PORCINE SOMATOTROPIN DIFFERENTIALLY DOWN-REGULATES EXPRESSION OF THE GLUT4 AND FATTY-ACID SYNTHASE GENES IN PIG ADIPOSE-TISSUE

The present study was conducted to determine whether porcine somatotro pin (pST) differentially regulates expression of the GLUT4 and fatty a cid synthase (FAS) genes in pig adipose tissue. Three different experi ments were conducted in which pigs were treated daily with different d oses of pST for different time periods (7 or 14 d and from 60 to 90 kg of body wt). in these experiments, pST significantly and consistently decreased FAS mRNA levels (80%, 65% and 85%, respectively); however, GLUT4 mRNA was not affected by PST in two of the three experiments, an d in the one showing an effect (Experiment 2), the decrease was less t han observed for FAS (44%). Because of these results, we conducted sub sequent experiments to see if the effects of pST on glucose metabolism in cultured pig adipose tissue (48 h) differed when glucose concentra tions were changed from 1 to 5 mmol/L. These studies revealed that the antagonistic effect of pST on insulin action was more potent when glu cose transport was saturated (5 mmol/L) than when glucose concentratio n limited glucose entry into the cell (1 mmol/L). In summary, these re sults suggest that the effects of pST on glucose transport in pig adip ocytes are secondary to changes elicited by the hormone on intracellul ar glucose use for lipogenesis, When considered in the context of the decrease previously observed in glucose transport in pig adipocytes, t he findings reported herein suggest that pST acts to decrease GLUT4 pr otein activity and/or distribution between the plasma membrane and the intracellular pool with little alteration in GLUT4 gene expression or total cell GLUT4 protein.