Prolactin interacts with gonadotropin through a suppression of c-AMP production probably as a LH-sensitive adenylate cyclase inhibitor.

The interaction between gonadotropin and prolactin (PRL) on ovarian steroidogenesis as well as c-AMP production was studied in rat ovaries. Ovaries obtained from adult female Wistar rats in a morning of proestrus were chopped into 30-40 pieces and subjected to short term incubation studies using various buffers. HCG-stimulated c-AMP, estradiol (E2), progesterone (P) secretions were suppressed in a dose-dependent manner by ovine (o) PRL in a plain Gey-Gey (G-G) buffer. Addition of 3-isobutyl-1-methyl-xanthine (IBMX) increased c-AMP accumulation as well as E2 and P secretions. Deletion of Ca++ from the IBMX buffer stimulated c-AMP production, but suppressed steroid secretion. The inhibitory effect of PRL on E2 and P was not demonstrated in IBMX buffer at any Ca++ concentration examined despite suppression of c-AMP production. In conclusion, it was demonstrated that PRL inhibited gonadotropin-stimulated production of E2 and P by inhibiting c-AMP production. IBMX stimulated accumulation of c-AMP, E2 and P and counteracted with the antigonadal effect of PRL. Ca++ inhibited c-AMP accumulation but stimulated E2 and P secretions. The data suggested that PRL exerts its antigonadal effect through an inhibition of adenylate cyclase action in a manner similar to that of Ca++.