A new technique for the evaluation of the capacity of the gastrointestinal tract to assimilate foods by using a stable isotope of nitrogen (15N)

A new technique is introduced for the evaluation of the capacity of the gastrointestinal tract to assimilate foods by using a stable isotope of nitrogen (15N) as a tracer. Four groups of male Wistar rats were fed 15N-labeled rice for one day following a basal diet, composed of 87% poudered rice. Then, 15N-labeled rice was switched to basal diet again for the next seven days. The four groups of rats consisted of: Group A-three pancreatic duct-ligated rats; Group B-four sham operated rats; Group C-five control rats and Group D-seven Streptozotocin-treated (20mg/kg) rats. The 15N contents were measured in the stool, urine and sera collected before feeding of 15N-labeled rice and one, three and seven days thereafter. In group A, the rate of 15N excretion into the stools, i.e., the amount of 15N in the stools against the total amount of 15N consumed, was higher as compared to the control group throughout the period of the study. On the contrary, the rate of urinary excretion of 15N as well as the contents of 15N in the urine and sera were apparently lower. In group D, the rate of 15N excretion into the stools as well as the contents of 15N in the sera and urine showed no difference as compared to the control group. The rate of 15N excretion into the urine, however, was apparently higher than that of the control group throughout the period of the study. These results indicate that this stable isotope of nitrogen (15N), which clearly reveals the existence of malabsorption of pancreatic origin, is valuable as a tracer for assimilation studies and technically applicable for clinical use. We have found no evidence of malassimilation in rats with Streptozotocin-induced diabetes in spite of the presence of previous reports that assert the existence of pancreatic exocrine dysfunction in these animals. (author)