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Biomedical subjects

R Mitchell

Publications and source records attributed to R Mitchell.

At least 325 records · Page 18Linked to original sources
PubMed1985

A simple in vitro approach to the estimation of the biopotency of drugs affecting adrenal steroidogenesis.

Dispersed guinea-pig adrenal cells can be maximally stimulated to secrete cortisol by adrenocorticotrophin (ACTH greater than 50 ng/l). Further, this stimulation appears to be specific to ACTH alone, with other naturally occurring chemicals (e.g. steroids, protein hormones) at supra-physiological concentrations being without effect on cortisol production. The effect of drugs of differing structure and therapeutic function (aminogluthethimide, metyrapone, trilostane, 17-ketotrilostane, danazol, epostane, megestrol acetate, stanozolol and etomidate) on ACTH-stimulated (50 ng/l) cortisol production has been tested in this system. All the drugs depressed steroid output in a similar dose-related fashion. The concentration of drug which inhibited cortisol output by 50% was (mumol/l, mean +/- SEM): etomidate 0.097 +/- 0.002: epostane 0.44 +/- 0.02: 17-ketotrilostane 0.55 +/- 0.04: trilostane 1.3 +/- 0.1: metyrapone 3.5 +/- 0.6: megestrol acetate, 11 +/- 2: danazol 22 +/- 2: aminogluthethimide 41 +/- 5: stanozolol 50 +/- 4. Thus, etomidate, an anaesthetic, is more potent than the established anti-steroidogenic drugs metyrapone, aminogluthethimide and trilostane. Further, direct anti-steroidogenic effects have been demonstrated for megestrol acetate and stanozolol for the first time. We conclude that this technique offers a promising new approach to the assessment of biological potency of drugs affecting endocrine tissues.

Adrenal Glands↗
PubMed1985

Some characteristics of human adrenal microsomal 21-hydroxylase activity.

The following general characteristics of 21-hydroxylase activity were determined using pooled microsomes obtained from three glands. Enzyme activity exhibited a broad pH dependence, being optimal between pH 7.4-pH 7.8, and was maximal with NADPH in the range 2 to 4.75 X 10(-4)mol/l. No microsomal 21-hydroxylase activity was detected in the absence of NADPH or substrate and when heat denatured microsomes were employed. Enzyme activity was depressed by greater than 75% in the presence of 100% oxygen or nitrogen. In a second set of experiments, microsomal fractions were prepared individually from 7 glands. In the presence of 17 alpha-hydroxy progesterone (2.0 X 10(-7) and 2.0 X 10(-6)mol/l) product formation was linear with time for up to 90 s when the microsomal protein concentration was 5, 10 and 20 micrograms/ml. Between 5 and 30% of the substrate was converted during the first 60 s. In 5/7 of the glands the addition of the autologous cytosol (20 micrograms protein/ml) was without effect, and enzyme activity (using a 60 s reaction and either 2.0 X 10(-7) or 2 X 10(-6)mol/l 17 alpha-hydroxy progesterone was directly proportional to the microsomal protein concentration (range 0-20 micrograms/ml). With the other 2 adrenals 21-hydroxylation was not proportional to the same range of microsomal protein concentrations, although it became so upon the addition of cytosol, which significantly augmented activity. There was considerable variation in enzyme activity between glands from different individuals (Vmax ranging from 2.6 to 16.6 X 10(-9) mol/min/mg protein) and in the apparent Km's (from 0.22 to 1.1 X 10(-6)mol/l). In the two preparations sensitive to cytosol, the Vmax increased 2-fold, and the Km was 3 times lower. Cytosol was without effect upon the kinetic characteristics of the other 5 microsomal preparations. Ascorbic acid (1 X 10(-3) mol/l) depressed enzyme activity by 25-43% whereas oxidised and reduced glutathione (1 X 10(-3) mol/l) showed a slight and variable effect upon 21-hydroxylation.

17-alpha-Hydroxyprogesterone↗
PubMed1985

Apparent reversals in trapezia: confirmation of the 'tan apex ratio' heuristic.

A new model for predicting the frequencies of apparent reversals in rotating trapezia, proposed by the authors in 1983, is validated and extended in two studies. Experiment 1 showed that the model retained its predictive efficiency over an increased range of shapes and viewing distances, and with trapezia made of sheet metal and not, as previously, of wire. Experiment 2 was designed to investigate an unexpected effect, in which the specificity of prediction was found to decrease as the corners of the stimulus objects were slightly rounded.

Humans↗
PubMed1985

Effect of propofol, thiopentone and etomidate on adrenal steroidogenesis in vitro.

The i.v. anaesthetic agents propofol, thiopentone and etomidate inhibited ACTH-stimulated production of cortisol by guineapig dispersed adrenal cells in a dose-related manner. For two of the drugs, propofol and thiopentone, inhibition occurred over a similar concentration range: 2 X 10(-5) - 5 X 10(-4) mol litre-1. With etomidate, inhibition occurred over a much lower concentration range (5 X 10(-8) - 5 X 10(-6) mol litre-1). The concentrations of anaesthetic which induced 50% inhibition of cortisol secretion were propofol 1.7 X 10(-4), thiopentone 1.6 X 10(-4), and etomidate 1.0 X 10(-7) mol litre-1.

Adrenal Glands↗
PubMed1985

Successes and failures of intravenous immunoglobulin.

11 patients suffering from primary and secondary severe haematological disorders of possible immune origin were treated with high-dose intravenous immunoglobulin. The responses obtained were partial in 3 and negligible in 8.

Adult↗
PubMed1985

Interactions in syntrophic associations of endospore-forming, butyrate-degrading bacteria and h(2)-consuming bacteria.

Butyrate is an important intermediate in the anaerobic degradation of organic matter. In sulfate-depleted environments butyrate is oxidized to acetate and hydrogen by obligate proton reducers, in syntrophic association with hydrogen-consuming methanogens. This paper describes two enrichments of endospore-forming bacteria degrading butyrate in consortia with methanogens. The isolates are readily established in coculture with H(2)-consuming, sulfate-reducing bacteria by pasteurizing the culture. The two original enrichments differed in that one grew to an optically dense culture while the second grew in clumps. Examination by scanning electron microscopy showed that clumping resulted from the production of large amounts of extracellular polymer. Several H(2)-consuming methanogens were identified in the enrichments. Some of them grew closely associated to the butyrate degraders. This attachment to the hydrogen producer may permit some methanogens to compete for the growth substrate against other bacteria having higher substrate affinity.

Journal Article↗
PubMed1985

Safety of intravenous immunoglobulin treatment.

In a prospective clinical and biochemical study of 16 patients treated with high doses of an immunoglobulin product that had been modified for intravenous use by mild pepsin treatment at pH 4 no evidence of hepatitis could be found. This contrasts with recent reports that intravenous immunoglobulin products can apparently transmit non-A, non-B hepatitis.

Alanine Transaminase↗
PubMed1985

On the biopotency and site of action of drugs affecting endocrine tissues with special reference to the anti-steroidogenic effect of anaesthetic agents.

Dispersed guinea-pig adrenal cells or mouse Leydig cells were stimulated with a saturating dose of adrenocorticotrophin (ACTH, 50 ng/1) or luteinizing hormone (LH, 5IU/1), respectively. The incubations were performed in the presence of increasing concentrations (10(-9) - 5 X 10(-4)mol/l) of the anaesthetic agents propofol, thiopentone and etomidate. At the end of this stimulation period, cortisol (from the adrenal preparation) or testosterone (from the Leydig cell culture) were assayed by radioimmunoassay. Propofol, thiopentone and etomidate all inhibited ACTH-stimulated cortisol secretion in a dose-related fashion. Similar inhibition of LH-stimulated testosterone output was found with propofol and thiopentone whereas etomidate was without effect at any concentration employed, an observation in accordance with its known site of action, 11 beta-hydroxylase, an enzyme which is not involved in the biosynthesis of testosterone. The concentration (mumol/l) of anaesthetics which gave 50% inhibition (ED50) of ACTH-stimulated cortisol secretion was 0.1 +/- 0.002 (n = 7), 160 +/- 18 (n = 3) and 170 +/- 18 (n = 3) (mean +/- s.e.m.) for etomidate, thiopentone and propofol, respectively. The corresponding values for the LH stimulated testosterone output from the Leydig cell preparations were 186 (thiopentone) and 180 (propofol) mumol/l. In a separate series of experiments adrenal cells were stimulated with (a) the cortisol precursor steroids (all at 10(-5)mol/l) pregnenolone, 17-hydroxypregnenolone, progesterone, 17-hydroxyprogesterone and 11-deoxycortisol, (b) dibutyryl cAMP (10(-3)mol/l) or (c) ACTH (100 ng/l) in the presence and absence of either etomidate (5 X 10(-5)mol/l), propofol (2.5 X 10(-4)mol/l) or thiopentone (5 X 10(-4)mol/l). All the stimulators increased cortisol production by > 7-fold over that seen in their absence. Propofol depressed ACTH and dibutyryl cAMP induced cortisol output by > 60% (P < 0.05) but was without effect when the steroid precursors were used, suggestive of an inhibition between the sequence involving ACTH binding -> pregnenolone production. In contrast, etomidate and thiopentone reduced cortisol secretion by > 40% (P < 0.05) regardless of the stimulator used, indicating that at least one site of action was at the level of the final enzymic step of cortisol synthesis, i.e. 11beta-hydroxylase.

Adrenocorticotropic Hormone↗
PubMed1985

Elastic fibres in the anulus fibrosus of the adult human lumbar intervertebral disc. A preliminary report.

Two intervertebral discs were removed at autopsy from the lumbar region of the spine from male or female adult human cases at the following ages: 26, 34, 43, 50 and 62 years. The discs were prepared by paraffin wax embedding, sectioned serially and stained with haematoxylin and eosin or by Verhoff's elastic fibre method. Four light microscopy photomicrographs were made of randomly selected 400 micron 2 areas of anulus fibrosus matrix (two each from different levels of a single disc). Each photomicrograph was examined for elastic fibres, and the areas occupied by them were quantitated by manual planimetry. Elastic fibres were observed in all lamellae of the anulus fibrosus at lumbar levels and they were circularly, obliquely and vertically oriented. Approximately 10% of the matrix of the anulus fibrosus consisted of elastic fibres and their numbers tended to decrease slightly with increasing age of the individual.

Adult↗
PubMed1984

Analysis of benzodiazepine binding sites in rat pituitary gland.

Benzodiazepine binding sites in rat pituitary gland were investigated by equilibrium binding assays in vitro. Using [3H]flunitrazepam [( 3H]FNM), specific binding was demonstrated in both anterior and neurointermediate lobes. Clonazepam and Ro 5-4864 were used to discriminate the binding to central and peripheral-type sites. Both types of binding site were found to be relatively concentrated in the neurointermediate lobe. Scatchard analysis demonstrated that Kd values for [3H]FNM for the two types of sites were similar to those reported in other areas.

Animals↗
PubMed1984

Investigation of the effects of muscimol on different components of [3H]propyl beta-carboline-3-carboxylate binding to rat hippocampal and cerebellar membranes.

The binding of [3H]propyl beta-carboline-3-carboxylate [( 3H]PCC) to rat hippocampal and cerebellar membranes was investigated together with the displacement by PCC of [3H]flunitrazepam [( 3H]FNM). Results were consistent with the presence of a single recognition site in cerebellum and two sites in hippocampys, but the affinity of neither of the hippocampal sites correlated with that in the cerebellum. Muscimol did not alter the affinity or capacity of any of these sites under the conditions used, indicating that PCC does not show the benzodiazepine-like property of GABAergic modulation, at any of the subpopulations of its binding sites.

Animals↗
PubMed1984

The bioavailability and metabolism of trilostane in normal subjects, a comparative study using high pressure liquid chromatographic and quantitative cytochemical assays.

High pressure liquid chromatographic (HPLC) analysis of plasma taken over 8 h from ten normal male subjects medicated with 120 mg of trilostane revealed that the drug is rapidly metabolised into at least one metabolite, 17-keto trilostane. Both compounds were detected in the blood stream at concentrations greater than 2 X 10(-7) M within an hour and were cleared from the blood by 6-8 h. Approximately 3 times the concentration of metabolite was detected compared to the parent compound in most samples analysed. There were large subject to subject variations in the handling of drug. Standard curves of pure 17-keto trilostane and trilostane were parallel as assessed by cytochemical bioassay. This assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase activity in unfixed tissue sections of the dioestrous rat ovary. The relative potency of the metabolite compared to trilostane was 1.71 (95% confidence 1.5-2.0) over the dose range 0.15-1.5 microM. Thus, the metabolite may be the major active agent when trilostane is administered for clinical purposes. In a further 4 volunteers, who also received 120 mg trilostane and were sampled over an 8 h period, plasma was analysed independently by HPLC and cytochemical assays. In the majority of cases the bioactivity recorded (relative to a trilostane standard curve) was substantially higher than the molar sum of circulating trilostane and 17-keto-trilostane (as assessed by HPLC). However, if the relative potency of 17-keto-trilostane is taken into consideration, correlation between the two assays was excellent (r = 0.947, n = 18, P less than 0.001). This also suggests that no further active metabolites were present in the plasma samples. The drug profiles seen in the second study were essentially the same as described for the first 10 volunteers. The combination of a bioassay, which detects trilostane-like bioactivity, and HPLC, which reveals the type of metabolism, should aid our understanding of the clinical value of this potentially important drug.

Adult↗