Feedback regulation by progesterone of stress-induced prolactin release in rats.

We have previously found that modifications to serum progesterone concentration have profound inhibitory effects on prolactin release in response to ether stress. The objective of the present study was to determine the effect of ether stress on progesterone secretion and the role of this steroid in ether-induced prolactin release. Serum progesterone concentration, 5 min after ether stress had been applied over a 2-min period, was consistently increased in male rats, in cyclic rats on the mornings of pro-oestrus and oestrus, and in androgenized rats in permanent oestrus. Ovariectomized androgenized rats showed the same response. Adrenalectomy of male and female rats abolished the progesterone increase induced by stress. Thus, the progesterone secreted by stressed rats is mostly of adrenal origin. In groups of male and pro-oestrous rats, circulating concentrations of prolactin and progesterone were measured from 5 to 60 min after stress. In both sexes the serum prolactin concentration was significantly increased at only 5 and 10 min after stress when compared with control values. In pro-oestrous rats the serum progesterone concentration was significantly higher than in controls at 5, 10 and 20 min after stress, whilst in male rats the concentration remained significantly higher at 30 min. Thirty minutes after the first stress, male and proestrous rats were etherized for 2 min, and bled 5 min after removal from the ether container. In female rats this second stress produced only a slight but significant increase in serum prolactin concentrations, whereas in male rats prolactin concentrations did not increase.(ABSTRACT TRUNCATED AT 250 WORDS)