Staphylococcal alpha toxin: a study with chronically instrumented awake sheep

The in vivo responses to staphylococcal alpha toxin are reported for 15 chronically instrumented awake yearling sheep. The data obtained from a total of 30 experiments are grouped into four categories of response: no response, noted in seven experiments done on 5 sheep; pressor response, obtained seven times in 4 sheep; fluid and solute exchange, noted on six occasions in 3 sheep; and acute heart failure and death, which occurred in 10 of the 15 sheep. "No response" denoted no change in any of the measured outcome variables. The group of sheep labeled as showing "pressor response" responded to alpha toxin infusion with an increase in pulmonary artery pressure, unaccompanied by changes either in lung lymph flow or in lung mechanics. "Changes in lung fluid and solute exchange" involve increases in lung lymph flow. The harbinger of the last category, acute left heart failure leading to death, was a marked elevation in left atrial pressure. The threshold response dose in sheep is approximately 21 micrograms/kg. A very steep dose-response curve is observed, with only a narrow window of doses, 15 to 25 micrograms/kg, between the group showing no response and the group showing death from acute heart failure. The data obtained in these studies indicate that the lethal effects of alpha toxin in sheep include acute heart failure, which may be due to direct toxicity to heart muscle and/or the coronary vasculature endothelium.