ISSN:
1432-1912
Keywords:
Postsynaptic α 1- α 2-adrenoceptors
;
Methoxamine
;
B-HT 920
;
Calcium antagonists
;
Divalent metal ions
;
Calcium ions
;
Vasoconstriction
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The influence of various calcium antagonists and divalent metal cations on the pressor responses induced by the selective α 1-adrenoceptor agonist methoxamine and the selective α 2-adrenoceptor stimulating agent B-HT 920 (2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine) was studied in pithed rats. 1. The calcium antagonists verapamil, D 600 and nifedipine, when given intraarterially (i.a.) in doses up to 1 mg/kg did not influence the pressor effects of methoxamine. Only higher amounts of these calcium antagonistic drugs (1–3 mg/kg i.a.) somewhat reduced this pressor response. 2. The vasoconstriction due to B-HT 920, as reflected by the increase in diastolic pressure, was markedly inhibited by verapamil, D 600 and nifedipine in a dose-dependent manner. In low doses a parallel displacement to the right was observed, whereas in higher amounts the shift was non-parallel. 3. The divalent cations Mn2+, Ni2+ and Co2+ (0.05–0.15 mmol/kg i.a.) hardly affected the pressor effect of methoxamine, whereas B-HT 920-induced vasoconstriction was highly sensitive to these metal ions. La3+ and Mg2+ were ineffective. 4. The calcium antagonists verapamil, D 600 and nifedipine displayed only minor affinities for [3H]prazosin (α 1) as well as [3H]clonidine (α 2) binding sites of rat brain membranes. 5. It is concluded that an influx of extracellular Ca2+ is necessary for the vasoconstriction in vivo initiated by stimulation of vascular postsynaptic α 2-adrenoceptors. On the other hand, vasopressor responses to α 1-adrenoceptor stimulation are not directly dependent on a transmembrane influx of calcium ions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00501359
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