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Biomedical subjects

R E Oakey

Publications and source records attributed to R E Oakey.

At least 19 recordsLinked to original sources
PubMed1995

Urinary multiple marker screening for Down's syndrome.

We have examined the possibility of using multiple markers in maternal urine rather than serum in order to screen for Down's syndrome. Urine samples were available from 36 cases (24 Down's syndrome, five Edwards' syndrome, three Turner's syndrome, one Klinefelter's syndrome, one triploidy, one triple-X, one twin discordant for Down's syndrome) and 294 controls, including three twins. Three markers were tested: the beta-core fragment of human chorionic gonadotrophin (hCG), total oestrogen (tE) and the free alpha subunit of hCG. Levels were corrected for creatinine excretion and expressed as multiples of the gestation-specific median (MOM) level from the singleton controls. The median value for the singleton Down's syndrome cases was 6.02, 0.74, and 1.08 MOM for beta-core-hCG, tE, and alpha-hCG, respectively. The increases in beta-core-hCG and the reduction in tE levels were highly significant (P < 0.0001 and 0.005, respectively; Wilcoxon rank sum test) but the increase in free alpha-hCG was not (P = 0.40). On the basis of a mathematical model, the expected detection rate for a 5 per cent false-positive rate was 79.6 per cent for beta-core-hCG alone, which increased to 82.3 per cent when combined with tE. Aneuploidies other than Down's syndrome were characterized by low levels of tE and either low or high beta-core-hCG.

Adult↗
PubMed1992

A method for the determination of sex hormone binding globulin using Concanavalin A-sepharose.

A binding assay for sex hormone binding globulin (SHBG) has been developed in which SHBG is saturated with tritiated dihydrotestosterone (DHT). Separation of bound and free DHT is achieved by using Concanavalin A-Sepharose as a solid phase matrix. The method is described and its performance, including linearity, imprecision and comparison with other methods, is assessed. The assay is simple and robust and is suitable for analysis of samples of plasma or serum for clinical or research use.

Dihydrotestosterone↗
PubMed1991

The effects of fasting on plasma corticosterone kinetics in rats.

Plasma corticosterone clearance in anaesthetized rats was measured from the disappearance of radioactivity after a bolus injection of [3H]corticosterone. Mean fractional clearance rates were significantly (P less than 0.05) reduced after a 48 h fast, by 32 and 22% for males and females respectively. Plasma corticosterone concentrations were increased by fasting in both sexes. Corticosterone secretion rates, calculated as the product of fractional clearance and plasma corticosterone concentration, did not differ between fed and fasted groups in either sex. The mean activity (U/liver) of the rate-limiting enzyme for corticosterone degradation, hepatic 4,5-dihydrocorticosterone:NADP+ delta 4-oxidoreductase, was significantly reduced by 51 and 78% after fasting in males and females respectively. This was due to changes in both the soluble and microsomal forms of the enzyme. The binding capacity of corticosterone-binding globulin in plasma was significantly reduced by fasting in females (P less than 0.001), but was not altered in males. The results suggest that reduced hormone clearance is the dominant cause of fasting hypercorticosteronaemia in the rat.

Animals↗
PubMed1989

Evidence for separate sites for aromatisation of androstenedione and 16 alpha-hydroxyandrostenedione in human placental microsomes.

Much greater quantities of 16 alpha-hydroxyoestrogens (e.g. oestriol) than of 16-deoxyoestrogens (e.g. oestradiol-17 beta) are formed in human pregnancy than might be expected from the relative availability to the placenta of the 16 alpha-hydroxy- and 16-deoxy-C19 precursors. To investigate this further, 16 alpha-hydroxyandrostenedione (16 alpha-OH-A4) and androstenedione (A4) were tested in vitro as substrates and mutual inhibitors of human placental aromatase. It was found that the Km for aromatisation of A4 (mean = 0.26 mumol/l) was very similar to Ki (0.30, 0.35 mumol/l) for the inhibition by A4 of the aromatisation of 16 alpha-OH-A4. Similarly, Km for aromatisation of 16 alpha-OH-A4 (mean = 1.21 mumol/l) had the same value as the Ki (1.0, 1.2 mumol/l) for the inhibition by 16 alpha-OH-A4 of the aromatisation of A4. From graphical analysis of Lineweaver-Burk plots, both inhibitions were characterised as noncompetitive. Hence, it was concluded that the two 16-deoxy- and 16-hydroxy-C19 substrates bind at separate, but interactive, sites and that each substrate on binding inhibits the aromatisation of the other. Additional evidence for the separate but interactive substrate binding sites for the 16-deoxy- and 16-hydroxy-C19 steroids was obtained by use of the suicide inhibitor 4-hydroxyandrostenedione (4-OH-A4), which is recognised as binding to the aromatisation site for A4. Aromatisation of 16 alpha-OH-A4 was found to be inhibited by pre-incubation of the microsomes with 4-OH-A4 (0.1 mumol/l). The presence of A4 (4.6 mumol/l), but not of 16 alpha-OH-A4 (4.0 mumol/l) during the pre-incubation successfully protected the subsequent aromatisation of 16 alpha-OH-A4 from this inhibition. In addition, the Km values, reported here, suggest also that the 16-deoxyandrogens are preferred to the 16 alpha-hydroxyandrogens as oestrogen precursors. In consequence, factors other than substrate affinity and plasma concentrations must be presumed to be involved in the overwhelming production of 16 alpha-hydroxyoestrogens in human pregnancy.

Androstenedione↗
PubMed1988

Oestriol binding to plasma proteins.

Simple diffusion experiments indicated that oestriol was retained by human pregnancy plasma more effectively than by albumin solutions of a corresponding concentration. Oestriol bound (Ka = 6 X 10(6) l/mol at 4 degrees C) to a glycoprotein which had been isolated from plasma by adsorption to Concanavalin A. The free energy of binding at 37 degrees C was -38 kJ/mol. Competition experiments indicated that the oestriol binding glycoprotein had properties expected of sex hormone binding globulin. The distribution of oestriol among the protein fractions of human pregnancy plasma--glycoprotein bound 7.8%, albumin bound 78.6%, unbound 13.6%--suggests that this glycoprotein plays little part in the transport of oestriol.

Binding, Competitive↗
PubMed1988

Steroid metabolism in testes of patients with incomplete masculinization due to androgen insensitivity or 17 beta-hydroxysteroid dehydrogenase deficiency and normally differentiated males.

For purposes of establishing suitable controls in studies of patients with a suspected enzyme deficiency, activities of enzymes involved in the biosynthesis of testosterone were compared in testes of patients with androgen insensitivity syndrome (AIS) and normally differentiated males with carcinoma of the prostate (Ca prostate) or testis (Ca testis). Activities of 17,20-desmolase and of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) were higher in the testes of pre-, peri- or postpubertal patients with AIS than in elderly men (58-80 yr) with Ca prostate. Activities of 17 beta-HSD (reductive direction) and 3 beta-HSD tended to be higher in peri- or postpubertal than in prepubertal patients with AIS. Activity of 3 beta-HSD was low in the patient with Ca testis. In a peripubertal (12 yr) patient with incomplete masculinization due to a severe deficiency of 17 beta-HSD, reductive activity of 17 beta-HSD was very low compared with that of patients with Ca prostate, Ca testis or AIS. In contrast, in testes from the younger sibling (4 yr), in whom the deficiency of 17 beta-HSD was less severe, 17 beta-HSD reduction of dehydroepiandrosterone was as high as that of men with Ca prostate, yet deficient in comparison with that of more closely age-matched patients with AIS. This emphasizes the desirability of using age-matched tissue for control purposes in enzyme studies.

17-Hydroxysteroid Dehydrogenases↗
PubMed1988

In-vivo and in-vitro endocrine investigation of pure gonadal dysgenesis.

Diagnosis of XY pure gonadal dysgenesis was established in a patient of female phenotype, with female internal genitalia, but with a chromosomal constitution of 46 XY. Streak gonads had undergone neoplastic transformation--gonadoblastoma and dysgerminoma. Before operation the concentrations of gonadotrophins in plasma were high and of oestradiol was low. Administration of oestradiol benzoate initially suppressed and then stimulated an increase in the plasma concentration of LH. These changes were not accompanied by changes in blood levels of endogenous sex steroids. A single injection of hCG failed to stimulate steroid secretion. The activities in vitro of steroid-metabolizing enzymes in the dysgenetic gonadal tissue more closely resembled those of ovarian tissue from a premenopausal and from a postmenopausal women than those in testes from two androgen-insensitive patients. However, aromatase activity was higher in the dysgenetic gonads than in the pre or post-menopausal ovaries. Examination of enzymes in genital skin fibroblasts demonstrated normal activities of 3 alpha/beta-beta-hydroxysteroid dehydrogenase and 17 beta-hydroxysteroid dehydrogenase (oxidative and reductive directions). However, 5 alpha-reductase activity was low in minces and fibroblasts of genital skin from the patient. Androgen binding was within the range for male controls.

Adolescent↗
PubMed1988

Antenatal detection of placental steroid sulphatase deficiency by measurement of urinary 16 alpha-hydroxydehydroepiandrosterone sulphate.

A simple gas chromatographic technique for the measurement of 16 alpha-hydroxydehydroepiandrosterone sulphate in urine from pregnant women is described. An assessment was made of the effectiveness of the measurement of this oestriol precursor for the antenatal diagnosis of placental steroid sulphatase deficiency. Twenty-two patients whose pregnancies were complicated by subnormal oestrogen excretion for gestation were studied. In nine of these, where placental steroid sulphatase activity was found subsequently in vitro to be normal, the excretion of 16 alpha-hydroxydehydroepiandrosterone sulphate was less than 27 mumol/24 h. In the remaining 13 patients, in whom postnatal in vitro assay demonstrated absence of placental steroid sulphatase activity, urinary excretion of 16 alpha-hydroxydehydroepiandrosterone sulphate was 59-360 mumol/24 h. The excretion of this metabolite was below the limit of detection (20 mumol/24 h) in 30 uncomplicated pregnancies. It is concluded that urinary excretion of 16 alpha-hydroxydehydroepiandrosterone sulphate greater than 50 mumol/day or a ratio of urinary 16 alpha-hydroxydehydroepiandrosterone sulphate to urinary oestrogen greater than 2.0 correctly identifies, before delivery, those pregnancies in which fetus and placenta are deficient in steroid sulphatase activity.

Adult↗
PubMed1988

Evidence for secondary 5 alpha-reductase deficiency in genital and supra-pubic skin of subjects with androgen insensitivity syndrome.

The activity of 5 alpha-reductase in genital and supra-pubic skin (homogenate or fibroblasts) from subjects with complete or incomplete androgen insensitivity syndrome was low compared with mean activity in samples from normally differentiated male controls. Also, in two subjects with incomplete androgen insensitivity syndrome the ratio of the concentration of testosterone to that of 5 alpha-dihydrotestosterone in plasma was raised after hCG stimulation but normal under basal conditions. In three subjects with complete androgen insensitivity syndrome there was no evidence of raised ratios of testosterone to 5 alpha-dihydrotestosterone in plasma under basal or hCG-stimulated conditions. The activities of other steroid metabolizing enzymes, e.g. 17 beta-hydroxysteroid dehydrogenase, 3 alpha/beta-hydroxysteroid dehydrogenase, were not decreased. The low 5 alpha-reductase activity of androgen insensitive subjects reported here, and by others, may imply that this enzyme in genital skin is in some way androgen dependent, or responsive to other factors associated with androgen insensitivity syndrome.

17-Hydroxysteroid Dehydrogenases↗
PubMed1987

Cloning of a cDNA for steroid sulfatase: frequent occurrence of gene deletions in patients with recessive X chromosome-linked ichthyosis.

A human steroid sulfatase (steryl-sulfatase; steryl-sulfate sulfohydrolase, EC 3.1.6.2) cDNA 2.4 kilobases long was isolated from a human placental lambda gt11 cDNA expression library. The library was screened with monospecific rabbit antibodies elicited by injection of steroid sulfatase protein purified from human placentas. Hybridization of the cDNA with EcoRI-digested genomic DNA indicated that patients from 14 of 15 apparently unrelated families have gross deletions of the gene for steroid sulfatase. One patient had genomic DNA fragments that were identical to those from normal individuals, indicating the absence of any major deletions as the cause of his lack of steroid sulfatase enzyme activity.

Chromosome Deletion↗
PubMed1986

Oestriol and non-protein-bound oestriol concentrations in human peripheral plasma before labour and delivery.

The concentration of oestriol and the proportion of this hormone not bound to plasma protein were measured using radioimmunoassay and centrifugal ultrafiltration respectively, in 55 samples of plasma obtained from 12 women in the last 2 to 7 weeks of uncomplicated pregnancy. Among individuals, the mean plasma concentration of oestriol varied from 25.8 +/- 94.8 nmol/l; in nine subjects, there was a tendency for oestriol concentrations to increase as delivery approached. The mean proportion of oestriol not bound to plasma protein in the different subjects varied from 13.1 to 18.9%, but values from any individual subject remained essentially constant during the periods of study. These measured values were used to calculate, for each sample, the apparent concentration of oestriol not bound to plasma protein. The results were combined with analogous values for oestradiol and progesterone obtained from the same plasma samples and described in a previous study. It was found that the mean ratio of the concentration of oestriol and oestradiol was 0.75, the mean concentration of non-protein-bound oestriol was 8.7 times that of non-protein-bound oestradiol, and in individual subjects, there was no consistent trend as delivery approached in the ratio of the concentration of progesterone to that of oestriol in either the total or non-protein-bound form.

Blood Proteins↗
PubMed1985

Non-protein-bound oestradiol and progesterone in human peripheral plasma before labour and delivery.

Plasma samples were obtained at weekly intervals from the peripheral circulation of 12 women in the last 2-7 weeks of pregnancy. The concentrations of oestradiol and progesterone (isolated by chromatography) were measured by radioimmunoassay; the proportion of each hormone which was not bound to protein was measured by steady-state gel filtration. From these, the apparent concentration of the non-protein-bound form of each hormone was calculated. The mean proportion of oestradiol not bound to protein varied from 0.84 to 2.71% in the different subjects, but within each subject variation was within experimental error. For progesterone, the mean proportion not bound to protein in the different subjects varied from 1.76 to 2.77%; within individuals the proportion remained essentially constant. There was no consistent, recognizable trend as labour approached in the concentration of oestradiol; the concentration of progesterone; the concentrations of non-protein-bound oestradiol or non-protein-bound progesterone; the ratio of the concentrations of progesterone and oestradiol; the ratio of the concentrations of non-protein-bound progesterone and oestradiol. In nine out of 12 subjects, the ratio of the concentration of non-protein-bound progesterone to that of non-protein-bound oestradiol was greater than the corresponding ratio based on total hormone concentrations. These results therefore provide no support for the hypothesis that human labour is preceded by alteration in the progesterone to oestradiol ratio which can be detected by measurement of these hormones in peripheral blood.

Chromatography, Gel↗
PubMed1985

Hydrolysis of deoxycorticosterone-21-yl sulphate and dehydroepiandrosterone sulphate by microsomal preparations of human placentae: evidence for a common enzyme.

The human placenta can hydrolyse both dehydroepiandrosterone-3 beta-yl sulphate (DHASO4-) and deoxycorticosterone-21-yl sulphate (DOCSO4-). There is some uncertainty as to whether the same or different enzymes are responsible for hydrolysis of these substrates. As a fresh approach to this problem we have compared the quantities of DHASO4- and DOCSO4- hydrolysed by microsomal preparations of placentae obtained from 14 normal pregnancies and from 14 pregnancies complicated by steroid sulphatase deficiency. Under the conditions used, and standardizing the results to unit time and quantity of protein, 1380-8830 fmol DHASO4- were hydrolysed by 14 normal placentae whereas less than 1000 fmol DHASO4- were hydrolysed by the other 14 placentae, thereby designated as steroid sulphatase deficient. Net hydrolysis of DOCSO4- by the preparations of normal tissue was 9-52 fmol; hydrolysis of this substrate by steroid sulphatase-deficient tissues was indistinguishable from that by boiled tissue (less than 29 fmol). Thus preparations of placentae which hydrolysed DHASO4- also hydrolysed DOCSO4-; tissues which did not hydrolyse DHASO4- also failed to hydrolyse DOCSO4-. The quantities of DHASO4- and DOCSO4- hydrolysed by the 28 individual placentae showed a positive correlation (r = 0.91, P less than 0.001). The apparent Michaelis constants for hydrolysis of DHASO4- and DOCSO4- were 38 and 274 mumol/l respectively. These results are consistent with the proposal that these substrates are hydrolysed by a common enzyme.

Dehydroepiandrosterone↗
PubMed1984

Cycle initiation in amenorrhoea; the effect of progesterone and oestrogen administration on the pulsatile release of gonadotrophins.

The modulation of pulsatile gonadotrophin release by endogenous ovarian steroids during the normal menstrual cycle may be involved in the initiation of the following menstrual cycle. The absence of this cyclical variation may, in some cases, be the cause of, or contribute to the cause of, amenorrhoea. To assess this the modulatory effect of gonadal steroid administration on the pulsatile release of gonadotrophins was studied in fourteen amenorrhoeic and four oligomenorrhoeic women. Pulsatility was assessed by samples collected at 10 min intervals during a 4 h morning period before and after treatment with either progesterone or micronized oestradiol or a sequential combination of both. Ten patients with intact positive oestrogen-gonadotrophin feedback responded to progesterone treatment by both a significant reduction in LH pulse frequency, from a mean of 4.1 to a mean of 2.1 pulses within the 4 h study period and an increase in pulse amplitude. Progesterone therapy did not affect mean LH concentrations but there was a significant reduction in mean FSH concentrations. In the eight patients with absence of positive feedback, none of the treatment regimes elicited significant changes in LH release. No definable FSH pulses were detected before or after treatment in either group. Both the changes in LH and FSH concentrations and their release observed in this study, support the concept that cycle initiation may be related to a reduced pituitary exposure to LHRH associated with elevated progesterone concentration in the luteal phase of the cycle. This selectively induces FSH synthesis and storage. Release of this stored FSH may occur as a result of failure of the corpus luteum and falling progesterone concentrations.

Adult↗
PubMed1984

Pathological mechanisms in polycystic ovary syndrome: modulation of LH pulsatility by progesterone.

The pulsatile discharge of luteinizing hormone (LH) in nine patients with polycystic ovary syndrome (PCO) and nine patients with amenorrhoea but without PCO, who exhibited LH discharge in response to oestrogen provocation, were studied by 4-h measurement of gonadotrophin pulsatility before and after a course of progesterone injections. No significant differences were found in the gonadotrophin pulsatility patterns of the two groups, although the LH/FSH ratio rose significantly in the patients without PCO after progesterone but not in the patients with PCO, suggesting an abnormality of FSH storage. The ability to discharge gonadotrophins in response to oestrogen provocation has been reported to be present in patients with greater than or equal to 3 LH pulses in a 4-h study period. This, however, was not demonstrated in five of the nine PCO patients despite the presence of 'normal' gonadotrophin pulsatility patterns.

Adult↗
PubMed1984

Antenatal detection of placental steroid sulphatase deficiency: use of a dehydroepiandrosterone sulphate loading test.

Dehydroepiandrosterone sulphate (50 mg) was given intravenously to 15 women in the third trimester of pregnancy in which urinary oestrogen excretion was subnormal (less than 32 mumol/24 h) without recognizable clinical or therapeutic cause. In six patients, this procedure was followed by a marked increase in plasma oestradiol concentrations [mean (SD), nmol/l] before treatment: 44 (13) and 30 min after injection: 279 (31). After delivery, the placentas from all these patients showed steroid sulphatase activity in vitro (greater than 450 units). In the other nine patients, all of whom subsequently showed negligible placental steroid sulphatase activity in vitro (less than 10 units), mean plasma oestradiol concentrations increased only from 18 (9) to 26 (11) nmol/l. Changes in plasma oestradiol concentrations in late pregnancy after injection of dehydroepiandrosterone sulphate therefore readily permit identification of those patients in whom a placental enzyme deficiency is the cause of the subnormal oestrogen production. The defect was identified as steroid sulphatase deficiency by an in-vitro test of placental tissue after delivery.

Dehydroepiandrosterone↗
PubMed1983

Aromatase activity of steroid sulphatase-deficient placentae.

Aromatase activity was measured in homogenates from steroid sulphatase deficient and steroid sulphatase positive placentae. The activity of the aromatase complex was determined from the rate of formation of [14C] oestrone plus [14C] oestradiol when [14C] testosterone was incubated with a rate-limiting quantity of homogenate. A reduced level of aromatase activity was found in vitro in 70% of steroid sulphatase-deficient placentae tested, but the deficiency was much less complete than that of steroid sulphatase. The mean (+/- SD) aromatase activity of steroid sulphatase-deficient placentae was 380 +/- 180 pmol product/h/g tissue (n = 10), significantly lower (P less than 0.001, t-test) than the mean aromatase activity of steroid sulphatase positive placentae (701 +/- 70 pmol product/h/g tissue, n = 10). Seventy per cent of the steroid sulphatase deficient placentae showed lower aromatase activity than that of normal placentae stored for a comparable period of time. Assay imprecision and the sex of the foetus were excluded as reasons for the diminished aromatase activity found. It may arise through an abnormal gene product and consequent alterations in the structure of the microsomal membrane in which both aromatase complex and steroid sulphatase enzymes are retained.

Acetylation↗