Electrical and Mechanical Responses of Vascular Smooth Muscle to Vasodilator Agents and Vasoactive Polypeptides

Abstract

Amyl nitrite or sodium nitrite repolarised and relaxed sheep carotid arteries which had been depolarised and contracted by norepinephrine or histamine. These agents had little electrical or mechanical effect on unstimulated arteries. Epinephrine in the presence of phentolamine or Hydergine produced similar effects but the electrical changes were smaller and more variable than with the nitrites. All these agents could cause some relaxation, without electrical changes, of arteries which had been completely depolarised by potassium-rich solution. Bradykinin and angiotensin, like acetylcholine, depolarised and contracted the arteries even after actions via nerves had been blocked by nicotine and other agents. The effects that they produced when in sustained high concentration were limited in duration. All three agents could contract arteries which were completely depolarised by potassium-rich solution, without any electrical change. None of these relaxant or stimulant agents had any significant effect at 5°C. In canine carotid arteries, norepinephrine produced depolarisation and contraction as it does in sheep carotid arteries, but acetylcholine had variable electrical and mechanical effects. The results suggest that all these vasodilator and vasoconstrictor agents produce their mechanical effects on the arteries partly by changing the cell membrane potential and partly by other means.