Wiklund, Lars

Experiments were designed to determine responses of pulmonary arteries from an acutely rejecting, transplanted lung to rejection-activated mononuclear cells. Pulmonary arteries and macrophage-depleted mononuclear cells were obtained from unoperated dogs (control) and dogs with rejecting single lung allotransplants (transplanted, rejecting). In some arteries, the endothelium was removed deliberately. Pulmonary arteries were suspended for measurement of isometric force in organ chambers. Contractions to potassium chloride (60 M) were greater in rings of pulmonary arteries from rejecting compared with control dogs. Mononuclear cells from both control and transplanted dogs caused cell number-dependent contractions of autogenous pulmonary arteries. Contractions to cells were decreased when the endothelium was present only in arteries from control dogs; these contractions were increased by the L-arginine analog N(G)-monomethyl-L-arginine (10(-4) M) but not by indomethacin (10(-5) M). Contractions to mononuclear cells were reduced by superoxide dismutase (150 U/ml) and catalase (1,200 U/ml) in arteries without endothelium from control but not transplanted dogs. In arteries from transplanted dogs, contractions to mononuclear cells were reduced by desferoxamine (10(-3) M). Results suggest that interactions between mononuclear cells and pulmonary arteries are modified during rejection of lung allografts so that, during rejection, 1) endothelium-derived nitric oxide no longer antagonizes contractions to substances produced by the mononuclear cells and 2) contractions of smooth muscle from rejecting arteries to mononuclear cells may be mediated by radicals other than superoxide.

Experiments were designed to evaluate endothelium-dependent responses of pulmonary arteries following prolonged exposure to oxygen-derived free radicals. Rings of canine pulmonary arteries with and without endothelium were suspended for measurement of isometric force in organ chambers and incubated with xanthine (10(-4)M) plus xanthine oxidase (0.015 U/ml) for 1 h in the absence and presence of either superoxide dismutase (SOD, 150 U/ml), catalase (1,200 U/ml), deferoxamine (10(-3)M), or a combination of all three scavengers. Xanthine plus xanthine oxidase caused significantly greater contractions of rings without compared with those with endothelium. In rings with endothelium, contractions were reduced by SOD or catalase but not by deferoxamine. Following 1 h of exposure to xanthine plus xanthine oxidase, endothelium-dependent relaxations to ADP were reduced but not those to bradykinin or the calcium ionophore A-23187 (calcimycin). Relaxations to ADP were not corrected by incubation with the antioxidants used singly or in combination during the exposure to xanthine plus xanthine oxidase. These results suggest that oxygen-derived free radicals generated from exogenously applied xanthine plus xanthine oxidase cause contractions of canine pulmonary arteries. In addition, even when contractions of rings with endothelium were prevented by SOD and catalase, subsequent expression of some but not all endothelium-dependent relaxations were reduced. Therefore, scavenging of oxygen-derived free radicals may prevent some but not all of the vascular injury caused by oxygen-derived free radicals.

PURPOSE Experiments were designed to determine whether or not leukocytes activated by acute pulmonary rejection cause contractions of isolated pulmonary arteries. METHODS AND RESULTS Separate suspensions of (a) polymorphonuclear cells (> 95%) and (b) mononuclear cells (85% lymphocytes/10% monocytes/5% polymorphonuclear cells), respectively, were obtained from the arterial blood of four groups of adult male mongrel dogs: unoperated dogs (controls), dogs with single-lung autotransplants, dogs with rejecting single-lung allotransplants, and unoperated dogs treated with the same immunosuppressants as allotransplanted dogs. These suspensions were added to rings of control intralobar pulmonary arteries suspended in organ chambers for measurement of isometric force. The endothelium was removed mechanically from selected rings. No significant change in basal tension of pulmonary arterial rings occurred by adding suspensions of polymorphonuclear cells from any of the four groups of dogs. Significant cell-number-dependent increases in tension occurred with suspensions of mononuclear cells from unoperated dogs, autotransplanted dogs, and unoperated, medicated dogs. These increases in tension were less in rings with compared to those without endothelium. Addition of a synthetic analogue of L-arginine abolished this difference. Suspensions of mononuclear cells from rejecting allotransplanted dogs caused significantly greater contractions in rings with endothelium than those observed with suspended cells from either unoperated, autotransplanted dogs or unoperated, medicated dogs. Addition of superoxide dismutase plus catalase or an antagonist of endothelin-A receptors (BQ-123) reduced contractions in rings with endothelium but not in those without endothelium to suspensions of mononuclear cells from rejecting allotransplanted dogs. CONCLUSIONS The results of this study suggest that mononuclear cells cause contraction of pulmonary arteries, which can be partially inhibited by endothelium-derived nitric oxide. However, if the mononuclear cells are activated by acute pulmonary rejection, contractions are no longer inhibited by the endothelium. Under conditions of rejection, contractions are mediated in part by oxygen radicals and endothelin(s).