Myocardial depressant fraction in the venom of Dendroaspis angusticeps.

Whole venom Dendroaspis angusticeps produced a negative chronotropic and ionotropic effect on the heart. Isolation of the fraction (T39) produced the same effect. Negative inotropic effect was blocked by atropine. The bradycardia may be due to a cholinergic effect and the negative ionotropic to a direct depressant effect on the myocardium.

Involvement of Central adrenergic mechanisms in the induction of cardiac arrhythmias by aconitine nitrate administered intraventricularly.

Aconitine, 10 mug, administered intraventricularly in cats produced cardiae arrhythmias. Intraventricular administration of phenoxybenzamine, propranolol and practolol abolishes the centrally induced cardiac arrhythmias. Intraventricular reserpinization also abolished these cardiac arrhythmias whereas intraventricular administration of 6-hydroxydopamine and tetrabenazine had no effect. Brain stem noradrenaline probably plays a role in these centrally induced cardiac arrhythmias by aconitine.