A histochemical study of the esterases of the rat heart

The histochemistry of esterases was studied in the rat heart, using various methods of tissue preparation and a large number of substrates, inhibitors and activators. Non‐specific esterase and cholinesterase was demonstrated in the fibers of the atrioventricular conduction system, in atrial and ventricular muscle fibers, in cardiac neurons and in some of the nerve fibers of the heart. The highest concentration of both types of enzymes was found in the conduction system and in the neural elements. Pericytes and macrophages showed only non‐specific esterase activity. Two broad types of non‐specific esterase activity, cytoplasmic and lysosomal, were distinguished in the pericytes, macrophages and cardiac muscle fibers by the use of selective inhibitors and activators. The cytoplasmic activity is due to the presence of B and C esterases and was better demonstrated with esters of a‐naphthol than with naphthol AS derivatives or indigogenic esters. The esterase activity of lysosomes appears to be due to a group of fluoride‐ and organophosphate‐resistant enzymes, some of which are probably cathepsins.