%0 Journal Article %A MARTIN A. WASSERMAN %A BERNARD LEVY %T SELECTIVE BETA ADRENERGIC RECEPTOR BLOCKADE IN THE RAT %D 1972 %J Journal of Pharmacology and Experimental Therapeutics %P 256-263 %V 182 %N 2 %X 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). © 1972 by The Williams & Wilkins Co. %U https://jpet.aspetjournals.org/content/jpet/182/2/256.full.pdf