Regional distribution in rat brain of phosphatidylinositol and phosphatidylcholine synthetic and intermembrane transfer activities.

Rat brains were dissected into major anatomical regions, including caudate nucleus, cerebellum, inferior and superior colliculi, cortex, hippocampus, olfactory bulb, pituitary gland, pons-medulla, spinal cord and thalamus. Tissue fractionation yielded microsomes and cytosol which were assayed for several phospholipid synthetic enzyme activities; using a vesicle-vesicle system the cytosol fractions were also examined for intermembrane phospholipid transfer activities. For the metabolism of phosphatidylinositol, specific activities were determined for CTP: phosphatidate cytidylyltransferase and CDP-diacylglycerol: inositol phosphatidyltransferase. Regions with high phosphatidylinositol synthetic activity were pituitary gland, pons-medulla, caudate and thalamus. For the metabolism of phosphatidylcholine the measured enzymes were CTP: phosphocholine cytidylyltransferase and CDP-choline: diacylglycerol cholinephosphotransferase. These enzymes showed the highest activity in the colliculi, olfactory bulb, pituitary gland and pons-medulla. The pons-medulla cytosol fraction contained the highest level of phosphatidylinositol transfer activity, while the colliculi and pons-medulla had the highest level of phosphatidylcholine transfer activity. In contrast, the pituitary gland displayed the lowest levels of both phosphatidylinositol and phosphatidylcholine transfer activity. The relationships between synthetic and transfer activities are discussed in terms of regional phospholipid metabolism.