EFFECTS OF PROLONGED TOURNIQUET ISCHEMIA AND SHORT-TERM VENOUS STASISON PLASMA ENDOTHELIN-1 LEVELS IN MAN

In vitro studies have indicated increased endothelial release of endot helin during tissue and cellular hypoxia. Therefore, we studied the ef fect of tourniquet ischaemia and venous stasis on plasma endothelin-1 (ET-1) levels in humans in vivo. The effect of hypoxia on plasma ET-1 levels in 16 patients subjected to an orthopaedic operation and six he althy volunteers was studied by (a) tourniquet ischaemia, in which a l imb is totally emptied of blood and kept ischaemic by means of a pneum atic tourniquet, and (b) venous stasis in an upper arm. The mean (SEM) basal plasma ET-1 concentration in the patients subjected to tourniqu et ischaemia of a lower limb was 4.1 (1.0) pg ml(-1). No significant c hange in plasma ET-1 levels during or after tourniquet ischaemia was f ound. The mean (SEM) plasma ET-1 concentration in six healthy subjects prior to venous occlusion in the right upper arm was 3.3 (0.7) and 2. 7 (0.3) pg ml(-1) in the right and left arm, respectively. A significa nt increase in plasma ET-1 concentration after 20 min was observed in the arm subjected to venous stasis, but not in the other, control, arm . Mean arterial blood pressure did not change significantly. Local tis sue hypoxia may not be an important stimulus for ET-1 release in human s in vivo, whereas short-term venous occlusion in an upper arm leads t o local release of ET-1 by an as yet unknown mechanism.