Net release or uptake of histidine and carnosine in kidney of dogs

Previous studies are equivocal as to whether the dog kidney produces histidine. Because one possible source of renal histidine is carnosine (beta-alanyl-L-histidine), we investigated net renal production (release) or utilization (uptake) (Qmet) of histidine and carnosine in 19 female dogs after they were fed histidine-free (9 dogs) or histidine-containing diets (10 dogs). Diets were fed in short-(2-11 days) or long-term (52-57 days) studies. Dogs were infused with half-normal saline for 120 min followed by an infusion of half-normal saline containing carnosine, 50 mumol/min. Renal Qmet histidine, calculated from either plasma or whole blood values, was positive during infusion of half-normal saline. During carnosine infusion, Qmet histidine increased markedly, and there was net renal uptake of carnosine. The Qmet histidine and carnosine were not different in the dogs fed histidine-free vs. histidine-containing diets. Thus there is net renal release of histidine in female dogs that increases when carnosine is administered. Qmet histidine or carnosine do not change adaptively when dogs are fed histidine-free diets.