Distribution of maltose intravenously administered to rabbits and its metabolism in the kidney

When 14C-U-maltose was injected intravenously to normal rabbits, 14C-maltose rapidly disappeared from the blood stream and circulating 14C-glucose rose gradually. In urine, 24% of total radioactivity was excreted as 14C-maltose, 6% as 14C-glucose and 12% as other 14C-compounds. In all organs 14C-glucose exceeded the level of 14C-maltose throughout the experiment for 12 hours. When maltose was administered to nephrectomized rabbits, 14C-maltose disappeared very slowly from the blood stream and the increase in 14C-glucose in blood was minimal. In the rabbits pretreated with phloridzin 14C-maltose decreased rapidly in blood and 14C-glucose did not increase. The difference between plasma maltose levels in the artery and the vein across the kidney was increased after maltose was injected to the normal rabbits, whereas the plasma glucose concentration in the renal vein exceeded that in the renal artery. In phloridzinized rabbits, the arteriovenous difference of maltose was smaller as compared with normal rabbits and plasma glucose levels in the renal vein did not exceed those in the artery. When the isolated kidney was perfused for 30minutes with maltose solution, the levels of maltose and glucose in the renal vein rose and not only maltose but also glucose were excreted in urine. Maltase activities in the cortex of the kidney were ten times as high as in the medulla. In the isolated glomeruli, however, little maltase activities were observed. These results suggest that the kidney plays an important role in the metabolism of maltose administered intravenously. The mechanism as to urinary excretion of glucose after maltose injection was discussed.