nitroarginine and 8-(4-((2-aminoethyl)aminocarbonylmethyloxy)phenyl)-1-3-dipropylxanthine

To determine whether nitric oxide (NO), adenosine (Ado) receptors, or ATP-sensitive potassium (K(ATP)) channels play a role in arteriolar dilations induced by muscle contraction, we used a cremaster preparation in anesthetized hamsters in which we stimulated four to five muscle fibers lying perpendicular to a transverse arteriole (maximal diameter approximately 35-65 microm). The diameter of the arteriole at the site of overlap of the stimulated muscle fibers (the local site) and at a remote site approximately 1,000 microm upstream (the upstream site) was measured before, during, and after muscle contraction. Two minutes of 4-Hz muscle stimulation (5-15 V, 0.4 ms) produced local and upstream dilations of 19 +/- 1 and 10 +/- 1 microm, respectively. N(omega)-nitro-L-arginine (10(-4) M; NO synthase inhibitor), xanthine amine congener (XAC; 10(-6) M; Ado A(1), A(2A), and A(2B) receptor antagonist), or glibenclamide (Glib; 10(-5) M; K(ATP) channel inhibitor) superfused over the preparation attenuated the local dilation (by 29.7 +/- 12.7, 61.8 +/- 9.0, and 51.9 +/- 14.9%, respectively), but only XAC and Glib attenuated the upstream dilation (by 68.9 +/- 6.8 and 89.1 +/- 6.4%, respectively). Furthermore, only Glib, when applied to the upstream site directly, attenuated the upstream dilation (48.1 +/- 9.1%). Neither XAC nor Glib applied directly to the arteriole between the local and the upstream sites had an effect on the magnitude of the upstream dilation. We conclude that NO, Ado receptors, and K(ATP) channels are involved in the local dilation initiated by contracting muscle and that both K(ATP) channels and Ado receptor stimulation, but not NO, play a role in the manifestation of the dilation at the upstream site.

Topics: Adenosine; Adenosine Triphosphate; Animals; Anti-Arrhythmia Agents; Arterioles; Cricetinae; Enzyme Inhibitors; Glyburide; Male; Mesocricetus; Muscle Contraction; Muscle, Skeletal; Nitric Oxide; Nitroarginine; Potassium Channels; Receptors, Purinergic P1; Vasodilation; Xanthines

1. Isolated hearts of guinea-pigs were perfused in vitro with a physiological salt solution via a retrograde aortic cannulation (Langendorff preparation) at constant perfusion pressure. Bolus intra-arterial injections of various vasodilator drugs were made and the coronary flow responses were measured with an electromagnetic flow probe placed in the arterial inflow circuit. Inhibitory drugs were infused intra-arterially. 2. Nitro-L-arginine (NLA; 500 microM), an NO synthesis inhibitor, decreased coronary baseline flow by 16 +/- 0.8%, converted acetylcholine-induced coronary vasodilatation to vasoconstriction and had no effect on coronary flow responses to adenosine or papaverine. Sodium nitroprusside-induced responses were enhanced during NLA infusion by 46 +/- 11%. 3. Adenosine 5'-triphosphate (ATP) increased coronary flow but coronary flow responses to ATP were not altered by infusion of NLA. 4. ATP-induced coronary dilatation was not significantly attenuated by infusion of the adenosine receptor antagonist XAC, (xanthine amine congener; 2 microM), whereas XAC decreased coronary flow responses to adenosine by 75% +/- 5%. 5. ATP-induced coronary flow responses were reduced by only 31 +/- 4% during indomethacin infusion (2.8 microM) whereas indomethacin completely eliminated the initial vasoconstriction phase and greatly attenuated the peak flow and duration of the later vasodilatation phase seen in response to arachidonic acid (0.75 nmol). Indomethacin had no effect on vasodilatations produced by adenosine or prostaglandin I2. 6. These results indicate that ATP-induced coronary dilatation in the isolated, perfused heart of the guinea-pig is not dependent upon NO production or upon degradation of ATP to adenosine. The coronary dilator action of ATP may be partially dependent (approximately 30%) upon the production of vasodilator prostaglandins.

Topics: Adenosine Triphosphate; Animals; Arginine; Guinea Pigs; Heart; In Vitro Techniques; Indomethacin; Male; Nitric Oxide; Nitroarginine; Perfusion; Prostaglandins; Vasodilation; Vasodilator Agents; Xanthines