Effects of various hormones on the pituitary-adrenal axis

Androgen receptor-mediated regulation of adrenocortical activity in the sand rat, Psammomys obesus

The wild sand rat, Psammomys obesus, displays seasonal variations in adrenocortical activity that parallel those of testicular activity, indicating functional cross-talk between the hypothalamo-pituitary-adrenal and hypothalamo-pituitary-gonadal axes. In the present study, we examined androgen receptor (AR)-mediated actions of testicular steroids in the regulation of adrenocortical function in the sand rat. Specifically, we examined the expression of AR in the adrenal cortex, as well as adrenal apoptosis in male sand rats that had been surgically castrated or castrated and supplemented with testosterone; biochemical indices of adrenocortical function and hormone profiles were also measured. Orchiectomy was followed by an increase in adrenocorticotropic hormone secretion from the anterior pituitary and subsequently, increased adrenocortical activity; the latter was evidenced by orchiectomy-induced increases in the adrenal content of cholesterol and lipids as well as adrenal hypertrophy (seen as an elevation of the RNA/DNA ratio). Further, androgen deprivation respectively up- and downregulated the incidence of apoptosis within the glucocorticoid-producing zona fasciculata and sex steroid-producing zona reticularis. Interestingly, orchiectomy resulted in increased expression of AR in the zona fasciculata. All of the orchiectomy-induced cellular and biochemical responses were reversible after testosterone substitution therapy. Together, these data suggest that adrenocortical activity in the sand rat is seasonally modulated by testicular androgens that act through AR located in the adrenal cortex itself.

Sex and strain variability in the rat hypothalamo-pituitary-adrenal (HPA) axis function

In the present investigation, we examined the influence of both genetic background and sex factors in the rat hypothalamo-pituitary-adrenal (HPA) axis function under both basal and post adrenalectomy (ADX) conditions. For these purposes adult female and male rats, from Sprague-Dawley (S-D), Fischer (F344/N), Lewis (LEW/N) and Buffalo (BUF) strains, were decapitated in basal condition or several (2, 7 and 14) days after ADX. Plasma stress hormones levels and adrenal corticosterone (B) concentration as well as peptide (ACTH, CRH and vasopressin, AVP) content in different tissues (anterior pituitary, AP; medial basal hypothalamus, MBH), were then evaluated by specific assays. Our results indicate that: a) despite no sex- and strain-related differences in AP ACTH and MBH ACTH secretagogues in basal condition, there exits a clear sexual dimorphism in plasma ACTH levels as well as in both plasma and adrenal B concentrations, with values significantly higher in females than in males, regardless the strain; b) ADX abolished plasma B levels and increased AP ACTH output in a time-dependent fashion up to the 14th day post surgery; c) AP ACTH content decreased 2 days after ADX, except in BUF female rats, thereafter tending to either recover or increase sham values by two weeks post ADX; d) ADX decreased MBH CRH at all periods studied, except in BUF female animals on day 14; e) ADX clearly diminished MBH AVP only in S-D rats, and f) a sexual dimorphism was also found in AP ACTH in 7-day-ADX S-D rats and in 14-day-ADX S-D and F344/N animals; also, a dimorphic pattern in MBH CRH was found in 7-day-ADX S-D as well as in 14-day-ADX F344/N and LEW/N rats.(ABSTRACT TRUNCATED AT 250 WORDS)