Bufodienolides as Endogenous Na⁺, K⁺-ATPase Inhibitors: Biosynthesis in Bovine and Rat Adrenals

The biosynthesis of digitalis-like compounds (DLC) was determined in bovine and rat adrenal homogenates by following changes in the concentration of DLC using three independent sensitive bioassays: inhibition of [³H]-ouabain binding to red blood cells and competitive ouabain and bufalin ELISA. The amounts of DLC in bovine and rat adrenal homogenates, as measured by the two first bioassays, increased with time when the mixtures were incubated under tissue culture conditions. These results suggest that Na⁺, K⁺-ATPase inhibitors which interact with cuabain antibodies, but not those which interact with bufalin antibodies, are synthesized in bovine and rat adrenals.