EFFECTS OF CLONIDINE, GUANFACINE AND 3 IMIDAZOLIDINE DERIVATIVES RELATED TO CLONIDINE ON BLOOD-PRESSURE, HEART-RATE AND GASTRIC-ACID SECRETION IN THE ANESTHETIZED RAT

  • 1 January 1979
    • journal article
    • research article
    • Vol. 240  (1) , 158-168
Abstract
The effects of histamine, guanfacine, clonidine (2,6-dichlorophenylimino-2-imidazolidine) and the 2,6-dibromo, 2,3- and 2,5-dichloro analogs of clonidine [2-(2,6-dibromoanilino)-2-imidazoline [St 454], 2-(2,3-dichloroanilino)-2-imidazoline [St 476] and 2-(2,5-dichloroanilino)-2-imidazoline [St 475], respectively] were assessed on blood pressure, heart rate and gastric acid secretion [GAS] in the anesthetized rat, with lumen-perfused stomach. Histamine (100 .mu.g/kg to 1 mg/kg) and clonidine (250 .mu.g/kg to 1 mg/kg) each caused acute increases in GAS, the magnitude and duration of which were dose-dependent. The secretory effect of clonidine was blocked by cimetidine (2 mg/kg). Histamine produced a short-lasting hypotension with no effect on heart rate, whereas clonidine produced an initial transient rise followed by a prolonged fall in blood pressure accompanied by a marked bradycardia. Guanfacine and the 3 clonidine analogs all produced cardiovascular effects similar to those of clonidine; however, only the 2,6-dibromo analog increased GAS. These results agree with findings that only imidazolidine derivatives with 2,6-substitution in the phenyl ring activate histamine H2-receptors in the guinea pig atria. This is not so for the hypotensive and bradycardic effects of the compounds.

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