Streptococcus pneumoniae-induced pulmonary hypertension and systemic hypotension in anesthetized sheep

Because some patients with Streptococcus pneumoniae bacteremia may present with shock, we reasoned that this organism may produce substances that cause shock. To test this hypothesis, type III pneumococcus supernatant, suspended in 10 ml of sterile water, was infused over 1 min in 8 adult anesthetized sheep. Normal saline was used as a control and had no effect on any of the hemodynamic parameters. Infusion of supernatant resulted in a precipitous fall in cardiac output from a control value of 4.25 +/- 0.54 to 2.80 +/- 0.43 (SE) l/min, a fall in mean systemic arterial pressure from 70 +/- 4 to 49 +/- 8 mmHg, and an increase in the mean pulmonary arterial pressure from 13 +/- 2 to 23 +/- 4 mmHg within 1 min after the infusion was completed. The peak hemodynamic effects were observed at approximately 3 min and returned to normal within 10 min after the infusion was completed. The thromboxane B2 level increased from a control value of 10 +/- 5 to 156 +/- 43 pg/ml at 3 min after the infusion was completed and decreased to 63 +/- 34 pg/ml at 20 min. A second identical dose of pneumococcal supernatant, repeated within 2 h of the first dose, had no effect on hemodynamic variables. Pretreatment with indomethacin, 5 mg/kg body wt, completely blocked the hemodynamic effects of pneumococcal supernatant (n = 3 sheep). Thus, we conclude that S. pneumoniae supernatant contains substances that cause septic shock syndrome through the synthesis of arachidonic acid metabolites and that a sublethal dose of the supernatant causes rapid tachyphylaxis.