The present study was undertaken to determine the effects of porcine somatotropin (pST) on glucose flux rates, lipogenic enzyme activities, and the abundance of fatty acid synthase mRNA in pig adipose tissue. Barrows were injected daily with 120 micrograms of pST/kg BW (n = 6) or excipient (n = 6). On d 11 of treatment, pigs were slaughtered (empty BW = 77 +/- 2 kg) and subcutaneous adipose tissue was collected. Basal incorporation of [14C]glucose into total lipid decreased by 86% with pST treatment, whereas glucose oxidation to CO2 decreased by 79%. Insulin (10 ng/mL) stimulated both glucose oxidation and incorporation into lipid by a small increment of similar magnitude for both treatment groups. Rates of lipogenesis determined in vitro were highly correlated with similar measurements made in vivo on the same set of animals (r = .76). The reduction in basal rates of lipogenesis corresponded to a 79% decrease in total (activated) acetyl-coenzyme A carboxylase activity and a 67% decrease in fatty acid synthase activity. Reduced nicotinamide adenine dinucleotide phosphate-generating enzymes were decreased to a lesser extent. Northern blot analysis of RNA from the same animals reveal a 90% decrease in mRNA for fatty acid synthase in the pST-treated group. The correlation between mRNA abundance and enzyme activity for fatty acid synthase was .90. These data indicate that the pST-induced reduction in adipose tissue lipid accretion in growing barrows is largely a result of diminished rates of lipogenesis that are manifestations of the decreased activities of the fatty acid-synthesizing enzymes. These changes seem to result from suppression of genes that encode for the lipogenic enzymes.