Porcine somatotropin (pST) increases IGF-I mRNA abundance in liver and subcutaneous adipose tissue but not in skeletal muscle of growing pigs
1994
Coleman, M.E. | Russell, L. | Etherton, T.D.
The present study was undertaken to determine the effects of exogenous porcine somatotropin (pST) on IGF-I gene expression in liver, skeletal muscle (longissimus dorsi), and s.c. adipose tissue of growing pigs. Twenty prepubertal gilts (approximately 60 kg BW) were allotted to four treatment groups (n = 5) and treated with either 0, 35, 70, or 140 micrograms/kg BW of recombinantly derived pST by daily i.m. injection for 7 d. Serum concentrations of IGF-I were determined by RIA and IGF-I mRNA levels were determined by direct counting of individual samples on slot blots. Administration of pST increased IGF-I concentration in serum. This was accompanied by significant increases (P < .05) in IGF-I mRNA abundance in liver and s.c. adipose tissue; the effects were maximal at the lowest dose of pST. Insulin-like growth factor I mRNA levels were increased 2.5- and 4.5-fold, respectively. Levels of IGF-I mRNA were very low in longissimus muscle and were unaffected by administration of pST. When expressed as picograms of mRNA/10 micrograms of total RNA, IGF-I mRNA levels were highest in s.c. adipose tissue. Levels of IGF-I mRNA were 1.9-fold higher in s.c. adipose tissue than in liver of control animals, and PST administration increased this difference to 3.2-fold. Our results suggest that 1) the effects of pST administered by daily i.m. injection on IGF-I gene expression in pigs are tissue-specific and 2) the stimulatory effects of pST administered in this manner on muscle growth in pigs are not associated with increased expression of the IGF-I gene in skeletal muscle.
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