Net hepatic lactate balance following mixed meal feeding in the four-day fasted conscious dog

Abstract

The present experiments were undertaken to determine whether four days of fasting and marked hepatic glycogen depletion would alter the effect of mixed meal feeding on net hepatic lactate balance in the conscious dog. Dogs were fasted for four days and were then fed a mixed meal over a ten-minute period. Net hepatic glucose and lactate balance were monitored for the next eight hours using the A-V difference technique. The arterial plasma glucose level rose to a maximum of 121 ± 3 mg/dL three hours after feeding and then decreased. Net hepatic glucose output declined to 0.44 ± 0.44 mg/kg/min but the liver never became a net consumer of glucose. The arterial blood lactate level rose from 678 ± 71 to 1000 ± 158 μmol/L as the liver switched from net lactate uptake (12.2 ± 2.0 μmol/kg/min) to net lactate production (4.3 ± 1.7 μmol/kg/min). Over the course of the eight-hour postprandial period 25 g of glycogen were deposited in the liver. The net hepatic uptake of the gluconeogenic amino acids rose from 6.1 ± 1.2 μmol/kg/min to a peak of 15.4 ± 4.3 μmol/kg/min one hour after feeding. Net hepatic uptake of glycerol fell from 3.0 ± 0.3 μmol/kg/min to an average of 1.5 ± 0.4 μmol/kg/min. The plasma insulin level increased from 13 ± 2 μU/mL to a peak of 50 ± 4 μU/mL at 3.5 hours and fell to 32 ± 7 μU/mL by 8 hours. The plasma glucagon level rose from 22 ± 3 pg/mL to 93 ± 12 pg/mL 1.5 hours after feeding and fell to 68 ± 6 pg/mL 8 hours after feeding. It is concluded that in the long-fasted dog fed a mixed meal, (1) the liver switches from net lactate uptake to net lactate output, (2) net hepatic glucose production decreases, but net hepatic glucose uptake does not occur, and (3) hepatic glycogen synthesis occurs despite the absence of net glucose and lactate uptake by the liver.