Use of intracoronary KCl in the beating and asystolic heart to determine the mechanism of initiation of the left ventricular mechanoreceptor reflex.

To provide further evidence that the veratrum alkaloids' mechanical, positive inotropic effect and not their chemical depolarising action predominates in initiating the left ventricular mechanoreceptor (including the Bezold) reflex the effect of intracoronary KCl, a chemical depolarising agent like the veratrum alkaloids, but with a negative inotropic effect, was studied in beating and verapamil-asystolic hearts. Five dogs were placed on a total cardiac bypass, pneumonectomised and their coronary and systemic circulations isolated and perfused separately, at a constant rate, so that changes in systemic pressure reflected changes in systemic resistance. Injection of 5 mmol X litre-1 KCl into the isolated coronary circulation caused cardiac asystole and a resultant reflex rise in systemic pressure (resistance) of 26 +/- 9% (p less than 0.05) above the control of 10.5 +/- 0.7 kPa (79 +/- 5 mmHg). This pressure rise, which indicates predominance of KCl's mechanical, negative inotropic over its chemical depolarising effect, was abolished by vagotomy, indicating its reflex nature. Contrariwise, in five other pneumonectomised dogs, similarly perfused on total cardiac bypass but with cardiac asystole from intracoronary verapamil, a subsequent, similar intracoronary dose of KCl now produced a fall in systemic pressure (resistance) of 8 +/- 2% (p less than 0.005) below the control of 12.8 +/- 0.5 kPa (96 +/- 4 mmHg). This pressure fall, presumably due to chemical depolarisation of the left ventricular mechanoreceptors, was also abolished by vagotomy.(ABSTRACT TRUNCATED AT 250 WORDS)