[Changes in myocardial sensitivity after sudden with withdrawal of calcium channel blockers]

Our previous experiments have suggested that besides the receptor cont and/or sensitivity a decrease of intracellular calcium level significantly participates in the mechanism of beta-blocker withdrawal 'rebound' phenomenon. This suggestion initiated studies in which possible changes in myocardial responsibility to cardioactive drugs were investigated in the condition of withdrawal of treatment with calcium entry blockers. The results showed increased cardiotoxicity of ouabain, aconitine and CaCl2, as well as an increased response of the heart to isoprenaline 24 hours after sudden cessation of treatment with verapamil (2 mg.kg-1 x 12 hours-1), diltiazem (3 mg.kg-1 x 12 hours-1) and nifedipine (0.5 mg.kg-1 x 12 hours-1). These results support the hypothesis of a common mechanism of the withdrawal syndrome of beta-lytics and calcium antagonists involving changes in intra-cellular calcium level. (Tab. 2, Fig. 4, Ref. 33.).