Intraventricular pressure measurement in Langendorff-perfused rat hearts

The rats were anesthetized with pentobarbital sodium (50 mg/kg, i.p.) and placed on an operating table. Rat hearts were immediately excised, mounted on a Langendorff apparatus, and perfused at a constant pressure of approximately 55 mmHg with oxygenated (95% O₂ and 5% CO₂) normal Tyrode’s solution containing (in mM): NaCl 137.0, KCl 5.4, MgCl₂ 1.1, NaHCO₃ 11.9, NaH₂PO₄ 0.33, CaCl₂ 1.8, and dextrose 11.0 at 37°C as previously described [21]. A latex balloon (size No. 5, Radnoti, Monrovia, CA, USA) connected by a short stainless steel tube to a pressure transducer (P23XL-1, Becton, Dickinson & Co., Franklin Lakes, NJ, USA) was inserted into the LV cavity via the left atrium. The balloon was inflated with 0.04 mL distilled water, sufficient to produce an end-diastolic pressure of 8–12 mmHg. The ventricles were paced electrically at 300 beats per minute by platinum contact electrodes positioned on the right ventricular apex. Data were recorded on a WindowGraf recorder (Gould Inc., Cleveland, OH, USA) and digitized with a computer-based data acquisition system (PowerLab/4SP with Chart 5 software, ADInstruments). Each preparation was allowed to equilibrate for 2–2.5 h before drug testing. LV developed pressure (LVDP) was calculated by subtracting LVEDP from the LV peak systolic pressure. LVP signal differentiation was used to determine LV +dP/dt_max and–dP/dt_max.