Parasympathomimetic action of scorpion venom on the cardiovascular system.

Although the precise mechanism of the cardiovascular effects in man evoked by the venom of the yellow scorpion has yet to be completely elucidated, previous studies indicate that excessive adrenergic activity is present in many of the cases. This report describes two patients in whom yellow scorpion sting was followed by bradyarrhythmia with varying degrees of atrioventricular block which promptly regressed after the administration of atropine; this is consistent with a direct parasympathomimetic effect of the venom or with a central effect producing increased vagal tone. It is suggested that the cardiovascular actions of the venom may represent a wide spectrum of effects on the autonomic nervous system, ranging from the predominantly sympathomimetic to the predominantly parasympathomimetic.