Exogenous growth hormone stimulates somatotropic axis function and growth in neonatal pigs

We studied the effects of exogenous porcine growth hormone (pGH) administration on circulating insulin-like growth factor I (IGF-I) concentration, IGF-binding proteins (IGFBP), tissue growth, and protein synthesis in neonatal pigs. One-day-old pigs were given daily intramuscular injections of either pGH (1 mg/kg body wt) (n = 6) or saline (n = 5) for 7 days, after which time we measured in vivo protein synthesis using a bolus of [H-3]-phenylalanine. Mean plasma pGH concentration in pGH-treated pigs measured on day 7 was 22-fold higher than in controls. The plasma IGF-I concentration in pGH-treated pigs was significantly greater than in controls after 1 day of treatment and plateaued at 285% of control values after 4 days. After 7 days of treatment, plasma IGFBP-3 concentrations and the plasma glucose response to a meal were also greater in pGH-treated than control pigs. pGH treatment significantly increased body weight gain and food conversion efficiency and the protein synthesis rate in several visceral organs. Our results demonstrate that exogenous pGH increases circulating IGF-I and IGFBP-3 concentrations and visceral organ growth in neonatal pigs, suggesting that the somatotrophic axis is functional in the neonate.