Acute exposure to the insecticide O,S-dimethyl phosphoramidothioate (methamidophos) leads to impairment of cardiovascular reflexes in rats

Poisoning by organophosphorus insecticides is often accompanied by cardiac complications which may be serious and even fatal. However, the effects of these compounds on the cardiovascular mechanisms involved in blood pressure regulation are not known. The aim of this study was to evaluate the effects of a sublethal dose (8 mg/kg, i.p.) of the organophosphorus methamidophos on chemoreceptor (CR) and Bezold–Jarisch (BJR) cardiovascular reflexes. Male Wistar rats were treated with single intraperitoneal injections of methamidophos in saline (n=23) or saline (0.9 percent, n=20) and underwent catheterization of femoral artery and vein one day after the injections. Cardiovascular recordings were performed 24 h after the catheterization procedure. Plasma cholinesterase (ChE) activity was measured 24 h after similar treatments in separate groups (n=10/group). The bradycardic component of CR and BJR was significantly attenuated in animals treated with methamidophos. The ChE activity was 80 percent reduced in the methamidophos-treated animals. Methamidophos impairment of the bradycardic component of two important cardiovascular reflexes may contribute to the cardiovascular toxicity associated with acute organophosphorus insecticides exposure.

Research highlights
► Cardiac complications often accompany poisoning by organophosphorus pesticides.
► Organophosphorus pesticides effects on cardiovascular reflexes remained unknown.
► We examined the effects of methamidophos on cardiovascular reflexes in rats.
► Methamidophos reduced the bradycardic responses of cardiovascular reflexes.
► Methamidophos effects on cardiovascular reflexes may contribute to its toxicity.