SELECTIVITY OF CLENBUTEROL (NAB 365) IN GUINEA-PIG ISOLATED TISSUES CONTAINING BETA-ADRENOCEPTORS

  • 1 January 1976
    • journal article
    • research article
    • Vol. 224  (2) , 190-198
Abstract
The effects of clenbuterol (NAB 365), an aminohalogen substituted phenylethanolamine, were examined on isolated tissue preparations from guinea-pigs. Clenbuterol produced concentration (or dose)-dependent relaxations of tracheal chains, decreases in perfusion pressure of hind limb blood vessels, inhibitions of acetylcholine-induced contractions of the uterus, increases in atrial rate and inhibitions of electrically-induced contractions of the ileum. These responses were blocked by propranolol. Clenbuterol was similar in potency to isoprenaline on the trachea (carbachol-contracted), hind limb and uterus (.beta.2-adrenoceptors) but was significantly less potent than isoprenaline on the atria and the ileum (.beta.1-adrenoceptors). Clenbuterol produced marked relaxation of intrinsic tone tracheal preparations in concentrations up to 3000 times less than were required on carbachol-contracted preparations, whereas for isoprenaline the concentrations required on intrinsic tone preparations were only 55-fold less. Clenbuterol appears to be a .beta.-adrenoceptor agonist and a partial agonist on the carbachol-stimulated trachea, on the atria and on hind limb blood vessels. It showed .beta.2-selectivity in that its potency, relative to that of isoprenaline, on the preparations containing .beta.2-adrenoceptors was much higher than on those with .beta.1-adrenoceptors. On intrinsic tone tracheal preparations it may produce an additional relaxant effect responsible for its high potency on that preparation.

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