Effects of corticosterone administration on nitrogen excretion and nitrogen balance in adrenalectomized rats

Adrenalectomized rats were implanted with pellets containing corticosterone in proportions varying from 0% to 100%, plus cholesterol. Stable concentrations of plasma corticosterone resulted, varying from subnormal (A) to physiologic (B) to supraphysiologic (C). When food was ingested ad libitum, weight gain was maximal in B at plasma corticosterone concentrations of 0.14-0.20 mumol/L; weight loss occurred in C, despite higher food intake. Even when rats had constant limited food intake, weight gain and positive nitrogen balance were significantly reduced in A compared with B because fecal nitrogen rose significantly and the retention of absorbed nitrogen for growth decreased. In C, weight decreased despite constant intake, and nitrogen balance became negative because urinary nitrogen increased markedly. We conclude that glucocorticoid insufficiency reduces nitrogen balance by impairing intestinal absorption of dietary protein and the utilization of absorbed nitrogen, whereas glucocorticoid excess reduces nitrogen balance by augmenting urinary nitrogen despite constant nitrogen intake.