Circadian rhythmicity in the stimulation of bioluminescence by biogenic amines and MAO inhibitors in Gonyaulax polyedra

In the dinoflagellate Gonyaulax polyedra, bioluminescence was investigated in constant darkness. Light emission was stimulated considerably and specifically by the biogenic amines epinephrine, 5-methoxytryptamine, and kynuramine. Various analogues and metabolites of these substances, such as norepinephrine, isoproterenol, phenylephrine, synephrine, metanephrine, dopamine, 3,4-dihydroxymandelic and 3-methoxy-4-hydroxymandelic acids, serotonin, N-acetylserotonin, melatonin, 5-hydroxytryptophol, 5-methoxytryptophol, kynurenine, 4-hydroxyquinoline, 3-hydroxyanthranilic, and quinolinic acids were much less effective. Strong enhancement of bioluminescence, in the range of those obtained with the three stimulatory biogenic amines, was also observed after administration of several compounds acting as MAO inhibitors in mammalian systems, in particular, pargyline, amitriptyline, p-benzoquinone, tranylcypromine, harmaline, and noreleagnine. The responsiveness of cells towards epinephrine, 5-methoxytryptamine, kynuramine, amitriptyline, p-benzoquinone, and noreleagnine varied considerably within the circadian cycle, with the highest stimulations obtained during subjective night. These rhythms can be only partially explained by periodic bioluminescence capacity, and seem to comprise a cyclicity in the sensitivity of cells to the compounds mentioned.