Summary Using a sensitive method of blood bradykinin estimation, arterial and venous levels were compared in the human forearm. Arterial levels were usually higher, the ratio of arterial to venous levels ranging from 4 to approx. 1. Changes in blood bradykinin in venous blood from the hand were studied during hyperaemic states in the hand produced by warming, cooling and ischaemia. Increas of bradykinin up to 53% in effluent blood from the hand occurred when the hand was warmed to 45°. However, bradykinin levels fell in the dffluent blood in association with reactive hyperaemia and cold vasodilatation. An increase in sympathetic nervous activity caused a fall in arterial bradykinin level of 20% in one case and almost complete disappearance in another Generalised sympathetic blockade with bethanidine brought about a 7·5‐fold increase The ability of increased sympathetic nervous activity to lower blood bradykinin level may possibly contribute to the decreased venous bradykinin levels found in cold vasodilatation and reactive hyperaemia where an increase in sympathetic nervous activity occurs a result of the pain and discomfort associated with these procedures.
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Mashford et al. (1967) studied this question.