Boc-Nω-(nitro)-L-homoarginine

Diabetes mellitus is associated with decreased nitric oxide bioavailability thereby affecting renal blood flow regulation. Previous reports have demonstrated that cellular uptake of l-arginine is rate limiting for nitric oxide production and that plasma l-arginine concentration is decreased in diabetes. We therefore investigated whether regional renal blood flow regulation is affected by cellular l-arginine uptake in streptozotocin-induced diabetic rats. Rats were anesthetized with thiobutabarbital, and the left kidney was exposed. Total, cortical, and medullary renal blood flow was investigated before and after renal artery infusion of increasing doses of either l-homoarginine to inhibit cellular uptake of l-arginine or Nω-nitro- l-arginine methyl ester (l-NAME) to inhibit nitric oxide synthase. l-Homoarginine infusion did not affect total or cortical blood flow in any of the groups, but caused a dose-dependent reduction in medullary blood flow. l-NAME decreased total, cortical and medullary blood flow in both groups. However, the reductions in medullary blood flow in response to both l-homoarginine and l-NAME were more pronounced in the control groups compared with the diabetic groups. Isolated cortical tubular cells displayed similar l-arginine uptake capacity whereas medullary tubular cells isolated from diabetic rats had increased l-arginine uptake capacity. Diabetics had reduced l-arginine concentrations in plasma and medullary tissue but increased l-arginine concentration in cortical tissue. In conclusion, the reduced l-arginine availability in plasma and medullary tissue in diabetes results in reduced nitric oxide-mediated regulation of renal medullary hemodynamics. Cortical blood flow regulation displays less dependency on extracellular l-arginine and the upregulated cortical tissue l-arginine may protect cortical hemodynamics in diabetes.

1. The effects of L-NG-nitro-arginine (L-NOARG) and some other arginine analogues on non-adrenergic, non-cholinergic (NANC) relaxations of the rat anococcygeus muscle were investigated. 2. L-NOARG (5-200 microM) produced concentration-related inhibition of the NANC response; 100 microM L-NOARG produced 90% inhibition. 3. L-Arginine (5-200 microM) produced a concentration-related reversal of the inhibitory effect of 20 microM L-NOARG; a five fold excess of L-arginine (100 microM) was required to obtain the maximum reversal of 90%. D-Arginine (100 microM) produced no such reversal, but significant reversal was produced by L-citrulline, L-arginine-L-aspartate, L-homoarginine and L-arginine-methyl-ester (all at 100 microM). 4. L-NG-nitro-arginine-methyl-ester (L-NAME; 5-200 microM) also reduced NANC relaxations, with a potency similar to that of L-NOARG; both L-NOARG and L-NAME were some ten times more potent than L-NG-monomethyl-arginine (L-NMMA). Like L-NOARG, the effects of L-NAME (20 microM) were reversed by 100 microM L- but not D-arginine. 5. Neither L-NOARG nor L-NAME (both 20 microM) affected submaximal relaxations induced by 10 microM sodium nitroprusside or 20 microM hydroxylamine. 6. D-NOARG, L-NG-tosyl-arginine and L-N alpha-(t-butyl-oxycarbonyl)-NG-nitro-arginine (all at 100 microM) had no effect on NANC relaxations. 7. Thus, in the rat anococcygeus, L-NOARG and L-NAME are more potent than L-NMMA as prejunctional inhibitors of NANC transmission. The reversibility of the effect of L-NOARG by arginine analogues suggests that the NANC system of the anococcygeus shows similarities to the endogenous nitrate system recently described in the brain.

1. The effects of L-NG-monomethyl arginine (L-NMMA) and L-NG-nitro arginine (L-NOARG) on non-adrenergic, non-cholinergic (NANC) relaxations of the mouse anococcygeus were investigated. 2. L-NMMA (10-200 microM) produced a concentration-related inhibition of the NANC response; the inhibitory effect of 50 microM L-NMMA was completely reversed by L-arginine but not D-arginine (both 100 microM). 3. L-NOARG (1-50 microM) also produced a concentration-related inhibition of the NANC response and was some 30-50 times more potent than L-NMMA; again, the effects of 10 microM L-NOARG were reversed by 100 microM L-, but not D-, arginine. By itself 100 microM L-arginine did not relax the tissue, but did cause a slight potentiation of the NANC response. 4. Sodium nitroprusside (0.01-10 microM), hydroxylamine (0.1-100 microM), sodium azide (1-100 microM) and nitric oxide (3-120 microM) all relaxed carbachol-induced tone; relaxations to submaximal concentrations of these nitrovasodilators were unaffected by either 50 microM L-NMMA or 10 microM L-NOARG. 5. L-NOARG 10 microM did not inhibit, but rather potentiated, contractions of the mouse anococcygeus due to stimulation of its sympathetic nerves. 6. The inhibitory effects of 10 microM L-NOARG on NANC relaxations were reversed by L-arginine (by 131%), L-citrulline (by 75%), L-arginine methyl ester (by 46%) and L-homoarginine (by 22%), but were unaffected by a variety of other amino acids and their derivatives (all at 100 microM). 7. The results provide strong evidence that NANC relaxations of the mouse anococcygeus are mediated by an endogenous nitrate material, probably derived from L-arginine, and confirm that L-NOARG provides a very useful and potent drug for the investigation of endogenous nitrate function.