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

CHISARI, AN; PERONE, MJ; GIOVAMBATTISTA, A; SPINEDI, E

JOURNAL OF ENDOCRINOLOGICAL INVESTIGATION

EDITRICE KURTIS S R L

Año: 1998

0391-4097

The aim of the present study was to determine the role of the endogenous sex steroid environment in the hypothalamo-corticotrope (HC) function in both sham-operated (SHAM) and bi-laterally adrenalectomized (ADX) rats. For this pur-pose adult rats of both sexes were used 3 and 6 weeks after either SHAM or ADX. The results in-dicate that: a) in SHAM animals, basal plasma ACTH levels were significantly higher in females than in males, and this sexual dimorphism was overridden by ADX, regardless of the time post-surgery; b) although basal anterior pituitary (AP) ACTH content was similar in SHAM animals 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), increased several fold over the respective SHAM-value and, although no sexual dimorphism was found at week 3 post-ADX, by 6-weeks post ADX, these ratios were sig-INTRODUCTION Hypothalamo-pituitary-adrenal (HPA) axis function is the result of different feedback mechanisms at the three levels of the neuroendocrine system (1). CRH and arginine-vasopressin (AVP) are the major mediators of anterior pituitary (AP) ACTH synthesis and secretion (1). In the paraventricular nucleus (PVN) of the hypothalamus, CRH and AVP are co-lo-calized in parvicellular neurons that project to the external zone of the median eminence (ME) (2). Key-words: Adrenalectomy, CRH, AVP, ACTH, neurosecretion, sex steroids. Correspondence: Dr. Eduardo Spinedi, IMBICE, cc 403, 1900 La Plata, Argentina. Accepted July 6, 1998. 737 nificantly higher in both brain tissues of females than in those of males; and d) the in vitro ME CRH and AVP output in response to high potassium concentrations (hK+; 28 and 56 mmol/l), was con-centration-related, regardless of sex and surgery, and was characterized by enhanced secretion of neuropeptides by MEs from ADX in comparison to SHAM rats of both sexes, and a sexual dimor-phism was found in this parameter, consisting in general, in greater neuropeptide output from tis-sues of female than of male animals. Our results in-dicate that: 1) there is a gender-dependent char-acteristic of the HC axis function in glucocorticoid-replete rats and 2) the absence of the glucocorti-coid negative feedback mechanism is responsible for either the expression or for the override of the sexual dimorphism in different parameters, a phe-nomenon which dependent on the time elapsed after ADX.