Histopathological studies of cardiac lesions after an acute high dose administration of methamphetamine

Eighteen male Wistar rats aged six weeks were divided equally into Methamphetamine (MA), Placebo and Control group. MA group were injected with 50mg/kg body weight of Methamphetamine hydrochloride (MAHCl) in normal saline, Placebo group were injected with normal saline only, while Control group not injected with anything. Five MA group rats died within four hours of injection and their hearts collected on the same day. Another MA group rat was sacrificed two days after injection. Placebo and control group were sacrificed at similar intervals. Collected hearts were studied for cardiac lesions under light microscopy using special staining and immunohistochemistry. Microscopic examination of the myocardium of the rats that died on the first day of injection showed loss of nuclei in some myocytes, indicating cell death. Some areas in the sub-endocardium region showed internalization and enlargement of myocyte nuclei, consistent with regeneration of cells. There were very few foci of necrosis observed in these samples. The heart samples from the single rat that survived injection for two days showed foci of infiltration of macrophage-like cells that were later revealed to be regenerating myocytes. There were also spindle-like fibroblasts, macrophages and a few leucocytes found within these foci. The overall appearance of the myocardium did not indicate any inflammatory response, and the expected signs of necrosis were not observed. These results suggest a need to re-evaluate the toxic and lethal dosages of MA for use in animals testing. Cause of death was suspected to be due to failure of other major organs from acute administration of MA. Death occurred within a time period where significant changes due to necrosis may not be evident in the myocardium. Further investigations of other organs are necessary to help detect death due to acute dosage of MA.