Somatotropin regulates adipose tissue metabolism in neonatal swine

Somatotropin (ST) reduces lipid deposition in growing and adult animals, but its effect in neonatal pigs is not clear. In this study, we tested the hypothesis that ST inhibits lipid deposition in neonatal pig adipose tissue. Four neonatal (2.9 +/- 0.1 kg, 7 d of age) and four growing (17.0 +/- 1.4 kg, 60 +/- 3 d of age) crossbred pigs were used. Subscapular adipose tissue fragments were cultured with or without ST (4.5 nmol/L) for 24 h in the absence or presence of insulin (7 nmol/L). After culture for 24 h with insulin alone, adipocytes from neonatal and growing pig adipose tissue maintained the capacity to incorporate glucose into total lipid at rates comparable to those in fresh tissue. Culture for 24 h with ST in the presence or absence of insulin decreased adipocyte glucose incorporation into fatty acids. Addition of ST, in the absence or presence of insulin, also increased the accumulation of glycerol in the medium during culture of neonatal and growing pig adipose tissue. Furthermore, culture for 24 h with ST resulted in higher basal lipolysis measured during incubation of isolated adipocytes in the presence of adenosine deaminase. In addition, culture with ST decreased adipose tissue lipoprotein lipase (LPL) activity and completely blocked the stimulatory effect of insulin on activity of this enzyme. The present study is the first to demonstrate in neonatal pigs that, as in growing pigs, ST regulates adipose tissue metabolism through decreasing lipid synthesis and LPL activity and increasing lipolysis. Thus, ST may play an important role in nutrient partitioning during the neonatal period.