Characterization of β-adrenoceptor-mediated relaxation signals in isolated pulmonary artery of Dahl salt-sensitive hypertensive and normotensive rats

1?Relaxant responses to isoprenaline (ISO) were studied in the pulmonary arteries of normotensive and hypertensive Dahl salt-sensitive rats. Rats were fed either a high-salt (4.0%) or low-salt (0.14%) diet for 5 weeks. Animals fed a high-salt diet (167/123±2/2 mmHg) had a significantly higher blood pressure compared to those fed a low-salt diet (127/87 ± 2/2 mmHg). 2?Isoprenaline-elicited relaxations were not significantly different in tissues from hypertensive compared to normotensive animals. Responses to ISO were significantly attenuated in denuded tissues and substantially more so in hypertensive compared to normotensive animals. While relaxant responses to ISO were resistant to inhibition by Nω-nitro-L-arginine methyl ester, indomethacin, glibenclamide or a combination of barium chloride and ouabain, they were inhibited by Rp-cAMP, anandamide and acidic buffer. The inhibitory impact of anandamide and acidic buffer was significantly greater in tissues from hypertensive vs. normotensive rats. 3?The resting membrane potential (Em) of smooth muscle cells was -67.0±0.7 mV (n=43 cells) and -66.6±0.8 mV (n=55 cells) in pulmonary arteries from hypertensive and normotensive rats, respectively. Isoprenaline produced hyperpolarization of E(m) which was significant in the blood vessels of hypertensive (-71.6±0.8 mV; n=29 cells) but not normotensive (-68.1±0.7 mV; n=49 cells) rats. 4?The endothelium plays a critical role in β-adrenoceptor-mediated relaxation but nitric oxide is not the mediator for the response. It is possible that the greater hyperpolarization caused by ISO in blood vessels from hypertensive compared to normotensive rats is mediated by activation of TASK-1 channels.     

Cardiovascular responses to retigabine in conscious rats – under normotensive and hypertensive conditions

Background and Purpose

Retigabine is a recently approved antiepileptic agent which activates K_v7.2–7.5 potassium channels. It is emerging that these channels have an important role in vascular regulation, but the vascular effects of retigabine in the conscious state are unknown. Hence, in the present study we assessed the regional haemodynamic responses to retigabine in conscious rats.

Experimental Approach

Male Sprague Dawley rats were chronically instrumented with pulsed Doppler flow probes to measure regional haemodynamic responses to retigabine under control conditions and during acute hypertension induced by infusion of angiotensin II and arginine vasopressin. Further experiments were performed, using the β-adrenoceptor antagonists CGP 20712A, ICI 118551 and propranolol, to elucidate the roles of β-adrenoceptors in the responses to retigabine in vivo and in vitro.

Key Results

Under normotensive conditions, retigabine induced dose-dependent hypotension and hindquarters vasodilatation, with small, transient renal and mesenteric vasodilatations. In the acutely hypertensive state, the renal and mesenteric, but not hindquarters, vasodilatations were enhanced. The response of the hindquarters vascular bed to retigabine was mediated, in part, by β₂-adrenoceptors. However, in vitro experiments confirmed that retigabine did not act as a β-adrenoceptor agonist.

Conclusions and Implications

We demonstrated that retigabine causes regionally specific vasodilatations, which are different under normotensive and hypertensive conditions, and are, in part, mediated by β₂-adrenoceptors in some vascular beds but not in others. These results broadly support previous findings and further indicate that K_v7 channels are a potential therapeutic target for the treatment of vascular diseases associated with inappropriate vasoconstriction.     

Effect of age on the prejunctional α-adrenoceptor-mediated feedback in the heart of spontaneously hypertensive rats and normotensive Wistar Kyoto rats

Summary The prejunctional ₂-adrenoceptor-mediated feed-back in the heart of pithed young and adult spontaneously hypertensive rats (SHR) and corresponding normotensive Wistar Kyoto rats (WKY) was studied. After electrical stimulation of the sympathetic outflow from the spinal cord to the heart, B-HT 920 induced an inhibition of the cardiac response, which was significant at stimulation frequencies up to 1 Hz in young SHR and WKY and up to 2 Hz in the adult animals. Rauwolscine produced a potentiation of the cardiac response to electrical stimulation in SHR, which was significant from 0.2–10 Hz in young SHR and from 0.1–10 Hz in adult SHR. In young WKY, rauwolscine did not potentiate the increase in heart rate to sympathetic nerve stimulation, whereas in adult WKY ₂-adrenoceptor blockade by rauwolscine significantly potentiated the cardiac response to electrical stimulation at frequencies in the range of 0.2–10 Hz. In SHR the potentiation of the cardiac response to sympathetic nerve stimulation by rauwolscine was much stronger than in WKY.These results suggest that in adult animals the prejunctional ₂-adrenoceptor mediated feedback is more developed than in young rats. In contrast with young WKY, a significant endogenous feedback can be demonstrated in adult WKY. In SHR, however, the physiological role of prejunctional ₂-adrenoceptors is much more important.     

Modulation of serum concentrations and hepatic metabolism of 17β-estradiol and testosterone by amitraz in rats

The present study has investigated the ability of amitraz, a widely used formamidine pesticide, to modulate serum concentrations and liver microsomal metabolism of 17β-estradiol (E2) and testosterone in rats. Amitraz was administered intraperitoneally to male rats for 4 days and to intact female rats or ovariectomized (OVX) and 0.5 mg/kg E2-supplemented female rats for 7 days. E2 and metabolites were analyzed by gas chromatography-electron capture detection and testosterone and metabolites were analyzed by high-pressure liquid chromatography. In OVX and E2-supplemented females, 50 mg/kg amitraz caused an 85% decrease of serum E2 concentration and a marked increase of 2-OH-E2 concentration. Amitraz at 25 and 50 mg/kg produced 9.0-fold or greater increases of serum testosterone and 2β-OH-testosterone levels in males. Amitraz at 25 mg/kg resulted in no or minimal increases of liver microsomal formation of E2 or testosterone metabolites. Amitraz at 50 mg/kg produced 1.4- to 3.6-fold increases of 2-OH-E2; estrone; 2β-, 6β-, and 16α-OH-testosterone; and androstenedione formation in males and intact females. Amitraz at 50 mg/kg preferentially increased intact female 16β-OH-testosterone production by 8.6-fold. In OVX females, E2 supplement alone or cotreatment with E2 and 50 mg/kg amitraz produced 1.3- to several-fold increases of 2- and 4-OH-E2 formation and 2β- and 16α-OH-testosterone production. The cotreatment increased 6β- and 16β-OH-testosterone formation by 1.8- and 1.6-fold, respectively. The present findings show that amitraz induces hepatic E2 and testosterone metabolism in male and female rats, decreases serum E2 concentration in OVX and E2-supplemented females, but increases serum testosterone in males.     

Does brain histamine contribute to the development of hypertension in spontaneously hypertensive rats?

Summary Histaminergic neurons of the brain have been implicated in genetic hypertension. We investigated the effect of inhibition of histamine synthesis by -fluoromethylhistidine (-FMH), the irreversible inhibitor of histidine decarboxylase, on the development and maintenance of hypertension in spontaneously hypertensive rats.Young (3-week-old) and adult (7-week-old) rats were treated with -fluoromethylhistidine for 29 and 13 days, respectively. Treatment of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats with -fluoromethylhistidine led to a pronounced decrease in the histidine decarboxylase activity and in the histamine concentration in the brain (hypothalamus, brainstem, cortex —midbrain). In adult spontaneously hypertensive rats, the development of hypertension was not influenced by -fluoromethylhistidine. In young spontaneously hypertensive rats, -fluoromethylhistidine led to a transient delay in the development of hypertension which was followed by a transient tendency to increased blood pressure.It is concluded that histaminergic neurons of the brain play only a subordinate role, if any at all, in the development of hypertension in spontaneously hypertensive rats.This work was supported by the Fonds zur Förderung der wissenschaftlichen Forschung     

Effect of γ-aminobutyric acid and nattokinase-enriched fermented beans on the blood pressure of spontaneously hypertensive and normotensive Wistar–Kyoto rats

In this study we have evaluated the changes in arterial blood pressure in spontaneously hypertensive rats (SHR) caused by the short-term intake of Bacillus subtilis B060-fermented beans with significant γ-aminobutyric acid (GABA) and nattokinase activity. After being weaned, 7-week-old male SHR and 7-week-old male Wistar–Kyoto (WKY) rats were randomized into seven groups. Until the 8^th week of life, the rats in each group were given one of the following: Group 1, high dose of GABA and nattokinase in the SHR (SHD); Group 2, medium dose of GABA and nattokinase in the SHR (SMD); Group 3, low dose of GABA and nattokinase in the SHR (SLD); Group 4, negative control in the SHR (SD); Group 5, positive control in the SHR (SM); Group 6, high dose of GABA and nattokinase in the WKY (WHD); and Group 7, negative control in the WKY (WD). Distilled water served as the negative control, and captopril (50 mg/kg), a known ACE inhibitor, served as the positive control. Systolic blood pressure and diastolic blood pressure values were measured weekly from the 8^th week to the 16^th week of life using the tail-cuff method. A definite decrease in systolic and diastolic blood pressure values could be observed in the rats treated with captopril and in the rats that received GABA and nattokinase. The greatest antihypertensive effect was observed when the pharmacological treatment was administered. The effect of the daily intake of fermented beans containing GABA and nattokinase may be helpful in controlling blood pressure levels in hypertensive model animals. The fermentation of beans with B. subtilis B060 may therefore constitute a successful strategy for producing a functional food with antihypertensive activity.     

Proliferation of aortic smooth muscle cells and renin-angiotensin system in SHR rats

目的：探讨ＳＨＲ大鼠主动脉平滑肌细胞（ＡＳＭＣ）异常增殖和肾素血管紧张素系统（ＲＡＳ）的关系．方法：测定血管紧张素Ｉ（Ａｎｇ）、卡托普利（Ｃａｐ）、沙拉新（Ｓａｒ）对培养的ＳＨＲ、ＷＫＹＡＳＭＣ增殖和Ａｎｇ、血管紧张素转化酶（ＡＣＥ）的影响．结果：Ａｎｇ在２％血清培养基中可刺激ＳＨＲＡＳＭＣ增生．ＳＨＲＡＳＭＣ分裂增殖能力比ＷＫＹ强，ＳＨＲＡＳＭＣＲＡＳ处于高功能状态．Ｃａｐ长期（４周）干预显著抑制ＳＨＲＡＳＭＣ异常增殖和Ａｎｇ、ＡＣＥ活性，Ｓａｒ长期干预同样抑制ＳＨＲＡＳＭＣ的增殖和ＡＣＥ活性，但Ａｎｇ水平反而升高．Ｃａｐ短期（２４小时）干预不影响两种大鼠ＡＳＭＣＲＡＳ．结论：Ｃａｐ和Ｓａｒ长期干预通过减少ＳＨＲＡＳＭＣＡｎｇ生成或阻断Ａｎｇ和特异受体结合，抑制其异常增殖．     

Plasma concentration and vascular effect of β-endorphin in spontaneously hypertensive and Wistar Kyoto rats

Summary In order to find out whether -endorphin (-E) is involved in the development of hypertension, we performed two series of experiments. Firstly, spontaneously hypertensive rats (SHR) and their normotensive Wistar Kyoto controls (WKY) were submitted to ether stress. Plasma concentrations of -endorphin-like immunoreactivity (-EI), adrenocorticotropin (ACTH) and -melanotropin (-MSH) were measured by radioimmunoassay. The basal concentration of -EI was similar in WKY and SHR, whereas WKY had higher levels of ACTH and lower levels of -MSH than SHR. In both strains acute stress enhanced the plasma concentration of -EI to the same extent and with a similar time-course. The increase of plasma -El coincided with a rise in ACTH but not -MSH. Gel chromatography of -EI revealed that plasma extracts contain similar amounts of -lipotropin- (-LPH) and -E-sized immunoreactive components, and that acute stress elevated both forms of -El. Secondly, isolated tail arteries of SHR and WKY were perfused and field stimulated with two pulses at 1 Hz. -E depressed stimulation-evoked vasconstriction with the same potency in both strains. Thus, basal and stress-induced levels of -EI did not differ in SHR and WKY. Moreover, in the tail artery of both strains the sensitivity of presynaptic opioid receptors towards -E was almost identical. If the -E sensitivity of these receptors in other arteries of WKY and SHR is also similar, a major role of the circulating peptide in the development of hypertension is rather unlikely.This work was partly supported by the Deutsche Forschungsgemeinschaft (SFB 325) Send offprint requests to B. Bucher at the above address     

Do trandolapril and indomethacin influence renal function and renal functional reserve in hypertensive patients?

Aims To assess the effect of trandolapril (2 mg once daily) and indomethacin (25 mg three times daily), alone and in combination, on renal function and renal functional reserve in hypertensive patients (DBP 95–115 mmHg) requiring regular non-steroidal anti-inflammatory drugs (NSAIDs). Methods Randomized, double-blind, placebo-controlled, four way crossover design. After 3 weeks treatment renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured using the p-aminohippurate (PAH) and inulin methods. Renal functional reserve was estimated by measuring RPF and GFR at the end of an intravenous infusion of dopamine 2 μg kg⁻¹ and 10% amino acid solution. Results There was no significant difference in RPF between treatments: −22.79 ml min⁻¹ (95% CI −54.82, 9.24) for placebo and trandolapril, −10.37 ml min⁻¹ (95% CI −30.7, 9.96) for placebo and indomethacin, −14.78 ml min⁻¹ (95% CI −50.33, 20.77) for placebo and trandolapril with indomethacin. There was no significant difference in functional reserve RPF between treatments: −34.96 ml min⁻¹ (95% CI −119.8, 49.88) for placebo and trandolapril, 29.78 ml min⁻¹, −15.18, 74.74) for placebo and indomethacin, and −25.84 ml min⁻¹ (95% CI −87.62, 35.94) for placebo and trandolapril with indomethacin. There was no significant difference in GFR between treatments: −1.01 ml min⁻¹ (95% CI −7.45, 5.42) for placebo and trandolapril, −7.88 ml min⁻¹ (95% CI −15.08, −0.68) for placebo and indomethacin, and −0.36 ml min⁻¹ (95% CI −7.58, 6.86) for placebo and trandolapril with indomethacin. There was no significant difference in functional reserve GFR between treatments: 5.13 ml min⁻¹ (95% CI −4.97, 15.23) for placebo and trandolapril, 6.31 ml min⁻¹ (95% CI −1.88, 14.5) for placebo and indomethacin, 7.21 ml min⁻¹ (95% CI 1.26, 13.16) for placebo and trandolapril with indomethacin. Conclusion In hypertensives chronic treatment with NSAIDs or ACEI alone or in combination did not change RPF or GFR and did not change renal functional reserve capacity of RPF or GFR.     

Possible mechanisms of action of the hypotensive effect of Annona muricata (soursop) in normotensive Sprague–Dawley rats

Context: Annona muricata Linn (Annonaceae) (soursop) is a food plant reported to have antihypertensive properties.

Objective: We investigated the blood pressure reducing effect of its aqueous leaf extract and the possible mechanisms that may be responsible.

Methods: Intravenous administration of an aqueous leaf extract (9.17–48.5 mg/kg) of A. muricata on the mean arterial pressure and heart rate were recorded invasively on anaesthetized, normotensive Sprague–Dawley rats. Contractile responses of rat aortic rings to the extract (0.5–4.0 mg/mL) were studied using standard organ bath techniques.

Results: A. muricata (9.17–48.5 mg/kg) caused significant (p < 0.05) dose-dependent reduction in blood pressure without affecting the heart rates. The hypotensive effects were unaffected by atropine (2 mg/kg), mepyramine (5 mg/kg), propranolol (1 mg/kg) and L-NAME (5 mg/kg). A. muricata leaf aqueous extract significantly (p < 0.05) relaxed phenylephrine (10^?9–10^?4 M) and 80 mM KCl induced contractions in endothelium intact and denuded aortic rings; and caused a significant (p < 0.05) rightward shift of the Ca²⁺ dose response curves in Ca²⁺-free Kreb’s solution containing 0.1 mM EGTA.

Conclusions: The hypotensive effects of A. muricata are not mediated through muscarinic, histaminergic, adrenergic and nitric oxide pathways, but through peripheral mechanisms involving antagonism of Ca²⁺.     

NF-κB activation and proinflammatory cytokines mediated protective effect of Indigofera caerulea Roxb. on CCl4 induced liver damage in rats

Indigofera caerulea Roxb. is a well known shrub among native medical practitioners in folk medicine used for the treatment of jaundice, epilepsy, night blindness and snake bites. It is also reported to have antioxidant and antimicrobial properties. However its actual efficacy and hepatoprotective mechanism in particular is uncertain. Thus the present study investigates the hepatoprotective effect of the methanolic extract of I. caerulea Roxb. leaves (MIL) and elucidation of its mode of action against carbon tetrachloride (CCl₄) induced liver injury in rats. HPLC analysis of MIL when carried out showed peaks close to standard ferulic acid and quercetin. Intragastric administration of MIL up to 2000 mg/kg bw, didn't show any toxicity and mortality in acute toxicity studies. During “in-vivo” study, hepatic injury was established by intraperitoneal administration of CCl₄ 3 ml/kg bw (30% CCl₄ in olive oil; v/v) twice a week for 4 weeks in Sprague–Dawley rats. Further, hepatoprotective activity of MIL assessed using two different doses (100 and 200 mg/kg bw) showed that intra-gastric administration of MIL (200 mg/kg bw) significantly attenuates liver injury. Investigation of the underlying mechanism revealed that MIL treatment was capable of reducing inflammation by an antioxidant defense mechanism that blocks the activation of NF-κB as well as inhibits the release of proinflammatory cytokine TNF-α and IL-1β. The results suggest that MIL has a significant hepatoprotective activity which might be due to the presence of phytochemicals namely analogues of ferulic acid and other phytochemicals which together may suppress the inflammatory signaling pathways and promote hepatoprotective activity against CCl₄ intoxicated liver damage.     

High glucose increases the expression of proinflammatory cytokines and secretion of TNFα and β-hexosaminidase in human mast cells

Epidemiological studies demonstrated that obesity, which is a high-risk factor for development of hyperglycemia-associated metabolic syndromes, is associated with prevalence/incidence of allergic diseases. To elucidate the underlying mechanisms of the relationship between hyperglycemia and allergy, we examined the effect of high glucose on the activation of human mast cell lines, HMC-1 and LAD2. HMC-1 and LAD2 cells were cultured in low (5.5 mM) and high (25 mM)-glucose Dulbecco's modified Eagle's medium (DMEM). High-glucose medium increased the intracellular reactive oxygen species levels in HMC-1 and LAD2 cells after 2 days of incubation; in HMC-1 cells, the expression levels of tumor necrosis factor (TNF) α, interleukin (IL)-1β, IL-6, and IL-13 were increased significantly. The β-hexosaminidase release rates were not significantly different between LAD2 cells cultured in both media; however, the intracellular and extracellular activities of β-hexosaminidase in cells were significantly higher in high-glucose than in low-glucose media. High glucose increased the secretion of TNFα by unstimulated HMC-1 cells and IgE crosslinking-stimulated LAD2 cells. High glucose increased the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinases (MAPKs), which regulate the expression of TNFα and other inflammatory cytokines, in both HMC-1 and LAD2 cells. Thus, high glucose increased the expression of proinflammatory and proallergic cytokines, the secretion of TNFα, and β-hexosaminidase activity in human mast cells. Our result suggests that hyperglycemia promotes the activation of human mast cells associated with allergy and inflammation under unstimulated and stimulated conditions.     

Possible mechanisms of action of the aqueous extract of Artocarpus altilis (breadfruit) leaves in producing hypotension in normotensive Sprague–Dawley rats

Context and objectives: Artocarpus altilis (Parkinson) Fosberg (Moraceae) (breadfruit) leaves are used as an antihypertensive remedy. We investigated the possible mechanisms of action of its aqueous extract and its effect on cytochromes P450 (CYP) enzyme activities.

Materials and methods: Intravenous administration of an aqueous leaf extract (20.88–146.18 mg/kg) of A. altilis on mean arterial pressure and heart rate were recorded via cannulation of the carotid artery on anaesthetized normotensive Sprague–Dawley rats. Recordings of the contractile activity of the aortic rings to the extract (0.71–4.26 mg/mL) were studied using standard organ bath techniques. Inhibitions of human CYP3A4 and CYP2D6 enzyme activities were evaluated by means of a fluorometric assay in 96 well plates using heterologously expressed microsomes.

Results: A. altilis caused significant (p < 0.05) hypotensive and bradycardiac responses unaffected by atropine (2 mg/kg) and mepyramine (5 mg/kg), but attenuated by propranolol (1 mg/kg) and N(G)-nitro-l-arginine methyl ester (5 mg/kg). The extract (0.71–4.26 mg/mL) significantly (p < 0.05) relaxed phenylephrine (10^?9–10^?4 M) and 80 mM KCl-induced contractions in endothelium intact and denuded aortic rings; and caused a significant (p < 0.05) rightward shift of the Ca²⁺ dose-response curves in Ca²⁺-free Kreb’s solution. Moderate inhibitions of cytochrome P450s (CYP3A4 and CYP2D6) enzyme activities with IC₅₀ values of 0.695 ± 0.187 and 0.512 ± 0.131 mg/mL, respectively, were produced.

Conclusion: A. altilis exhibits negative chronotropic and hypotensive effects through α-adrenoceptor and Ca²⁺ channel antagonism. Drug adversity effects are unlikely if the aqueous leaf extract is consumed with other medications reliant on CYP3A4 and CYP2D6 metabolism. This study thus provides scientific evidence for the use of the breadfruit in the treatment of hypertension.     

The influence of mianserin on TNF-α, IL-6 and IL-10 serum levels in rats under chronic mild stress

BackgroundAntidepressants are known to affect the immunological system through mechanisms which are not completely understood. The aim of the present study was to evaluate the effect of the atypical antidepressant mianserin on the levels of tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6) and interleukin-10 (IL-10) in the blood of rats in an experimental model of depression.MethodsMale Wistar rats were subjected to chronic mild stress (CMS) according to Willner's method for 6 weeks. Following the development of anhedonia, the stressed and control rats (non-stressed animals) were treated with mianserin (10 mg/kg ip, twice daily) for three weeks. On the last day of the experiment, a lipopolysaccharide (LPS, 100 μg/kg ip) was injected to mianserin- or vehicle-treated rats. TNFα, IL-6 and IL-10 levels in the blood of the rats were assayed using ELISA methods.ResultsThe results indicated a significantly increased TNFα level in stressed animals when compared with the non-stressed (control) group. The levels of IL-6 and IL-10 were also elevated, especially after LPS administration. Treatment with mianserin resulted in a significant lowering of TNFα and IL-6 levels both in LPS-treated and LPS-untreated animals. There was also a decrease in IL-10 concentration in LPS-treated stressed animals.ConclusionsThe results confirm an increase in proinflammatory cytokines in the blood of rats with experimentally induced depression and show the protective role of the activity of mianserin on the cytokine levels, expressed in a lowering of TNFα and IL-6 levels in stressed animals, and of IL-10 levels after LPS administration.     

The influence of antibodies to TNF-α and IL-1β on haemodynamic responses to the cytokines,and to lipopolysaccharide,in conscious rats

1. Male, Long Evans rats (350–450 g) were anaesthetized and had pulsed Doppler probes and intravascular catheters implanted to allow monitoring of regional (renal, mesenteric and hindquarters) haemodynamics in the conscious state. Our main objectives were to:- assess the effects of administering human recombinant tumour necrosis factor (TNF)-α and human recombinant interleukin-1 (IL-1)β, alone and together; determine the influence of pretreatment with a mixture of antibodies to TNF-α and IL-1β on responses to co-administration of the cytokines; ascertain if pretreatment with a mixture of the antibodies to TNF-α and IL-1β had any influence on the responses to lipopolysaccharide (LPS).
2. TNF-α (10, 100 and 250 μg kg⁻¹, in separate groups, n=3, 9 and 8, respectively) caused tachycardia (maximum Δ, +101±9 beats min⁻¹) and modest hypotension (maximum Δ, −10±2 mmHg), accompanied by variable changes in renal and mesenteric vascular conductance, but clear increases in hindquarters vascular conductance; only the latter were dose-related (maximum Δ, +6±6, +27±9, and +61±12% at 10, 100 and 250 μg kg⁻¹, respectively).
3. IL-1β (1, 10, and 100 μg kg⁻¹ in separate groups, n=8, 8 and 9, respectively) evoked changes similar to those of TNF-α (maximum Δ heart rate, +69±15 beats min⁻¹; maximum Δ mean blood pressure, −14±2 mmHg; maximum Δ hindquarters vascular conductance, +49±17%), but with no clear dose-dependency.
4. TNF-α (250 μg kg⁻¹) and IL-1β (10 μg kg⁻¹) together caused tachycardia (maximum Δ, +76±15 beats min⁻¹) and hypotension (maximum Δ, −24±2 mmHg) accompanied by increases in renal, mesenteric and hindquarters vascular conductances (+52±6%, +23±8%, and +52±11%, respectively). Thereafter, blood pressure recovered, in association with marked reductions in mesenteric and hindquarters vascular conductances (maximum Δ, −50±3% and −58±3%, respectively). Although bolus injection of LPS (3.5 mg kg⁻¹) caused an initial hypotension (maximum Δ, −27±11 mmHg) similar to that seen with co-administration of the cytokines, it did not cause mesenteric or hindquarters vasodilatation, and there was only a slow onset renal vasodilatation. The recovery in blood pressure following LPS was less than after the cytokines, and in the former condition there was no mesenteric vasoconstriction. By 24 h after co-administration of TNF-α and IL-1β or after bolus injection of LPS, the secondary reduction in blood pressure was similar (−16±2 and −13±3 mmHg, respectively), but in the former group the tachycardia (+117±14 beats min⁻¹) and increase in hindquarters vascular conductance (+99±21%) were greater than after bolus injection of LPS (+54±16 beats min⁻¹ and +43±9%, respectively).
5. Pretreatment with antibodies to TNF-α and IL-1β (300 mg kg⁻¹) blocked the initial hypotensive and mesenteric and hindquarters vasodilator responses to co-administration of the cytokines subsequently. However, tachycardia and renal vasodilatation were still apparent. Premixing antibodies and cytokines before administration prevented most of the effects of the latter, but tachycardia was still present at 24 h.
6. Pretreatment with antibodies to TNF-α and IL-1β before infusion of LPS (150 μg kg⁻¹ h⁻¹ for 24 h) did not affect the initial fall in blood pressure, but suppressed the hindquarters vasodilatation and caused a slight improvement in the recovery of blood pressure. However, pretreatment with the antibodies had no effect on the subsequent cardiovascular sequelae of LPS infusion.
7. The results indicate that although co-administration of TNF-α and IL-1β can evoke cardiovascular responses which, in some respects, mimic those of LPS, and although antibodies to the cytokines can suppress most of the cardiovascular effects of the cytokines, the antibodies have little influence on the haemodynamic responses to LPS, possibly because, during infusion of LPS, the sites of production and local action of endogenous cytokines, are not accessible to exogenous antibodies.

     

Differential effects of α-β-methylene ATP on responses to nerve stimulation in SHR and WKY tail arteries

Summary The effects of ,-methylene-adenosine triphosphate, (,-methylene ATP, a P₂-receptor desensitising agent) have been evaluated on vasoconstrictor responses elicited by exogenous agonists or electrical field stimulation in isolated perfused SHR or WKY tail arteries and on tritium release elicited by electrical field stimulation in SHR-tail arteries pre-labeled with ³H-noradrenaline.Exposure to ,-methylene ATP (0.1 mol/l) significantly inhibited vasoconstrictor responses to electrical field stimulation in SHR tail arteries. These inhibitory effects were not further increased at a higher concentration of ,-methylene ATP (1 mol/l). In WKY tail arteries, ,-methylene ATP (1 mol/l) failed to significantly inhibit vasoconstrictor responses to electrical stimulation.In SHR tail arteries prelabelled with ³H-noradrenaline, ,-methyleneATP (1 mol/l) did not inhibit the stimulation evoked release of tritium. However, at this concentration, ,-methylene ATP significantly antagonized the vasoconstrictor responses of SHR tail arteries induced by exogenous ATP (1 mol/l), ,-methylene ATP (30 mol/l), a stable agonist at P₂-receptors, or 60 mmol/l KCl. These effects of ,-methylene ATP on contractile responses to KCl were not observed in WKY-tail arteries.In tail arteries obtained from reserpine pretreated SHR, despite a 85–95% decrease in endogenous noradrenaline tissue content, the vasoconstrictor responses induced by periarterial field stimulation were greatly diminished, but not abolished. These residual responses to periarterial field stimulation were not antagonized by prazosin (0.1 mol/l), but were practically abolished by the addition of ,-methylene ATP (1 mol/l).In tail arteries from WKY rats pretreated with reserpine, exposure to prazosin (0.1 mol/l) further reduced the residual responses elicited by electrical field stimulation. In these WKY-tail arteries, addition of ,-methylene ATP (1 mol/l) did not further inhibit the remaining vasoconstrictor response obtained in the presence of prazosin.While our results suggest a significantly greater cotransmitter role for ATP with noradrenaline in tail arteries of SHR compared with control normotensive WKY rats, additional effects of ,-methylene ATP not involving P₂ receptors cannot be entirely excluded.     

Inhibition of reactive oxygen species in hypothalamic paraventricular nucleus attenuates the renin–angiotensin system and proinflammatory cytokines in hypertension

Aims

To explore whether reactive oxygen species (ROS) scavenger (tempol) in the hypothalamic paraventricular nucleus (PVN) attenuates renin–angiotensin system (RAS) and proinflammatory cytokines (PICs), and decreases the blood pressure and sympathetic activity in angiotensin II (ANG II)-induced hypertension.

Methods and results

Male Sprague–Dawley rats were infused intravenously with ANG II (10 ng/kg per min) or normal saline (NS) for 4 weeks. These rats were treated with bilateral PVN infusion of oxygen free radical scavenger tempol (TEMP, 20 μg/h) or vehicle (artificial cerebrospinal fluid, aCSF) for 4 weeks. ANG II infusion resulted in increased mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). These ANG II-infused rats also had higher levels of gp91^phox (a subunit of NAD(P)H oxidase), angiotensin-converting enzyme (ACE), and interleukin-1beta (IL-1β) in the PVN than the control animals. Treatment with PVN infusion of TEMP attenuated the overexpression of gp91^phox, ACE and IL-1β within the PVN, and decreased sympathetic activity and MAP in ANG II-infused rats.

Conclusion

These findings suggest that ANG II infusion induces elevated PICs and oxidative stress in the PVN, which contribute to the sympathoexcitation in hypertension. Inhibition of reactive oxygen species in hypothalamic paraventricular nucleus attenuates the renin–angiotensin system, proinflammatory cytokines and oxidative stress in ANG II-induced hypertension.     

Does impairment of renal and hepatic function influence the metabolism of thrombolytics in patients with myocardial infarction?

Thrombolytic agents activate plasminogen and induce a systemic fibrinolytic and anticoagulant state. Two thrombolytic drugs are used frequently in practice: streptokinase (SK) and alteplase (t-PA). Streptokinase mainly undergoes renal elimination with a half-life of 11-17 min, while alteplase is eliminating by the liver with a half-life of 4-6 min. Our goal was to examine whether renal and hepatic function influence the elimination and metabolism of thrombolytics and the efficacy of percutaneous coronary intervention (PCI) after using alteplase or streptokinase. 416 patients with myocardial infarction (MI) were treated from January 2001 to December 2003 (228 male and 189 female). Alteplase was used in 9 men and 6 women (mean age: 53.88 +/- 9.61 vs. 65.33 +/- 9.87 years, p = 0.07). Patients who underwent rescue PCI after administration of alteplase had slightly higher hepatic enzyme levels/alanine transaminase (ALT): 47.85 vs. 41.4 U/l; gamma-glutamyl transpeptidase (GGT): 69.5 vs. 44.8 U/l/. All patients treated with alteplase survived, rescue PCI was done in 8 cases. Streptokinase was used in 36 men and 28 women (mean age: 63.33 +/- 10.51 vs. 63 +/- 12.03 years, p = 0.9). We did not find a difference between serum creatinine levels of patients who received streptokinase and underwent PCI as compared to those who had not. Rescue PCI was done in 16 cases. 12 patients died in this group. In conclusion we have not found a significant correlation between the use of the thrombolytics and hepatic or renal function; this could indicate that such a slight impairment of liver and renal function does not influence pharmacokinetic properties of thrombolytics.