Characterization of receptors mediating vascular responses to endothelin-1 in the conscious rat.

1. The present study has determined the receptors mediating the vascular responses (pressor and depressor actions and vascular permeability effect) to endothelin-1 (ET-1) in the conscious rat by using the novel non-peptide ETA/ETB receptor antagonist, bosentan (Ro 47-0203, 4-tert-butyl-N-[6-(2 hydroxyethoxy)-5-(2-methoxy-phenoxy)-2,2'-bipyrimidine- 4-yl]benzene-sulphonamide), the ETA receptor-selective antagonist, FR 139317 and the ETB receptor-selective peptide agonist, IRL 1620. 2. Bolus injection of ET-1 (1 nmol kg-1, i.v.) resulted in a prolonged pressor effect (maximum increase in mean arterial blood pressure (MABP) was 47 +/- 3 mmHg, n = 6) preceded by a transient depressor response (maximum decrease in MABP was 17 +/- 1 mmHg). Both these responses were inhibited by bosentan (1-20 mg kg-1, i.v. bolus) in a dose-dependent manner. The maximum inhibition of ET-induced depressor and pressor responses did not exceed 53 and 87%, respectively. FR 139317 (2.5 mg kg-1, i.v.) attenuated the pressor response to ET-1 by 75% without affecting the depressor response. Furthermore, FR 139317, but not bosentan, prolonged the depressor action of ET-1. Corresponding to changes in blood pressure, a small transient tachycardia (delta heart rate 15 +/- 5 beats min-1) followed by a sustained bradycardia (delta heart rate -48 +/- 10 beats min-1, n = 6) was observed following injection of 1 nmol kg-1 ET-1. FR 139317 and bosentan (10 mg kg-1) inhibited ET-1-induced bradycardia by 79% and 71%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

The involvement of endothelial dysfunction, nitric oxide and prostanoids in the rat gastric microcirculatory responses to endothelin-1.

1. The role of endothelial dysfunction in the gastric microcirculatory responses during local endothelin-1 (ET-1) infusion has been investigated in the pentobarbitone-anaesthetized rat. Furthermore, the involvement of prostanoids or nitric oxide (NO) in these actions has been investigated by the use of indomethacin to inhibit cyclo-oxygenase and NG-nitro-L-arginine methyl ester (L-NAME) to inhibit NO synthase. 2. Close-arterial infusion of ET-1 (1-10 pmol kg-1 min-1 for 10 min) induced a dose-dependent increase in the gastric leakage of radiolabelled albumin, used as an index of endothelial cell dysfunction. 3. Close-arterial infusion of a submaximal dose of ET-1 (5 pmol kg-1 min-1 for 10 min) significantly increased gastric albumin leakage after 2 min infusion, which reached maximal levels after 10 min, and only slowly declined during the 30 min observation period. 4. By contrast, gastric blood flow, as assessed by laser Doppler flowmetry, did not significantly increase until after 5 min of infusion of ET-1 (5 pmol kg-1 min-1 for 10 min), reaching a maximum after 17 min, and was sustained for the 30 min observation period. 5. Pretreatment with L-NAME (2 mg kg-1, i.v.) or indomethacin (5 mg kg-1, i.v.) significantly reduced both the hyperaemic response to ET-1 and the increase in gastric albumin leakage, and in combination abolished these responses. 6. These results suggest that locally released NO and prostanoids mediate the gastric vasodilator response to close arterial infusion of ET-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Baroreceptor reflexes and vascular reactivity during inhibition of nitric oxide synthesis in conscious rabbits.

The effect of the nitric oxide (NO) synthase inhibitor N-nitro-L-arginine (NOLA) on vascular reactivity and the baroreceptor heart rate reflex was examined in chronically instrumented conscious rabbits. NOLA (15 mg/kg i.v.) significantly increased mean arterial pressure and hindlimb vascular resistance and decreased heart rate. Increases and decreases in arterial pressure were produced by the intravenous injection of phenylephrine and sodium nitroprusside respectively and the values obtained relating mean arterial blood pressure to heart rate were fitted to a sigmoid curve. NOLA significantly reduced the lower plateau of the arterial pressure--heart rate curve but did not significantly affect baroreceptor sensitivity. Depressor and hindlimb vasodilator responses to acetylcholine were significantly impaired by NOLA whereas responses to sodium nitroprusside were significantly enhanced. The pressor and hindlimb vasoconstrictor responses to phenylephrine were significantly enhanced in the presence of NOLA. We conclude that the bradycardia produced by NOLA does not result from a change in baroreceptor sensitivity. The continuous generation of NO appears to be important in regulating basal vascular resistance and in modulating vascular reactivity to both vasodilator and vasoconstrictor agents.     

Regional haemodynamic responses to intravenous and intraarterial endothelin-1 and big endothelin-1 in conscious rats.

1. In the same chronically-instrumented conscious Long Evans rats, we assessed regional haemodynamic responses to i.v. and i.a. injections of endothelin-1 (ET-1) and big endothelin-1 at doses of 0.05 (n = 4) and 0.5 nmol kg-1 (n = 7). 2. For ET-1, the cardiovascular effects (initial hypotension and tachycardia with transient hindquarters vasodilation, followed by hypertension, bradycardia and renal, mesenteric and hindquarters vasoconstrictions) of i.v. and i.a. injections were not different. 3. Similarly, for big ET-1, the cardiovascular effects (hypertension, bradycardia and renal, mesenteric, and hindquarters vasoconstrictions) of i.v. and i.a. injections were not different.(ABSTRACT TRUNCATED AT 250 WORDS)     

ETA receptor-mediated responses to endothelin-1 and big endothelin-1 in the rat kidney.

1. Renal clearance experiments were conducted in anaesthetized Sprague-Dawley rats to determine the effect of the ETA receptor antagonist, BQ-123, on the renal haemodynamic response to endothelin-1 (ET-1) and its precursor, big endothelin-1 (big ET-1) at doses that produce an equivalent degree of renal vasoconstriction. 2. Infusion of either big ET-1 at 100 pmol kg-1 min-1 or ET-1 at 12 pmol kg-1 min-1 for 60 min produced almost identical decreases in renal blood flow (RBF) and glomerular filtration rate (GFR). Big ET-1 produced an increase in mean arterial pressure (MAP) that was significantly larger than the increase produced by ET-1. 3. Co-infusion with BQ-123 (0.1 mg kg-1 min-1) prevented the rise in MAP produced by big ET-1 and completely blocked the renal response. Similarly, BQ-123 inhibited both the increase in MAP and the decrease in RPF and GFR produced by ET-1. 4. Big ET-1 but not ET-1, produced a significant increase in water and sodium excretion. BQ-123 had no effect on the diuretic and natriuretic response to big ET-1 consistent with possible ETB-mediated inhibition of tubular reabsorption. 5. We have previously shown that at higher doses of ET-1, BQ-123 was unable to inhibit the renal vasoconstrictor response despite blockade of the pressor response. Taken together, these results indicate that ET-1 activates primarily ETA receptors at moderately low doses to produce renal vasoconstriction while higher doses also involve non-ETA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral blood flow and cerebrovascular reactivity after inhibition of nitric oxide synthesis in conscious goats.

1. The role of nitric oxide in the cerebral circulation under basal conditions and after vasodilator stimulation was studied in instrumented, conscious goats, by examining the action of inhibiting endogenous nitric oxide production with NG-nitro-L-arginine methyl ester (L-NAME). 2. In 6 unanaesthetized goats, blood flow to one brain hemisphere (electromagnetically measured), systemic arterial blood pressure and heart rate were continuously recorded. L-NAME (35 mg kg-1 by i.v. bolus) decreased resting cerebral blood flow by 43 +/- 3%, increased mean arterial pressure by 21 +/- 2%, and decreased heart rate by 41 +/- 2%; cerebrovascular resistance increased by 114 +/- 13% (P < 0.01); the immediate addition of i.v. infusion of L-NAME (0.15-0.20 mg kg-1 during 60-80 min) did not significantly modify these effects. Cerebral blood flow recovered at 72 h, arterial pressure and cerebrovascular resistance at 48 h, and heart rate at 6 days after L-NAME treatment. 3. A second treatment with L-NAME scheduled as above reproduced the immediate haemodynamic effects of the first treatment, which (except bradycardia) reversed with L-arginine (200-300 mg kg-1 by i.v. bolus). 4. Acetylcholine (0.01-0.3 micrograms), sodium nitroprusside (3-100 micrograms) and diazoxide (0.3-9 mg), injected into the cerebral circulation of 5 conscious goats, produced dose-dependent increases in cerebral blood flow, and decreases in cerebrovascular resistance; sodium nitroprusside (30 and 100 micrograms) also caused hypotension and tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)     

NG-hydroxy-L-arginine prevents the haemodynamic effects of nitric oxide synthesis inhibition in the anaesthetized rat.

1. We have investigated the effects of L-hydroxy-L-arginine (L-HOArg), an intermediate in the biosynthesis of nitric oxide (NO) from L-arginine (L-Arg), on the haemodynamic effects (systemic blood pressure and renal blood flow) of the NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in the anaesthetized rat. 2. L-Arg or L-HOArg (3 mg kg-1 min-1), but not D-arginine (D-Arg) or NG-hydroxy-D-arginine (D-HOArg), elicited a slight but significant increase in total renal blood flow (RBF) of 11 +/- 2% and 11 +/- 1%. Since mean arterial blood pressure (MAP) did not change this dose of L-Arg or L-HOArg resulted in a reduced renal vascular resistance (RVR) of the same magnitude. 3. Bolus injections of L-NAME, at 0.3 or 1 mg kg-1 i.v., produced a significant fall in RBF of 11 +/- 2% and 32 +/- 5% and an increase in MAP of 7 +/- 3 mmHg and 22 +/- 5 mmHg, respectively. Consequently, RVR was elevated by 21 +/- 5% and 52 +/- 10%. 4. L-Arg or L-HOArg (3 mg kg-1 min-1) reduced the L-NAME-induced (0.3 or 1 mg kg-1) falls in RBF and increases in RVR by more than 65%. Neither D-Arg nor D-HOArg (3 mg kg-1 min-1) had any significant effect on the changes in RBF or RVR induced by L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vascular reactivity in mesenteric resistance arteries following chronic nitric oxide synthase inhibition in Wistar rats.

1. Chronic inhibition of nitric oxide synthase (NOS) induces a sustained hypertension in rats. We studied the effects of chronic inhibition on the in vitro vasoreactivity of mesenteric resistance arteries in Wistar rats. We also investigated the effects of acute in vitro NOS inhibition in these vessels. 2. Acute NOS inhibition (N omega-nitro-L-arginine, L-NOARG, 10 microM) had no effect on the contractile response to KCl (125 mM), enhanced the response to the phorbol ester, phorbol dibutyrate (1 microM; 69 +/- 9% of KCl response, n = 6; 38 +/- 7% control, n = 6, P < 0.05), increased sensitivity to phenylephrine (EC50: 1.68 +/- 0.14 microM, n = 5; 2.35 +/- 0.23 microM control, n = 5, P < 0.05) and sodium nitroprusside (SNP; EC50 1.79 +/- 0.61 nM, n = 6; 20.44 +/- 6.87 nM control, n = 6, P < 0.05) and decreased sensitivity to acetylcholine (EC50 123 +/- 12 nM, n = 6; 45 +/- 10 nM control, n = 13, P < 0.05). 3. In contrast, contractile responses to KCl (125 mM; 170 +/- 12 mN mm-3, n = 10; 257 +/- 21 mN mm-3 in control, n = 13, P < 0.005) and phenylephrine (maximum response, 30 microM: 169 +/- 24 mN mm-3, n = 10; 295 +/- 19 mN mm-3 in control, n = 13, P < 0.001) were significantly reduced in magnitude following chronic NOS inhibition. Sensitivity to phenylephrine was not significantly altered. 4. The effects of chronic NOS inhibition (N omega-nitro-L-arginine methyl ester, L-NAME, 10 mg kg-1 daily for 3 weeks) were similar to those of acute NOS blockade with respect to the relaxant responses to SNP and acetylcholine, and also the contraction in response to protein kinase C activation. 5. Chronic inhibition of NOS significantly increased medial cross sectional area of mesenteric resistance arteries (0.013 +/- 0.002 mm2, n = 7; 0.009 +/- 0.0005 mm2 control, n = 15, P < 0.05). 6. Thus, in contrast to the acute effects of NOS inhibition, chronic NOS inhibition results in a down-regulation of the contractile responses to KCl and phenylephrine in mesenteric resistance arteries, despite an increase in medial cross sectional area. However protein kinase C-dependent contraction remains relatively enhanced. Endothelium-dependent relaxation is reduced and endothelium-independent relaxation is enhanced in a manner similar to the effects of acute NOS blockade.     

Alpha-vascular responses after short-term and long-term inhibition of nitric oxide synthesis

Apart from the direct actions of nitric oxide (NO) on vascular smooth muscle, this factor may regulate cardiovascular functions through specific actions on alpha-adrenergic constrictor mechanisms. In this study we aim to establish whether the inhibition of the synthesis of this mediator could alter the vasoconstrictor responses mediated by alpha-adrenoceptor stimulation. We have been able to demonstrate that the blockage of the NO synthase really does exist, when both short- and long-term treatments with Nomega-nitro-Larginine methyl ester (L-NAME) are carried out. We have evaluated the concentration-dependent contractions induced by the selective alpha1-adrenoceptor agonists methoxamine and phenylephrine in isolated rat aorta rings in the following groups of animals: control, short-term L-NAME-treated (100 mg/kg i.p. 20 min before subjecting the animals to the experiments) and long-term L-NAME-treated (100 mg/kg per day in the drinking water for 7, 21, or 45 days). We have also evaluated the pressor responses to methoxamine and to the selective alpha-adrenoceptor agonist B-HT 920 using the pithed rat preparation in the same groups of animals. The contractile responses to methoxamine and phenylephrine were similar in the rat aorta preparations from control and short-term L-NAME-treated animals. On the contrary, in the rat aorta preparations from long-term L-NAME-treated animals these responses were clearly reduced when compared with the corresponding responses in those from control animals, the reduction being more marked when the treatment lasted longer. The pressor responses to methoxamine were also similar in control and short-term L-NAME-treated pithed rats. Nevertheless, the responses to B-HT 920 were greater in the latter. On the other hand, the dose-response curves to both alpha-adrenoceptor agonists were shifted to the right in a non-parallel manner in rats treated long term with L-NAME, the shift being, in the case of B-HT 920, more accentuated when the treatment lasted 21 or 45 days than when it lasted only 7 days. These results indicate that the short-term decrease in NO synthesis does not modify the vascular smooth muscle responses mediated by alpha1-adrenoceptor stimulation, but it does induce a potentiation of sympathetic vasoconstriction mediated by alpha2-adrenoceptors. Nevertheless, the long-term inhibition of NO synthesis causes a compensating decrease in the alpha1- and alpha2-vascular smooth muscle contractile responses.     

The role of nitric oxide in the regional vasodilator effects of endothelin-1 in the rat.

1. The role of nitic oxide (NO) derived from L-arginine in the regional vasodilator effects of endothelin-1 has been investigated in anaesthetized, spontaneously hypertensive (SH) rats in which autonomic reflexes were abolished by ganglion blockade. The experimental design incorporated animals infused with phenylephrine to mimic the peripheral vasconstrictor effects of the NO biosynthesis inhibitors and a single dose per animal paradigm to obviate problems of tachyphylaxis to the vasodilator effects of endothelin-1. 2. Infusion of the inhibitor of NO synthase, N-monomethyl-L-arginine (L-NMMA) at a dose (5 mg kg-1 min-1) which maximally raised blood pressure did not influence either the fall in blood pressure or the vasodilator responses induced in the hindquarters and carotid vascular beds by endothelin-1 (1 nmol kg-1, i.v.) The duration (but not the initial magnitude) of the vasodepressor response to endothelin-1 was however significantly attenuated (by 49%) during infusion of the more potent inhibitor of NO synthase, NG-nitro-L-arginine methyl ester (L-NAME), 2 mg kg-1 min-1. 3. Increasing the dose of L-NAME to 10 and 25 mg kg-1min-1 significantly attenuated, but did not abolish, the falls in blood pressure and hindquarters vasodilator responses to acetylcholine, 1 microgram kg-1, and endothelin-1, 1 nmol kg-1 min-1. The effects were selective in that vasodepressor responses to the endothelium-independent vasodilator, sodium nitroprusside, 1-10 micrograms kg-1 min-1, were unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation by nitric oxide of platelet-activating factor-induced albumin extravasation in the conscious rat.

1. The objective of this study was to assess whether or not endogenous nitric oxide (NO) could mediate the hypotensive response to platelet-activating factor (PAF) and modulate PAF-induced microvascular albumin leakage in the conscious rat. 2. PAF (0.19 and 1.9 nmol kg-1, i.v.) evoked dose-dependent hypotension and significantly enhanced albumin extravasation in the large airways, pancreas, stomach and duodenum 15 min after its administration. Inhibition of NO synthesis by NG-nitro-L-arginine methyl ester (L-NAME, 0.125-2 mg kg-1, i.v.) produced marked dose-dependent increases in albumin accumulation (up to 290%) in large airways, liver, spleen, pancreas, kidney, stomach and duodenum as measured by the extravasation of Evans blue dye. L-NAME (2 mg kg-1) treatment markedly potentiated PAF (1.9 nmol kg-1)-induced albumin extravasation in these tissues, whereas it did not modify the hypotensive response to PAF. 3. Maintenance of mean arterial blood pressure at the level observed following 2 mg kg-1 L-NAME by infusion of noradrenaline (620-790 ng kg-1 min-1) neither affected significantly albumin extravasation nor potentiated the permeability effect of PAF in the vascular beds studied with the exception of large airways, where noradrenaline mimicked the effects of L-NAME. 4. These results indicate that inhibition of endogenous NO formation leads to an increase in albumin extravasation and to potentiation of the vascular permeability effect of PAF, whereas the hypotensive action of PAF seems to be independent of NO formation in the conscious rat. These data suggest an important role for NO in the regulation of albumin extravasation.     

Teratological consequences of nitric oxide synthesis inhibition

Nitric oxide (NO) is generated by a family of NO synthase (NOS) enzymes, including endothelial (eNOS), inducible (iNOS) and neuronal (nNOS). NO is an important bioregulator of a wide variety of physiological processes. Recent experimental evidence indicates that inhibition of NO synthesis can lead to teratogenesis. The current review focuses on this aspect of NOS. Exposure of pregnant rodents to non-selective NOS inhibitors, such as N(G)-nitro-L-arginine-methyl ester (L-NAME) and N(G)-nitro-L-arginine (L-NNA), has been linked to limb reduction defects. The teratogenic phenotype, characterized by hemorrhage and transverse terminal tissue destruction, has been regarded to be compatible with a vascular origin. The critical time for teratogenic response was traced to advanced stages of gestation. Similar limb reduction defects have been described in mice deficient in eNOS, but not in other NOS isoforms. Several observations have led to the proposal that hypoxia and possible consequential generation of reactive oxygen species are involved in the causation of NOS inhibitors induced limb defects.     

The effects of extended nitric oxide release on responses of the human non-pregnant myometrium to endothelin-1 or vasopressin

BackgroundUterotonic mediators: endothelin-1 (ET-1), arginine vasopressin (AVP), and nitric oxide (NO) play important roles in the regulation of uterine contractility. We hypothesize that NO affects both ET-1 or AVP. Therefore, this study investigated the involvement of extended exogenous NO release in the regulation of responses of the human non-pregnant myometrium to ET-1 and AVP.MethodsSpecimens were obtained from 10 premenopausal women, undergoing hysterectomy for benign gynecological disorders. Responses of the myometrial strips to ET-1 or AVP in the absence and presence of an exogenous NO donor (diethylenetriamine; DETA/NO; 10⁻⁴ mol/L) were recorded under isometric conditions. To inhibit endogenous NO, a competitive inhibitor of NO synthase, L-N^G-nitroarginine (L-NNA) was added to the organ bath.ResultsET-1 enhanced the spontaneous contractile activity of the myometrium more powerfully (p < 0.01) than AVP. Preincubation with exogenous NO weakened ET-1- or AVP-induced increases in this contractile activity (p < 0.05). However, unexpected results were obtained after preincubation with L-NNA and with DETA/NO then added. Both ET-1 and AVP induced augmented contractile effects in almost all concentrations compared with the responses to these peptides alone or after NOS synthase inhibition (both p < 0.01).ConclusionsThis study demonstrated for the first time that extended incubation with a NO donor influences the uterine muscle response evoked by ET-1 and AVP. Both endogenous and exogenous NO is involved in the control of the uterine responses to ET-1 or AVP of non-pregnant myometrium. Furthermore, both peptides stimulate increased uterine contractility when the local imbalance between the constrictive and relaxing mediators takes place.     

Comparison of the ability of nicardipine, theophylline and zaprinast to restore cardiovascular haemodynamics following inhibition of nitric oxide synthesis.

1. The use of pharmacological inhibitors of nitric oxide (NO) synthesis to treat patients with septic shock is limited by the observation that they cause a fall in cardiac output in some subjects. The aim of this work was to investigate this fall and to test whether it was reversible by subsequent administration of nicardipine, theophylline or the cyclic GMP-selective phosphodiesterase inhibitor, zaprinast (M&B 22948). 2. In pentobarbitone-anaesthetized pigs, haemodynamic indices were measured before and after intravenous administration of NG-nitro-L-arginine methyl ester (L-NAME) in a dose-response protocol (0.2-20 mg kg-1; n = 6) and as a single bolus of 10 mg kg-1 either alone or followed by increasing doses of nicardipine, theophylline or zaprinast (n = 8 in each group). 3. L-NAME caused a dose-dependent rise in systemic vascular resistance and mean systemic arterial pressure and a dose-dependent fall in cardiac output. A single bolus of L-NAME (10 mg kg-1) produced these effects within 15 min. 4. Subsequent administration of nicardipine (0.05-0.2 mg kg-1) caused complete reversal of systemic vasoconstriction and hypertension and in doing so completely restored cardiac output. Theophylline (7.5-10 mg kg-1) partially reversed the rise in systemic vascular resistance and partially restored cardiac output but the effect was small compared to that of nicardipine. Zaprinast (1-5 mg kg-1) had no significant effect on any of these variables.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of endothelin-1 in the hyper-responsiveness to nitrovasodilators following acute NOS inhibition

BACKGROUND AND PURPOSE

Acute NOS inhibition in humans and animals is associated with hypersensitivity to NO donors. The mechanisms underlying this phenomenon have not been fully elucidated. The purpose of the present study was to assess whether hypersensitivity to NOS-blockade is linked to endothelin-1 (ET-1) signalling.

EXPERIMENTAL APPROACH

Sprague Dawley rats were instrumented with indwelling arterial and venous catheters for continuous assessments of haemodynamic parameters and drug delivery, respectively. Mesenteric arteries were isolated and tested for reactivity by wire myography.

KEY RESULTS

NOS blockade with L-N^G-nitroarginine methyl ester (L-NAME) caused a pronounced increase in arterial blood pressure (BP) (∼40 mmHg). In L-NAME-treated animals, the dose of sodium nitroprusside (SNP) required to cause a significant reduction in arterial BP was lower than in vehicle-treated rats (P < 0.001), and the magnitude of the reduction in BP was greater. Similar results were obtained with other NO mimetics, but not isoprenaline; moreover, decreasing the BP back to baseline levels with prazosin after L-NAME treatment did not attenuate the hyper-responsiveness to NO donors. The increased responsiveness to NO donors was abolished by pretreatment with the ET_A/B receptor antagonist, PD145065, or the ET_A receptor-specific antagonist ABT627. Ex vivo, L-NAME treatment potentiated the constriction induced by big endothelin-1 (bET-1), the precursor to active ET-1, but had no effect on the ET-1-mediated constriction.

CONCLUSIONS AND IMPLICATIONS

These data suggest that the increased sensitivity to NO donors is mediated, at least in part, by ET-1 in vivo, and the mechanism may involve the conversion of bET-1 to ET-1.     

Neurotoxicity in conscious rats following intraventricular SNAP,a nitric oxide donor

A solution containing S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO-releasing compound, was microinjected in doses of 0.25–2 μmol into a lateral ventricle of conscious rats. SNAP produced dose-dependent convulsions similar to those associated with limbic stimulation, such as tonic extension of the hindlimbs and tail, and dystonia of the forepaws. At 2 μmol, SNAP evoked hyperventilation (arterial hypocapnia), arterial hyperglycemia and caused necrotic lesions of periventricular gray (e.g. lateral septal nucleus) and white matter structures. In the caudate nucleus and lateral septal nucleus ipsilateral to injection, SNAP elicited a bipolar metabolic pattern of low glucose metabolism proximal to the ventricle with higher values occurring more distally. In control studies, we proved that the residue of SNAP decomposition, N-acetylpenicillamine disulfide injected intraventricularly (2 μmol), was without physiological, behavioral, or histological effects. Ventricular pretreatment with methylene blue (2 nmol), a putative inhibitor of guanylate cyclase and Superoxide generator, suppressed several of the behavioral manifestations of 1 μmol SNAP, such as the forepaw dystonia, squinting, and facial clonus, but was ineffective on the physiological and histological variables affected by the 2 μmol SNAP dose. Another NO donor, sodium nitroprusside (2 μmol), produced fewer behavioral and cytotoxic effects over a 55-min observation period, but caused more intense and widely distributed metabolic stimulation, especially in commissural and projection white matter tracts. The results are the basis for a conscious rat model using intraventricular injection of nitrocompounds to examine the physiological, behavioral, metabolic and cytotoxic properties of NO in the brain.     

一氧化氮及内皮素1在急性肾功能衰竭中的作用

目的 观察一氧化氮（NO）和内皮素1（ET-1）含量变化在急性肾功能衰竭（ARF）中的作用。方法 实验用肌肉注射甘油和皮下注射HgCl2法复制成大鼠ARF模型,以硝酸还原法、化学显色法分别检测血清及肾组织NO含量及其一氧化氮合成酶NOS、iNOS活性,并用放免检测和免疫组化方法对ARF大鼠肾组织中ET-1进行定量与定位分析。结果 模型组NO含量及其合酶活性均显著增加,ET-1水平在24h明显增高,以后逐渐降低。结论 NO及其合酶、ET-1在ARF的发生、发展过程中均起着重要的作用。     

Reciprocal inhibition of nitric oxide and prostacyclin synthesis in human saphenous vein.

1. Angiotensin II (AII) causes contraction of isolated rings of human saphenous vein, responses that are attenuated by the presence of functional endothelium. In this study, we have investigated the mechanisms controlling the release by AII of two endothelial-derived vasorelaxants, prostacyclin (PGI2) and nitric oxide (NO). 2. Myotropic and biochemical changes were measured in response to AII. The biochemical responses measured were the output of PGI2 (as 6-oxo-PGF1 alpha) and of NO (as cyclic GMP). Inhibitors of cyclo-oxygenase (COX; piroxicam) or NO synthase (NOS; L-NAME), were added to the system to determine the influence of endogenous prostaglandins and NO on both myotropic and biochemical responses. Furthermore, to mimic the effects of endogenous, PGI2 or NO, exogenous forms of these relaxants were added, during inhibition of their endogenous release. 3. Contractions of the rings of saphenous vein in response to AII (1-100 nM) were unaffected by treatment with either piroxicam (5 microM) or L-NAME (200 microM) individually. However, when these two inhibitors were used together, there was an increase in the contractions in response to AII. 4. Biochemical analyses revealed that during stimulation by AII, levels of PGI2 and NO were enhanced when synthesis of the other vasodilator was inhibited, suggesting that endogenous NO inhibits PGI2 synthesis and endogenous, PGI2 or another vasorelaxant PG can inhibit NO synthesis. 5. Exogenous PGI2 (as iloprost) or NO (from glyceryl trinitrate) inhibited the increased output of endogenous NO or PGI2 respectively. 6. These results demonstrate the presence, in human saphenous vein, of a mechanism which ensures that levels of vasodilatation are maintained through a compensatory increase in one relaxant agonist when output of the other is decreased. If present in vivo such a mechanism would be important in maintaining saphenous vein graft patency as both PGI2 and NO are not only vasodilators, but inhibit platelet aggregation and myoinitimal hyperplasia, processes implicated in degeneration of graft function.