Regulation of plasma lactic dehydrogenases in chronic respiratory acidosis

Abstract

Total lactic dehydrogenase (LDH) activity as well as the relative distribution of the five isozymes of LDH were measured in the plasma of guinea pigs during prolonged exposure to 15% carbon dioxide in 21% oxygen. During the uncompensated phase of respiratory acidosis (24 hours of exposure) total LDH ACTIVITY ROSE MORE THAN TWOFOLD) This change was mainly due to a fivefold increase in muscle subunit activity. After compensation of the respiratory acidosis, both total LDH activity and distribution of heart and muscle subunits returned to initial values. Cell necrosis, hepatic congestion, and hypoxic conditions could be excluded as possible causes of the observed changes. It is concluded that the CO2-induced alterations of LDH activity and of LDH isozymes represent an unspecific pH-dependent effect which is associated with increased blood corticosteroid levels.