Sex-related differences in the analgesic response to the rat tail immersion test

The analgesic response was evaluated by the tail immersion test in adult male (N = 30), female (N = 21) and androgenized female Wistar rats (N = 15). The reaction time for tail withdrawal from the hot water bath was faster for male than for female rats (3.48 +/- 0.12 vs 6.46 +/- 0.42 s). The reaction time of androgenized female rats was similar to that of male rats (3.08 +/- 0.16 s). Blockade of opiate receptors with naloxone (2 mg/kg, ip) decreased the sensitivity to the noxious stimuli in males (4.08 +/- 0.10 s) and in androgenized females (3.69 +/- 0.19 s) but increased it in female rats (5.01 +/- 0.41 s). These data show sex-related differences in the analgesic response evaluated by the tail immersion test and indicate that administration of androgens to newborn female rats affects their pain sensitivity.

Sex-related differences in cardiovascular responses to common carotid occlusion in conscious rats

Mean arterial pressure and heart rate were determined in conscious, unrestrained groups of 10 male, female and androgenized female Wistar rats 20 s (early pressor response) and 1 min (late sustained response) after bilateral carotid artery occlusion. The early pressor response, which is carotid reflex origin, was 40% greater in female than in male rats (45 ñ 2 vs 63 ñ 3 mmHg, respectively). The late sustained response, which is of central origin (probably ischemic), did not differ between male and female rats (32 ñ 2 vs 37 ñ 4 mmHg, respectively). The magnitude of the early pressor response of androgenized female rats (50 ñ 2 mmHg) was similar to that of male rats (45 ñ 2 mmHg) but the late sustained response was 19% smaller (26 ñ 2 mmHg). Common carotid occlusion caused increases in haert rate which were greater in female (51 ñ 9 and 34 ñ 9 beats/min in the early pressor response and late sustained response respectively) than in male rats (31 ñ 5 and 8 ñ 4 beats/min, respectively). In androgenized female rats, heart rate decreased during common carotid occlusion (34 ñ 7 and 35 ñ 8 beats/min after 20 s and 1 min, respectively). These data provide evidence that there are substantial sex-related differences in the cardiovascular responses to common carotid occlusion in conscoious rats and indicate that administration of androgens to newborn female rats affects the baroreceptor reflex control of their arterial pressure

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

Participation of opioid receptors in the modulation of the analgesic response by adrenal and gonadal glands

The invovlement of opiodi receptors in the analgesic response was evaluated by the tail-immersion test in simultaneously adrenalectomized and ovariectomized female Wistar rats (210-250g). The reaction time (mean ñ SEM) for tail withdrawal from hot water decreased significantly 2 weeks after surgery (3.52 ñ 0.20 s) when compared to intact animals (6.09 ñ 0.23 s). Hormonal replacement with dexamethasone (50*/day) did not affect reaction time (3.38 ñ 0.19 s). However, this response was restored by combined adrenal and gonadal steroid substitution (estradiol 5*g/day and progesterone 1.5*g 6h before the test) therapy (5.11 ñ 0.45 s) in animal treated with dexamethasone plus estradiol and 5.04 ñ 0.43 s in animals treated with dexamethasone plus estradiol plus progesterone). Naloxone (2mg/Kg decreased the reaction time of animals treated with adrenal and gonadal steroids (5.11 ñ 0.45 vs 4.15 ñ 0.44 and 5.04 ñ 0.43 vs 3.87 ñ 0.28 s, respectively, before and after naloxone) but failed to decrease it in rats treated with dexamethasone only (3.88 ñ 0.18 vs 4.34 ñ 0.25 s, before and after naloxone). These observations indicate that gonadal steroids are the most important steroid factors involved in the reaction time to tail immersion in hot water and confirm other reports that the opioid pathways modulating the neuronal circuitry require the presence of these hormones

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

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