Glucose-lactate interrelationships: effect of ethanol.

The effect of ethanol on the interrelationship of lactate and glucose metabolism was investigated in eight human volunteers. Lactate and glucose kinetics and intervconversion rates were determined by the sequential administration of L-(+) lactate-U-(14)C and glucose-1-(14)C over an 8 hr period. After a 12 hr fast, the glucose turnover and recycling rates were 94.0 +/-3.8 (SEM) and 13.7 +/-1.1 mg/kg per hr, respectively. Approximately 50% of the glucose turnover or 40.7 +/-2.1 mg/kg per hr was converted to lactate, accounting for 50% of the lactate turnover rate. Lactate turnover and lactate conversion to glucose were 81.8 +/-6.2 and 16.7 +/-1.1 mg/kg per hr, respectively. Approximately 20% of the glucose turnover was derived from lactate under these conditions. During the administration of ethanol, the blood lactate concentration doubled and the lactate turnover rate declined slightly. Lactate conversion to glucose was markedly inhibited, decreasing from 16 to 5 mg/kg per hr, and the per cent of the glucose turnover derived from lactate decreased from 18 to 6. Despite the marked inhibition of lactate conversion to glucose, neither the blood glucose concentration nor the glucose turnover rate changed. Both glucose recycling and glucose conversion to lactate were decreased, indicating that ethanol inhibited peripheral glucose utilization. There was no difference in the degree of inhibition of lactate incorporation into glucose produced by ethanol when nonfasted subjects were compared with two subjects who had fasted for 48-72 hr despite the presence of hypoglycemia in the latter. These results indicate that starvation is not a prerequisite for ethanol inhibition of gluconeogenesis from lactate in humans but is necessary for the development of hypoglycemia. Inhibition of lactate incorporation into glucose in nonfasted subjects is probably masked by a concomitant increase in glycogenolysis which prevents hypoglycemia. Ethanol decreases glucose conversion to lactate as well as lactate conversion to glucose, thus inhibiting the Cori cycle.