Effects of estradiol and progesterone on PRL release from dispersed pituitary cells of immature female lambs.

The effects of 17 beta-estradiol (E2), progesterone (P) and their combination on PRL release were studied in immature female lamb pituitary cells. Lambs born in February (slaughtered at 12-13 weeks of age) (Y) or older (O) born out of season in the previous year and carried over to April (hoggets) were used as pituitary donors. The cells were preincubated for 24 h in the presence or absence of steroids, then washed and incubated for 2 h. E2 (100 pg ml-1) and P at the highest dose used (10 ng ml-1) depressed significantly the PRL release in Y. In contrast to these effects E2 (100 or 1000 pg ml-1) stimulated PRL release while P (0.1-10 ng ml-1), inversely related to the concentration, had a positive effect in O. In (E2+P)-treated cells, P (1 or 10 ng ml-1) led to a reversal of the inhibitory effect of E2 (100 pg ml-1) in Y. On the other hand when older pituitary donors were used the effect of simultaneous administration of E2 and P was additive. The results suggest that E2 and P can alter PRL release at the pituitary level. Negative or positive effects of the steroids were dependent on the steroid used, its concentration and the developmental stage of the pituitary donors. The stimulating effect was higher when the steroids were used simultaneously.