Histamine was considered to be the chief mediator in inflammatory reactions until it was shown that specific antihistamine drugs did not always inhibit-these reactions. The idea of the polypeptide nature of some of the unidentified permeability factors in inflammatory exudates was introduced by Menkin (1936). Armstrong, Jepson, Keele & Stewart (1957) noted the similarity of the actions of these factors with those of bradykinin, a nonapeptide. This compound or others related to it have since been found in many oedema fluids and were detected in the perfusates of rat paws after the application of heat (Rocha e Silva & Antonio, 1960).It was considered important to investigate in more detail the extent to which kinins participate in this so-called thermic oedema by following changes in four-kinin parameters in the perfusates. As rats which are resistant to the anaphylactoid reaction produced by dextran (the so-called non-reactors) also showed greater resistance-to thermic oedema than did the reactors giving the anaphylactoid reaction (Gecse, Karady, Starr & West, 1965), a comparison of the activity of the kinin systems in the perfusates collected from the heated paws of both types of rat was also made. In addition, a study of the effects of drugs on both the development of thermic oedema and the actions of bradykinin has been included.
METHODSAdult Wistar albino rats were obtained from Fison's Ltd. (Holmes Chapel) and from the Agricultural Research Council's Field Station at Compton. They were tested for their reactivity to dextran (240 mg/kg, intraperitoneally) on three occasions, oedema developing in the extremities over a 2-hr period only in reactor rats (Harris & West, 1961). Both reactor and non-reactor rats were anaesthetized with pentobarbitone sodium (45 mg/kg, intraperitoneally) and their hind paws were perfused according to the method of Rocha e Silva & Antonio (1960). Before collecting the perfusates, the paw space was washed free of blood. The flow of perfusing fluid (Tyrode solution) was regulated to 5-10 drops/min, and then the paw was immersed in a water-bath maintained at the desired temperature for 30 min. Perfusates were collected for three consecutive periods of 10 min during the heating and for further periods after the heating. Samples were also collected from unheated paws to serve as controls.In other experiments, paws were heated without perfusion after the rats had been anaesthetized and given azovan blue dye intravenously (18 mg/kg, Bonaccorsi & West, 1963). The paws were then examined for the presence of oedema using the plethysmographic method of Buttle, D'Arcy,