Effect of administration of a gonadotropin-releasing hormone (GnRH) antagonist (Nal-Glu) during the periovulatory period: the luteinizing hormone surge requires secretion of GnRH

In primates, the LH surge that triggers ovulation is induced by an increase in circulating estradiol (E2) levels. Although several studies suggest that E2 acts on the pituitary, it is still not clear whether GnRH is involved. We investigated the role of GnRH during the periovulatory period in normal women by treating them with the GnRH antagonist Nal-Glu ([Ac-D2Nal1,D4-ClPhe2,D3Pal3,Arg5,DGlu6 (AA),DAla10] when E2 levels exceeded 550 pmol/L. In the first study (A), Nal-Glu was administered in five regimens (n = 4 in each group): a single sc injection of 10 mg (group 1), a single injection of 20 mg (group 2), and an injection of 10 mg, sc, on 2 (group 3), 3 (group 4), and 5 consecutive days (group 5). In the second study (B; n = 4), Nal-Glu (10 mg, sc, on 3 consecutive days) was coadministered with E2 benzoate (EB; 0.5 mg, im, every 12 h on 3 consecutive days). Controls (n = 4) were treated with EB alone at the same stage of the cycle. In the third study (C), three women received 10 mg/day Nal-Glu, sc, on ...