The Effect of Melatonin on LH-RH Induced Changes in Pituitary and Gonadal Function of Immature Domestic Fowl1

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Abstract
Single comb White Leghorn cockerels received daily s.c. injections of 100 .mu.g melatonin at 1700 h from age 2 through 13 days (LD [light, dark] 14:10; lights on at 0530). Groups of animals then received a single s.c. injection of 2.5 .mu.g LH-RH [luteinizing hormone releasing hormone] (age = 14 days) at different times before autopsy. Testicular response was assayed by the testicular uptake of 32P (administered carrier-free). Melatonin inhibited the LH-RG induced increase in 32P 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 gonadotropin levels decrease, possibly indicating the release of gonadotrophic hormones. During the following 30 min and possibly longer, the pituitary gonadotropin levels increase, possibly indicating the synthesis of new quantities of gonadotropin. A mechanism to explain these results is proposed.