Pattern of adenohypophyseal hormone changes induced by various stressors in female and male rats.

Plasma modifications of adenohypophyseal hormones were investigated in groups of female and male rats stressed for 15, 30 min, 1, 2, 4 or 6 h, either by cold (4 degrees C), forced muscular exercise (FME), or immobilization. GH levels in both female and male rats were consistently decreased by the 3 stressing agents. Immobilization in the female and the 3 stressors in the male elicited an early secretory response of prolactin (Prl), while only in immobilized female rats plasma LH levels showed an early, short-lived increment. A more prolonged exposure to stress had an inhibitory influence on plasma Prl and LH levels in both sexes. FSH concentrations were not modified in females, but were decreased in male rats submitted to either one of the 3 stressors. In both male and female rats plasma TSH levels rose during cold exposure, while they were decreased by FME and by immobilization. Our data indicate that the character of the hormonal secretory response during stress is nonspecific. Indeed, to the exception of the specific stimulation of TSH release by cold, stress-induced hormonal changes are not related to the nature but rather to the intensity and duration of the stressing agent.