SEX AND STRAIN VARIABILITY IN THE RAT HYPOTHALAMO-PITUITARY-ADRENAL (HPA) AXIS FUNCTION

In the present investigation, we examined the influence of both geneti c background and sex factors in the rat hypothalamo-pituitary-adrenal (HPA) axis function under both basal and post adrenalectomy (ADX) cond itions, For these purposes adult female and male rats, from Sprague-Da wley (S-D), Fischer (F344/N), Lewis (LEW/N) and Buffalo (BUF) strains, were decapitated in basal condition or several (2, 7 and 14) days aft er ADX, Plasma stress hormones levels and adrenal corticosterone (B) c oncentration as well as peptide (ACTH, CRH and vasopressin, AVP) conte nt in different tissues (anterior pituitary, AP; medial basal hypothal amus, MBH), were then evaluated by specific assays, Our results indica te that: a) despite no sex- and strain-related differences in AP ACTH and MBH ACTH secretagogues in basal condition, there exits a clear sex ual dimorphism in plasma ACTH levels as well as in both plasma and adr enal B concentrations, with values significantly higher in females tha n in males, regardless the strain; b) ADX abolished plasma B levels an d 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, excep t 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 pe riods 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 al so found in AP ACTH in 7-day-ADX SD rats and in 14-day-ADX S-D and F34 4/N animals; also, a dimorphic pattern in MBH CRH was found in 7-day-A DX S-D as well as in 14-day-ADX F344/N and LEW/N rats, Our findings fu rther indicate that both sex- and genetic-factors are able to modulate the rat HPA axis function under both physiological and pathophysiolog ical conditions.