Inhibition of ovulation in the rat by a hCG antagonist

Chemically deglycosylated preparations of hCG (DG-hCG) which have been shown to have hormonal antagonistic activity in vitro were able to compete with 125I-labeled hCG for binding sites in the ovary in pseudo-pregnant rats. DG-hCG at 100 micrograms dose inhibited ovulation by 73% in PMSG-treated rats. Administration of DG-hCG prior to and concurrent with 25 IU hCG reduced ovulation by 37% (P less than 0.05). In mature cycling rats, DG-hCG was capable of inhibiting ovulation when injected on the afternoon of proestrus. These results indicate that DG-hCG can exert its hormonal antagonistic activity in vivo in rats.