DISTRIBUTION OF DE-NOVO SYNTHESIZED BETAINE IN RAT-KIDNEY - ROLE OF RENAL SYNTHESIS ON MEDULLARY BETAINE ACCUMULATION

The trimethylamine glycine-betaine is accumulated to high concentratio ns in medullary cells of mammalian kidneys, whereas betaine synthesis from choline is predominant in the renal cortex. We investigated the c ontribution of renal betaine synthesis to medullary betaine accumulati on. De novo synthesis of betaine in situ was accomplished by injecting [C-14] choline into the renal artery of male Sprague-Dawley rats. [C- 14]betaine was measured in the renal cortex and medulla, as well as in serum and urine samples. Betaine concentration in the cortex decrease d from 3.5 +/- 1.3 at 5 min to 0.4 +/- 0.2 nmol/mg protein at 60 min, but it increased from 1.4 +/- 0.1 to 2.5 +/- 0.6 nmol/mg protein in th e medulla. Serum and total urine [C-14]betaine increased from 2.7 +/- 1.3 and 0.9 +/- 0.1 nmol/ml at 5 min to 5.3 +/- 0.3 and 2.1 +/- 0.4 nm ol/ml at 60 min, respectively. Concentrations of newly synthesized bet aine were not decreased by the ligation of the hepatic artery and port al vein, suggesting that most [C-14]betaine was synthesized in the kid ney Coinjection with 5 mM dimethylaminoethanol, a choline oxidase inhi bitor, and 100 mM cold betaine reduced medullary betaine accumulation by 80 and 76%, respectively. Water deprivation for 60 h increased both cortical and medullary [C-14]betaine, whereas furosemide diuresis dec reased the medullary [C-14]betaine concentration. We concluded that be taine synthesized in the kidney can be accumulated in the medulla and that the medullary concentrations of newly synthesized betaine are clo sely related to the hydration state of the animal.