HEXOKINASE AND PHOSPHATASE ACTIVITIES OF INTESTINAL MUCOSA FOLLOWING THYROIDECTOMY AND THYROID ADMINISTRATION12

Abstract

The evidence for phosphorylation and dephosphorylation as an explanation for the “active” transfer of hexoses across the intestinal and renal epithelium is indirect and complicated by many findings that do not support this theory (1). Since the absorption of hexoses is increased significantly in hyperthyroid animals and humans and decreased in the hypothyroid state (2, 3), it was postulated that if phosphorylation and dephosphorylation were even in part responsible for hexose absorption, corresponding changes might be found in the activities of the enzymes considered to mediate hexose transfer, namely, hexo-kinase and phosphatase. The hexokinase activity of intestinal mucosa was found to increase significantly in thyroid-treated rats and to decrease significantly in thyroidectomized animals. The phosphatase activity of intestinal mucosa, on the other hand, did not differ significantly from that of control animals in either of these conditions. Although the hexokinase activity does change in the same direction as does glucose absorption in the hyper- and hypothyroid states and although the results appear to support the phosphory-lation hypothesis, this correspondence may be fortuitous. The hexokinase activity of the intestinal epithelium may merely reflect the level of metabolic-activity which provides the energy necessary for driving active transfer mechanisms.