Characteristics of intestinal glucose secretion in normal and diabetic rats

A method was developed to characterize and quantitate the transfer of glucose from the plasma to the intestinal lumen. In normal rats, there was a linear correlation between the blood glucose concentration and the rate of appearance of plasma glucose into the intestinal lumen perfused with Krebs-Ringer buffer (r = 0.88, P less than 0.01). Intestinal perfusion with buffers containing either mannitol, glucose, or phlorizin significantly increased the recovery of secreted glucose compared with plain buffer. Rats perfused with buffer containing mannitol or those undergoing plasma volume expansion with dextran demonstrated a change in water movement from net absorption to secretion coupled with a significant increase in glucose secretion. During luminal perfusion with a buffer containing 21 mM glucose, glucose secretion represented 14% of the net glucose absorption rate. Intestinal perfusion with phlorizin gave the highest measured recovery of glucose, probably by blocking active reabsorption of secreted glucose. A series of simultaneous perfusions performed in the jejunum and ileum revealed similar rates of glucose transfer in both segments of intestine. Measurement of glucose secretion in rats with streptozotocin diabetes gave the highest values for the plasma-to-lumen movement of glucose. Treatment with insulin reduced the blood sugar and glucose transfer rate. These data demonstrate that glucose moves bidirectionally across the rat intestine, and its secretion is a passive process.