Abstract
The metabolism of pineal indoles is closely related to alterations in the light and dark phases of a daily cycle. Recent research showed important interspecies differences in the pineal biochemistry, and a strong impact of monochromatic light on many physiological processes in birds. Therefore, the aims of study were to characterize the metabolism of melatonin-synthesis indoles in the pineal organ of the domestic turkey, and to determine the changes occurring in this metabolism under the influence of different wavelengths and intensities of light. For this purpose, 3-week-old turkeys were kept under 16 lx white light, or under blue, green, and red light with intensities of 16, 32, and 64 lx during the photophase, and after 7 d were sacrificed at 4 h intervals. The activities of melatonin-synthesizing enzymes and the contents of indoles were measured in the same pineal organ. The results revealed that the activities of tryptophan hydroxylase and arylalkylamine N-acetyltransferase, and the levels of all tryptophan derivatives had significant daily changes in birds kept under each light condition used. The profile of pineal indole metabolism in 4-week-old turkeys was characterized by high-amplitude rhythms in the activity of arylalkylamine N-acetyltransferase and the contents of N-acetylserotonin and melatonin, equal relative amounts of serotonin and 5-hydroxyindoleacetic acid, and higher content of melatonin than N-acetylserotonin. The monochromatic light significantly modified the pineal indole metabolism, and its effects were dependent on the color and intensity of light. Pronounced changes occurred in the level of serotonin synthesis and the daily rhythm course of melatonin synthesis.
Highlights
Many physiological processes in birds are closely correlated with day and night alterations
The tryptophan hydroxylase (TPH) activity was significantly increased, at all time-points, in animals kept under red light with intensities of 32 and 64 lx, compared with turkeys from other groups
The profile of pineal indole metabolism in 4-week-old turkeys is characterized by (i) high-amplitude rhythms in arylalkylamine N-acetyltransferase (AA-NAT) activity and the contents of NAS and MLT, (ii) equal relative amounts of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA), and (iii) higher content of MLT than NAS. This profile differs markedly from that in the chicken by the intensity of 5-HT oxidative deamination and the mechanisms responsible for the generation of 5-methoxyindoleacetic acid (5-MIAA) and 5-MTOL rhythms, and from those in the goose and duck pineal organs by the amplitudes of NAS and MLT rhythms and the proportion of NAS to MLT. These data strongly support the idea that metabolism of pineal indoles shows important species-specific features
Summary
Many physiological processes in birds are closely correlated with day and night alterations. The pineal organ and its main hormone, melatonin (MLT), play an important role in regulating these phenomena [1]. Pinopsin is specific to the pineal organ, and controls the daily melatonin output [3,5,6]. Melanopsin occurs both in the pineal organ and the retina [7] and is involved in entrainment of the circadian clocks [8]. The axons of melanopsin-containing retinal ganglion cells build the retinal-hypothalamic tract that terminates in the suprachiasmatic nucleus [9,10]. The multisynaptic neuronal pathway connects this nucleus with the pineal organ, both in birds and mammals [11,12]
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