We have studied the development of phospholipase A2 (PLA2) and lysophosphatidylcholine (lysoPC)-metabolising enzyme activities in the neonatal rat intestine and its relation to the intestinal permeability of macromolecules. The permeability was determined by feeding young rats a mixture of bovine serum albumin, bovine immunoglobulin G and fluorescein-isothiocyanate-conjugated dextran 70,000, and analysing the serum concentrations after six hours. The animals were then killed and the intestinal mucosa was homogenised and assessed for PLA2 and lysoPC-metabolising enzyme activities. The intestine was 'open' to the macromolecules in 14 day old animals, but 'closed' in 22 and 32 day old animals and in 14 day old rats treated with cortisone acetate on day 10, 11, and 12 postpartum. The activity of PLA2 (at pH 6 and 2 mM Ca2+) was higher in 32, 22, and cortisone treated 14 day old animals, than in untreated, 14 day old animals. Incubation of 14C-acyl-lysoPC with mucosa from 14 day old rats did not change the radioactivity pattern as shown by thin layer chromatography, whereas after incubation with mucosa from 22 or 32 day old animals all the radiolabel was found in free 14C-fatty acid and in 14C-phosphatidylcholine. These findings indicate that mucosal PLA2 activity increases during intestinal maturation and that the mucosa acquires the ability to acylate and deacylate lysoPC when it is 'closed' to macromolecules.
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