663 ADAPTATION OF HEPATIC UREA CYCLE ENZYMES DURING PREGNANCY AND LACTATION IN THE RAT

Abstract

Little is known about mechanisms of nitrogen (N) conservation in pregnancy and lactation. The purpose of this study was to document adaptation of three of the five hepatic urea cycle enzymes during pregnancy and lactation in Sprague-Dawley rats fed a 20% casein diet ad lib. Rats were killed on days 14 and 21 of pregnancy, at 24 hr post partum, and on day 14 of lactation. In pregnancy, the specific activities of ornithine transcarbamylase (OTC), argininosuccinate lyase (ASL), and arginase in the liver are significantly lower than control values at days 14 and 21. On day 21, the specific activities expressed as a percent of control values are 74% for OTC, 64% for ASL, and 76% for arginase. Because livers of pregnant rats are larger than control livers at days 14 and 21 (14.97g vs. 10.80 at day 14 and 16.97g vs. 11.45g at day 21), total activities for the pregnant rats are not significantly different from control values for OTC and are greater than control values for ASL and arginase. Twenty-four hours post partum, liver weight and specific and total activities of OTC are not significantly different from control values. At the peak of lactation, day 14, the specific activity of OTC is not different from the control level; but because of a significantly larger liver weight (22.20g vs. 11.92g), the OTC total activity is significantly greater. These results suggest that adaptation of urea cycle enzymes is not the major basis for N conservation during pregnancy and lactation. (Supported in part by NIH Grant # 08 T2 GM07379B.)