Effect of vasoactive intestinal peptide on monkey prolactin secretion and cyclic AMP in culture: interaction with estradiol and phenol red

To test the hypothesis that estrogenic compounds may decrease the sensitivity of primate lactotropes to adenylate cyclase-mediated secretagogues, the effect of VIP on prolactin secretion and cAMP levels in serum-free monkey pituitary monolayer cultures was examined in the presence and absence of estradiol (E) and phenol red. In two experimental designs, E treatment was initiated on either the day after dispersion (split plate design) or 10 days after serum-free culture (whole plate design). VIP challenges (5, 50 and 500 nM) were administered for 4 h on days 10 and 20 of culture. There was a significant decrease in the maximal percent stimulation of prolactin by VIP when cultures were treated with E or phenol red. The average percent increase in prolactin at 5, 50 and 500 nM VIP equalled 23, 83 and 156% in the absence of phenol red, but equalled 14, 43 and 112% when E was added to phenol red-free cultures. The percent stimulation by VIP in the presence of phenol red averaged 32, 62 and 97%, but addition of E with phenol red decreased the average stimulation to 26, 45 and 72%, respectively. Basal levels of cAMP were increased by E and phenol red. However, the maximal percent stimulation of cAMP by VIP was decreased in the presence of E and phenol red. In summary, E and phenol red act to decrease the maximal percent stimulation of prolactin secretion by VIP. This effect is reflected by a decrease in the maximal percent stimulation of intracellular cAMP.