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Biomedical subjects

G Verhoeven

Publications and source records attributed to G Verhoeven.

At least 181 records · Page 10Linked to original sources
PubMed1976

Interconversion between 17 beta-hydroxy-5alpha-androstan-3-one (5alpha-dihydrotestosterone) and 5alpha-androstane-3alpha, 17 beta-diol in rat kidney: heterogeneity of 3alpha-hydroxysteroid oxidoreductases.

3alpha-Hydroxysteroid oxidoreductases catalyzing the interconversion between 17 beta-hydroxy-5alpha-androstan-3-one (5alpha-dihydrotestosterone) and 5alpha-androstane-3alpha, 17 beta-diol (3alpha-androstanediol) have been studied in rat kidney. Three enzymes can be distinguished: a soluble NADPH-dependent oxidoreductase, a microsomal NADPH-dependent enzyme and a microsomal NADH-linked enzyme. Traces of the microsomal enzymes are consistently observed in the 108 000 X g supernatant. Studies on crude preparations reveal that these enzymes differ not only in subcellular localization and co-factor requirement, but also in optimum pH, kinetic characteristics, sensitivity to potential steroidal inhibitors and sensitivity to detergents, ionic strength and temperature. Moreover, salient sex differences exist in the activity of all three kidney enzymes. The soluble NADPH-dependent enzyme is more active in female rats whereas both microsomal enzymes are considerably more active in male animals. The microsomal NADH-dependent oxidoreductase displays favorable characteristics to catalyze the 3alpha-dehydrogenation of 3alpha-androstanediol. Evidence is presented that it is mainly this enzyme that enables the kidney to use 3alpha-androstanediol as an efficient precursor for the local formation of 5alpha-dihydrotestosterone.

Androstane-3,17-diol↗
PubMed1976

Cytosol androgen binding in submandibular gland and kidney of the normal mouse and the mouse with testicular feminization.

Androgen binding was investigated in the cytosol of the submandibular gland and the kidney from normal mice, mice with testicular feminization (Tfm), and carriers of the Tfm gene. In both tissues from normal mice an androgen-binding complex was observed from birth throughout life that could not be detected in Tfm animals at any age. This complex was precipitated at 35 and 40% saturation with ammonium sulfate in the kidney and the submandibular gland, respectively, and had an approximate sedimentation coefficient of 8S in the submandibular gland and 10S in the kidney. In both tissues of the normal female, the apparent dissociation constants (Kd) for testosterone and dihydrotestosterone were about 1 nM, and the binding capacity averaged 20 fmol-mg protein-1. The number of binding sites in preparations from Tfm carriers was intermediate between that in the Tfm and the normal female . In 0.5M KCl the 8S receptor of normal submandibular gland sediments at about 3S, and the 10S receptor of normal kidney sediments at about 4.5S. In the submandibular gland, binding of approximate 3S size was also observed. The latter was present in Tfm animals as well as in normal mice, it precipitated at 70% saturation with ammonium sulfate, and it was detectable from birth. In the kidney the only low molecular weight binding for androgen was about 4.5S in size.

Androgen-Insensitivity Syndrome↗
PubMed1975

Ammonium sulfate precipitation as a tool for the study of androgen receptor proteins in rat prostate and mouse kidney.

Ammonium sulfate precipitation has been used for the separation of bound and free steroids in rat prostate and mouse kidney cytosol equilibrated with tritiated androgens. A high affinity, low capacity binding protein has been identified in the 35% saturation precipitate. Biochemical and physiological data indicate that this protein is identical with the previously described 8-10 S androgen receptor. It has been demonstrated that this receptor protein binds 17 beta - hydroxy-5alpha-androstan-3-one (DHT) and testosterone in both tissues. The apparent dissociation constant (Kd) of the prostatic receptor for DHT and of the renal receptor for testosterone is 1-2 nM. The number of binding sites equals 57 and 23 fmoles/mg protein in prostate and kidney respectively. Dterminations of apparent inhibition constants (Ki) for 26 steroidal and non-steroidal compounds suggest that the binding sites in these tissues is similar or identical.

Ammonium Sulfate↗
PubMed1975

Effects of testosterone mediated or modulated by pituitary factors.

Adult rats of both sexes were either gonadectomized or hypophysectomized and gonadectomized. Three to eight weeks later they were treated for 14 consecutive days with oil or with 75 or 200 mug testosterone propionate (TP) per 100 g body weight. The animals were killed and for each sex the gonadectomized animals were compared with the hypophysectomized-gonadectomized animals as far as their NADPH- and NADH-dependent 3alpha-hydroxy-steroid dehydrogenases (3alpha-HSD) in renal microsomes, transcortin levels in serum and five organ weights relative to total body weight were concerned. For two of the latter, i.e. the relative kidney and prostatic weights, no significant differences were found. Transcortin levels, relative adrenal weights and renal NADPH-dependent 3alpha-HSD activities were higher in oil-treated gonadectomized animals than in oil-treated hypophysectomized-gonadectomized animals. The opposite was found for the relative weights of uterus and seminal vesicles and renal NADH-dependent 3alpha-HSD activities. These differences between gonadectomized and hypophysectomized-gonadectomized animals disappeared after TP treatment as far as transcortin levels were concerned but remained for the five other parameters. After gonadectomy sexual differences subsisted for all parameters studied. But whereas intact male rats had higher NADH-dependent 3alpha-HSD activities than female rats the opposite was found after gonadectomy. After gonadectomy plus hypophysectomy the between sex differences disappeared as far as transcortin levels were concerned but remained in the other parameters studied.

Adrenal Glands↗
PubMedDate not supplied

Selective DNA binding by the androgen receptor as a mechanism for hormone-specific gene regulation.

Steroid hormones control many physiological processes by activating specific receptors that act as transcription factors. In vivo, each of these receptors has a specific set of target genes, but in vitro the glucocorticoid, progesterone, mineralocorticoid and androgen receptors (class I receptors) all recognise response elements which are organised as inverted repeats of 5'-TGTTCT-3'-like sequences with a three nucleotide spacer. This poses the question how the in vivo specificity of the different steroid responses is mediated. To unravel the mechanisms involved, we have compared the structural features of the androgen-selective enhancers of the probasin, the secretory component and the sex-limited protein genes with those of non-selective enhancers in the mouse mammary tumour viral promoter and the C3(1) gene. The probasin promoter contains an androgen response element which is recognised with high affinity by the androgen receptor, but not by the other class I receptors. Swapping experiments between the DNA-binding domains of the androgen and glucocorticoid receptor revealed that it is not the first zinc finger, but rather the second zinc finger and part of the hinge region which contribute to this specificity. Three AR-specific aminoacids are involved in the probasin ARE recognition, but not in the C3(1) ARE binding by the AR. The location of these residues strongly suggests that an alternative dimerisation interface is involved in the probasin ARE binding. We could subsequently demonstrate that the AR binds direct repeats of 5'-TGTTCT-3'-like sequences in gel retardation assays as well as in transfection experiments. Moreover, the androgen-specific enhancers all contain direct repeats, and point mutations that change the nature of these elements into inverted repeats result in a change of specificity. It seems, therefore, that direct repeat elements can be the determinants of the AR-specificity. It will be exciting to learn how such DNA elements will affect the properties of the receptor dimer with respect to ligand binding, interactions between the aminoterminal domain and the ligand-binding domain, the recruitement of co-activators and cooperativity with other transcription factors.

Animals↗