Simple method of determining pulmonary blood flow in the anesthetized rat

We have developed a simple, accurate, and relatively inexpensive method of measuring pulmonary blood flow in the anesthetized rat using a modification of the dye dilution technique. The method is attractive because it allows for the measurement of pulmonary blood flow and also the determination of pulmonary substrate flux. Using rats with a catheter in the carotid artery and a doubly cannulated right ventricle (RV), a constant infusion of [14C]P-aminohippurate ([14C]PAH) is begun via the distal RV catheter. After steady state is obtained the infusion of [14C]PAH is then stopped and blood is immediately withdrawn from the proximal RV cannula. This maneuver insures that [14C]PAH from the infusate is not sampled through the proximal RV catheter. Obtaining the blood from the proximal RV catheter within 5 s after clearing the infusion catheter insures that no dilution of [14C]PAH in the right ventricle (from recirculating blood) occurs. Catheter position is verified at autopsy. Calculations are performed to determine pulmonary blood flow. In 20 normal rats studied, the pulmonary blood flow was 24 +/- 1 mL/100 g body wt min-1 and in 12 endotoxin-treated rats (10 mg/kg body wt) the pulmonary blood flow was 32 +/- 2 mL/100 g body wt. These values are similar to values obtained with other methods used to measure total pulmonary blood flow.