Growth hormone increases whole-body protein turnover in growing pigs

Ten pigs with an average initial live weight of 65 kg were used to investigate the effects of daily exogenous porcine pituitary growth hormone (pGH; .1 mg center dot kg to the -1 center dot d to the -1) for a 13-d period on N retention and whole-body protein turnover. Feed intake was restricted to both the control (treated with excipient) and pGH-treated groups to ensure that animals in each group consumed equal amounts. Whole-body protein turnover was estimated from the excretion of 15N in urinary urea and ammonia after a single oral dose of (15N)glycine. Nitrogen balance and whole-body N flux were increased by 35 to 40% with pGH treatment (P < .001). Protein synthesis and breakdown were increased by 56 and 59% (P < .001), respectively, in pGH-treated pigs relative to controls. These higher rates of protein turnover seemed to lower slightly the efficiency of the metabolic process for protein deposition. However, the absolute increment in protein synthesis rate was greater than that for breakdown, leading to the increased net N retention. Thus, pGH treatment improved the utilization of dietary amino acids for protein deposition.