THE ACTIVATION OF THE ARGININE CITRULLINE CYCLE IN MACROPHAGES FROM THE SPONTANEOUSLY DIABETIC BB RAT

The activity of the arginine-citrulline cycle was investigated in macr ophages from the spontaneous immunologically mediated diabetic BB rat. Peritoneal macrophages were prepared from male diabetes-prone (BBdp), diabetic (BBd) and age-matched non-diabetes-prone (BBn) rats. Cells w ere incubated at 37-degrees-C for 2 h in Krebs-Henseleit bicarbonate b uffer containing 0.5 mM L-arginine, 0.1 mM L-[ureido-C-14]citrulline a nd 5 mM D-glucose to measure the activity of the arginine-citrulline c ycle. The uptakes of citrulline and arginine by macrophages were measu red during a 5 min incubation period with L-[ureido-C-14]citrulline an d L-[2,3-H-3]arginine respectively. The production of NO3- (the major stable oxidation product of NO) increased (P < 0.01) by 112% and 151% in 75-day-old BBdp and 115-day-old BBd macrophages respectively, compa red with age-matched BBn cells. The conversion of [C-14]citrulline int o [C-14]arginine increased (P < 0.01) by 704%, 892% and 904% in 50- an d 75-day-old BBdp and 115-day-old BBd macrophages respectively, compar ed with age-matched BBn cells. The enhanced NO synthesis in BBdp and B Bd macrophages was associated with a 25-35% increase in the uptake of L-arginine. However, there were no differences in the uptake of citrul line between BBdp or BBd macrophages and age-matched BBn cells. Our re sults demonstrate for the first time the activation of the arginine-ci trulline cycle in macrophages in an autoimmune condition. The inherent increase in the recycling of L-Citrulline to L-arginine in BBdp and B Bd macrophages may reflect an innate metabolic disorder in these cells . This increased L-arginine synthesis froM L-Citrulline may play a rol e in sustaining a sufficient intracellular L-arginine concentration fo r prolonged generation of NO in BBdp and BBd macrophages. A role for N O in the autoimmune destruction of pancreatic beta-cells in insulin-de pendent diabetes mellitus warrants further investigation.