Effects of perivascular nerve stimulation on the contraction and automaticity of the blood-perfused canine papillary muscle.

1. Effects of ventricular perivascular nerve stimulation (p.n.s.) on the ventricular contractility and idioventricular rate were investigated with the blood-perfused papillary muscle of the canine right ventricle.2. Perivascular nerve stimulation of supramaximal voltage and 1 msec pulse-duration caused a definite positive inotropic response at a frequency of 1 Hz, which gradually reached a maximum at 15 to 20 Hz when the papillary muscle was electrically driven at 120 beats/min at a constant temperature of 38-39 degrees C. The frequency-response curve was sigmoid.3. The spontaneous regular idioventricular rate of 46+/-4 beats/min was accelerated to at most 60+/-4 beats/min (n=11) by p.n.s. The stimulus frequency-response relations between chronotropic and inotropic responses to p.n.s. were almost the same.4. Tetrodotoxin blocked completely the responses to p.n.s. while it had little or no effect on the inotropic response to exogenous noradrenaline.5. Positive inotropic responses to p.n.s. were diminished by beta-adrenoceptor blocking agents (alprenolol, propranolol and pindolol) and were enhanced during infusion of cocaine.6. In reserpine- or guanethidine-pretreated muscles, p.n.s. as well as field stimulation produced negative inotropic responses, which were enhanced by physostigmine and were blocked by atropine.7. Hexamethonium enhanced slightly the positive inotropic responses to p.n.s. as well as field stimulation.8. It was concluded that the perivascular nerves of the coronary artery of the canine ventricle are mainly composed of postganglionic adrenergic fibres but there are also pre- and postganglionic cholinergic nerve fibres.