1. Academic Validation
  2. Evidence against beta-adrenoceptor blocking activity of diltiazem, a drug with calcium antagonist properties

Evidence against beta-adrenoceptor blocking activity of diltiazem, a drug with calcium antagonist properties

  • Br J Pharmacol. 1980 Aug;69(4):669-73. doi: 10.1111/j.1476-5381.1980.tb07920.x.
M Briley I Cavero S Z Langer A G Roach
Abstract

1 The isolated spontaneously beating atria of the rat, diltiazem (0.01 to 0.1 microM) shifted the atrial rate concentration-response curves to isoprenaline to the right in a non-parallel manner and depressed their maxima. Under the same experimental conditions, (+/-)-propranolol (0.03 to 0.1 microM) behaved as a competitive beta-adrenoceptor antagonist. 2 Whereas (+/-)-propranolol (IC50 = 12 nM) and isoprenaline (IC50 = 0.9 microM) inhibited (-)-[3H]-dihydroalprenolol binding to rat brain membrane preparations, diltiazem failed to do so in concentrations up to 10 microM. 3 Diltiazem but not (+/-)-propranolol, antagonized the positive chronotropic responses to calcium in spontaneously beating rat atria. 4 It is proposed that diltiazem inhibited the tachycardia induced by isoprenaline through an effect on calcium which may be an essential modulator of the sequence of events linking the beta-adrenoceptor activation and heart rate response.

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