Mechanism of the Vascular Angiotensin II/α2-Adrenoceptor Interaction

α2A-Adrenergic Receptor Inhibits the Progression of Cervical Cancer Through Blocking PI3K/AKT/mTOR Pathway

Objective

The study aimed to investigate the effect of α2A-adrenergic receptor (ADRA2A) on cervical cancer and the potential mechanisms of ADRA2A on phosphatidylinositol 3′-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway in cervical cancer cells.

Methods

In our study, ADRA2A expression was evaluated by analyzing cervical cancer RNA sequencing dataset from the GEPIA. The prognostic values of ADRA2A were evaluated by Kaplan–Meier method using the Cancer Genome Atlas (TCGA) database data. In addition, the expression of ADRA2A in cervical cancer cell lines was detected by qRT-PCR and Western blot. Subsequently, the roles of ADRA2A on cell proliferation, apoptosis, migration, invasion and senescence in HeLa and SiHa cells were evaluated. Moreover, tumorigenesis in nude mice was used to investigate the role of ADRA2A in vivo. We also detected the expression changes of key factors in PI3K/Akt/mTOR pathway after overexpression and silencing of ADRA2A in HeLa and SiHa cells.

Results

ADRA2A expression was significantly downregulated in cervical cancer tissues and cell lines. The high expression of ADRA2A was significantly associated with a better prognosis in cervical cancer patients. ADRA2A overexpression significantly suppressed cell proliferation, migration and invasion, and promoted cell senescence and apoptosis in cervical cancer cells. On the contrary, silencing ADRA2A dramatically facilitated cell proliferation, migration and invasion, and inhibited cell senescence and apoptosis in cervical cancer cells. The expressions of p-PI3K, p-AKT and p-mTOR in cervical cancer cells were notably decreased by ADRA2A overexpression and increased by silencing ADRA2A. In addition, we also confirmed that ADRA2A overexpression could suppress the xenograft tumor growth in vivo.

Conclusion

Our study demonstrated that ADRA2A could suppress cell proliferation, migration and invasion, as well as promote cell senescence and apoptosis through inhibiting PI3K/Akt/mTOR pathway in cervical cancer.

α 2-Adrenoceptors: Challenges and Opportunities-Enlightenment from the Kidney

It was indeed a Don Quixote-like pursuit of the mechanism of essential hypertension when we serendipitously discovered α₂-adrenoceptors (α₂-ARs) in skin-lightening experiments in the frog. Now α₂-ARs lurk on the horizon involving hypertension causality, renal denervation for hypertension, injury from falling in the elderly and prazosin's mechanism of action in anxiety states such as posttraumatic stress disorder (PTSD). Our goal here is to focus on this horizon and bring into clear view the role of α₂-AR-mediated mechanisms in these seemingly unrelated conditions. Our narrative begins with an explanation of how experiments in isolated perfused kidneys led to the discovery of a sodium-retaining process, a fundamental mechanism of hypertension, mediated by α₂-ARs. In this model system and in the setting of furosemide-induced sodium excretion, α₂-AR activation inhibited adenylate cyclase, suppressed cAMP formation, and caused sodium retention. Further investigations led to the realization that renal α₂-AR expression in hypertensive animals is elevated, thus supporting a key role for kidney α₂-ARs in the pathophysiology of essential hypertension. Subsequent studies clarified the molecular pathways by which α₂-ARs activate prohypertensive biochemical systems. While investigating the role of α₁-adrenoceptors (α₁-ARs) versus α₂-ARs in renal sympathetic neurotransmission, we noted an astonishing result: in the kidney α₁-ARs suppress the postjunctional expression of α₂-ARs. Here, we describe how this finding relates to a broader understanding of the role of α₂-ARs in diverse disease states. Because of the capacity for qualitative and quantitative monitoring of α₂-AR-induced regulatory mechanisms in the kidney, we looked to the kidney and found enlightenment.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

RACK1 regulates angiotensin II-induced contractions of SHR preglomerular vascular smooth muscle cells

The preglomerular microcirculation of spontaneously hypertensive rats (SHR) is hypersensitive to angiotensin (ANG) II, and studies have shown that this is likely due to enhanced coincident signaling between G protein subunits αq (Gαq; released by ANG II) and βγ (Gβγ; released by Gi-coupled receptors) to active phospholipase C (PLC). Here we investigated the molecular basis for the enhanced coincident signaling between Gβγ and Gαq in SHR preglomerular vascular smooth muscle cells (PGVSMCs). Because receptor for activated C kinase 1 (RACK1; a scaffolding protein) organizes interactions between Gβγ, Gαq, and PLC, we included RACK1 in this investigation. Cell fractionation studies demonstrated increased levels of membrane (but not cytosolic) Gβ, Gαq, PLCβ3, and RACK1 in SHR PGVSMCs compared with Wistar-Kyoto rat PGVSMCs. In SHR PGVSMCs, coimmunoprecipitation demonstrated RACK1 binding to Gβ and PLCβ3, but only at cell membranes. Pertussis toxin (which blocks Gβγ) and U73122 (which blocks PLC) reduced membrane RACK1; however, RACK1 knockdown (shRNA) did not affect membrane levels of Gβ, Gαq, or PLCβ3 In a novel gel contraction assay, RACK1 knockdown in SHR PGVSMCs attenuated contractions to ANG II and abrogated the ability of neuropeptide Y (which signals via Gβγ) to enhance ANG II-induced contractions. We conclude that in SHR PGVSMCs the enlarged pool of Gβγ and PLCβ3 recruits RACK1 to membranes and RACK1 then organizes signaling. Consequently, knockdown of RACK1 prevents coincident signaling between ANG II and the Gi pathway. This is the first study to implicate RACK1 in vascular smooth muscle cell contraction and suggests that RACK1 inhibitors could be effective cardiovascular drugs.

Effect of dipeptidyl peptidase 4 inhibition on arterial blood pressure is context dependent

Because the effects of dipeptidyl peptidase 4 (DPP4) inhibitors on blood pressure are controversial, we examined the long-term effects of sitagliptin (80 mg/kg per day) on blood pressure (radiotelemetry) in spontaneously hypertensive rats (SHR), Wistar-Kyoto rats, and Zucker Diabetic-Sprague Dawley rats (metabolic syndrome model). In SHR, chronic (3 weeks) sitagliptin significantly increased systolic, mean, and diastolic blood pressures by 10.3, 9.2, and 7.9 mm Hg, respectively, a response abolished by coadministration of BIBP3226 (2 mg/kg per day; selective Y1-receptor antagonist). Sitagliptin also significantly increased blood pressure in SHR treated with hydralazine (vasodilator; 25 mg/kg per day) or enalapril (angiotensin-converting enzyme inhibitor; 10 mg/kg per day). In Wistar-Kyoto rats, chronic sitagliptin slightly decreased systolic, mean, and diastolic blood pressures (-1.8, -1.1, and -0.4 mm Hg, respectively). In Zucker Diabetic-Sprague Dawley rats, chronic sitagliptin decreased systolic, mean, and diastolic blood pressures by -7.7, -5.8, and -4.3 mm Hg, respectively, and did not alter the antihypertensive effects of chronic enalapril. Because DPP4 inhibitors impair the metabolism of neuropeptide Y1-36 (NPY1-36; Y1-receptor agonist) and glucagon-like peptide (GLP)-1(7-36)NH2 (GLP-1 receptor agonist), we examined renovascular responses to NPY1-36 and GLP-1(7-36)NH2 in isolated perfused SHR and Zucker Diabetic-Sprague Dawley kidneys pretreated with norepinephrine (to induce basal tone). In Zucker Diabetic-Sprague Dawley kidneys, NPY1-36 and GLP-1(7-36)NH2 exerted little, if any, effect on renovascular tone. In contrast, in SHR kidneys, both NPY1-36 and GLP-1(7-36)NH2 elicited potent and efficacious vasoconstriction.

IN CONCLUSION

(1) The effects of DPP4 inhibitors on blood pressure are context dependent; (2) The context-dependent effects of DPP4 inhibitors are due in part to differential renovascular responses to DPP4’s most important substrates (NPY1–36 and GLP-1(7–36)NH2) [corrected]; (3) Y1 receptor antagonists may prevent the prohypertensive and possibly augment the antihypertensive effects of DPP4 inhibitors.

Alpha2-adrenoceptor and adenosine A1 receptor within the nucleus tractus solitarii in hypertension development

Alpha2-adrenoceptor and A1 adenosine receptor systems within the nucleus tractus solitarii (NTS) play an important role in cardiovascular control. Deregulation of these systems may result in an elevated sympathetic tone, one of the root causes of neurogenic hypertension. The dorsomedial/dorsolateral and subpostremal NTS subnuclei of spontaneously hypertensive rats (SHR) show density changes in both receptors, even at 15 days of age, prior to the onset of hypertension. In addition, adenosine A1 receptors have been specifically reported to modulate alpha2-adrenoceptors in several brain regions, including the NTS, via a PLC-dependent pathway involving cross regulation between sympathetic neurons and astrocytes. The physiological cross talk between these receptor systems is also deregulated in SHR suggesting that alpha2-adrenoceptor and A1 adenosine receptor might be germane to the development of hypertension. In this review, we will focus on these systems within the NTS during development, pointing out some interesting modulations in processes, and chemical changes within specific subnuclei of NTS circuitry, that might have implications for neurogenic hypertension.

Endogenous adenosine contributes to renal sympathetic neurotransmission via postjunctional A1 receptor-mediated coincident signaling

Adenosine A(1) receptor antagonists have diuretic/natriuretic activity and may be useful for treating sodium-retaining diseases, many of which are associated with increased renal sympathetic tone. Therefore, it is important to determine whether A(1) receptor antagonists alter renal sympathetic neurotransmission. In isolated, perfused rat kidneys, renal vasoconstriction induced by renal sympathetic nerve simulation was attenuated by 1) 1,3-dipropyl-8-p-sulfophenylxanthine (xanthine analog that is a nonselective adenosine receptor antagonist, but is cell membrane impermeable and thus does not block intracellular phosphodiesterases), 2) xanthine amine congener (xanthine analog that is a selective A(1) receptor antagonist), 3) 1,3-dipropyl-8-cyclopentylxanthine (xanthine analog that is a highly selective A(1) receptor antagonist), and 4) FK453 (nonxanthine analog that is a highly selective A(1) receptor antagonist). In contrast, FR113452 (enantiomer of FK453 that does not block A(1) receptors), MRS-1754 (selective A(2B) receptor antagonist), and VUF-5574 (selective A(3) receptor antagonist) did not alter responses to renal sympathetic nerve stimulation, and ZM-241385 (selective A(2A) receptor antagonist) enhanced responses. Antagonism of A(1) receptors did not alter renal spillover of norepinephrine. 2-Chloro-N(6)-cyclopentyladenosine (highly selective A(1) receptor agonist) increased renal vasoconstriction induced by exogenous norepinephrine, an effect that was blocked by 1,3-dipropyl-8-cyclopentylxanthine, U73122 (phospholipase C inhibitor), GF109203X (protein kinase C inhibitor), PP1 (c-src inhibitor), wortmannin (phosphatidylinositol 3-kinase inhibitor), and OSU-03012 (3-phosphoinositide-dependent protein kinase-1 inhibitor). These results indicate that adenosine formed during renal sympathetic nerve stimulation enhances the postjunctional effects of released norepinephrine via coincident signaling and contributes to renal sympathetic neurotransmission. Likely, the coincident signaling pathway is: phospholipase C → protein kinase C → c-src → phosphatidylinositol 3-kinase → 3-phosphoinositide-dependent protein kinase-1.

Sitagliptin augments angiotensin II-induced renal vasoconstriction in kidneys from rats with metabolic syndrome

1. Dipeptidyl peptidase (DPP) IV inhibitors enhance renovascular responses to angiotensin (Ang) II in spontaneously hypertensive rats (SHR), but not Wistar-Kyoto rats. Because DPPIV inhibitors are often used in metabolic syndrome, it is important to determine whether DPPIV inhibition in this setting enhances renovascular responses to AngII. 2. Six-week-old Lean-ZSF1 rats (harbouring SHR genes, but without metabolic syndrome; n = 11) and Obese-ZSF1 rats (harbouring SHR genes and expressing metabolic syndrome; n = 10) were provided food and water ad libitum, and metabolic parameters and renovascular responses to AngII were assessed when the animals were 7 and 8 weeks of age, respectively. 3. At 7 weeks of age, compared with Lean-ZSF1, Obese-ZSF1 demonstrated significant (P < 0.05) increases in bodyweight (262 +/- 8 vs 310 +/- 13 g), plasma glucose (112 +/- 4 vs 153 +/- 9 mg/dL), haemoglobin A1c (4.7 +/- 0.1 vs 5.8 +/- 0.4%), urinary glucose excretion (0.021 +/- 0.003 vs 6.70 +/- 1.80 g/kg bodyweight per 24 h) and urinary protein excretion (100 +/- 7 vs 313 +/- 77 mg/kg bodyweight per 24 h). Mean blood pressure was high (133 +/- 7 mmHg) in both strains. 4. At 8 weeks of age, kidneys were isolated and perfused. In Lean-ZSF1 rats, renovascular responses (i.e. changes in perfusion pressure) to physiological levels of AngII (0.1 nmol/L) were 3.4 +/- 1.3 and 18.2 +/- 5.9 mmHg in untreated (n = 5) and 1 micromol/L sitagliptin-treated (n = 6) kidneys, respectively. In Obese-ZSF1 rats, renovascular responses to AngII were 5.5 +/- 1.3 and 17.8 +/- 8.2 mmHg in untreated (n = 4) and sitagliptin-treated (n = 6) kidneys, respectively. Analysis of variance revealed a significant (P = 0.0367) effect of sitagliptin on renovascular responses to AngII that was independent of strain. 5. In conclusion, sitagliptin enhances renovascular responses to AngII in rats harbouring SHR genes and this effect persists in rats with diabetic nephropathy and metabolic syndrome.

Roles of Phosphatidylinositol 3-Kinase-Akt and NADPH Oxidase in Adenosine 5′-Triphosphate–Sensitive K + Channel Function Impaired by High Glucose in the Human Artery

The present study was designed to examine roles of the phosphatidylinositol 3-kinase-Akt pathway and reduced nicotinamide-adenine dinucleotide phosphate oxidases in the reduced ATP-sensitive K + channel function via superoxide produced by high glucose in the human artery. We evaluated the activity of the phosphatidylinositol 3-kinase-Akt pathway, as well as reduced nicotinamide-adenine dinucleotide phosphate oxidases, the intracellular levels of superoxide and ATP-sensitive K + channel function in the human omental artery without endothelium. Levels of the p85-α subunit and reduced nicotinamide-adenine dinucleotide phosphate oxidase subunits, including p47phox, p22phox, and Rac-1, increased in the membrane fraction from arteries treated with d -glucose (20 mmol/L) accompanied by increased intracellular superoxide production. High glucose simultaneously augmented Akt phosphorylation at Ser 473, as well as Thr 308 in the human vascular smooth muscle cells. A phosphatidylinositol 3-kinase inhibitor LY294002, as well as tiron and apocynin, restored vasorelaxation and hyperpolarization in response to an ATP-sensitive K + channel opener levcromakalim. Therefore, it can be concluded that the activation of the phosphatidylinositol 3-kinase-Akt pathway, in combination with the translocation of p47phox, p22phox, and Rac-1, contributes to the superoxide production induced by high glucose, resulting in the impairment of ATP-sensitive K + channel function in the human visceral artery.

Alpha2-adrenoceptors enhance angiotensin II-induced renal vasoconstriction: role for NADPH oxidase and RhoA

Alpha(2)-adrenoceptors potentiate renal vascular responses to angiotensin II via coincident signaling at phospholipase C. This leads to increased activation of the phospholipase C/protein kinase C/c-src pathway. Studies suggest that c-src activates the reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase/superoxide system, and reactive oxygen species stimulate the RhoA/Rho kinase pathway. Therefore, we hypothesized that NADPH oxidase/superoxide and RhoA/Rho kinase are downstream components of the signal transduction pathway that mediate the interaction between alpha(2)-adrenoceptors and angiotensin II on renal vascular resistance. In rat kidneys, both in vivo and in vitro, intrarenal infusions of angiotensin II increased renal vascular resistance, and UK14,304 (alpha(2)-adrenoceptor agonist) enhanced this response. Intrarenal Tempol (superoxide dismutase mimetic) or Y27632 (Rho kinase inhibitor) abolished the interaction between UK14,304 and angiotensin II both in vivo and in vitro. The interaction was also blocked by inhibitors of NADPH oxidase (in vivo using chronic gp91ds-tat administration and in vitro with diphenyleneiodonium). In cultured preglomerular vascular smooth muscle cells, UK14,304 enhanced angiotensin II-induced intracellular superoxide (2-hydroxyethidium production) and potentiated activation of RhoA (Western blot of activated RhoA bound to the binding domain of rhotekin). The interaction between angiotensin II and UK14,304 on superoxide generation and RhoA activation was blocked by inhibitors of phospholipase C (U73312), protein kinase C (GF109203X), c-src (PP1), NADPH oxidase (diphenyleneiodonium), or superoxide (Tempol). We conclude that NADPH oxidase/superoxide and RhoA/Rho kinase are involved in the interaction between alpha(2)-adrenoceptors and angiotensin II on renal vascular resistance by mediating signaling events downstream of the phospholipase C/protein kinase C/c-src pathway.

Inhibition of renal dipeptidyl peptidase IV enhances peptide YY1-36-induced potentiation of angiotensin II-mediated renal vasoconstriction in spontaneously hypertensive rats

Dipeptidyl peptidase IV inhibitors are a new class of antidiabetic drugs. It is urgent, therefore, to fully understand the pharmacology of these inhibitors. Although dipeptidyl peptidase IV metabolizes at least 24 endogenous substrates, the pharmacological consequences of inhibiting the metabolism of most of these substrates is unknown. Our previous results show that Y(1) receptors, but not Y(2) receptors, enhance renovascular responses to angiotensin II in kidneys from genetically susceptible animals (spontaneously hypertensive rats). Dipeptidyl peptidase IV converts peptide YY(1-36) (circulating hormone) to peptide YY(3-36), and peptide YY(1-36) is a Y(1)-receptor agonist, whereas peptide YY(3-36) is a selective Y(2)-receptor agonist. Therefore, it is conceivable that inhibition of dipeptidyl peptidase IV in genetically susceptible kidneys may increase the ability of peptide YY(1-36) to potentiate angiotensin II-induced renal vasoconstriction. Here we demonstrate that in kidneys from spontaneously hypertensive rats 1) peptide YY(1-36) potentiates renovascular responses to angiotensin II, whereas peptide YY(3-36) has little effect, 2) 3-N-[(2S,3S)-2-amino-3-methylpentanoyl]-1,3-thiazolidine (P32/98) (dipeptidyl peptidase IV inhibitor) augments the ability of peptide YY(1-36) to enhance renovascular responses to angiotensin II, 3) dipeptidyl peptidase IV is expressed in preglomerular microvessels and glomeruli, 4) kidneys metabolize arterial PYY(1-36) to PYY(3-36) via a mechanism blocked by P32/98, and 5) preglomerular microvessels and glomeruli convert peptide YY(1-36) to peptide YY(3-36), and this conversion is inhibited by P32/98. We conclude that dipeptidyl peptidase IV is expressed in the renal microcirculation and inhibition of this ecto-enzyme causes arterial PYY(1-36) to more effectively enhance angiotensin II-induced renal vasoconstriction in genetically susceptible kidneys.

Phospholipase C and Src modulate angiotensin II-induced cyclic AMP production in preglomerular microvascular smooth-muscle cells from spontaneously hypertensive rats

Our previous study indicates that the phospholipase C family (PLC) and Src kinase family (Src) modulate adrenoceptor-induced cAMP production in a negative and positive manner, respectively, in preglomerular vascular smooth-muscle cells (PGSMCs) obtained from spontaneously hypertensive rats (SHR). Because angiotensin II (Ang II) activates PLC and Src, and because PLC and Src inhibit and augment cAMP production, respectively, it is conceivable that the balance between these signal-transduction pathways determines whether Ang II increases or decreases cAMP production in SHR PGSMCs. In SHR PGSMCs, Ang II (500 nM) did not alter cAMP production in the absence or presence of PP1 (100 nM; inhibitor of Src). In the presence of U73122 (3 microM; inhibitor of PLC), Ang II stimulated cAMP production from 2.2 +/- 0.062 to 4.7 +/- 0.73 pmol/well. In another study in U73122-pretreated SHR PGSMCs, Ang II increased cAMP from 3.0 +/- 0.07 to 6.3 +/- 0.40 pmol/well, and this response was blocked by PP1. RT-PCR of 10 isoforms of Scr (Lck, Hck, Frk Fyn, Blk, Lyn, Fgr, Yes, Yrk, and c-Src) indicated that SHR PGSMCs preferentially express Frk, Fyn, Lyn, and c-Src. We conclude that in SHR PGSMCs, inhibition of PLC uncovers a stimulatory effect of Ang II on cAMP production that is mediated by Src family kinases, most likely Frk, Fyn, Lyn, and/or c-Src.

Role of renal sympathetic nerves in regulating renovascular responses to angiotensin II in spontaneously hypertensive rats

The purpose of this study was to test the hypothesis that renal sympathetic nerves modulate angiotensin II-induced renal vasoconstriction in kidneys from genetically hypertensive rats via Y1 receptors activating the Gi pathway. In isolated, perfused kidneys from spontaneously hypertensive rats, the naturally occurring renal sympathetic cotransmitter neuropeptide Y at 6 nM enhanced angiotensin II (0.3 nM)-induced changes in perfusion pressure by 47 +/- 7 mm Hg, and this effect was inhibited by BIBP3226 [N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)-methyl]-D-arginine amide)], a selective Y1 receptor antagonist (1 microM). We next examined whether periarterial nerve stimulation (5 Hz) enhances renal vascular responses to a physiological level of angiotensin II (100 pM). Kidneys were pretreated with prazosin (a selective alpha1-adrenoceptor antagonist) to block nerve stimulation-induced changes in perfusion pressure. In kidneys from spontaneously hypertensive rats, but not normotensive rats, periarterial nerve stimulation significantly augmented angiotensin II-induced changes in perfusion pressure (177 +/- 26% of response in absence of stimulation). BIBP3226, but not rauwolscine (a selective alpha2-adrenoceptor antagonist), abolished periarterial nerve stimulation-induced enhancement of angiotensin II-mediated renal vasoconstriction. Pretreatment of hypertensive animals with pertussis toxin 3 days prior to kidney perfusion significantly (p < 0.000001) decreased mean blood pressure (203 +/- 2 versus 145 +/- 6 mm Hg in nonpretreated versus pertussis toxin-pretreated spontaneously hypertensive rats) and abolished periarterial nerve stimulation-induced enhancement of angiotensin II-mediated renal vasoconstriction. We conclude that, in spontaneously hypertensive rats but not normotensive rats, sympathetic nerve stimulation enhances renal vascular responses to physiological levels of angiotensin II via a mechanism mainly involving Y1 receptors coupled to Gi proteins.

Pancreatic Polypeptide-Fold Peptide Receptors and Angiotensin II–Induced Renal Vasoconstriction

The Gi pathway augments renal vasoconstriction induced by angiotensin II in spontaneously hypertensive but not normotensive Wistar-Kyoto rats. Because the Gi-coupled pancreatic polypeptide (PP)-fold peptide receptors Y1 and Y2 are expressed in kidneys and are activated by endogenous PP-fold peptides, we tested the hypothesis that these receptors regulate angiotensin II-induced renal vasoconstriction in kidneys from hypertensive but not normotensive rats. A selective Y1-receptor agonist [(Leu31,Pro34)-neuropeptide Y; 6 to 10 nmol/L] greatly potentiated angiotensin II-induced changes in perfusion pressure in isolated, perfused kidneys from hypertensive but not normotensive rats. A selective Y2-receptor agonist (peptide YY(3-36); 6 nM) only slightly potentiated angiotensin II-induced renal vasoconstriction and only in kidneys from hypertensive rats. Neither the Y1-receptor nor the Y2-receptor agonist increased basal perfusion pressure. BIBP3226 (1 micromol/L, highly selective Y1-receptor antagonist) and BIIE0246 (1 micromol/L, highly selective Y2-receptor antagonist) completely abolished potentiation by (Leu31,Pro34)-neuropeptide Y and peptide YY(3-36), respectively. Y1-receptor and Y2-receptor mRNA and protein levels were expressed in renal microvessels and whole kidneys, but the abundance was similar in kidneys from hypertensive and normotensive rats. Both Y1-receptor-induced and Y2-receptor-induced potentiation of angiotensin II-mediated renal vasoconstriction was completely abolished by pretreatment with pertussis toxin (30 microg/kg IV, blocks Gi proteins). These data indicate that, in kidneys from genetically hypertensive but not normotensive rats, Y1-receptor activation markedly enhances angiotensin II-mediated renal vasoconstriction by a mechanism involving Gi. Although Y2 receptors can also potentiate angiotensin II-mediated renal vasoconstriction via Gi, the effect is modest compared with Y1 receptors. These findings may have important implications for the etiology of genetic hypertension.