Rhythmic changes of melatonin in the circulation and tissues of broiler chickens

Veterinarni Medicina 44, 1999, 263-267

Besides the well known role of melatonin in regulation of daily rhythmicity in birds and seasonal cycles in photoperiodic mammals, pleiotropic effects of melatonin mediated by interactions with endocrine and immune systems or through specific receptors in peripheral tissues, were suggested. In the present study we measured melatonin levels in the pineal gland, plasma and tissues of 5-7-day-old broiler chicks in the middle of the light : dark cycle 12 : 12 and assessed whether melatonin concentrations exert a daily rhythm. Melatonin levels were measured by radioimmunoassay, directly in plasma and after solvent extraction with methanol in pineal glands and chloroform in the duodenum, jejunum, pancreas, spleen, kidneys and bursa of Fabricius. As expected, melatonin concentrations in the pineal gland and plasma exerted the distinct daily rhythm with high level during the dark period. Similarly, the clear daily melatonin rhythm was observed in the duodenum, jejunum, pancreas, spleen and bursa of Fabricius (P < 0.001, t-test). On the contrary, melatonin levels in the kidneys were low and did not exert rhythmic changes. Daytime melatonin levels in the spleen, kidneys and bursa of Fabricius were lower than melatonin levels in the gastrointestinal tract acid pancreas (34.0-63.0 pg/g of wet tissue versus 116.3-179.3 pg/g of wet tissue, respectively). Our results demonstrated that rhythmic melatonin synthesis in the pineal gland results in rhythmic changes of melatonin concentrations in peripheral tissues. Since bright light suppresses melatonin biosynthesis, high light intensities should be avoided in broiler rearing because they can negatively influence physiological processes and efficiency of production

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