Background: Similar to endothelial modulation of vascular tone, myocardial contraction may be modulated by cardioactive agents released from the coronary endothelium. To investigate such modulation in humans, we performed invasive assessment of left ventricular (LV) function before, during, and after bicoronary infusion of substance P, which releases nitric oxide from the endothelium.
Methods and results: Eight healthy subjects were investigated during diagnostic coronary angiography and eight transplant recipients during annual catheterization. Tip-micromanometer LV pressure was recorded before, during, and after bicoronary (n = 16) and right atrial (n = 14) infusion of substance P (20 pmol/min). LV angiograms (n = 11) were obtained before and at the end of the substance P infusion. At the end of the intracoronary substance P infusion, we observed (1) a fall in LV peak systolic pressure from 147 +/- 16 to 139 +/- 15 mm Hg (P < .01) in healthy subjects and from 147 +/- 25 to 141 +/- 22 mmHg (P < .05) in transplant recipients; (2) a downward and rightward shift of the average LV end-systolic pressure-volume point consistent with depressed systolic performance; and (3) a rise in LV end-diastolic volume at comparable end-diastolic pressure, consistent with increased end-diastolic distensibility. Five minutes after the substance P infusion, LV peak systolic pressure was higher than at baseline in healthy subjects (154 +/- 18 mm Hg; P < .05). Right atrial infusion of substance P did not reproduce these changes.
Conclusions: Bicoronary infusion of substance P modulates LV function in humans, probably through paracrine myocardial action of cardioactive agents released from the coronary endothelium.