The effect of insulin infusion on whole-body protein metabolism in patients with gastrointestinal disease fed parenterally.

The effect of insulin infusion on whole-body protein metabolism was studied in six non-diabetic patients with gastrointestinal disease receiving constant total parenteral feeding, with each patient as his own control. Insulin added to the parenteral feed significantly raised the plasma insulin concentration and lowered the blood glucose. With insulin infusion there was a significant increase in the rates of urea output and ammonia excretion, but no change in 3-methylhistidine excretion or in the urinary 3-methylhistidine/creatinine ratio. Studies of whole-body protein turnover were performed with a tracer injection of 15N-glycine and both urea and ammonia as end products. Without insulin urea as end product gave an estimate of flux 18 per cent greater than that given by ammonia. With both end products rates of whole-body protein synthesis were significantly greater than rates of breakdown. When insulin was infused the estimate of flux from ammonia increased significantly, resulting in close agreement with the estimate from urea, and there was no longer a significant difference between rates of whole-body protein synthesis and breakdown. Our data, taken with the results of other studies, suggest that insulin infusion is not beneficial as a means of increasing nitrogen retention in non-diabetic parenterally-fed patients.