DYNAMICS OF PHOTO-INDUCED ALTERATIONS IN PINEAL BLOOD FLOW

Abstract

Department of Physiology and Biophysics, Colorado State University, Fort Collins, Colorado 80523, U.S.A. ( Received 13 September 1977) Mammalian pineal gland activity is controlled by environmental lighting schedules. Light exerts its influence via a neuronal pathway originating in the retina (Moore & Klein, 1974) and as a consequence of this photoperiodic control, the concentration of melatonin in the plasma is raised during periods of darkness and depressed during periods of light (Rollag & Niswender, 1976). The response of the pineal gland to photostimulation is surprisingly rapid. Within 5 min of a darkness to light transition, there is a precipitous decline in pineal N -acetyltransferase activity in the rat (Deguchi & Axelrod, 1972; Klein & Weller, 1972). In sheep, peripheral concentrations of melatonin decline within 5–10 min of a darkness to light transition (Rollag, O'Callaghan & Niswender, 1978). A circadian rhythm of blood flow to the pineal gland analogous to the rhythm of melatonin