Brain asymmetry in phospholipid polar head group metabolism: parallel in vivo and in vitro studies

Phospholipid content and 32P-incorporation have been studied in individual rat cerebral hemispheres. The total phospholipid content was 44.9 +/- 0.9 and 47.9 +/- 1.3 mumol lipid P/100 mg protein for the right and left hemispheres respectively. Individually, only sphingomyelin was significantly (about 30%) higher in the left hemisphere. Metabolic experiments have been conducted in vivo using i.p. injection of 32P and following its incorporation into total and individual phospholipids in each cerebral hemisphere. Higher incorporations were attained by phosphatidate and phosphatidylinositol-4,5-bisphosphate (PIP2) in the left cerebral hemisphere than in the right. In an attempt to determine whether phospholipid metabolism is also lateralized in specific subcellular compartments related with the neurotransmission process, we have studied in vitro the [32P] incorporation into phosphoglycerides of synaptosomal fractions obtained from each cerebral cortex. The precursor was taken up differently by the two cerebral cortex preparations, resulting in different profiles of distribution among lipids. In addition, the kinetics of lipid labeling showed higher rates of 32P-incorporation in fractions derived from the left cerebral cortex, mainly in PIP and PIP2. These results are interpreted to indicate that several enzymes involved in lipid metabolism are modulated to a different extent in the two hemispheres.