Contradictory effects of uncomplicated versus complicated abdominal surgery on the hepatic capacity for urea synthesis in rats

Abstract

Female Wistar rats weighing 217 g were subjected to two types of surgical stress: uncomplicated (hysterectomy) and complicated (spleen and uterus ligated, crushed, and left in situ). Liver function as assessed by amino-N conversion was measured as the capacity for urea-N synthesis preoperatively (control animals) and on Days 1, 3, and 6 postoperatively. Uncomplicated surgery transiently increased the capacity for urea-N synthesis by 30% the first postoperative day ( P < 0.001). Complicated surgery decreased the capacity for urea-N synthesis to 55% throughout the investigation period ( P < 0.001). This was not due to a general change in liver mass since galactose elimination capacity remained constant. The increase in the capacity for urea-N synthesis after uncomplicated surgery is probably due to glucagon since plasma glucagon increased whereas plasma insulin and blood glucose remained unchanged after amino acid loading. The persistent decrease in the capacity for urea-N synthesis in complicated surgery is not due to changes in these regulators: glucagon increased, insulin decreased, and the rats were hypoglycemic. All changes are expected to increase the capacity for urea-N synthesis. The mechanism for the emergence of these two distinct metabolic patterns is not known. The phenomenon is probably important for interpretation of metabolic data on clinical stress.