Observations on lysophosphatide and triglyceride hydrolysis by rat liver preparations

Changes in enzyme activities of glycerolipid metabolism of guinea-pig cerebral hemispheres during experimental hypoxia

Hypoxic treatment causes changes of some enzymatic activities involved in the glycerolipid metabolism in subcellular fractions of guinea pig cerebral hemispheres. The activity of lysophosphatidylcholine acyltransferase, choline phosphotransferase, glycerol-3-phosphate acyltransferase(s), as well as the activity of triacylglycerol lipase significantly decreased in the microsomes of cerebral hemispheres of animals intermittently exposed to hypoxic treatment for eighty hours. At the same time, a marked activation of microsomal and mitochondrial phospholipase A2 occurred. The changes of the above-mentioned enzymatic activities after the hypoxic treatment correlated well with the increase in the level of brain and blood free fatty acids. The changes also correlated with the decrease of labeled lipid precursors incorporated into lipids of the cerebral hemispheres, observed during oxygen insufficiency.

Glyceride lipases in nerve endings of guinea-pig brain and their stimulation by noradrenaline, 5-hydroxytryptamine and adrenaline

1. Combined guinea-pig cortex and cerebellum was shown to contain triglyceride lipase, diglyceride lipase and monoglyceride lipase, which were assayed by the release of [1-(14)C]palmitate from [1-(14)C]palmitoylglycerol esters. Triglyceride lipase and diglyceride lipase were found in all particulate fractions. 2. With osmotically ruptured synaptosomes the rates of release of palmitate from glyceryl tripalmitate and glyceryl dipalmitate were 7-25mumol/h per g of protein and 0.18-0.69mmol/h per g of protein respectively. The logarithm of the rate of hydrolysis of glyceryl monopalmitate increased linearly with the logarithm of protein concentration. The pH optima of triglyceride lipase and diglyceride lipase were between 7 and 8. The pH optimum for monoglyceride lipase was approx. 8. 3. Triglyceride lipase and diglyceride lipase of osmotically ruptured synaptosomes were stimulated by noradrenaline, 5-hydroxytryptamine and adrenaline. Triglyceride lipase of isolated synaptic membranes was stimulated by 0.01-1mm-noradrenaline. Aging of membranes at 0 degrees C decreased activity, which could still be stimulated by noradrenaline. Diglyceride lipase of isolated membranes was stimulated by 1mum-1mm-noradrenaline. The activity of triglyceride lipase in isolated synaptic vesicles was diminished by 1mm-5-hydroxytryptamine.