CORRELATION OF SERUM GH AND IGF-1 WITH SATELLITE CELL RESPONSIVENESS IN TARGHEE RAMS

This study tons performed to assess the relationship between serum gro wth hormone (GH) and insulin-like growth factor 1 (IGF-1) levels, slau ghter weight, and myogenic satellite cell growth kinetics of Targhee r ams. Serum was collected from 19 rams at 15-min intervals over a perio d of 4 h. Radionimmunoassays of serum samples for GH revealed consider able variation (within individual rams) over the sampling period, with mean values ranging from 0 . 63 to 4 . 88 mu g/l mean overall 2 . 3 ( s.e. 0 . 33) mu g/l; no. = 19). There was no significant correlation b etween GH levels and slaughter weight (r = -0 . 11; P > 0 . 05) at 155 (s.e. 1 . 08) days. Serum IGF-1 levels of (individual) rams were inva riant over the sampling period, with individual means ranging from 62 to 233 mu g/l (mean overall of 117 (s.e. 45 . 6) mu g/l; no. = 19). IG F-1 was not strongly correlated with slaughter weight (r = +0 . 35; P > 0 . 05). Satellite cells were isolated from the left m. semimembrano sus of all rams at slaughter and grown in culture to evaluate prolifer ation amount and differentiation extent. The correlations between seru m GH levels and satellite cell proliferation and differentiation in vi tro were r = -0 . 53 (P < 0 . 05) and r = -0 . 52 (P < 0 . 05), respec tively. Serum IGF-1 showed no significant correlations to proliferatio n (r = +0 . 07; P > 0 . 05) or to differentiation (r = -0 . 07; P > 0 . 05) of the satellite cells. These data suggest that serum GH levels in Targhee rams may not reflect muscle growth potential if correlated to body weight of 155 days. Furthermore, as IGF-1 was not correlated s ignificantly with slaughter weight or to variables of satellite cell p roliferation and differentiation, another mode of satellite cell regul ation (possibly paracrine controllers) is more likely at play to coord inate the satellite cell involvement in muscle growth in Targhee rams at 155 days.