Appearance of intraportally infused [15N]urea in blood and urine of domestic fowl

The time course of the occurrence of intraportally infused 15N]urea in blood and urine was investigated in chickens. The infused urea appeared in ureteral urine, mostly in the form of urea, as early as 30 min after the start of infusion and the excretion further increased up to the end of 2 hr infusion. Blood urea concentration rapidly increased and reached about three times the initial level at the end of the experiment (P < 0.05 after 20 min), but no significant effects were observed on uric acid, ammonia and glutamine concentrations. Fifty-seven percent of blood urea N and 3% of blood glutamine-amide N and 1% of blood ammonia N, which were determined at the end of experiment, were derived from the infused urea N. It is concluded that urea, which is rapidly increased in blood and urine after feeding urea to chickens, is mostly derived from dietary urea.