Dopaminergic modulation of circadian thyrotropin rhythms and thyroid hormone levels in euthyroid subjects.

Basal TSH levels are known to rise during the evening, but the mechanism by which this rise occurs is poorly understood. The rise in TSH in response to dopamine (DA) receptor blockade with metoclopramide in the morning in normal subjects and hypothyroid patients has provided evidence for a tonic inhibitory role for DA in the control of TSH secretion. We have tested the hypothesis in normal, euthyroid volunteers (14 females, aged 20--40 yr; 12 males, aged 22--45 yr) that the nocturnal elevation of serum TSH levels might result from a reduction in DA action on the thyrotroph, in which case a reduced TSH response to metoclopramide would be expected. We found, however, that the TSH response to DA receptor blockade with metoclopramide (10 mg, iv) was significantly greater at 2300 h than at 1100 h [net incremental response over 120 min, 14.9 +/- 2.5 vs. 6.7 +/- 1.6 mU/liter (mean +/- SE); P < 0.001], indicating greater DA inhibition of TSH release at night. Thus, the nocturnal elevation of TSH is not due to decreased DA action on the thyrotroph; rather, increased DA tone is present and may limit the TSH response to other as yet unknown factors. Thyroid hormone levels also rose significantly after metoclopramide at both 1100 and 2300 h compared with control values after placebo [incremental difference (in nanomoles per liter) between 0 and 120 min values (mean +/- SE): 1100 h, T3, 0.24 +/- 0.09 vs. -0.05 +/- 0.08 (P < 0.02); T4, 19.4 +/- 6.1 vs. -1.8 +/- 2.5 (P < 0.01); 2300 h, T3 +/- 0.53 +/-0.07 vs. 0.04 +/- 0.07 (P < 0.01); T4 20.9 +/- 5.6 vs. 2.8 +/- 3.2 (P < 0.01)]. Incremental thyroid hormone and TSH responses to metoclopramide were directly related (T3 vs. TSH, r = 0.59 and P < 0.001; T4 vs. TSH, r = 0.41 and P < 0.01), suggesting that the thyroid hormone responses were mediated by TSH and illustrating the sensitivity of the thyroid gland to even small increases in endogenous TSH levels.

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.

A rapid radioassay for human IgG produced in lymphocyte in vitro culture systems.

Protein A bearing Staphylococcus aureus was used to develop a solid-phase radioassay for IgG immunoglobulins. The assay was specifically optimised for use with in vitro human lymphocyte culture work. Compared with a solid-phase radioimmunoassay for IgG produced in lymphocyte culture, this assay had similar performance profile and the advantages of rapidly and technical ease.

beta-thromboglobulin in antecubital vein blood--the influence of age, sex and blood group.

Samples of blood for estimation of beta-thromboglobulin (B.T.G.) in normal subjects have been obtained both from blood donors at the end of their donation and from other volunteers by standard venepuncture. The former was a satisfactory method in males only. By standard venepuncture females have on average lower values than males and in the pre-menopausal age groups the difference is statistically significant. Mean values vary little up to 59 years after which they rise slowly but steadily. There is no significant difference in the mean B.T.G. values between the ABO blood groups.

Cross-reaction of eye muscle antibodies with thyroid tissue in thyroid-associated ophthalmopathy.

The nature of the association of ophthalmopathy with autoimmune thyroid disease is not understood. Serum autoantibodies to eye muscle have previously been identified and in this study we have explored the hypothesis that there may be shared antigenic determinants between orbital and thyroid tissues. Sera were obtained from patients in whom eye muscle antibodies (EMAb) had been detected by an enzyme-linked immunosorbent assay (ELISA); the sera were preincubated with membrane preparations of thyroid or eye muscle, hepatic membranes being used as control. Tissue-binding antibodies were removed from serum by centrifugation and the supernatant serum was analysed using an indirect ELISA and by immunoblotting. In the ELISA, all sera gave a positive response for EMAb. In one serum, the binding was entirely non-specific. All sera showed significant neutralization of EMAb by eye muscle. In six sera there was reduction of EMAb after exposure to thyroidal antigens, indicative of cross-reaction. Western blotting confirmed the non-specific nature of the binding in one serum. In five of the remaining nine sera, protein bands were identified which interacted specifically with eye muscle and, in two of these, the same determinants were neutralized by preincubation with thyroid tissue. The Western blots confirmed the findings in the ELISA. The determinants recognized by IgG were variable between patients and no common antigen could be identified. This study demonstrates that, in some cases of thyroid-associated ophthalmopathy, there is cross-reaction of EMAb with thyroidal antigens, but this is variable and not found in every case. This may explain the association of the disease with autoimmune thyroid disease, at least in some cases.

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)

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.

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.

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.

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.

The ultrastruct of normal human muscle in relation to fibre type.

A quantitative analysis using a stereological point-counting method was made of the volume fractions of the components of healthy human muscle in an attempt to distinguish between Type I and Type II fibres ultrastructurally. The Z-line widths of each fibre were also measured using the 38.5 nm axial periodicity in the I-band as a reference measurement. There was a wide range of values for the parameters measured. The volume of mitochondria was 5.14 plus or minus 1.85% (mean plus or minus standard deviation, n=24 fibres), the volume of the membrane systems was 1.59 plus or minus 0.31%, the volume of the sarcoplasm was 9.37 plus or minus 2.50% and the volume of lipid was 0.63 plus or minus 0.43%. The width of the Z-lines was 89.0 plus or minus 18.65 nm. The results show that no single feature can be used to distinguish fibre types reliably. If 2 factors are measured and certain assumptions are made, it is possible to classify about 50% of the fibres examined. These conclusions are discussed in relation to other workers' findings on the effects of age, sex and athleticism on the ultrastructure of muscle.

Cell counts in the human cerebral cortex using a traditional and an automatic method.

This study compares the results of cell counting in the human cerebral cortex by a traditional and an automatic procedure. Four blocks were taken from standard areas of each of 10 brains from individuals aged 18-95 years and showing no neurological abnormality. Sections from each block were counted by traditional and automatic methods, both of which are described. The traditional method used photomicrographs and the automatic procedure used the quantimet 720 Image Analysing Computer. The degree of reproducibility of each method was measured and the results are discussed and tabulated. Comparison are made of the total cell counts, and the counts of cells measuring greater than 20 um across. The results show a high level of correlation between the two procedures but the manual count yields higher number for total cells and smaller numbers for large cells than the automatic method. The reasons for these discrepancies are discussed and examples of the arterfacts which produce them are giver. Using the traditional method described the amount of meterial examined took about 4 months to study. The sane tissue can be assessed in 1 day using the automatic apparatus. The high speed and close correlation achieved by the automatic procedure makes it a valuable aid in quantitative cell studies in the central nervous system.

A comparison of the structure of small blood vessels in normal, denervated and dystrophic human muscle.

A light- and electron-microscopic study of the small arterial vessels and capillaries in muscle from 20 patients with Duchenne muscular dystrophy failed to adduce any direct morphological evidence that the necrobiotic muscle lesions in this disease are produced by muscle ischaemia. However the electron-microscopic studies showed that the basement membrane width in 3 out of 4 cases of Duchenne dystrophy so studied was significantly less than that or normal control material. In further case of Duchenne dystrophy, selected for study because some vessels in the biopsy muscle were surrounded by small round cell infilitrates, the basement membrane width was significantly greater than that in the normal control material. In the single case of spinal muscular atrophy studied, the basement membrane width was also significantly less than the control measurements. The possible relationship of these observations to the "ischaemic" theory of the pathogenesis of muscular dystrophy is discussed.