RELATIONSHIP BETWEEN PROLINE BALANCE IN THE RAT-KIDNEY AND INTRARENALCONCENTRATION OF AMINO-ACIDS

In the present study, a proline-deficient diet was fed to rats in orde r to reduce the plasma proline concentration to that observed during f asting and then the carotid-artery-renal-vein differences in various a mino acids and intrarenal amino acid concentrations were measured in o rder to investigate the kinetics of amino acid metabolism in the kidne y. The plasma proline concentration in the carotid arteries of the pro line-deficient diet group 8 h after the beginning of the last feed was significantly lower than that in the control group, and the concentra tion of proline was as low as that of the fasted rats in the control g roup. The results of the carotid artery-renal vein difference in proli ne showed that, at 8 and 16 h after the beginning of the last feed, pr oline was absorbed by the kidney in the control group and was released from the kidney in the proline-deficient diet group. The results of t he carotid artery-renal difference in arginine 8 h after the beginning of the last feed showed that the amount of arginine released from the kidney was significantly lower in the proline-deficient diet group th an in the control diet group. The results of the carotid artery-renal vein difference in intrarenal free amino acids 8 h after the beginning of the last feed showed that the concentrations of amino acids that a re metabolically related to proline, such as, arginine, ornithine and alanine, were significantly lower in the proline-deficient diet group than in the control diet group. There was significant positive correla tion between the intrarenal proline concentration and the arteriovenou s difference in proline 8 h after the beginning of the last feed (r=0. 653, p < 0.05). At 8 h after the beginning of the last feed, the relea se of proline from the kidney was observed in the proline-deficient di et group, and there was significant positive correlation between the c arotid-artery-vein difference in proline and intrarenal arginine conce ntration (r = 0.887, p < 0.05).The above findings suggest that when th e intrarenal proline concentration decreases, proline is released from the kidney and when the intrarenal proline concentration increases, p roline is absorbed by the kidney. In addition, when the amount of prol ine released from the kidney increases, the intrarenal arginine concen tration decreases. In combination, these results indicate that a porti on of the proline released from the kidney is synthesized from arginin e in the kidney.