Smooth muscle responses of the rat septal artery are not influenced by surrounding passive cardiac tissue

Abstract

We investigated the possible contribution of surrounding passive cardiac tissue to the smooth muscle responses of coronary arteries. The vasoactive properties of the intramyocardial septal artery (outer diameter 350-400 microns) of the rat heart were investigated when it was freed from the surrounding cardiac tissue (dissected artery) and when it remained in the left ventricle and was thus embedded in passive cardiac tissue (in situ). The changes in external diameter relative to the maximal diameter (isoproterenol) resulting from the application of 125 mM KCl and 1,000 microU/ml vasopressin were measured at 37 degrees C, a transmural pressure of 100 cm H2O, and zero flow. In the dissected septal arteries (n = 5) the maximum diameter was 402 +/- 16 microns, while during exposure to KCl and vasopressin the diameter was reduced to 66.1 +/- 4.6% and 74.2 +/- 3.0%, respectively. For the in situ arteries (n = 6), the maximal diameter was 386 +/- 28 microns, a value not statistically different from the dissected vessels and the diameters reduced to 63.2 +/- 5.5% and 65.6 +/- 7.2% due to KCl and vasopressin, respectively. The constrictions of dissected arteries and in situ arteries were statistically not different. The results show that the maximally-dilated diameter and the constriction responses of intramyocardial conduit arteries of the rat heart are not affected by the surrounding passive cardiac tissue.

Segmental Differences in Geometric, Elastic and Contractile Characteristics of Small Intramural Coronary Arteries of the Rat

“…The proximal part of the left coronary artery of Wistar rats was found to develop more tension in response to similar doses of serotonin than distal, intramural segments of the same artery studied in vascular ring preparations [43]. In isolated, cannulated small septal coronary arteries of the rat, maximal doses of vasopressin induced an active contraction of similar extent than it was done by PGF 2α in our studies [44]. Contractions induced by PGF 2α were significantly greater in larger and medium-sized vessels than in small arteries in dog helical coronary artery strips [45].…”

“…At the present stage of our knowledge we can only speculate on the significance of the segmental variations of geometry, elasticity and contractility found by us and other authors [1, 2, 3, 5, 43, 44, 45]for the organization of the control processes of the whole microcirculatory system. Increasing relative wall thickness and spontaneous tone toward smaller intramural arteries, as we found, make vasodilatory and vasoconstrictor influences more effective in this region.…”

“…An interesting finding is the segmental maximum of sensitivity to PGF 2α . Segmental differences in contraction and relaxation also described in the literature [1, 2, 3, 5, 43, 44, 45]may influence the distribution of flow and pressure in the complex network of coronary microcirculation in a very complicated manner. Such complexity of coronary microcirculation mostly remains hidden when classical methods of study of coronary microvessels are applied (e.g.…”