Responses of the cardiac sympathetic receptors to various substances.

Abstract

Responses of the sympathetic receptors of the left ventricle to various substances, including those which increase following myocardial ischemia and algesic agents, were examined in dogs anesthetized with pentobarbitone sodium under artificial respiration and the following results were obtained:(1) The injection of dopamine, epinephrine and norepinephrine into the right femoral vein or the left atrium resulted in a rise in the left ventricular pressure (LVP) and left ventricular tension (LVT) as well as a marked increase in the number of the afferent impulses per beat. The injections of l-dopa, dihydroxymandelic acid and vanilmandelic acid, on the contrary, were little effective.(2) Angiotensin II and isoproterenol produced an increase in LVP, LVT and in the number of the impulses. Also, the impulses increased following the injection of acetylcholine.(3) LVP and LVT showed various response patterns to the injections of l- and dl-lactic acids and pyruvic acid. However, the impulses increased markedly even when LVP, LVT and heart rate were reduced following the administration of these agents in most experiments. On the other hand, LVP, LVT and the impulses decreased at first and then increased slightly following the injection of sodium lactate and sodium pyruvate in large doses. Acetic acid and HCl produced the same responses with those produced by lactic or pyruvic acid.(4) LVP and LVT decreased following the injection of histamine and bradykinin. The impulses were decreased or slightly increased by histamine, but were increased markedly by bradykinin. LVP, LVT and the impulses increased following the administration of serotonin.(5) Adenosine and its phosphorylated derivatives reduced LVP and LVT, but increased the impulses slightly.(6) A large dose of KCl produced a fall in LVP and LVT, but a slight increase in the number of the impulses in some cases. The impulses increased slightly following the injection of a large dose of NaCl. On the other hand, CaCl2 and MgCl2 were little effective.(7) Phenoxybenzamine, propranolol and nitroglycerin reduced LVP, LVT and the number of the impulses, whereas ethyl-alcohol was little effective.From the findings obtained in the present studies, it was concluded that the sympathetic receptors in the wall of the left ventricle were activated by various substances including those which increase during myocardial ischemia and algesic ones. It was supposed that they might be activated directly by several substances, while indirectly by some other substances through increased left ventricular contraction or through other mechanisms, and that these receptors have the characters of both mechanoreceptor and chemoreceptor.