Vasopressor Response Research Articles

Specific role of α2A - and α2B -, but not α2C -, adrenoceptor subtypes in the inhibition of the vasopressor sympathetic out-flow in diabetic pithed rats.

Several lines of evidence have shown an association of diabetes with a catecholamines' aberrant homeostasis involving a drastic change in the expression of adrenoceptors. This homeostatic alteration includes, among other things, atypical actions of α2 -adrenoceptor agonists within central and peripheral α2 -adrenoceptors (e.g. profound antinociceptive effects in diabetic subjects). Hence, this study investigated the pharmacological profile of the α2 -adrenoceptor subtypes that inhibit the vasopressor sympathetic out-flow in streptozotocin-pre-treated (diabetic) pithed rats. For this purpose, B-HT 933 (up to 30 μg/kg min) was used as a selective α2 -adrenoceptor agonist and rauwolscine as a non-selective α2A/2B/2C -adrenoceptor antagonist; in addition, BRL 44408, imiloxan and JP-1302 were used as subtype-selective α2A -, α2B - and α2C -adrenoceptor antagonists, respectively (all given i.v.). I.v. continuous infusions of B-HT 933 inhibited the vasopressor responses induced by electrical sympathetic stimulation without affecting those by i.v. bolus injections of noradrenaline in both normoglycaemic and diabetic rats. Interestingly, the ED50 for B-HT 933 in diabetic rats (25 μg/kg min) was almost 1-log unit greater than that in normoglycaemic rats (3 μg/kg.min). Moreover, the sympatho-inhibition induced by 10 μg/kg min B-HT 933 in diabetic rats was (i) abolished by 300 μg/kg rauwolscine or 100 and 300 μg/kg BRL 44408; (ii) partially blocked by 1000 μg/kg imiloxan; and (iii) unchanged by 1000 μg/kg JP-1302. Our findings, taken together, suggest that B-HT 933 has a less potent inhibitory effect on the sympathetic vasopressor responses in diabetic (compared to normoglycaemic) rats and that can probably be ascribed to a down-regulation of α2C -adrenoceptors.

The adrenal medulla, not CB1 receptors, mediates the inhibitory effect of acute transverse aortic constriction on the neurogenic vasopressor response.

Abstract Aims This study was performed to examine whether acute pressure overload induced by transverse aortic constriction (TAC) inhibits the neurogenic vasopressor response and, if so, to check the role of cannabinoid CB 1 receptors and/or other mechanisms. Main methods TAC or a sham operation was performed in pithed and vagotomised rats; sham-operated rats were infused with vasopressin to ensure a basal systolic blood pressure (SBP) comparable to that of TAC animals. SBP was increased by 40 mm Hg by electrical stimulation of the preganglionic sympathetic nerve fibres or phenylephrine injection. At the end of the experiments, the atria and aorta were isolated. Key findings TAC reduced the electrically (but not the chemically) induced pressor response by 80%; sham operation plus vasopressin had no effect. While the cannabinoid receptor agonist CP55940 and antagonists of CB 1 receptors (AM251), α 2 -adrenoceptors (rauwolscine) and K ATP channels (glibenclamide) did not modify the inhibitory effect of TAC, adrenal medulla removal did prevent this effect. The contractile effects of noradrenaline and isoprenaline were reduced (isolated left atria), whereas their chronotropic effects (right atria) were not affected by TAC, which also spared the vasoconstrictor responses to phenylephrine (isolated aorta). Significance Acute pressure overload induced by TAC reduces the neurogenic vasopressor response via an unknown presynaptic mechanism, an increase in heart rate induced by catecholamines released from the adrenal medulla and a decrease in the catecholamine-induced heart contractility. A better understanding of the negative consequences induced by the acute pressure overload may help in the design of future heart failure therapies.

Establishment and Characterisation of a Murine Model of Brain Death and Syngeneic Renal Transplantation.

Aim: Donor brain death (BD) adversely affects organ quality. It has been associated with more rapid rejection of renal transplants and may also compromise the ability to achieve tolerance. Here, we aimed to establish a model of donor brain death and subsequent renal transplantation in mice. Methods: C57BL/6 mice were anaesthetised using Ketamine/Xylazine. A burr-hole was created, through which a 2F Fogarty balloon catheter was introduced. Pressure-controlled mechanical ventilation was commenced via a tracheostomy. Ventilator settings included 5cmH2O PEEP. Mean arterial pressure (MAP) was measured via a femoral cannula. MAP, HR, core temperature and O2 saturation were continuously monitored. BD was induced by controlled inflation of the balloon with 80-100μL at 5μl/min, and was confirmed by the absence of spontaneous respiration after ventilator disconnection. MAP was maintained ≥40mmHg for >3 hours using boluses of 0.25mL gelofusine iv. Samples were collected at 30 mins, 1 and 3 hrs after the induction of BD. Kidneys from some mice at 1 hr post-BD were grafted into syngeneic recipients. Samples were collected at d1 and 4 post-Tx. Serum HMGB1, S100B and cytokines were quantitated, and renal histology, cellular infiltration and gene expression determined. Results: A typical Cushing response was observed with a spike in MAP from 60mmHg to over 90mmHg, accompanied by tachycardia. Tachycardia persisted, whilst MAP slowly declined. Serum S100B (10163±2387pg/ml cf 1731±557, p=0.03), HMGB1 (25.0±3.2ng/ml cf 8.1±1.2, p<0.01), cytokines, and cytokine gene expression in kidneys were substantially increased by 1 hour after BD induction, notably IL-6 (105 pg/ml cf 18±15, p<0.01), KC (8830±1170pg/ml cf 97±29, p=0.02), and IL-1β (150±21pg/ml cf 3±0, p=0.02). The extent of neutrophil and macrophage infiltration was dramatically increased in kidneys from BD donors on day 4 post-Tx, compared with that in ctrl syngeneic grafts (nΦ 25.7±6.0/HPF cf 1.4±0.3, p<0.01 and F4/80 65.1±9.1/HPF cf 23.7±6.2, p<0.01). Gene expression for RAGE, TLR4, CXCL10, MCP-1, IL-6, TNF-α, TGF-β, IL-1β and HSP2 was considerably greater in kidneys from BD donors. Conclusions: A mouse model of brain death and subsequent renal transplantation was successfully established. Physiological and biochemical changes parallel those observed in clinical transplantation.

Pharmacological evidence that 5-HT1A/1B/1D, α2-adrenoceptors and D2-like receptors mediate ergotamine-induced inhibition of the vasopressor sympathetic outflow in pithed rats

The sympathetic nervous system that innervates the peripheral circulation is regulated by several mechanisms/receptors. It has been reported that prejunctional 5-HT1A, 5-HT1B, 5-HT1D, D2-like receptors and α2-adrenoceptors mediate the inhibition of the vasopressor sympathetic outflow in pithed rats. In addition, ergotamine, an antimigraine drug, displays affinity at the above receptors and may explain some of its adverse/therapeutic effects. Thus, the aims of this study were to investigate in pithed rats: (i) whether ergotamine produces inhibition of the vasopressor sympathetic outflow; and (ii) the major receptors involved in this effect. For this purpose, male Wistar pithed rats were pre-treated with gallamine (25mg/kg; i.v.) and desipramine (50µg/kg) and prepared to stimulate the vasopressor sympathetic outflow (T7–T9; 0.03–3Hz) or to receive i.v. bolus of exogenous noradrenaline (0.03–3µg/kg). I.v. continuous infusions of ergotamine (1 and 1.8μg/kgmin) dose-dependently inhibited the vasopressor responses to sympathetic stimulation but not those to exogenous noradrenaline. The sympatho-inhibition elicited by 1.8μg/kgmin ergotamine was (i) unaffected by saline (1ml/kg); (ii) partially antagonised by WAY 100635 (5-HT1A; 30μg/kg) and rauwolscine (α2-adrenoceptor; 300μg/kg), and (iii) dose-dependently blocked by GR 127935 (5-HT1B/1D; 100 and 300μg/kg) or raclopride (D2-like; 300 and 1000μg/kg), The above doses of antagonists did not modify per se the sympathetically-induced vasopressor responses. The above results suggest that ergotamine induces inhibition of the vasopressor sympathetic outflow by activation of prejunctional 5-HT1A, 5-HT1B/1D, α2-adrenoceptors and D2-like receptors in pithed rats.

Antiarrhythmic, hypotensive and α1-adrenolytic properties of new 2-methoxyphenylpiperazine derivatives of xanthone

The main goal of this study was to assess antiarrhythmic and hypotensive activity of new 2-methoxyphenylpiperazine derivatives of xanthone. In order to better understand mechanism of action of studied compounds, their abilities to antagonize the increase in blood pressure elicited by adrenaline, noradrenaline and methoxamine, as well as the antagonistic properties for α1-adrenoceptors on isolated rat aorta were evaluated. Therapeutic antiarrhythmic activity was investigated in an adrenaline-induced model of arrhythmia. Hypotensive activity in normotensive rats was evaluated after oral administration. Influence on blood vasopressor response and α1-adrenoceptors in rat thoracic aorta was evaluated to determine if the observed cardiovascular effects could be related to α1-adrenolytic properties. Tested compounds produced antiarrhythmic and hypotensive activity. The most active compound was MH-99 – (R,S)-4-(2-hydroxy-3-(4-(2-methoxyphenyl)piperazine-1-yl)propoxy)-9H-xanthen-9-one hydrochloride. All studied compounds showed α1-adrenolytic properties in the in vivo and in vitro tests. The results indicate that the new valuable compounds with antiarrhythmic and hypotensive activity might be found in the group of xanthone derivatives. Further pharmacological utility of these compounds should be investigated.

Central administration of IL‐1 receptor antagonist increases vasopressin secretion in late phase of sepsis in rats (876.7)

Clinical and experimental studies have reported that the initial phase of sepsis is characterized by elevated plasma vasopressin (AVP) concentrations. However, in the late phase, despite of the significant decrease in the arterial pressure, the AVP secretion decrease and the plasma concentrations remain unusually low, contributing to the hypotension, vasodilator shock, and death. Considering the role of AVP in the vasopressor response, the elucidation of the mechanisms of this deficient hormone secretion may contribute to therapy during sepsis.The aim of this study was to analyze the effect of IL‐1ra (an Interleukin‐1 receptor antagonist) on sepsis‐induced alterations in plasma AVP and NO, and cerebrospinal fluid (CSF) NO levels. After Wistar rats were intracerebroventricullary injected with 2 ul of IL‐1ra (9 nmol/ or vehicle (PBS 0.01M) sepsis was induced by cecal ligation and puncture (CLP). Blood samples were collected from different groups of rats (n=6‐8/group) by decapitation after 4‐, 6‐ and 24‐h. Specific ELISA and Chemiluminescence assays were used for measurement of AVP and NO concentrations, respectively. All experiments were carried out according to an institutional ethical committee approved protocol.IL‐1ra administration did not alter plasma vasopressin after 4‐ and 6‐h as compared to vehicle in CLP animals. In contrast, after 24‐h AVP levels were significantly (P&lt;0.01) higher in IL‐1ra treated animals as compared to vehicle treated animals. IL‐1ra administration significantly (P&lt;0.01) decreased NO concentration in CSF but not in plasma. Moreover, the survival rate of IL‐1ra treated rats increased by 38% in comparison to vehicle administered animals.In conclusion, the central administration of IL‐1ra increases AVP secretion in the late phase of sepsis which was beneficial for survival. We believe that one of the mechanisms for this effect of IL‐1ra is through reduction of NO concentration in CSF of the septic rats.

Hypoxic incubation alters cardiovascular response to Ang II in embryonic chickens (Gallus gallus) (1067.3)

The renin angiotensin system (RAS) is a critical regulatory mechanism contributing to cardiovascular homeostasis. Angiotensin II (Ang II) is the primary peptide of the system eliciting a strong vasopressor response. While blood volume stress has been the primary perturbation used to study the RAS during vertebrate development, hypoxia has been largely ignored. We hypothesized that the RAS activity would increase and the pressor response to Ang II would be attenuated in embryonic chickens subjected to chronic hypoxic (15% O2) stress. We investigated some of the components that underlie the Ang II cardiovascular response in chicken embryos and how 15% O2 incubation alters the response. Hypoxic incubation blunted the pressor response to Ang I, and Ang II in embryonic chickens. Following alpha‐adrenergic receptor blockade, the pressor response to Ang II was blunted in the normoxic but not the hypoxic embryos. In addition following alpha‐adrenergic blockade the Ang II pressure response did not differ between the normoxic and hypoxic incubated embryos. This suggests that hypoxic incubation blunts the pressor response to Ang II possibly attributed to saturation of the alpha‐adrenergic receptors in embryonic chickens.Grant Funding Source: Supported by NSF career grant to DAC IBN IOS 084574

Evidence that chronic administration of 17β‐estradiol decreased the vasopressor responses in streptozotocin‐diabetic female rats (1051.9)

In vitro studies have shown that 17β‐estradiol has beneficial effects in the cardiovascular system by activation of nitric oxide pathway. However, these effects have not been demonstrated in streptozotocin‐induced diabetic rats in the systemic vasculature in vivo. Thus, this study determined the effect of 17β‐estradiol on the vasopressor responses induced by sympathetic stimulation or i.v. injections of noradrenaline, methoxamine and B HT 933 in sham‐operated or ovariectomized, diabetic or non‐diabetic female rats. For this purpose, rats were ovariectomized or sham‐operated. One week later the animals were treated with streptozotocin (60 mg/kg, i.p.) or its vehicle. Two weeks later these rats were treated with 17β‐estradiol (10 μg/kg, s.c.) or its vehicle daily during five weeks. Then, under anaesthesia with ketamine and xylazine, the animals were pithed and prepared to measure blood pressure and heart rate. 17β‐estradiol failed to modify the vasopressor responses to: (i) sympathetic stimulation, noradrenaline, methoxamine or B HT 933 in sham‐operated non‐diabetic rats; (ii) sympathetic stimulation or B‐HT 933 in sham‐ operated diabetic rats; (iii) noradrenaline or methoxamine in ovariectomized non‐diabetic rats. In contrast, 17β‐estradiol significantly decreased the vasopressor responses to: (i) noradrenaline and methoxamine in sham‐operated diabetic rats; (ii) sympathetic stimulation or B‐HT 933 in ovariectomized non‐diabetic rats; and (iii) sympathetic stimulation, noradrenaline, methoxamine or B HT 933 in ovariectomized diabetic rats. These results, taken together, suggest that chronic administration of 17β‐estradiol produced a protective effect in the systemic vasculature in streptozotocin‐induced diabetic rats. This is the first in vivo study showing this protective effect of 17β‐estradiol during diabetes.This project was financially supported by Conacyt (Grant number 152534).Grant Funding Source: Supported by Conacyt 152534

The Introduction of an Integrated Early Warning Score Observation Chart–A Picture Paints a Thousand Words

Previous studies have demonstrated that abnormal physiological observations are often recorded on patients' observation charts but not acted on, with ensuing negative consequences. To address this issue within our hospital, traditional charts with a graphic depiction of observations were replaced with new charts combining early warning scores (EWS) with numerically depicted observations. However, the replacement did not include a graphic display of observations in the form of trend graphs. The present study compared the speed and accuracy of data interpretation between the 2 charts. Six clinical scenarios (low-grade temperature, spiking temperature, tachypnea, Cushing's response, hypovolaemic shock and normal observations) were identically depicted on old and new charts, creating 12 charts. One hundred health-care professionals were asked to study each of the charts, and the time taken to give a diagnosis was recorded. Time taken and accuracy of response were compared between the 2 charts. The old chart was associated with faster responses in all of the scenarios, reaching statistical significance in 5 of the 6 scenarios (P < 0.0001). Additionally, the response was more accurate in all of the scenarios, reaching statistical significance in 3 of the 6 scenarios (P < 0.0001). Overall, response to the old chart was 1.6 times faster (P < 0.0001) and 15% more accurate (90% versus 75%, P < 0.0001) than the new chart. Graphic display of data is associated with faster and more accurate assimilation of information. Hence, charts combining EWS with graphic portrayal of observation trends may contribute to earlier recognition of sick patients.

Evidence that chronic administration of 17β-oestradiol decreases the vasopressor responses to adrenergic system stimulation in streptozotocin-diabetic female rats

In vitro studies have indicated that 17β-oestradiol exerts beneficial effects on the cardiovascular system by activating the nitric oxide pathway. However, these effects have not been demonstrated in vivo in the systemic vasculature of rats made diabetic through streptozotocin induction. Therefore, the goal of this study was to determine the effect of 17β-oestradiol on vasopressor responses induced by sympathetic stimulation or i.v. injections of noradrenaline, methoxamine and B-HT 933 in sham-operated or ovariectomised, diabetic or non-diabetic female rats. Thus, rats were ovariectomised or sham-operated for this experiment. One week later, the animals were treated with streptozotocin (60mg/kg, i.p.) or its vehicle. Two weeks later, these rats were treated daily with 17β-oestradiol (10μg/kg, s.c.) or its vehicle for five weeks. Next, under anaesthesia, the animals were pithed and prepared for blood pressure and heart rate measurements. 17β-oestradiol failed to modify the vasopressor responses to (i) sympathetic stimulation, noradrenaline, methoxamine or B-HT 933 in sham-operated non-diabetic rats; (ii) sympathetic stimulation or B-HT 933 in sham-operated diabetic rats; (iii) noradrenaline or methoxamine in ovariectomised non-diabetic rats. In contrast, 17β-oestradiol significantly decreased the vasopressor responses to (i) noradrenaline and methoxamine in sham-operated diabetic rats; (ii) sympathetic stimulation or B-HT 933 in ovariectomised non-diabetic rats; and (iii) sympathetic stimulation, noradrenaline, methoxamine or B-HT 933 in ovariectomised diabetic rats. These results suggest that chronic administration of 17β-oestradiol decreases the vasopressor responses to adrenergic system stimulation in streptozotocin-induced diabetic rats. This report describes the first in vivo study reporting this effect of 17β-oestradiol in diabetes.

Vasopressor meets vasodepressor: The AT1–B2 receptor heterodimer

The AT1 receptor for the vasopressor angiotensin II is one of the most important drug targets for the treatment of cardiovascular diseases. Sensitization of the AT1 receptor system is a common feature contributing to the pathogenesis of many cardiovascular disorders but underlying mechanisms are not fully understood. More than a decade ago, evidence was provided for control of AT1R activation by heterodimerization with the B2 receptor for the vasodepressor peptide, bradykinin, a physiological counterpart of the vasoconstrictor angiotensin II. AT1–B2 receptor heterodimerization was shown to enhance AT1R-stimulated signaling under pathophysiological conditions such as experimental and human pregnancy hypertension. Notably, AT1R signal sensitization of patients with preeclampsia hypertension was attributed to AT1R–B2R heterodimerization. Vice versa, transgenic mice lacking the AT1–B2 receptor heterodimer due to targeted deletion of the B2R gene showed a significantly reduced AT1R-stimulated vasopressor response compared to transgenic mice with abundant AT1R–B2R heterodimerization. Biophysical methods such as BRET and FRET confirmed those data by demonstrating efficient AT1–B2 receptor heterodimerization in transfected cells and transgenic mice. Recently, a study on AT1R-specific biased agonism directed the focus to the AT1–B2 receptor heterodimer again. The β-arrestin-biased [Sar1,Ile4,Ile8]-angiotensin II promoted not only the recruitment of β-arrestin to the AT1R but also stimulated the down-regulation of the AT1R-associated B2 receptor by co-internalization. Thereby specific targeting of the AT1R–B2R heterodimer became feasible and could open the way to a new class of drugs, which specifically interfere with pathological angiotensin II-AT1 receptor system activation.

子どもの疲労自覚症状の実態と自律神経機能との関連：

The purpose of this study was to clarify childrenʼs subjective symptoms of fatigue and their relationship to the autonomic nervous system through a method of questionnaire and cold pressor test. The subjects were 254 boys and 184 girls (3rd-6th grade elementary school student, 3rd grade junior high school student, and 1st-3rd grade high school student). The investigation was carried out during May 2007 and May 2009. The results are summarized as follows：1 ) The total subjective symptoms of fatigue score rose as the school year progressed, and the score for girls was higher than for boys among high school students. Moreover, the percentage of those with a score of 0 points was only 7.4%. In addition, “I feel sleepy” and “I give a yawn” ranked as the two worst complaint items. The rate of complaint showed a relationship of Ⅰ group＞Ⅱ group＞Ⅲ group, assuming a tiredness type of “Mental work and night shift.” 2 ) The values derived from the vasopressor response by the cold pressor test were similar to the values of the previous study in 14.0±10.5 mmHg. Moreover, when these values were compared against past standards, 65.8% of subjects saw responses that were either low or excessive. 3 ) About the relations with subjective symptoms of fatigue and the autonomic nervous system, in the high school and the junior high school student, the relevance was not confirmed among both, but in the elementary school children, the group with a high tiredness score showed a larger vasopressor response than the low tiredness score group. From this, we surmise that an excessive sympathetic response to stimulation is operating behind the subjective symptoms of fatigue among the elementary group. And it is thought that an action to fix the imbalance of such an autonomic nervous system is necessary for the reduction of fatigue subjective symptoms.

Invasive and Ultrasound Based Monitoring of the Intracranial Pressure in an Experimental Model of Epidural Hematoma Progressing towards Brain Tamponade on Rabbits

Introduction. An experimental epidural hematoma model was used to study the relation of ultrasound indices, namely, transcranial color-coded-Doppler (TCCD) derived pulsatility index (PI), optic nerve sheath diameter (ONSD), and pupil constriction velocity (V) which was derived from a consensual sonographic pupillary light reflex (PLR) test with invasive intracranial pressure (ICP) measurements. Material and Methods. Twenty rabbits participated in the study. An intraparenchymal ICP catheter and a 5F Swan-Ganz catheter (SG) for the hematoma reproduction were used. We successively introduced 0.1 mL increments of autologous blood into the SG until the Cushing reaction occurred. Synchronous ICP and ultrasound measurements were performed accordingly. Results. A constant increase of PI and ONSD and a decrease of V values were observed with increased ICP values. The relationship between the ultrasound variables and ICP was exponential; thus curved prediction equations of ICP were used. PI, ONSD, and V were significantly correlated with ICP (r 2 = 0.84 ± 0.076, r 2 = 0.62 ± 0.119, and r 2 = 0.78 ± 0.09, resp. (all P < 0.001)). Conclusion. Although statistically significant prediction models of ICP were derived from ultrasound indices, the exponential relationship between the parameters underpins that results should be interpreted with caution and in the current experimental context.

Ranolazine's sweet side – improvement of glycaemic control by the novel mechanism of skeletal muscle microvascular recruitment

Type II diabetes mellitus is a major public health problem afflicting in excess of 250 million individuals worldwide. The presence of this condition in patients with coronary artery disease more than doubles their risk for cardiovascular events. Among the most critical factors are the attendant development of endothelial dysfunction and insulin resistance, which contribute to impaired glycaemic control and acceleration of atherosclerosis. Contemporary therapies have important limitations and safety concerns, as treatment with agents in extensive clinical use, including β-adrenergic receptor blocking agents, thiazide diuretics, and calcium channel antagonists, is associated with increased rates of newly diagnosed diabetes as a result of pro-diabetic effects. These limitations have prompted a search for alternative modalities of drug action. In the current issue of The Journal of Physiology, Fu and colleagues (2013) explored whether ranolazine can improve blood flow and distribution of insulin through α-adrenergic receptor-mediated vasodilatation. Ranolazine is a weak competitive antagonist of α-adrenergic receptors (Allely et al. 1993) and in the conscious dog this antagonism is unmasked by activation of the autonomic nervous system (Zhao et al. 2011). Fu and colleagues (2013) reported that in the therapeutic range of doses ranolazine recruited muscle microvasculature, resulting in a significant >2-fold increase in skeletal muscle blood flow and volume and a substantial enhancement of insulin-mediated whole-body disposal in the range of 30%. In addition, ranolazine improved delivery of insulin into skeletal muscle. Ranolazine increased endothelial nitric oxide synthase (eNOS) phosphorylation and cyclic adenosine monophosphate (cAMP) production without affecting endothelial insulin uptake. Isolated phenylephrine pre-constricted arterial rings were relaxed in the presence of ranolazine, indicating an α-adrenergic receptor-mediated effect. This observation is consistent with evidence obtained in vivo in which the vasoconstrictor effect of intracoronary phenylephrine was abolished by ranolazine (Nieminen et al. 2011) and the vasopressor response to methoxamine was blunted by ranolazine in a dose-dependent manner (Wang et al. 2008). Fu and colleagues (2013) also found that the vasodilatory effects on the pre-capillary arterioles occurred via actions on both the endothelium and smooth muscle cells. Overall, their observations indicate that at therapeutic concentrations ranolazine acutely recruits skeletal muscle microvasculature, increasing microvascular exchange surface area and perfusion. This effect, in combination with the drug's α-adrenergically mediated vasodilatation of pre-capillary arterioles, improves insulin delivery to skeletal muscle and glucose use. This intriguing study by Fu and coworkers (2013) raises important questions relevant to potential clinical applications. As the present studies were performed on an acute basis in normal rats, it remains to be determined whether microvascular recruitment persists following chronic administration in a diabetic animal model. Also, is there evidence that this action of ranolazine on muscle microvasculature operates in patients with various degrees of insulin resistance and early and late stage type 2 diabetes? Clinical trials have demonstrated that ranolazine significantly improves glycaemic control as suggested by reduced levels of glycated haemoglobin (HbA1c) in diabetic as well as non-diabetic subjects (Timmis et al. 2006; Morrow et al. 2009; Chisholm et al. 2010; Kosiborod et al. 2013). Use of ranolazine is also attractive in light of the excellent safety profile shown in the MERLIN-TIMI 36 (Metabolic Efficiency With Ranolazine for Less Ischemia in NonST-Elevation Acute Coronary Syndromes Thrombolysis in Myocardial Infarction 36) trial, which enrolled 6560 patients with cardiovascular disease, 2028 (31%) of whom had pre-existing diabetes (Morrow et al. 2009). However, the mechanisms whereby ranolazine reduces HbA1c remain unknown. The clinical implications of this study are multifold and significant. Essentially, the authors have identified mechanisms that may underlie ranolazine's unique salutary effects, which can potentially improve the cardiovascular health of diabetic patients while reducing myocardial ischaemic events and risk for atrial and ventricular arrhythmias. Although considerable further work will be required to assess fully the clinical applicability of Fu and coworkers’ novel findings (2013), available clinical evidence suggests that the basic concept presented in the current study is promising and worthy of vigorous pursuit.

Analysis of anandamide- and lysophosphatidylinositol-induced inhibition of the vasopressor responses produced by sympathetic stimulation or noradrenaline in pithed rats

The endocannabinoid system exhibits multiple functions in cardiovascular regulation mainly by cannabinoid (CB1 and CB2) receptors, vanilloid TRPV1 receptors and, probably, by the orphan G protein-coupled receptor 55 (GPR55). Hence, the role of these receptors was investigated in Wistar pithed rats on anandamide- and lysophosphatidylinositol (LPI)-induced inhibition of the vasopressor responses induced by preganglionic (T7-T9) stimulation of the vasopressor sympathetic outflow or i.v. bolus injections of noradrenaline. The corresponding frequency- and dose-dependent vasopressor responses were analyzed before and during i.v. continuous infusions of anandamide (CB1, CB2, TRPV1 and GPR55), JWH-015 (CB2) and LPI (GPR55) in animals receiving (i.v.) the antagonists NIDA41020 (CB1), AM630 (CB2), capsazepine (TRPV1) and/or cannabidiol (GPR55). Anandamide (0.1-3.1μg/kgmin) inhibited the vasopressor responses by electrical stimulation, but not those by noradrenaline; while LPI (5.6–10μg/kgmin) inhibited both responses. In contrast, JWH-015 (5.6–10μg/kgmin) failed to induce sympatho-inhibition. Anandamide-induced sympatho-inhibition was: (i) dose-dependently blocked by 31 and 100μg/kg NIDA41020; (ii) slightly blocked by 310μg/kg AM630 or 31μg/kg cannabidiol; and (iii) unaffected by 310μg/kg capsazepine. Moreover, LPI-induced inhibition of both vasopressor responses was blocked and abolished by 10 and 31μg/kg cannabidiol, respectively, and weakly blocked by 100μg/kg NIDA41020. Thus, the sympatho-inhibition by anandamide is primarily mediated by cannabinoid CB1 and, minimally, by cannabidiol-sensitive receptors. In contrast, LPI-induced inhibition of both responses seems to be mainly mediated by postjunctional cannabidiol-sensitive (presumably endothelial GPR55) receptors.

The α2-adrenoceptors mediating inhibition of the vasopressor sympathetic outflow in pithed rats: Pharmacological correlation with α2A, α2B and α2C subtypes

α2-Adrenoceptors were first described as presynaptic receptors inhibiting the release of various transmitters from neurons in the central and peripheral nervous systems. In vitro studies have confirmed that α2A, α2B and α2C subtypes inhibited noradrenaline release from postganglionic sympathetic neurons but no study has been reported their involvement in the vasopressor sympathetic outflow in vivo. Thus, this study analysed the subtype(s) involved in the inhibition produced by the α2-adrenoceptor agonist, B-HT 933, on the vasopressor sympathetic outflow. Male Wistar pithed rats were pre-treated with i.v. bolus injections of gallamine (25mg/kg) and desipramine (50µg/kg) and prepared to stimulate the vasopressor sympathetic outflow (T7–T9) or to receive i.v. bolus of exogenous noradrenaline. Sympathetic stimulation or exogenous noradrenaline produced, respectively, frequency-dependent and dose-dependent vasopressor responses. I.v. continuous infusion of B-HT 933 (30μg/kgmin) failed to modify the vasopressor responses to exogenous noradrenaline and inhibited those induced by preganglionic stimulation of the vasopressor sympathetic outflow at all frequencies of stimulation (0.03–3Hz). The sympatho-inhibition elicited by B-HT 933 was: (i) unaffected by vehicles (1ml/kg); (ii) partially antagonised by BRL44408 (300μg/kg; α2A), imiloxan (3000μg/kg; α2B) and/or JP-1302 (300μg/kg; α2C) given separately; and (iii) completely blocked by rauwolscine (300μg/kg) or the combination of BRL44408 (300μg/kg)+imiloxan (3000μg/kg)+JP-1302 (300μg/kg). The above doses of antagonists did not modify per se the sympathetically-induced vasopressor responses. These results suggest that the vasopressor sympatho-inhibition to B-HT 933 is primarily mediated by activation of α2A/2B/2C-adrenoceptors in pithed rats.

Differential role of cyclooxygenase-1 and -2 on renal vasoconstriction to α1-adrenoceptor stimulation in normotensive and hypertensive rats

AimsHypertension is associated with the impairment of renal cyclooxygenase (COX) activity, which regulates vascular tone, salt and water balance and renin release. We aimed to evaluate the functional role of COX isoforms in kidneys isolated from spontaneously hypertensive rats (SHR) after α1-adrenoceptor (α1-AR) stimulation. Main methodsMale six-month-old SHR and normotensive Wistar-Kyoto rats (WKY) were used. The kidneys were isolated to measure perfusion pressure and COX-1- or COX-2-derived prostanoids in response to α1-AR activation. Key findingsThe basal perfusion pressure was higher in SHR kidneys compared with WKY kidneys (95±11 vs. 68±6mmHg, P<0.05). Phenylephrine induced a greater vasopressor response in SHR kidneys (EC50 of 1.89±0.58nmol) than WKY kidneys (EC50 of 3.30±0.54nmol, P<0.05 vs. SHR). COX-1 inhibition decreased the α1-AR-induced vasoconstrictor response in WKY but did not affect SHR response, while COX-2 inhibition diminished the response in SHR. Both basal prostacyclin (PGI2) and thromboxane A2 (TxA2) values were higher in SHR kidney perfusates (P<0.05) and were reduced by COX-1 and COX-2 inhibitors in both strains. Furthermore, phenylephrine increased PGI2 through COX-2 in WKY and through COX-1 in SHR, but the agonist did not significantly modify TxA2 in both strains. SignificanceThe data suggest that COX-1contributes to vasoconstrictor effects in WKY kidneys and that COX-2 has the same effect in SHR kidneys. The results also suggest that basal release of COX-2-derived vasoconstrictor prostanoids is involved in renal vascular hypersensitivity in SHR.

Pharmacological identification of α1- and α2-adrenoceptor subtypes involved in the vasopressor responses induced by ergotamine in pithed rats

Ergotamine has been used in clinical practice for the acute treatment of migraine for over 90 years. So far, it is known that ergotamine interacts with diverse receptors (including α1/2-adrenoceptors, 5-HT1, 5-HT2 and D2-like receptors) and that produces increases in mean blood pressure which are significantly blocked by yohimbine, a classical α2-adrenoceptor antagonist with a moderate affinity for α1-adrenoceptors. Since α1/2-adrenoceptors mediate vasopressor and vasoconstrictor responses in the cardiovascular system, this study was designed to identify the α-adrenoceptor subtypes (α1A, α1B, α1D, α2A, α2B and α2C) involved in ergotamine-induced vasopressor responses in pithed rats. In male Wistar pithed rats baseline heart rate and blood pressure were recorded. Then, the vasopressor responses to intravenous (i.v.) bolus injections of ergotamine were determined after administration of vehicle or several α1⧸2-adrenoceptor antagonists. I.v. administration of the antagonists prazosin (α1, 0.1–30µg/kg), rauwolscine (α2, 0.3–300µg/kg), prazosin (0.1µg/kg) plus rauwolscine (0.3µg/kg), 5-methylurapidil (α1A, 100 and 300µg/kg), L-765,314 (α1B, 100 and 300µg/kg), BMY 7378 (α1D, 100 and 300µg/kg), BRL44408 (α2A, 300 and 1000µg/kg) and JP-1302 (α2C, 300µg/kg), significantly blocked the vasopressor responses to ergotamine, whereas imiloxan (α2B, 1000 and 3000µg/kg), JP-1302 (100µg/kg) or the corresponding vehicles (saline 0.9%, propylene glycol 20% or dimethyl sulfoxide 10%; 1ml/kg) failed to modify the responses to ergotamine. The above results suggest that the vasopressor responses to ergotamine in pithed rats are mainly mediated by α1A-, α1B-, α1D-, α2A- and α2C-adrenoceptors and may explain its adverse/therapeutic effects.

The endocannabinoid degradation inhibitors URB597 and JZL184 slightly enhance the inhibitory effect of acute myocardial ischemia on the neurogenic tachycardic and vasopressor responses

The endocannabinoid degradation inhibitors URB597 and JZL184 slightly enhance the inhibitory effect of acute myocardial ischemia on the neurogenic tachycardic and vasopressor responses

Involvement of a presynaptic mechanism in the inhibition of the neurogenic vasopressor response by transverse aortic constriction in pithed rats

Involvement of a presynaptic mechanism in the inhibition of the neurogenic vasopressor response by transverse aortic constriction in pithed rats