Effect of aminophylline and verapamil upon diaphragmatic force generation in dogs

The effects on the diaphragm of verapamil (VPM) and aminophylline (AMP) were studied in dogs during stimulation of phrenic nerves at the 5th cervical roots (5th-PS) or transvenously at the trunk (T-PS). Transdiaphragmatic pressure (Pdi)/frequency curves were constructed. Our findings were: 1) AMP increased Pdi at all stimulation frequencies (p less than 0.01) during 5th-PS but only at 10-30 Hz during T-PS; 2) in other dogs infusion of VPM (0.14 mg.kg-1.min-1) decreased Pdi at all frequencies (p less than 0.025) without change in diaphragmatic blood flow; 3) the effects of VPM were completely reverted by AMP; 4) after a large amount of AMP, infusion of VPM (0.21 mg.kg-1.min-1) decreased Pdi at all frequencies. Since these drugs have several mechanisms of action and do not show mutual blocking effect, different action sites are suggested.