Segmental differences in geometric, elastic and contractile characteristics of small intramural coronary arteries of the rat.

The depedence of elastic and contractile properties on the caliber of small intramural coronary arteries was investigated in the rat in vitro. Different segments of the left anterior descending coronary artery branching system were prepared for microarteriography. The segments were cannulated at both ends, immersed in oxygenated normal Krebs Ringer (nKR) solution. Intraluminal pressure was changed at a rate of about 0.5 mm Hg/s between 0 and 150 mm Hg in repeated cycles. The outer diameter was continuously measured with microangiometry. Pressure-diameter curves were recorded after preconditioning pressure cycles in nKR, with PGF2alpha in the bath (7.5 x 10(-6) M), and in maximal relaxation with papaverine (2.8 x 10(-4) M). Biomechanical parameters were computed for vessels grouped according to their calibers (inner diameters: 50-150, 150-250, 250-350, >350 microm). Distensibility and contractility decreased with increasing caliber of the vessels, while the elastic modulus increased. Spontaneous tone was (at 100 mm Hg in mechanically preconditioned vessels) 18.8 +/- 4.5, 8.4 +/- 4.4, 9.7 +/- 3.7 and 8.3 +/- 3.8% in the four groups, respectively. PGF2alpha contraction was maximal around the 300- microm caliber. Our study is the first direct demonstration that intramural small coronary arteries exhibit characteristic variability in their elastic and contractile properties as a function of their caliber. Such differences may be important in segmentally specific control processes of the coronary microcirculation.