Unmasking of activated histamine H3- receptors in myocardial ischemia: Their role as regulators of exocytotic norepinephrine release Academic Article uri icon

Overview

MeSH Major

  • Exocytosis
  • Myocardial Ischemia
  • Norepinephrine
  • Receptors, Histamine H3

abstract

  • We had previously found that histamine H3- receptors are negatively coupled to norepinephrine exocytosis in atrial tissue. We report here that in the presence of H1- and H2- receptor blockers, histamine significantly inhibits the tachycardia and norepinephrine release elicited by sympathetic nerve stimulation is isolated guinea pig hearts, an effect prevented by the H3 antagonist, thioperamide. Sympathetic nerve stimulation also caused a 1.5-fold increase in histamine overflow, which was insufficient to activate H3 receptors because thioperamide affected neither the tachycardia nor the norepinephrine release. Hence. We questioned whether H3 receptors become activated when adrenergic activity is greatly enhanced, as in myocardial ischemia. Guinea pig hearts underwent 10-min global ischemia. At reperfusion, norepinephrine exocytosis was markedly augmented and was associated with a 3.5-fold increase in histamine overflow. (R)alpha-methylhistamine, an H3 agonist, did not modify norepinephrine release, whereas thioperamide doubled it. Thus, in physiologic conditions, cardiac H3 receptors are quiescent, yet available for activation by exogenous ligands. In contrast, in the ischemic myocardium, H3 receptors appear to be fully activated by an endogenous ligand, probably histamine. Hence, cardiac H3 receptors may play an important role by negatively modulating exocytotic norepinephrine release associated with ischemic states.

publication date

  • January 1994

Research

keywords

  • Academic Article

Identity

Language

  • eng

PubMed ID

  • 7527852

Additional Document Info

start page

  • 1259

end page

  • 66

volume

  • 271

number

  • 3