Norepinephrine sensitivity of isolated rabbit aorta strips in solutions of varying pH and electrolyte content

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Abstract
Using a preparation of isolated vessel wall, observations have been made upon the sensitivity of the smooth muscle to 10 µg/l. of norepinephrine in various extracellular media. Varying the pH from 7.14 to pH 7.56 did not alter the sensitivity. More gross alterations in pH in either direction (pH 6.80 or 7.70) diminished the response equally. Lowering the sodium concentration and raising the potassium concentration both singly or together increased the sensitivity of the arterial strip. A rise in sodium concentration and a fall in potassium concentration either individually or in combination caused a lessened response to norepinephrine. Increasing the norepinephrine concentration to 100 µg/l. caused a greater contraction of the vascular smooth muscle, the degree of this response then being unaltered by pH and electrolyte changes in its environment within the range investigated. This strip of vessel wall from the largest vascular compartment outside of the heart appears to show a remarkable stability and regularity of reaction, despite wide variation in its extracellular environment, well beyond the limits of acid-base and electrolyte alteration commonly encountered in clinical medicine and surgery.