Role of sex and sex steroids in mediating pituitary-adrenal responses to acute buspirone treatment in sheep

Serotonergic effects on feeding, but not hypothalamus-pituitary-adrenal secretion, are altered in ovine pregnancy

In ovine pregnancy, as in human pregnancy, hypothalamus-pituitary-adrenal activity is chronically increased. These studies were designed to test the hypotheses that expression of serotonergic genes and responsiveness to serotonin are increased in pregnancy. We tested the stimulatory effect of an acute, intracerebroventricular injection of the serotonin reuptake inhibitor fluoxetine on plasma ACTH and cortisol in ewes during late pregnancy or postpartum. We also tested the effect of lower-dose, longer-term stimulation by intracerebroventricular infusion of fluoxetine in pregnant and nonpregnant ewes over 6 days. Overall, we found that the stimulatory effect of fluoxetine on ACTH and cortisol was not significantly different between late-gestation and nonpregnant ewes, although the effect of acute fluoxetine administration was inversely related to plasma progesterone concentrations. Also, there were no differences in hypothalamic expression of the glucocorticoid and mineralocorticoid receptors, corticotropin-releasing hormone, AVP, the serotonin reuptake transporter, or the serotonin [5-hydroxytryptamine (5-HT)] receptors 5-HT(1A) and 5-HT(2A) with pregnancy or fluoxetine treatment. However, chronic fluoxetine infusion reduced food intake in the nonpregnant, but not pregnant, ewes. Expression of proopiomelanocortin mRNA in the hypothalamus was reduced in pregnant compared with nonpregnant ewes. Our results indicate that pregnancy does not increase responsiveness of ACTH and cortisol to serotonergic stimulation but, rather, that progesterone reduces the ACTH response. In addition, we found a reduced ability of serotonin to inhibit feeding in the pregnant ewes, consistent with a reduction in anorexic mechanisms in the pregnant state.

Dihydrotestosterone differentially modulates the cortisol response of the hypothalamic-pituitary-adrenal axis in male and female rhesus macaques, and restores circadian secretion of cortisol in females

Here we used a within-subject design to evaluate hypothalamic-pituitary-adrenal (HPA) activity following replacement of low and high physiological levels of testosterone (T) to adult, gonadally-suppressed, male rhesus macaques, and replacement with sex-specific low and high physiological doses of dihydrotestosterone (DHT) in the same adult males as well as in adult, gonadally-suppressed, female rhesus macaques. As indexes of HPA axis activation following T and DHT replacement, serum levels of cortisol (CORT) were measured before and following dexamethasone (DEX) inhibition, and corticotrophin-releasing factor (CRF) induced activation. Female monkeys were assessed for differences in response associated with dominant (DOM) and subordinate (SUB) social status. Data show that the high physiological dose of DHT significantly decreased basal CORT in both male and female monkeys irrespective of social status, but reduced CRF-stimulated CORT only in males. SUB female monkeys showed a trend towards increased CRF-stimulated CORT release under high-dose DHT replacement compared to DOM females or males given the same treatment, indicating that androgens likely have no influence on reducing HPA activation under chronic psychosocial stress in females. The normal circadian rhythm of CORT release was absent in placebo-replaced SUB and DOM females and was restored with low-dose DHT replacement. These results indicate that DHT significantly reduces CRF-stimulated CORT release only in male monkeys, and plays a role in maintaining circadian changes in CORT release in female monkeys.