Action of protein kinase A regulators on secretory activity of porcine granulosa cells in vitro

Abstract

To understand the role of protein kinase A (PKA) in the control of ovarian secretory activity, we examined effects of stimulators (db-cAMP, 6-Phe-cAMP, Sp-cDBIMPS) or inhibitors (Rp-cAMPS, KT5720) of PKA on the release of insulin-like growth factor I (IGF-I), progesterone (P) and estradiol (E) by cultured porcine granulosa cells using RIA. All the PKA stimulators db-cAMP (10–10,000 ng/ml), 6-Phe-cAMP (10–10,000 pmol) or Sp-cDBIMPS (1–10,000 pmol) increased IGF-I almost at all doses tested. P release was stimulated by db-cAMP (at doses 100–10,000 ng/ml), Sp-cDBIMPS (at 10–1000 pmol) and 6-Phe-cAMP (at 1000 and 10,000 pmol). The release of E was stimulated by Sp-cDBIMPS (1–100 pmol), db-cAMP (1000 and 10,000 ng/ml) and 6-Phe-cAMP (1000 and 10,000 pmol). Since Sp-cDBIMPS, which activates preferentially PKA isozyme type II, showed stimulating effects at doses lower than those of 6-Phe-cAMP, a preferential activator of both, type I and II of PKA, it is assumed that PKA type II is more important for the control of ovarian steroidogenesis than type I. A PKA inhibitor Rp-cAMPS inhibited release of IGF-I (10,000 pmol), P (1000 pmol) and E (1000 and 10,000 pmol), whereas Rp-cAMPS, at doses higher than 1000 pmol, tended to reverse this inhibitory effect. Other PKA inhibitor KT5720 suppressed P (at 10–1000 ng/ml), but not IGF-I or E release. The stimulation of growth factor and sex steroid release by PKA activators, and suppression of the secretion some of these substances by PKA inhibitors may indicate the implication of PKA (probably site B) in up- and down-regulation of ovarian IGF-I and steroid release.