CENTRAL CARDIOVASCULAR EFFECTS OF ALPHA-ADRENERGIC DRUGS - DIFFERENCES BETWEEN CATECHOLAMINES AND IMIDAZOLINES

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 230  (1) , 232-236
Abstract
To check whether the central hypotensive effect of .alpha.-adrenergic agonists is linked with the stimulation of .alpha.2-receptors, such drugs were administered directly to the nucleus reticularis lateralis, which is an important site for the hypotensive action of clonidine. These experiments were carried out by microinjections (0.5 .mu.l on each side) in normotensive cats anesthetized with pentobarbital. .alpha.-Methylnorepinephrine, a selective .alpha.2-agonist (0.1-10 .mu.g/kg), had no hypotensive effect in this region, whereas potent .alpha.1-agonists such as cirazoline (0.01-1 .mu.g/kg) and ST 587 [2-(2-chloro-5-trifluoromethyl-phenyl-imino)-imidazolidine nitrate] (1-10 .mu.g/kg), like clonidine, produced dose-dependent hypotensive effects. That .alpha.2 selective catecholamines are apparently not active in the nucleus reticularis lateralis region, whereas imidazolines induce a hypotensive effect whatever their affinity for 1 subtype of .alpha.-adrenoceptors, was suggested. There may be some form of structure-activity relationship which would indicate the existence, in this particular region of the medulla oblongata, of sites preferring the imidazoline structure.