Tissue IGF-I protein and mRNA responses to a single injection of somatotropin

Swine were divided into four groups of 11 animals at 40 kg body wt. Swine within a group were given a single porcine somatotropin (pST) injection (200 micrograms/kg) or buffer at 0800. Blood, liver (L), latissimus dorsi (LD), semitendinosus (STS), vastus lateralis (VL), dorsal subcutaneous (SQ), and perirenal (PR) adipose tissues were sampled at 0, 1, 2, 4, 8, 12, 16, and 24 h postinjection. Blood urea nitrogen was depressed by 16 h. Insulin was elevated by approximately 350% at 8 h. Lipogenic enzyme activities in adipose tissues were not affected by pST treatment. Insulin-like growth factor I (IGF-I) mRNA levels increased rapidly in SQ, PR, and L to a single pST administration, whereas they increased only slightly in VL. IGF-I mRNA concentrations in LD and STS were unaffected by pST treatment. IGF-I protein content of tissues changed little during the first 24 h postinjection. These data suggest that individual tissues differ in timing and degree of response to pST. Conflicting results reported after pST treatment could, in part, be due to tissue selection for sampling or sample timing.