EFFECTS OF VASOCONSTRICTOR AGENTS ON CARDIAC IRRITABILITY

¹ Department of Physiology, State University of New York, College of Medicine at New York City

A study was made of the effects of the vasoconstrictor drugs epinephrine, levarterenol, methoxamine and mephentermine, on excitability, refractory period, rhythmic abnormalities, conduction times and action potential of the heart. The principal observations were as follows:

These drugs with the exception of methoxamine, in doses so graded as to maintain blood pressure levels 30 to 50 mm. Hg above control values, induced ectopic pacemaker action, abnormal spontaneous beats, and abnormal and multiple responses to test stimuli.

The action of methoxamine on the heart can be said to be depressant in that it prolonged the action potential and the absolute refractory period, raised the threshold to stimulation and slowed A-V conduction significantly. This was not due to reflex vagal action.

All four drugs exhibited some degree of tachyphylaxis with respect to blood pressure maintenance and some other actions.

Other details of the comparative effects of these drugs are given in the discussion of results obtained.