L-arginine prevents cyclosporin A-induced pulmonary vascular dysfunction

Cyclosporin A is known to alter endothelium-dependent responses to different agonists. Few data are available concerning the effect of cyclosporin A on the pulmonary vascular bed.

The endothelium-dependent responses to acetylcholine (20 micrograms), bradykinin (5 micrograms), and substance P (5 micrograms) were investigated in a dog model of left lung autoperfusion at constant flow.

The vasodilator response to bradykinin and substance P was significantly decreased with cyclosporin A (20 mg) administration. The average decreases in pulmonary arterial pressure with bradykinin were 5.4 +/- 1.5 mm Hg and 2.4 +/- 0.4 mm Hg before and after cyclosporin A administration, respectively (p = 0.04). The average decreases in pulmonary arterial pressure with substance P were 4.4 +/- 1.0 mm Hg and 1.8 +/- 0.5 mm Hg before and after cyclosporin A administration, respectively (p = 0.04). The responses to acetylcholine and the endothelium-independent relaxing agent nitroglycerin were not significantly affected by cyclosporin A. The effects of cyclosporin A on endothelium-dependent responses to bradykinin and substance P were overcome by the administration of L-arginine (200 mg/kg intravenously). The decreased response to bradykinin and substance P after cyclosporin A administration was not significantly affected by indomethacin, a cyclooxygenase inhibitor. The pulmonary angiotensin-converting enzyme activity was also measured using [3H]benzoyl-phenylalanyl-glycyl-proline, an inactive angiotensin-converting enzyme substrate. There was an average [3H]benzoyl-phenylalanyl-glycyl-proline hydrolysis of 54% +/- 2% and 55% +/- 2% before and after cyclosporin A administration, respectively (not significant).

The present study suggests that cyclosporin A selectively decreases endothelium-dependent responses to bradykinin and substance P without affecting the cyclic guanosine monophosphate-dependent pathway in the canine pulmonary vascular bed. The decreased endothelium-dependent responses to bradykinin and substance P are not related to increased angiotensin-converting enzyme activity. The toxic effect of cyclosporin A on endothelium-dependent responses is reversible by the administration of L-arginine, a source of substrate for nitric oxide.