Use of liver snips for studies on gluconeogenesis

measured in perchloric acid extracts of medium by the hexokinase/glucose-6-phosphate dehydrogenase method (Bergmeyer et al., 1974) and protein in the cell pellets by the method of Lowry et al. (1951). Figures show mean values +s.E.M. and data were analysed using Student’s t-test. Fig. la shows that in CdC12-pretreated rats, gluconeogenesis from pyruvate is stimulated by 35% (P<0.05) compared with controls. Glucose production in the absence of pyruvate was negligible in both groups. The magnitude of the stimulation of gluconeogenesis is very similar to the reported increases in activities of hepatic gluconeogenic enzymes in CdC12-pretreated rats, although the dose, chronic dosing schedule, and route of administration varied between different groups of workers (see Singhal et al., 1974; Chapatwala et al., 1980). Fig. Ib shows that the addition of CdCI, to incubations of normal hepatocytes in vitro produced a dose-related inhibitory response on gluconeogenesis from pyruvate. In the case of incubations with 1 or I0mM-CdCl2 a high concentration of glucose was found both in the presence and absence of pyruvate, suggesting that at these concentrations cytotoxicity and cell death were occurring (viability <40%). These results are similar to the more limited data obtained by others with rat kidney cortex slices (Rutman et al., 1965; Seiller et al . , 1979). The effects of cadmium in the in citro experiments is considered to be a non-specific aspect of generalized hepatoxicity. Interference with energy metabolism at the mitochondria1 level is probably a major factor in the hepatotoxic response, but inhibitory effects of cadmium on a wide variety of enzymes containing divalent-metal ions as cofactors or essential thiol groups may also contribute. Chronic administration of CdCI, to rats results in a stimulation of hepatic gluconeogenic flux which will contribute to the hyperglycaemic action of this agent in uivo. A direct effect of CdCI, on the liver in uico to account for this stimulation is considered unlikely since, even at low (micromolar) concentrations, gluconeogenesis is inhibited in incubations with hepatocytes in vitro. A possible explanation for the stimulation of gluconeogenesis after chronic dosing in uiuo may be related to the sensitivity of the pancreatic /3-cells to cadmium and the observed inhibition of insulin secretion (Ghafghazi & Mennear, 1975; Ithakissios et al., 1975). The stimulation of adenylate cyclase and increased hepatic cyclic AMP concentration in rats exposed to cadmium (Merali & Singhal, 1975; Merali et al., 1975) is not inconsistent with this hypothesis, and could therefore indirectly be responsible for the stimulation of gluconeogenesis.