Reactivity of isolated porcine coronary resistance arteries to cholinergic and adrenergic drugs and transmural pressure changes.

The reactivity of porcine intramyocardial resistance arteries (223 +/- 7 micron i.d., n = 30) was investigated with a pressurized in vitro preparation. Diameter changes in response to acetylcholine and to adrenergic drugs and dynamic changes in transmural pressure changes were investigated. Acetylcholine produced concentration-dependent constrictions, causing maximal reductions of 71 +/- 3% in lumen diameter, with EC50 values averaging 1.9 X 10(-7) M (n = 7). These responses were inhibited by atropine (10(-7) M) and therefore were mediated by muscarinic receptors. In addition, acetylcholine did not elicit relaxation in nine out of 10 vessels precontracted with U46619 (10(-7) M). Norepinephrine and epinephrine never produced constrictions (n = 6) even in the presence of propranolol (10(-6) M). Both norepinephrine and isoproterenol caused dose-dependent relaxations in acetylcholine-precontracted vessels, with IC50 values of 8.2 X 10(-7) M (n = 5) and 6.6 X 10(-8) M (n = 6), respectively. These relaxations were suppressed by propranolol. Between transmural pressures of 10 and 90 mm Hg, there was no intrinsic myogenic tone (n = 7). In addition, the vessels responded only passively to sudden pressure changes of 40 mm Hg. In all vessels, the functional integrity of the endothelium was verified by relaxations to substance P (10(-8) M) and/or bradykinin (10(-8) M).(ABSTRACT TRUNCATED AT 250 WORDS)