Effects of inhibitors of protein synthesis on the ovulatory process of the perfused rat ovary

The effects of two different protein synthesis inhibitors (cycloheximide and puromycin) on the ovulatory process were examined in vitro using a perfused rat ovary model. Ovaries of PMSG (20 i.u.)-primed rats were perfused for 21 h. Release of cyclic adenosine 3',5'-monophosphate (cAMP) and steroids (progesterone, testosterone, and oestradiol) was measured and the number of ovulations was estimated by counting released oocytes. Unstimulated control ovaries did not ovulate whereas addition of LH (0.1 microgram/ml) plus 3-isobutyl-1-methylxanthine (IBMX; 0.2 mM) resulted in 16.7 +/- 3.5 ovulations per treated ovary. Cycloheximide (5 micrograms/ml) totally inhibited the ovulatory effect of LH + IBMX when present from the beginning of the perfusions and also when added 8 h after LH + IBMX. No inhibition was seen when cycloheximide was added 10 h after LH + IBMX (1-1.5 h before the first ovulation; 15.2 +/- 4.4 ovulations per treated ovary). Puromycin (200 micrograms/ml) completely blocked ovulation when present from the beginning of the perfusions and the inhibition was congruent to 60% (6.5 +/- 2.2 ovulations per treated ovary) when the compound was added 8 h after LH + IBMX. Both inhibitors increased LH + IBMX-stimulated cAMP release substantially, but decreased the release of progesterone, testosterone and oestradiol. These results indicate that de-novo protein synthesis is important late in the ovulatory process for follicular rupture to occur.