Depression of papillary muscle contractility by plasma incubated with pneumococci

Mechanisms of death in pneumococcal disease are poorly understood. We have previously shown that intravenous pneumococcal products in dogs caused a mean decrease in cardiac output of 58%. The present study used measurements of the force and rate of contraction of isolated rabbit papillary muscle to determine whether pneumococci (PNC) altered myocardial contractility. Nine papillary muscles were superfused with various solutions including Tyrode's, Tyrode's incubated with sonicated type 1 PNC, normal rabbit plasma, and rabbit plasma incubated with PNC. Compared to untreated Tyrode's solution, PNC-treated Tyrode's solution did not alter papillary muscle contractility. However, compared to untreated rabbit plasma, plasma incubated with PNC caused a mean decrease of 18% in the force of contraction and 16.7% in the maximum rate of force development in nine studies. We conclude that PNC do not directly affect papillary muscle contractility. However, the interaction of PNC and plasma does cause a decrease in rabbit papillary muscle contractility.