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Journal of Pharmacology And Experimental Therapeutics, Vol. 182, Issue 2, 256-263, 1972
Copyright © 1972 by American Society for Pharmacology and Experimental Therapeutics

SELECTIVE BETA ADRENERGIC RECEPTOR BLOCKADE IN THE RAT

MARTIN A. WASSERMAN 1 and BERNARD LEVY 1

1 Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas

Experiments were designed to compare the beta receptor antagonizing Properties of propranolol, practolol and butoxamine on the responses of the isolated rat uterus, atria and fundus to isoproterenol. Concentration-response data were obtained for isoproterenol alone and in the presence of increasing concentrations of antagonists. The pA2 values and slopes of regression lines were calculated from plots of log10 (concentration ratio -1) vs. log10 antagonist concentration. Propranolol antagonized the responses to isoproterenol in the three tissues used. Propranolol exhibited beta receptor antagonizing effects in the rat uterus (pA2 = 9.56, slope = 1.02), rat atria (pA2 = 10.12, slope = 0.65) and rat fundus (pA = 8.30, slope = 0.66). Practolol (10-6 M) exerted weak beta receptor antagonism in the rat fundus, but since a 10-fold increase in the concentration of practolol exerted no greater effect, a meaningful pA2 could not be calculated and a mechanism other than simple competitive-reversible antagonism may be present. In the rat uterus, practolol did not antagonize the effects of isoproterenol, but in the rat atria, antagonism was achieved (pA2 = 7.37, slope = 0.76). Unlike propranolol, butoxamine competitively antagonized the effects of isoproterenol in the rat uterus (pA2 = 6.91, slope = 0.86) and only weakly in the fundus. Butoxamine, in high concentrations (10-4 M), depressed chronotropic activity of the atria. From results involving propranolol, practolol and butoxamine, we have found three different populations of beta adrenergic receptors (those of the rat atria, rat uterus and rat fundus).

Submitted on December 30, 1971
Accepted on April 18, 1972




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K. Fujii, U. Onaka, K. Goto, I. Abe, and M. Fujishima
Impaired Isoproterenol-Induced Hyperpolarization in Isolated Mesenteric Arteries of Aged Rats
Hypertension, August 1, 1999; 34(2): 222 - 228.
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