RETRACTED ARTICLE: Nicardipine inhibits amrinone-enhanced contractility in fatigued diaphragm

The purpose of this study was to examine the effect of amrinone, a bipyridine derivative, with and without nicardipine, a calcium channel blocker, on the contractility of fatigued diaphragm in dogs. Twenty dogs were divided into two groups of ten each: amrinone group (group A) and combined amrinone and nicardipine group (group AN). Diaphragmatic fatigue was induced by intermittent supramaximal bilateral electrophrenic stimulation at a frequency of 20 Hz applied for 30 min. Diaphragmatic contractility was assessed from changes in transdiaphragmatic pressure (P_di). In group A, after producing fatigue, amrinone (0.75 mg·kg⁻¹ loading dose plus 10 μg·kg⁻¹·min⁻¹ maintenance dose) was administered iv. In group AN, nicardipine 5 μg·kg⁻¹·min⁻¹ was infused iv simultaneously with amrinone during this period. After diaphragmatic fatigue, P_di at low-frequency (10–30 Hz) stimulation decreased compared with the prefatigue values (P<0.05), whereas no change in P_di was observed at high-frequency (50–100 Hz), stimulation. The P_di at each stimulus were increased compared with the fatigued values (P<0.05) by administering amrinone, and returned to these values after this agent was discontinued. The P_di values at any frequency of stimulation did not change when amrinone was administered with nicardipine. Our results suggest that amirinone may enhance contractility in fatigued diaphragm via its effect on transmembrane calcium movement.