Evidence in rat skeletal muscle suggests that local metabolic control of blood flow is facilitated by the reliance on alpha sub 2D-adrenergic receptors (ARs) for constriction of arterioles, together with the strong sensitivity of this constriction to inhibition by hypoxia. The present study examined the role of ATP-sensitive K sup plus (KATP) channels in the selective interaction between alpha2D-ARs and hypoxia. Arterioles from rat cremaster muscle that possess both alpha1D(alpha1A/D)- and alpha2D-AR subtypes were microcannulated, pressurized, and isolated in a tissue bath for measurement of changes in lumen diameter. Three studies first examined whether stimulation of alpha2D- and alpha1D-ARs involves inhibition of the KATPchannel. Concentration-dependent constriction by the KATPantagonists glibenclamide (GLB, 0.01 to 10 mu mol/L) and disopyramide (0.001 to 1 mmol/L) were abolished during alpha2Dstimulation but unaffected during alpha1Dstimulation. Activation of the KATPchannel by cromakalim inhibited alpha2Dconstriction with greater potency than alpha1D(EC50, 7.0 plus minus 0.2 versus 6.3 plus minus 0.1). Finally, GLB (0.5 mu mol/L) abolished dose-dependent alpha2Dconstriction, whereas alpha1Dwas unaffected. These data suggest that alpha2Dbut not alpha1Dstimulation is ``coupled'' with closure of the KATPchannel, leading to depolarization and contraction of vascular smooth muscle. In a second series, hypoxic (PO2, 6 mm Hg) inhibition of intrinsic smooth muscle tone was completely reversed by 0.1 mu mol/L GLB, concentration-dependent GLB constriction was enhanced during hypoxia, and hypoxia reversed GLB constriction. These data confirm reports by others that hypoxia potentiates the activation of K sub ATP channels, leading to hyperpolarization and relaxation. Finally, GLB constriction, which was abolished by concomitant alpha2Dstimulation, was completely restored by simultaneous activation of KATPchannels with hypoxia. These findings suggest that the sensitivity of alpha2D-AR constriction to inhibition by hypoxia arises through ``antagonistic coupling'' between these two stimuli, by which the alpha2D-AR inhibits and hypoxia activates KATPchannels.(Circ Res. 1995;76:53-63.)