Ovulation induction and antifertility effects of an LH-RH analogue (AY 25,205) in cyclic rats.

Pro-oestrous rats, treated with fluphenazine dihydrochloride to block ovulation, were used to compare the ovulation-inducing activity of synthetic LH-RH with one of its analogues, [D-Ala-6, des-Gly-NH2-10]-LH-RH ethylamide (AY-25,205). The lowest dose of LH-RH which produced a significant response was 125 ng compared with 2.9 ng AY-25,205. Statistical analysis of the data showed that AY-25,205 was approximately thirty-six times more potent than LH-RH. Treatment with AY-25,205 also induced partial ovulation in metoestrous rats (80 or 160 ng/rat) and apparently normal ovulation in dioestrous rats (10 to 160 ng/rat). The compound (160 ng) failed to induce further ovulation in oestrous rats which ovulated during the previous night. Advancement of premature ovulation in dioestrous rats with AY-25,205 prevented mating behaviour and pregnancy during the treatment cycle. The antifertility effect of the compound disappeared during the following cycle.