Biomedical subjects

S J Lewis

Publications and source records attributed to S J Lewis.

At least 19 recordsLinked to original sources

PubMed1997

Actions of S-nitrosocysteine in the nucleus tractus solitarii are unrelated to release of nitric oxide.

Cardiovascular effects elicited by microinjection of L-S-nitrosocysteine in the nucleus tractus solitarii (NTS) were compared and contrasted with those produced by the dextroisomer, other nitric oxide donors and nitric oxide itself. L-S-nitrosocysteine produced dose-related decreases of arterial pressure and heart rate. In contrast, D-S-nitrosocysteine, S-nitrosoglutathione, glyceryl trinitrate, and sodium nitroprusside produced minimal responses that were not dose-related. Likewise, injection of cystine and nitric oxide, two products of S-nitrosocysteine breakdown, produced no significant response. Headspace analysis using chemiluminescence revealed that L- and D-S-nitrosocysteine released identical amounts of nitric oxide when exposed to homogenates of whole rat brain. Responses to L-S-nitrosocysteine were not affected by local injection of oxyhemoglobin or the nitric oxide synthase inhibitor L-nitroarginine methylester. Although injection of L-cysteine into the NTS produced responses similar to those seen with injection of L-S-nitrosocysteine, blockade of excitatory amino acid receptors with kynurenic acid inhibited responses to cysteine but not those to the nitrosothiol. The study demonstrates that S-nitrosocysteine is biologically active in the NTS. Its action is independent of release of nitric oxide from the nitrosothiol but may be mediated through stereoselective sites on target neurons.

Animals↗

PubMed1996

L- and D-S-nitroso-beta,beta-dimethylcysteine differentially increase cGMP in cultured vascular smooth muscle cells.

We examined the effects of the L- and D-isomers of S-nitroso-beta,beta-dimethylcysteine (L- and D-S-nitrosopenicillamine, 10(-7)-10(-5) M) on the guanosine 3',5'-cyclic monophosphate (cGMP) content of cultured porcine aortic smooth muscle cells and the decomposition of these stereoisomers to nitric oxide (NO). L-S-nitrosopenicillamine was a more potent generator of cGMP than D-S-nitrosopenicillamine although both stereoisomers equally decomposed to NO. The 10(-7) M concentration of L- or D-S-nitrosopenicillamine did not generate detectable amounts of NO although 10(-7) M L-S-nitrosopenicillamine but not D-S-nitrosopenicillamine generated significant amounts of cGMP. This study shows that the stereoisomeric configuration of S-nitrosopenicillamine is an important factor in its biological potency. The data suggest that the extracellular or intracellular generation of NO is not the only mechanism by which this S-nitrosothiol generates cGMP in vascular smooth muscle.

Analysis of Variance↗

PubMed1996

The peroxynitrite product 3-nitro-L-tyrosine attenuates the hemodynamic responses to angiotensin II in vivo.

Peroxynitrite is a potent oxidant formed endogenously by the near diffusion-limited reaction of nitric oxide with superoxide anion. Peroxynitrite specifically adds a nitro group to the ortho position of the phenolic ring of free and protein-associated tyrosines to form the stable product 3-nitro-L-tyrosine. Systemic administration of 3-nitro-L-tyrosine markedly inhibits the subsequent hemodynamic responses to alpha 1- and beta-adrenoceptor agonists in anesthetized rats. Angiotensin II is an important modulator of vascular tone. The vasoconstrictor effects of this hormone are known to involve the release of catecholamines from sympathetic tissues. In the present study, we examined whether 3-nitro-L-tyrosine (2.5 mumol/kg i.v.) would attenuate the hemodynamic responses produced by angiotensin II (0.1-1.0 microgram/kg i.v.). Angiotensin II produced increases in mean arterial pressure, and renal and mesenteric vascular resistances, but no changes in hindquarter vascular resistance. The pressor and renal and mesenteric vasoconstrictor responses produced by angiotensin II were significantly attenuated 30-60 min following the administration of 3-nitro-L-tyrosine. Further attenuation of these responses was evident 120-180 min following the administration of 3-nitro-L-tyrosine. The alpha 1-adrenoceptor antagonist prazosin also diminished the pressor and renal and mesenteric vasoconstrictor responses produced by angiotensin II. These results demonstrate that 3-nitro-L-tyrosine inhibits the hemodynamic responses to angiotensin II, possibly through the inhibition of alpha 1-adrenoceptor-mediated events. The effect of 3-nitro-L-tyrosine on the hemodynamic action of angiotensin II raises the possibility that 3-nitro-L-tyrosine may be involved in the pathogenesis of the hemodynamic disturbances associated with inflammatory conditions, such as atherosclerosis, ischemia-reperfusion, and sepsis, where formation of peroxynitrite is favored.

Anesthesia↗

PubMed1996

Evaluation of investigations to diagnose the cause of dizziness in elderly people: a community based controlled study.

OBJECTIVE: To compare the findings in dizzy elderly people with those in controls of a similar age to identify which investigations differentiate dizzy from non-dizzy patients and to design an investigational algorithm. DESIGN: Community based study of clinical and laboratory findings in dizzy and control elderly people. SETTING: Research outpatient clinic at a teaching hospital. SUBJECTS: 149 dizzy and 97 control subjects aged over 65 years recruited from a community survey and articles in the local press. MAIN OUTCOME MEASURES: Findings on physical examination, blood testing, electrocardiography (at rest and over 24 hours), electronystagmography, posturography, and magnetic resonance imaging of head and neck (125 (84%) dizzy subjects and 86 (89%) controls); hospital anxiety and depression score; responses to hyperventilation, carotid sinus massage, and the Hallpike manoeuvre. RESULTS: Blood profile, electrocardiography, electronystagmography, and magnetic resonance imaging failed to distinguish dizzy from control subjects because of the frequency of asymptomatic abnormalities in controls. Posturography and clinical assessment (physical examination, dizziness provocation, and psychological assessment) showed significant differences between the groups. A cause of the dizziness was identified from clinical diagnostic criteria based on accepted definitions in 143 subjects, with 126 having more than one cause. The most common diagnoses were central vascular disease (105) and cervical spondylosis (98), often accompanied by poor vision and anxiety. CONCLUSION: Expensive investigations are rarely helpful in dizzy elderly people. The cause of the dizziness can be diagnosed in most cases on the basis of a thorough clinical examination without recourse to hospital referral.

Aged↗

PubMed1996

Stereoselective S-nitrosocysteine recognition sites in rat brain.

We examined the effects of intracisternal (i.c.) injections (10-250 nmol) of the L- and D-isomers of S-nitrosocysteine (L- and D-S-nitrosocysteine) on the mean arterial blood pressure and heart rate of conscious rats, and the decomposition of L- and D-S-nitrosocysteine to nitric oxide (NO) upon addition to brain homogenates. The i.c. injection of L-S-nitrosocysteine produced initial falls in mean arterial blood pressure and heart rate which were followed by increases in these parameters. The i.c. injection of D-S-nitrosocysteine did not produce initial falls in mean arterial blood pressure or heart rate but produced the subsequent increases in these parameters. L- and D-S-nitrosocysteine decomposed equally to NO. These results suggest that the initial effects of L-S-nitrosocysteine may be due to the activation of stereoselective recognition sites on brain neurons.

Animals↗

PubMed1996

Nitrotyrosine attenuates the hemodynamic effects of adrenoceptor agonists in vivo: relevance to the pathophysiology of peroxynitrite.

Peroxynitrite, which attenuates catecholamine-mediated hemodynamic responses in vivo, nitrates free tyrosine residues to form the specific product, 3-nitro-L-tyrosine. The chemical structure of 3-nitro-L-tyrosine is similar to that of the endogenous catecholamines. Therefore, 3-nitro-L-tyrosine may interfere with catecholamine hemodynamic function in vivo. The hemodynamic responses produced by norepinephrine (1-4 micrograms/kg, i.v., n = 6), epinephrine (0.5-4 micrograms/kg, i.v., n = 7), phenylephrine (1-8 micrograms/kg, i.v., n = 5), and isoproterenol (100-400 ng/kg, i.v., n = 5) were attenuated, while the hemodynamic responses produced by arginine vasopressin (50-250 ng/kg; i.v., n = 5) were unaffected following the administration of 3-nitro-L-tyrosine (2.5 mumol/kg, i.v.) in pentobarbital-anesthetized rats. These results demonstrate substantial and selective attenuation of the hemodynamic effects produced by alpha- and beta-adrenoceptor agonists, raising the possibility that 3-nitro-L-tyrosine may play a role in the hemodynamic dysfunction associated with inflammatory conditions in which the formation of peroxynitrite is favored.

Adrenergic Agonists↗

PubMed1996

Loss of [125I]-pindolol binding to beta-adrenoceptors on rat nodose ganglion after chronic isoprenaline treatment.

The nodose ganglion contains the cell bodies of afferent nerves which convey predominantly sensory information from the viscera to the central nervous system (CNS). Autoradiographic studies show binding sites for beta-adrenoceptor ligands are present on sections of the rat nodose ganglion and also on the corresponding inferior vagal ganglion in humans, indicating the presence of beta-adrenoceptors in these ganglia. Since prolonged stimulation of beta-adrenoceptors in rats with the nonselective beta-adrenoceptor agonist isoprenaline (400 micrograms kg-1 day-1 s.c.) for 14 days results in desensitisation and/or down-regulation of receptors in peripheral tissues, such as heart, kidney and blood vessels, the effects of this treatment on the beta-adrenoceptor population on the nodose ganglion have been examined. Using [125I]-pindolol as a radioligand, autoradiographic studies revealed that specific binding was reduced by 74% in ganglia from isoprenaline-pretreated rats compared to that in ganglia from vehicle-pretreated rats, demonstrating down-regulation of receptors by isoprenaline. [125I]-Pindolol binding was sensitive to inhibition by ICI 118.551 (selective beta 2-adrenoceptor antagonist) but not to atenolol (selective beta 1-adrenoceptor antagonist), indicating receptors are predominantly of the beta 2-adrenoceptor subtype. No change in binding was apparent over the vagus nerve. The nodose ganglion appears to be an additional site at which beta 2-adrenoceptors may be down-regulated in vivo, possibly interfering with normal baro-, chemo- and sensory reflexes.

Animals↗

PubMed1996

Elevation in arterial blood pressure following the development of tachyphylaxis to peroxynitrite.

The systemic administration of peroxynitrite produces transient reductions in mean arterial pressure and vascular resistances in anesthetized rats. The repeated administration of peroxynitrite results in tachyphylaxis. We now report that anesthetized rats (n = 8) treated with peroxynitrite (10 injections of 10 mumol/kg i.v.) subsequently develop increases in mean arterial pressure (20 +/- 4%) and hindquarter (153 +/- 28%), renal (93 +/- 21%), and mesenteric (133 +/- 25%) vascular resistances. These findings suggest that the in vivo production of peroxynitrite may contribute to the pathogenesis of hypertension.

Animals↗

PubMed1996

Anteroventral third ventricle lesions attenuate pressor responses to serotonin in anesthetized rats.

When administered intravenously, serotonin (5-hydroxytryptamine; 5-HT) evokes a triphasic blood pressure response, consisting of the Bezold-Jarisch-associated depressor response, a pressor action, and long-lasting depressor response. Because the pressor response may, in part, be caused by central nervous system (CNS) activation by 5-HT, we predicted that destruction of the anteroventral third ventricle (AV3V) region, an area rich in 5-HT receptors, would attenuate increases in blood pressure to intravenous 5-HT. In anesthetized sham-lesioned and AV3V-lesioned Sprague-Dawley rats, we measured mean arterial pressure (MAP), heart rate (HR), and lumbar sympathetic nerve activity (SNA) to increasing bolus doses of intravenous 5-HT (1, 2.5, 5, 10, 25 mu g/kg), before and after blockade of bradycardia using methylatropine (200 mu g/kg). In all rats, bolus injections of 5-HT elicited bradycardia accompanied by a fall in lumbar SNA and an initial hypotension followed by a pressor response and a longer lasting hypotensive response. The bradycardia, reduction in lumbar SNA, and both depressor responses were equivalent in sham-lesioned and AV3V-lesioned groups. Importantly, AV3V lesions attenuated pressor responses to increasing doses of 5-HT (3 +/- 1, 6 +/- 4, 6 +/- 4, 17 -/+ 4 35 +/- 3 mmHg) compared to sham-lesioned controls (6 +/- 3, 16 +/- 7, 33 +/- 5, 54 +/- 4, 51 +/- 6 mmHg; P < 0.0001). This attenuation was conserved following blockade of bradycardia with methylatropine (P < 0.01). In summary, pressor responses to intravenous 5-HT are diminished by AV3V lesions. These data indicate that the pressor component of the blood pressure response to intravenous 5-HT is partly dependent upon interaction with the CNS.

Animals↗

PubMed1996

Development of a sensitive porcine granulosa cell bioassay for follicle-stimulating hormone (FSH).

PURPOSE: Our objective was to develop a sensitive in vitro bioassay for follicle-stimulating hormone (FSH) that does not require the housing of animals in a research facility. MATERIALS AND METHODS: Porcine granulosa cells from 1- to 3-mm follicles were cultured on laminin for 48 hr in serum-free medium in the absence or presence of FSH or with other purified pituitary hormones, supplemented with 19-OH androstenedione. Estradiol accumulation in medium per microgram of DNA of cells was determined as a reflection of FSH-induced aromatase activity. RESULTS: FSH (0.01-10 ng/ml) caused a dose-dependent increase in estradiol production per microgram of DNA, with 1, 10, and 100 ng/ml significantly higher than control. Porcine FSH was approximately two fold more biopotent than rat FSH in this system. Higher doses of FSH (100 ng/ml) caused less estradiol accumulation, presumably reflecting FSH receptor down regulation. No other pituitary hormone produced significant estradiol accumulation. Unextracted serum from a patient with premature ovarian failure (10-50 microliters) was tested in parallel to purified rat FSH (0-50 ng/ml) in this system, resulting in similar estradiol accumulation per microgram of DNA. CONCLUSIONS: We have developed a porcine granulosa cell bioassay for FSH which is sensitive, is specific for FSH, and does not require the housing of animals on site. It can be completed by a technician within 4 working days and can detect FSH in a sample of human serum.

Androstenedione↗

PubMed1996

Stimulation of lumbar sympathetic nerves may produce hindlimb vasodilation via the release of pre-formed stores of nitrosyl factors.

The physiological activation of lumbar sympathetic nerves by air-jet stress produces a hindlimb vasodilation in conscious rats. Although the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester markedly reduces the duration of this air-jet stress-induced vasodilation, it does not prevent the initial fall in resistance. These data suggest that the vasodilation is initiated by the release of an as yet unidentified factor, whereas the vasodilation is sustained by the release of nitric oxide or newly synthesized nitrosyl factors such as S-nitrosothiols. At present, the possibility that neurogenic vasodilation may be initiated by the release of pre-formed pools of nitrosyl factors from storage sites within the hindlimb vasculature has not been addressed. We reasoned that if nitrosyl factors do exist in storage pools, then we should be able to demonstrate a "use-dependent" loss of vasodilation after nitric oxide synthesis inhibition which would be the result of a gradual depletion of the releasable pools of these nitrosyl factors. In the present study, we examined the effects of repeated episodes of direct electrical stimulation of the lumbar sympathetic chain on ipsilateral hindlimb vascular resistance in pentobarbital-anesthetized rats prior to and following administration of the nitric oxide synthesis inhibitors N(G)-nitro-L-arginine methyl ester (10, 25 or 100 mumol/kg i.v.) or N(G)-nitro-L-arginine (50 mumol/kg i.v.). Three episodes of electrical stimulation of 3.2 +/- 0.4 V (20 Hz, 5 ms duration, 5 ms delay for 10 s given 5 min apart) produced pronounced and reproducible reductions in hindlimb vascular resistance in the ipsilateral hindlimb (-56 +/- 5%, -55 +/- 5% and -53 +/- 6%, respectively), but no changes in mean arterial pressure. Three episodes of electrical stimulation at 4.8 +/- 0.4 V also caused reproducible decreases in hindlimb resistance (-59 +/- 7%, -61 +/- 9% and -64 +/- 12%) and minor but reproducible decreases in blood pressure. The vasodilation produced by the first electrical stimulation at 3.2 +/- 0.4 V was completely abolished by a 25 mumol/kg dose of N(G)-nitro-L-arginine methyl ester (-11 +/- 9%). The initial episode of electrical stimulation at 4.8 +/- 0.4 V produced a pronounced fall in ipsilateral hindlimb resistance in the N(G)-nitro-L-arginine methyl ester-treated animals whereas the second and third stimulations produced progressively smaller vasodilations (-55 +/- 4%, -34 +/- 3% and -19 +/- 2%, respectively). The 10 mumol/kg dose of N(G)-nitro-L-arginine methyl ester was not effective whereas the 100 mumol/kg dose produced similar effects as the 25 mumol/kg dose. The 50 mumol/kg dose of N(G)-nitro-L-arginine produced similar effects as the higher doses of N(G)-nitro-L-arginine methyl ester. Those results suggest that lower intensity electrical stimulation of the lumbar sympathetic nerves produces vasodilation via the release of nitric oxide or newly synthesized nitrosyl factors such as S-nitrosothiols. In contrast, the vasodilation produced by higher intensity electrical stimulation may involve the mobilization and release of pre-formed pools of nitrosyl factors which undergo a "use-dependent" depletion in the absence of nitric oxide synthesis. These pre-formed pools of nitrosyl factors may exist within the sympathetic nerves themselves. In addition, they may be stored within the vascular endothelium and released by neurogenically-derived neurotransmitters/neuromodulators.

Adrenergic Fibers↗

PubMed1996

Altered bowel function and duodenal bacterial overgrowth in patients treated with omeprazole.

BACKGROUND: The dramatic inhibitory effect of proton pump inhibitors on acid secretion has raised concern about possible side-effects, such as small bowel bacterial overgrowth, which may result in further gut dysfunction. The aim of this study was to assess the effect of proton pump inhibitors on duodenal bacteriology, carbohydrate absorption and bowel habit. METHODS: Small bowel bacterial overgrowth and xylose absorption were measured by culture of aspirated duodenal fluid and a combined 1 g 14C-D-xylose absorption-metabolism test in 20 patients with peptic ulcer disease. Tests were repeated after 4 weeks of treatment with omeprazole 20 mg daily. Intestinal transit was assessed by recording interdefecatory intervals and stool form. RESULTS: All patients showed an increase in duodenal bacterial counts following treatment, geometric mean counts increasing from 330 to 95000 CFU/mL. The geometric mean of the difference was 290 CFU/mL (95% CI, 110-720 CFU/mL; P < 0.0001). No changes were noted in the xylose absorption or metabolism tests. Mean interdefecatory intervals decreased by 32% from 31.7 to 21.6 h, the mean difference being 10.1 h (95% CI, 1.6-18.5 h: P = 0.01). The mean stool form index increased from 2.95 to 4.70, mean difference 1.75 (95% CI, 1.10-2.40: P < 0.0001), with four patients reporting diarrhoea. CONCLUSION: The results indicate that conventional treatment for duodenal ulcers with a proton pump inhibitor significantly increases bacterial colonization of the duodenum and the speed of intestinal transit.

Adult↗

PubMed1996

Use-dependent loss of active sympathetic neurogenic vasodilation after nitric oxide synthase inhibition in conscious rats. Evidence for the presence of preformed stores of nitric oxide-containing factors.

In this study, we examined whether air-jet stress-induced active sympathetic hindlimb vasodilation in conscious rats involves the release of preformed stores of nitric oxide-containing factors. We determined the effects of repeated episodes of air-jet stress (six episodes given 5 minutes apart) on mean arterial pressure and vascular resistances in the mesenteric bed and intact and sympathetically denervated hindlimb beds of conscious rats treated with saline or the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV). In saline-treated rats, air-jet stress produced alerting behavior, minor changes in blood pressure, pronounced mesenteric vaso-constriction, and immediate and marked vasodilation in the sympathetically intact hindlimb but a minor vasodilation in the sympathetically denervated hindlimb. Each air-jet stress produced virtually identical responses. In L-NAME-treated rats, the first air-jet stress produced vasodilator responses in the sympathetically intact and sympathetically denervated hindlimbs that were similar to those in the saline-treated rats. However, each subsequent air-jet stress produced progressively smaller vasodilator responses in the sympathetically intact but not the sympathetically denervated hindlimb. There was no loss of air-jet stress-induced alerting behavior or mesenteric vasoconstriction, suggesting that L-NAME did not interfere with the central processing of the air-jet or the resultant changes in autonomic nerve activity. The progressive diminution of air-jet stress-induced vasodilation in the intact hindlimb of L-NAME-treated rats may be due to the use-dependent depletion of preformed stores of nitric oxide-containing factors that cannot be replenished in the absence of nitric oxide synthesis.

Air↗

PubMed1996

Use-dependent loss of acetylcholine- and bradykinin-mediated vasodilation after nitric oxide synthase inhibition. Evidence for preformed stores of nitric oxide-containing factors in vascular endothelial cells.

In the present study, we examined the possibility that the endothelium-dependent vasodilators acetylcholine and bradykinin release preformed pools of nitric oxide-containing factors. Successive injections of selected doses of acetylcholine (1.18 +/- 0.3 micrograms/kg IV) or bradykinin (5 micrograms/kg IV) caused reproducible hypotensive and vasodilator responses within sympathetically intact and sympathetically denervated hindlimbs of conscious rats. After administration of the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV), the first injection of acetylcholine or bradykinin produced pronounced depressor and vasodilator responses that, in the case of bradykinin, were greater than those observed before L-NAME administration. However, each successive injection of acetylcholine and bradykinin produced progressively smaller responses, such that the later injections elicited a markedly diminished hypotension and vasodilation. This "use-dependent" loss of endothelium-dependent vasodilation was not due to the diminished vasorelaxant potency of nitric oxide-containing factors because the vasodilator effects of the nitric oxide donor sodium nitroprusside (32 micrograms/kg IV) and the S-nitrosothiol compound S-nitro-socysteine (200 nmol/kg IV) were augmented in the presence of L-NAME. These results suggest that the use-dependent loss of the hemodynamic effects of acetylcholine and bradykinin in L-NAME-treated rats may be due to the release and subsequent depletion of a factor whose synthesis depends on the bioavailability of nitric oxide. Taken together, these results suggest that preformed pools of nitric oxide-containing factors exist within the endothelium of resistance vessels and that endothelium-dependent agonists exert their vasorelaxant effects at least in part by the mobilization of these performed pools.

Acetylcholine↗

PubMed1996

Hemodynamic effects of L- and D-S-nitrosocysteine in the rat. Stereoselective S-nitrosothiol recognition sites.

The vasorelaxant effects of the endothelium-derived relaxing factor S-nitrosocysteine (SNC) may not be simply due to its decomposition to NO. The biological actions of SNC may also involve the transnitrosation of amino acids in the blood and in plasma membranes. The possibility that the SNC moiety possesses biological activity prompted us to examine whether the hemodynamic effects of this S-nitrosothiol involves the activation of stereoselective S-nitrosothiol receptors within the cardiovascular system. We examined (1) the hemodynamic effects produced by intravenous injections of the L and D isomers of SNC (L- and D-SNC, respectively; 100 to 800 nmol/kg), the L and D isomers of the parent thiols (L- and D-cysteine, respectively; 100 to 800 nmol/kg), the oxidized thiol L-cystine (100 to 800 nmol/kg), and the NO donor sodium nitroprusside (SNP, 1 to 36 micrograms/kg) in conscious freely moving rats, (2) the baroreceptor reflex-mediated changes in heart rate elicited in response to the falls in arterial pressure produced by L- and D-SNC and SNP in conscious rats, and (3) the relative decomposition of L- and D-SNC to NO upon addition to heparinized rat blood or upon direct application to cultured porcine aortic smooth muscle (PASM) cells. We now report that (1) L-SNC is a more potent hypotensive and vasodilator agent within the mesenteric bed and sympathetically intact and sympathetically denervated hindlimb beds of conscious rats than is D-SNC, (2) L- and D-SNC markedly inhibit baroreceptor reflex-mediated tachycardia in conscious rats and D-SNC is considerably more effective than L-SNC, (3) the intravenous injections of L- and D-cysteine or L-cystine do not affect arterial blood pressure or vascular resistances, and (4) L- and D-SNC decompose equally to NO upon application to rat blood or cultured PASM cells. These results suggest that the hemodynamic effects of endogenous SNC may involve its interaction with stereoselective S-nitrosothiol recognition sites within the vasculature and the baroreflex arc. These findings provide tentative evidence that membrane-bound S-nitrosothiol receptors may exist within the cardiovascular system.

Animals↗

PubMed1996

A-4, a tertiary amine analog of HC-3, lowers arterial pressure in spontaneously hypertensive rats.

The 4-methyl piperidine analog (A-4) of hemicholinium-3 is a tertiary amine. A-4, like hemicholinium-3, inhibits sodium-dependent, high-affinity choline transport. The present study examined whether central cholinergic systems are involved in the expression of genetic hypertension. We examined the effects of i.v. and i.c.v. administration of A-4 in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY; control). Basal mean arterial pressure and heart rate values were 108 +/- 4 mm Hg and 370 +/- 5 bpm in WKY and 167 +/- 5 mm Hg and 337 +/- 13 bpm in SHR. The i.v. injection of A-4 (5, 10 and 20 mumol/kg) evoked a dose-dependent decrease in MAP in SHR, but not in WKY. The maximal decrease in MAP was 18 +/- 6 mm Hg (P < .01) in SHR. Depressor responses appeared within 1 min and reached maximum within 10 min. The reductions in MAP were not associated with reductions in peripheral vascular resistances, suggesting that the hypotension was due to a reduction in cardiac output. The i.c.v. injection of A-4 (100 nmol/rat) significantly decreased MAP in SHR (-23.8 +/- 2.4 mm Hg, P < .01), but not in WKY. The maximal decrease in MAP appeared within 1 min and reached maximum 10 min later. These falls in MAP were associated with falls in vascular resistances, suggesting that the hypotension was due to peripheral vasodilation. This dose was ineffective when given i.v. in either strain. A-4-induced decreases in MAP were accompanied by significant tachycardia, which was maximal within 3 min of injection. These studies demonstrate that A-4 lowers MAP in SHR, but not in WKY. The rapid onset of hypotension in SHR after A-4 administration suggests that there is rapid turnover of brain acetylcholine which may be directly involved in maintaining elevated arterial pressure in SHR.

Animals↗

PubMed1996

Lipopolysaccharide inhibits acetylcholine- and nitric oxide-mediated vasodilation in vivo.

The bacterial endotoxin lipopolysaccharide (LPS) inhibits endothelium-dependent relaxation. At present, there is no evidence that this is due to a diminution in the vasorelaxant potencies of nitric oxide (NO) or related nitrosyl factors such as S-nitroso-cysteine (SNC). The aim of the present study was to determine whether the systemic administration of LPS reduces endothelium-dependent vasodilation in rats by diminishing the vasorelaxant potencies of NO or related nitrosyl factors. We examined the time course of effects of a low dose of LPS (2 mg/kg i.v.) on base-line mean arterial pressure and vascular resistances and the hemodynamic responses produced by i.v. injection of the endothelium-dependent vasodilator ACh, the NO donor sodium nitroprusside (SNP) and SNC in urethane-anesthetized rats. LPS produced a sustained fall in mean arterial pressure after 90-120 min due to a reduction in cardiac output. The vasodilator effects of ACh, SNP and SNC in the hindquarter bed were diminished 30 to 75 min after the administration of LPS. The vasodilator effects of ACh in this bed were unaffected 120 to 180 min after LPS. In contrast, the vasodilator effects of SNP were markedly augmented, whereas those of SNC were markedly diminished, 120 to 180 min after LPS. The vasodilator responses produced by ACh in the renal and mesenteric beds were diminished 30 to 75 min and 120 to 180 min, respectively, after LPS. The vasodilator actions of SNP and SNC were not substantially reduced in these beds. These results demonstrate that LPS inhibits ACh-induced vasodilation in vivo. In the hindquarter bed, this may involve loss of the vasodilator effectiveness of NO or related nitrosyl factors. In the renal and mesenteric beds, the loss of ACh-induced responses may be due to the LPS-induced inhibition of muscarinic receptor-mediated signal transduction mechanisms.

Acetylcholine↗

PubMed1995

One sequence, two folds: a metastable structure of CD2.

When expressed as part of a glutathione S-transferase fusion protein the NH2-terminal domain of the lymphocyte cell adhesion molecule CD2 is shown to adopt two different folds. The immunoglobulin superfamily structure of the major (85%) monomeric component has previously been determined by both x-ray crystallography and NMR spectroscopy. We now describe the structure of a second, dimeric, form present in about 15% of recombinant CD2 molecules. After denaturation and refolding in the absence of the fusion partner, dimeric CD2 is converted to monomer, illustrating that the dimeric form represents a metastable folded state. The crystal structure of this dimeric form, refined to 2.0-A resolution, reveals two domains with overall similarity to the IgSF fold found in the monomer. However, in the dimer each domain is formed by the intercalation of two polypeptide chains. Hence each domain represents a distinct folding unit that can assemble in two different ways. In the dimer the two domains fold around a hydrophilic interface believed to mimic the cell adhesion interaction at the cell surface, and the formation of dimer can be regulated by mutating single residues at this interface. This unusual misfolded form of the protein, which appears to result from inter- rather than intramolecular interactions being favored by an intermediate structure formed during the folding process, illustrates that evolution of protein oligomers is possible from the sequence for a single protein domain.

Animals↗