Urea production and excretion by the chicken kidney

¹ Departments of Medicine, Duke University Medical Center and Veterans Administration Hospital, Durham, North Carolina

Using the Sperber technique, renal urea excretion was studied in the chicken during the constant unilateral infusion of either l-arginine, urea, or l-arginine-C¹⁴. After the prior injection of urea-C¹⁴ in some birds, the effect of a unilateral arginine infusion on the specific activities of plasma and urine urea-C¹⁴ was determined. During l-arginine infusion, urine urea excretion increased greatly from both kidneys. Urea/inulin clearance ratios always rose above 1.0 (maximum: 7.5). This response was not inhibited by pretreatment with 2,4-dinitrophenol. Urea/inulin clearance ratios greater than 1.0 were not observed during an infusion of exogenous urea. A constant unilateral infusion of tracer amounts of l-arginine-C¹⁴ was attended by a bilateral rise of urea-C¹⁴/inulin ratios to values much above 1.0 (higher on the side of infusion) at a time when total urea/inulin ratios remained less than 1.0. After equilibration of an administered dose of urea-C¹⁴, arginine infusion depressed the specific activity of urine urea-C¹⁴ much more than that of plasma. A double reciprocal plot indicated a straight-line relationship between the plasma arginine concentration and the simultaneous rate of urine urea excretion. These results provide conclusive in vivo evidence that the kidney of at least one species can synthesize urea from exogenous or endogenous plasma arginine via a rate-limited process, and that this urea is subsequently excreted by direct release into tubular urine.

Key Words: arginine • arginase

Submitted on November 12, 1963