Carnitine, carnitine acyltransferases, and rat brain function
The concentrations of free, short chain, and long chain acylcarnitines and the enzyme activities of carnitine acetyltransferase (CAT) and carnitine palmityltransferase (CPT) were studied in different rat brain regions. The fate of tritium-labeled carnitine was studied in different brain regions in vivo after i.p. injection in 3-month-old Sprague-Dawley rats. The tritium counts were particularly high in the hypothalamic region. At 24 h after hydrocortisone injection, a significant increase in counts was observed in the hypothalamus (P < 0.01). A high concentration of total carnitine was found in the hypothalamus (4.00 nmol/mg noncollagen protein) and in other regions such as the spinal cord (1.29 nmol/mg noncollagen protein), cerebellum (1.19), and olfactory tracts (0.66) carnitine concentration was much lower. Carnitine content was proportional to CPT, an inner mitochondrial enzyme. The activity of the enzyme CAT was found to be high in rat hippocampus and hypothalamus. This enzyme in brain may be involved in the transport of acyl groups outside the mitochondria and in the regulation of pyruvate utilization, contributing to acetylcholine synthesis or regulation.