REUTILIZATION (RU) OF SURFACTANT (NS) PHOSPHATIDYLCHOLINE (PC) IN ADULT RABBITS (R)

Several studies have demonstrated RU of NS PC in developing and adult R. The magnitude of RU in adult R has not been determined. We injected 87 1 kg R with two solutions simultaneously. [14C]palmitate was given IV and a solution of [3H]choline labeled NS plus [32P]dipalmitoylPC (DPC) was injected intratracheally (IT). R were sacrificed from 10 min to 72 hrs after injection. From each R we collected a complete alveolar wash (AW) and isolated a lamellar body (LB) fraction. We measured total [3H]PC and [32P]PC recovered in the AW and [14C]PC specific activity (SA) in the AW and in LB. From curves of [14C]PC SA in the LB and the AW vs time, we calculated the flux of PC from the LB into the AW (PC flux) and the turnover times (Tt) for alveolar PC (Tt=total AW PC/PC flux). A computer generated equation describing the total AW [3H]PC vs time was obtained and used to independently calculate the PC flux, the Tt, the % RU of NS PC and the LB PC pool size. The results are shown in the table.Also, the ratio of [3H]PC to [32P]PC in the AW did not change with time. We concluded that 1) IT and IV labeling gave comparable results. 2) IT NS and the added DPC behaved metabolically like endogenous NS. 3) That RU of PC in adult R (31%) is less than that of developing R (>90%).