Melatonin Receptors in Pineal

Melatonin coupled to a binding material has been identified in the pineal gland of the rat using a semi-quantitative immunohistological procedure. Bound melatonin has a daily pattern markedly different from melatonin determined by radioimmunoassay, with low levels early in the light, increasing through the day to a maximum in the early dark. This change is suppressed by acute melatonin or vehicle injection, regardless of when during the day the injections are given. The functional properties of this binding substance are unknown.