Filtrates possessing a high a-haemolytic titre, obtained from cultures of Staphylococcus pyogenes, were reported by Feldberg & Keogh (1937) to release histamine from cat and guinea-pig perfused isolated lungs, and by Feldberg & Kellaway (1937) to release histamine and a slow-contracting substance from dog perfused lung and liver. Brown, Prichard & Quilliam (1959) were unable to detect the release by the a-toxin of any spasmogenic substance from segments of guinea-pig isolated ileum. Smith & Miles (1960) observed no increase in the amount of histamine in the peritoneal cavity of rats treated with staphylococcal a-toxin or with live staphylococci. This paper reports the results of a further investigation into the possible histamineliberating action of staphylococcal a-toxin, using the preparation of a-toxin employed previously (Brown et al., 1959). The work forms part of an attempt to determine whether histamine release might play a role in the pharmacological actions of the a-toxin, such as the smooth muscle spasmogenic action reported by Brown et al. (1959) and by Wiegershausen (1962).
METHODS
Isolated TissuesTissues obtained from freshly-killed guinea-pigs and rats, or from anaesthetized cats, were cut into small pieces (about 0.5 cm', or, with skin, strips about 1 cm long by 1 to 2 mm wide), and incubated in 1 or 2 ml. of magnesium-free Tyrode solution at 37' C previously equilibrated with a mixture of 95% oxygen and 5% carbon dioxide. Between periods of incubation the tissues were immersed for a standard time, usually 90 sec, in a similar solution containing staphylococcal a-toxin, Compound 48/80, or no added agent (controls). After incubation the tissues were removed, blotted and weighed, and the incubation fluids were assayed for histamine content as described below.
A naesthetized catsCats were anaesthetized with pentobarbitone (35 mg/kg, intraperitoneally) and carotid blood pressure was recorded with a mercury manometer. A femoral artery was cannulated and blood withdrawn into centrifuge tubes containing 100 units of heparin in 0.1 ml. before and after intravenous injection of staphylococcal a-toxin or Compound 48/80. The blood was centrifuged and the plasma was assayed for histamine content after suitable dilution with Tyrode solution.
Histamine assayThe isolated terminal ileum of the guinea-pig was superfused with magnesium-free Tyrode solution at 30' C. bubbled with a mixture of 95% oxygen and 5% carbon dioxide, and containing