Comparison of amlodipine or nifedipine treatment with developing congestive heart failure: Effects on myocyte contractility

Past studies have suggested that amlodipine, a dihydropyridine L-type Ca(2+) channel antagonist, may exert useful effects in congestive heart failure (CHF). The present study examined the effects of amlodipine or nifedipine treatment in a model of developing CHF on left ventricular (LV) pump function and myocyte contractility.Pigs (25 kg) were randomly assigned to 1 of 4 groups: 1) pacing-induced CHF (rapid atrial pacing at 240 bpm) for 3 weeks (n = 9), 2) concomitant Ca(2+) channel blockade with amlodipine (1.5 mg/kg/day) and rapid pacing (n = 7), 3) concomitant Ca(2+) channel blockade with nifedipine (0.7 mg/kg twice daily) and rapid pacing (n = 7), and 4) sham controls (n = 7). LV fractional shortening fell with pacing CHF from baseline values (17% +/- 1% v 42% +/- 1%, P.05). With rapid pacing and concomitant amlodipine treatment, LV fractional shortening increased from pacing CHF values (24% +/- 1%, P.05) but was unchanged with concomitant nifedipine treatment (20% +/- 2%, P =.2). LV myocyte velocity of shortening, as measured by high speed videomicroscopy, was reduced with pacing CHF compared with controls (42 +/- 2 microm/s v 87 +/- 9 microm/s, P.05), and increased from pacing CHF values with amlodipine or nifedipine treatment (62 +/- 8 microm/s, 64 +/- 4 microm/s, respectively; P.05). Inotropic response to extracellular Ca(2+) (8 mmol/L) was reduced with pacing CHF (94 +/- 5 microm/s v 160 +/- 15 microm/s, P.05) and increased from CHF values with amlodipine or nifedipine treatment (132 +/- 14 microm/s and 133 +/- 7 microm/s, respectively, P.05) CONCLUSIONS: These results suggest that the primary mechanism for the effects of amlodipine on myocyte contractility in developing CHF is because of direct Ca(2+) channel blockade.