Melatonin Mediates Monochromatic Light-induced Insulin-like Growth Factor 1 Secretion of Chick Liver: Involvement of Membrane Receptors.

Monochromatic lights influenced the proliferation and differentiation of skeletal satellite cells in broilers by the enhancement of insulin-like growth factor 1 (IGF-1) secretion. However, whether melatonin (MEL)-mediated monochromatic lights influenced the IGF-1 secretion remains unclear. Newly hatched broilers, including intact, sham operation and pinealectomy groups, were exposed to blue (BL), green (GL), red (RL) and white light (WL) from a light-emitting diode system for 14 days. The results showed that GL effectively promoted the secretion of MEL and IGF-1, the expression of proliferating cell nuclear antigen and MEL receptor subtypes Mel1a, Mel1b and Mel1c in the liver compared to BL and RL in vivo. Moreover, those was a positive correlation between MEL and IGF-1 (r = 0.834). After pinealectomy, however, these parameters declined, and there were no differences between GL and other monochromatic light treatments. In vitro, exogenous MEL increased hepatocyte proliferation and IGF-1 secretion. Meanwhile, the MEL enhancements were suppressed by prazosin (selective Mel1c antagonist), followed by luzindole (nonselective Mel1a/Mel1b antagonist), but not suppressed by 4-phenyl-2-propionamideotetralin (selective Mel1b antagonist). These findings demonstrated that MEL mediated the monochromatic light-induced secretion of IGF-1 in chicks' livers by Mel1c and that Mel1a may be involved in this process.

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