Abstract
Drug receptor in smooth muscles was examined with vascular strip from a guinea pig and following conclusions were drawn with regard to vascular smooth muscles.
1) Adrenaline, noradrenaline, and phenylephrine effect the strongest contraction, followed by histamine and barium chloride. Acetylcholine and posterior pituitary hormone have only a weak activity.
2) Vascular strip which had undergone the maximum contraction by the action of noradrenaline and phenylephrine does not undergo further contraction on addition of adrenaline but the strip contracted by the action of barium chloride, histamine, and acetylcholine undergoes further contraction on addition of adrenaline, to the same degree as that caused by single addition of adrenaline. Higher concentration of ephedrine inhibits the action of adrenaline.
3) Morphine and Aspaminol show reversible, competitive antagonism against barium chloride. Morphine, which does not affect contraction by adrenaline, does not antagonize irreversible, non-competitive anti-adrenaline action of Aspaminol. This point differs from intestinal smooth muscle.
4) Reversible, competitive antagonism against barium chloride appears at pH 6.25 and 5.83, from which the apparent pKa of the barium receptor is calculated as 7.37.
