INFLUENCES OF SOMATOTROPIN ON NA-K+-ATPASE, MG2+-ATPASE AND CA2+-ATPASES OF PORCINE VISCERAL TISSUES()

Two experiments were conducted to determine the overall influence of p orcine somatotropin (pST) administration on the specific activity of v isceral tissue ATPases. Pigs were fed a corn-soybean meal-skim milk-ba sed diet approximately 85% of ad libitum, such that for each experimen t, control and pST-treated consumed similar amounts of feed. As observ ed for pigs chronically treated with PST, enhanced growth of visceral tissues was evident in pigs treated for 6 and 14 days (d) with pST. Th e specific activity of detergent-activated Na+-K+-ATPase (ouabain-sens itive adenosine triphosphatase activity) was determined in fresh tissu e homogenates prepared from liver, heart, kidney and duodenum. Treatme nt with PST was associated with a 19% increase in Na+-K+-ATPase-specif ic activity in the liver; specific activity of Mg2+-ATPase was not inf luenced by PST. Whole liver Naf-KC-ATPase and Mg2+-ATPase activities w ere 35% and 25% greater, respectively, in somatotropin-treated pigs. T he specific activities of Na+-K+-ATPase and Mg2+-ATPase in heart, kidn ey and duodenum were similar for controls and pigs treated for 14 d wi th pST. The specific activities of high- and low-affinity Ca2+-ATPases in kidney medulla were 20 and 26% lower, respectively, in pigs treate d for 14 d with pST compared with controls. In contrast, Ca2+-ATPases in other tissues, including kidney cortex, were not influenced by PST treatment. These data indicate that some of the observed increase in e nergy expenditure associated with pST treatment may be attributable to increased organ size as well as to enhanced hepatic Na+ and K+ flux. While Na+-K+-ATPase activity is specifically enhanced in the liver, PS T does not appear to be a general Na+-K+-ATPase activator in all tissu es and may be associated with depressed activity of Ca2+-ATPases in th e kidney.