1. Endothelium-derived relaxing factor and the effects of acetylcholine and histamine on resistance blood vessels
R Bhardwaj, P K Moore Br J Pharmacol. 1988 Nov;95(3):835-43. doi: 10.1111/j.1476-5381.1988.tb11712.x.
1. The role of endothelium-derived relaxing factor (EDRF) in the action of vasodilator (acetylcholine, histamine, nitroprusside) and vasoconstrictor (noradrenaline, vasopressin) drugs on vascular resistance in the isolated perfused kidney and mesentery of the rat was studied. 2. Acetylcholine (EC50 = 0.18 +/- 0.05 nmol and 3.1 +/- 0.06 nmol, n = 8) and histamine (EC50 = 31.2 +/- 4.9 nmol and 46.2 +/- 3.9 nmol, n = 8) produced dose-related vasodilatation in noradrenaline-preconstricted (i.e. 'high tone') rat renal and mesenteric blood vessels. The response to both vasodilators (but not nitroprusside) was abolished by infusion of CHAPS (4.7 mg ml-1, 30 s). By use of an immunocytochemical staining procedure CHAPS was demonstrated to remove vascular endothelial cells lining intrarenal blood vessels. 3. Gossypol (3 microM), metyrapone (10 microM) and nordihydroguaiaretic acid, (NDGA, 30 microM), presumed inhibitors of EDRF biosynthesis, reduced or abolished the response to acetylcholine and histamine in perfused kidney and mesentery of the rat without affecting vasodilatation due to nitroprusside. Mepacrine (10 microM) similarly abolished the response to acetylcholine and histamine but in addition, reduced the response to nitroprusside in both preparations. 4. Methylene blue (100 microM), a presumed antagonist of the effect of EDRF, abolished vasodilatation due to acetylcholine and histamine and reduced the response to nitroprusside in perfused rat kidney and mesentery. Superoxide dismutase, SOD (15 u ml-1), was without effect. 5. While CHAPS treatment significantly augmented the vasoconstrictor response to both noradrenaline and vasopressin in perfused renal and mesenteric vessels this effect was not mimicked by metyrapone or gossypol suggesting that the enhanced effect of vasopressor agents in CHAPSperfused rat organs is due to the removal of a permeability barrier rather than impaired EDRF formation. 6. Responses to vasoconstrictor and vasodilator drugs in the perfused kidney and mesentery were obtained in the presence of indomethacin (8 microM) which produced in excess of 90% inhibition of prostacyclin (PGI2) release as measured by radioimmunoassay of 6-oxo-prostaglandin F1 alpha,. (6-oxo- PGF1 alpha) in the Krebs effluent. 7. We provide evidence that EDRF mediates the vasodilator response to acetylcholine and histamine in resistance blood vessels in perfused rat kidney and mesentery. The possibility that EDRF has a physiological role to play in regulating the calibre of resistance blood vessels is discussed.
2. Vasodilatory property of N-alpha benzoyl-L-arginine ethyl ester in the rat isolated pulmonary artery and perfused lung
M Y Farhat, G Thomas, C M Cunard, E Cole, A K Myers, P W Ramwell J Pharmacol Exp Ther. 1990 Jul;254(1):289-93.
L-arginine has been proposed to be the precursor of the endothelium-derived relaxing factor. In this study, we evaluated the pulmonary vascular effects of L-arginine-HCl and its benzoyl derivative N-alpha-benzoyl-L-arginine ethyl ester (BAEE) in the rat, in comparison with other vasodilators such as acetylcholine and sodium nitroprusside. In isolated pulmonary artery rings incubated with indomethacin (10 microM) and precontracted with phenylephrine (2 microM), BAEE (10(-6)-10(-5) M) significantly (P less than .05) relaxed the rings more than L-arginine. This effect was potentiated by the endothelium (P less than .05). The relaxing effect of BAEE (ED50 = 2.1 X 10(-6) M) and acetylcholine (ED50 = 2.4 X 10(-7) M) was significantly less potent than that of sodium nitroprusside (ED50 = 1.1 X 10(-8) M). Moreover, pretreatment with the soluble guanylate cyclase inhibitors methylene blue (10(-5) M) and hemoglobin (10(-5) M) antagonized BAEE-induced relaxation in intact pulmonary rings but had no effect on the relaxation elicited with atrial natriuretic peptide. In the isolated lung preparations perfused with the endoperoxide analog U46619 (5-10 nmol/min), sodium nitroprusside (10(-10)-10(-8) M) elicited potent vasodilation (ED50 = 2.8 X 10(-9) mol) whereas no vasodilation was observed with acetylcholine (10(-8)-10(-5) mol). BAEE (10(-6)-10(-5) M) decreased in a dose-dependent manner pulmonary perfusion pressure, and similar doses of L-arginine showed only a mild vasodilating effect.(ABSTRACT TRUNCATED AT 250 WORDS)
3. The effect of arginine and nitric oxide on resistance blood vessels of the perfused rat kidney
R Bhardwaj, P K Moore Br J Pharmacol. 1989 Jul;97(3):739-44. doi: 10.1111/j.1476-5381.1989.tb12011.x.
1. The vasodilator effects of arginine, nitric oxide (NO), acetylcholine (ACh) and sodium nitroprusside (NP) in the noradrenaline-preconstricted ('high tone') perfused rat kidney have been examined. 2. L-Arginine (0.6-23 mumol) caused a biphasic change in renal perfusion pressure. D-Arginine (0.6-23 mumol) was without effect. The second vasodilator component was abolished and the first vasoconstrictor effect augmented following CHAPS-induced removal of the vascular endothelium suggesting that vasodilatation was endothelium-dependent. 3. L-Arginine salts produced transient and dose-related vasodilatation. L-Arginine methylester was the most potent with an ED50 of 2.2 +/- 0.4 mumol (n = 6). The rank order of potency of the salts tested was: methylester greater than hydroxamate greater than chloride. L-Homoarginine chloride was also vasodilator (ED50, 12.0 +/- 1.3 mumol, n = 5). D-Arginine chloride was without effect at doses up to 170 mumol. Responses to L-arginine chloride were endothelium-derived relaxing factor (EDRF)-dependent being abolished by CHAPS (4.7 mg ml-1, 30 s) and significantly inhibited (greater than 70%) by gossypol (3 microM) and nordihydroguaiaretic acid (NDGA, 10 microM). 4. Vasodilatation due to NO was unaffected by CHAPS and gossypol treatment but inhibited by NDGA. NO was approximately 3 times less potent than ACh but 3000 times more potent than L-arginine methylester. 5. Kidneys perfused for 1 h with Krebs solution containing L-arginine chloride (100 microM) or L-canavanine (50 microM) showed no change in sensitivity towards ACh or NP. Higher concentrations of L-arginine chloride (500 microM) or L-canavanine (150 microM) significantly reduced the response to both vasodilators 6. L-Arginine salts dilate resistance blood vessels of the perfused rat kidney by a mechanism which may involve the release of EDRF from vascular endothelial cells of the perfused rat kidney..
