199 DEVELOPMENT OF GLYCOGEN AND PHOSPHOLIPID METABOLISM IN FETAL AND NEWBORN RAT LUNG

Abstract

Fetal rat lung glycogen content decreases as phosphatidyl-choline (PC) content increases during lung maturation. We have investigated glycogen and PC metabolism in fetal and newborn rat lung. Lung glycogen concentration was maximal on day 20 of gestation (term = 22 days) and then fell to low levels by 1 day of age. Glycogen synthetase I (the active form in adult muscle) activity increased two fold from day 18 of gestation to day 21. Glycogen synthetase D activity was 6-7 times greater than synthetase I, increased two fold from day 19 to day 22 and fell by 50% after birth. Glycogen phosphorylase a (the active form) activity increased two fold from day 19 to day 22 and fell after birth. Phosphorylase b activity remained low throughout the study period. The PC content of the lungs increased by 60% from day 19 to day 1 of life. Seventy-five percent of this increase was due to an increase in the disaturated form. The rate of incorporation of 14C-choline into PC increased 10 fold from day 19 to day 1 of age. During this time, the fraction of labelled PC that was disaturated increased from 35% to 43%. This temporal relationship between decreasing lung glycogen content and increasing lung PC content and synthesis suggests that carbohydrate derived from glycogenolysis in fetal rat lung may provide substrate or energy for PC synthesis.