The increase in activity of acid hydrolases in muscles of rats after subcutaneous administration of dimethyl-para-phenylene diamine. A combined histochemical and biochemical investigation. I. The histochemical investigation.

The activity of acid hydrolases in skeletal muscles of normal rats and of rats after subcutaneous administration of dimethyl-para-phenylene diamine (DPPD) was studied with a combined histochemical and biochemical investigation. In this communication the histochemical findings are presented. After 4 days of DPPD treatment, coagulation necrosis, fragmentation and disintegration of fibres were seen in the muscles. An inflammatory infiltrate was seen between the muscle fibres. These pathological changes reached maximum intensity after 7 to 9 days. After 11 days the changes became less, despite continued treatment with DPPD. From the histochemical findings it appeared that the activity of acid phosphatase, beta-glucuronidase and E600 resistant non-specific esterase was increased in both a granular and a diffuse pattern in the skeletal muscles of the DPPD rats. The increase in activity of leucine aminopeptidase was much less pronounced and was mainly granular. The increase in the activity of acid hydrolases ran parallel to the severity of the pathological changes and reached a maximum after 7 to 9 days of DPPD treatment. The statistical calculations of the histochemical findings revealed that the increased activity of one acid hydrolase was significantly paralleled by an increased activity of a second hydrolase. There was a moderate probability that the activity of all other histochemically studied acid hydrolases, with the exception of leucine aminopeptidase, was increased. There was no difference in activity and localization of the acid hydrolases studied in aerobic type I and anaerobic type II fibres. The localization of acid phosphatase and beta-glucuronidase activity in muscle fibres and in inflammatory infiltrate mostly coincided. In cases where these enzymes were localized both centrally and in the subsarcolemnal areas of the muscle fibres, the activity of E600 resistant non-specific esterase was usually, and the activity of leucine aminopeptidase was exclusively located in the subsarcolemnal areas. All of the acid hydrolases examined were found to be present in the inflammatory exudate and in the connective tissue.