Leucocyte-induced endothelium-dependent vasodilatation and post-ischaemic vasospasm in the isolated rat superior mesenteric artery.

The purpose of this study was to investigate the possible role of leucocytes in the pathogenesis of reperfusion-induced vasospasm of ischaemic mesenteric arteries. Scanning electron microscopy of the rat superior mesenteric artery (SMA) after 30 min of ischaemia in vivo revealed adherence of leucocytes to the vessel wall. Isolated SMA preparations were perfused with Krebs-Henseleit buffer containing noradrenaline. Infusion of homologous leucocytes resuspended in perfusate (3 x 10(6) cells/ml) into these preconstricted preparations caused a fall in resistance of 29 +/- 2%. Removal of the endothelium by collagenase treatment abolished this response. Indeed, leucocyte infusion caused an increase in resistance of 39 +/- 8% under these circumstances. Following 30 min of normothermic ischaemia, leucocyte infusion caused a transient vasodilatation of 31 +/- 4% followed by an increase of 38 +/- 11% in the perfusion resistance of isolated SMA preparations. In each case, a similar response was obtained to infusion of the cell-free supernatant. These results suggest that leucocyte activation occurs in vivo during reperfusion of the SMA after as little as 30 min of ischaemia, and that activated leucocytes can release humoral vasoactive factors which evoke an endothelium-dependent vasodilator response in normal vessels but a predominantly vasoconstrictor response following brief intervals of ischaemia.