Biochemical and subcellular changes in carp exposed to the organophosphorus methidathion and the pyrethroid deltamethrin

The in vitro and in vivo effects of the insecticides methidathion (MD) and deltamethrin (DM) on acetylcholinesterase (AChE, EC 3.1.1.7) in different tissues were examined in adult carp (Cyprinus carpio L.). The changes in biochemical blood parameters, such as the levels of glutamic-oxaloacetic transaminase (GOT, EC 2.6.1.1), lactate dehydrogenase (LDH, EC 1.1.2.3) and glucose, were also studied in DM-treated fish. The in vitro kinetic results for both insecticides showed that the inhibition of brain AChE was of mixed type, with K-I(MD) = 6.0 +/- 1.0 mu M and K-I(DM)= 15.6 +/- 2.4 mu M. In vivo treatment with 2 mg/l MD for 5 days caused a 70-90% decrease in the AChE activity of different organs, while treatment with 2 mu g/l DM for 3 days did not result in such a drastically inhibited AChE. The relative distribution of the AChE molecular forms in the liver of MD-treated carps was significantly different from that in the control animals. The content of the G(1) form increased, while that of G(4) decreased. The extents of the differences were much lower in the other tissues investigated for both MD and DM treatments. In vivo DM treatment for 3 days caused a 20% decrease in the AChE activity of the blood serum, while the GOT and LDH activities increased 2.5-fold (72-h sample) and 1.5-fold (6-h sample) as compared with those of the control carp. The blood glucose level was 30%, higher (6-h sample) than that of the control fish. After the fish were returned to clean water, the parameters revealed that the recovery took only 24-48 h. The accumulation of MD was highest in the liver and the roe, while the content of the skeletal muscle could not be detected by the methods used. No DM could be detected in any of the tissues, though the sensitivity of the measurement was 0.0005 mg/1000 g wet tissue. Electronmicroscopy indicated subcellular changes in the hepatocytes. All the observed changes demonstrate the effects of MD and DM on different fish enzymes under laboratory conditions. The changes in AChE indicate how serious the neuronal damage is, while the other parameters relate to the stressed state of the fish.