Role of Melatonin in Monochromatic Light Affecting the Expression of Somatostatin in Hypothalamus and Pituitary of Chicks

Abstract

Background: Melatonin (MEL) plays an important role in regulating the growth and development of organism and the metabolism of cells. A study was conducted to explore the effect of MEL-mediated monochromatic light on the secretion of somatostatin (SST) in the hypothalamus and pituitary.Results: The newly hatched broilers were exposed to white (WL), red (RL), green (GL) and blue (BL) lights through the pinealectomy model. The results showed that SST immunoreactive neurons and fibers were distributed in hypothalamus. The mRNA and protein levels of SST and SST receptor 2 (SSTR2) in hypothalamus and pituitary in RL were higher than those of in GL and BL. After pinealectomy, mRNA and protein levels of SST and SSTR2 in hypothalamus and pituitary in different light groups were increased and the differences were disapeared. Meanwhile, the trend of SSTR5 mRNA in pituitary is the same as the SSTR2 mRNA in pituitary. In vitro, the exogenous SST inhibited the growth hormone (GH) secretion, and SSTR2 and SSTR5 selective antogonists promoted GH secretion. While, melatonin receptor 1b (Mel1b) and Mel1c selective antagonists increased relative concentraitons of SST in adenohypophysis cells.Conclusion: Monochromatic light affected the expression of SST in chick hypothalamus and pituitary. MEL via Mel1b and Mel1c decreased SST secretion under GL, which is related to inhibiting the combination of SST, SSTR2 and SSTR5 in adenohypophysis cells.