TRANSIENT SEX-RELATED CHANGES IN THE MICE HYPOTHALAMO-PITUITARY-ADRENAL (HPA) AXIS DURING THE ACUTE-PHASE OF THE INFLAMMATORY PROCESS

THE potential role of endogenous sex hormones in regulating hypothalam o-pituitary-adrenal (HPA) axis function was investigated after a singl e, injection of endotoxin in adult (8 week old) BALB/c mice of both se xes. The effect of LPS on plasma ACTH, corticosterone (B), testosteron e and oestradiol (E) levels and on anterior pituitary (AP) ACTH and ad renal B contents at different times after treatment was studied. The r esults indicate that: (a) basal B but not ACTH plasma levels were sign ificantly higher in female than in male mice; (b) LPS significantly in creased both ACTH and B plasma levels over the baseline 2 h after inje ction, both hormone levels being higher in female than in male mice; ( c) although plasma ACTH concentrations recovered the basal value at 72 h after LPS in animals of both sexes, plasma B levels returned to the baseline only at 120 h after treatment; (d) E plasma levels significa ntly increased 2 h after LPS and returned to the baseline at 72 h post -treatment, in both sexes; (e) at 2 h after LPS, testosterone plasma l evels significantly decreased in male mice and increased in female mic e, recovering the baseline level at 120 and 72 h after LPS, respective ly; (f) AP ACTH content was similar in both sexes in basal condition a nd it was significantly diminished 72 h post-treatment without sex dif ference; whereas AP ACTH returned to basal content 120 h after LPS in males, it remained significantly decreased in females; (g) basal adren al B content was higher in female than in male mice, and it significan tly increased in both sexes 2 h post-LPS, maintaining this sex differe nce. Whereas adrenal B returned to basal content 72 h after treatment in male mice, it remained significantly enhanced up to 120 h post-LPS in female animals. The data demonstrate the existence of a clear sexua l dimorphism in basal condition and during the acute phase response as well as in the recovery of the HPA axis function shortly after infect ion.