The effect of pinacidil on human isolated uterine artery rings was investigated. Pinacidil (10 nM-300 microM) induced a concentration-dependent relaxation of the precontracted arterial segments (pD2: 6.26; maximal response: 98.5%). Apamin (1 microM) and tetraethylammonium (6 mM) had no effects on the pinacidil-evoked relaxation, while 4-aminopyridine (0.1-6 mM) and glibenclamide (1-10 microM) competitively antagonized the response to pinacidil. The dissociation constants for 4-aminopyridine and glibenclamide were 240 microM and 0.40 microM, respectively. It is concluded that, in human uterine arteries, pinacidil induces relaxation. On the basis of differential antagonist affinities, we suggest that pinacidil produces a relaxation of this blood vessel through activation of glibenclamide-sensitive, ATP-dependent potassium channels.