Insulin to inhibit protein catabolism after injury.

Using patients with varying degrees of trauma as their own controls we compared three isocaloric regimens in three-day crossover studies; 9.4 g of nitrogen as l-amino acids was also given daily. The urea production rate was used as an index of protein breakdown. We found that in catabolic patients, insulin and glucose produced a strikingly greater inhibition of protein breakdown that glucose alone, and that glucose alone was marginally more protein sparing than a regimen containing mainly fat (intralipid and sorbitol). These differences were not seen in noncatabolic patients (urea production rate less than 15 g daily). In the catabolic patients (urea production rate greater than 15 g daily) the protein-sparing effect of insulin was proportional to the initial urea production rate. We therefore concluded that insulin has important protein-sparing effects in severely ill traumatized patients, but little effect when there is no increased catabolic rate.