Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm

We present a new measurement of the positive muon magnetic anomaly, a_{μ}≡(g_{μ}-2)/2, from the Fermilab Muon g-2 Experiment using data collected in 2019 and 2020. We have analyzed more than 4 times the number of positrons from muon decay than in our previous result from 2018 data. The systematic error is reduced by more than a factor of 2 due to better running conditions, a more stable beam, and improved knowledge of the magnetic field weighted by the muon distribution, ω[over ˜]_{p}^{'}, and of the anomalous precession frequency corrected for beam dynamics effects, ω_{a}. From the ratio ω_{a}/ω[over ˜]_{p}^{'}, together with precisely determined external parameters, we determine a_{μ}=116 592 057(25)×10^{-11} (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a_{μ}(FNAL)=116 592 055(24)×10^{-11} (0.20 ppm). The new experimental world average is a_{μ}(exp)=116 592 059(22)×10^{-11} (0.19 ppm), which represents a factor of 2 improvement in precision.

Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm

We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon g-2 Experiment for the positive muon magnetic anomaly a_{μ}≡(g_{μ}-2)/2. The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency ω_{a} between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured using nuclear magnetic resonance probes calibrated in terms of the equivalent proton spin precession frequency ω[over ˜]_{p}^{'} in a spherical water sample at 34.7 °C. The ratio ω_{a}/ω[over ˜]_{p}^{'}, together with known fundamental constants, determines a_{μ}(FNAL)=116 592 040(54)×10^{-11} (0.46 ppm). The result is 3.3 standard deviations greater than the standard model prediction and is in excellent agreement with the previous Brookhaven National Laboratory (BNL) E821 measurement. After combination with previous measurements of both μ^{+} and μ^{-}, the new experimental average of a_{μ}(Exp)=116 592 061(41)×10^{-11} (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.

What has the National Cancer Database taught us about oral cavity squamous cell carcinoma?

The wealth of data in the National Cancer Database (NCDB) has allowed numerous studies investigating patient, disease, and treatment-related factors in oral cavity squamous cell carcinoma (OCSCC); however, to date, no summation of these studies has been performed. The aim of this study was to provide a concise review of the NCDB studies on OCSCC, with the hopes of providing a framework for future, novel studies aimed at enhancing our understanding of clinical parameters related to OCSCC. Two databases were searched, and 27 studies published between 2002 and 2020 were included. The average sample size was 13,776 patients (range 356-50,896 patients). Four areas of research focus were identified: demographic and socioeconomic status, diagnosis, prognosis, and treatment. This review highlights the impact of age, sex, ethnicity, and socioeconomic status on the prognosis and management of OCSCC, describes the prognostic factors, and details the modalities and indications for neck dissection and adjuvant therapy in OCSCC. In conclusion, the NCDB is a very valuable resource for clinicians and researchers involved in the management of OCSCC, offering an incomparable perspective on a large dataset of patients. Future developments regarding hospital information management, review of data accuracy and completeness, and wider accessibility will help clinicians to improve the care of patients affected by OCSCC.

Measurement of muon capture on the proton to 1% precision and determination of the pseudoscalar coupling gP

The MuCap experiment at the Paul Scherrer Institute has measured the rate Λ(S) of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. Λ(S) is determined from the difference between the μ(-) disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 × 10(10) μ(-) decays, from which we extract the capture rate Λ(S) = (714.9 ± 5.4(stat) ± 5.1(syst)) s(-1) and derive the proton's pseudoscalar coupling g(P)(q(0)(2) = -0.88 m(μ)(2)) = 8.06 ± 0.55.

Measurement of the positive muon lifetime and determination of the Fermi constant to part-per-million precision

We report a measurement of the positive muon lifetime to a precision of 1.0 ppm; it is the most precise particle lifetime ever measured. The experiment used a time-structured, low-energy muon beam and a segmented plastic scintillator array to record more than 2×10(12) decays. Two different stopping target configurations were employed in independent data-taking periods. The combined results give τ(μ(+)) (MuLan)=2 196 980.3(2.2)  ps, more than 15 times as precise as any previous experiment. The muon lifetime gives the most precise value for the Fermi constant: G(F) (MuLan)=1.166 378 8(7)×10(-5)  GeV(-2) (0.6 ppm). It is also used to extract the μ(-)p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g(P).

Search for Lorentz and CPT violation effects in Muon spin precession

The spin precession frequency of muons stored in the (g-2) storage ring has been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT violation signatures were searched for a nonzero delta omega a(=omega a mu+ - omega a mu-) and a sidereal variation of omega a mu+/-). No significant effect is found, and the following limits on the standard-model extension parameters are obtained: bZ = -(1.0+/-1.1) x 10(-23) GeV; (m mu dZ0 + HXY)=(1.8+/-6.0) x 10(-23) GeV; and the 95% confidence level limits b perpendicular mu+ <1.4 x 10(-24) GeV and b perpendicular mu- <2.6 x 10(-24) GeV.

Improved measurement of the positive-muon lifetime and determination of the Fermi constant

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, tau(micro)=2.197 013(24) micros, is in excellent agreement with the previous world average. The new world average tau(micro)=2.197 019(21) micros determines the Fermi constant G(F)=1.166 371(6)x10(-5) GeV-2 (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g(P).

Measurement of the negative muon anomalous magnetic moment to 0.7 ppm

The anomalous magnetic moment of the negative muon has been measured to a precision of 0.7 ppm (ppm) at the Brookhaven Alternating Gradient Synchrotron. This result is based on data collected in 2001, and is over an order of magnitude more precise than the previous measurement for the negative muon. The result a(mu(-))=11 659 214(8)(3) x 10(-10) (0.7 ppm), where the first uncertainty is statistical and the second is systematic, is consistent with previous measurements of the anomaly for the positive and the negative muon. The average of the measurements of the muon anomaly is a(mu)(exp)=11 659 208(6) x 10(-10) (0.5 ppm).

Measurement of the positive muon anomalous magnetic moment to 0.7 ppm

A higher precision measurement of the anomalous g value, a(mu)=(g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000. The result a(mu(+))=11 659 204(7)(5)x10(-10) (0.7 ppm) is in good agreement with previous measurements and has an error about one-half that of the combined previous data. The present world average experimental value is a(mu)(expt)=11 659 203(8)x10(-10) (0.7 ppm).

Angiotensin type 2 receptor-mediated hypotension in angiotensin type-1 receptor-blocked rats

The type-2 (AT(2)) angiotensin (Ang) II receptor has been characterized as potentially counterregulatory to the actions of Ang II at its type-1 (AT(1)) receptor. We investigated the effects of Ang II and CGP-42112A (CGP), a selective peptide AT(2) receptor agonist, on blood pressure (BP) in rats with or without pharmacological blockade of the AT(1) receptor with losartan (LOS) or valsartan (VAL). In anesthetized rats (n=5 per group) receiving normal sodium intake, Ang II (200 pmol/kg per minute IV) alone increased BP from a control of 112+/-3 to 168+/-7 mm Hg (P<0.001) and LOS (30 mg/kg) alone decreased BP to 89+/-7 mm Hg (P<0.0001 from control). Ang II administered together with LOS decreased BP further to 71+/-4 mm Hg (P<0.00001 from control and LOS alone). AT(2) receptor antagonist PD 123,319 (PD) completely blocked the hypotensive response to LOS combined with Ang II (P=NS from control). In conscious rats (n=5 per group) receiving normal sodium intake, VAL (10 mg/kg) alone decreased BP from a control of 98+/-5 to 86+/-3 mm Hg (P<0.00001). Ang II combined with VAL induced a consistent, highly significant decline in BP for 6 days to a nadir of 69+/-3 mm Hg (P<0.01 versus daily VAL alone). PD completely blocked the chronic hypotensive response to the combination of Ang II and VAL to control levels before VAL administration. In another study in conscious rats (n=5 per group), CGP (70 microg/kg per minute) also decreased BP in VAL-treated conscious rats. BP was 119+/-3 mm Hg during the control period, decreased to 86+/-6 mm Hg during 3 days of VAL alone, (P<0.00001) and decreased further to 65+/-7 mm Hg (P<0.001 from daily VAL alone) with 7 days of CGP in the presence of VAL. In the absence of VAL, CGP decreased BP for 4 consecutive days, and this response was blocked by PD. Also, the CGP-induced decrease in BP over a 7-day period was blocked by N(G)-nitro-L-arginine methyl ester, an inhibitor of NO synthase. The results strongly suggest that the AT(2) receptor induces a systemic vasodilator response mediated by NO that counterbalances the vasoconstrictor action of Ang II at the AT(1) receptor.

Theodore Cooper Lecture: Renal dopamine system: paracrine regulator of sodium homeostasis and blood pressure

All of the components of a complete dopamine system are present within the kidney, where dopamine acts as a paracrine substance in the control of sodium excretion. Dopamine receptors can be divided into D(1)-like (D(1) and D(5)) receptors that stimulate adenylyl cyclase and D(2)-like (D(2), D(3), and D(4)) receptors that inhibit adenylyl cyclase. All 5 receptor subtypes are expressed in the kidney, albeit in low copy. Dopamine is synthesized extraneuronally in proximal tubule cells, exported from these cells largely into the tubule lumen, and interacts with D(1)-like receptors to inhibit the Na(+)-H(+) exchanger and Na(+),K(+)-ATPase, decreasing tubule sodium reabsorption. During moderate sodium surfeit, dopamine tone at D(1)-like receptors accounts for approximately 50% of sodium excretion. In experimental and human hypertension, 2 renal dopaminergic defects have been described: (1) decreased renal generation of dopamine and (2) a D(1) receptor-G protein coupling defect. Both defects lead to renal sodium retention, and each may play an important role in the pathophysiology of essential hypertension.

Renal interstitial cGMP mediates natriuresis by direct tubule mechanism

The objective of this study was to test the hypothesis that renal interstitial (RI) cGMP is natriuretic in vivo. In conscious rats (n=8), urinary sodium excretion (U(Na)V) was significantly greater on days 3 and 4 of RI infusion of cGMP (1.17+/-0.14 and 1.61+/-0.11 mmol/24 h, respectively) than during vehicle infusion (0.56+/-0.15 and 0.70+/-0.17 mmol/24 h, respectively) (P<0.01). Similarly, U(Na)V was greater on days 3 and 4 of RI infusion of 8-bromo-cGMP (2.15+/-0.42 and 2.16+/-0.1 mmol/24 h, respectively). Protein kinase G inhibitor Rp-8-pCPT-cGMPS reduced cGMP-induced and 8-bromo-cGMP-induced U(Na)V to control levels. Acute RI infusion of L-arginine (L-Arg, 40 mg. kg(-1). min(-1)), but not D-arginine, caused an increase in U(Na)V from 1.65+/-0.11 to 4.07+/-0.1 micromol/30 min (P<0.01). This increase was blocked by RI infusion of N(G)-nitro-L-arginine methyl ester (100 ng. kg(-1). min(-1)) by the phosphodiesterase (PDE II) activator 5,6DMcBIMP (0.01 micromol/microL), by PDE II (0.03 U. kg(-1). min(-1)) itself, or by the soluble guanylyl cyclase inhibitor 1-H-[1,2,4]oxadiazolo-[4,2-alpha]quinoxalin-1-one (ODQ, 0.12 mg. kg(-1). min(-1)). The PDE II activator also blocked L-Arg-stimulated cGMP levels. The NO donor S-nitroso-N-acetylpenicillamine (SNAP, 0.12 micromol. L(-1). kg(-1). min(-1)) increased U(Na)V from 1.65+/-0.11 to 2.93+/-0.08 micromol/30 min (P<0.01), and this response was blocked completely by ODQ. Renal arterial but not RI administration of the heat-stable enterotoxin of Escherichia coli induced natriuresis. RA infusion of cGMP (3 microg/min) increased U(Na)V, renal blood flow (RBF), and glomerular filtration rate (GFR). Renal cortical interstitial cGMP infusion increased U(Na)V with no effect on total RBF, renal cortical blood flow, or GFR. Similarly, the natriuretic actions of renal interstitial L-Arg or SNAP were not accompanied by any change in RBF or GFR. Medullary cGMP infusion had no effect on U(Na)V, total RBF, or medullary blood flow. Texas red-labeled cGMP infused via the RI space was distributed exclusively to cortical renal tubular cells. The results demonstrate that RI cGMP inhibits renal tubular sodium absorption via protein kinase G independently of hemodynamic changes. These observations indicate that the cortical interstitial compartment provides a potentially important domain for cell-to-cell signaling within the kidney.

Angiotensin-converting enzyme inhibition potentiates angiotensin II type 1 receptor effects on renal bradykinin and cGMP

Angiotensin (Ang) receptor blockers (ARBs) increase bradykinin (BK) by antagonizing Ang II at its type 1 (AT(1)) receptors and diverting Ang II to its counterregulatory type 2 (AT(2)) receptors. Because the effect of ARBs on BK is constrained by the short half-life of BK and because ACE inhibitors block the degradation of BK, this study was designed to test the hypothesis that an ACE inhibitor can potentiate ARB-induced increases in renal interstitial fluid (RIF) BK levels. We used a microdialysis technique to recover BK and cGMP in vivo from the RIF of sodium-depleted, conscious Sprague-Dawley rats infused for 60 minutes with the AT(1) receptor blocker valsartan (0.17 mg/kg per minute), with the active metabolite of the ACE inhibitor benazepril (benazeprilate, 0.05 mg/kg per minute), or with the specific AT(2) receptor blocker PD 123,319 (50 microg/kg per minute) alone or combined. Each animal served as its own control. RIF BK and cGMP levels increased significantly over 1 hour in response to valsartan, benazeprilate, or both but not to a vehicle control (P<0.01). The combined benazeprilate-valsartan effect was greater than the sum of their individual effects, suggesting potentiation rather than addition, and was abolished by PD 123,319. We demonstrate for the first time that an ACE inhibitor (benazepril) and an ARB (valsartan) potentiate each other, and we postulate that such combinations may be beneficial in clinical states marked by Ang II elevation, such as chronic heart failure, postinfarction left ventricular dysfunction, and hypertension.

Selective inhibition of the renal angiotensin type 2 receptor increases blood pressure in conscious rats

The angiotensin II type 2 (AT(2)) receptor is present in rat kidney; however, its function is not well understood. The purpose of this study was to evaluate the role of the AT(2) receptor in blood pressure (BP) regulation. The effects of selective inhibition of the renal AT(2) receptor with phosphorothioated antisense oligodeoxynucleotide (AS-ODN) were examined in conscious uninephrectomized rats. Oligodeoxynucleotides (AS-ODN or scrambled [S-ODN]) were infused directly into the renal interstitial space by using an osmotic pump at 1 microL/h for 7 days. Texas red-labeled AS-ODN was distributed in renal tubules in the infused but not the contralateral kidney of normal rats. Continuous renal interstitial infusion of the AS-ODN, but not S-ODN, caused a significant (P<0.01) increase in BP 1 to 5 days after the initiation of the infusion. AS-ODN-treated rats experienced an increase in systolic BP from 109+/-4 to 130+/-4 mm Hg (n=8, P<0.01), whereas S-ODN-treated (n=8) and vehicle-treated (n=8) rats did not show any significant change in BP. On day 5 of the oligodeoxynucleotide infusion, AS-ODN-treated rats exhibited a greater pressor response to systemic angiotensin II infusion (30 ng/kg per hour) than did S-ODN-treated rats (P<0.01). Renal interstitial fluid cGMP decreased from 11.9+/-0.8 to 3.6+/-0.5 pmol/mL (P<0.001), and bradykinin decreased from 0.05+/-0.05 to 0.18+/-0.03 ng/mL (P<0.001) in response to AS-ODN, but they were not significantly changed in response to S-ODN. To evaluate the effects of AS-ODN and S-ODN on AT(2) receptor expression, Western Blot analysis was performed on treated kidneys. Kidneys treated with AS-ODN had approximately 40% less expression of AT(2) receptor than did kidneys treated with S-ODN or vehicle (P<0.05). These results suggest that AS-ODN directed selectively against the renal AT(2) receptor decreased receptor expression and caused an increase in BP. We conclude that the renal AT(2) receptor plays an important role in the regulation of BP via a bradykinin/cGMP vasodilator signaling cascade.

Vascular expression of angiotensin type 2 receptor in the adult rat: influence of angiotensin II infusion

OBJECTIVE

The aim of this study was to investigate the relative role of the angiotensin type 1 (AT1) and type 2 (AT2) receptors in mediating angiotensin II-induced regulation of AT2 receptor in mesenteric artery.

DESIGN

Sprague-Dawley rats were infused with either angiotensin II or vehicle for 14 days at a dose of 58.3 ng/min. Ang II-infused rats were allocated to receive either an AT1 antagonist, valsartan at a dose of 30 mg/kg per day or the AT2 receptor antagonist PD123319 at a dose of 830 ng/min.

METHODS

Gene and protein expression of the AT2 receptor in the mesenteric vasculature was assessed by quantitative reverse transcriptase polymerase chain reaction, immunohistochemistry and by in vitro autoradiography with a specific radioligand, 1251-CGP 42112B.

RESULTS

The AT2 receptor mRNA and protein were detected in the mesenteric artery from adult rats. Both nuclear emulsion and immunohistochemical staining showed expression of the AT2 receptor in the adventitial and medial layers. Compared to control rats, angiotensin II infusion was associated with a significant increase in the AT2 receptor expression. Valsartan treatment significantly reduced AT2 receptor gene expression, with no significant effect of PD123319 on this parameter.

CONCLUSIONS

This study confirms that the presence of the AT2 receptor in mesenteric arteries in adult rats, shows an up-regulation of the AT2 receptor following angiotensin II infusion and suggests a role for the AT1 receptor in this regulation. In view of the recently demonstrated effects of the AT2 receptor, these findings may be relevant to the role of the AT2 receptor in the pathophysiology of vascular remodeling.

Role of the angiotensin AT2 receptor in blood pressure regulation and therapeutic implications

The angiotensin (ANG) Type 2 (AT2) receptor is one of two major ANG II receptors that have been identified, cloned, and sequenced. Most of the biologic actions of ANG II are thought to be mediated by the AT1 receptor, but evidence is beginning to emerge that the AT2 receptor has a significant role in the regulation of blood pressure. In the adult rat, the AT2 receptor is expressed, albeit in low concentrations in kidney, mesenteric blood vessels, and heart. Most of the evidence suggests that the AT2 receptor stimulates a vasodilator signaling cascade that includes bradykinin, nitric oxide, and guanosine cyclic 3',5'-monophosphate. At lease some of the beneficial actions of AT1 receptor blockade are mediated by the AT2 receptor through this pathway. Several recent studies suggest that AT2 receptors may mediate vasodilation and hypotension. The AT2 receptor represents a potential therapeutic target for agonist action and a candidate molecule in the pathophysiology of hypertension.

Precise measurement of the positive muon anomalous magnetic moment

A precise measurement of the anomalous g value, a(mu) = (g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron. The result a(mu+) = 11 659 202(14) (6) x 10(-10) (1.3 ppm) is in good agreement with previous measurements and has an error one third that of the combined previous data. The current theoretical value from the standard model is a(mu)(SM) = 11 659 159.6(6.7) x 10(-10) (0.57 ppm) and a(mu)(exp) - a(mu)(SM) = 43(16) x 10(-10) in which a(mu)(exp) is the world average experimental value.

Early streptozotocin-diabetes mellitus downregulates rat kidney AT2 receptors

The interaction of ANG II with intrarenal AT1 receptors has been implicated in the progression of diabetic nephropathy, but the role of intrarenal AT2 receptors is unknown. The present studies determined the effect of early diabetes on components of the glomerular renin-angiotensin system and on expression of kidney AT2 receptors. Three groups of rats were studied after 2 wk: 1) control (C), 2) streptozotocin (STZ)-induced diabetic (D), and 3) STZ-induced diabetic with insulin implant (D+I), to maintain normoglycemia. By competitive RT-PCR, early diabetes had no significant effect on glomerular mRNA expression for renin, angiotensinogen, or angiotensin-converting enzyme (ACE). In isolated glomeruli, nonglycosylated (41-kDa) AT1 receptor protein expression (AT1A and AT1B) was increased in D rats, with no change in glycosylated (53-kDa) AT1 receptor protein or in AT1 receptor mRNA. By contrast, STZ diabetes caused a significant decrease in glomerular AT2 receptor protein expression (47.0 +/- 6.5% of C; P < 0.001; n = 6), with partial reversal in D+I rats. In normal rat kidney, AT2 receptor immunostaining was localized to glomerular endothelial cells and tubular epithelial cells in the cortex, interstitial, and tubular cells in the outer medulla, and inner medullary collecting duct cells. STZ diabetes caused a significant decrease in AT2 receptor immunostaining in all kidney regions, an effect partially reversed in D+I rats. In summary, early diabetes has no effect on glomerular mRNA expression for renin, angiotensinogen, or ACE. AT2 receptors are present in glomeruli and are downregulated in early diabetes, as are all kidney AT2 receptors. Our data suggest that alterations in the balance of kidney AT1 and AT2 receptor expression may contribute to ANG II-mediated glomerular injury in progressive diabetic nephropathy.

Distribution of type-1 and type-2 angiotensin receptors in the normal human lung and in lungs from patients with chronic obstructive pulmonary disease

This study was designed to examine the cellular distribution of the angiotensin II type-1 (AT1) and type-2 (AT2) receptors in the normal human and pathological human lung. Riboprobes were prepared against specific portions of each receptor DNA and labelled with FITC for detection using an anti-FITC antibody in combination with the alkaline phosphatase-anti-alkaline phosphatase technique and new Fuchsin. These were used to detect the presence of receptor mRNA in the lung. Specific antibodies were used to detect receptor protein in cells by immunocytochemistry. Image analysis was used in order to semi-quantify receptor density. AT1 receptor mRNA and protein were localised on vascular smooth muscle cells, macrophages and in the stroma underlying the airways epithelium probably relating to underlying fibroblasts. The AT1 receptor protein was not expressed in the epithelium although there was a low level of mRNA. In contrast, AT2 receptor RNA and protein was observed in the epithelium, with strong staining on the bronchial epithelial cell brush border and also on many of the underlying mucous glands. The AT2 receptor was also present on some endothelial cells. These findings were supported by the presence of mRNA in each case. In patients with chronic obstructive pulmonary disease, there was a five- to sixfold increase in the ratio of AT1 to AT2 receptors in the regions of marked fibrosis surrounding the bronchioles. This correlated well with the reduced lung function as expressed by the forced expiratory volume.

Angiotensin type 2 receptors: potential importance in the regulation of blood pressure

The angiotensin type 2 receptor is one of two major angiotensin II receptors that has been identified, cloned and sequenced. The other major receptor, the angiotensin type 1 receptor, is thought to mediate most of the biological responses to the peptide. The angiotensin type 2 receptor is expressed heavily in fetal tissues, but only at a low level in the adult. Documented angiotensin type 2 receptor expression sites in the adult include kidney, heart and mesenteric blood vessels. The function of the angiotensin type 2 receptor is just beginning to be explored. Most of the evidence suggests that the angiotensin type 2 receptor mediates a vasodilator signalling cascade that includes bradykinin, nitric oxide and cyclic guanosine 5-monophosphate. At least some of the beneficial actions of angiotensin type 1 receptor blockade, such as hypotension, are mediated by stimulation of the angiotensin type 2 receptor. Several recent papers suggest that angiotensin type 2 receptors, presumably located in systemic blood vessels, mediate vasodilation and hypotension. The angiotensin type 2 receptor may be a new therapeutic target and candidate gene for the pathophysiology of hypertension.

Dopamine(1) receptor, G(salpha), and Na(+)-H(+) exchanger interactions in the kidney in hypertension

The ability of dopamine(1) (D(1)) receptors to inhibit luminal Na(+)-H(+) exchanger (NHE) activity in renal proximal tubules and induce a natriuresis is impaired in spontaneously hypertensive rats (SHR). However, it is not clear whether the defect is at the level of the D(1) receptor, G(salpha), or effector proteins. The coupling of the D(1) receptor to G(salpha) and NHE3 was studied in renal brush border membranes (BBM), devoid of cytoplasmic second messengers. D(1) receptor, G(salpha), and NHE3 expressions were similar in SHR and their normotensive controls, Wistar-Kyoto rats (WKY). Guanosine-5'-O:-(3-thiotriphosphate) (GTPgammaS) decreased NHE activity and increased NHE3 linked with G(salpha) similarly in WKY and SHR, indicating normal G(salpha) and NHE3 regulation in SHR. However, D(1) agonists increased NHE3 linked with G(salpha) in WKY but not in SHR, and the inhibitory effects of D(1) agonists on NHE activity were less in SHR than in WKY. Moreover, GTPgammaS enhanced the inhibitory effect of D(1) agonist on NHE activity in WKY but not in SHR, suggesting an uncoupling of the D(1) receptor from G(salpha)/NHE3 in SHR. Similar results were obtained with the use of immortalized renal proximal tubule cells from WKY and SHR. We conclude that the defective D(1) receptor function in renal proximal tubules in SHR is proximal to G(salpha)/effectors and presumably at the receptor level. The mechanism(s) responsible for the uncoupling of the D(1) receptor from G proteins remains to be determined. Because the primary structure of the D(1) receptor is not different between normotensive and hypertensive rats, differences in D(1) receptor posttranslational modification are possible.

Identification and regional distribution of the dopamine D(1A) receptor in the gastrointestinal tract

Dopamine (DA) is regarded as an important modulator of enteric function. Recent experiments have suggested that newly cloned DA receptor subtypes are widely expressed in peripheral organs, including the gastrointestinal tract. In the present studies, the D(1A) receptor subtype was identified in rat gut regions through localization of receptor protein by means of light microscopic immunohistochemistry and Western blot analysis and receptor mRNA by RT-PCR and in situ amplification and hybridization (3SR in situ). D(1A) receptor immunoreactivity was shown to have a diverse distribution in the gastrointestinal tract, being present in the gastroesophageal junction, stomach, pylorus, small intestine, and colon. The receptor has a transmural distribution present in both epithelial and muscle layers as well as in blood vessels and lamina propria cells of different gastrointestinal regions. Western blot analysis demonstrated a single 50-kDa band for esophagus, stomach, duodenum, jejunum, and colon. The in situ hybridization signal was localized to the same sites revealed by D(1A) receptor immunoreactivity. RT-PCR revealed an appropriate sized signal in similar regions. This study is the first to identify expression of the central D(1A) receptor throughout the normal mammalian gastrointestinal tract.

Novel expression and regulation of the renin-angiotensin system in metanephric organ culture

To evaluate the presence and regulation of the renin-angiotensin system (RAS) in metanephric organ culture, embryonic day 14 (E14) rat metanephroi were cultured for 6 days. mRNAs for renin and both ANG II receptors (AT(1) and AT(2)) are expressed at E14, and all three genes continue to be expressed in culture. Renin mRNA is localized to developing tubules and ureteral branches in the cultured explants. At E14, renin immunostaining is found in isolated cells scattered within the mesenchyme. As differentiation progresses, renin localizes to the ureteric epithelium, developing tubules and glomeruli. E14 metanephroi contain ANG II, and peptide production persists in culture. Renin activity is present at E14 (6.13 +/- 0.61 pg ANG I. kidney(-1). h(-1)) and in cultured explants (28.84 +/- 1. 13 pg ANG I. kidney(-1). h(-1)). Renin activity in explants is increased by ANG II treatment (70.1 +/- 6.36 vs. 40.97 +/- 1.94 pg ANG I. kidney(-1). h(-1) in control). This increase is prevented by AT(1) blockade, whereas AT(2) antagonism has no effect. These studies document an operational local RAS and a previously undescribed positive-feedback mechanism for renin generation in avascular, cultured developing metanephroi. This novel expression pattern and regulatory mechanism highlight the unique ability of developing renal cells to express an active RAS.

Type 1A dopamine receptor expression in the heart is not altered in spontaneously hypertensive rats

We have recently demonstrated that type 1A dopamine (D1A) receptor is expressed in the rat heart, but its function still remains unknown. In the present study, we investigated possible changes in the expression level and the distribution of the cardiac D1A receptor in the development of left ventricular hypertrophy in spontaneously hypertensive rats/Izumo strain (SHR/Izm) at the ages of 4, 8, and 20 weeks. We examined D1A receptor protein distribution by immunohistochemistry and gene expression by competitive polymerase chain reaction (competitive PCR). In SHR/Izm, compared with the age-matched Wistar Kyoto rats/Izmo strain (WKY/Izm), blood pressure and heart/body weight ratio were significantly increased at 8 and 20 weeks. By immunohistochemistry, the D1A receptor was localized in cardiomyocytes and vascular smooth muscle cells of coronary arteries, but not in interstitial fibrotic tissue. D1A receptor distribution was not changed either by the strain or the age. Competitive PCR analysis showed that the D1A receptor mRNA level was significantly higher at 4 weeks than at 8 and 20 weeks in both strains of rats and that there was no significant difference in D1A receptor mRNA between SHR/Izm and WKY/Izm at any age (43.2 +/- 10.4 attomol x 10(-3)/L v 43.1 +/- 11.2 attomol x 10(-3)/L at 4 weeks, P = not significant, 3.9 +/- 0.9 attomol x 10(-3)/L v 4.0 +/- 1.3 attomol x 10(-3)/L at 8 weeks, P = not significant, 3.0 +/- 1.2 attomol x 10(-3)/L v 1.9 +/- 1.6 attomol x 10(-3)/L at 20 weeks, P = not significant). These results do not support the hypothesis that changes in D1A receptor expression are associated with the development of left ventricular hypertrophy in SHR.

Angiotensin type 2 receptor mediates valsartan-induced hypotension in conscious rats

Inhibition of the renin-angiotensin system is associated with vasodilation and reduction in blood pressure. We hypothesized that angiotensin type 1 (AT(1)) receptor (AT(1)R) blockade is associated with increased production of renal nitric oxide (NO) mediated by release of bradykinin (BK). By use of a microdialysis technique, changes in renal interstitial fluid (RIF) BK, NO end products nitrite and nitrate (NOX), and cGMP were monitored in response to intravenous infusion of the AT(1)R blocker valsartan (10 mg/kg), the angiotensin type 2 (AT(2)) receptor (AT(2)R) blocker PD123319 (50 microg x kg(-1) x min(-1)), and the BK B(2) receptor blocker icatibant (10 microg x kg(-1) x min(-1)) in conscious rats (n=10) during low sodium intake. RIF BK, NOX, and cGMP significantly increased during valsartan treatment, whereas AT(2)R blockade caused a significant decrease in these autacoids. During icatibant infusion, RIF NOX and cGMP decreased by 64% and 40%, respectively, whereas BK increased. Combined administration of valsartan and icatibant, of valsartan and PD123319, or of valsartan, PD123319, and icatibant prevented the increase in RIF cGMP and NOX in response to valsartan alone. These data demonstrate that AT(1)R blockade with valsartan is associated with release of renal BK, which in turn mediates NO production. The results suggest that increased angiotensin II, in response to sodium restriction and valsartan infusion, stimulates AT(2)R, which mediates a BK and NO cascade.

Update: role of the angiotensin type-2 (AT(2)) receptor in blood pressure regulation

In the past, virtually all of the physiologic actions of angiotensin II (ANG II) were thought to be mediated by the type-1 ANG II receptor. However, there is now a compelling body of evidence suggesting that the type-2 (AT2) receptor is an important regulator of renal function and blood pressure (BP). The AT2 receptor stimulates a bradykinin (BK)-nitric oxide (NO)-cyclic GMP vasodilator cascade in blood vessels and in the kidney. Recent studies have shown that absence of the AT2 receptor lends to pressor and natriuretic hypersensitivity to ANG II. Furthermore, there is now excellent evidence that the AT2 receptor mediates pressure natriuresis. The AT2 receptor also stimulates the conversion of prostaglandin E2 (PGE2) to PGF2. In addition, it is now apparent that the therapeutic reduction in BP with AT1 receptor blockade (eg, losartan, valsartan, candesartan) is mediated by ANG II stimulation of the AT2 receptor, leading to increased levels of BK, NO, and cGMP. Current evidence predicts that AT2 receptor agonists would be beneficial in the treatment of hypertension.

Expression and localization of angiotensin subtype receptor proteins in the hypertensive rat heart

The cellular localization of the AT(2) receptor and the regulation of its expression in hypertrophied left ventricle are not well known. We compared the expression of the cardiac AT(1) and AT(2) receptor in spontaneously hypertensive rats/Izumo strain (SHR/Izm) and Wistar Kyoto rats/Izumo strain (WKY/Izm), ages 4, 12, and 20 wk, by means of immunohistochemistry and Western blot analysis. In SHR/Izm, compared with WKY/Izm, blood pressure (161 +/- 2 vs. 120 +/- 2 mmHg at 12 wk, P </= 0.01, and 199 +/- 3 vs. 123 +/- 3 mmHg at 20 wk, P </= 0.01) and heart-to-body weight ratio (3.76 +/- 0.07 vs. 3.06 +/- 0.06 mg/g at 12 wk, P </= 0.01, and 3.90 +/- 0.08 vs. 3.01 +/- 0.12 mg/g at 20 wk, P </= 0.01) were significantly elevated. There was no difference in these values between the two strains at 4 wk of age. Histologically, 20-wk-old SHR/Izm demonstrated myocardial hypertrophy, a thickening of the smooth muscle layer of the intracardiac arteries, and perivascular fibrosis. By immunohistochemistry, the AT(2) receptor was localized to cardiomyocytes and vascular endothelial cells, but not in the vascular smooth muscle cells. No major AT(2) receptor signal was observed in perivascular fibrosis at any age in either strain of rats. No difference was detected in this localization between the two strains. By Western blotting, a single 44-kDa band for the AT(2) receptor and a single 60-kDa band for the AT(1) receptor were detected in ventricles from both strains of rats at all ages. Densitometric analysis demonstrated that the AT(2) receptor 44-kDa band was decreased by 20% at 12 wk and 32% at 20 wk (P < 0.01) in SHR/Izm compared with WKY/Izm. The intensity of the AT(1) receptor 60-kDa band was increased by 57% in 20-wk-old SHR/Izm compared with WKY/Izm (P < 0.05). There was no significant difference in the intensity of the 44- or 60-kDa bands in 4-wk-old animals of either strain. We demonstrated a decrease in the AT(2) receptor and an increase in the AT(1) receptor protein with no change in their localizations in hypertrophied left ventricular myocytes of SHR/Izm.

Role of the angiotensin type 2 receptor in the regulation of blood pressure and renal function

The renin-angiotensin system is a major physiological regulator of body fluid volume, electrolyte balance, and arterial pressure. Virtually all of the biological actions of the principle effector peptide angiotensin II (ANG II) have been attributed to an action at the type 1 (AT(1)) ANG receptor. Until recently, the functional role of the type 2 (AT(2)) receptor, if any, has been unknown, possibly because the AT(2) receptor has a low degree of expression compared with that of the AT(1) receptor. Evidence has now accumulated that the AT(2) receptor opposes functions mediated by the AT(1) receptor. Whereas the AT(1) receptor stimulates cell proliferation, the AT(2) receptor inhibits proliferation and promotes cell differentiation. These differences in growth responses have been ascribed to different cell signaling pathways in which the AT(1) receptor stimulates protein phosphorylation and the AT(2) receptor dephosphorylation. During the past 5 years, studies have demonstrated that the AT(2) receptor is responsible for vasodilation and natriuresis, thus opposing the vasoconstrictor and antinatriuretic effects of ANG II mediated through the AT(1) receptor. Work from our laboratory and others indicates that the AT(2) receptor stimulates vasodilation and natriuresis by an autocrine cascade including bradykinin, nitric oxide, and cyclic GMP. The AT(2) receptor also has been found to control vasodilator prostaglandins, which have a role in blood pressure regulation. The AT(2) receptor appears to play a counterregulatory protective role in the regulation of blood pressure and sodium excretion that opposes the AT(1) receptor.

Nitric oxide: a physiological mediator of the type 2 (AT2) angiotensin receptor

Virtually all of the biological actions of angiotensin II (ANG II) have been thought to be mediated by the type 1 (AT1) angiotensin receptor and the function of the type 2 (AT2) receptor is unknown. We now describe a novel physiological action of ANG II to release nitric oxide (NO) mediated by the AT2 receptor in both the kidney and gastrointestinal tract. We present an integrated model for a counter-regulatory protective action of the AT2 receptor mediated by nitric oxide. In the kidney, ANG II at the AT2 receptor stimulates a vasodilator cascade of bradykinin (BK), NO and cyclic GMP which is tonically activated only during conditions of increased ANG II, such as sodium depletion. In the absence of the AT2 receptor, pressor and antinatriuretic hypersensitivity to ANG II is associated with BK and NO deficiency. In angiotensin-dependent hypertension, the hypotensive effect at AT1 receptor blockade is due at least in part to AT2 receptor stimulation and consequent increased activity of the vasodilator cascade. In the gastrointestinal tract, physiological quantities of ANG II stimulate the AT2 receptor releasing NO and cGMP leading to increased sodium and water absorption. In conclusion, NO is an important physiological mediator of ANG II at the AT2 receptor.

Vascular endothelial growth factor induces nephrogenesis and vasculogenesis

The expression of vascular endothelial growth factor (VEGF) and its receptors Flt-1 and Flk-1 in the rat kidney was examined during ontogeny using Northern blot analysis and immunocytochemistry. In prevascular embryonic kidneys (embryonic day 14 [E14]), immunoreactive Flt-1 and Flk-1 were observed in isolated angioblasts, whereas VEGF was not detected. Angioblasts aligned forming cords before morphologically differentiating into endothelial cells. In late fetal kidneys (E19), immunoreactive VEGF was detected in glomerular epithelial and tubular cells, whereas Flt-1 and Flk-1 were expressed in contiguous endothelial cells. To determine whether VEGF induces endothelial cell differentiation and vascular development in the kidney, the effect of recombinant human VEGF (5 ng/ml) was examined on rat metanephric organ culture, a model known to recapitulate nephrogenesis in the absence of vessels. After 6 d in culture in serum-free, defined media, metanephric kidney growth and morphology were assessed. DNA content was higher in VEGF-treated explants (1.9 +/- 0.17 microg/kidney, n = 9) than in paired control explants (1.4 +/- 0.10 microg/kidney, n = 9) (P < 0.05). VEGF induced proliferation of tubular epithelial cells, as indicated by an increased number of tubules and tubular proliferating cell nuclear antigen-containing cells. VEGF induced upregulation of Flk-1 and Flt-1 expression, as assessed by Western blot analysis. Developing endothelial cells were identified and localized using immunocytochemistry and electron microscopy. Flt-1, Flk-1, and angiotensin-converting enzyme-containing cells were detected in VEGF-treated explants, whereas control explants were negative. These studies confirmed previous reports indicating that the expression of VEGF and its receptors is temporally and spatially associated with kidney vascularization and identified angioblasts expressing Flt-1 and Flk-1 in prevascular embryonic kidneys. The data indicate that VEGF expression is downregulated in standard culture conditions and that VEGF stimulates growth of embryonic kidney explants by expanding both endothelium and epithelium, resulting in vasculogenesis and enhanced tubulogenesis. These data suggest that VEGF plays a critical role in renal development by promoting endothelial cell differentiation, capillary formation, and proliferation of tubular epithelia.

Increased renal vasodilator prostanoids prevent hypertension in mice lacking the angiotensin subtype-2 receptor

The angiotensin subtype-1 (AT(1)) receptor mediates renal prostaglandin E(2) (PGE(2)) production, and pharmacological blockade of the angiotensin subtype-2 (AT(2)) receptor potentiates the action of angiotensin II (Ang II) to increase PGE(2) levels. We investigated the role of the AT(2) receptor in prostaglandin metabolism in mice with targeted deletion of the AT(2) receptor gene. Mice lacking the AT(2) receptor (AT(2)-null) had normal blood pressure that was slightly elevated compared with that of wild-type (WT) control mice. AT(2)-null mice had higher renal interstitial fluid (RIF) 6-keto-PGF(1alpha) (a stable hydrolysis product of prostacyclin [PGI(2)]) and PGE(2) levels than did WT mice, and had similar increases in PGE(2) and 6-keto-PGF(1alpha) in response to dietary sodium restriction and Ang II infusion. In contrast, AT(2)-null mice had lower PGF(2alpha) levels compared with WT mice during basal conditions and in response to dietary sodium restriction or infusion of Ang II. RIF cAMP was markedly higher in AT(2)-null mice than in WT mice, both during basal conditions and during sodium restriction or Ang II infusion. AT(1) receptor blockade with losartan decreased PGE(2), PGI(2), and cAMP to levels observed in WT mice. To determine whether increased vasodilator prostanoids prevented hypertension in AT(2)-null mice, we treated AT(2)-null and WT mice with indomethacin for 14 days. PGI(2), PGE(2), and cAMP were markedly decreased in both WT and AT(2)-null mice. Blood pressure increased to hypertensive levels in AT(2)-null mice but was unchanged in WT. These results demonstrate that in the absence of the AT(2) receptor, increased vasodilator prostanoids protect against the development of hypertension.

Sustained hypersensitivity to angiotensin II and its mechanism in mice lacking the subtype-2 (AT2) angiotensin receptor

The vast majority of the known biological effects of the renin-angiotensin system are mediated by the type-1 (AT1) receptor, and the functions of the type-2 (AT2) receptor are largely unknown. We investigated the role of the AT2 receptor in the vascular and renal responses to physiological increases in angiotensin II (ANG II) in mice with targeted deletion of the AT2 receptor gene. Mice lacking the AT2 receptor (AT2-null mice) had slightly elevated systolic blood pressure (SBP) compared with that of wild-type (WT) control mice (P < 0.0001). In AT2-null mice, infusion of ANG II (4 pmol/kg/min) for 7 days produced a marked and sustained increase in SBP [from 116 +/- 0.5 to 208 +/- 1 mmHg (P < 0.0001) (1 mmHg = 133 Pa)] and reduction in urinary sodium excretion (UNaV) [from 0.6 +/- 0.01 to 0.05 +/- 0.002 mM/day (P < 0.0001)] whereas neither SBP nor UNaV changed in WT mice. AT2-null mice had low basal levels of renal interstitial fluid bradykinin (BK), and cyclic guanosine 3', 5'-monophosphate, an index of nitric oxide production, compared with WT mice. In WT mice, dietary sodium restriction or ANG II infusion increased renal interstitial fluid BK, and cyclic guanosine 3', 5'-monophosphate by approximately 4-fold (P < 0.0001) whereas no changes were observed in AT2-null mice. These results demonstrate that the AT2 receptor is necessary for normal physiological responses of BK and nitric oxide to ANG II. Absence of the AT2 receptor leads to vascular and renal hypersensitivity to ANG II, including sustained antinatriuresis and hypertension. These results strongly suggest that the AT2 receptor plays a counterregulatory protective role mediated via BK and nitric oxide against the antinatriuretic and pressor actions of ANG II.

Protective role of the angiotensin AT2 receptor in a renal wrap hypertension model

We evaluated the role of the renal angiotensin II type 2 (AT2) receptor in blood pressure regulation in rats with 2-kidney, 1 figure-8 wrap (Grollman) hypertension. Renal wrapping increased systolic blood pressure (SBP). Renal interstitial fluid (RIF) bradykinin (BK), nitric oxide end-products (NOX), and cGMP were higher in the contralateral intact kidney than in the wrapped kidney. In rats with Grollman hypertension, losartan normalized SBP and increased renal function, RIF BK, NOX, and cGMP only in contralateral kidneys. In contrast, PD 123319, a specific AT2-receptor antagonist, significantly increased SBP and decreased RIF BK, NOX, and cGMP in both kidneys. Combined administration of losartan and PD 123319 prevented the decrease in SBP and the increase in RIF BK, NOX, and cGMP levels observed with losartan alone. BK-receptor blockade caused a significant increase in RIF BK and a decrease in RIF NOX and cGMP in both kidneys similar to that observed during administration of PD 123319. In rats that underwent sham operation, RIF BK increased in response to angiotensin II, an effect that was blocked by PD 123319. These data demonstrate that angiotensin II mediates renal production of BK, which, in turn, releases nitric oxide and cGMP via stimulation of AT2 receptors. The increase in blood pressure and the decrease in renal BK, nitric oxide, and cGMP during AT2-receptor blockade suggests that the AT2 receptor mediates counterregulatory vasodilation in Grollman hypertension and prevents a further increase in blood pressure.

Dopamine-1 receptor coupling defect in renal proximal tubule cells in hypertension

The ability of the dopamine-1 (D1)-like receptor to stimulate adenylyl cyclase (AC) and phospholipase C (PLC), inhibit sodium transport in the renal proximal tubule (RPT), and produce natriuresis is attenuated in several rat models of hypertension. Since the inhibitory effect of D1-like receptors on RPT sodium transport is also reduced in some patients with essential hypertension, we measured D1-like receptor coupling to AC and PLC in cultures of human RPT cells from normotensive (NT) and hypertensive (HT) subjects. Basal cAMP concentrations were the same in NT (n=6) and HT (n=4). However, the D1-like receptor agonist fenoldopam increased cAMP production to a greater extent in NT (maximum response=67+/-1%) than in HT (maximum response=17+/-5%), with a potency ratio of 105. Dopamine also increased cAMP production to a greater extent in NT (32+/-3%) than in HT (14+/-3%). The fenoldopam-mediated increase in cAMP production was blocked by SCH23390 (a D1-like receptor antagonist) and by antisense D1 oligonucleotides in both HT and NT, indicating action at the D1 receptor. The stimulatory effects of forskolin and parathyroid hormone-related protein of cAMP accumulation were not statistically different in NT and HT, indicating receptor specificity and an intact G-protein/AC pathway. The fenoldopam-stimulated PLC activity was not impaired in HT, and the primary sequence and expression of the D1 receptor were the same in NT and HT. However, D1 receptor serine phosphorylation in the basal state was greater in HT than in NT and was not responsive to fenoldopam stimulation in HT. These studies demonstrate the expression of D1 receptors in human RPT cells in culture. The uncoupling of the D1 receptor in both rats (previously described) and humans (described here) suggests that this mechanism may be involved in the pathogenesis of hypertension; the uncoupling may be due to ligand-independent phosphorylation of the D1 receptor in hypertension.

The Medical Academic Advancement Program at the University of Virginia School of Medicine

Since 1984 the University of Virginia School of Medicine has conducted the Medical Academic Advancement Program for minority and disadvantaged students interested in careers in medicine. The program is a six-week residential program for approximately 130 undergraduate and post-baccalaureate students per year. It emphasizes academic course work--biology, chemistry, physics, and essay writing--to prepare the participants for the Medical College Admission Test. Non-graded activities, such as a clinical medicine lecture series, clinical experiences, and a special lecture series, and special workshops are also offered. The participants take two simulated MCAT exams. Between 1984 and 1998, 1,497 students have participated in the program, with complete follow-up information available for 690 (46%). Of the 1,487 participants, 80 (5%) have graduated from the University of Virginia School of Medicine and 174 (12%) from other medical schools; 44 (3%) are attending the medical school now, and 237 (16%) are at other medical schools; 44 (3%) have graduated from other health professions schools, and 54 (3%) are attending such schools. The retention rate for participants at the University of Virginia School of Medicine is 91% (that is, all but seven of the 80 who matriculated have been retained past the first year). The Medical Academic Advancement Program has been successful in increasing the number of underrepresented minority students matriculating into and continuing in medical education. Such programs warrant continued support and encouragement.

Novel actions of angiotensin II via its renal type-2 (AT(2)) receptor

The vast majority of the biologic effects of angiotensin II have been considered to be mediated by the subtype-1 (AT(1)) receptor. The AT(2) receptor is expressed to a low degree in most adult cells and tissues, and its function has not been understood. Recent studies, however, have identified novel actions of angiotensin II mediated by the AT(2) receptor in the kidney. These AT(2) receptor actions have importance in the control of blood pressure and hypertension. The AT(2) receptor mediates a renal vasodilator cascade, including generation of bradykinin, nitric oxide, and cyclic GMP. This action of angiotensin II occurs when the renin-angiotensin system is activated, as in sodium depletion. The AT(2) receptor also appears to mediate prostaglandin (PG) F(2)(a) formation, probably by stimulating conversion of PGE2 to PGF(2)(a). The AT(2) receptor plays a counter-regulatory vasodilator role opposing the vasoconstrictor actions of angiotensin II. The AT(1) and AT(2) receptors engage in inter-receptor "cross-talk." In the absence of the AT(2) receptor, sustained angiotensin II pressor and antinatriuretic hypersensitivity occurs, mediated by a deficiency of bradykinin, nitric oxide, and cyclic GMP. The AT(2) receptor may play an important role in stimulating pressure natriuresis, but definitive studies are required to resolve this issue. The AT(2) receptor mediates several renal actions of angiotensin II, appears to be important in the physiologic regulation of blood pressure, and may be involved in the pathophysiology of hypertension.

Compartmentalization of extracellular cGMP determines absorptive or secretory responses in the rat jejunum

We examined potential mechanisms by which angiotensin subtype-2 (AT2) receptor stimulation induces net fluid absorption and serosal guanosine cyclic 3',5'-monophosphate (cGMP) formation in the rat jejunum. L-arginine (L-ARG) given intravenously or interstitially enhanced net fluid absorption and cGMP formation, which were completely blocked by the nitric oxide (NO) synthase inhibitor, N-nitro-L-arginine methylester (L-NAME), but not by the specific AT2 receptor antagonist, PD-123319 (PD). Dietary sodium restriction also increased jejunal interstitial fluid cGMP and fluid absorption. Both could be blocked by PD or L-NAME, suggesting that the effects of sodium restriction occur via ANG II at the AT2 receptor. L-ARG-stimulated fluid absorption was blocked by the soluble guanylyl cyclase inhibitor 1-H-[1,2,4]oxadiazolo[4, 2-alpha]quinoxalin-1-one (ODQ). Cyclic GMP-specific phosphodiesterase in the interstitial space decreased extracellular cGMP content and prevented the absorptive effects of L-ARG. Angiotensin II (ANG II) caused an increase in net Na+ and Cl- ion absorption and 22Na+ unidirectional efflux (absorption) from the jejunal loop. In contrast, intraluminal heat-stable enterotoxin of Escherichia coli (STa) increased loop cGMP and fluid secretion that were not blocked by either L-NAME or ODQ. These findings suggest that ANG II acts at the serosal side via AT2 receptors to stimulate cGMP production via soluble guanylyl cyclase activation and absorption through the generation of NO, but that mucosal STa activation of particulate guanylyl cyclase causes secretion independently of NO, thus demonstrating the opposite effects of cGMP in the mucosal and serosal compartments of the jejunum.

Differential regulation of renal angiotensin subtype AT1A and AT2 receptor protein in rats with angiotensin-dependent hypertension

-This study was designed to investigate distribution and regulation of the renal AT1A and AT2 subtype receptors in rats with either systemic angiotensin II (Ang II)-induced hypertension or acute phase renal hypertension (2-kidney, 1-clip [2K1C] or 2-kidney, 1-figure-of-8-wrap [2K1W]). In normal rat kidneys, positive immunostaining for the AT1A receptor was observed in the intrarenal vasculature, glomeruli, proximal and distal tubules, and collecting ducts. The AT2 receptor was localized mainly to the glomeruli. The AT1A but not AT2 receptor protein expression was significantly reduced in rats with 10-day systemic Ang II-induced hypertension. In both 7-day 2K1C and 3-day 2K1W rats, the AT1A receptor was significantly reduced in ischemic and contralateral kidneys compared with sham-operated control rats. Reduction in AT2 receptor expression was observed only in the ischemic kidneys in 2K1C and 2K1W renal hypertensive rats. These results demonstrate that the AT1A receptor is widely distributed in the glomerulus and all other nephron segments of the rat kidney. Renal AT1A but not AT2 receptor protein is downregulated in rats with Ang II-induced hypertension. In renal hypertensive rats, the AT1A receptor is bilaterally downregulated and the AT2 receptor is downregulated only in the ischemic kidney.

Selective inhibition of the renal dopamine subtype D1A receptor induces antinatriuresis in conscious rats

Both dopamine D1-like (D1A and D1B) and D2-like (D2, D3, and D4) receptor subfamilies are present in the kidney. Blockade of the intrarenal D1-like receptor family is associated with natriuresis and diuresis. Because the D1A and D1B receptor subtypes are not distinguishable by currently available dopaminergic agents, their functional role remains undefined. In the present study, the effect of selective inhibition of the renal D1A receptor with phosphorothioated antisense oligodeoxynucleotide (AS-ODN) was investigated in conscious uninephrectomized rats. After renal interstitial administration of Texas red-labeled D1A receptor AS-ODN, intense fluorescent signal was localized in the renal tubular epithelium and vasculature. In rats on normal salt intake, AS-ODN injected interstitially into the kidney reduced daily urinary sodium excretion (1.4+/-0.04 versus 0.8+/-0.2 mEq/d, n=5, P<0.05) and urine output (16.9+/-3.8 versus 12.5+/-3.6 mL/d, n=5, P<0.05). In rats on high sodium intake, continuous renal interstitial administration of D1A receptor AS-ODN transiently decreased daily urinary sodium excretion (5.4+/-0.5 versus 4.2+/-0.3 mEq/d, n=7, P<0.01) and urine output (27.6+/-4.5 versus 18.1+/-1.8 mL/d, n=7, P<0.01). Neither vehicle nor sense oligodeoxynucleotide had significant effects. Systolic blood pressure remained unchanged. The renal D1A receptor protein was significantly decreased by 35% and 46% at the end of the study in AS-ODN-treated rats on normal and high salt intake, respectively, whereas the D1B receptor and beta-actin were not affected. These results provide the first direct evidence that the renal D1A receptor subtype plays an important role in the control of sodium excretion.

Reductive assays for S-nitrosothiols: implications for measurements in biological systems

Bioactive SNOs are found in many tissues. We speculated SNOs might be misidentified in conventional assays which reduce NO-3 to NO. S-Nitrosothiols were exposed to saturated VCl3 in HCl, 1% KI in acetic acid, photolysis, or CuCl and CSH in He; NO was measured by chemiluminescence. S-Nitrosothiols were readily detected in VCl3 but not in KI. Reduction in CuCl/cysteine was linear (r2 = 1.0, n = 6), sensitive to 10 pmol, and eliminated by HgCl2; it did not detect NO-2, NO-3, or 3-nitrotyrosine. S-Nitrosothiols represented approximately 2.9% of NOx assayed by VCl3 in human serum, of which <5% were low-mass species. In summary, (i) conventional assays may misidentify NO-3, but not NO-2, as SNOs; and (ii) chemiluminescence/reduction systems may be sensitive and specific as SNO assays. We suggest that assay of the SNO fraction in biological NOx may be more relevant and feasible than is now appreciated.

Expression of the dopamine D3 receptor protein in the rat kidney

The dopamine D3 receptor subtype was identified in rat kidney using both light microscopic immunohistochemistry and electron microscopic immunocytochemistry. Antipeptide polyclonal antisera were directed to both extracellular and intracellular regions of the native D3 receptor. Selectivity of the antipeptide antisera was validated by their ability to recognize native receptor protein expressed in permanently transfected mouse LTK- cells or Spodoptera fragiperda (Sf9) cell membranes. Light microscopic immunohistochemical staining for the D3 receptor was observed only in the cortex. Specific staining was present in proximal and distal tubules, cortical collecting ducts, glomeruli, and renal vasculature. Immunostaining was observed predominantly in the apical portion of both the proximal and distal tubules. Renal arterial staining was prominent in the medial and adventitial layers. Electron microscopic immunocytochemistry revealed immunogold particles in arteriolar smooth muscle cells of the renal vasculature. In proximal and distal tubules and cortical collecting duct, immunogold staining was localized to apical portions of tubule cells. D3 receptor immunogold staining in the glomeruli was clearly present in podocytes. Western blot analysis demonstrated a single D3 receptor band in infected Sf9 cell membranes, in transfected LTK- cells, and in kidney and brain but not in noninfected Sf9 cell membranes or in D2 or D3 receptor transfected or nontransfected LTK- cells. The use of receptor subtype-selective antibodies allows for the tissue localization of specific dopamine receptors that are not distinguished by current pharmacological or ligand-binding technology. The rat kidney expresses the D3 receptor at sites previously deemed to have D2-like receptors.

Molecular cloning of KS, a novel rat gene expressed exclusively in the kidney

BACKGROUND

We aimed to identify genes with kidney specific, developmentally regulated expression. Here we report the cDNA sequence and expression pattern of KS, a novel kidney-specific rat gene.

METHODS

A partial cDNA was identified by differential display polymerase chain reaction (PCR) of a renal cell fraction enriched for proximal tubular and renin-expressing cells. Using the partial cDNA as a probe, a rat kidney cDNA library was screened. The full-length KS sequence was obtained by PCR amplification of cDNA ends. The expression pattern of KS was investigated by Northern blot. RNA was extracted from several organs of newborn and adult rats, as well as from the kidneys of rats with altered tubular function, that is, rats that had undergone unilateral nephrectomy, unilateral ureteral obstruction, neonatal losartan treatment, and the appropriate control animals. The expression of KS was also investigated in the kidneys of rats with spontaneous or renovascular hypertension.

RESULTS

The KS cDNA (2426 bp) contained one open reading frame encoding a predicted 572 amino acid protein. The derived peptide sequence displayed approximately 70% similarity to the hypertension-related SA gene product and approximately 50% similarity to prokaryotic and eukaryotic acetyl-CoA synthases (EC 6. 2.1.1). KS was expressed in the kidney and not in any other organ assayed. KS RNA was not detected in fetal and newborn rat kidney but became apparent after one week of postnatal life. Gene expression was downregulated in rat models of altered tubular function. KS expression was decreased in spontaneously hypertensive rats but not in renovascular hypertension.

CONCLUSION

KS, a novel rat gene, exhibits a unique tissue-specific expression exclusively in mature kidneys. The data suggest KS may encode an adenosine monophosphate binding enzyme.

Regulation of jejunal sodium and water absorption by angiotensin subtype receptors

The purpose of this study was to determine the precise role of angiotensin subtype-1 (AT1) and -2 (AT2) receptors and the mechanisms by which they act to alter fluid transport in the rat jejunum. In rats on normal sodium intake, ANG II at low dose stimulated net jejunal fluid absorption, whereas at a high dose the peptide inhibited absorption. Low-dose ANG II-stimulated fluid absorption was blocked completely by the specific AT2 receptor antagonist PD-123319 (PD) but was unchanged by the AT1 receptor antagonist losartan (Los). The AT2 receptor agonist CGP-42112A, caused an inversely dose-dependent increase in fluid absorption, which also was totally prevented by PD but was unaltered by Los. Conversely, high-dose ANG II inhibition of absorption was blocked by Los but not by PD. In animals receiving normal sodium intake, neither Los nor PD alone altered fluid absorption. In sodium-restricted animals, however, Los alone increased absorption and PD alone inhibited absorption. In rats on normal sodium intake, low-dose ANG II increased jejunal interstitial and luminal (loop) fluid concentrations of cGMP. These increases in cGMP were blocked with PD but not with Los. 8-Bromoguanosine-3',5'-cyclic monophosphate administered via the mesenteric artery or the submucosal interstitial space markedly increased absorption, but it inhibited absorption when administered into the loop. High-dose ANG II decreased jejunal interstitial and loop fluid cAMP and increased PGE2. The increase in PGE2 was blocked by Los but not by PD. The data demonstrate that ANG II mediates jejunal sodium and water absorption by an action at the AT2 receptor involving cGMP formation. The data also show that ANG II inhibits absorption via the AT1 receptor by a mechanism that is both negatively coupled to cAMP and increases jejunal PGE2 production.

Disruption of the dopamine D3 receptor gene produces renin-dependent hypertension

Since dopamine receptors are important in the regulation of renal and cardiovascular function, we studied the cardiovascular consequences of the disruption of the D3 receptor, a member of the family of D2-like receptors, expressed in renal proximal tubules and juxtaglomerular cells. Systolic and diastolic blood pressures were higher (approximately 20 mmHg) in heterozygous and homozygous than in wild-type mice. An acute saline load increased urine flow rate and sodium excretion to a similar extent in wild-type and heterozygous mice but the increase was attenuated in homozygous mice. Renal renin activity was much greater in homozygous than in wild-type mice; values for heterozygous mice were intermediate. Blockade of angiotensin II subtype-1 receptors decreased systolic blood pressure for a longer duration in mutant than in wild-type mice. Thus, disruption of the D3 receptor increases renal renin production and produces renal sodium retention and renin-dependent hypertension.

Immunolocalization of subtype 2 angiotensin II (AT2) receptor protein in rat heart

Angiotensin II exerts its effects on cardiovascular function and water and sodium homeostasis by interacting with plasma membrane receptors on target organs. The existence of subtype 2 angiotensin II (AT2) receptors in the rat heart has been demonstrated by ligand binding and reverse transcription-polymerase chain reaction. In the present study, the expression and localization of AT2 receptor protein in the rat heart was investigated using an antipeptide polyclonal antibody against the native rat AT2 receptor by light microscopic immunocytochemistry and Western blot analysis. In frozen tissue sections, positive immunostaining was observed in the myocardium and coronary vessels throughout the ventricle and atrium of neonatal and young rat hearts. Coronary vessels of the neonatal heart were more intensely stained compared with the surrounding myocardium. Positive immunoreactivity in the coronary vessels of young rats was localized to vascular endothelium but not in the smooth muscle cells. Preadsorption controls were all negative. Western blot analysis showed that the AT2 receptor protein (approximately 44 kDa) was detectable from the AT2 receptor-transfected COS-7 cells and neonatal rat cardiac myocytes but not from fibroblasts or young rat aortic smooth muscle cells. The neonatal rat heart expressed significantly more AT2 receptors than young rat heart. These data provide the first direct evidence for the expression and localization of AT2 receptor protein in the rat heart.