[Effects of guanfacine on pre- and postsynaptic alpha-adrenoceptors studied in comparison with those of clonidine].
Nihon Yakurigaku Zasshi
; 79(5): 431-9, 1982 May.
Article
em Ja
| MEDLINE
| ID: mdl-6127290
ABSTRACT
Intravenous injections of guanfacine (1 microgram-3 mg/kg) elevated dose-dependently blood pressure in adrenalectomized, pitched rats. The vasopressor activity of guanfacine was weaker than those of clonidine, an alpha 2-agonist and 1-phenylephrine, an alpha 1-agonist. However, the maximal response produced by guanfacine was the same as that produced by clonidine, while it was much smaller than that produced by 1-phenylephrine. The dose-response curve to guanfacine for increase in blood pressure was shifted in a parallel fashion to the right by 1 mg/kg of yohimbine, an alpha 2-antagonist and by 1 mg/kg of phentolamine, a nonselective alpha 1- and alpha 2-antagonist. However, 0.1 mg/kg of prazosin, a selective alpha 1-antagonist, produced an inhibition of the blood pressure rise induced by higher doses of guanfacine, but not that induced by lower doses. Guanfacine (1 microgram-1 mg/kg) inhibited dose-dependently the tachycardia induced by electrical stimulation of spinal nerves at C7-Th1 in adrenalectomized, pithed rats. The maximal inhibition by guanfacine of heart rate increase induced by electrical stimulation was about 60%. These inhibitory effects were antagonized by yohimbine and phentolamine, but not by prazosin. These results indicate that guanfacine is an alpha 2-agonist with approximately equal potency towards the pre- and postsynaptic alpha 2-adrenoceptors, just as clonidine is, but is weaker as an alpha 2-agonist than clonidine.
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Base de dados:
MEDLINE
Assunto principal:
Fenilacetatos
/
Clonidina
/
Agonistas alfa-Adrenérgicos
/
Guanidinas
/
Anti-Hipertensivos
Idioma:
Ja
Ano de publicação:
1982
Tipo de documento:
Article