In vivo and in vitro studies on effects of beta-endorphin and naloxone on sex steroids in the water frog, Rana esculenta.

The effects of beta-endorphin and its receptor antagonist, naloxone, on progesterone, androgens, and oestradiol-17 beta release in male and female Rana esculenta were studied in vivo and in vitro. In the in vivo experiments the frogs underwent hypophysectomy, gonadectomy or both, or were left intact; the animals were injected with beta-endorphin or naloxone and killed after 15, 30, 90 and 240 min. In the in vitro experiments inter-renal, testis and ovary, all with and without added pituitary, were incubated with beta-endorphin or naloxone for 10, 20, 40 and 80 min. The in vivo and in vitro data from males and females were in agreement. In vivo beta-endorphin increased progesterone in all experimental groups and oestradiol in intact and hypophysectomized frogs, while it decreased androgens in all experimental groups. In vitro beta-endorphin increased progesterone in inter-renal and gonadal tissue, and oestradiol in gonads only, while it decreased androgens in inter-renals and gonads. In vivo and in vitro naloxone induced opposite effects to beta-endorphin. These data suggest that in Rana esculenta, opioids are involved in the modulation of hypothalamo-pituitary-inter-renal and gonadal axes. In particular, the data indicate a direct effect of opioids on inter-renal and gonadal sex steroid production