Cyclic AMP in isolated corpora lutea of the rat: influence of gonadotrophins and prostaglandins.

Abstract

ABSTRACT Corpora lutea were isolated from 34–39 day-old rats injected with 10 IU PMSG when 30 days old leading to ovulation early in the morning of day 33. Three day-old corpora lutea were incubated in Krebs bicarbonate buffer containing 5.5 mmol/l glucose. Addition of LH to the incubation medium increased accumulation of cyclic 3′, 5′-AMP (cAMP) in a dose-dependent way in the isolated tissue and caused a release of cAMP to the incubation medium. cAMP was determined by the protein binding technique of Gilman (1970). There was a continuous rise in the levels of cAMP in both tissue and medium with increasing incubation time in presence of LH. Neither prolactin nor FSH could influence the cAMP levels in the corpus luteum tissue in vitro. Prostaglandin E2 (PGE2) caused a stimulation with respect to cAMP formation. The time-course of the PGE2 effect was quite different from that of LH: PGE2 gave maximal tissue cAMP content within 5–15 min with decreasing levels thereafter, compared to the continuous rise with LH stimulation for at least 1 h. In experiments performed on corpora lutea of different ages (1–7 day-old), tissue levels of cAMP were determined after incubations with LH or PGE2. There was a dramatic increase of tissue cAMP in the very young corpus luteum and a marked decrease in sensitivity to LH with increasing age of the corpus luteum with a very small but still significant effect on the old corpora lutea. The stimulatory effect of PGE2 on cAMP levels on the other hand showed only a minimal change. A few experiments on the first generation of corpora lutea from mature cycling rats are also reported for comparison.