INCREASED VASOPRESSINERGIC ACTIVITY AS A POSSIBLE COMPENSATORY MECHANISM FOR A NORMAL HYPOTHALAMIC-PITUITARY-ADRENAL AXIS RESPONSE TO STRESS IN BALB C NUDE-MICE/

A bidirectional relationship between the immune and neuroendocrine sys tems is now widely accepted. Since it is well known that the thymus pl ays an important role in the regulation of the immune function, we dec ided to explore whether a lack of the thymic function may influence hy pothalamic-pituitary-adrenal (HPA) axis activity. Eight-week-old femal e mice of both strains, nude and control BALB/c, were used to study: ( a) the in vivo response of the HPA axis to several stress stimuli acti ng at either the hypothalamic (insulin administration and ether vapor inhalation), pituitary (CRH and vasopressin injections) or adrenal (AC TH treatment) level and (b) the in vitro response of hypothalamic frag ments to high KCl (48 mM) stimulation. The results indicate that: (1) basal plasma ACTH and vasopressin levels were significantly (p < 0.05) higher in nude than in control BALB/c mice, whereas basal plasma cort icosterone concentrations were similar in both strains of mice; (2) al though no significant strain-related difference in the stress-induced ACTH secretion in plasma was found, hypothalamic stimuli were able to induce a significantly (p < 0.05) higher secretion of glucocorticoid i n plasma in nude than in control BALB/c mice; (3) the pattern of in vi tro hypothalamic CRH release was similar in both strains of animals; h owever, basal AVP output and that stimulated by 48 mM KCl were signifi cantly (p < 0.05) higher in nude than in control hypothalamic fragment s, and (4) whereas hypothalamic CRH, pituitary ACTH and adrenal glucoc orticoid contents were similar in both strains, hypothalamic AVP conte nt was significantly (p < 0.05) higher in athymic than in control mice . In summary, our results indicate that nude mice have an increased va sopressinergic function which could contribute to a normal HPA axis ac tivity; thus, adult athymic mice of BALB/c origin could compensate, du e to their increased vasopressinergic function, for a robust glucocort icoid release to protect themselves immediately after aggression. It r emains to be determined whether this enhanced vasopressinergic functio n is a result of an early adrenal insufficiency due to congenital defi ciency of thymic factors known to stimulate HPA axis function.