β-Adrenoceptor-mediated vascular relaxation in spontaneously hypertensive rats

The sympathetic transmitter norepinephrine inhibits VSMC proliferation induced by TGFβ by suppressing the expression of the TGFβ receptor ALK5 in aorta remodeling

The sympathetic system is involved in the arterial diseases, but its mechanism remains poorly understood. The present study aimed to explore the impact of the sympathetic neurotransmitter norepinephrine (NE) on transforming growth factor (TGF) β signaling and the role of NE in aortic remodeling. Guanethidine was used to induce a regional chemical sympathetic denervation (CSD) in angiotensin II (AngII) and β-aminopropionitrile (BAPN)-induced aortic aneurysm models. The diameter of the aorta was measured, and elastic fiber staining was performed. TGFβ type I receptor kinase (ALK5) expression in rat aortic NE-treated vascular smooth muscle cells (VSMCs) was detected by reverse transcription-quantitative PCR and western blotting. The effects of NE and ALK5 overexpression on migration, proliferation, apoptosis and TGFβ signaling were also evaluated. Furthermore, adrenergic receptor blockers were used to determine which receptor was involved in the modulation on TGFβ signaling by NE. The results of the present study demonstrated that CSD protected rats from AngII+BAPN-induced aortic remodeling and aneurysm formation. Compared with the control group, NE inhibited VSMC proliferation and migration, but promoted apoptosis by suppressing ALK5 expression, reversing the effects of TGFβ signaling through the suppression of the SMAD-dependent canonical pathway and promotion of the non-canonical pathway. These effects were prevented by ALK5 overexpression. The inhibition of α- or β-adrenergic receptors alleviated the NE-mediated suppression of ALK5 expression. In conclusion, regional CSD protected rats from aortic aneurysm. NE inhibited SMAD2/3-dependent TGFβ signaling by suppressing ALK5 expression, which may serve an important role in VSMC biological functions. Both α- and β-adrenergic receptors were involved in the regulation of ALK5 expression by NE. Abnormal sympathetic innervation of the aorta may be used as a therapeutic target in aortic diseases.

LPA1 receptor-mediated thromboxane A2 release is responsible for lysophosphatidic acid-induced vascular smooth muscle contraction

Lysophosphatidic acid (LPA) has been recognized recently as an endothelium-dependent vasodilator, but several lines of evidence indicate that it may also stimulate vascular smooth muscle cells (VSMCs), thereby contributing to vasoregulation and remodeling. In the present study, mRNA expression of all 6 LPA receptor genes was detected in murine aortic VSMCs, with the highest levels of LPA₁, LPA₂, LPA₄, and LPA₆ In endothelium-denuded thoracic aorta (TA) and abdominal aorta (AA) segments, 1-oleoyl-LPA and the LPA_1-3 agonist VPC31143 induced dose-dependent vasoconstriction. VPC31143-induced AA contraction was sensitive to pertussis toxin (PTX), the LPA_1&3 antagonist Ki16425, and genetic deletion of LPA₁ but not that of LPA₂ or inhibition of LPA₃, by diacylglycerol pyrophosphate. Surprisingly, vasoconstriction was also diminished in vessels lacking cyclooxygenase-1 [COX1 knockout (KO)] or the thromboxane prostanoid (TP) receptor (TP KO). VPC31143 increased thromboxane A₂ (TXA₂) release from TA of wild-type, TP-KO, and LPA₂-KO mice but not from LPA₁-KO or COX1-KO mice, and PTX blocked this effect. Our findings indicate that LPA causes vasoconstriction in VSMCs, mediated by LPA₁-, G_i-, and COX1-dependent autocrine/paracrine TXA₂ release and consequent TP activation. We propose that this new-found interaction between the LPA/LPA₁ and TXA₂/TP pathways plays significant roles in vasoregulation, hemostasis, thrombosis, and vascular remodeling.-Dancs, P. T., Ruisanchez, E., Balogh, A., Panta, C. R., Miklós, Z., Nüsing, R. M., Aoki, J., Chun, J., Offermanns, S., Tigyi, G., Benyó, Z. LPA₁ receptor-mediated thromboxane A₂ release is responsible for lysophosphatidic acid-induced vascular smooth muscle contraction.

Pressor recovery after acute stress is impaired in high fructose-fed Lean Zucker rats

Insulin resistance is a powerful predictor of cardiovascular disease; however, the mechanistic link remains unclear. This study aims to determine if early cardiovascular changes associated with short‐term fructose feeding in the absence of obesity manifest as abnormal blood pressure control. Metabolic dysfunction was induced in Lean Zucker rats by short‐term high‐fructose feeding. Rats were implanted with telemetry devices for the measurement of mean arterial blood pressure (MAP) and subjected to air jet stress at 5 and 8 weeks after feeding. Additional animals were catheterized under anesthesia for the determination of MAP and blood flow responses in the hind limb and mesenteric vascular beds to intravenous injection of isoproterenol (0.001–0.5 μm), a β‐adrenergic agonist. Metabolic dysfunction in high‐fructose rats was not accompanied by changes in 24‐h MAP. Yet, animals fed a high‐fructose diet for 8 weeks exhibited a marked impairment in blood pressure recovery after air‐jet stress. Dose‐dependent decreases in MAP and peripheral blood flow in response to isoproterenol treatment were significantly attenuated in high‐fructose rats. These data suggest that impaired blood pressure recovery to acute mental stress precedes the onset of hypertension in the early stages of insulin resistance. Further, blunted responses to isoproterenol implicate β₂‐adrenergic sensitivity as a possible mechanism responsible for altered blood pressure control after short‐term high‐fructose feeding.

Blood pressure variability provokes vascular β-adrenoceptor desensitization in rats

Spontaneous variation in blood pressure is defined as 'blood pressure variability' (BPV). Sinoaortic denervation (SAD) is characterized by BPV without sustained hypertension. In the present study, we investigated whether BPV could be related to vascular β-adrenoceptor desensitization in rats. Three days after surgery (SAD and control), aortic rings were placed in an organ chamber and the relaxation stimulated by β-adrenoceptor agonists, isoprenaline, terbutaline, BRL37344 and cyanopindolol was verified. The participation of intracellular nucleotides signaling pathways was also verified using forskolin, sodium nitroprusside and acetylcholine to induce relaxation. The effects of BPV on the increase in endothelial cytosolic Ca(2+) concentration stimulated by the β2-adrenoceptor agonist was examined by confocal microscopy. In addition, the vascular expression of the β2-adrenoceptor was also examined by immunohistochemistry. The results show that isoprenaline and terbutaline-induced relaxation was lower in the aortas of rats with BPV. Relaxation responses to other vasorelaxant compounds were similar in both groups of rats. Histological analysis revealed a lower level of β2-adrenoceptor and confocal microscopy showed minor cytosolic Ca(2+) concentration in endothelial cells stimulated by the β2-adrenoceptor agonist in rats with BPV. In conclusion, BPV leads to desensitization of the β2-adrenoceptor, which could contribute to worse β-adrenoceptor agonist-induced relaxation in isolated aortas.

β3-adrenoceptors inhibit stimulated norepinephrine release in spontaneously hypertensive rats

Here, the influence of β₃-adrenoceptors on catecholamine release in normotensive and spontaneously hypertensive rats was analyzed. Blood pressure was recorded through a femoral artery catheter, and cardiac output by ascending aorta flow. Time from onset of flow to maximum rise in flow indicated inotropy. Total peripheral vascular resistance (TPR) was calculated. Norepinephrine release was stimulated with tyramine, which allowed presynaptic release-control to be reflected as changes in the plasma norepinephrine concentration. β₃-adrenoceptor agonist (BRL37344) reduced baseline vascular resistance, the tyramine-stimulated norepinephrine overflow and the positive inotropic response to tyramine in hypertensive but not normotensive rats. β₃-adrenoceptor antagonist (SR59230A) reduced tyramine-stimulated norepinephrine release in both strains and the secretion of epinephrine in hypertensive rats. SR59230A reduced tyramine-induced tachycardia in normotensive rats, and prevented down-regulation of the tyramine-induced rise in resistance in hypertensive rats. It was concluded that the contradicting results obtained by agonist vs. antagonist, could be explained by their interaction with two different β-adrenoceptors: The BRL37344-dependent inhibition of stimulated norepinephrine release and positive inotropic response to tyramine was compatible with stimulation of β₃-adrenoceptor coupling to inhibitory G-protein. This was observed only in hypertensive rats during stimulated, high levels of circulating catecholamines. The effect of BRL37344 on baseline vascular resistance was compatible with activation of β₃-adrenoceptor coupling to endothelial nitric oxide synthase. The inhibitory effect of SR59230A on tyramine-stimulated norepinephrine release in both strains, the increased TPR-response to tyramine in hypertensive rats and tachycardia in normotensive rats may result from inhibition of the low-affinity-state β₁-adrenoceptor, also known as the putative β₄-adrenoceptor.

Different β-adrenoceptor subtypes coupling to cAMP or NO/cGMP pathways: implications in the relaxant response of rat conductance and resistance vessels

BACKGROUND AND PURPOSE

To analyse the relative contribution of β1 -, β2 - and β3 -adrenoceptors (Adrb) to vasodilatation in conductance and resistance vessels, assessing the role of cAMP and/or NO/cGMP signalling pathways.

EXPERIMENTAL APPROACH

Rat mesenteric resistance artery (MRA) and aorta were used to analyse the Adrb expression by real-time-PCR and immunohistochemistry, and for the pharmacological characterization of Adrb-mediated activity by wire myography and tissue nucleotide accumulation.

KEY RESULTS

The mRNAs and protein for all Adrb were identified in endothelium and/or smooth muscle cells (SMCs) in both vessels. In MRA, Adrb1 signalled through cAMP, Adrb3 through both cAMP and cGMP, but Adrb2, did not activate nucleotide formation; isoprenaline relaxation was inhibited by propranolol (β1 , β2 ), CGP20712A (β1 ), and SQ22536 (adenylyl cyclase inhibitor), but not by ICI118,551 (β2 ), SR59230A (β3 ), ODQ (soluble guanylyl cyclase inhibitor), L-NAME or endothelium removal. In aorta, Adrb1 signalled through cAMP, while β2 - and β3 -subtypes through cGMP; isoprenaline relaxation was inhibited by propranolol, ICI118,551, ODQ, L-NAME, and to a lesser extent, by endothelium removal. CL316243 (β3 -agonist) relaxed aorta, but not MRA.

CONCLUSION AND IMPLICATION

Despite all three Adrb subtypes being found in both vessels, Adrb1, located in SMCs and acting through the adenylyl cyclase/cAMP pathway, are primarily responsible for vasodilatation in MRA. However, Adrb-mediated vasodilatation in aorta is driven by endothelial Adrb2 and Adrb3, but also by the Adrb2 present in SMCs, and is coupled to the NO/cGMP pathway. These results could help to understand the different physiological roles played by Adrb signalling in regulating conductance and resistance vessels.

Involvement of BKCa and KV potassium channels in cAMP-induced vasodilatation: their insufficient function in genetic hypertension

Spontaneously hypertensive rats (SHR) are characterized by enhanced sympathetic vasoconstriction, whereas their vasodilator mechanisms are relatively attenuated compared to their high BP. The objective of our in vivo study was to evaluate whether the impaired function of BKCa and/or KV channels is responsible for abnormal cAMP-induced vasodilatation in genetic hypertension. Using conscious SHR and normotensive WKY rats we have shown that under the basal conditions cAMP overproduction elicited by the infusion of beta-adrenoceptor agonist (isoprenaline) caused a more pronounced decrease of baseline blood pressure (BP) in SHR compared to WKY rats. Isoprenaline infusion prevented BP rises induced by acute NO synthase blockade in both strains and it also completely abolished the fully developed BP response to NO synthase blockade. These cAMP-induced vasodilator effects were diminished by the inhibition of either BKCa or KV channels in SHR but simultaneous blockade of both K(+) channel types was necessary in WKY rats. Under basal conditions, the vasodilator action of both K(+) channels was enhanced in SHR compared to WKY rats. However, the overall contribution of K(+) channels to cAMP-induced vasodilator mechanisms is insufficient in genetic hypertension since a concurrent activation of both K(+) channels by cAMP overproduction is necessary for the prevention of BP rise elicited by acute NO/cGMP deficiency in SHR. This might be caused by less effective activation of these K(+) channels by cAMP in SHR. In conclusion, K(+) channels seem to have higher activity in SHR, but their vasodilator action cannot match sufficiently the augmented vasoconstriction in this hypertensive strain.

Exercício físico, receptores β-adrenérgicos e resposta vascular

O exercício aeróbio promove efeitos benéficos na prevenção e tratamento de doenças como hipertensão arterial, aterosclerose, insuficiência venosa e doença arterial periférica. Os receptores β-adrenérgicos estão presentes em várias células. No sistema cardiovascular, promovem inotropismo e cronotropismo positivo cardíaco e relaxamento vascular. Embora os efeitos do exercício tenham sido investigados em receptores cardíacos, estudos focados nos vasos são escassos e controversos. Esta revisão abordará os efeitos do exercício físico sobre os receptores β-adrenérgicos vasculares em modelos animais e humanos e os mecanismos celulares envolvidos na resposta relaxante. Em geral, os estudos mostram resultantes conflitantes, onde observam diminuição, aumento ou nenhum efeito do exercício físico sobre a resposta relaxante. Assim, os efeitos do exercício na sensibilidade β-adrenérgica vascular merecem maior atenção, e os resultados mostram que a área de fisiopatologia vascular é um campo aberto para a descoberta de novos compostos e avanços na prática clínica.

Nonlinear mixed effects models applied to cumulative concentration–response curves

Objectives

In experimental pharmacology, drug effect studies currently establish and analyse cumulative concentration–response curves (CCRC) under repeated measurements designs. Usually the CCRC parameters are estimated using the Hill's function in a nonlinear regression for independent data. The two-way analysis of variance is generally used to identify a statistical difference between the responses for two treatments but that analysis does not take into account the nonlinearity of the model and the heteroscedasticity (uneven distribution) of the data. We presently tested the possibility of finding a statistical solution for the nonlinear response in repeated measurements data using the nonlinear mixed effects (nlme) models.

Methods

Experimental data sets, originating from studies on β-adrenoceptor-induced relaxation in rat thoracic aorta ring, were analysed using the nlme methods.

Key findings

Comparison with classical methods showed the superiority of the nlme models approach. For each pharmacological parameter (Em, n, pD2), a point estimate, a standard error and a confidence interval are returned by the nlme procedures respecting the assumption of independency and normality of the residuals.

Conclusions

Using the method presently described, it is now possible to detect significant differences for each pharmacological parameter estimated in different situations, even for designs with small samples size (i.e. at least six complete curves).

The impact of alpha1-adrenoceptors up-regulation accompanied by the impairment of beta-adrenergic vasodilatation in hypertension

In human and animal hypertension models, increased activity of G-protein-coupled receptor kinase (GRK) 2 determines a generalized decrease of beta-adrenergic vasodilatation. We analyzed the possibility of differential changes in the expression and functionality of alpha(1A), alpha(1B), alpha(1D), beta(1), beta(2), and beta(3)-ARs also being involved in the process. We combined the quantification of mRNA levels with immunoblotting and functional studies in aortas of young and adult spontaneously hypertensive rats (SHRs) and their controls (Wistar Kyoto). We found the expression and function of beta(1)-adrenoceptors in young prehypertensive SHRs to be higher, whereas a generalized increase in the expression of the six adrenoceptors and GRK2 was observed in aortas of adult hypertensive SHRs. alpha(1D)- and beta(3)-adrenoceptors, the subtypes that are more resistant to GRK2-mediated internalization and mostly expressed in rat aorta, exhibited an increased functional role in hypertensive animals, showing two hemodynamic consequences: 1) an increased sensitivity to the vasoconstrictor stimulus accompanied by a decreased sensitivity to the vasodilator stimulus (alpha(1D)-ARs are the most sensitive to agonists, and beta(3)-ARs are the least sensitive to agonists); and 2) a slower recovery of the basal tone after adrenergic stimulus removal because of the kinetic characteristic of the alpha(1D) subtype. These functional changes might be involved in the greater sympathetic vasoconstrictor tone observed in hypertension.

Role of nitrosative stress in early neuropathy and vascular dysfunction in streptozotocin-diabetic rats

Evidence for important roles of the highly reactive oxidant peroxynitrite in diabetic complications is emerging. We evaluated the role of peroxynitrite in early peripheral neuropathy and vascular dysfunction in STZ-diabetic rats. In the first dose-finding study, control and STZ-diabetic rats were maintained with or without the potent peroxynitrite decomposition catalyst Fe(III)tetrakis-2-(N-triethylene glycol monomethyl ether) pyridyl porphyrin (FP15) at 3, 5, or 10 mg.kg(-1).day(-1) in the drinking water for 4 wk after an initial 2 wk without treatment for assessment of early neuropathy. In the second study with similar experimental design, control and STZ-diabetic rats were maintained with or without FP15, 5 mg.kg(-1).day(-1), for vascular studies. Rats with 6-wk duration of diabetes developed motor and sensory nerve conduction velocity deficits, mechanical hyperalgesia, and tactile allodynia in the absence of small sensory nerve fiber degeneration. They also had increased nitrotyrosine and poly(ADP-ribose) immunofluorescence in the sciatic nerve and dorsal root ganglia. All these variables were dose-dependently corrected by FP15, with minimal differences between the 5 and 10 mg.kg(-1).day(-1) doses. FP15, 5 mg.kg(-1).day(-1), also corrected endoneurial nutritive blood flow and nitrotyrosine, but not superoxide, fluorescence in aorta and epineurial arterioles. Diabetes-induced decreases in acetylcholine-mediated relaxation by epineurial arterioles and coronary and mesenteric arteries, as well as bradykinin-induced relaxation by coronary and mesenteric arteries, were alleviated by FP15 treatment. The findings reveal the important role of nitrosative stress in early neuropathy and vasculopathy and provide the rationale for further studies of peroxynitrite decomposition catalysts in long-term diabetic models.

Defective vasodilatory mechanisms in hypertension: a G-protein-coupled receptor perspective

PURPOSE OF REVIEW

The purpose of this article is to review recent evidence relating to the regulation of vasodilatation and alterations in these mechanisms in the hypertensive state. In particular, we will focus on signaling systems regulating nitric oxide synthase and intracellular cyclic AMP - the two principal mechanisms mediating vasodilatation.

RECENT FINDINGS

G-protein-coupled-receptor-mediated, endothelial-dependent processes are increasingly being seen as critical vasodilatory mechanisms. Impairment of endothelial responses to G-protein-coupled receptor activation is a key component of the decrease in G-protein-coupled-receptor-mediated vasodilatation in hypertension. In addition, an 'uncoupling' of the G-protein-coupled receptor/G-protein complex is the principal mechanism underlying impaired G-protein-coupled-receptor-mediated vasodilatation in hypertension. Alterations in G-protein-coupled receptor kinase function have a central role underlying this defect. Finally, the importance of the expression of genetic variants of G-protein-coupled receptors and G-proteins underlying the defect in vasodilatation in hypertension remains contentious.

SUMMARY

G-protein signaling pathways in the vasculature play an important role in both the development and the maintenance of the hypertensive state. It is unlikely, however, that any single defect in the G-protein-linked vasodilatory pathway will ever be shown to be the sole cause of hypertension.

Positive inotropic and lusitropic effects mediated via the low-affinity state of beta1-adrenoceptors in pithed rats

1 Activation by CGP 12177 and cyanopindolol of the human and rat low-affinity state of beta(1)-adrenoceptors increases frequency and contractile force and hastens relaxation in isolated cardiac tissues, and probably relaxes isolated vessels. In order to identify the positive inotropic, positive lusitropic and vasodilator effects of both agonists also in vivo, we have determined their effects on the left ventricular systolic pressure (LVSP), the rate of intraventricular pressure rise (+dP dt(-1)(max)) and decline (-dP dt(-1)(max)), the diastolic blood pressure (DBP) and the mesenteric blood flow (MBF) in pithed and vagotomized rats. 2 CGP 12177 (0.1-100 nmol kg(-1)) and cyanopindolol (1-1000 nmol kg(-1)) dose-dependently enhanced all cardiac parameters. The nonselective beta-adrenoceptor antagonist bupranolol 10 micromol kg(-1) diminished the CGP 12177 (100 nmol kg(-1))-stimulated increases in LVSP from 26.3+/-8.2 to 13.1+/-1.8 mmHg (P<0.05), +dP dt(-1)(max) from 5287+/-290 to 2439+/-296 mmHg s(-1) (P<0.001) and -dP dt(-1)(max) from -3836+/-301 to -2187+/-443 mmHg s(-1) (P<0.05), respectively. The beta(1)-adrenoceptor antagonist CGP 20712A 10 micromol kg(-1) (known to block the low-affinity state of beta(1)-adrenoceptors at high doses) inhibited increases in +/-dP dt(-1)(max) elicited by the highest dose of CGP 12177. 3 The highest doses of CGP 12177 and cyanopindolol increased DBP by about 10 mmHg and MBF by 1.4+/-0.3 and 0.6+/-0.3 ml min(-1), respectively. The vascular effects of CGP 12177 were not affected by bupranolol and CGP 20712A. 4 In conclusion, activation of the low-affinity state of beta(1)-adrenoceptors by CGP 12177 and cyanopindolol in pithed rats causes a positive inotropic and lusitropic effect. By contrast, the vascular effects of CGP 12177 and cyanopindolol are not mediated by these receptors and have only marginal influence under in vivo conditions.