Abstract

PIP: 10 groups of 4-7 volunteers with regular menstrual cycles participating in 3 protocols were recruited from among 20-40 year old women with no risk of pregnancy for this study of the effect of the luteinizing hormone releasing hormone (LHRH) agonist Buserelin on the onset of pregnancy. 50, 100, 200, 500, 1000, and 1500 mcg doses of Buserelin were administered by a nasal spray device between days 6-12 after the luteinizing hormone (LH) peak. To study the effect of the LHRH agonist treatment on the possible onset of a pregnancy, Buserelin was administered at varying times before and during increasing injections of human chorionic gonadotropin (hCG) mimicking the beginning of pregnancy. The results of the dose-effect study indicated that the corpus luteum is sensitive to a single but high intranasal dose of Buserelin. Administration of 2 successive smaller doses at mid-luteal phases has the same effect and appears preferable. When administered early in the luteal phase, pharmacological doses of LHRH agonist impair the establishment of a normal corpus luteum function leading to luteal phase insufficiency without shortening of the luteal phase. When administered at mid-luteal phase, the LHRH agonist treatment induces luteolysis leading to precocious menses, providing an approach for postcoital contraception in normally cycling women. Preliminary data indicate that LHRH agonist treatment after ovulation could have antifertility effects when administered before implantation. LHRH agonist treatment is ineffective when administered late in the luteal phase concomitantly with the injection of increasing amounts of hCG. Treatment early after ovulation might possibly prevent implantation or lead to impaired secretion of hCG. The mechanism of action of the antifertility effects of LHRH and its analogs remains to be clarified, but several explanations are currently under investigation.