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M E Oblin

Publications and source records attributed to M E Oblin.

9 recordsLinked to original sources
PubMed1992

Immunohistochemical and biochemical evidence for a cardiovascular mineralocorticoid receptor.

The presence of mineralocorticoid receptors (MRs) and their physicochemical characteristics were investigated in the heart and blood vessels of rabbits. Immunohistochemical methods using the monoclonal anti-idiotypic antibody H10E, which interacts with the steroid binding domain of MRs, revealed the presence of immunoreactive material in the heart and large blood vessels. In the heart, a positive staining was observed in myocytes and endothelial cells of atria and ventricles. In vessels, MRs were detected in the aorta and pulmonary artery. They were localized in endothelial and vascular smooth muscle cells. No staining was present in the small vascular bed, arterioles, and capillaries. In all these studies, the mineralocorticoid specificity of the staining was assessed by in situ competition experiments with aldosterone and RU486, a glucocorticoid antagonist. The presence of MRs in the heart and vessels was further demonstrated by specific aldosterone binding to one class of high affinity binding sites in the cytosol of the adrenalectomized rabbit heart (Kd, 0.25 nM; maximum MR concentration, 15-20 fmol/mg protein), whose mineralocorticoid specificity has been clearly established by competition studies. Sedimentation gradient analyses revealed that the cardiovascular MR is an 8.5S hetero-oligomer that includes the heat shock protein 90. The physicochemical characteristics of the cardiovascular MRs are virtually identical to those of the renal MRs. Altogether, our results clearly demonstrate the presence of MRs in the cardiovascular system. This supports the possibility of direct aldosterone actions in the heart and blood vessels.

Adrenalectomy↗
PubMed1991

Immunolocalization of gluco- and mineralocorticoid receptors in rabbit kidney.

The localization of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) was determined in the rabbit kidney by immunohistochemistry with the use of a monoclonal, anti-GR antibody and a monoclonal, anti-idiotypic, anti-MR antibody. Immunostaining was performed on serial histological sections from normal and adrenalectomized rabbits. The specificity of immunostaining was assessed for MR by in situ competition studies with steroids and for GR by presaturation of the antibody with GR preparation. Immunostaining by both the anti-MR and the anti-GR antibodies was present in all parts of the distal nephron (beyond proximal tubule) and absent in the glomerulus and proximal tubule. The absence of staining by the anti-GR antibody in the proximal tubule suggests that the effects of glucocorticoids in this structure involve either a GR different from that of distal structures or a non-receptor mediated mechanism of action. MR immunostaining predominates in the distal and all along the collecting tubule in its cortical, medullary, and papillary portions. GR immunostaining was most abundant in the medullary ascending limb and distal tubule. Immunostaining by both antibodies was present in papillary interstitial cells and cells of the epithelium lining the papilla. Fifteen to twenty percent of the cells of the cortical collecting tubule, presumably intercalated cells, were devoid of MR and GR immunostaining. Immunostaining was present in both nuclear and cytoplasmic cell compartments. No clear difference was observed between normal and adrenalectomized rabbits. This study is the first report on renal immunolocalization of GR compared with MR. In addition, we show evidence for new targets for corticosteroid hormones such as papillary interstitial cells and papillary epithelium.

Animals↗
PubMed1990

Immunohistochemical localization of renal mineralocorticoid receptor by using an anti-idiotypic antibody that is an internal image of aldosterone.

A monoclonal antibody (H10E), generated by an auto-anti-idiotypic procedure and directed at the aldosterone-binding site of mineralocorticoid receptor (MR), was used in immunohistochemical studies to localize MR in rabbit kidney preparations. In agreement with earlier physiological and biochemical observations, MR was detected in connecting and cortical collecting tubules. Additionally, MR was detected in the distal tubules, the medullary and papillary collecting ducts, and in the epithelial cells lining the papilla. The internal image properties of the antibody were exploited to assess the specificity of MR detection by means of competition studies with hormones and antihormones. Immunostaining was completely abolished by preincubation with aldosterone but not with RU 486, a steroid antagonist that does not bind MR. On the cellular level, immunostaining occurred in the cytoplasm and, in the majority of cells, in the nucleus as well. The nucleocytoplasmic distribution of MR was unaffected by adrenalectomy or by administration of aldosterone. The availability of this specific monoclonal antibody makes it feasible to study MR expression in other target tissues and in pathological disorders.

Adrenalectomy↗
PubMed1989

Aldosterone receptors in A6 cells: physicochemical characterization and autoradiographic study.

The A6 cell line is derived from the kidney of Xenopus laevis. Aldosterone increases sodium transport across A6 cell epithelia. In the present study, aldosterone binding characteristics were studied in A6 cell cytosol. Both type I (mineralocorticoid) and type II (glucocorticoid) receptors are present in the cytosolic fraction of these cells. Aldosterone and corticosterone had a high affinity for type I sites (Kd = 1.25 and 0.16 nM, respectively) and a lower affinity for type II sites (Kd = 39 and 10 nM, respectively). Testosterone and estradiol did not compete for aldosterone binding. RU 26988, a highly specific glucocorticoid agonist, competed with aldosterone for type II but not for type I sites. Hydrodynamic parameters of both type I and type II corticosterone receptor complexes were identical. Their Stokes radius was approximately 6 nm, as estimated by high-performance size-exclusion chromatography, and their sedimentation coefficient determined by ultracentrifugation on glycerol gradients was approximately 9s. The molecular mass calculated from these parameters was approximately 200 kDa, a value that is very close to the value estimated for nontransformed mineralocorticoid and glucocorticoid receptors of other species. The [3H]aldosterone labeling of intact A6 cells was examined by autohistoradiography. At every concentration tested (2, 20, and 50 nM), all cells were found to be specifically labeled in both cytoplasm and nucleus. At 20 nM, in the presence of an excess of RU 26988, labeling was also detected. At every concentration the labeling data was compatible with a Gaussian distribution, indicating that A6 cells correspond to a homogeneous population with regard to aldosterone binding and that probably both type I and type II sites are present in the same cells.

Aldosterone↗
PubMed1985

Cytoplasmic and nuclear uptake of aldosterone in toad bladder: a mathematical modeling approach.

The mechanism of aldosterone uptake in the epithelial cells of toad bladder was studied using mathematical modeling. Two complementary approaches were used. The first involved analysis of cytosolic aldosterone binding at steady state according to models defined by the sum of independent noninteractive binding sites. The best model describing the experimental data corresponded to two specific binding sites with mean dissociation constant values of 0.20 and 60 nM for types 1 and 2, respectively. The second approach was based on the analysis of cytoplasmic and nuclear aldosterone uptake kinetics at 25 and 0 degrees C in intact bladder. Two models (A and B) were studied. They both implied the existence of two types of aldosterone binding sites as precursors of the corresponding chromatin bound complexes. In model A, nuclear translocation of the two types of receptors was assumed to obey first-order kinetics. In model B, the translocation process for type 1 sites involved a time lag leading to delayed binding to chromatin. Both models were found to fit the experimental data satisfactorily. The fit obtained for model B appeared to be better at low aldosterone concentrations.

Aldosterone↗
PubMed1979

Sickness absence after inguinal herniorrhaphy.

Eight hundred and ninety-nine men were studied, aged 16-65 inclusive, who underwent an elective inguinal herniorrhaphy during 1970 and 1971 in eight hospitals in Wessex, and under nine consultant surgeons. There was a significant variation in postoperative inpatient stay and total sickness absence between hospitals and between consultants. The physical activity involved in the patient's occupation, his age at operation, previous sickness absence, bilateral herniorrhaphy, attendance at follow-up outpatients' clinic, type of repair, and the influence exerted by three hospitals and two consultants accounted for only 21% of the variation in total sickness absence. The general practitioners who had referred patients to the hospitals for herniorrhaphy, and the consultant surgeons who carried out the operations, were sent a questionnaire to ascertain their attitudes towards follow-up outpatient appointments and the various factors identified in the first part of the study as significantly influencing total sickness absence. A higher proportion of GPs who felt that an outpatient appointment was necessary before return to work was found in relation to the patients who had the longest mean total sickness absences than among the GPs who looked after the patients with shorter total sickness absences.

Adolescent↗
PubMed1977

Effect of acute potassium loading on plasma renin and on urinary aldosterone in rats.

The disposition of aldosterone radiometabolites in rats has been studied following iv [3H]aldosterone administration. Of injected [3H]-aldosterone, 0.31% is recovered in 24 h urine as free aldosterone and 0.08% as acid-labile conjugate. A simple, sensitive and reliable radioimmunoassay of free aldosterone has been developed and the effect of acute oral potassium loading (171, 513 or 769 mueq of KCl/100 g body weight) on 4 h aldosterone excretion, plasma renin concentration and sodium and potassium balance has been investigated. There was a positive correlation between log urinary aldosterone and potassium load (r = 0.92, P less than 0.001). Potassium induced a natriuresis which was correlated directly with the dose of potassium administered (r = 0.89, P less than 0.001). Ptasssium loading also increased plasma renin concentration which was correlated with the sodium excretion rate (r = 0.64, P less than 0.01). Prevention of a negative sodium balance during the 769 mueq potassium load was obtained by administration of 513 mueq sodium. In this experiment, plasma renin concentration increased little, whereas the aldosterone excretion rate was as high as during the 769 mueq potassium load without sodium addition.

Aldosterone↗