats only the initial peak of the pressor response was markedly attenuated. These findings demonstrate that age is an important factor in the response to common carotid artery occlusion wich is more marked for the initial than the maintained response

Pressor responses to common carotid occlusion in female rats: effects of gonadectomy and treatment with gonadal steroid hormones

The pressor responses to common carotid occlusion were studied in conscious female rats throughout the estrous cycle, after gonadectomy and after gonadectomy followed by treatment with estrogen and progesterone. The initial peak pressor response was highest during proestrus and fell significantly over the remaining 3 days of the estrous cycle. The maintained pressor response was relatively unchanged throughout the cycle, except during diestrus 1 when it decreased markedly. Gonadectomy reduced and treatment with estradiol alone increased the initial pressor component, respectively. Treatment of gonadectomized rats with estradiol plus progesterone enhanced both components. These findings suggest that gonadal steroid hormones are important modulators of the pressor to common carotid occlusion