A neuromodulatory role for neuronal nitric oxide in the rabbit renal artery

1 The effects of the nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME) on vasoconstrictor responses to transmural electrical nerve stimulation and noradrenaline were examined in the rabbit isolated renal artery with and without an intact endothelium. In addition, the effect of removing the endothelium from the renal artery on vasoconstrictor responses to transmural electrical nerve stimulation and noradrenaline was also investigated. Immunohistofluorescence techniques were carried out to determine if there were any nitrergic nerves supplying the renal artery. 2 The vasoconstriction produced in response to transmural electrical nerve stimulation (2-64 Hz) was significantly enhanced in the presence of L-NAME (3 x 10(-6), 10(-5), 3 x 10(-5) and 10(-4) M). 3 L-NAME (3 x 10(-6), 10(-5), 3 x 10(-5) and 10(-4) M) did not significantly affect the maximum vasoconstriction produced in response to noradrenaline. However, the noradrenaline dose-response curve was significantly shifted to the left by the addition of L-NAME (3 x 10(-6), 10(-5), 3 x 10(-5) and 10(-4) M). 4 The increase in the amplitude of the vasoconstriction, produced in response to transmural electrical nerve stimulation (16 Hz) and noradrenaline (10(-5) M) in the presence of L-NAME (10(-5) M) was not observed when L-arginine (10(-3) M) was added in addition to L-NAME (10(-5) M). 5 Removing the endothelium did not significantly affect the response to transmural electrical nerve stimulation (1-64 Hz). The maximum vasoconstriction in response to noradrenaline was also unaffected by the removal of the endothelium. The pD(2) value for noradrenaline obtained from vessels with no endothelium was significantly greater than the pD(2) value obtained from vessels with an intact endothelium (5.90+/-0.11 and 5.16+/-0.03, respectively). 6 On renal artery segments with no endothelium L-NAME (3 x 10(-5) M) significantly enhanced the response to transmural electrical nerve stimulation (2-64 Hz). L-NAME did not affect the maximum response to noradrenaline. However, there was a significant shift to the right of the noradrenaline dose-response curve in the presence of L-NAME (3 x 10(-5) M). 7 Both nitric oxide synthase-containing and NADPH-diaphorase stained nerves were located on the adventitial-medial border of the rabbit renal artery. 8 The present study has suggested a presynaptic inhibitory action for nitric oxide (probably derived from identified perivascular nitrergic nerves), on perivascular sympathetic vasoconstrictor nerve mediated responses of the rabbit renal artery. In contrast, the enhancement of the response to noradrenaline by L-NAME can be attributed to inhibition of the synthesis of endothelium-derived nitric oxide.