Lack of specific prostaglandin antagonistic effects of 7-oxa-13-prostynoic acid on ovarian metabolism in vitro.

Prostaglandins (PGs) have been proposed to function as obligatory intermediates in the action of luteinizing hormone (LH) (Kuehl et al. 1970). This based on experiments on isolated mouse ovaries where the substance 7-oxa-13-prostynoic acid (7-oxa-13-PA) was found to block the effect of both PGE1 and LH on ovarian cyclic AMP formation and progesterone synthesis. We have studied whether 7-oxa-13-PA acts as a PG antagonist also on the isolated rat ovary, where PGs of the E type have many effects. Prepubertal rat ovaries were incubated up to 4 h in modified Krebs bicarbonate buffer containing glucose with PGE1 and 7-oxa-13-PA, alone and in combination. PGE1 stimulated the uptake of the non-utilizable amino acids alpha-aminoisobutyric acid (AIB) and cycloleucine in an equally wide dose-range as has earlier been found for the stimulation of lactic acid and cyclic AMP production as well as protein synthesis. 7-oxa-13-PA alone, in concentrations exceeding 25 microgram/ml, stimulated lactic acid production, but inhibited the incorporation of labelled leucine and the uptake of AIB. The uptake of cycloleucine was slightly stimulated. 7-oxa-13-PA did not antagonize the PGE1 effect on lactic acid production. 7-oxa-13-PA diminished the PGE1 effect on the uptake of amino acids and the incorporation into protein, but only in concentrations where it in itself inhibited the protein synthesis. These results show that 7-oxa-13-PA does not act as a PG-antagonist in the prepubertal rat ovary, since it cannot block the effects of PGs without having marked inherent effects.