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EFFECTS OF IMPROMIDINE, A SPECIFIC H 2 ‐RECEPTOR AGONIST AND 2‐(2‐PYRIDYL)‐ETHYLAMINE, AN H 1 ‐RECEPTOR AGONIST, ON STIMULATION‐INDUCED RELEASE OF [ 3 H]‐NORADRENALINE IN GUINEA‐PIG ISOLATED ATRIA
Author(s) -
RAND M.J.,
STORY D.F.,
WONGDUSTING HELEN
Publication year - 1982
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1982.tb09221.x
Subject(s) - mepyramine , cimetidine , endocrinology , agonist , medicine , histamine , chemistry , stimulation , histamine h2 receptor , competitive antagonist , antagonist , receptor , biology
1 The specific histamine H 2 ‐receptor agonist, impromidine (3–100 nmol/l), increased the rate and force of beating of guinea‐pig isolated atria. These effects were blocked by the H 2 ‐receptor antagonist, cimetidine (30 μmol/l), but not by the H 1 ‐receptor antagonist, mepyramine (0.1 μmol/l). 2 In atria that had previously been incubated in [ 3 H]‐noradrenaline, impromidine (3–100 nmol/l) had no effect on the resting efflux of radioactivity, but concentrations of 50 and 100 nmol/l significantly increased the efflux induced by electrical stimulation (2 Hz for 10 s) of the intramural sympathetic nerves by approximately 38%; lower concentrations (3, 10 and 25 nmol/l) had no effect. 3 The effect of impromidine in enhancing stimulation‐induced efflux of radioactivity was abolished by cimetidine (30 μmol/l) and by mepyramine (0.1 μmol/l). It was unaffected by the α‐adrenoceptor antagonist, phentolamine (30 μmol/l). 4 Impromidine produced some inhibition of the uptake of [ 3 H]‐noradrenaline, but this did not account for the enhancement of the stimulation‐induced efflux of radioactivity, since impromidine (50 nmol/l) still increased release in the presence of cocaine (30 μmol/l). 5 The specific H 1 ‐receptor agonist, 2‐(2‐pyridyl)‐ethylamine (10–100 μmol/l), increased both the resting and stimulation‐induced efflux of radioactivity. These effects were not blocked by mepyramine (0.1 μmol/l) or the β‐adrenoceptor antagonist, metoprolol (0.1 μmol/l). 6 The prejunctional inhibitory histamine receptors in guinea‐pig atria are not classifiable into H 1 ‐or H 2 ‐type by the use of relatively specific postjunctional histamine H 1 ‐ or H 2 ‐receptor agonists and antagonists.