Vasoactive properties of rat coronary artery: in the tissue and isolated.

Perfusion of the heart takes place mainly in diastole. It is therefore important to study the factors that affect coronary diastolic flow. One of the factors that may limit coronary artery vasoactive responses is the surrounding cardiac tissue. We have therefore studied the intramyocardial septal artery, both when still embedded in the diastolic, unstretched myocardial tissue and after complete dissection (n = 6). In situ, the average external diameter was 351 +/- 21 microns; after dissection, it was 362 +/- 21 microns. These values were not significantly different. The average response of the vessel to KCl (125 mM, receptor-independent constriction) reduced the diameter to 56.1 +/- 5.0% and 69.4 +/- 3.7% of the maximal diameter for in situ and dissected vessels, respectively. The reduction in diameter after dissection was significantly less than the reduction in situ. The response to vasopressin (1,000 microU/ml, a receptor-dependent constrictor) was a reduction to 62.6 +/- 4.7% and 70.4 +/- 4.5%, respectively. The reduction in diameter of the dissected vessel is significantly smaller than that of the in situ vessel. The average values of the ratios of the diameter reductions for vasopressin and KCl were 0.85 +/- 0.06 in the in situ condition and 0.95 +/- 0.08 after dissection and were not significantly different (paired t-test). The results show that the dilated diameter and the diameter responses of intramyocardial conduit arteries are not affected by the surrounding diastolic cardiac tissue.