Effects of luteinizing hormone-releasing hormone on fetal survival in pregnant rabbits.

The effect of synthetic luteinizing hormone-releasing hormone (LH-RH) on ovulation, implantation, and fetal survival rate was tested in pregnant rabbits. Single doses ranging from 2 to 900 mug, injected intravenously on the 3rd, 5th, or 6th postmating day, did not prevent implantation. Following the intravenous infusion of 20 to 200 mug of LH-RH on day 10 of pregnancy, the fetal survival rate was comparable to that of control rabbits laparotomized at the same stage of pregnancy. However, after repeated doses of 100 mug of LH-RH injected subcutaneously in a delaying vehicle either once or twice daily between the 8th and 13th days of gestation, multiple ovulations and severe luteolysis of original corpora lutea occurred, and fetal survival to term was highly variable. The results suggest that, depending on the dosage administered, LH-RH may either interrupt pregnancy by luteolysis or support fetal survival by stimulating luteotropic activity.