The influence of melatonin (MEL)-free pineal extract on luteinizing hormone (LH) and follicle stimulating hormone (FSH) was studied comparatively with that of MEL. Administration of pineal extract to rats, 3 days running, was found to induce a statistically significant decrease of serum LH and FSH. This effect was also demonstrated by the biological tests used, namely, a decrease in weight of both rat ventral prostate (anti-LH activity) and mouse uterus (anti-FSH activity). MEL administered for 3 days, in doses of 1 μg/day in the ventral prostate weight test or of 10 μg in the uterine weight test, failed to induce comparable effects. The identity of the pineal substances responsible for the anti-gonadotropic activity of the pineal gland is discussed.

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