title: The effects of melatonin in human platelets.
abstract: Pineal melatonin has been implicated in the control of several physiological processes, including circadian rhythmicity and the photoperiodic control of seasonal breeding in mammals. However, its role in humans remains largely undefined. Presumably, melatonin acts on the CNS to affect biologic rhythms; additionally, a number of studies indicate the existence of direct effects of melatonin in peripheral organs, like the platelets. This article discusses experimental data indicating that the human platelets are peripheral cells sensitive to melatonin that could be potentially employed in clinic studies. Melatonin inhibits several physiological processes in platelets including the aggregation phenomenon the release of ATP and serotonin (indexes of the platelet secretory mechanism), and the production of thromboxane B2 A generally greater, and dose-dependent, effect of nanomolar melatonin concentrations in the evening as compared to morning melatonin found in vivo. The maximum in melatonin activity on platelet function precedes the peak in melatonin concentration in blood, indicating the existence of a dissociation between circulating levels and sensitivity to platelet the hormone in normal subjects. In binding studies employing 3H-melatonin as ligand, binding sites in human platelet membranes with a Kd within the nanomolar range were detected. The data suggest the feasibility to employ platelets as peripheral "windows" of central melatonin activity in humans.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Buenos Aires, Argentina.
authors.forename: D P
authors.initials: DP
authors.lastname: Cardinali
authors.forename: M M
authors.initials: MM
authors.lastname: Del Zar
authors.forename: M I
authors.initials: MI
authors.lastname: Vacas
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D001792:Blood Platelets / Q000502:physiology*; D001921:Brain / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D008550:Melatonin / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000378:metabolism; D044094:Receptors, Melatonin; D013929:Thromboxane B2 / Q000096:biosynthesis
chemical_list: D011956:Receptors, Cell Surface; D044094:Receptors, Melatonin; D013929:Thromboxane B2; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D008550:Melatonin