© 1990 Oxford University Press
research-article |
Modulation of Glucose Metabolism in Isolated Rat Hepatocytes by 1,1,1,2-Tetrafluoroethane1
*Biomedical Science Department, General Motors Research Laboratories Warren, Michigan 48090
Harrison Radiator Division General Motors Corporation, Lockport, New York 14094
Received December 11, 1989; accepted April 10, 1990
Modulation of Glucose Metabolism in Isolated Rat Hepatocytes by 1,1,1,2-Tetrafluoroethane. OLSON, M.J., REIDY,C. A., AND JOHNSON, J.T. (1990). Fundam Appl Toxicol. 15,270–280. The thennodynamic behavior and lack of ozone-depleting potential of 1,1,1,2-tetrafluoro-ethane (R-134a) suggest it as a likely replacement for dichlorodifluoromethane (R-12), now used as the refrigerant in many air-conditioning systems. To further the presently incomplete toxicological analysis of R- 134a, the effects of R-134a on cell viability and functional competence of glucose metabolism were evaluated in suspension cultures of hepatocytes derived from fed or fasted rats. R-134a concentrations up to and including 75% (750,000 ppm) in the gas phase of sealed culture flasks did not produce evidence of cytolethality (LDH leakage) following 2 hr of exposure; in contrast, halothane (l,l,l-trifluoro-2-bromo-2-chloroethane) caused cell death at a gas phase concentration of only 1250 ppm. In hepatocytes isolated from fed rats, R-134a at concentrations of 12.5 to 75% increased glycolysis (production of lactate + pyruvate) in a concentration-dependent manner, no effect was observed at 5%. At 25%, R-12 and 1,1,2,2-tetrafluoro-l,2-dichloroethane(R-l 14) were of equal potency to R-134a in stimulating glycolysis; l,l,l,2,2-pentafluoro-2-chloroethane (R-115) depressed glycolysis slightly. Halothane, at concentrations as low as 300 ppm, markedly increased rates of glycolysis. Glucose production by hepatocytes of fed rats was decreased by R-134a, R-12, and R-114 only at concentrations of 25% or more. On the other hand, halothane (>300 ppm) potently decreased glucose production by hepatocytes. In cells isolated from livers of fasted rats, R-134a exposure inhibited gluconeo-genesis in a concentration-dependent manner although this effect was not significant until R-134a concentrations reached 12.5%. Comparative potency studies showed that R-l 34a, R-12, or R-l 14 (25% gas phase) inhibited gluconeogenesis about equally while as little as 300 ppm halothane was effective and R-115 (25%) was without effect. Considering that the threshold for alteration of the rate of glucose metabolism in this in vitro paradigm is about 12.5% R-134a, we conclude that toxicologically significant alteration of glucose-linked bioenergetics is unlikely at the levels of R-l34a exposure anticipated in workplace or environment