Extravascular CBG-like sites in rat kidney and mineralocorticoid receptor specificity

The Concise Guide to PHARMACOLOGY 2013/14: nuclear hormone 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.

Nuclear hormone 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, 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.

Stimulation of testosterone production in rat Leydig cells by aldosterone is mineralocorticoid receptor mediated

The testis is known to be a site of corticosterone action, and testosterone production in Leydig cells is directly inhibited by glucocorticoids. Glucocorticoids bind to both glucocorticoid receptors (GRs) and to mineralocorticoid receptors (MRs). In Leydig cells, selective mineralocorticoid binding could result from oxidative inactivation of glucocorticoid by type 1 and/or 2 11beta-hydroxysteroid dehydrogenase (11betaHSD), as both isoforms are expressed. However, it remains unclear whether Leydig cells express MRs and respond directly to mineralocorticoid action. Therefore, the aims of the present study were to ascertain: (1) whether MR mRNA, protein and receptor binding are present in Leydig cells; and (2) if the mineralocorticoid modulates testosterone production. The mRNA encoding MR, as well as protein, and binding activity were each observed in adult rat Leydig cells. MR-ligand binding specificity within isolated Leydig cells was evaluated further by measuring displacement of MR binding to aldosterone by corticosterone in the presence and absence of carbenoxolone, an inhibitor of 11betaHSD1 and 2 that decreases conversion to biologically inert 11-dehydrocorticosterone. Carbenoxolone inhibited 11betaHSD oxidative activity, and reduced corticosterone-binding by 50%. Mineralocorticoid effects on steroidogenesis were assessed in the presence of aldosterone (0.01-10 nM) with or without the MR antagonist, RU28318. Aldosterone induced dose-dependent increases in both basal and luteinizing hormone-stimulated testosterone production. RU28318 eliminated the increase, indicating that these effects of aldosterone were mediated by the MR. The effects of aldosterone and luteinizing hormone (0.1 ng/ml) on testosterone production were synergistic, suggesting that the two hormones increased steroidogenesis through separate pathways. We conclude that Leydig cells express MRs and that testosterone production is subject to regulation by aldosterone.

Vasopressin potentiates mineralocorticoid selectivity by stimulating 11 beta hydroxysteroid deshydrogenase in rat collecting duct

Arginine vasopressin (AVP) and corticosteroid hormones are involved in sodium reabsorption regulation in the renal collecting duct. Synergy between AVP and aldosterone has been well documented, although its mechanism remains unclear. Both aldosterone and glucocorticoid hormones bind to the mineralocorticoid receptor (MR), and mineralocorticoid selectivity depends on the MR-protecting enzyme 11 beta hydroxysteroid deshydrogenase (11-HSD), which metabolizes glucocorticoids into derivatives with low affinity for MR. We have investigated whether the activity of 11-HSD could be influenced by AVP and corticosteroid hormones. This study shows that in isolated rat renal collecting ducts, AVP increases 11-HSD catalytic activity. This effect is maximal at 10(-8) M AVP (a concentration clearly above the normal physiological range of AVP concentrations) and involves the V2 receptor pathway, while activation of protein kinase C or changes in intracellular calcium are ineffective. The stimulatory effect of AVP on 11-HSD is largely reduced after adrenalectomy, and is selectively restored by infusion of aldosterone, not glucocorticoids. We conclude that this synergy between AVP and aldosterone in controlling the activity of 11-HSD is likely to play a pivotal role in resetting mineralocorticoid selectivity, and hence sodium reabsorption capacities of the renal collecting duct.