Functional effects of Morin in rat isolated pulmonary arteries

Morin, a natural flavonoid, has antioxidant, antiapoptotic, anti-inflammatory, antifibrotic, antineoplastic, neuroprotective effects as well as protective effects on cardiovascular system. Morin reduced blood pressure in a rat model of hypertension induced by L-NAME, and had positive effects on blood pressure in rats fed a high-fructose diet by improving insulin sensitivity and reducing Endothelin-1 levels in thoracic aorta. Agents inducing relaxation in pulmonary artery may provide new therapeutic approaches for treatment of pulmonary hypertension, which is a significant health problem. The mechanisms for the favorable effects of Morin on blood pressure have been studied to a limited extent in a small number of studies in large-diameter conductance and small-diameter resistance arteries, but its effects on functional responses of pulmonary arteries and the mechanisms mediating these effects have not yet been examined. We examined the potential relaxant effect of Morin in isolated pulmonary artery preparations and the mechanisms underlying this effect. Morin, administered cumulatively in isolated pulmonary artery rings obtained from 8-12 week old, healthy, adult male Wistar-Albino rats weighing 250-300 grams, induced endothelial and concentration-dependent relaxation responses on contractions induced by submaximal concentrations of Phe and 80 mM KCl solution. The relaxant effect of morin did not show a statistically significant change after incubation with NOS blocker L-NAME, COX blocker Indomethacin, superoxide radical scavenger SOD and H2O2 scavenger Catalase. After incubation of vessels contracted with 80 mM KCl solution with L-NAME and Indomethacin, Morin induced relaxations similar to those produced in the absence of these blockers. Present results suggest that NO, cyclooxygenase products, or free oxygen radicals are not involved in relaxant effect of Morin in isolated pulmonary artery rings and that it is mainly mediated by EDHF. These favorable results obtained at the preclinical level rings need to be supported and improved by further studies to demonstrate the possible therapeutic potential of Morin in pulmonary arterial hypertension.