Vasomotor tone affects diastolic coronary flow and flow impediment by cardiac contraction similarly.

We studied the effect of cardiac contraction on coronary arterial flow with vasomotor tone (control) and during maximal vasodilation with adenosine in the isolated blood-perfused rat heart at constant perfusion pressure (105 mmHg) with a left ventricular balloon (n = 6). Ventricular pressure was changed by volume changes and contractility via postextrasystolic potentiation. Contractility was expressed as the slope of the end-systolic pressure-volume ratio, elastance. Constant vasomotor tone was judged from stable diastolic flow. Coronary flow reduction (diastolic minus systolic flow, delta CBF, ml.min-1.g-1) due to contraction was related to developed ventricular pressure (devPLV) and developed elastance (devELV, systolic minus diastolic elastance) by multiple regression: delta CBF = SP.devPLV+SE.devELV+I, where SP and SE represent changes in coronary blood flow due to changes in devPLV and devELV, respectively, and I is intercept. In control, delta CBF = (0.016 +/- 0.008).devPLV + (0.0022 +/- 0.0009).devELV + (0.29 +/- 0.77); during vasodilation, delta CBF = (0.046 +/- 0.011).devPLV + (0.009 +/- 0.0053).devELV + (2.50 +/- 2.56). Diastolic flow increased by a factor of 4.06 +/- 1.57 (SD) during vasodilation. The increases in diastolic flow, SP, and SE were not different. We conclude that vasodilation has similar effects on diastolic flow and flow amplitude without affecting the relative contributions of ventricular pressure and contractility.