Submitted to: American Journal of Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 2001
Publication Date: N/A
Interpretive Summary: There are many factors influencing and regulating skeletal muscle differentiation in birds and mammals. Previous studies have shown that when young chicks are exposed to high environmental temperature, the chicks undergo a period of compensatory growth, which includes increased breast muscle growth. Prior research has reported that in adult animals muscle growth requires the recruitment of satellite cells, which are under the control of insulin-like growth factor-I. In our study insulin-like growth factor tissue and blood concentrations were determined in thermal conditioned and control chicks. The results demonstrate that in thermal conditioned chicks, tissue concentrations of insulin-like growth factor-I were increased over control chicks, and that satellite cell numbers were also increased. This strongly suggests that increased tissue insulin-like growth factor levels stimulate the increased muscle growth occurring after high heat exposure. These results provide new and additional information on factors regulating muscle growth in poultry, and would primarily be of interest to other scientists.
Exposure of young chicks to mild heat stress (i.e. 37oC for 24 h) resulted in significant improvement of body and muscle growth at later age (54). We hypothesized that thermal challenge (TC) causes an increase in satellite cell activity, necessary for further muscle hypertrophy. Immediate increase was observed in satellite cell DNA synthesis in culture and in vivo in response to TC of 3-day-old chicks, to levels that were significantly higher than that of non-treated chicks. This was accompanied with the induction of insulin-like growth factor-I (IGF-I), but not hepatocyte growth factor (HGF) in the breast muscle of the TC chicks, followed by a significant elevation of number of cells per gram of muscle. No significant change in plasma IGF-I levels was observed. A marked elevation in muscle regulatory factors, on day 5 followed by a decline in cell proliferation on day 6, together with continues high levels of IGF-I in the TC chick muscle suggested an accelerated cell differentiation. Thes data suggest that the immediate stimulation of satellite cells myogenic processes in response to heat exposure is directly mediated by IGF-I.