Search PubMed⌕ Search

Biomedical subjects

R Mitchell

Publications and source records attributed to R Mitchell.

At least 289 records · Page 16Linked to original sources
PubMed1986

The effect of ketoconazole on adrenal and testicular steroidogenesis in vitro.

The effect of the anti-fungal agent, ketoconazole, on cortisol secretion from adrenal cells stimulated with ACTH (1-24, 50 ng/l) and on testosterone secretion from Leydig cells stimulated with LH (5 i.u./l), has been tested. The concentration of drug which inhibited cortisol and testosterone secretion by 50% (ED50) was 3.6 +/- 0.7 mumol/l and 0.61 +/- 0.03 mumol/l, respectively. The effect of ketoconazole on adrenal and testicular steroidogenesis was completely reversible. Thus, adrenal and testicular cells which had been washed after exposure to greater than 95% inhibitory dose of ketoconazole responded in a similar manner to hormone stimulation as cells similarly washed and which had not been exposed to drug. The sites of the anti-steroidogenic effect of ketoconazole have been established using a method based upon the sequential stimulation by the exogenous precursor steroids of the various steps leading to the biosynthesis of cortisol by adrenal cells and testosterone by Leydig cells. We conclude that ketoconazole reversibly inhibits the sequence between ACTH/LH binding and pregnenolone production and also inhibits testicular C-17-C-20, lyase activity.

Adrenal Glands↗
PubMed1986

Is there Ca2+(Sr2+)-3-hydroxybutyrate symport in rat-liver mitochondria? A reappraisal.

The observation in this laboratory that respiration and Sr2+ import were stimulated by the addition of 3-hydroxybutyrate to suspensions of N-ethylmaleimide-treated mitochondria respiring in state 6, after the addition of Sr2+, in a sucrose medium containing choline as substrate, led to the proposal by Moyle and Mitchell [(1977) FEBS Lett. 84, 135-140] that there is a Ca2+(Sr2+)-3-hydroxybutyrate symporter in rat liver mitochondria. However, experiments described in the present paper support a different interpretation. Under the conditions of the experiments by Moyle and Mitchell, the rate of respiration and the poise of Sr2+ accumulation are mainly limited, not by delta mu H+, but by lack of respiratory substrate. Even though N-ethylmaleimide is a potent inhibitor of 3-hydroxybutyrate dehydrogenase, we have found that, somewhat surprisingly, under the special conditions of these experiments, sufficient 3-hydroxybutyrate dehydrogenase activity remains available to account for the 3-hydroxybutyrate-dependent respiratory stimulation and Sr2+ import.

3-Hydroxybutyric Acid↗
PubMed1986

Proton translocation by cytochrome oxidase in (antimycin + myxothiazol)-treated rat liver mitochondria using ferrocyanide or hexammineruthenium as electron donor.

When O2 was injected into an anaerobic suspension of valinomycin-treated rat liver mitochondria inhibited with rotenone, antimycin, and myxothiazol, a small amount of O2 (0.23-0.33 ng-atom of O/mg of protein) was reduced extremely rapidly (within the 2 s time-resolution of the oxygen electrode). The subsequent steady-state rate of flow of electrons to oxygen was very low [less than 3 nequiv. X s-1 X (g of mitochondrial protein)-1]. In the presence of valinomycin there was a rapid ejection of protons synchronous with the rapid phase of O2 consumption corresponding to 0.38-0.61 nequiv. of H+ X (mg of mitochondrial protein)-1. When valinomycin was replaced by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) there was a rapid alkalification of the medium corresponding to 0.20-0.42 nequiv. of H+ X (mg of mitochondrial protein)-1. When 2 mM-Fe(CN)6(4-) was present to re-reduce endogenous cytochrome c, O2 consumption was still biphasic but the second phase of O2 consumption was very much more rapid [600 nequiv. X s-1 X (g of protein)-1], and resulted in the virtually complete consumption of the O2 in the pulse within 4 s. With 60 microM-Ru(NH3)6(2+) as reductant, O2 consumption was even faster [1200 nequiv. X s-1 X (g of protein)-1]. In a medium containing 150 mM-choline chloride with Ru(NH3)6(2+) as reductant, the proton per reducing equivalent stoichiometry (delta H+O/e-) was +0.95 in the presence of valinomycin and -0.94 in the presence of FCCP. In choline chloride medium containing Ru(NH3)6(2+) and valinomycin, there was an uptake of K+ ions corresponding to 1.86 K+/e-. It is concluded that nearly 1 proton is translocated outwards through cytochrome oxidase per oxidizing equivalent injected in this medium. In low ionic strength sucrose-based medium, with Ru(NH3)6(2+) as reductant, delta H+O/e- was 1.05 in the presence of valinomycin, and -0.71 in the presence of FCCP. It is concluded that the translocation of protons is accompanied by net acid production in this medium.

Animals↗
PubMed1986

Biphasic effect of GABAA receptor agonists on prolactin secretion: evidence for two types of GABAA receptor complex on lactotrophes.

The effects of GABA receptor agonists on prolactin secretion in vitro was examined using a rapid superfusion system. GABA and muscimol caused a biphasic effect on prolactin secretion, both components of which were antagonised by bicuculline methiodide, while baclofen had no effect on basal or stimulated secretion, demonstrating the GABAA receptor specificity of both components. Homocarnosine caused only inhibition of secretion, and a range of partly rigid GABA analogues were relatively poor at causing stimulation of secretion. Both effects of muscimol were antagonised by low-chloride medium and the anion channel blocker DIDS, but strychnine and picrotoxinin were both potent and selective antagonists of the stimulatory effect. These results demonstrate a novel biphasic effect of GABAA agonists or prolactin secretion, the two components of which appear to be independent and mediated by different types or states of GABAA receptor/chloride channel complex.

Animals↗
PubMed1986

Measurement of the proton-motive stoichiometry of the respiratory chain of rat liver mitochondria: the effect of N-ethylmaleimide.

The apparent proton-motive stoichiometry as measured by the oxygen-pulse technique in KCl medium is depressed by the rapid uptake of inorganic phosphate, unless endogenous phosphate is depleted or uptake is inhibited. In sucrose or choline chloride media, where the internal pH is more acid than in KCl media, uptake may be greatly diminished. In the absence of significant phosphate uptake, the observed stoichiometry of around 8, obtained with no added substrate or respiratory inhibitors, appears to be characteristic of NADH oxidation without significant participation of the proton-translocating NAD(P) transhydrogenase. A mechanistic stoichiometry of at least 8 is indicated.

Animals↗
PubMed1986

Benzodiazepine- and barbiturate-interactions with GABAA receptor responses on lactotrophs.

Modulation of the biphasic effect of muscimol on prolactin secretion by benzodiazepines and secobarbital was investigated, using an in vitro superfusion system. The stimulatory effect of low concentrations of muscimol was potentiated by both classes of drugs, and the effect of benzodiazepines appeared to be mediated by central-type benzodiazepine receptors. Neither benzodiazepines nor secobarbital affected the inhibitory response to muscimol. Clonazepam reduced the potency of bicuculline methiodide as an antagonist of the stimulatory effect, but did not alter the potency of picrotoxinin. These results demonstrate a selective potentiation of one component of the GABAA receptor effect on lactotrophs by benzodiazepines and barbiturates and provide evidence for a functional effect of these drugs at a site without the CNS.

Animals↗
PubMed1986

Distribution of GABA binding site subtypes in rat pituitary gland.

GABAA and GABAB binding sites in rat pituitary gland were investigated using equilibrium binding assays in vitro. Specific binding of both [3H]GABA and [3H]muscimol could be detected in both anterior and neurointermediate lobes, with a relative concentration in the anterior lobe. [3H]GABA binding was discriminated into GABAA and GABAB receptor type binding using baclofen. GABAB sites were detectable in the anterior but not in the neurointermediate lobe. Saturation analysis of [3H]muscimol binding to whole pituitary gland membranes demonstrated that the pituitary contains two classes of GABAA sites differing in affinity, as found in the CNS, although the number of sites is considerably lower than in the CNS.

Animals↗
PubMed1986

Frozen recovered red cell boosting of female donors for anti-D-production.

A selected group of women previously immunized in pregnancy by the Rh(D) antigen were boosted with 0.5 ml of Rh(D)-positive frozen recovered red cells from an accredited donor panel. The response was prompt and sustained and increased the anti-D content by almost 10-fold. In spite of the reduced rate of clinical immunisation to the Rh(D) antigen, it was possible to recruit females with anti-D, acquired in pregnancy, for secondary boosting and a programme is recommended which maximizes efficiency and safety.

Adult↗
PubMed1986

Uptake and autoreceptor-controlled release of [3H]-GABA by the hypothalamic median eminence and pituitary neurointermediate lobe.

The uptake and release of gamma-[3H]-aminobutyric acid ([3H]-GABA) by the median eminence and the neurointermediate lobe of the pituitary was investigated using sucrose homogenates as crude synaptosomal preparations. Uptake in both areas showed predominantly neuronal specificity and similar Km values, but the median eminence had a considerably greater Vmax value. Release of [3H]-GABA could be stimulated by elevated K+ concentrations, in a Ca2+-dependent manner. Stimulated release was reduced by muscimol, implying the existence of presynaptic autoreceptors in both areas. A number of other transmitters and peptide hormones were demonstrated to have no effect on stimulated release of [3H]-GABA in either area.

Animals↗
PubMed1986

Secretory cells in the nucleus pulposus of the adult human intervertebral disc. A preliminary report.

A light microscopical study was conducted to ascertain the type of cells in the nucleus pulposus of the adult human intervertrebral disc. Three lumbar intervertebral discs were removed from each of 15 male and female adults at autopsy (ages ranged from 19 to 62 years). The tissue was fixed in formalin, decalcified in formic acid, dehydrated in a graded series of ethanol, embedded in paraffin, and serially sectioned at 7-10 micron. Tissue sections were affixed to albuminized glass slides and stained either by hematoxylin and eosin or hematoxylin and Van Gieson's stain. The cells of the bulk of the nucleus pulposus consisted of chondrocytes and a few fibroblasts; however, the subchondral matrix of the nucleus pulposos contained numerous stellate cells with (from 1 to 8) unusually long (up to 80 micron) primary cytoplasmic processes that often branch into secondary processes. The cell processes contained cytoplasmic varicosities at various intervals along their lengths; and their endings often expanded into bulbous, vesicle-filled process terminals. The surrounding extracellular matrix usually contained numerous, vesicle-filled, eosinophil matrix bodies. Morphological similarities of cytoplasmic varicosities, process terminals, and matrix bodies, as well as the apparent budding of process terminals, suggest that these previously unidentified cells are secreting an unknown matrix component into the subchondral matrix of the nucleus pulposus of the adult human.

Adult↗
PubMed1986

On the assessment of the in vitro biopotency and site(s) of action of drugs affecting adrenal steroidogenesis.

Dispersed guinea-pig adrenal cells have been employed in the in vitro estimation of the biological potency and sites of action of drugs acting against the adrenal. The effect of 12 drugs on cortisol secretion from cells stimulated with adrenocorticotrophin (ACTH, 50 ng/L, a 95% saturating dose) has been tested. All the drugs depressed cortisol output in a dose-related fashion. The concentration of drug which inhibited secretion by 50% was (mumol/L, mean +/- SEM): etomidate 0.1 +/- 0.002; epostane 0.44 +/- 0.02: 17-ketotrilostane 0.55 +/- 0.04: trilostane 1.3 +/- 0.1: metyrapone 3.5 +/- 0.6: cyproterone acetate 4.6 +/- 0.2: megestrol acetate 11 +/- 2: danazol 22 +/- 2: aminoglutethimide 41 +/- 5: stanozolol 50 +/- 4: thiopentone 160 +/- 18: propofol 170 +/- 18. The sites of the anti-steroidogenic effect of seven of these drugs have also been established using a method based upon the sequential stimulation by the exogenous precursor steroids of the various steps leading to the biosynthesis of cortisol by adrenal cells. Propofol acts between ACTH binding and pregnenolone production, trilostane, megestrol acetate and cyproterone acetate are 3 beta-hydroxysteroid dehydrogenase inhibitors whereas metyrapone, etomidate and thiopentone act at 11 beta-hydroxylase.

Adrenal Cortex↗
PubMed1986

Intravenous immunoglobulin therapy for idiopathic thrombocytopenic purpura.

Twenty-two patients with idiopathic thrombocytopenic purpura were treated with high-dose intravenous immunoglobulin infusions using an intact intravenous immunoglobulin preparation and a product designed for intramuscular administration. Seventeen patients (77%) responded favourably (rise in platelet count to 100 X 10(9)/1 or above). Children responded better than the adults, and the acute cases better than the chronic. Splenectomy and the presence of detectable platelet antibody had no effect on the response rate. Both products induced identical responses.

Acute Disease↗
PubMed1986

Effects of gamma-aminobutyric acid receptor agonists on the secretion of growth hormone, luteinizing hormone, adrenocorticotrophic hormone and thyroid-stimulating hormone from the rat pituitary gland in vitro.

The effects of the gamma-aminobutyric acid receptor agonists muscimol and baclofen were investigated on the secretion of GH, LH, ACTH and TSH from the anterior pituitary in vitro using a rapid superfusion system. A bicuculline-sensitive stimulatory effect of muscimol was demonstrated on the secretion of GH, LH and ACTH but not TSH. Baclofen had no effect on the basal secretion of any of the hormones, but inhibited LH-releasing hormone-stimulated release of LH and K+- and Ba2+-stimulated release of ACTH. The benzodiazepine Roll-6896 and the barbiturate secobarbital were found to potentiate the effect of muscimol on GH secretion. These results demonstrate the presence of GABAA receptors on somatotrophs, gonadotrophs and corticotrophs, and the presence of GABAB receptors on gonadotrophs and corticotrophs. Thyrotrophs appear devoid of GABA receptors.

Adrenocorticotropic Hormone↗