Insulin and glucose decreases the capacity of urea-N synthesis in the rat.

The relationship between insulin concentration (32-980 mU/l) and the capacity of urea-N synthesis (CUNS) was investigated with alanine as nitrogen source in 26 nephrectomized rats. The blood glucose concentration was kept constant by the 'glucose clamp' technique, and the endocrine pancreatic response was controlled by somatostatin. The CUNS was determined as the accumulation of urea corrected for intestinal hydrolysis at a constant amino acid concentration within the interval 7.3-11.6 mmol/l. At insulin concentration above 200 mU/l CUNS was decreased from 10 to 6 mumol (min X 100 g body wt)-1. At lower insulin concentrations the decrease was proportional. Hyperglycaemia 14.8 mmol/l decreased CUNS to 6.3 mumol (min X 100 g body wt)-1. The basal rate of urea-N synthesis was reduced from 3.8 to 1.9 mumol (min X 100 g body wt)-1 by insulin concentrations above 200 mU/l. The estimated alanine elimination (5.8 mumol(min X 100 g body wt)-1) was unchanged by insulin and reduced to 3.3 mumol(min X 100 g body wt)-1) by hyperglycaemia. Somatostatin infusion had no effect on CUNS or alanine elimination. It is suggested that the capacity of urea-N synthesis is subject to short term regulation independently by insulin and glucose.