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Biomedical subjects

R Mitchell

Publications and source records attributed to R Mitchell.

At least 343 records · Page 19Linked to original sources
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↗
PubMed1984

Central-type benzodiazepine binding sites in rat pituitary gland are of the BZ1 subtype.

Experiments were performed to investigate the subtype of central-type benzodiazepine binding site present in rat pituitary gland. Bmax values for [3H] n-propyl beta-carboline-3-carboxylate and [3H] flunitrazepam (for central-type binding only) were similar. Displacement of [3H] flunitrazepam by n-propyl beta-carboline-3-carboxylate gave a linear Hofstee plot and a Hill coefficient close to unity. These results suggest that the central benzodiazepine binding sites in the pituitary are predominantly of the BZ1 subtype, as found in the cerebellum.

Animals↗
PubMed1984

Intramolecular dislocation of the COOH terminus of the lac carrier protein in reconstituted proteoliposomes.

A dodecapeptide corresponding to the carboxyl terminus of the lac carrier of Escherichia coli was synthesized, coupled to thyroglobulin, and the conjugate was used to generate site-directed polyclonal antibodies. The antibodies react with the carboxyl-terminal peptide and with the lac carrier protein, while monoclonal antibody 4B1 reacts with intact lac carrier protein, but not with the carboxyl-terminal peptide. Antibody 4B1 binds preferentially to right-side-out membrane vesicles relative to inside-out vesicles, confirming the presence of the 4B1 epitope on the periplasmic surface of the membrane. Alternatively, anti-carboxyl-terminal antibody binds preferentially to inside-out vesicles, demonstrating that the carboxyl terminus of the lac carrier protein is on the cytoplasmic surface. Surprisingly, both antibodies bind to proteoliposomes reconstituted with purified lac carrier protein, and quantitative binding assays indicate that the epitopes are equally accessible. When proteoliposomes containing purified lac carrier protein are digested with carboxypeptidases A and B, binding of anti-carboxyl-terminal antibodies decreases by greater than 80%, while binding of antibody 4B1 and various transport activities remain essentially unchanged. It is suggested that during reconstitution, the lac carrier protein undergoes intramolecular dislocation of the carboxyl terminus with no significant effect on its catalytic activity.

Amino Acid Sequence↗
PubMed1984

Relationship of menopausal status and exercise level to HDL-cholesterol in women.

The relationship between exercise habits, menopausal status and HDL cholesterol (HDL-C) was studied in 44 long-distance runners, 47 joggers, and 45 relatively inactive females. In each group, some women were post-menopausal (Post-M) and some pre-menopausal (Pre-M). HDL-C level was higher in runners (77.6 mg/dl) and joggers (70.4 mg/dl) than in the inactive group (62.1 mg/dl), but was not different Pre-M vs Post-M. Total cholesterol (TC) and LDL-C were higher in Post-M than in Pre-M subjects, but did not differ among exercise groups. Body weight and % fat were lower in Pre-M vs Post-M groups and were lower in the runners vs inactive subjects. The HDL-C/TC ratio was higher in the runners vs inactive subjects and there was a significant exercise-menopausal interaction indicating a beneficial exercise effect. Adjustment of lipoprotein values for possible confounding variables did not alter these results. Endurance exercise by Post-M females may help prevent adverse lipid and lipoprotein changes which might predispose them to coronary heart disease.

Adult↗
PubMed1984

A cytochemical section bioassay for plasma trilostane: an orally active inhibitor of 3 beta-hydroxysteroid dehydrogenase activity.

Trilostane is a competitive inhibitor of 3 beta-hydroxysteroid dehydrogenase activity in vitro and an orally active inhibitor of steroidogenesis in vivo. A cytochemical section bioassay for this drug (4 alpha, 5-epoxy-17 beta-hydroxy-3-oxo-5 alpha-androstane-2 alpha-carbonitrile) in human plasma has been developed. The assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the corpus luteum of unfixed tissue sections (6 micron) of the mature dioestrous rat ovary. Trilostane is extracted from plasma by a simple chloroform procedure. The standard curve (0.15-2.5 mumol/l pure trilostane) exhibits a four-fold change in 3 beta-HSD activity and is constructed in the presence of extract from control plasma pools. The detection limit of the plasma assay is 2 mumol/l trilostane after allowing for dilution effects and recovery losses. This level gives a significantly different response from the zero quality control (P less than 0.05) and has an inter-assay coefficient of variation of less than 15%. No false positives have been recorded to date and the majority of samples from subjects receiving therapeutic doses of the drug have levels of greater than 2 mumol/l. Intra- and inter-assay coefficients of variation using both plasma quality controls and unknown samples are 4% (n = 15) and 13.9% (n = 27) respectively. Recovery is 80 +/- 9% (n = 13) and 79 +/- 10% (n = 10) for plasma quality controls containing 12 and 4.8 mumol/l trilostane respectively. Dilutions (up to 1:5) of plasma extracts are parallel to the standard curve and the assay throughput is approximately 16 samples/week technician.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed1984

On the site of action of the anti-adrenal steroidogenic effect of etomidate and megestrol acetate.

The sites of action of the anti-steroidogenic action of etomidate and megestrol acetate have been established with a novel in vitro approach based upon the inhibition of cortisol (Co) secretion by dispersed guinea-pig adrenal cells. The cells were challenged with the Co precursor steroids (all at 10(-5) mol/l) pregnenolone (Pe), 17-hydroxy-pregnenolone (17-Pe), progesterone (Po), 17-hydroxyprogesterone (17-Po), 21-deoxycortisol (21-DOC) and 11-deoxycortisol (11-DOC), or 1-24 adrenocorticotrophin (ACTH, 100 ng/l) in the presence or absence of either etomidate, megestrol acetate, metyrapone or trilostane (all at 5 X 10(-5) mol/l). In the absence of drug, the steroid precursors or ACTH provoked a cortisol secretion of greater than 14 times that secreted by cells incubated in their absence. ACTH-stimulated Co secretion was inhibited by greater than 85% by all the drugs employed. In the presence of trilostane and megestrol acetate, Co secretion provoked by the delta 4 3-keto steroids (Po, 17-Po, 21-DOC and 11-DOC) was similar to the controls. However, with the delta 5, 3 beta-hydroxy steroids, 17-Pe and Pe, Co secretion was inhibited by greater than 57% in the presence of these drugs. In contrast, etomidate and metyrapone inhibited Co secretion by greater than 60% when 11-deoxycortisol was employed, indicative of a block at 11 beta-hydroxylase, the final step in the cortisol biosynthetic pathway. Similar results were seen with Pe, 17-Pe, Po and 17-Po, all of which are converted to cortisol via a biosynthetic route which includes catalysis by 11 beta-hydroxylase.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed1984

Production and immunochemical characterization of mouse monoclonal antibodies to human Lewis blood group structures.

Two mouse monoclonal antibodies with specificity for the Lea blood group determinant of human red cells have been produced by immunising mice with soluble Lewis substance. Both antibodies were of the IgM class and agglutinated only trypsinised or papainised Lea-positive red cells. The precise antigenic conformations recognised by these antibodies have been defined by inhibition studies with monosaccharides, disaccharides and synthetic blood group oligosaccharides. These studies have suggested that the alpha-side of a 1-substituted D-galactosyl residue is a central part of the determinants recognised by the antibodies. Preliminary studies have shown these antibodies to be superior to many of the presently available human and animal polyclonal reagents for routine Lea typing of red cells.

Animals↗
PubMed1984

Lithium and lecithin treatment in Alzheimer's disease: a pilot study.

Ten patients with presumed Alzheimer's disease were entered into a pilot study to evaluate the combined effects of lithium and lecithin on cognitive and behavioral parameters. The loss of patients from the study because of toxic effects of lithium was high (30%), and one patient was dropped because of an intervening illness. Of the six remaining patients who completed the study, only two showed behavioral improvement; none showed improvement on measures of cognitive functioning. The possible mechanisms of action are discussed.

Aged↗
PubMed1983

A modified flap for apicectomy.

A modified flap for apicectomy is described which is of considerable value for apicectomy performed where there is advanced crown and bridge work and extensive apical pathology. It eliminates many of the major disadvantages of other standard flaps. This is a technique which is designed to deal with cases which for one reason or another are not suitable for routine apical surgery. It ensures an adequate layer closure with deep support to the suture line.

Apicoectomy↗
PubMed1983

Effects of GABA receptor agonists on [3H] flunitrazepam binding to rat cerebellar and hippocampal membranes.

The effects of GABA agonists on [3H] flunitrazepam binding were examined in membranes from CNS areas proposed to contain different populations of benzodiazepine binding site subtypes (BZ1/BZ2). Since these effects were broadly similar in both cerebellar and hippocampal membranes, it seems unlikely that GABA receptors interacting with the proposed BZ1/BZ2 binding sites have markedly different properties. Sodium chloride clearly facilitated the potentiating effect of muscimol on [3H] flunitrazepam binding but produced a complex interaction with the effects of GABA itself and the partial agonist imidazoleacetic acid in the phosphate buffer system used.

Animals↗