| Abstrakt: |
Various aspects of lactate metabolism were compared in perfused livers from normal and hypophysectomized rats. Glucose production by livers from hypophysectomized animals exceeded that by normal rat livers largely due to enhanced rates of lactate gluconeogenesis. When perfusion was carried out with a nonrecirculating medium containing physiological levels of lactate (1 to 4 mm), the rate of glucose synthesis from labeled lactate by livers from hypophysectomized rats was 3 to 4 times that of normal rat livers. Saturating levels of substrate were 6 to 8 mmlactate for livers from hypophysectomized rats and 14 mmlactate for normal rat livers. At these levels, the rates of gluconeogenesis in both groups were similar. Over a range of lactate concentrations from physiological to saturating levels, the rates of conversion of lactate to CO2, glycogen, protein, and fatty acids were reduced below normal in livers from hypophysectomized rats. In livers perfused with 1 mmlactate, tissue levels of pyruvate, P-enolpyruvate, 2-P-glycerate, 3-P-glycerate, and glucose-6-P were increased above normal by hypophysectomy. At saturating lactate concentrations, levels of gluconeogenic intermediates in livers from normal and hypophysectomized rats were similar. These data, in addition to the similar rates of total lactate utilization, indicated that hypophysectomy affected a redistribution of substrate among competitive metabolic pathways. It was suggested that at physiological levels of lactate a reduction in pyruvate oxidation led to an increased availability of substrate for gluconeogenesis. |
