[Effects of medullary pyramidal stimulation on myocardial contractility in anesthetized dogs]

In anaesthetized dogs, medullary pyramid stimulation produces a decrease of myocardial contractility. The peak of the first derivative of the left ventricular pressure (dP/dt max) was used to assess myocardial contractility; this index is independent of afterload. Medullary pyramid stimulation produces a decrease of dP/dt max and of the maximal left ventricular pressure (L.V.P. max) also, after bilateral vagotomy. But the same stimulation induces only a decrease of L.V.P. max after inhibiting beta-adrenergic efferences and bilateral vagotomy. Just as corticopyramidal fibres inhibiting alpha-adrenergic vascular tone, one does consider the existence of corticopyramidal fibres inhibiting beta-adrenergic efferences to myocardium.