Lung water and proton magnetic resonance relaxation in preterm and term rabbit pups:: Their relation to tissue hyaluronan

The present study was performed to investigate simultaneously total lung water, T-1 and T-2 relaxation times, and hyaluronan (HA) in preterm and term rabbits. Attempts were also made to establish the relationship of HA to total lung water and to T-2-derived motionally distinct water fractions. Experiments were performed in fetal Pannon white rabbit pups at gestational ages of 25, 27, 29, and 31 d and at a postnatal age of 4 d. Lung tissue water content (desiccation method), T-1 and T-2 relaxation times (H-1-NMR method), and HA concentration (radioassay) were measured, and free and bound water fractions were calculated by using multicomponent fits of the T-2 relaxation curves. Lung water content and T-1 and T-2 relaxation times were highest at a gestational age of 27 d and then declined steadily during the whole study period. Similar trends and time courses were seen for the fast and slow components of the T-2 relaxation curve. The T-2-derived free water fraction remained unchanged at a gestational age of 25-29 d (similar to 67%), but increased progressively to a value of 78.5 +/- 7.9% at 31 d (p < 0.001) and to 83.4 +/- 9.4% at the postnatal age of 4 d (p < 0.01), Opposite changes occurred in the bound water fraction. Lung HA concentration decreased with advancing gestation from 870.8 +/- 205.2 mu g/g dry weight at 25 d to 162.6 +/- 32.4 mu g/g dry weight at 31 d (p < 0.001), but it was increased 2-fold postnatally, EIA correlated positively with total lung water (r = 0.39; p < 0.001) but not with the bound water fraction. It is suggested that the physiologic lung dehydration is associated with macromolecule-related reorganization of lung water and that the role of IIA in this process needs to be further investigated.