Prolongation of the effects of gonadotrophins and prostaglandin E2 on ovarian cyclic AMP formation by inhibitors of protein synthesis.
The effects of LH, FSH and PGE2 on the accumulation of cyclic AMP by isolated whole ovaries from 23-24 day-old rats were studied in time-course experiments in presence and absence of two inhibitors of protein synthesis, puromycin and cycloheximide. In absence of these inhibitors ovarian cyclic AMP levels reached peak levels within 30 min for all three stimulators and returned towards pre-stimulation levels within 2-4 h. When puromycin (500 microgram/ml) or cycloheximide (5 microgram/ml) was present together with LH, FSH or PGE2, respectively, ovarian cyclic AMP levels did not decrease after the initial peak but remained high for the entire incubation period (4-5 h). The release of cyclic AMP to the incubation medium was also much higher when puromycin or cycloheximide was present, illustrating that the effect of puromycin and cycloheximide was not caused by an inhibition of the cyclic AMP release. The effects of puromycin and cycloheximide were, in principle, the same when a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, was present. The results indicate either that there are, in the ovary, proteins with very rapid turn-over, necessary for the mechanism leading to refractoriness of the cyclic AMP system, or that the gonadotrophins and PGE2 as an early effect stimulate the production of a specific protein necessary for the development of refractoriness.