Methamphetamine, morphine or cocaine was injected intraperitoneally into Wistar rats (male, 6 weeks old) at a dose of 50 mg/kg, 125 mg/kg, or 50 mg/kg body weight, respectively. These doses of drugs were determined to ensure that the rats would show signs of drug intoxication and survive for a day. Over the period from 5 min to 18 hr after injection, concentrations of the drugs and metabolites in blood were analyzed by the GC/MS method, and the histopathological changes of the heart, lungs, liver and kidneys were examined by light microscopy. The time of maximum drug concentration in the blood after injection was 5 min in the methamphetamine-treated group, 1 hr (total morphine) in the morphine group and 5 min in the cocaine group. These blood concentrations decreased with time. In the liver at 2.5 hr after injection of methamphetamine, centrolobular vacuolation and diffuse eosinophilic changes of hepatocytes appeared. At 6 hr this damage spread to the midzone of the liver and partial necrosis of the centrolobe was found. At 18 hr the liver damage became worse and necrosis was also found in the midzone of the liver. In the heart, from 2.5 hr, eosinophilic changes of the myocardium were observed diffusely. Furthermore, at 18 hr, partial inflammatory cell infiltration and contraction bands were observed. The degree of histopathological damage did not coincide with the time of maximum drug concentration. In the morphine group, centrolobular and midzonal vacuolation, diffuse fatty degeneration and eosinophilic changes were observed in the liver from 2.5 hr to 18 hr after the administration. No necrosis was found, perhaps because the rats did not suffer the hyperthermia observed in the methamphetamine group. The degree of histopathological damage became more serious with time, as it did in the methamphetamine group. In the cocaine group, no histopathological changes were observed, probably because the doses of cocaine were too small to cause histopathological damage, and because cocaine is more rapidly metabolized than methamphetamine or morphine. These results suggest that in histopathological investigations necessitated by drug intoxication, measuring drug concentrations in the blood might be useful in determining the causes of histopathological changes more clearly.
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