TISSUE IGF-I PROTEIN AND MESSENGER-RNA RESPONSES TO A SINGLE INJECTION OF SOMATOTROPIN

Swine were divided into four groups of 11 animals at 40 kg body wt. Sw ine within a group were given a single porcine somatotropin (pST) inje ction (200 mu g/kg) or buffer at 0800. Blood, liver (L), latissimus do rsi (LD), semitendinosus (STS), vastus lateralis (VL), dorsal subcutan eous (SQ), and perirenal (PR) adipose tissues were sampled at 0, 1, 2, 4, 8, 12, 16, and 24 h postinjection. Blood urea nitrogen was depress ed by 16 h. Insulin was elevated by similar to 350% at 8 h. Lipogenic enzyme activities in adipose tissues were not affected by pST treatmen t. Insulin-like growth factor I (IGF-I) mRNA levels increased rapidly in SQ, PR, and L to a single PST administration, whereas they increase d only slightly in VL. IGF-I mRNA concentrations in LD and STS were un affected by pST treatment. IGF-I protein content of tissues changed li ttle during the first 24 h postinjection. These data suggest that indi vidual tissues differ in timing and degree of response to pST. Conflic ting results reported after pST treatment could, in part, be due to ti ssue selection for sampling or sample timing.