Relationship between dog saphenous vein reactivity and Na content

Abstract

The physiological significance of the wide range of spontaneous variation in the total Na content of the dog saphenous vein (SV) was investigated. The SV of pentobarbital-anesthetized male mongrel dogs was perfused in vitro with the dogs' own venous blood, and its reactivity to acetylcholine (ACh) and norepinephrine (NE) was measured. The contralateral SV was removed for measurements of total and intracellular (Li exchange at 4 degrees C) Na and K content, DNA content, and muscle width. Reactivity to ACh correlated directly with total and extracellular SV Na content, and reactivity to NE correlated directly with total and intracellular K content. Reactivity to NE was unrelated to ACh reactivity, plasma NE concentration, or venous wall DNA content or muscle width. ACh-mediated venoconstriction was approximately 10 times more sensitive to inhibition by amiloride, an inhibitor of Na-entry pathways, than NE-mediated venoconstriction. The finding that extracellular Na content is a marker of reactivity to ACh is compatible with experimental evidence that the mode of action of ACh may be the stimulation of Na influx. The positive correlation between the K content and reactivity of veins to NE suggests that there is a link between intracellular K content and the release of Ca from the sarcoplasmic reticulum in response to NE.