Pre- and Postcoital Contraceptive Activity of LH-RH in the Rat

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Abstract
Synthetic LU-RH was evaluated for pre- and postcoital contraceptive activity after acute and chronic sc administration. LH-RH produced a dose-related delay in vaginal cornification and mating after acute (1230 h) metestrous or diestrous administration to 4 day cycling rats. Acute proestrous LU-RH injection (100 percent ovulatory dose in nembutalized rats) did not delay the estrous cycle or mating. Daily administration of LH-RH (for 4 or 7 days; beginning on metestrus) also produced significant dose-related delays in the vaginal estrous cycle and mating. Rats receiving high (100 ug) either acute or chronic (7 days) precoital injections of LH-RH had a significant decrease in the number of pregnancies and a reduced litter size when mating was delayed. Acute postcoital administration of LH-RH at 1230 h of either Day 3 (D3) or Day 8(D8) of pregnancy produced a significant, dose-related decrease in pregnancy. Acute morning (0900 h) or late afternoon (1500-1600 h) injection of LH-RH on D3 or D8 had a negligible contraceptive effect. Acute injection of LU-RH (1230 h) on days prior to D3, between D3 and D8 had a reduced postcoital contraceptive effect. The data suggest that LH-RH has pre- and postcoital contraceptive activity which may be exerted via the hypothalamo-hypophyseal-gonadal axis.

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