Effect of melatonin administration on thyroid hormones, cortisol and expression profile of heat shock proteins in goats (Capra hircus) exposed to heat stress

Heat stress had been a constant challenge to goat farming under tropical climate as more chance exist for exposure to solar radiation for most of the day while grazing with exaggeration by nutritional constraints. Menacing global rise in surface temperature compelled more focus of research over mitigation of heat stress. With 6 female goats of uniform age and weight experimental group (n = 6) and were acclimatized for initial 5 days in psychrometric chamber and kept at 25 degrees C. From 6th day, the animals were exposed daily 6 h (07:00 h to 13:00 h) for 6 days each at 35 degrees C and 40 degrees C in psychrometric chamber. Melatonin was administered I/V at the dose rate of 0.1 mg/kg at 12:00 h throughout the experimental period from 5th day to 17th day. Cardinal physiological response assessment was done at 30 min before and after melatonin administration respectively. Blood samples were collected after 1 h of melatonin administration on alternate experimental days starting from 5th day. Level of hormones T3, T4 and cortisol was assessed in serum samples and relative expression of genes like HSP 60, HSP 70, HSP 90 and ubiquitin was studied in peripheral blood mononuclear cells. In control group as well as treatment group rectal temperature and pulse rate increased significantly (P < 0.05) as the exposure temperature increased. No significant change was observed in T3, however T4 significantly (P < 0.05) decline at 40 degrees C in melatonin treated group. The cortisol level rose significantly (P < 0.05) with increase in exposure temperature in control animals. Significantly (P < 0.05) low level of cortisol was observed in melatonin treated group at all exposure temperature. HSP 60, HSP 70, HSP 90 and ubiquitin showed significant (P < 0.05) up regulation as a protective effects under heat stress in both the groups. The relative expression of HSP GO was increased manifold in melatonin treated group at 40 degrees C exposure temperature. In conclusion, the present study clearly supported heat alleviating and cell protective role of melatonin with suppression in serum cortisol level and upregulation of genes like HSP-60 in PBMCs. (C) 2012 Elsevier B.V. All rights reserved.