Subcellular distribution of disaturated phosphatidylcholine in developing rabbit lung

Alveolar metabolism of natural vs. synthetic surfactants in preterm newborn rabbits

We compared the recoveries of four surfactant preparations: two natural [term fetal rabbit surfactant (FRS) and adult rabbit surfactant (ARS)] and two commercially available preparations [apoprotein-based Survanta (S) and synthetic Exosurf (E)] from 27-day gestation rabbit pups treated at birth and ventilated up to 120 min. At 5, 60, and 120 min, we measured the recovery of the heavy-aggregate, metabolically active form (H) and the light-aggregate, nonsurface active metabolic breakdown form (L) of alveolar surfactant and determined the phospholipid content and composition of the intracellularly stored lamellar body (LB) pool. Pups treated with FRS had <15% loss of H by 2 h. ARS-treated pups had a >50% loss of H by 1 h, and E- and S-treated pups had approximately 50% loss by 5 min, with a slower rate of continuing loss of up to 80% by 2 h. The major losses of H phospholipid were not explained by the L-form recovery. LB phospholipid significantly increased only in the E-treated pups and only at 2 h. FRS provides a biologically active form (H) of surfactant that appeared to remain in the airway for a significantly longer time than the other surfactant preparations. The unique properties of FRS merit further study.

Ca(+2)-phosphatidylserine-dependent protein kinase C activity in fetal, neonatal and adult rabbit lung and isolated lamellar bodies

Evidence indicates that Ca(+2)-phosphatidylserine-dependent protein kinase C (PKC) is involved in regulation of surfactant secretion. This study was done to examine PKC activity in lung as surfactant synthesis and secretion is initiated, and at birth and to compare these enzyme levels with those in the adult lung. NZW rabbits were used. Fetal and adult lungs were fractionated into subcellular compartments including a lamellar body fraction, which represents intracellular surfactant. The time course for microsomal enzyme activity was compared between 24th gestational day and adult rabbit lung. The reactivity appeared similar in both fractions. PKC specific activity displayed a prominent peak between the 27th and 30th gestational days in total homogenate and lamellar bodies. Specific activity was also high in nuclear, mitochondrial and microsomal fractions the day prior to birth. Adult levels were similar or higher. Total PKC activity was high during late gestation but declined sharply the day prior to birth. A marked increase was present on the first postnatal day. In contrast lamellar bodies displayed a peak in activity between the 27th and 30th gestational days followed by a decline to adult levels. Delipidation of lamellar body fraction indicated that the high enzyme activity in this fraction on the 27th gestational day was not artifactual. The changes observed in PKC in fetal, neonatal and adult lung indicate this enzyme activity changes in lung during the period of onset of surfactant synthesis and secretion during late gestation and may be associated with lamellar bodies, in 27th gestational day fetal lung.

Mouse alveolar surfactant: characterization of subtypes prepared by differential centrifugation

To characterize the properties of alveolar surfactant subfractions obtained from mouse lung by differential centrifugation, lavage fluid, following a preliminary centrifugation at 140 x g for 5 min to yield a cellular pellet (Pc), was sequentially centrifuged at 10,000 x g for 30 min, 60,000 x g for 60 min and 100,000 x g for 15 h; and the resultant pellets, respectively referred to as P10, P60 and P100, were harvested for electron microscopy, phospholipid analysis and surface tension measurements. Ultrastructural differences were observed, in that P10 contained large multilamellated structures which were typical of newly secreted surfactant, P100 contained small unilamellar vesicular structures, typical of catabolic end products of alveolar surfactant and P60 appeared to contain a mixture of structures present in P10 and P100 in addition to numerous, large unilamellar vesicles which were not present in either P10 or P100. Slight but significant differences were found in the phospholipid compositions of the three subfractions but not in the fatty acid composition of their phosphatidylcholine (PC) component. There were no significant differences in their disaturated PC/total PC ratios, but significant differences in their phospholipid/protein ratios. P60 had the highest proportion of phospholipid to protein. P10 and P60 demonstrated surface activity but P100 did not. Total alveolar surfactant phospholipid was evenly distributed among the three fractions. This pattern of distribution was significantly different from that observed in rabbit subfractions prepared by the same procedure. These data indicate that mouse alveolar surfactant consists of three distinct subfractions or subtypes which can be separately and quantitatively isolated by differential centrifugation.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between alveolar saturated phosphatidylcholine pool sizes and compliance of preterm rabbit lungs. The effect of maternal corticosteroid treatment

The relationship between alveolar saturated phosphatidylcholine pool size and compliance was evaluated in control and maternal corticosteroid-treated 27-, 28-, and 29-day gestational age preterm ventilated rabbits. Surfactant pool sizes below about 0.7 mumol saturated phosphatidylcholine/kg body weight did not alter compliance in either group. Compliance increased to values comparable to surfactant-treated or term newborn rabbits over a narrow range of saturated phosphatidylcholine pool sizes from about 0.7 to 1.2 mumol/kg for corticosteroid-treated rabbits and from about 0.9 to about 2.3 mumol/kg for control rabbits (p less than 0.01). When these results are compared with those from surfactant-treated rabbits, almost an order of magnitude less endogenous surfactant than exogenous surfactant is needed to alter compliance in preterm ventilated rabbits.