SPECTRAL-ANALYSIS OF INTERCYCLE HEART FLUCTUATIONS IN XENOPUS-LAEVIS,CONSCIOUS OR SPINALIZED, TREATED WITH CALCIUM-CHANNEL BLOCKERS .1.

1. In this study, electrocardiographic second lead tracings were recor ded and analyzed online and offline in the conscious and spinalized Xe nopus laevis under control conditions and after treatment with at leas t two effective doses of racemic diltiazem, nifedipine and racemic ver apamil hydrochlorides. 2. Heart rates (HR) and intercycle heart rate p ower spectra (IHRPS) were calculated in the various experimental condi tions. 3. Dose-dependent bradycardia was found in most cases, which wa s associated with dose-related increases in the overall dynamic range of the largest peak of HR variability (increased IHRPS), this being pa rticularly marked at the higher nifedipine dose. The frequency positio n of the largest peak was unchanged in the spinalized preparation, as well as in the various treatments. 4. These findings may contribute to ward a more complete pharmacodynamic definition of calcium channel blo ckers in their current therapeutic use. (C) 1997 Elsevier Science Inc.