effect of melatonin on LH RH induced changes in pituitary and gonadal function of immature domestic fowl

Single comb White Leghorn cockerels received daily subcutaneous injections of 100 µg melatonin at 1700 h from age 2- through 13-days (LD 14:10; lights on at 0530). Groups of animals then received a single subcutaneous injection of 2.5 µg LH-RH (age = 14-days) at different times before autopsy. Testicular response was assayed by the testicular uptake of 3 2 P (administered carrier-free). Melatonin inhibited the LH-RH induced increase in 3 2 P uptake by the testes. Gonadotrophin bioassays of the anterior pituitary glands from treated animals showed that during the first 90 min of LH-RH availability the pituitary gonadotrophin levels decrease, possibly indicating the release of gonadotrophic hormones. Then, during the following 30 min and possibly longer, the pituitary gonadotrophin levels increase, possibly indicating the synthesis of new quantities of gonadotrophin. A mechanism to explain these results is proposed.