Characteristics and origin of myogenic response in isolated mesenteric arterioles.

Responses to changes in intravascular pressure of isolated rat mesenteric arterioles were investigated under no-flow conditions. First-, second-, third-, and fourth-generation arterioles were isolated and cannulated. Vascular diameters were measured with an image-shearing device and recorded. The arterioles (except for the first-generation vessels) developed spontaneous tone, corresponding to the step increases in intravascular pressure (from 20 to 160 mmHg, by 20-mmHg steps). For example, at 80 mmHg pressure the mean diameters of first-, second-, third-, and fourth-generation vessels were 286.9 +/- 5.0, 203.4 +/- 8.2, 92.5 +/- 4.6, and 35.6 +/- 4.8 microns, respectively; by use of a Ca(2+)-free solution containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (1 mM) and sodium nitroprusside (SNP; 10(-4) M) the passive diameters of these vessels were 295.6 +/- 6.3, 238.4 +/- 11.7, 120.3 +/- 3.7, and 59.4 +/- 3.1 microns, respectively, demonstrating that the degree of pressure-induced constriction increased with the increasing order of generations (3, 14, 24, and 43%, respectively). The vasoactive function of endothelium and vascular smooth muscle was assessed by the responses of arterioles to acetylcholine (ACh; 10(-6) M) and SNP (10(-7) M) before and after removal of the endothelium with air. After removal of the endothelium, dilation to ACh was abolished while dilation to SNP was retained. Removal of the endothelium did not significantly alter the changes in the diameter of arterioles in response to step increases in intravascular pressure.(ABSTRACT TRUNCATED AT 250 WORDS)