Cross Talk between Angiotensin II and Alpha 1 Adrenergic Receptors in Rabbit Aorta: Role of Endothelium

The α1D-adrenoreceptor antagonist BMY 7378 reverses cardiac hypertrophy in spontaneously hypertensive rats

OBJECTIVE

The α1D-adrenoreceptor (α1D-AR) is involved in angiotensin II-induced vascular remodeling and hypertension. Whether α1D-AR plays a role in hypertension-associated cardiac hypertrophy is unclear. Here we investigated effects of BMY 7378, a selective α1D-AR antagonist, on cardiac status in aged spontaneously hypertensive rats (SHR).

METHODS

Male SHR were studied during the phase of developing hypertension (5 and 10 weeks old) and once hypertension was established (20 and 30 weeks old) to assess the evolution of cardiac hypertrophy. Age-matched WKY rats were studied as controls. Thirty-week-old SHR were treated for 4 weeks with BMY 7378 (10 mg/kg per day, o.a.), or captopril (angiotensin-converting enzyme inhibitor, 40 mg/kg per day, o.a.) (as a positive control). Blood pressure and cardiac function were measured in vivo, cardiac hypertrophy by histology, and α1D-AR protein expression by immunofluorescence.

RESULTS

By 30 weeks of age, SHR exhibited significant hypertension and cardiac hypertrophy. BMY 7378 and captopril decreased blood pressure and improved hemodynamic parameters and cardiac function in treated SHR vs. untreated SHR (P < 0.05). Histology showed increased cardiomyocyte size, fibrosis, and left ventricular hypertrophy in SHR hearts. BMY 7378 ameliorated fibrosis and cardiac hypertrophy, but had no effect on cardiomyocyte size in SHR. Effects of BMY 7378 were associated with increased α1D-AR protein expression in SHR.

CONCLUSION

Our data indicate that pharmacological antagonism of α1D-AR reduces blood pressure and associated cardiac hypertrophy in aged SHR. These findings suggest that the α1D-AR plays a pathophysiological role in the development of hypertension and cardiac target organ damage in SHR.

Evidence of changes in alpha-1/AT1 receptor function generated by diet-induced obesity

To study whether hypercaloric diet-induced obesity deteriorates vascular contractility of rat aorta through functional changes in α₁ adrenergic and/or AT1 Angiotensin II receptors. Angiotensin II- or phenylephrine-induced contraction was tested on isolated aorta rings with and without endothelium from female Wistar rats fed for 7 weeks with hypercaloric diet or standard diet. Vascular expression of Angiotensin II Receptor type 1 (AT1R), Angiotensin II Receptor type 2 (AT2R), Cyclooxygenase-1 (COX-1), Cyclooxygenase-2 (COX-2), inducible Nitric Oxide Synthase (iNOS) and endothelial Nitric Oxide Synthase (eNOS), as well as blood pressure, glucose, insulin and angiotensin II blood levels were measured. Diet-induced obesity did not significantly change agonist-induced contractions (Emax and pD₂ hypercaloric diet vs standard diet n.s.d.) of both intact (e+) or endothelium free (e-) vessels but significantly decrease both phenylephrine and angiotensin II contraction (Emax p < 0.01 hypercaloric diet vs standard diet) in the presence of both prazosin and losartan but only in endothelium-intact vessels. Diet-induced obesity did not change angiotensin II AT1, AT2 receptor proteins expression but reduced COX-1 and NOS2 ( p < 0.05 vs standard diet). Seven-week hypercaloric diet-induced obesity produces alterations in vascular adrenergic and angiotensin II receptor dynamics that suggest an endothelium-dependent adrenergic/angiotensin II crosstalk. These changes reflect early-stage vascular responses to obesity.

Elucidation of the profound antagonism of contractile action of phenylephrine in rat aorta effected by an atypical sympathomimetic decongestant

Vasoconstrictive properties of sympathomimetic drugs are the basis of their widespread use as decongestants and possible source of adverse responses. Insufficiently substantiated practice of combining decongestants in some marketed preparations, such are those containing phenylephrine and lerimazoline, may affect the overall contractile activity, and thus their therapeutic utility. This study aimed to examine the interaction between lerimazoline and phenylephrine in isolated rat aortic rings, and also to assess the substrate of the obtained lerimazoline-induced attenuation of phenylephrine contraction. Namely, while lower concentrations of lerimazoline (10⁻⁶ M and especially 10⁻⁷ M) expectedly tended to potentiate the phenylephrine-induced contractions, lerimazoline in higher concentrations (10⁻⁴ M and above) unexpectedly and profoundly depleted the phenylephrine concentration-response curve. Suppression of NO with NO synthase (NOS) inhibitor N^w-nitro-L-arginine methyl ester (L-NAME; 10⁻⁴ M) or NO scavanger OHB₁₂ (10⁻³ M), as well as non-specific inhibition of K⁺-channels with tetraethylammonium (TEA; 10⁻³ M), have reversed lerimazoline-induced relaxation of phenylephrine contractions, while cyclooxygenase inhibitor indomethacin (10⁻⁵ M) did not affect the interaction between two vasoconstrictors. At the receptor level, non-selective 5-HT receptor antagonist methiothepin reversed the attenuating effect of lerimazoline on phenylephrine contraction when applied at 3×10⁻⁷ and 10⁻⁶ M, but not at the highest concentration (10⁻⁴ M). Neither the 5-HT_1D-receptor selective antagonist BRL 15572 (10⁻⁶ M) nor 5-HT₇ receptor selective antagonist SB 269970 (10⁻⁶ M) affected the lerimazoline-induced attenuation of phenylephrine activity. The mechanism of lerimazoline-induced suppression of phenylephrine contractions may involve potentiation of activity of NO and K⁺-channels and activation of some methiothepin-sensitive receptors, possibly of the 5-HT_2B subtype.

Experimental gestational diabetes mellitus induces blunted vasoconstriction and functional changes in the rat aorta

Diabetic conditions increase vascular reactivity to angiotensin II in several studies but there are scarce reports on cardiovascular effects of hypercaloric diet (HD) induced gestational diabetes mellitus (GDM), so the objective of this work was to determine the effects of HD induced GDM on vascular responses. Angiotensin II as well as phenylephrine induced vascular contraction was tested in isolated aorta rings with and without endothelium from rats fed for 7 weeks (4 before and 3 weeks during pregnancy) with standard (SD) or hypercaloric (HD) diet. Also, protein expression of AT₁R, AT₂R, COX-1, COX-2, NOS-1, and NOS-3 and plasma glucose, insulin, and angiotensin II levels were measured. GDM impaired vasoconstrictor response (P < 0.05 versus SD) in intact (e+) but not in endothelium-free (e−) vessels. Losartan reduced GDM but not SD e− vasoconstriction (P < 0.01 versus SD). AT₁R, AT₂R, and COX-1 and COX-2 protein expression were significantly increased in GDM vessels (P < 0.05 versus SD). Results suggest an increased participation of endothelium vasodilator mediators, probably prostaglandins, as well as of AT₂ vasodilator receptors as a compensatory mechanism for vasoconstrictor changes generated by experimental GDM. Considering the short term of rat pregnancy findings can reflect early stage GDM adaptations.

Alterations in the baroreceptor-heart rate reflex in conscious inbred polydipsic (STR/N) mice

STR/N is an inbred strain of mice which is known to exhibit extreme polydipsia and polyuria. We previously found central administration of angiotensin II enhanced cardiovascular responses in STR/N mice than normal mice, suggesting that STR/N mice might exhibit different cardiovascular responses. Therefore, in this study, we investigated daily mean arterial blood pressure and heart rate, and changes in the baroreceptor-heart rate reflex in conscious STR/N mice and control (ICR) mice. We found that variability in daily mean arterial blood pressure and heart rate was significantly larger in STR/N mice than in ICR mice (p<0.05). There was a stronger response to phenylephrine (PE) in STR/N mice than in ICR mice. For baroreceptor reflex sensitivity, in the rapid response period, the slopes of PE and sodium nitroprusside (SNP) were more negative in STR/N mice than in ICR mice. In the later period, the slopes of PE and SNP were negatively correlated between heart rate and blood pressure in ICR mice, but their slopes were positively correlated in STR/N mice. These results indicated that STR/N mice exhibited the different cardiovascular responses than ICR mice, suggesting that the dysfunction of baroreceptor reflex happened in conscious STR/N mice.

Vascular Reactivity Concerning Orthosiphon stamineus Benth-Mediated Antihypertensive in Aortic Rings of Spontaneously Hypertensive Rats

Orthosiphon stamineus Benth has been traditionally used to treat hypertension. The study aimed to investigate the vascular reactivity of water extract (WOS) and water : methanolic (1 : 1) extract (WMOS) of Orthosiphon stamineus Benth and AT₁ receptors blocker in the mechanisms of antihypertensive mediated by α₁-adrenergic receptor and EDNO and PGI₂ releases in the SHR aortic rings. SHR (230–280 g) were divided into four groups: control, WOS, WMOS, and losartan. After being fed orally for 14 days, the aorta was harvested and subjected to PE (10⁻⁹ to 10⁻⁵ M) and ACh (10⁻⁹ to 10⁻⁵ M) with and without L-NAME (100 µM) and indomethacin (10 µM), respectively. WOS, WMOS, and losartan significantly reduced the contractile responses to PE intact suggesting the importance of endothelium in vasorelaxation. Losartan significantly enhanced the ACh-induced vasorelaxation. L-NAME significantly inhibited the ACh-induced relaxation in all groups. Indomethacin enhanced ACh-induced vasorelaxation in WMOS. Collectively, Orthosiphon stamineus leaves extract reduced vasoconstriction responses by the alteration of α₁-adrenergic and AT₁ receptors activities. The involvement of EDNO releases was clearly observed in this plant. In WOS, PGI₂ releases might not participate in the ACh-induced vasorelaxation. However, in WMOS, enhancement of vasorelaxation possibly due to continuous release of PGI₂.

Vascular hyporeactivity to angiotensin II and noradrenaline in a rabbit model of obesity

This study was conducted to explore the vascular reactivity of angiotensin II and noradrenaline and their relationship with endothelial function in rabbits fed a high-fat diet (HFD). The animals were fed either an HFD or regular chow [control diet (CD)]. After 12 weeks, the rabbits fed the HFD showed higher blood pressure, body weight, and insulin levels. Glucose tolerance was impaired and positively related to blood pressure. An endothelium-independent decrease of the sensitivity to angiotensin II [pD2 endothelium-intact aortic rings (E+) in CD: 8.02 ± 0.07 vs. HFD: 7.60 ± 0.01; pD2 endothelium-removed aortic rings (E-) in CD: 8.16 ± 0.11 vs. HFD: 7.83 ± 0.16] and noradrenaline (pD2 E+ in CD: 6.36 ± 0.06 vs. HFD: 5.29 ± 0.06; pD2 E- in CD: 6.11 ± 0.08 vs. HFD: 5.80 ± 0.08) was found. Noradrenaline desensitized the angiotensin II response (pD2 with noradrenaline pretreatment in E+: 7.03 ± 0.16; in E-: 7.10 ± 0.02), but angiotensin II did not change the noradrenaline response. Acetylcholine maximal relaxation and basal nitric oxide (NO) release were comparable in both diet groups. The efficacy of angiotensin II (Rmax CD: 4604 ± 574 mg vs. HFD: 3251 ± 533 mg) and noradrenaline (Rmax CD: 11,675 ± 804 mg vs. HFD: 7975 ± 960 mg) was reduced in E+. L-N-nitroarginine methyl ester (L-NAME) recovered the efficacy of noradrenaline (Rmax L-NAME: 12,015 ± 317 mg). In contrast, L-NAME had no effect on the angiotensin II response. Noradrenaline enhanced NO levels, but angiotensin II did not. Therefore, NO was associated with hyporeactivity to noradrenaline. The resting potential was more negative in E+, and the endothelium diminished the angiotensin II-induced depolarization. These findings demonstrated that the crosstalk and the endothelium may induce hyporeactivity to angiotensin II and noradrenaline as a mechanism to compensate the increase in the blood pressure in HFD-induced obesity.

MMP-2 mediates angiotensin II-induced hypertension under the transcriptional control of MMP-7 and TACE

Development of cardiovascular disease induced by excessive Gq protein-coupled receptor agonist stimulation depends on signaling networks involving multiple matrix metalloproteinases (MMPs) and metalloproteinase disintegrins (ADAMs). Here, we hypothesized that MMP-2, being a major gelatinase in cardiac and vascular tissue, was likely to play a key role in cardiovascular homeostasis. We targeted MMP-2 using complementary and overlapping approaches involving pharmacological inhibition and RNA interference in mice treated with angiotensin II (1.4 mg/kg per day) for 12 days. We studied the development of hypertension (by tail cuff plethysmography), cardiac hypertrophy (by M-mode echocardiography, cardiomyocyte cross-sectional area, and quantitative real-time polymerase chain reaction (qRT-PCR) analysis of hypertrophy marker genes), and fibrosis (by picrosirius red collagen staining and qRT-PCR analysis of fibrosis marker genes) in mice receiving angiotensin II. We found that angiotensin II infusion upregulated MMP-2 concurrent with the development of hypertension, hypertrophy, and fibrosis. This upregulation of MMP-2 depended on MMP-7 and TACE (tumor necrosis factor-α convertase, ADAM-17). RNA interference targeting MMP-7 and TACE attenuated the angiotensin II-induced upregulation of MMP-2 and prevented the development of hypertension, as well as development of cardiac hypertrophy and fibrosis. In contrast, pharmacological inhibition and RNA interference of MMP-2 attenuated angiotensin II-induced hypertension, without influencing development of cardiac hypertrophy or fibrosis. Downstream of MMP-7 and TACE, MMP-2 mediated angiotensin II-induced hypertension, but did not mediate cardiac hypertrophy or fibrosis. This suggests a functional specialization of MMP-2 in agonist-induced cardiovascular disease development that has potential implications for the design of metalloproteinase-based therapeutic strategies.

Age-dependent differential crosstalk between alpha(1)-adrenergic and angiotensin receptors

BACKGROUND

Previous reports of crosstalk between alpha(1)- adrenergic receptors (alpha(1)-AR) and angiotensin receptors (ATR) have pointed to the existence of physiological regulation between the sympathetic nervous system and the renin-angiotensin system at the receptor level. This regulation may have an important role in the control of blood pressure and may be modified in different cardiovascular pathologies. Aging is considered to be an independent cardiovascular risk factor. Nevertheless, neither the variation in physiological action or interaction of signal transduction between these two receptors as a result of aging has been established. To clarify these aspects, the interaction between alpha(1)-AR and ATR was evaluated.

METHODS

The inotropic response of alpha(1)-AR to agonists was assessed in the presence and absence of angiotensin II using the left atria of 3.5-, 12-, 18- and 24-month-old (young adult, middle aged, elderly and aged, respectively) male Wistar rats. In the four age groups of rat hearts, the activities of tyrosine kinase were measured when just the AT(1)R subtype was activated, or when both alpha(1)-AR and AT(1)R were activated. The activities of cytosolic phospholipase A(2) and the levels of cyclic GMP were investigated when just the AT(2)R subtype was activated, or when both alpha(1)-AR and AT(2)R were activated.

RESULTS

No effect was found on the cumulative concentration-response curve for phenylephrine when AT(1)R was activated in 3.5- or 12-month-old rats. However, in 18- and 24-month-old rats, the maximum positive inotropic response and the negative logarithm of the effective 50% concentration increased markedly. No effect was found on the cumulative concentration response curve induced by phenylephrine when AT(2)R was activated. The activities of tyrosine kinase increased significantly in 3.5- and 12-month-old rats, but there was no difference in 18- and 24-month-old rats when alpha(1)-AR and AT(1)R were both activated compared with when just AT(1)R was activated. Cytosolic phospholipase A(2) activity and cyclic GMP levels decreased significantly when both alpha(1)-AR and AT(2)R were activated compared with when just AT(2)R was activated.

CONCLUSIONS

In the isolated left atria of elderly and aged rats, the activation of AT(1)R enhanced the positive inotropic response induced by the activation of alpha(1)-AR. The activation of AT(2)R had no effect on the positive inotropic response induced by the activation of alpha(1)-AR. The action of alpha(1)-AR increased the signal transduction of AT(1)R in young-adult and middle-aged rat hearts but had no effect in elderly and aged hearts. The action of alpha(1)-AR had no effect on AT(2)R signal transduction.

Bidirectional regulation of dopamine D2 and neurotensin NTS1 receptors in dopamine neurons

Several lines of evidence suggest a close association between dopamine (DA) and neurotensin (NT) systems in the CNS. Indeed, in the rodent brain, abundant NT-containing fibres are found in DA-rich areas such as the ventral tegmental area and substantia nigra. Moreover, it has been shown in vivo that NT, acting through its high-affinity receptor (NTS1), reduces the physiological and behavioural effects of DA D2 receptor (D2R) activation, a critical autoreceptor feedback system regulating DA neurotransmission. However, the mechanism of this interaction is still elusive. The aim of our study was thus to reproduce in vitro the interaction between D2R and NTS1, and then to characterize the mechanisms implicated. We used a primary culture model of DA neurons prepared from transgenic mice expressing green fluorescent protein under the control of the tyrosine hydroxylase promoter. In these cultures, DA neurons endogenously express both D2R and NTS1. Using electrophysiological recordings, we show that activation of D2R directly inhibits the firing rate of DA neurons. In addition, we find that NT, acting through a NTS1-like receptor, is able to reduce D2R autoreceptor function independently of its ability to enhance DA neuron firing, and that this interaction occurs through a protein kinase C- and Ca(2+)-dependent mechanism. Furthermore, prior activation of D2R reduces the ability of NTS1 to induce intracellular Ca(2+) mobilization. Our findings provide evidence for bidirectional interaction between D2R and NTS1 in DA neurons, a regulatory mechanism that could play a key role in the control of the activity of these neurons.

Nitric oxide modulates angiotensin II-induced endothelial vasoconstrictor prostanoid release

This study investigated the modulation of angiotensin II-induced endothelial prostanoid release in rabbit aortic rings. Two cumulative dose response curves with 90-min washing interval were performed. Incubation with L-N(G)-nitroarginine methyl ester (L-NAME) 10(-4) M increased angiotensin II maximal contractile response (E(max)). This effect was reversed by indomethacin 10(-5) M, diphenyliodinum 10(-5) M, Tempol 10(-5) M or ascorbic acid 10(-4) M in both cumulative dose response curves and by SQ 29548 10(-6) M in the second cumulative dose response curve. When segments were treated with tetraethylamonium 10(-3) M but not with glibenclamide 10(-5) M during the washing period, L-NAME recovered its ability to enhance the E(max) in arteries incubated with SQ 29548.

CONCLUSIONS

nitric oxide modulates angiotensin II-induced endothelial release of cyclooxygenase-dependent eicosanoids, one of which acts through thromboxane A(2)/prostaglandin H(2) receptors and would decrease K(Ca) channel activity. An increase in free radical production may account for the enhancement of such prostanoid release. Furthermore, it was found that in the present conditions, the release of the hyperpolarizing factor would improve in order to maintain the vascular tone.