A Comparison of (125I)iodomelatonin Binding Sites in Testes and Brains of Heavy Meat-Type Japanese Quail With a Randombred Strain

Testes and brain tissue of Japanese quail (Coturnix japonica) from a heavy strain and a randombred strain were assayed for density of [125I]iodomelatonin binding sites (Bmax) and their binding affinity (Kd). The fact that iodomelatonin and melatonin have similar biological action suggests that the [125I]iodomelatonin binding sites are putative melatonin receptors. The heavy strain has lower fertility, higher early embryonic mortality, and lower hatchability than the randombred strain. Although the testes of the heavy males were significantly heavier than those of the randombred males, their testes had significantly fewer melatonin binding sites per milligram of protein as well as relative to total testis protein. There was no difference in the Kd of these binding sites between the two strains. Bmax and Kd of brain tissue of the two strains were not different. Our results suggest a direct relationship between the pineal and the gonads. Selection for fast growth rate may significantly affect the direct regulatory role of melatonin on gonadal function via changes in the sensitivity of the reproductive organ (downregulation) to the action of melatonin.