INTERACTION BETWEEN CICLETANINE AND THE EICOSANOID SYSTEM IN HUMAN SUBCUTANEOUS RESISTANCE ARTERIES

In human subcutaneous resistance arteries in-vitro, the relaxation produced by the novel furopyridine compound cicletanine (30-mu-M) was inhibited by 51 % (P < 0.0001) in the presence of 20-mu-M of the cyclo-oxygenase inhibitor indomethacin. Maximal cicletanine-induced relaxation was reduced by both the cyclo-oxygenase inhibitor mefenamic acid and the relatively specific blocker of prostacyclin synthetase, tranylcypromine by 55% (P < 0.0005) and 43 % (P < 0.01), respectively. The potassium channel blocker, glibenclamide (100-mu-M), did not affect the relaxation produced by cicletanine but did inhibit the relaxation produced by the potassium channel blocker cromakalim (P < 0.0001). Cromakalim-induced relaxation was inhibited in the presence of indomethacin; relaxation induced by cromakalim (30-mu-M) was reduced by 22% (P < 0.02). The relaxation produced by the hypotensive agonists sodium nitroprusside, hydrochlorothiazide, bumetanide and nicardipine was unaffected by incubation with indomethacin. The results suggest that the vascular eicosanoid system, specifically prostacyclin, may be involved in the mechanism of the acute vasodilator action of cicletanine. Although at high doses cicletanine is a diuretic, in this mode it did not act like either a thiazide or a loop diuretic. The acute vasodilator action of the thiazide diuretic, hydrochlorothiazide was a novel finding of this study. Cromakalim showed a reduced response in the presence of indomethacin suggesting an involvement of the eicosanoid system in its mechanism of action.