Effects of dietary L-arginine on structure and function of flow-restrictedvein grafts

Purpose: Experiments were designed to determine effects of dietary suppleme ntation with L-arginine on structure and function of flow-restricted vein g rafts. Methods: Saphenous veins were placed as bilateral interposition grafts in f emoral arteries of two groups of adult male mongrel dogs; one group was mai ntained on a normal diet (control), the other group supplemented with L-arg inine (200 mg/kg per day) beginning 1 week before surgery. In each dog, flo w was reduced by 50% in one graft by placing an adjustable clamp on the art ery distal to the distal anastomosis. Plasma amino acids and oxidized produ cts of nitric oxide (NOx) were measured before and after L-arginine feeding . At postoperative week 4, grafts were removed and pre pared for organ cham ber studies to determine functions of the endothelium or smooth muscle and for histology. Results: Plasma L-arginine increased within 3 hours after feeding and incre ased from 141 +/- 8 nmol/mL to 169 +/- 11 nmol/mL (n = 6) after 5 weeks of supplementation. Plasma ornithine and citrulline paralleled arginine, where as circulating NOx was unchanged. Maximal contractions to 60 mmol/L KCl wer e reduced in grafts from L-arginine-fed dogs. Endothelium-dependent relaxat ions to the calcium ionophore A23187 and relaxations of the smooth muscle N O were reduced in grafts from L-arginine-fed dogs. Neointimal hyperplasia w as increased in grafts with reduced flow and not affected by arginine feedi ng. Conclusions: Dietary supplementation with L-arginine did not increase plasm a NO in dogs with peripheral vein grafts or increase endothelium-dependent relaxations in control or flow-restricted grafts. Therefore, dietary supple mentation with L-arginine may not improve long-term functions of flow-restr icted peripheral bypass grafts.