CARBON-SOURCES FOR D-LACTATE FORMATION IN RAT-LIVER

Carbon sources for D-lactate formation were investigated in vitro usin g 6,000Xg supernatant of rat liver homogenate and by rat liver perfusi on in situ. As carbon sources, L-threonine, glucose, glycerol, acetone , and acetoacetate were tested. Glycerol was the best substrate for D- lactate formation via methylglyoxal in rat liver. Glucose was the seco nd most preferred substrate, while L-threonine, acetone, and acetoacet ate were poor substrates for D-lactate formation, Glycerol was several times more effective than normal as a substrate of D-lactate in the s upernatants of liver homogenates of diabetic and starved rats, while i t was less effective as a substrate of L-lactate. The glycerol kinase [EC 2.7.1.30] activities in livers increased in the diabetic and starv ed states. These and other results can explain why the plasma concentr ation of D-lactate increases several-fold after running and why the D- lactate contents in plasma, liver, and skeletal muscle are markedly in creases in diabetic and starved rats.