Carbohydrate metabolism in pregnancy. X. Metabolic disposition of alanine by the perfused liver of the fasting pregnant rat

Hepatocytes from pregnant rats fasted during late gestation are larger and more abundant than in littermate virgin animals and in vivo are exposed to hypoglycemia. To evaluate their intrinsic potential for biosynthetic transformations of alanine, a modified liver perfusion system was employed. Livers from 24 hour fasted, 19 day pregnant and virgin littermate rats were subjected to 'wash out' perfusion for 25 minutes prior to definitive perfusion for 60 minutes with fresh media containing supramaximal amounts of L alanine ¹⁴C (17 mM). Under such conditions, livers from pregnant rats displayed an enhanced capacity to assimilate alanine ¹⁴C and to establish concentration gradients for alanine between hepatocytes and perfusion medium. Significantly more alanine carbons were incorporated into glucose, lactate, glyceride glycerol, and glutamate per hepatocyte by livers of pregnant rats. Glyceride glycerol formation was disproportionately enhanced suggesting that there may be mechanisms operative during pregnancy for selectively diverting triose phosphates toward the esterification of intrahepatic fatty acids. Despite the augmented disposition of alanine carbons, livers from pregnant animals formed significantly less urea. Instead, a much greater proportion of the nitrogen derived during alanine catabolism was released in a potentially reutilizable form, ammonia. Thus, hepatocytes from fasted pregnant animals have an enhanced capacity for assimilating 'loading' doses of alanine and for incorporating the carbons into glucose, lactate, glyceride glycerol, and glutamate, while preserving more of the amino nitrogen in a form that can be reutilized.