α1-AR Antagonists Research Articles

Alpha1‐Adrenoceptor Antagonists Improve Bladder Storage Function Through Reduction of Afferent Activity in Rats With Bladder Outlet Obstruction

Using a rat BOO model, we determined whether α1-adrenoceptor (AR) antagonists (silodosin, prazosin) improve the bladder storage function by reducing afferent input from the lower urinary tract. Male rats received partial bladder outlet obstruction or sham surgery were used. Four weeks following surgery, their voiding behavior was measured in a metabolic cage. BOO-rats were administered silodosin, prazosin or vehicle for 2 weeks subcutaneously using osmotic pump. At the post-drug condition, voiding behavior was measured again. The L6 spinal cord was removed and immunostained using anti c-Fos antibody. The rats were also performed continuous cystometry with saline without anesthesia or restraint at the pre- and post-drug conditions. Metabolic cage study showed the voiding behavior of BOO-rats was characterized by increase in frequency of urination and decrease in volume voided. Cystometric evaluation also showed the significant increase both in the number of successive voiding contraction and in contraction pressure. The administration of silodosin or prazosin significantly decreased urinary frequency and the number of micturition reflex but affected neither bladder contraction pressure nor residual volume. The number of c-Fos-positive cell significantly increased in BOO-rats, while significantly decreased in those receiving αl-AR antagonists. The present study demonstrates that α1-AR antagonists silodosin and prazosin have an inhibitory effect on afferent input from the lower urinary tract independently of reducing urethral resistance, and thereby reduce the storage dysfunction secondary to BOO. This result suggests that αl-AR, particularly αlA-AR, may play an important role in the activation of the afferent pathway.

690 UNIQUE GROWTH-INHIBITORY EFFECTS OF SUBTYPE SELECTIVE α1-ADRENOCEPTOR ANTAGONISTS ON HUMAN PROSTATE CANCER CELLS

You have accessJournal of UrologyProstate Cancer: Basic Research V1 Apr 2010690 UNIQUE GROWTH-INHIBITORY EFFECTS OF SUBTYPE SELECTIVE α1-ADRENOCEPTOR ANTAGONISTS ON HUMAN PROSTATE CANCER CELLS Yasuhide Hori, Kenichiro Ishii, Hideki Kanda, Kouhie Nishikawa, Yuko Yoshio, Norihito Soga, Hideaki Kise, Kiminobu Arima, and Yoshiki Sugimura Yasuhide HoriYasuhide Hori More articles by this author , Kenichiro IshiiKenichiro Ishii More articles by this author , Hideki KandaHideki Kanda More articles by this author , Kouhie NishikawaKouhie Nishikawa More articles by this author , Yuko YoshioYuko Yoshio More articles by this author , Norihito SogaNorihito Soga More articles by this author , Hideaki KiseHideaki Kise More articles by this author , Kiminobu ArimaKiminobu Arima More articles by this author , and Yoshiki SugimuraYoshiki Sugimura More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.1089AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES It has been well established that α1-adrenoceptor (α1-AR) antagonists, therapeutic drugs for BPH, have growth-inhibitory effects on human prostate cancer (hPCa) cells. In Japan, subtype selective α1-AR antagonists are frequently used because of low incidence of side effects. Although we have recently reported the growth-inhibitory effects of the α1d-selective antagonist naftopidil on hPCa cells, little is known about the relationship between the growth-inhibitory effects of naftopidil and the androgen receptor signal or the α1-AR signal in hPCa cells. In this study, we investigated the biochemical mechanisms of growth-inhibitory effects by subtype selective α1-AR antagonists in terms of androgen sensitivity of hPCa cells and α1-AR selectivity of each antagonist. METHODS The three α1a selective-AR antagonists (tamsulosin, silodosin, and RS100329) and two α1d selective antagonists (naftopidil and BMY7378) were used. We first evaluated the effects of each antagonist (10 μM) on the cell proliferation of LNCaP and the derived two sublines E9 and AIDL differing in hormone sensitive status. Next, to simulate the tumor microenvironment in an in vivo transplant model, we recombined E9 and human prostatic stromal cells (PrSC) in collagen gels and grafted them beneath the renal capsule of athymic mice. Mice were treated with each antagonist (10 mg/Kg/day) by oral gavage. RESULTS The parental LNCaP, androgen-low-sensitive E9, and androgen-insensitive AIDL expressed mRNAs of both α1a- and α1d-subtype, mainly α1d-subtype, and mainly α1a-subtype, respectively. Silodosin and naftopidil but not tamsulosin showed approximately equivalent growth-inhibitory effects on LNCaP, E9, and AIDL cells in vitro. FACS analysis revealed induction of apoptosis in silodosin-treated hPCa cells and increase of G1 arrest in naftopidil-treated hPCa cells. Tumorigenic study in vivo showed that significant reduction of E9 + PrSC tumor weight was observed in mice treated with not only silodosin and naftopidil but also tamsulosin. CONCLUSIONS We have demonstrated that subtype selective α1-AR antagonists have unique growth-inhibitory effects on hPCa cells. The growth-inhibitory effects of subtype selective α1-AR antagonists are not related to both androgen sensitivity of hPCa cells and α1-AR subtype expression in each hPCa cells, suggesting that subtype selective α1-AR antagonists are potentially effective to prevent not only development of hPCa but also recurrence of hPCa. Tsu City, Japan© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e269-e270 Peer Review Report Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yasuhide Hori More articles by this author Kenichiro Ishii More articles by this author Hideki Kanda More articles by this author Kouhie Nishikawa More articles by this author Yuko Yoshio More articles by this author Norihito Soga More articles by this author Hideaki Kise More articles by this author Kiminobu Arima More articles by this author Yoshiki Sugimura More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

New Drug Approvals: Silodosin for Benign Prostatic Hyperplasia

To review the pharmacology, pharmacokinetics, clinical trials, and safety of silodosin, a recently approved alpha(1A)-adrenergic receptor (AR) antagonist for benign prostatic hyperplasia (BPH). English-only articles obtained from MEDLINE (1966-October 2009) using the search terms silodosin and KMD-3213 were reviewed. In addition, a search of International Pharmaceutical Abstracts (1970-October 2009) was conducted. Available English-language articles were reviewed, as well as abstracts from available non-English articles. Silodosin reduces urinary symptoms associated with BPH in as little as 1 day after initiation. The largest clinical trial conducted to date demonstrated a decrease in International Prostate Symptom Score of -6.4 +/- 6.63 points compared to -3.5 +/- 5.84 in patients receiving placebo (p < 0.0001). Silodosin also improved urinary flow rates by approximately 2.8 +/- 3.44 mL/sec, which is comparable to other alpha(1)-AR antagonists. The usual dose of silodosin is 8 mg once daily and should be reduced to 4 mg for patients with moderate renal dysfunction. Use is contraindicated in patients with severe renal and hepatic impairment or taking strong CYP3A4 inhibitors. In clinical trials, the most prevalent adverse effects were ejaculatory disturbances, occurring in approximately 28% of patients, although only 2.8% of patients discontinued treatment due to this adverse effect. Preliminary data suggest that, similar to other third-generation alpha(1A)-AR antagonists, silodosin has little potential to cause significant cardiovascular adverse effects such as orthostatic hypotension or syncope. To confirm these findings, long-term studies are still needed, especially in patients taking antihypertensive agents and in those with a history of intolerance to other alpha(1)-AR antagonists. Silodosin was approved by the Food and Drug Administration in 2008. Long-term studies demonstrating improvement in clinically important outcomes of BPH have yet to be published. In addition, pharmacoeconomic analyses would assist in defining its current place in therapy. Until this information is available, silodosin may be best reserved as an alternative to other second- and third-generation alpha(1)-AR antagonists.

The Alpha-1D Is the Predominant Alpha-1-Adrenergic Receptor Subtype in Human Epicardial Coronary Arteries

The goal was to identify alpha-1-adrenergic receptor (AR) subtypes in human coronary arteries. The alpha1-ARs regulate human coronary blood flow. The alpha1-ARs exist as 3 molecular subtypes, alpha1A, alpha1B, and alpha1D, and the alpha1D subtype mediates coronary vasoconstriction in the mouse. However, the alpha1A is thought to be the only subtype in human coronary arteries. We obtained human epicardial coronary arteries and left ventricular (LV) myocardium from 19 transplant recipients and 6 unused donors (age 19 to 70 years; 68% male; 32% with coronary artery disease). We cultured coronary rings and human coronary smooth muscle cells. We assayed alpha1- and beta-AR subtype messenger ribonucleic acid (mRNA) by quantitative real-time reverse transcription polymerase chain reaction and subtype proteins by radioligand binding and extracellular signal-regulated kinase (ERK) activation. The alpha1D subtype was 85% of total coronary alpha1-AR mRNA and 75% of total alpha1-AR protein, and alpha1D stimulation activated ERK. In contrast, the alpha1D was low in LV myocardium. Total coronary alpha1-AR levels were one-third of beta-ARs, which were 99% the beta2 subtype. The alpha1D subtype is predominant and functional in human epicardial coronary arteries, whereas the alpha1A and alpha1B are present at very low levels. This distribution is similar to the mouse, where myocardial alpha1A- and alpha1B-ARs mediate beneficial functional responses and coronary alpha1Ds mediate vasoconstriction. Thus, alpha1D-selective antagonists might mediate coronary vasodilation, without the negative cardiac effects of nonselective alpha1-AR antagonists in current use. Furthermore, it could be possible to selectively activate beneficial myocardial alpha1A- and/or alpha1B-AR signaling without causing coronary vasoconstriction.

Role of α1‐adrenergic receptors in detrusor overactivity induced by cold stress in conscious rats

alpha(1)-Adrenergic receptors (ARs) are involved in micturition control both centrally and peripherally. alpha(1)-AR antagonists improve not only voiding but also storage symptoms in patients with bladder outlet obstruction. We investigated the role of alpha(1)-AR mechanisms involved in detrusor overactivity induced by cold stress in conscious rats. Continuous cystometry was performed at room temperature (RT, 28 +/- 2 degrees C) and for 40 min at cold temperature (CT, 4 +/- 2 degrees C). Voiding interval (VI), micturition volume (MV), and bladder capacity (BC) were evaluated before and after intravenous administration of KMD-3213 (selective alpha(1A)-AR antagonist), naftopidil (selective alpha(1D)-AR antagonist), tamsulosin (selective alpha(1A/1D)-AR antagonist), and prazosin (non-selective alpha(1)-AR antagonist). Blood pressure (BP), cumulative voided volume and body temperature were also evaluated. At RT, none of the AR antagonists caused significant change in the cystometric parameters. During 40 min of cold stress cumulative voided volume and body temperature did not change, but there were significant decreases in VI, MV, and BC. Low doses of the AR antagonists had no effect on CT-induced decreases of these variables. However, high doses of KMD-3213, tamsulosin, naftopidil and prazosin significantly inhibited the CT-induced decreases in VI, MV, and BC. CT caused a significant increase in BP, and this was not affected by low doses of the AR antagonists. However, high doses of prazosin significantly lowered the CT-induced increase of BP. Cold stress induces detrusor overactivity and increases BP in conscious rats. These effects are mediated, at least in part, by alpha(1A)-AR and alpha(1D)-AR subtypes and can be prevented/reduced by alpha(1)-AR antagonists.

Intraoperative Floppy Iris Syndrome Associated with α1-Adrenergic Receptor Antagonists

To describe intraoperative floppy iris syndrome (IFIS) in association with alpha(1)-adrenergic receptor (alpha(1)AR) antagonists by conducting a thorough literature review. Literature retrieval was accomplished by searching MEDLINE (2000-December 2007) using the terms intraoperative floppy iris syndrome (IFIS), adrenergic alpha-antagonist(s), tamsulosin, doxazosin, terazosin, and/or alfuzosin. In addition, reference lists from identified publications were reviewed to identify additional reports and studies of interest. All articles in English identified from data sources were reviewed for relevance and uniqueness prior to inclusion. IFIS was first described in 2005 as a clinical triad observed during cataract surgery that includes fluttering and billowing of the iris stroma, propensity for iris prolapse, and constriction of the pupil. IFIS increases the risk of complications during cataract surgery. Numerous reports have linked IFIS to use of alpha(1)AR antagonists, most notably tamsulosin, which is prescribed for benign prostatic hyperplasia. Tamsulosin blocks prostatic alpha(1A)ARs but may also selectively block alpha(1A)ARs in the iris dilator muscle, preventing mydriasis during cataract surgery. Other alpha(1)AR antagonists, including terazosin, doxazosin, and alfuzosin, have also been linked to IFIS; however, their relationship to the syndrome is not as definitive. When ophthalmologists are aware of a patient's previous alpha(1)AR antagonist exposure, specific steps can be taken to reduce the risk of surgical complications. Corrective measures used during surgery have included iris expansion hooks, intracameral phenylephrine, and preoperative atropine. IFIS is a clinical syndrome observed during cataract surgery reported in patients taking systemic alpha(1)AR antagonists. It has been most strongly linked to use of tamsulosin. Medication washout periods of up to 2 weeks and specific surgical procedures have been attempted to reduce risk of complications from alpha(1)AR antagonists in the setting of cataract surgery. Patients should be educated regarding potential risks of this drug class so that they can discuss them with their healthcare providers, specifically ophthalmologists, prior to cataract surgery.

Recent Advances in &amp;#945;1-Adrenoreceptor Antagonists as Pharmacological Tools and Therapeutic Agents

Native alpha(1)-adrenoreceptors (ARs) appear to exist as three different subtypes encoded by three genes, alpha(1A/1a), alpha(1B/1b), and alpha(1D/1d). Historically, the discovery of agents selective for each of the three alpha(1)-AR subtypes has been an active area of medicinal chemistry research because of the wide number of possible therapeutic applications. Initially introduced for the management of hypertension, alpha(1)-AR antagonists have, in fact, become increasingly common in the treatment of benign prostatic hyperplasia (BPH), and are effective therapeutic tools, when characterized by an appropriate uroselective profile. The majority of these derivatives display a competitive mechanism of action and belong to a variety of structural classes, but this review is focused on compounds belonging to the quinazoline, benzodioxane, arylpiperazine, and 1,4-dihydropyridine classes.

Trends in the Development of New Drugs for Treatment of Benign Prostatic Hyperplasia

Benign prostatic hyperplasia (BPH) is a common condition in aging men that is characterized by nonmalignant enlargement of the prostate gland, and is frequently accompanied by urinary obstruction, and lower urinary tract symptoms (LUST). Currently pharmacotherapy of BPH is based on two classes of drugs: alpha(1)-adrenoceptor (alpha(1)-AR) antagonists and 5alpha-reductase inhibitors. It has been shown that alpha(1)-AR antagonists reduce symptom scores and increase peak urinary flow rates in BPH. Of particular importance for BPH therapy are uroselective alpha(1)-AR antagonists for which the hypotensive related side-effect caused by alpha(1)-AR blockade is reduced. 5alpha-Reductase inhibitors reduce prostate volume and symptom scores, while increasing peak urinary flow rates. This review describes new alpha(1)-AR antagonists and 5alpha-reductase inhibitors in the treatment of BPH. The new alpha(1)-AR antagonists represent various structures such as quinazolines, phenylethylamines, piperidines, and arylpiperazines. 5alpha-Reductase inhibitors are classified into two groups: steroidal and non-steroidal. The newer non-steroidal inhibitors include derivatives of benzo[c]quinolizinones, benzo[f]quinolonones, piperidones and carboxylic acids. Besides the development of new compounds belonging to the above mentioned groups, new agents for BPH treatment are sought among combined 5alpha-reductase/alpha(1)-AR inhibitors, endothelins, androgen receptors antagonists, growth factors, estrogens and phosphodiesterase isoenzymes as well as several phytomedicines, used for prevention and treatment of prostate disorders. These new agents can be used for the design of future targets and development of new drugs in the treatment of BPH. The discovery of a number of active leads may also ultimately help in developing new safe and effective drugs.

Quantification of alpha1-adrenoceptor subtypes by real-time RT-PCR and correlation with age and prostate volume in benign prostatic hyperplasia patients

We used a real-time reverse transcriptase polymerase chain reaction (RT-PCR) method for quantification of each alpha(1)-adrenoceptor (alpha(1)-AR) subtype expression level, and examined whether age and prostate volume influence human prostate alpha(1)-AR subtype expression. Enrolled in our study were 75 men with lower urinary tract symptoms (LUTS) secondary to untreated benign prostatic hyperplasia (BPH). Real-time RT-PCR was performed using prostate biopsy specimens to quantify the expression level of each alpha(1)-AR subtype. The median expression level (interquartile range) was 1.24 (0.66-2.32), 0.16 (0.10-0.33), and 1.11 (0.75-2.27) x 1,000 copies/beta-actin for alpha(1a)-, alpha(1b)-, and alpha(1d)-AR mRNA, respectively. The expression levels differed with the individual. The expression levels of alpha(1a)-AR, alpha(1d)-AR, and total alpha(1)-AR mRNA showed a significant positive correlation with patient age, but did not correlate with prostate volume. The difference in the expression of the alpha(1)-AR subtype with the patient may be the cause of the difference in the effectiveness of several subtype-selective alpha(1)-AR antagonists from patient to patient. The increase of alpha(1)-AR mRNA expression level with age could be an important factor in the pathogenesis of clinically significant BPH.

Effects of Silodosin (KMD-3213) on Phenylephrine-induced Increase in Intraurethral Pressure and Blood Pressure in Rats—Study of the Selectivity for Lower Urinary Tract—

The effects of silodosin, an alpha(1A)-adrenoceptor (AR) antagonist, and of other alpha(1)-AR antagonists on the phenylephrine (PE)-induced increase in intraurethral pressure (IUP) and on blood pressure (BP) were studied in anesthetized rats. The drugs were administered intravenously (i.v. study) or intraduodenally (i.d. study). IUP and BP were measured via catheters inserted into the prostatic urethra and common carotid artery, respectively. In the i.v. study, drugs were administered every 30 min for effects on BP, and 5 min before each PE-injection (30 microg/kg, every 60 min) with stepwise increases in dose for effects on IUP. In the i.d. study, one dose of drug was administered per rat, then IUP and BP were observed for 4 h [IUP being measured time-dependently following PE-injection (30 microg/kg)], and IUP and BP were expressed as a percentage of the values without any drugs. ID(50) for IUP and ED(15) for BP were calculated, and uroselectivity was determined as ED(15)/ID(50) for each drug. All drugs both inhibited the IUP increase and lowered BP, each effect being dose-dependent. The order of uroselectivities was silodosin (11.7)>tamuslosin (2.24)>naftopidil (0.133) in the i.v. study, and silodosin (26.0)>tamuslosin (3.82)>naftopidil (1.39) in the i.d. study. Selectivity for the lower urinary tract (LUT) was higher for silodosin than for tamsulosin (alpha(1A)/alpha(1D)-AR), naftopidil (alpha(1D)-AR), or prazosin (non-selective alpha(1)-AR). These results suggested that an alpha(1A)-AR selective antagonist like silodosin might be effective in the LUT without causing hypotension.

Mode of action of α-adrenoceptor antagonists in the treatment of lower urinary tract symptoms

It generally is thought that the beneficial effect of α1-adrenoceptor (AR) antagonists on lower urinary tract symptoms (LUTS) in men with benign prostatic hyperplasia is caused mainly by relaxation of prostatic/urethral smooth muscle. However, the frail correlation between LUTS and prostatic enlargement or outflow obstruction have focused interest on the role of extraprostatic a-ARs in the pathogenesis of LUTS. However, the exact mode and sites of action of the α1-AR antagonists used for the treatment of LUTS have not been established.

Doxazosin-induced up-regulation of α1A-adrenoceptor mRNA in the rat lower urinary tract

Alpha1-adrenoceptor (AR) antagonists can provide effective treatment of symptoms caused by benign prostatic hyperplasia. However, their mechanisms of action have not been fully elucidated. We previously reported that chronic administration of doxazosin causes an up-regulation in the mRNA expression of all three alpha1-AR subtypes in the rat prostate. As alpha1-AR antagonists might also affect the properties of alpha1-ARs in the lower urinary tract, we examined the effects of doxazosin (2 or 4 mg/kg daily subcutaneously, supplemented with 4 mg/kg daily orally for 8 or 12 weeks) on alpha1-AR subtype mRNAs in the rat bladder dome, bladder base, and urethra using real-time reverse transcription PCR. Rats that received the highest doses of doxazosin had significantly heavier bladder base and prostatic urethra than controls. PCR data showed that all three alpha1-AR subtypes were expressed in all tissues studied. Doxazosin treatment caused an up-regulation in the mRNA levels of alpha1A-AR in the rat bladder base and prostatic urethra, indicating that chronic doxazosin treatment may cause an alteration in the properties of alpha1A-AR subtype mRNA in these two areas. Furthermore, the heavier bladder base and prostatic urethra in the doxazosin-treated rats suggest that alpha1-AR antagonist treatment might also influence the growth process in these areas of the rat lower urinary tract.

Alpha(1)-adrenoceptor stimulation directly induces growth of vascular wall in vivo.

Previous studies suggesting that norepinephrine is directly trophic for the vascular wall have been confounded by concomitant hemodynamic disturbances. Herein, a microcatheter connected to an osmotic minipump was implanted adjacent to the rat carotid for 2-wk perivascular suffusion of agents at systemic levels ~1,000 times below the threshold for altering arterial pressure. Norepinephrine decreased lumen and adventitial areas and circumference by 10, 14, and 5%, respectively (all P < 0.05); a nonsubtype-specific alpha(1)-adrenoceptor (AR) antagonist had no effect. When begun at the time of balloon injury, 2-wk norepinephrine increased lumen loss by 45%, increased neointimal area by 64% and collagen content by 33%, and reduced vessel circumference by 5% (all P < 0.05). alpha(1)-AR antagonists decreased neointimal area by 33% (all P < 0.05). alpha(1)A-AR antagonist reduced lumen loss by 70%, neointimal area by 54%, circumference decline by 84%, and adventitial thickening by 87% (all P < 0.05), whereas alpha(1B)-, alpha(1D)-, alpha(2)- and beta-AR antagonists were without effect. These are the first in vivo studies demonstrating that norepinephrine is directly trophic for the vascular wall and augments injury-induced intimal lesion growth.

α-Adrenoceptors and benign prostatic hyperplasia: basic principles for treatment with α-adrenoceptor antagonists.

The selective blockade of α1-adrenoceptors (ARs) is now a well-accepted and widely used treatment for patients presenting with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) and bladder outlet obstruction. The sites of action of the currently used α1-AR antagonists when relieving LUTS have not yet been established, but it seems clear that effects on prostatic as well as non-prostatic tissues are important. α1-ARs in the bladder, urethra, and vas deferens, on ganglia and nerve terminals, and in the central nervous system (CNS) may all influence LUTS and the clinical effects of α1-AR antagonists. The relevance of α1-AR subtype selectivity for the clinical usefulness of existing drug therapy has still not been clarified, but it cannot be dismissed that blockading both α1A- and α1D-ARs is necessary for optimal clinical effect. Despite the above uncertainties, there seems to be a consensus that clinically available α1-AR antagonists provide a safe, effective and generally well-tolerated therapy for patients with LUTS.

α1-Adrenergic and m3-Muscarinic Receptor Stimulation of Phosphatidylinositol 4,5-Bisphosphate-Specific Phospholipase C Are Independently Mediated by Gαq/11 in Rat Parotid Gland Membranes

Stimulation of m3-muscarinic cholinergic receptors (m3AChR) in the rat parotid gland increases the hydrolysis of phosphatidylinositol 4, 5-bisphosphate (PIP2) via activation of the Gαq/11 family of G-proteins (Sawaki et al. (1993) Arch. Biochem. Biophys., 546-550). Herein we report that α1-adrenergic receptor (α1-AR) stimulation of PIP2 hydrolysis is also mediated via α subunits of the Gq/11 family of G-proteins. The α1-AR agonist, epinephrine, induced a dose-dependent increase (1.5-fold maximum) of exogenously added PIP2 in the presence of guanosine 5′-O-(3-thiotriphosphate) (GTPγS), which was inhibited by the α1-AR antagonist, phentolamine, but not by the β-adrenergic receptor antagonist, propranolol. The epinephrine-stimulated component of PIP2 hydrolysis was significantly inhibited by pretreating the membranes with an antiserum against Gαq/11. When carbachol and epinephrine were present simultaneously (with GTPγS), the increase in PIP2 hydrolysis obtained was not significantly different from the sum of the increases in PIP2 hydrolysis obtained with each agonist alone. PIP2 hydrolysis stimulated in the presence of carbachol and epinephrine was inhibited by α1-AR and m3AChR antagonists, phentolamine and atropine respectively, to the level obtained with each agonist alone. Notably, in the presence of both agonists the inhibition of PIP2 hydrolysis by anti-Gαq/11 antiserum was not significantly different from the sum of the inhibitions obtained with each agonist alone. These results indicate that m3AChR and α1-AR stimulation of PIP2 hydrolysis in rat parotid gland membranes are independently mediated by the Gαq/11 family of G-proteins.

α1-Adrenoceptor subtypes mediating contraction of the femoral artery in spontaneously hypertensive rats

alpha 1-Adrenoceptors (ARs) were divided into alpha 1H and alpha 1L subtypes by their different affinities for bunazosin or prazosin. alpha 1H-ARs were further subdivided into alpha 1A, alpha 1B, and alpha 1C subtypes. Therefore, this study was undertaken to determine which alpha 1-AR subtypes were involved in the activation of femoral artery preparations by alpha 1-AR agonists in spontaneously hypertensive rats (SHR). For comparison, aortic strips were also incorporated in the present study. In the presence of propranolol, deoxycorticosterone, and desipramine, norepinephrine (NE) contracted the vascular strips in a dose-dependent manner. Negative log EC50 values and maximum responses of NE-induced contraction of the SHR femoral artery were unchanged and increased, respectively, compared with those of Sprague-Dawley and Wistar-Kyoto rats (WKY). Contractile responses of the SHR aortae to NE were similar to those of the normotensive tissues. Schild plot data for alpha 1-AR antagonists indicated that alpha 1-AR subtypes mediating contraction of the aorta were homogeneous and had high affinities for bunazosin (pA2 9.4, alpha 1H subtype) and WB 4101 (pA2 9.3) and a low affinity for 5-methylurapidil (pA2 7.7). In the femoral artery, because Schild plots for bunazosin had slopes of less than 1.0, there were alpha 1H and alpha 1L subtypes. Bunazosin, at 10(-9) M, which could mask the alpha 1H subtype, yielded a Schild plot for bunazosin with a slope not different from unity and decreased the pA2 value for bunazosin (pA2 9.4 vs. 8.5).(ABSTRACT TRUNCATED AT 250 WORDS)