METABOLISM OF ARACHIDONOYL PHOSPHOGLYCERIDES IN MOUSE BRAIN SUBCELLULAR FRACTIONS

Abstract

Abstract— Mouse brain subcellular fractions were prepared at 1, 12, and 24 h and 3 and 8 days after intracerebral injections of [1‐14C]arachidonate. Initially, radioactivity was mainly distributed in the microsomal and synaptosomal fractions, but the proportion of radioactivity in the myelin increased from 5 to 16% within 8 days. Radioactivity of the microsomal lipids started to decline at 1 h after injection, and the decay was represented by two pools with half‐lives of 19 h and 10 days, respectively. Radioactivity in the synaptosomal and myelin fractions did not reach a maximum until 24 h after injections. The half‐life for turnover of synaptosomal lipids was 9 days.The decline of radioactivity measured in the microsomal fraction was due mainly to diacyl‐GPC and diacyl‐GPI, since radioactivity of other phosphoglycerides (diacyl‐GPS, diacyl‐GPE and alkenyl‐acyl‐GPE) continued to increase for 12‐24 h. In this fraction, half‐lives of 10‐14 h were obtained for the fast turnover pools of diacyl‐GPC and diacyl‐GPI, and slow turnover pools with half‐lives of 7 days for diacyl‐GPI and 10‐14 days for other phosphoglycerides were also present. Among the synaptosomal phosphoglycerides, radioactivity of diacyl‐GPI declined in a biphasic mode, thus exhibiting half‐lives of 5 h and 5 days. Incorporation of labelled arachidonate into diacyl‐GPE and diacyl‐GPS in the synaptosomal fractions was observed for a period of 24 h. The half‐lives for these phosphoglycerides ranged from 8 to 12 days. Results of the study have demonstrated the presence of small pools of arachidonoyl‐GPI in synaptosomal and microsomal fractions which were metabolically more active than other arachidonoyl containing phosphoglycerides.