Hyperoxia prevents carrageenan-induced enlargement of functional residual lung capacity in rats

Experimental pneumonia induced by intratracheal application of carrageenan or paraquat increases the functional residual lung capacity (FRC) in rats. The mechanism of this increase is not clear, but a decrease in PO(2) may be involved. To test this possibility, we attempted to eliminate the PO(2) decrease in carrageenan-treated rats by exposing them to hyperoxia. Animals of the first group were exposed to 7 days of hyperoxia (F(I)O(2) 0.78-0.84, group Car+O(2)) after intratracheal application of carrageenan (0.5 ml of 0.7 % carrageenan in saline), whereas animals of the second group were given the same dose of carrageenan but breathed air (group Car+A). The third group of rats was kept for seven days in hyperoxia (group O(2)) and the fourth group served as controls (C). The animals were then anesthetized and intubated and their ventilatory parameters and FRC were measured during air breathing. Carrageenan application induced a FRC increase (Car+A 2.0+/-0.2 ml, C 1.6+/-0.1 ml), which was not seen in carrageenan-treated rats exposed to hyperoxia (Car+O(2) 1.6+/-0.1 ml). Hyperoxia alone did not affect the value of FRC (O(2) 1.5+/-0.1 ml). These results support the hypothesis that a decrease in PO(2) plays an important role in the carrageenan-induced increase of FRC in rats.