Influence of chronic vagotomy on inotropic responses of isolated cat heart papillary muscle.

Isolated cat heart papillary muscle bathed at 37 degrees C, electrically driven at the rate of 30 per min, subjected to high voltage stimulation, or the addition of tyramine 1.7 microM, or high doses of acetylcholine (0.55mM) induced a positive inotropic effect revealed by an increase of peak tension developed (PTD). Papillary muscles obtained from cats after 7 to 8 days chronic bilateral cervical vagotomy showed a basic PTD (mg) similar to papillary muscles from non vagotomized control or sham operated cats. The inotropic effect of both tyramine and high voltage stimulation was absent in these animals as compared to controls or sham operated cats. Nevertheless, the inotropic effect of high acetylcholine concentration was still present and was of similar magnitude than in muscles of sham operated cats. The results suggest the existence of a neural cholinergic mechanism that is suppressed by chronic vagotomy which might be necessary for the synthesis, storage and/or release of adrenergic neurotransmitter in ventricular myocardium. It is suggested also, that suppression of general trophic function of vagus nerve might interfere with inotropic actions mediated by norepinephrine release.