Characterization of 2-[125I]iodomelatonin-binding sites in quail testes at mid-light and mid-dark

Abstract The binding and pharmacological characteristics of 2-[ 125 I]iodomelatonin binding sites in testis membrane preparations of quails were examined. Scatchard analyses yielded an equilibrium dissociation constant ( K d ) of 46.6 ± 8.6 pmol/l and maximum binding capacity ( B max ) of 2.77 ± 0.20 fmol/mg protein for the gonadal 2-[ 125 I]iodomelatonin binding sites. Except for melatonin, 6-chloromelatonin, 2-iodomelatonin and N -acetylsero-tonin, all compounds tested elicited no significant inhibition of radioligand binding. Significant diurnal variations were detected in serum melatonin levels of 24-week-old quails while no diurnal difference was detected in the affinities or densities of the gonadal 2-[ 125 I]iodomelatonin binding sites in quails. Results of the present study suggest possible direct gonadal action by pineal melatonin in birds.