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Study of the mechanism of the relaxant action of (+)‐glaucine in rat vas deferens
Author(s) -
Orallo Francisco,
Alzueta Alejandro Fdez.,
Loza M. Isabel,
Vivas Nuria,
Badía Albert,
Campos Manuel,
Honrubia M. Angeles,
Cadavid M. Isabel
Publication year - 1993
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.1476-5381.1993.tb13904.x
Subject(s) - vas deferens , methoxamine , chemistry , prazosin , calcium , mechanism of action , antagonist , endocrinology , medicine , nifedipine , stereochemistry , biochemistry , biology , agonist , receptor , organic chemistry , in vitro
1 Effects of the aporphinoid alkaloid, (+)‐glaucine, on rat vas deferens were investigated. 2 (+)‐Glaucine (2–18 μ m ) competitively inhibited contractions induced by noradrenaline and methoxamine with a pA 2 value of about 6. 3 (+)‐Glaucine (2 and 18 μ m ) did not change the accumulation of tritium during incubation of the vas deferens with [ 3 H]‐noradrenaline. 4 (+)‐Glaucine (0.3 n m‐ ‐0.1 m m ) inhibited specific [ 3 H]‐prazosin binding to membranes from rat vas deferens with a p K i value of 6.63, which is close to the pA 2 value obtained against noradrenaline and methoxamine in functional studies. 5 In electrically‐stimulated rat vas deferens, (+)‐glaucine (0.3–10 μ m ) enhanced twitch contractions and competitively antagonized the inhibitory effect of clonidine with a pA 2 value of 5.91. 6 In tissues incubated in depolarizing calcium‐free high‐potassium medium, (+)‐glaucine (30–80 μ m ) inhibited Ca 2+ ‐induced contractions with depression of the maximal response at higher doses and with a pD' 2 value of 3.65. Furthermore, (+)‐glaucine (50 μ m ) did not modify basal 45 Ca uptake but strongly inhibited the influx of 45 Ca induced by K + . 7 These results suggest that (+)‐glaucine has non‐selective α 1 ‐ and α 2 ‐adrenoceptor blocking properties. At higher doses, (+)‐glaucine shows calcium antagonist activity which may be responsible, at least in part, for the inhibition of the contractions induced by Ca 2+ in calcium‐free high‐potassium medium.