Search PubMed⌕ Search

Biomedical subjects

D R Weightman

Publications and source records attributed to D R Weightman.

At least 19 recordsLinked to original sources
PubMed2000

Brain oestradiol and testosterone levels in Alzheimer's disease.

Epidemiological studies indicate that oestrogen improves memory and may delay the onset of Alzheimer's disease (AD) in postmenopausal women. Furthermore, evidence from experimental studies suggests beneficial effects of oestrogen on several pathogenic mechanisms implicated in AD. We have therefore measured the levels of oestradiol and testosterone in control and AD brains. The results show that in control brain, oestradiol levels are 3.5 fold higher in females than males, though testosterone levels are equivalent. In AD, oestradiol levels were not significantly increased compared to those in control brain, while testosterone levels were unaffected in AD. The results do not support the hypothesis that a lack of oestrogen is a contributory factor in AD.

Aged↗
PubMed1999

Sex differences in cognition: the role of testosterone and sexual orientation.

The performance of both heterosexual and homosexual males and females was compared on four cognitive tasks which have been shown to reveal evidence of sexual dimorphism. In one spatial and one verbal task, significant sex and orientation effects were found. Significant relationships were also found between salivary free-testosterone levels and performance on both spatial tasks, but no significant associations were found for performance on the two verbal tasks. The present study revealed both within- and between-sex differences in cognition and indicates that these differences may be partly accounted for by the activational effects of free testosterone.

Adolescent↗
PubMed1997

Characterization of corticotropin-releasing hormone binding sites in the human placenta.

The human placenta synthesizes and secretes large amounts of corticotropin-releasing hormone (CRH) which has been implicated in the triggering of parturition. The placental CRH was found to act in a paracrine manner to stimulate secretion of ACTH and beta-endorphin. In view of this we sought to characterize CRH binding sites in the human placenta. The specific binding of 125I-tyrosyl-ovine CRH (125I-oCRH) to placental membranes was dependent on time, temperature, pH, divalent cations and was reversible on addition of excess oCRH. Scatchard analysis revealed a high afinity binding site with a dissociation constant of approximately 0.7 nmol/L and maximum number of binding sites approximately 44 fmol/mg protein. Disuccinimidyl suberate, a chemical cross-linker, was used to covalently attach 125I-oCRH to placental membranes. The labelled placental membranes were analyzed by SDS-PAGE and autoradiography. A major radioactively labelled band with a molecular weight of 55,000 Da was identified. In this study we have identified placental binding sites for CRH with properties similar to CRH receptors described in a number of human and animal tissues and with a molecular weight similar to that of the brain CRH receptor. These binding sites may be involved in the regulation of the placental CRH/ACTH-beta-endorphin axis during pregnancy and parturition.

Autoradiography↗
PubMed1993

Autoantibodies to IGF-1 binding sites in thyroid associated ophthalmopathy.

Graves' disease is an autoimmune disorder but the nature of the association between hyperthyroidism and ophthalmopathy is not yet understood. Serum autoantibodies to orbital tissues have previously been identified and the cross-reactivity with orbital and thyroid antigens has been implicated in the development of thyroid-associated ophthalmopathy (TAO). The ophthalmopathy of Graves' disease is remarkable for the hypertrophy of extraocular muscles and proliferation of fibroblasts within the orbit; features which suggest a possible involvement of growth factors. The present study was therefore undertaken to investigate the interaction of IgGs extracted from the sera of patients with Graves' disease, with or without overt ophthalmopathy, with respect to IGF-1 receptor binding sites on fibroblasts from human orbital tissue. IGF-1 binding sites were demonstrated on human orbital fibroblast monolayers grown from eye muscle explants. These cells exhibited a population of high affinity IGF-1 binding sites (Kd, 0.5nM SEM +/- 0.05). IgG prepared from sera taken from patients with Graves' disease (n = 23) significantly inhibited [125I]IGF-1 binding to orbital fibroblasts when compared to IgGs prepared from normal volunteers (n = 13, p < 0.002). It was found that 12 of 23 (52%) patients' IgG samples gave rise to significant levels of inhibition of [125I]IGF-1 binding to orbital fibroblasts. The IgG preparations did not bind directly to IGF-1. This study demonstrates that IgG prepared from patients with Graves' disease with or without overt ophthalmopathy interact with IGF-1 binding sites on orbital fibroblasts whereas IgG from normal subjects had no significant effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody Specificity↗
PubMed1991

Measurement of cell proliferation by enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody to bromodeoxyuridine.

An ELISA was developed and optimized to measure cell proliferation using a monoclonal antibody to bromodeoxyuridine (BrdUrd). Incorporation of BrdUrd into myoblast monolayers, measured as the optical density at 492 nm, increased in response to fetal calf serum, IGF-I and EGF, the ELISA data correlated closely with data obtained by BrdUrd immunocytochemistry (r = 0.984), cell counting (r = 0.972) and tritiated thymidine uptake by liquid scintillation counting (r = 0.990). The BrdUrd ELISA is a useful alternative to measurement of tritiated thymidine uptake by scintillation counting, and has the added advantages of dispensing with the use of radioactivity and of being less labour intensive.

Animals↗
PubMed1990

Azathioprine in the treatment of thyroid-associated ophthalmopathy.

Azathioprine is used in the treatment of thyroid-associated ophthalmopathy, but its effectiveness has not been evaluated. In the present study 20 patients with moderately severe ophthalmopathy were recruited; 10 patients received azathioprine and the other 10 matched patients served as controls. During the treatment period (lasting 1 year) and 1 year later, no changes were detected in exophthalmometer readings, visual acuity or measurement of palpebral aperture. Differential intraocular pressure fell with time in both groups. Azathioprine treatment did not significantly influence these parameters, although it did induce significant decrease in thyroid microsomal antibodies and in thyroid-stimulating hormone binding inhibiting immunoglobulin index. The study demonstrates that thyroid-associated ophthalmopathy of moderate severity, often improves with time without treatment. Azathioprine is not an effective treatment for patients with moderately severe thyroid-associated ophthalmopathy. The study emphasises the necessity for an adequately matched control population in the evaluation of therapy.

Azathioprine↗
PubMed1988

Antibodies that block stimulation by TSH or TSAb of thyroid hormone secretion in primary hypothyroidism.

Antibodies that inhibit the stimulation of the thyroid by TSH have been studied in 63 patients with primary hypothyroidism of whom 34 had thyroid atrophy and 29 goitrous Hashimoto's thyroiditis. The method used measured the secretion of tri-iodothyronine (T3) from porcine thyroid slices incubated in vitro. The aims of the study were to assess the frequency and clinical correlates of blocking antibodies in an unselected series of patients, to establish their IgG nature and to examine their action in relation to the TSH receptor. Blocking antibodies were found in 25% of patients and occurred in association with both atrophic (32%) and goitrous (17%) hypothyroidism. These antibodies did not bind TSH (with one exception) nor did they inhibit binding of TSH to its receptor (also with one exception). Blocking-antibody activity was abolished by treatment of the serum with anti-hIgG or with protein A, and the activity was purified from serum by affinity chromatography on protein A sepharose-4B, thus establishing the IgG nature of the antibodies. The stimulation of T3 secretion by thyroid-stimulating antibodies was also blocked and in one case, where IgG did not block stimulation by bTSH, stimulation by hTSH was blocked. Antibodies blocking the action of TSH probably represent an important mechanism in the pathogenesis of primary hypothyroidism in some patients.

Adult↗
PubMed1987

Evaluation of enzyme inhibitors of pregnancy associated oxytocinase: application to the measurement of plasma immunoreactive oxytocin during human labour.

The presence of the human placental enzyme, oxytocinase, in blood samples taken during pregnancy causes major methological problems in the radioimmunoassay for plasma oxytocin. Inadequate inhibition of the enzyme activity may lead to spuriously high or low values of plasma oxytocin. This study systematically investigates a variety of enzyme inhibitors. The optimum inhibitory system was obtained by the addition of 10 microliters of cold 125 mmol/l 1.10 phenanthrolene and 1 mol/l EDTA per ml of whole blood into the syringe. Complete enzyme inhibition was maintained for up to 60 min, during which time the lithium heparinized plasma samples were extracted by the Florisil method. Following extraction there was no enzyme activity in the extract residue. Concentrations of phenanthrolene and EDTA necessary to eliminate enzyme activity were 50- and 10-fold greater, respectively, than in any previously reported method. Recovery of synthetic oxytocin added to pregnancy plasma with inhibitors was 80% or higher, over the concentration range 1-100 pmol/l. Extract residue could be stored at -20 degrees C for up to 7 weeks. Dilutions of pregnancy plasma extracts ran parallel to the oxytocin standard curve. Studies on plasma concentrations of oxytocin (OT) during the first stage of labour in 6 patients showed that 3 had pulsatile plasma OT, peak values ranging from 4-10 pmol/l in phase with uterine concentrations, but 2 who had regular uterine activity had no episodic changes in plasma OT. One patient with hypocontractile labour had low non-fluctuating plasma OT.

Aminopeptidases↗
PubMed1985

Rat brain membranes possess two high-affinity binding sites for [3H]somatostatin.

This report described the first use of [4-3H-Phe6]somatostatin-14 to characterize binding sites on rat brain membranes for somatostatin-14. This ligand is superior to previously used iodinated analogues and is chemically and biologically identical to the natural ligand. Two high-affinity binding sites were found, from Scatchard analysis of competitive displacement experiments, with Kd SS1 = 0.41 and Kd SS2 = 22.9 nM. Specific binding was reversible, and kinetic analysis of the dissociation and association time-course gave an apparent Kd of 0.44 nM, in good agreement with the Kd of the higher-affinity site. Specific binding of the ligand was enriched in cerebral cortex and hippocampus, with intermediate levels in the striatum, hypothalamus and midbrain, and low levels in the pons/medulla and cerebellum. This ligand should prove to be valuable for elucidating the physiological and pharmacological significance of the two subtypes of somatostatin binding sites we have demonstrated.

Animals↗
PubMed1985

The inability of dynamic tests of prolactin and TSH secretion to differentiate between tumorous and non-tumorous hyperprolactinemia.

Certain hyperprolactinemic patients have an obvious pituitary tumor while others with normal pituitary radiology may or may not harbor a pituitary microadenoma. A variety of biochemical tests have been proposed to distinguish between those with and those without pituitary tumors. The aims of this study were: firstly to examine these tests to assess their efficacy in differentiating between patients with radiologically-demonstrated pituitary tumors and normal controls; and secondly to establish if those hyperprolactinemic patients with normal radiology formed two distinct groups biochemically as might be expected if some did and some did not have tumors. The prolactin (PRL) and thyroid stimulating hormone (TSH) response to domperidone and the PRL response to TRH and insulin-induced hypoglycemia have thus been examined in hyperprolactinemic subjects with and without radiological evidence of an adenoma and in normal controls. The basal serum PRL was similar in patients with and without radiological evidence of a pituitary adenoma. The serum PRL response to all stimuli studied, expressed as a percentage of initial values, was blunted in patients with known pituitary tumors with total separation from values in control subjects. Results for patients with normal pituitary radiology were similar to those for patients with tumors with minimal overlap with controls. The peak TSH increment after domperidone was exaggerated in patients with known tumors, but overlap with control values was observed in 25%. In patients with normal radiology the peak TSH increment after domperidone was similarly increased but again overlap with control values occurred in 28%. Cluster analysis showed no evidence of two subgroups of response with in the hyperprolactinemic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗
PubMed1985

The binding of somatostatin to rat synaptosomal membranes: effects of detergent solubilisation and of bacitracin.

Specific high and low affinity binding sites for somatostatin have been demonstrated in rat brain synaptosomal membranes using 125I [Tyr"] somatostatin tracer. When incubations were carried out in the presence of low concentrations of bacitracin (0.01% w/v), a 66% increase in association constant of the high affinity binding site to Ka = 1.71 X 10(10) M-1 and a 70% increase in the Ka of the low affinity site to 0.034 X 10(10) M-1 were observed; a similar (50%) increase in the binding capacity of the low affinity site but no increase in the binding capacity of the high affinity site was seen. These results may indicate a direct effect of bacitracin on the membrane that is distinct from its effect as an inhibitor of tracer degradation. The somatostatin-binding capacity of the membranes was solubilised by treatment with Triton X-100 and the apparent molecular weight of the receptor-ligand-detergent micelle complex was estimated by gel filtration to be approximately 250,000.

Animals↗
PubMed1985

Solid phase radioimmunoassay for direct measurement of human plasma oxytocin.

Synthetic oxytocin (OT) conjugated to bovine thyroglobulin by the carbodiimide reaction was injected into rabbits to raise a high titre, specific OT antiserum which was then coupled to microcrystalline cellulose activated by cyanogen bromide. High affinity of the coupled antiserum was defined by Scatchard analysis, Keq = 7.1 X 10(11)1/mol. Cross-reactivity studies revealed little binding of antiserum to analogues of OT. Iodination was performed by the Chloramine T method, giving specific activity of 125I-OT, range 1.1 - 1.7 X 10(3) Ci/mmol. After incubation for 40 hours under disequilibrium conditions, specific and non-specific bindings were 10.6 +/- 2.7% and 0.2 +/- 0.1% (n=15), respectively. Displacement of 50% 125I-OT occurred with 2.9 pg OT/tube. Coefficients of variation of standard OT concentrations (0.03 - 16 pg/tube) were less than 5%. Limit of detection was 2 pg OT/ml plasma. Recovery of synthetic OT added to non-pregnant plasma was 81.8% (n=34) at 20 pg/ml and 97.4% (n=32) at 100 pg/ml. Two patients, 17 and 18 weeks post-partum, had increases in plasma OT from less than 2 pg/ml to 18.3 and 16.0 pg/ml after 6 and 4 minutes breast feeding infants, respectively. We conclude that this solid phase OT radioimmunoassay is quick, relatively sensitive and reliable, and does not require prior extraction of plasma samples.

Antibody Specificity↗
PubMed1984

Blocking activity to action of thyroid stimulating hormone in serum from patients with primary hypothyroidism.

Spontaneous primary hypothyroidism in adults is usually associated with autoimmune thyroiditis. The hypothesis that hypothyroidism may result from the presence in serum of a factor that blocks stimulation of the thyroid by thyroid stimulating hormone was examined. Serum samples were collected from 28 patients with recently diagnosed primary hypothyroidism. After removal of endogenous thyroid stimulating hormone the effect of the serum on secretion of triiodothyronine induced by thyroid stimulating hormone or thyroid stimulating antibodies was examined in thyroid slices incubated in vitro. Serum samples from six of the patients demonstrated significant blocking of the stimulation by bovine thyroid stimulating hormone. Inhibition of the stimulatory action of thyroid stimulating antibodies was also exhibited by serum samples with blocking activity. It is concluded that in some patients with primary hypothyroidism a serum factor, which is probably an IgG, exists that can block the thyroid response to thyroid stimulating hormone and thyroid stimulating antibodies; it may represent an important mechanism in the pathogenesis of hypothyroidism.

Adult↗
PubMed1984

The effect of ketanserin, a specific serotonin antagonist on the PRL, GH, ACTH and cortisol responses to hypoglycaemia in normal subjects.

The role of serotonin in the prolactin, growth hormone, ACTH and cortisol responses to hypoglycaemia has been investigated in normal subjects using a selective serotonin (5HT2) receptor antagonist, ketanserin. Circulating concentrations of these hormones were measured after administration of insulin (0.1 units/kg body weight iv) to eight normal male subjects with and without simultaneous iv ketanserin (10 mg). Plasma glucose fell to less than 2.0 mmol/1 in all subjects and was unaffected by ketanserin. Ketanserin induced a 50% decrease in the serum prolactin response to hypoglycaemia, 45 and 60 min after administration of insulin (increase in serum prolactin at 60 min: 1145 +/- 295 mU/l without ketanserin; 558 +/- 176 mU/l with ketanserin, P less than 0.05). The peak ACTH response was reduced by 30% (95.3 +/- 33.6 ng/l without ketanserin; 60.0 +/- 22.9 ng/l with ketanserin, P less than 0.05) but the plasma cortisol response was not significantly altered. The serum growth hormone response was unaffected by serotonin blockade. These findings suggest that serotonin, probably acting through 5HT2 receptors, is involved in the stimulation of prolactin and ACTH release but not in the release of growth hormone, during insulin induced hypoglycaemia.

Adrenocorticotropic Hormone↗