1. Cortisol treatment of rabbit foetuses in utero at 24 days gestation produced a significant decrease in the lung-weight to body-weight ratio compared with littermate controls by day 26. Histological examination revealed that the alveoli of the treated lungs were more open, the walls were thinner and the osmiophilic bodies were more numerous. 2. Cortisol treatment as described above produced significant increases (P<0.05) in the rates of incorporation of [14C]choline into phosphatidylcholine and of [14C]ethanolamine into phosphatidylethanolamine in vitro compared with littermate controls. This indicates that glucocorticoids produce an overall increase in phospholipid metabolism rather than a specific increase in phosphatidylcholine production. 3. The addition of 1,2-diacyl-sn-glycerols from egg phosphatidylcholine produced a 10-fold increase in the activity of choline phosphotransferase and a 3-fold increase in the activity of ethanolamine phosphotransferase in rabbit lung homogenates. The addition of 1,2-dipalmitoyl-sn-glycerol did not affect these activities. These results demonstrate that in the presence of exogenous 1,2-dipalmitoyl-sn-glycerol, the activities of these enzymes are dependent on the presence of endogenous 1,2-diacylglycerols. 4. Cortisol administration had no significant effect on the activity of choline phosphotransferase or ethanolamine phosphotransferase with endogenous or exogenously added diacylglycerols. The activities of other endoplasmic-reticulum enzymes (sn-glycerol 3-phosphate phosphatidyltransferase, sn-glycerol 3-phosphate acyltransferase and NADPH–cytochrome c reductase) were not significantly altered by the hormone administration. Oestrone sulphate sulphohydrolase activity was significantly decreased (P<0.05) by cortisol injection, but this effect varied with the foetuses from different does. 5. Cortisol administration had no effect on the activities of mitochondrial (monoamine oxidase, succinate dehydrogenase), plasma-membrane (5′-nucleotidase) or lysosomal (acid phosphatase, N-acetyl-β-d-glucosaminidase) enzymes. The activity of membrane-associated phosphatidate phosphohydrolase, an enzyme associated with the osmiophilic granules of the type-II alveolar cells, was increased in the lungs of treated foetuses, but the difference was not significant (0.10>P>0.05).

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