RELAXATION OF VASCULAR SMOOTH-MUSCLE BY ISOPROTERENOL, DIBUTYRYL-CYCLIC AMP AND THEOPHYLLINE

  • 1 January 1981
    • journal article
    • research article
    • Vol. 217  (1) , 26-35
Abstract
There is evidence that the relaxation of vascular smooth muscle produced by isoproterenol or cAMP is mediated by membrane hyperpolarization. The possibility that this hyperpolarization, and hence the relaxation, may be produced by activation of the electrogenic Na pump was investigated. Rat and pig tail artery strips were placed in a 1.0 mM K+ solution for 15 min. This procedure results in a decrease in the activity of the Na pump. The strips were then made to contract in response to norepinephrine. Two minutes later, the concentration of K was increased to 6.0 mM and a relaxation occurred. The amplitude of this relaxation reflects the activity of the Na pump. Either isoproterenol or dibutyryl-cAMP causes an enhancement (time or degree) of K-induced relaxation. Theophylline potentiated K-induced relaxation in pig arteries but not in rat arteries. The relaxant action of isoproterenol on 1.0 mM Ba contractures of rat arteries was inhibited by treatment with ouabain or with K-free solution. Ouabain inhibited the relaxant action of isoproterenol in pig arteries contracted with depolarizing K solution but not in rat tail arteries. Dibutyryl-cAMP, theophylline and nitroprus side caused relaxation of serotonin-induced contractions; in rat arteries these responses were not inhibited by ouabain or by the absence of K. Similar studies on tail arteries from baboons, dogs, pigs and cats showed that relaxation by dibutyryl-cAMP or by theophylline had some dependency on the activity of the Na pump. These observations are evidently consistent with the following conclusions: isoproterenol and cAMP potentiate the electrogenic pumping of Na and K responsible for K-induced relaxation; the relaxing action of isoproterenol, dibutyryl-cAMP and theophylline are dependent upon experimental conditions and the species from which the vascular tissue is obtained; and there is a component of isoproterenol- and cAMP-induced relaxation which is not altered by inhibition of the electrogenic Na pump in the rat.