Pinealectomy advances the time of development of steroid feedback on luteinizing hormone release in immature female rats.

The effect of pinealectomy (Px) on the development of steroid positive feedback on luteinizing hormone (LH) release was examined in female rats subjected to surgery at 10 days of age. Estradiol-progesterone injection decreased serum LH in sham Px or intact controls younger than 20 days, while a significant LH release was found at day 22; Px rats showed a steroid-induced LH depression only at day 16, a positive feedback being detectable at day 20, 2 days earlier than in sham Px or intact rats. Daily injections of 10-50 micrograms melatonin to intact rats disrupted the LH negative feedback response at day 20, and diminished steroid-induced LH release at day 24.