ABSTRACT
In this chapter, topics on melatonin secretion and its rhythm in body fluids are discussed. In the retina, Redburn and Mitchell reported that potassium-induced depolarization was not effective in stimulating melatonin secretion, thus further substantiating the role of passive diffusion in melatonin release. The rhythm of pineal melatonin secretion in mammals depends on an endogenous oscillator which is entrained by the lighting signal received by the retina. The continued elevation in serum melatonin levels following successful irradiation in those patients with initially increased pineal melatonin secretion raises the uncertainty of whether dysregulation of pineal secretory activity may result from either melatonin production by the tumor itself or from the effects of the tumor on normal pineal tissue. Nevertheless, melatonin secretion and its rhythms in biological fluids remain to be an important and productive area of research in the elucidation of pineal melatonin function.
