Bevan J A, Joyce E H
Department of Pharmacology, College of Medicine, University of Vermont, Burlington 05405.
Am J Physiol. 1992 Jul;263(1 Pt 2):H182-7. doi: 10.1152/ajpheart.1992.263.1.H182.
Physiological salt solution infused through the lumen of a resistance branch of the rabbit central ear artery mounted in an isometric myograph causes both contraction and relaxation. The effect of reductions in extracellular Na up to 26 mM (20% of the NaCl content of the physiological saline solution) on these flow-induced changes in wall force and on the contraction to norepinephrine (10(-6) M) and relaxation to acetylcholine (10(-8) to 3 x 10(-6) M) and papaverine (10(-6) to 3 x 10(-5) M) has been studied. Na in the physiological saline solution was reduced by substitution of NaCl with sucrose or N-methyl-D-glucamine. The effect of either of these substitutions was to reduce both responses, contraction and relaxation, to the same extent. This sensitivity is such that physiological changes in blood Na concentration would be expected to influence flow-induced changes in wall tone. Responses to norepinephrine, acetylcholine, and papaverine were not significantly changed by these alterations in Na. It is argued that since reduction of extracellular Na diminished both contraction and relaxation to a similar extent, leading to relaxation and contraction respectively, that this effect probably occurs at a site common to both flow responses. Because both flow effects occur after endothelium removal and the extracellular matrix binds a large proportion of the Na in the blood vessel wall, this may represent the location of a flow-sensitive mechanism.
通过安装在等长肌动描记器中的兔中耳动脉阻力分支内腔注入生理盐溶液会引起收缩和舒张。研究了细胞外钠浓度降低至26 mM（生理盐溶液中NaCl含量的20%）对这些血流诱导的壁力变化以及对去甲肾上腺素（10⁻⁶ M）收缩、乙酰胆碱（10⁻⁸至3×10⁻⁶ M）和罂粟碱（10⁻⁶至3×10⁻⁵ M）舒张的影响。通过用蔗糖或N-甲基-D-葡萄糖胺替代NaCl来降低生理盐溶液中的钠。这两种替代物中的任何一种的作用都是在相同程度上降低收缩和舒张这两种反应。这种敏感性使得预计血钠浓度的生理变化会影响血流诱导的壁张力变化。钠的这些改变对去甲肾上腺素、乙酰胆碱和罂粟碱的反应没有显著影响。有人认为，由于细胞外钠的减少在相似程度上降低了收缩和舒张，分别导致舒张和收缩，这种效应可能发生在两种血流反应共有的部位。因为两种血流效应在内皮去除后都会出现，并且细胞外基质结合了血管壁中很大一部分钠，这可能代表了一个血流敏感机制的位置。
