Adrenergic influence in the coronary circulation of conscious dogs during maximal vasodilation with adenosine.

The coronary arteries receive rich adrenergic innervation. The present study examines the effects of changes in adrenergic activity on the coronary circulation without the complicating influence of autoregulation. Diastolic and mean circumflex coronary artery pressure-flow relations were generated in conscious dogs and were described by their slope and zero-flow, pressure-axis intercept during vasodilation produced by intracoronary adenosine, at a dose that abolished reactive hyperemia. /3-Adrenergic blockade with propranolol (1 mg/kg, iv) decreased coronary flow at all pressures, increasing diastolic pressure-axis intercept from 20.5 (4.7) (mean and SD) to 24.7 (SD 4.5) mm Hg, without a significant change in Aslope, a-Adrenergic blockade with phentolamine (0.3 mg/ kg, iv) increased flow at all pressures, with the greatest increases occurring at lower pressures. Thus, diastolic pressure-axis intercept decreased from 24.0 (SD 5.5) to 20.9 (SD 6.3) mm Hg, and calculated slope decreased slightly from 3.9 (SD 1.3) to 3.5 (SD 1.0) ml/min per mm Hg. a-Adrenergic agonist stimulation with intracoronary phenylephrine (0.3 jug/kg per min) produced little change in pressureflow relations; however, in the presence of /S-adrenergic blockade, the same dose of phenylephrine decreased coronary flow at all pressures, thus increasing diastolic pressure-axis intercept from 24.4 (SD 3.7) to 29.1 (SD 3.6) mm Hg. /S-Adrenergic agonist stimulation with isoproterenol (0.03 jug/kg per min, iv) produced small further increases in flow as compared with control, decreasing diastolic pressure-axis intercept from 26.0 (SD 2.9) to 24.9 (SD 2.8) mm Hg. These results suggest that significant resting aand /8-adrenergic tone can be demonstrated in coronary circulation during maximal adenosine-induced vasodilation. Resting /3-adrenergic tone is near maximal, and changes in adrenergic tone exert their influence on maximal flow primarily through changes in pressure-axis intercept, rather than through changes in the slope of the pressure-flow relationship. (Circ Res 51: 371-384, 1982)