Phenotype pharmacology of lower urinary tract α(1)-adrenoceptors

Effect of perioperative tamsulosin on successful ureteral access sheath placement and stent-related symptom relief: A double-blinded, randomized, placebo-controlled study

PURPOSE

This study investigated the effect of administering tamsulosin before surgery on the successful insertion of a 12/14 French (F) ureteral access sheath (UAS) during the procedure, as well as the impact of preoperative and postoperative tamsulosin use on symptoms related to the ureteral stent.

MATERIALS AND METHODS

This study was a randomized, single-center, double-blinded, placebo-controlled trial involving 200 patients who underwent unilateral retrograde intrarenal surgery. Patients received either tamsulosin (0.4 mg) or placebo 1 week before surgery until stent removal. Patients were randomly assigned to one of four groups. Group 1 received tamsulosin throughout the study period. Group 2 received tamsulosin before surgery and placebo after surgery. Group 3 received placebo before surgery and tamsulosin after surgery. Group 4 received placebo before and after surgery. The USSQ (Ureteral Stent Symptom Questionnaire) was completed between postoperative days 7 and 14 immediately before stent removal.

RESULTS

A total of 160 patients were included in this analysis. Their mean age was 55.0±11.0 years, and 48 patients (30.0%) were female. In the group that received preoperative tamsulosin, the success rate of 12/14F UAS deployment was significantly higher than that of the preoperative placebo group (88.0 vs. 75.3%, p=0.038). Preoperative and postoperative tamsulosin did not significantly alleviate symptoms related to the ureteral stent.

CONCLUSIONS

Our results revealed that preoperative administration of tamsulosin improved the success of larger-sized UAS, whereas preoperative and postoperative tamsulosin use did not significantly alleviate symptoms related to ureteral stents.

Bladder pain induced by prolonged peripheral alpha 1A adrenoceptor stimulation involves the enhancement of transient receptor potential vanilloid 1 activity and an increase of urothelial adenosine triphosphate release

AIM

Pathophysiological mechanisms of chronic visceral pain (CVP) are unknown. This study explores the association between the sympathetic system and bladder nociceptors activity by testing the effect of a prolonged adrenergic stimulation on transient receptor potential vanilloid 1 (TRPV1) activity and on urothelial adenosine triphosphate (ATP) release.

METHODS

Female Wistar rats received saline, phenylephrine (PHE), PHE + silodosin, PHE + naftopidil or PHE + prazosin. TRPV1 knockout and wild-type mice received saline or PHE. Visceral pain behaviour tests were performed before and after treatment. Cystometry was performed, during saline and capsaicin infusion. Fos immunoreactivity was assessed in L6 spinal cord segment. Human urothelial ATP release induced by mechanical and thermal stimulation was evaluated.

RESULTS

Subcutaneous, but not intrathecal, PHE administration induced pain, which was reversed by silodosin, a selective alpha 1A adrenoceptor antagonist, but not by naftopidil, a relatively selective antagonist for alpha 1D adrenoceptor. Silodosin also reversed PHE-induced bladder hyperactivity and L6 spinal cord Fos expression. Thus, in subsequent experiments, only silodosin was used. Wild-type, but not TRPV1 knockout, mice exhibited phenylephrine-induced pain. Capsaicin induced a greater increase in voiding contractions in PHE-treated rats than in control animals, and silodosin reversed this effect. When treated with PHE, ATP release from human urothelial cells was enhanced either by mechanical stimulation or by lowering the thermal threshold of urothelial TRPV1, which becomes abnormally responsive at body temperature.

CONCLUSION

This study suggests that the activation of peripheral alpha 1A adrenoceptors induces CVP, probably through its interaction with TRPV1 and ATP release.

Agonist pharmacology at recombinant α1A - and α1L -adrenoceptors and in lower urinary tract α1 -adrenoceptors

BACKGROUND AND PURPOSE

Two distinct α1 -adrenoceptor phenotypes (α1A and α1L ) have recently been demonstrated to originate from a single α1A -adrenoceptor gene. Here, we examined the agonist profiles of recombinant α1A and α1L phenotypes and of lower urinary tract (LUT) α1 -adrenoceptors.

EXPERIMENTAL APPROACH

A series of drugs (A61603, Ro 115-1240, NS-49 , MK017 and ESR1150) originally developed for stress urinary incontinence (SUI) therapy were used to stimulate recombinant α1A - and α1L -adrenoceptor phenotypes, and their potencies and intrinsic activity estimated from Ca(2+) responses. Agonist-induced contractions were also examined in LUT tissues of rats and humans and in human mesenteric artery and rat tail artery.

KEY RESULTS

All the drugs were potent agonists of the α1A -adrenoceptor compared with the α1L -adrenoceptor phenotype. Among them, Ro 115-1240 was shown to be an α1A -specific partial agonist that produced partial contractions through α1A -adrenoceptors in rat prostate and tail artery, but not in the other LUT tissues and human mesenteric artery. In contrast, P-come 102 showed full agonist activity at α1A - and α1L -adrenoceptors, but was less selective than noradrenaline for α1A -adrenoceptors. Like noradrenaline, P-come 102 was highly potent at inducing contractions in all of the LUT tissues tested. However, the potency and intrinsic activity of P-come 102 were significantly lower than those of noradrenaline in human mesenteric artery.

CONCLUSIONS AND IMPLICATIONS

The α1A - and α1L -adrenoceptor phenotypes and LUT α1 -adrenoceptors were demonstrated to have distinct agonist profiles. As adrenergic contractions in LUT are predominantly mediated through α1L -adrenoceptors, the development of α1L -selective agonists may provide clinically useful drugs for SUI therapy.

Pharmacologically distinct phenotypes of α1B -adrenoceptors: variation in binding and functional affinities for antagonists

BACKGROUND AND PURPOSE

The pharmacological properties of particular receptors have recently been suggested to vary under different conditions. We compared the pharmacological properties of the α1B -adrenoceptor subtype in various tissue preparations and under various conditions.

EXPERIMENTAL APPROACH

[(3) H]-prazosin binding to α1B -adrenoceptors in rat liver (segments, dispersed hepatocytes and homogenates) was assessed and the pharmacological profiles were compared with the functional and binding profiles in rat carotid artery and recombinant α1B -adrenoceptors.

KEY RESULTS

In association and saturation-binding experiments with rat liver, binding affinity for [(3) H]-prazosin varied significantly between preparations (KD value approximately ten times higher in segments than in homogenates). The binding profile for various drugs in liver segments also deviated from the representative α1B -adrenoceptor profile observed in liver homogenates and recombinant receptors. L-765,314 and ALS-77, selective antagonists of α1B -adrenoceptors, showed high binding and antagonist affinities in liver homogenates and recombinant α1B -adrenoceptors. However, binding affinities for both ligands in the segments of rat liver and carotid artery were 10 times lower, and the antagonist potencies in α1B -adrenoceptor-mediated contractions of carotid artery were more than 100 times lower than the representative α1B -adrenoceptor profile.

CONCLUSIONS AND IMPLICATIONS

In contrast to the consistent profile of recombinant α1B -adrenoceptors, the pharmacological profile of native α1B -adrenoceptors of rat liver and carotid artery varied markedly under various receptor environments, showing significantly different binding properties between intact tissues and homogenates, and dissociation between functional and binding affinities. In addition to conventional 'subtype' characterization, 'phenotype' pharmacology must be considered in native receptor evaluations in vivo and in future pharmacotherapy.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

α-Adrenoceptor assays

α-Adrenoceptors mediate responses to activation of both peripheral sympathetic nerves and central noradrenergic neurons. They also serve as autoreceptors that modulate the release of norepinephrine (NE) and other neurotransmitters. There are two major classes of α-adrenoceptors, the α(1)- and α(2). Each class is subdivided into three subtypes: α(1A), α(1B), α(1D), and α(2A), α(2B), α(2C). Described in this unit are in vitro isolated tissue methods used to study α-adrenoceptor functions and to identify novel ligands for these receptors. Detailed protocols describing use of isolated tissues to study the various α(1)- and α(2)-adrenoceptor subtypes are provided.

What makes the α(1A)-adrenoceptor gene express the α(1L)-adrenoceptor functional phenotype?

The α(1A)-adrenoceptor is therapeutically exploited because of its prevalence in the lower urinary tract. The pharmacology shown by this lower urinary tract α(1A)-adrenoceptor is different from that shown by other α(1A)-adrenoceptors, which has led to it being subclassified as an α(1L)-adrenoceptor. Only in the last few years was it shown that this pharmacologically distinct α(1L)-adrenoceptor is a product of the α(1A)-adrenoceptor gene. In this issue of the BJP, Nishimune et al. review the literature on α(1L)-adrenoceptor pharmacology and discuss the possible molecular mechanisms by which the α(1A)-adrenoceptor gene is able to produce two pharmacologically distinct adrenoceptor subtypes. Based primarily from their own research using cell lines transfected with α(1A)-adrenoceptors, they conclude that a protein that interacts with the receptor is the most plausible explanation. The challenge remains to identify any such interacting protein and show how it is able to change the pharmacology of the receptor for different ligands.

Re-evaluation of nicotinic acetylcholine receptors in rat brain by a tissue-segment binding assay

Nicotinic acetylcholine receptors (nAChRs) of the cerebral cortex and cerebellum of rats were evaluated by a radioligand binding assay, employing tissue segments, or homogenates as materials. [³H]-epibatidine specifically bound to nAChRs in rat cortex or cerebellum, but the dissociation constants for [³H]-epibatidine differed between segments and homogenates (187 pM for segments and 42 pM for homogenates in the cortex and 160 pM for segments and 84 pM for homogenates in the cerebellum). The abundance of total nAChRs was approximately 310 fmol/mg protein in the segments of cortex and 170 fmol/mg protein in the segments of cerebellum, which were significantly higher than those estimated in the homogenates (115 fmol/mg protein in the homogenates of the cortex and 76 fmol/mg protein in the homogenates of the cerebellum). Most of the [³H]-epibatidine binding sites in the cortex segments (approximately 70% of the population) showed high affinity for nicotine (pK_i = 7.9), dihydro-β-erythroidine, and cytisine, but the binding sites in the cerebellum segments had slightly lower affinity for nicotine (pK_i = 7.1). An upregulation of nAChRs by chronic administration of nicotine was observed in the cortex segments but not in the cerebellum segments with [³H]-epibatidine as a ligand. The upregulation in the cortex was caused by a specific increase in the high-affinity sites for nicotine (probably α4β2). The present study shows that the native environment of nAChRs is important for a precise quantitative as well as qualitative estimation of nAChRs in rat brain.