Canine Mesenteric Arteries Research Articles

Prejunctional regulation by endogenous and exogenous acetylcholine of adrenergic nerve function in isolated canine mesenteric arteries.

Transmural electrical stimulation (5-30 Hz) produced a frequency-dependent increase in the perfusion pressure of isolated, perfused dog mesenteric artery segments without the endothelium, which was abolished by prazosin or tetrodotoxin. Physostigmine inhibited the pressor response to transmural electrical stimulation, whereas atropine potentiated the response. Treatment with acetylcholine (10(-6) and 10(-5) M) dose-dependently inhibited the response to electrical nerve stimulation. The effect was reversed by the addition of atropine and AF-DX 116 at a concentration (10(-7) M) that selectively blocked the M2 receptor subtype, but not by pirenzepine or 4-DAMP. Acetylcholine did not alter the pressure raised by norepinephrine in perfused arterial segments nor the contraction caused by exogenous norepinephrine in the artery strips. 3H-overflow evoked by transmural electrical stimulation from tissues prelabeled with [3H] norepinephrine was decreased by acetylcholine (10(-6) M) in the superfused dog mesenteric arterial strips. It is concluded that acetylcholine inhibits adrenergic neurogenic contractions by interfering with the release of norepinephrine, which possibly results from activation of the prejunctional M2 receptor subtype.

Neuropeptide Y release and contractile properties: differences between canine veins and arteries

During intense sympathetic activation, as occurs during hemorrhage, veins constrict to a greater degree than do arteries. This study determined if differences in the amounts or actions of the sympathetic cotransmitter neuropeptide Y released from perivascular nerves could contribute to these differences. Strips of canine mesenteric and popliteal arteries and of saphenous and portal veins were superfused, and the releases of noradrenaline and neuropeptide Y evoked by transmural stimulation were assessed. Both compounds were released in greater amounts in the veins than in the arteries. In other experiments rings of each vessel were mounted in organ chambers for isometric-tension recording. Neuropeptide Y (up to 10 −4 M) did not contract any vessel; however, at 3 × 10 −7 M it shifted the frequency-response and concentration-response curves to noradrenaline in the arteries only. In the veins neuropeptide Y had no postsynaptic effect on strong contractions. These results suggest that neuropeptide Y functions locally to affect vasoconstriction of the arteries studied, and may have a different role in the veins. Further, processes involving neuropeptide Y do not appear to account for the differences in responsiveness of these arteries as compared to the veins during intense sympathetic stimulation.

Pre- and postjunctional modulation by endothelin-1 of the adrenergic neurogenic response in canine mesenteric arteries

Transmural electrical stimulation (5–30 Hz) produced a frequency-dependent increase in the perfusion pressure of isolated, perfused dog mesenteric artery segments, which was suppressed by prazosin and abolished by tetrodotoxin. Treatment with endothelin-1 in low concentrations (10 −10 and 3 × 10 −10 M) inhibited the response to electrical nerve stimulation. The effect was not affected by N G-nitro- l-arginine, indomethacin and removal of the endothelium. The endothelin-1-induced inhibition was antagonized by 10 −7 M BQ123 [cyclo( d-Trp- d-Asp- l-Pro- d-Val- l-Leu-)sodium], an endothelin ET A receptor antagonist, but not by 10 −5 M BQ788 [ N-cis-2,6-dimethyl-piperidinocarbonyl- l-γ-methylleucyl- d-1-methoxycarbonyltryptophanyl- d-norleucine], an antagonist of endothelin ET B1 and ET B2 receptors. IRL1620 [Suc-[Glu 9,Ala 11,15]endothelin-1-(8–21)], a selective endothelin ET B1 receptor agonist, did not alter the response to electrical stimulation. However, raising the concentration of endothelin-1 to 10 −9 M or higher potentiated the response. Similar results were also obtained in mesenteric artery strips in response to electrical stimulation. Endothelin-1 at low concentrations did not alter the contraction caused by exogenous norepinephrine in the artery strips, whereas the peptide at high concentrations potentiated the response. 3H-overflow evoked by transmural electrical stimulation from tissues prelabeled with [ 3H]norepinephrine was decreased by endothelin-1 (3 × 10 −10 M) in the superfused dog mesenteric arteries. It is concluded that endothelin-1 at low concentrations activates prejunctional endothelin ET A receptors and inhibits adrenergic nerve-mediated contractions by an inhibition of amine release, whereas the peptide at high concentrations potentiates the neurally induced contractions by a postjunctional enhancement, via endothelin ET A receptors, of the action of norepinephrine. Low concentrations of endothelin-1 appear to act as a vasodilator in adrenergically innervated mesenteric artery.

Pharmacological natures of caffeine-induced endothelium-dependent and -independent contraction in canine mesenteric artery

The present experiments were carried out to elucidate whether pharmacological nature of caffeine (1 mM)-induced endothelium-dependent contraction (EDC) is different from that of caffeine (10 mM)-induced endothelium-independent contraction (EIC) in canine mesenteric artery. Caffeine (1 mM)-induced EDC was abolished when arterial strips were incubated in Ca ++-free medium for 20 min, but EIC was not abolished. EGTA and EDTA (0.5 and 1 mM) attenuated the EDC, and at the concentration of 2.5 mM completely abolished the EDC. Nifedipine (10 − 6 and 3 × 10 − 6 M), diltiazem (10 −6 M) and verapamil (10 −6 M) did not affect the caffeine (1 mM)-induced EDC. Lemakalim (10 −8, 3 x 10 −8 and 10 −7 M) attenuated the caffeine (1 mM)-induced EDC in a concentration-dependent manner. Lemakalim (10 −7 M) nearly abolished the EDC. The inhibitory effect of lemakalim (10 −7 M) on the EDC was antagonized in the presence of glibenclamide (3 × 10 −6 M). In contrast, caffeine (10 mM)-induced EIC was resistant to lemakalim at higher concentration (3 × 10 −7 M). Forskolin (10 −6, 3 × 10 −6 and 10 −6 M) significantly attenuated both the caffeine (1 mM)-induced EDC and caffeine (10 mM)-induced EIC. The inhibitory effect of forskolin on the EDC was augmented in the presence of rolipram (10 −6 M). Nitroglycerin (10 −5 M) attenuated significantly caffeine-induced both EDC and EIC. The inhibitory effect of nitroglycerin on the EDC was augmented in the presence of zaprinast (10 −5 M). The present experiments demonstrate that caffeine-induced EDC is due to nifedipine-resistant and lemakalim-sensitive Ca ++ mobilization and the EIC is due to both nifedipine- and lemakalim-resistant Ca ++ mobilization in canine mesenteric artery.

Effects of Enflurane on Adrenergic Function in Canine Mesenteric Artery and Vein

We examined the pre-and postsynaptic effects of enflurane on the superior mesenteric artery and vein. We measured the release of norepinephrine (NE) from sympathetic nerve terminals caused by electrical stimulation (ES) or potassium and changes in vascular smooth muscle tension. The effect of enflurane was also examined in the presence of alpha1- and alpha2-adrenoceptor antagonists. Enflurane (1.4 to 1.6 minimum alveolar anesthetic concentration [MAC] in the dog) did not alter basal tension, but it significantly inhibited tension development caused by 40 mM KCl and ES in the canine mesenteric artery and vein. Enflurane inhibited the KCl- and ES-induced release of NE from sympathetic nerve terminals in the canine mesenteric vein. The alpha1- and alpha2-adrenoceptor antagonists, corynanthine or yohimbine, did not modify the effect of enflurane on the ES-induced frequency response curve of the mesenteric artery and vein. These data suggest that enflurane has at least two sites of action in mesenteric vascular beds. One site is presynaptic where it inhibits NE release, and the other is a postsynaptic site distal to the adrenergic receptor where it inhibits the smooth muscle contraction process. (Anesth Analg 1995;81:265-71)

Effects of enflurane on adrenergic function in canine mesenteric artery and vein.

We examined the pre- and postsynaptic effects of enflurane on the superior mesenteric artery and vein. We measured the release of norepinephrine (NE) from sympathetic nerve terminals caused by electrical stimulation (ES) or potassium and changes in vascular smooth muscle tension. The effect of enflurane was also examined in the presence of alpha 1- and alpha 2-adrenoceptor antagonists. Enflurane (1.4 to 1.6 minimum alveolar anesthetic concentration [MAC] in the dog) did not alter basal tension, but it significantly inhibited tension development caused by 40 mM KCl and ES in the canine mesenteric artery and vein. Enflurane inhibited the KCl- and ES-induced release of NE from sympathetic nerve terminals in the canine mesenteric vein. The alpha 1- and alpha 2-adrenoceptor antagonists, corynanthine or yohimbine, did not modify the effect of enflurane on the ES-induced frequency response curve of the mesenteric artery and vein. These data suggest that enflurane has at least two sites of action in mesenteric vascular beds. One site is presynaptic where it inhibits NE release, and the other is a postsynaptic site distal to the adrenergic receptor where it inhibits the smooth muscle contraction process.

Suppression of cerebral vasodilation with endothelin-1.

We investigated the effect of endothelin-1 on relaxation responses induced by vasodilator substances in canine middle cerebral arteries to better understand regulation of cerebrovascular tone and its potential impact on mechanism of cerebral vasospasm. Endothelin-1 elicited concentration-dependent contractions in helical strips of canine cerebral arteries (EC50; 4.62 x 10(-9) M). Pretreatment with 10(-9) M endothelin-1 significantly reduced endothelium-dependent relaxation elicited by substance P and endothelium-independent relaxations by nitroglycerin, prostaglandin I2, and KCl. Although endothelin-1 in a lower concentration (10(-10) M) did not affect these endothelium-independent relaxations, it did inhibit endothelium-dependent relaxation caused by substance P. A low concentration (10(-10) M) of endothelin-1 also significantly reduced endothelium-dependent relaxation of canine mesenteric arteries induced by acetylcholine. Other vasoconstrictor peptides such as angiotensin-II and vasopressin did not inhibit endothelium-dependent and -independent relaxations. These results indicate that endothelin-1 not only produces cerebral vasoconstriction but also interferes with vasodilator mechanisms and that endothelium-dependent vasodilation is more sensitive to the inhibitory effect of endothelin-1 than endothelium-independent vasodiltion.

Isolation and characterization of ovokinin, a bradykinin B1 agonist peptide derived from ovalbumin.

A vasorelaxing peptide was purified from a peptic digest of ovalbumin, after three steps of reverse-phase HPLC. The structure of the peptide was Phe-Arg-Ala-Asp-His-Pro-Phe-Leu, which corresponded to residues 358-365 of ovalbumin. The peptide was named ovokinin. Ovokinin showed relaxing activity for a canine mesenteric artery (EC50 = 6.3 microM). The relaxing activity was blocked by the bradykinin B1 antagonist [des-Arg9] [Leu8]bradykinin, but not by the B2 antagonist Hoe 140. Ovokinin binds to B1 receptors (IC50 = 64 microM). Prostaglandin I2 was released from the artery after ovokinin stimulation as a relaxing factor. Thus, ovokinin is a weak bradykinin B1 agonist peptide derived from food proteins.

Barbiturates inhibit endothelium-dependent and independent relaxations mediated by cyclic GMP.

The inhibitory effects of volatile and local, but not intravenous, anesthetics on endothelium-dependent relaxations of blood vessels have been demonstrated in vitro by several investigators. The aim of this study was to determine the effects of barbiturates on endothelium-dependent arterial relaxation and elucidate the mechanism(s) responsible. Canine mesenteric arteries and rat aortae were isolated, and tension changes in helical strips were recorded. Endothelium-dependent relaxations elicited by acetylcholine and bradykinin in canine mesenteric arteries, and those by acetylcholine in rat aortae, were significantly attenuated by thiopental (3 x 10(-4) M) pretreatment. Sodium nitroprusside (SNP)-induced, endothelium-independent relaxations were significantly attenuated by thiopental (10(-4)-3 x 10(-4) M). The effects of pentobarbital were less marked than those of thiopental. Acetylcholine (10(-5) M)-stimulated levels of 3',5'-cyclic guanosine monophosphate (cGMP) in rat aortae were reduced significantly by thiopental and pentobarbital (both 10(-3) M), and SNP (3 x 10(-7) M)-stimulated levels were reduced by thiopental (3 x 10(-4)-10(-3) M) and pentobarbital (10(-3) M). We conclude that barbiturates inhibit cGMP-mediated endothelium-dependent and independent arterial relaxations. Inhibition of endothelium-dependent relaxation by barbiturates may be mediated by their effects on vascular smooth muscle itself and not on endothelium.

An endothelium-dependent contraction in canine mesenteric artery caused by caffeine.

1. We examined whether or not caffeine caused an endothelium-dependent contraction (EDC) in canine mesenteric artery and whether the endothelium-dependent contracting factors (EDCF) were arachidonic acid metabolites. 2. Caffeine (1, 3 and 10 mM) caused a transient contraction in endothelium-intact arterial strips. Removal of the endothelium significantly attenuated the caffeine (1 and 3 mM)-induced contraction. 3. Caffeine (1 mM)-induced EDC was not affected by quinacrine and manoalide (phospholipase A2 inhibitors), indomethacin and aspirin (cyclo-oxygenase inhibitors), ONO-3078 and S-1452 (thromboxane A2 antagonists) or AA-861 and TMK-777 (lipoxygenase inhibitors). 4. Caffeine (1 mM)-induced EDC was also unaffected by 50-235 (an endothelin A receptor antagonist). In addition, catalase combined treatment with superoxide dismutase, or allopurinol (antioxidant) did not affect the EDC. 5. Gro-PIP and NCDC (phospholipase C inhibitors) did not affect the caffeine-induced EDC. However, wortmannin (a phospholipase D inhibitor) and staurosporine (a protein kinase C inhibitor) attenuated the caffeine-induced EDC. 6. The present experiments demonstrate that caffeine causes an EDC in canine mesenteric artery and suggest that the EDCF mediating this response is probably not arachidonic acid metabolites, endothelin or superoxide. Instead, caffeine-induced EDC may be due to activation of the phospholipase D pathway.

Vascular relaxing mechanism of denopamine in isolated canine coronary, femoral, mesenteric, and renal arteries.

We investigated the mechanism of vascular relaxation produced by denopamine (deno), an oral positive inotropic agent that has selective beta 1-adrenergic action. Deno concentration-dependently (0.1 microM-30 microM) relaxed ring segments of canine femoral, mesenteric, and renal arteries which were partially precontracted with 1 micron phenylephrine or norepinephrine, but did not relax those precontracted with 5 microM prostaglandin F2 alpha or 40 mM K+. The relaxation was not significantly inhibited by pretreatment with 10 microM propranolol or metoprolol. Deno produced a parallel rightward shift in concentration-response curves to phenylephrine in femoral and renal arteries. The Schild plot yielded linear regressions of slopes of 1.301 +/- 0.106 and 0.823 +/- 0.122, respectively, which were not significantly different from unity. The pA2 values of Deno against phenylephrine in femoral and renal arteries were 5.41 +/- 0.03 and 5.76 +/- 0.06, respectively. On the other hand, Deno concentration-dependently (10 nM-10 microM) relaxed ring segments of canine coronary arteries which were partially precontracted with 5 microM prostaglandin F2 alpha. The relaxation was significantly inhibited by pretreatment with 10 microM metoprolol. In conclusion, vascular smooth muscle relaxation by Deno was mediated through beta 1-adrenergic action in canine coronary arteries and through the blocking effect of alpha-adrenoceptors in canine femoral, mesenteric, and renal arteries.

Effect of ouabain on relaxation induced by cromakalim in human and canine mesenteric arteries

We investigated the effect of cromakalim, a K + channel opener, that activates indirectly the Na +-K + pump, in association with increased K + conductance in the mesenteric arteries. In 65% of human mesenteric arteries tested, the concentration-dependent relaxation curves for cromakalim were biphasic: the low concentration (<10 −7 M) effect was preferentially inhibited by ouabain, whereas the higher concentration effect was significantly inhibited by glibenclamide. In branches of canine mesenteric artery, the cromakalin-induced relaxation was inhibited by pretreatment with ouabain (1 μM) as well as by glibenclamide (1 μM). The reduction in contraction of human and canine mesenteric arterial strips caused by cromakalim was totally reversed by pretreatment with ouabain (1 μM) or glibenclamide (1 μM). On the other hand, in canine mesenteric artery, cromakalim caused a significant stimulation of 22Na + influx and ouabain-sensitive 86Rb + uptake in association with increased 86Rb + efflux, all of which were inhibited by glibenclamide (1 μM). Thus, it is suggested that cromakalim possesses the additional property to stimulate the Na +-K + pump through an elevation in intracellular Na +, resulting in strong relaxation of blood vessels.

Mechanism of Action of KRN2391, a Novel Vasodilator, in Canine Mesenteric Artery

The effect of vesnarinone (OPC-8212), an orally active positive inotropic agent was studied in tracheal muscle isolated from guinea pigs, and the mechanism of its action was analyzed. Vesnarinone (10(-6)-10(-4) M) caused a concentration-dependent relaxation of tracheal muscle pre-contracted by 10(-4) M histamine. The potency of the relaxing effect of vesnarinone was greater than that of theophylline; the pD2 values for vesnarinone and theophylline were 4.9 and 4.5, respectively. Vesnarinone reduced the high-K(+)-induced contracture of depolarized tracheal muscle non-competitively (pD'2 = 3.7). Vesnarinone at the low concentration of 3 x 10(-6) M shifted the concentration-response curve for isoproterenol in a parallel fashion to the left. Vesnarinone additively acted on the relaxing effect of isobutyl methyl xanthine. Propranolol (10(-5) M) and reserpine pre-treatment (5 mg/kg, i.p., 24 hr) had no effect on the relaxing effect of vesnarinone. These results suggested that vesnarinone elevated the intracellular cyclic AMP level via phosphodiesterase inhibition, resulting in the tracheal muscle relaxation.

O-300 - Possible involvement of prostanoids on "escape" of norepinephrine-induced contraction in canine mesenteric artery.

O-300 - Possible involvement of prostanoids on "escape" of norepinephrine-induced contraction in canine mesenteric artery.

Inhibitory Effects of Emedastine Difumarate on Histamine Release

The present study was performed to clarify the mechanism of vasodilation of KRN2391 in canine mesenteric artery compared with those of nicorandil and cromakalim. We used the responses of isolated cranial mesenteric artery in vitro and changes in mesenteric blood flow in vivo as indicators reflecting the responses of a conductive artery and resistive arterioles, respectively. In isolated cranial mesenteric artery, KRN2391 (10(-8)-10(-5) M), nicorandil (10(-7)-10(-4) M) and cromakalim (10(-7)-10(-5) M) relaxed contractions caused by 25 mM KCl in a concentration-dependent manner. The concentration-relaxation curve for KRN2391 was shifted to the right by either methylene blue (10(-5) M) or glibenclamide (10(-6) M), but the inhibitory effect of methylene blue was more potent than that of glibenclamide. The concentration-relaxation curve for nicorandil was shifted to the right by methylene blue, but not by glibenclamide. In addition, the curve for cromakalim was shifted to the right by glibenclamide, but not by methylene blue. In in vivo experiments, the injections of KRN2391 (0.3-3 micrograms/kg), nicorandil (10-100 micrograms/kg) or cromakalim (1-10 micrograms/kg) into the mesenteric artery increased mesenteric blood flow in a dose-dependent manner. Glibenclamide (5 mg/kg, i.v.) attenuated the increase in mesenteric blood flow caused by KRN2391, nicorandil and cromakalim, but had no effect on that caused by nifedipine (1 microgram/kg). The ED20 value increased about 4.7-fold for KRN2391, 3.7-fold for nicorandil and 11.5-fold for cromakalim after administration of glibenclamide, as estimated from the % change to the absolute increase in mesenteric blood flow induced by nifedipine (1 microgram/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Selective impairment of endothelium-dependent relaxation by sevoflurane: oxygen free radicals participation.

To determine whether sevoflurane alters endothelium-mediated vasodilation of vascular smooth muscle, isolated ring preparations of canine mesenteric arteries were suspended for isometric tension recordings in modified Krebs-Ringer bicarbonate solution at 37 degrees C. Following contraction with norepinephrine, cumulative concentration-response curves were generated using endothelium-dependent vasodilators (acetylcholine, bradykinin, and calcium ionophore A23187) or nitroglycerin. The relaxation produced by acetylcholine, bradykinin, or A23187 was impaired by sevoflurane (2.3 and 4.6 vol%); sevoflurane did not affect relaxation caused by nitroglycerin, which, in these vessels, acts by an endothelium-independent mechanism. Under the same experimental conditions as those used for the concentration-response relationship, electron spin resonance spin-trapping with 5,5-dimethyl-1-pyrroline N-oxide verified generation of hydroxyl radical from the sevoflurane-delivered bathing media; the generation of hydroxyl radical was inhibited by superoxide dismutase, a scavenger of superoxide anion radical, or by the powerful iron chelator deferoxamine. Furthermore, sevoflurane-induced impairment of the relaxation caused by the endothelium-dependent vasodilators used was significantly decreased by superoxide dismutase. These results indicate that superoxide anion radical and/or closely related species of oxygen free radicals, possibly hydroxyl radical, are involved in the observed effect of sevoflurane. We propose that sevoflurane selectively impairs endothelium-dependent relaxation in canine mesenteric arteries by an oxygen free radical mechanism, mainly due to inactivation of endothelium-derived relaxing factor.

Evidence for two types of internal Ca2+ stores in canine mesenteric artery with different refilling mechanisms.

Novel transient biphasic responses of the dog mesenteric artery to phenylephrine hydrochloride (PE, 10 microM) in Ca(2+)-free medium containing 50 microM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) have been analyzed. The initial component was significantly inhibited by ryanodine (30-100 microM), an agonist enhancing Ca2+ release from the sarcoplasmic reticulum, whereas the second was significantly inhibited by nifedipine (1 microM), and L-type Ca2+ channel antagonist, or EGTA, to chelate Ca2+, and was potentiated by BAY K 8644 (1 microM), an L-type Ca2+ channel agonist. After repletion of Ca2+ stores in normal Krebs solution or in high KCl (60 mM) Krebs, the first component was inhibited by cyclopiazonic acid (CPA, 30 microM), a putative, reversible, and selective microsomal Ca2+ pump adenosinetriphosphatase inhibitor. BAY K 8644 potentiated the second component in the presence of CPA. The inhibition of the first component by CPA suggests that the refilling ultimately requires the CPA-sensitive Ca2+ pump for Ca2+ resequestration. However, the second component may refill by a CPA-independent route opened by BAY K 8644. These results, taken as a whole, indicate that the biphasic PE response in Ca(2+)-free medium may reflect compartmentalization of Ca2+ storage related to the different routes of refilling.

Vascular relaxing mechanism of denopamine in isolated canine coronary, femoral, mesenteric and renal arteries

Vascular relaxing mechanism of denopamine in isolated canine coronary, femoral, mesenteric and renal arteries

The Effect of Thromboxane on Contraction of Canine Mesenteric and Lingual Arteries

Thromboxane A2 (TXA2), a potent vasoconstrictor agent, is released from platelets and smooth muscle during inflammation and trauma. TXA2 may cause lingual artery (LA) contraction, leading to lingual paresthesia. The effects of U-46619, a TxA2 mimetic, on isolated rings of canine LA and mesenteric artery (MA) were examined. U-46619 (1 nmol/L to 1 mumol/L) caused a triphasic contraction of LA and MA; a rapid, phasic contraction; a slow, sustained contraction; and, upon washout of U-46619, a maintained contraction. The MA relaxed slowly, but the LA remained contracted for at least three h after washout. Decreasing extracellular calcium ion (Ca2+o) to less than 0.1 mumol/L with 2 mmol/L EGTA relaxed MA, but not LA. EGTA (4 mmol/L) partially relaxed the maintained contraction of LA. Inhibition of protein kinase C with amphotericin B or staurosporine inhibited the phasic and sustained contractions of LA, but did not affect the maintained contraction in the presence or absence of EGTA. Thus, CA2+o was required for the initial contraction of the LA by U-46619, but did not appear to be required for the maintained contraction following washout of U-46619. The data support the conclusion that following a brief exposure to U-46619, maintained contraction of LA persists by a unique mechanism that may be independent of Ca2+ and protein kinase C. Sustained LA contraction after exposure to endogenous TXA2 during inflammation and trauma may contribute to impaired lingual blood flow and orofacial tissue injury.

Endothelium-Derived and Intraneuronal Nitric Oxide-Dependent Inhibition of Norepinephrine Efflux From Sympathetic Nerves by Bradykinin

Evidence is presented that bradykinin inhibits norepinephrine efflux from sympathetic nerves innervating canine mesenteric and pulmonary arteries, in part, by releasing endothelium-derived relaxing factor (EDRF) from the vascular endothelium. Moreover, in the absence of vascular endothelium, bradykinin also inhibits norepinephrine efflux from the sympathetic nerve terminals innervating these blood vessels. This inhibition is attenuated by canavanine and LNMMA, which inhibit the conversion of arginine to nitric oxide, and is enhanced after overnight incubation of blood vessels with arginine. In endothelium-rubbed blood vessels the inhibitory effect of bradykinin on norepinephrine efflux is enhanced by increasing extracellular calcium ion ([Ca2+]o) and attenuated by nitrendipine. We propose that bradykinin inhibits norepinephrine efflux by stimulating intraneuronal nitric oxide from arginine.