PT  - JOURNAL ARTICLE
AU  - PAUL M. VANHOUTTE
AU  - ROBERT R. LORENZ
AU  - GERTRUDE M. TYCE
TI  - INHIBITION OF NOREPINEPHRINE-<sup>3</sup>H RELEASE FROM SYMPATHETIC NERVE ENDINGS IN VEINS BY ACETYLCHOLINE
DP  - 1973 May 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 386--394
VI  - 185
IP  - 2
4099  - http://jpet.aspetjournals.org/content/185/2/386.short
4100  - http://jpet.aspetjournals.org/content/185/2/386.full
SO  - J Pharmacol Exp Ther1973 May 01; 185
AB  - Experiments were designed to determine if the relaxation obtained with acetylcholine during electric stimulation of cutaneous veins results from inhibition of norepinephrine release. Helical strips of dog saphenous veins were incubated (four hours) in Krebs-Ringer solution which contained norepinephrine-7-3H (5 x 10-8 g/ml). The preparations then were rinsed and mounted for superfusion (3 ml/min) and isometric tension recording. The superfusate was collected at timed intervals for estimation of total radioactivity or for column chromatographic separation of norepinephrine and its metabolites. Electric stimulation increased the tension and the total radioactivity of the superfusate; it increased the amount of intact norepinephrine-3H present more than the metabolite fractions. Acetylcholine (5 x 10-8-5 x 10-7 g/ml) depressed the contractions and diminished the norepinephrine-8H efflux. Isoproterenol depressed the contractions but did not affect the efflux of radioactivity. Tyramine (2 x 10-6 g/ml) augmented both tension and efflux of radioactivity, but these actions were not depressed by acetylcholine. These experiments show that acetylcholine causes relaxation of venous smooth muscle constricted by sympathetic stimulation and does so by inhibiting the release of norepinephrine from the nerve endings. By contrast, acetylcholine does not inhibit the release of norepinephrine by tyramine. © 1973 by The Williams & Wilkins Co.