Gender-dependent characteristics of the hypothalamo-corticotrope axis function in glucocorticoid-replete and glucocorticoid-depleted rats

The aim of the present study was to determine the role of the endogenous se x steroid environment in the hypothalamo-corticotrope (HC) function in both sham-operated (SHAM) and bilaterally adrenalectomized (ADX) rats. For this purpose adult rats of both sexes were used 3 and 6 weeks after either SHAM or ADX. The results indicate that: a) in SHAM animals, basal plasma ACTH l evels were significantly higher in females than in males, and this sexual d imorphism was overridden by ADX, regardless of the time postsurgery; b) alt hough basal anterior pituitary (AP) ACTH content was similar in SHAM animal s of both sexes, 3- and 6-week ADX induced higher AP ACTH in males than in females; c) at 3- and 6-weeks, ADX rats of hoth sexes had an AVP:CRH ratio (r), in the median eminence (ME) and medial basal hypothalamus (MBH), incre ased severalfold over the respective SHAM-value and, although no sexual dim orphism was found at week 3 postADX, by 6-weeks post ADX, these ratios were significantly higher in both brain tissues of females than in those of mal es; and d) the in vitro ME CRH and AVP output in response to high potassium concentrations (hK(+); 28 and 56 mmol/l), was concentration-related, regar dless of sex and surgery, and was characterized by enhanced secretion of ne uropeptides by MEs from ADX in comparison to SHAM rats of both sexes, and a sexual dimorphism was found in this parameter, consisting in general, in g reater neuropeptide output from tissues of female than of male animals. Our results indicate that: 1) there is a gender-dependent characteristic of th e HC axis function in glucocorticoidreplete rats and 2) the absence of the glucocorticoid negative feedback mechanism is responsible for either the ex pression or for the override of the sexual dimorphism in different paramete rs, a phenomenon which dependent on the time elapsed after ADX. (C)1998, Ed itrice Kurtis.