Melatonin binding sites in the Harderian gland of Syrian hamsters: sexual differences and effect of castration.

The presence of specific melatonin binding sites in the Harderian gland of Syrian hamsters was studied using [125I]melatonin. Saturation binding experiments conducted with [125I]melatonin at 37 degrees C using Harderian glands of both male and female Syrian hamsters revealed a single nanomolar-affinity site. The dissociation constants (Kd) were 6.47 and 6.94 nM for males and females, respectively. The concentration of the binding sites was 7.58 fmol/mg protein for males and 13.50 fmol/mg protein for females. Castration of male hamsters resulted in a significant increase in [125I]melatonin binding sites while chronic melatonin administration did not modify the binding properties. The results confirm the presence of melatonin binding sites in the Harderian glands of rodents. The gender-associated differences found together with the effects of castration in male hamsters suggest an androgenic control in [125I]melatonin binding sites of the Syrian hamster Harderian gland.