Acute effects of gonadotrophins and cyclic AMP on protein synthesis and progesterone production by isolated rat granulosa cells.

Abstract

Amino acid uptake, protein synthesis and progesterone production were studied in rat granulosa cells, isolated from follicles of different stages of development. The amino acid uptake in granulosa cells from prepubertal rats was rapid with a distribution ratio above 1 within 10 min. No significant effects of gonadotrophins were observed on this parameter. The acute influence of exogenous LH and FSH or dibutyryl cyclic AMP (dbcAMP) on incorporation of 3H-leucine or 3H-phenylalanine was investigated as a measure of the rate of protein synthesis. In most experiments progesterone production was determined concomitantly. Both FSH (10 micrograms/ml or 100 micrograms/100 g b.wt.) and dbcAMP (a mM) stimulated (1.6--1.8 fold) the incorporation of leucine into granulosa cell proteins from prepubertal rats while LH was without effect. Progesterone production in these granulosa cells was very low and neither the gonadotrophins nor dbcAMP were stimulatory. Similarly designed experiments were performed on granulosa cells isolated from preovulatory rat follicles. It was then found that both FSH (10 micrograms/ml or 100 micrograms/199 g bst.) and dbcAMP (1 and 5 mM) as well as LH (10 micrograms/ml or 100 micrograms/100 g b.wt.) significantly (1.2--2 fold) stimulated protein synthesis. Furthermore, basal progesterone production was higher and was markedly stimulated (3--6 fold) by all three substances tested. The observations that the protein synthesis in immature granulosa cells is increased by exposure to FSH and dbcAMP while progesterone production in not, whereas both these parameters are stimulated with FSH, LH and dbcAMP in the preovulatory granulosa cells suggest that there might be certain differences in the nature of the proteins synthesized by immature and preovulatory granulosa cells.