Regulation of Progestin Biosynthetic Enzymes in Cultured Rat Granulosa Cells: Effects of Prolactin, β₂-Adrenergic Agonist, Human Chorionic Gonadotropin and Gonadotropin Releasing Hormone¹

Abstract

Prolactin (Prl), β₂-adrenergic agents and human chorionic gonadotropin (hCG) are luteotropic in rats, whereas gonadotropin releasing hormone (GnRH) exerts direct inhibitory effects on ovarian steroidogenesis. The present study examined the modulation of the progestin biosynthetic pathway by the luteotropic agents, as well as the actions of GnRH. Rat granulosa cells were primed with follicle-stimulating hormone (FSH) to increase their responsiveness to the luteotropic agents. Subsequent treatment for 2 days with Prl, terbutaline (a β₂-adrenergic agonist) or hCG stimulated the production of progesterone, 20α-hydroxypregn-4-en-3-one (20α-OH-P), pregnenolone and the activity of 3β-hydroxysteroid dehydrogenase (3β-HSD). In contrast, treatment with Prl or terbutaline, but not hCG, inhibited 20α-hydroxysteroid dehydrogenase (20α-HSD) activity by decreasing the apparent maximal velocity of the enzyme with no change in its Km value. Concomitant treatment with GnRH inhibited progesterone, but increased 20α-OH-P production stimulated by Prl or terbutaline. These effects were associated with a stimulation of 20α-HSD activity, while neither 3β-HSD activity nor pregnenolone biosynthesis was decreased. In contrast, GnRH inhibited progesterone production in hCG-treated cells without affecting 20α-OH-P production. This was associated with an inhibitory effect of GnRH on pregnenolone biosynthesis with no effect upon 3β-HSD activity. Thus, Prl and the β₂-agonist stimulate progesterone production in granulosa cells by increasing pregnenolone production and 3β-HSD activity as well as by decreasing 20α-HSD activity, while hCG stimulates progesterone production by increasing pregnenolone production and 3β-HSD activity. The inhibitory effect of GnRH on Prl- or terbutaline-stimulated progesterone production appears to result from a preferential increase in 20α-HSD activity, while the GnRH inhibition of hCG-stimulated progesterone production appears to result from a preferential inhibition of pregnenolone production.

Author notes

¹

This work was supported by NIH research grant HD-14084 and program project grant HD-12303. In partial fulfillment of the PhD degree of P.B.C.J.

³

Recipient of Research Career Development Award HD-00375