Whereas l-arginine is clearly recognized as the precursor for nitric oxide synthesis, and its entry into endothelial cells via system y+ transport is established, few data exist regarding the acute regulation of this transport process. We specifically investigated the effect of ACh and isoprenaline (Iso) on l-arginine uptake in the human forearm and in cultured bovine aortic endothelial cells (BAEC). Sixteen healthy males were studied. During a steady-state intra-arterial infusion of [3H]l-arginine (100 nCi/min), the effects of ACh (9.25 and 37 μg/min), Iso (25–50 and 200 μg/min), and sodium nitroprusside (SNP) (1–2 and 8 μg/min) on forearm plasma flow (FPF), l-[3H]arginine uptake, and l-[3H]citrulline release were determined. In parallel experiments, the effects of ACh, Iso, and SNP on l-[3H]arginine uptake were studied in BAEC. l-Arginine uptake was inversely related to FPF ( r = −0.50; P < 0.005). At a similar FPF (ACh 56.82 ± 9.25, Iso 58.49 ± 5.56, SNP 57.92 ± 4.96 ml/min; P = ns), intra-arterial ACh significantly increased forearm uptake of l-[3H]arginine (54,655 ± 8,018 dpm/min), compared with that observed with either Iso (40,517.23 ± 6,841 dpm/min; P = 0.01) or SNP (36,816 ± 4,650 dpm/min; P = 0.011). This was associated with increased ACh-induced l-[3H]citrulline release compared with Iso and SNP ( P = 0.046). Similarly, in BAEC, ACh significantly increased l-[3H]arginine uptake compared with control, Iso, or SNP (ACh 12.0 × 107 ± 1.83 × 107 vs. control 6.67 × 107 ± 1.16 × 107 vs. Iso 7.35 × 107 ± 1.63 × 107 vs. SNP 6.01 × 107 ± 1.11 × 107 fmol·min−1·mg−1 at 300 μmol/l l-arginine; P = 0.043). Taken together, these data indicate that ACh stimulates l-arginine uptake in cultured endothelial cells and in human forearm circulation, indicating the potential for acute modulation of endothelial l-arginine uptake.
FUNCTIONAL ANGIOTENSIN II TYPE 2 RECEPTORS MEDIATE BOTH VASOCONSTRICTION AND VASODILATION IN THE HUMAN FOREARM CIRCULATION: 1D.01
