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

Summary The increase in activity of acid hydrolases in skeletal muscles of rats after subcutaneous administration of dimethyl-para-phenylene diamine (DPPD) was studied with a combined histochemical and biochemical investigation. In part I the histochemical findings were presented. In this communication the biochemical findings are reported and compared with the histochemical findings.In homogenates of m. biceps femoris, m. gastrocnemius and m. rectus femoris of DPPD-treated rats, the activity of the lysosomal acid hydrolases, cathepsin D, acid maltase, acid phosphatase, and -glucuronidase was increased. This increase in activity was maximal after 7 to 9 days of DPPD treatment and ran parallel to the severity of the pathological changes. Statistical calculations clearly reveal that the increased activity of one acid hydrolase was significantly paralleled by an increased activity of a second acid hydrolase. Moreover these calculations reveal that the biochemical activity findings correlated with the histochemical activity findings. However it was remarkable that in the histochemical study, the estimated increase in acid phosphatase activity was much more than the increase in acid phosphatase activity found biochemically, whilst on the other hand the histochemically estimated increase in -glucuronidase activity corresponded with the biochemical observations. The results of gel filtration techniques have shown that this discrepancy of acid phosphatase activity was caused by different substrate specificity of the different isoenzymes of acid phosphatase and that as a result of the DPPD treatment the isoenzyme pattern had been altered. The elution patterns showed three distinct isoenzymes of acid phosphatase of normal and of DPPD treated rats. These isoenzymes, termed I, II and III, have molecular weights of: 200,000 or more, 83,500–104,500 and 14,500–18,100. Isoenzymes I and II split the substrates 4-methylumbelliferyl phosphate and naphthol AS-BI phosphate and the activity is strongly increased in the muscles of the DPPD treated rats. Isoenzyme III does not split naphthol AS-BI phosphate and the activity is not increased in the muscles of the DPPD treated rats. Considering the fact that it has been shown that the activity of isoenzyme III is high compared with that of the isoenzymes I and II, it is important to realise that by using naphthol AS-BI phosphate not all acid phosphatase can be demonstrated in sections of skeletal muscle.This study was partly supported by a grant from the Prinses Beatrix Fonds, 's Gravenhage, The Netherlands, and was mainly extracted from the Ph. D. thesis of D.E. Israël (1977).