Isolated, perfused fetal rabbit lungs: Preparation and flow relationships

Abstract

An isolated, perfused, nonventilated, previable fetal rabbit lung preparation is described. Fetal rabbits were obtained by caesarean section from timed pregnancy does, and without allowing the fetus to gasp, the ductus arteriousus was ligated and the pulmonary vasculature was perfused with a Krebs-Ringer bicarbonate solution containing glucose and plasma expanders. The lungs were removed and maintained in an experimental chamber at 38° C and 100% relative humidity. The viability of the lungs was monitored by recording the pressure in the pulmonary artery. Fifty-four fetal lungs from 25 does were perfused at flows ranging from 0.66 to 5.94 ml/min. The retention time of a vascular marker dye (indocyanin green) decreased, from 37 seconds to about 5 seconds over this flow range. Fetal lungs retained a significant percentage of infused radioactive serotonin (5HT) (20 second infusion of 1.12 × 10⁻⁸ M ³H-5HT). At low flows (below about 2.0 ml/min) the percent³H-5HT retained was maximal at 50 to 55% of the infused dose, but when flow was increased so that dye retention time was less than about 12 seconds (flow was greater than about 3.0 ml/min) the % 5HT retained decreased in a flow-dependent manner, which is essential for characterization of the uptake process. Three interrelated purposes of this report — a) the description of the techniques involved in achieving an isolated fetal lung preparation, b) the concept of using the dye retention time as index of uptake surface area, and c) a description of potential 5HT uptake limitations at low flows — form the foundation for future research comparing the metabolism of the fetal lung with lungs at later stages of development.