REQUIREMENT FOR ENDOTHELIUM-DERIVED NITRIC-OXIDE IN VASODILATATION PRODUCED BY STIMULATION OF CHOLINERGIC NERVES IN RAT HINDQUARTERS

1 We aimed to determine whether nitric oxide (NO) and/or the endotheli um is involved in cholinergic neurogenic vasodilatation in the rat iso lated hindquarters. 2 The abdominal aorta was cannulated for perfusion of the rat hindquarters with Krebs bicarbonate solution containing ph enylephrine, to induce basal constrictor tone. In the presence of nora drenergic neurone blockade with guanethidine (200 mg kg(-1), i.p.) ele ctrical stimulation of peri-aortic nerves induced frequency-dependent decreases in hindquarters perfusion pressure, indicating vasodilatatio n. Both the endothelium-dependent vasodilator, acetylcholine (ACh) and the endothelium-independent vasodilator, sodium nitroprusside (SNP) i nduced dose-dependent decreases in perfusion pressure. In each experim ent, responses to either nerve stimulation, ACh or SNP were recorded b efore and after treatment with saline vehicle, atropine (1 mu M), N-G- nitro-L-arginine (L-NOARG, 100 mu M), L-arginine (1 mM), L-arginine pl us L-NOARG, or 3-3 cholamidopropyl dimethylammonio 1-propanesulphonate (CHAPS, 30 mg). Hindquarters dilatation after each treatment was expr essed as a percentage of the control response. 3 Following treatment w ith saline, responses to nerve stimulation and ACh were 99 +/- 9% and 107 +/- 10% of control, respectively demonstrating the reproducibility of these responses. Nerve stimulation-induced dilatation was abolishe d by atropine (0 +/- 0% of control, P<0.05) or reduced to 14 +/- 10% o f control by NO synthase inhibition with L-NOARG (P<0.05). Dilator res ponses to ACh were also abolished by atropine (0 +/- 0% of control, P< 0.05) or inhibited by L-NOARG (59 +/- 10% of control, P<0.05), indicat ing that the neurogenic dilatation is cholinergic and is mediated by N O, The administration of the NO precursor, L-arginine, prevented the i nhibitory effect of L-NOARG on dilator responses to nerve stimulation and ACh (L-arginine plus L-NOARG: 89 +/- 13% and 122 +/- 24% of contro l, respectively). In addition CHAPS, which removes endothelial cells, inhibited responses to both nerve stimulation (0 +/- 0% of control, P< 0.05) and ACh (33 +/- 8% of control, P<0.05). In contrast, no treatmen t significantly reduced the vasodilator responses to SNP. 4 These obse rvations suggest that cholinergic neurogenic vasodilatation in the rat isolated hindquarters requires the synthesis and release of NO from t he endothelium.