The effects of lactate loading on alanine and glucose metabolism in the conscious dog

The effect of lactate per se on alanine and glucose metabolism was studied in five overnight-fasted conscious dogs. Somatostatin was infused to inhibit endogenous pancreatic insulin and glucagon release and the hormones were replaced intraportally at basal rates. Saline (n = 5) or lactate (at 25 and 50 mumol.kg-1.min-1 for 90 minutes each) was infused, and blood samples were taken during the last 30 minutes of each 90-minute period. Insulin, epinephrine, norepinephrine, and cortisol levels remained unchanged during saline or lactate infusion. Glucagon level decreased slightly during lactate (94 +/- 7 to 74 +/- 9 and 79 +/- 8 pg/mL) and saline (91 +/- 8 to 90 +/- 4 and 81 +/- 11 pg/mL) infusions. There were no significant changes in lactate or alanine levels or net hepatic balances with saline infusion. Blood lactate level increased from 657 +/- 74 to 1,718 +/- 126 and 3,300 +/- 321 mumol/L (both P < .05) during the low- and high-lactate infusion periods, respectively. The liver produced lactate during the control (5.57 +/- 2.92 mumol.kg-1 x min-1) and low-lactate infusion (1.75 +/- 2.58 mumol.kg-1 x min-1) periods, but consumed lactate (3.89 +/- 3.31 mumol.kg-1 x min -1; P < .05) during the high-lactate infusion period.(ABSTRACT TRUNCATED AT 250 WORDS)