Effects of heat stress on somatostatin and some related immune factors in the small intestine of Wenchang chicks

To investigate the effects of heat stress (HS) on developmental changes in immune functions of chick intestinal mucosa, one-day-old broiler chicks were randomly assigned into control check (CK) and heat-stressed (HS) groups and raised under indoor temperature. The chicks in HS group were subjected to HS at 40 ± 0.5°C from 12:00 to14:00 h every day. Intestinal mucosa samples were collected weekly during 6 weeks, and the effects of HS on somatostatin and its related immune factors were examined using immunohistochemical, physiological, and biochemical methods. The results showed that HS obviously increased the amount and integral optical density of somatostatin positive cells, somatostatin content, as well as IFN-γ and IL-2 levels in the small intestine, and these increases reached statistical significance in some intestinal segments (P < 0.05). In addition, IgG, IgA, and IgM levels fluctuated in different intestinal segments and their levels in jejunum, duodenum, and ileum in 6-week-old chicks were significantly lower in HS group than in CK group (P < 0.05). The contents of immune-related enzymes also fluctuated, but the activities of acid phosphatase, lysozyme, and glutathione reductase in duodenum and jejunum were lower in 6-week-old chicks in HS group than in CK group, some reaching statistical significance (P < 0.05). Growth hormone (GH) and HSP70 contents in multiple intestinal segments in 6-week-old chicks were significantly higher in HS group than in CK group (P < 0.05). The results indicate that (1) HS could increase the expression and secretion of somatostatin and affect the normal development of immunoglobulins, cytokines, and immune-related enzymes in the small intestine, and thereby impact the chicks' intestine immune function; (2) GH and HSP70 in the small intestine were involved in self-protection mechanisms against HS-induced intestinal injury and somatostatin regulation might be one of the important components.