RAPID BLOCK OF GONADOTROPIN UPTAKE BY CORPORA-LUTEA INVIVO INDUCED BY PROSTAGLANDIN-F2ALPHA

I.v. administration of 125I-hCG [human chorionic gonadotropin] to 7-8 day pseudopregnant rats resulted in maximum uptake or radioactivity to corpora lutea 2 h after treatment. At this time tissue/plasma radioactivity ratios on an equal weight basis were: corpora lutea, 70.2 .+-. 12.8; ovarian interstitium, 4.6 .+-. 0.2; kidney, 2.2 .+-. 0.1. No appreciable uptake was seen by adrenals or liver. Radioactivity in corpora lutea was associated primarily with membranes which sedimented at 2000 g, and when released by heat it was more than 63% bound to luteal LH [luteinizing hormone] receptor preparation in vitro. Radioactivity in renal tissue was associated primarily with the 100,000 g supernatant fraction and was bound less than 1% to luteal LH receptors in vitro. PGF2.alpha. significantly reduced uptake (P < .001) of 125I-hCG by corpora lutea within 30 min (-63%) and at 1 (-64%), 2 (-75%), 4 (-68%) and 24 h (-85%). No clear effect of PGF2.alpha. on uptake of 125I-hCG by ovarian interstitial tissue was seen. Plasma progesterone was decreased (P < .001) within 30 min (-47%; P < .01) after PGF2.alpha. treatment at 1 (-65%), 2 (-85%), 4 (-68%) and 24 h (-92%). Two hours after PGF2.alpha. treatment the content of progesterone in corpora lutea was depressed (-46%; P .cntdot.001). The rapid inhibition of luteal progesterone production induced by PGF2.alpha. in vivo probably occurs through a block in gonadotropin uptake by corpora lutea.