The Effects of Sperm Extracts and Energy Sources on the Motility and Acrosome Reaction of Hamster Spermatozoa in vitro

Abstract

Gestation in rats has been divided into periods to determine when pregnancy can be terminated by LH-RH. After nidation, peptide administration (500 µg b.i.d.) on Day 9, 10 or 11 terminated pregnancy while minimal or no effects were demonstrable from Days 6 to 8 or from Days 13 to 16. Injection for more than one day was also effective if administration included one of Days 9-11. Also, injections on Days 7 and 8 were partially effective. On day 10, the ED₅₀ for b.i.d. administration was 150 µg whereas for a single injection, it was 550 µg. LH-RH treatment on Day 9 was followed by a measurable fall in circulating progesterone on Days 10 and 11. Pregnancy termination by LH-RH from Days 7-12 was reversed by simultaneous administration of large doses of progesterone; the effective progesterone doses were comparable to those required to maintain pregnancy in animals spayed on Day 7 or 8. Addition of estradiol-17β had no potentiating effect on progesterone, while alone it appeared to retard embryonic resorption slightly. These data suggest that the postnidatory antifertility effect of LH-RH is mediated via functional luteolysis.