Independent jejunal mechanisms for glycine and glycylglycine transfer in man in vivo.

I . Rates of absorption of glycine and glycylglycine from a 300 mm jejunal segment were compared in vivo when those compounds were given alone or together to six Zambian African subjects who had no clinical evidence of malnutrition or of gastro-intestinal disease. Solutions containing (A) glycine (~oommol/l), (B) glycine (Ioommol/l)+glycylglycine (50 mmol/l), and (C) glycglglycinc (50 mmolil) were infused into the upper jejunum by means of a doublelumen tube perfusion system. 2. Rate of absorption of glycine was significantly higher from the glycylglycine solution (C) than from the glycine solution (A). Glycine absorption rate from solution B (glycine+glycylglycine) was very similar to the sum of absorption rates of glycine from solutions A and C in each subject. Luminal disappearance rate of glycylglycine from solutions C and B were very similar; however, the rate was significantly greater than the total glycine absorption rate from solution C and indicates back-diffusion of glycine into the lumen after glycylglycine hydrolysis. 3. The results are interpreted as indicating that the transport mechanisms for glycine and glycylglycine in man are partly, and possibly wholly, separate.