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Biomedical subjects

M C Sheppard

Publications and source records attributed to M C Sheppard.

At least 217 records · Page 12Linked to original sources

Measurement of free thyroxine and free triiodothyronine in asymptomatic subjects with high concentrations of serum TSH and a history of radioiodine therapy.

Total and free thyroid hormones were measured in a group of asymptomatic subjects with high circulating TSH concentrations and a previous history of radioiodine therapy. Subjects in the high TSH group all fell within the normal range for measurements of total T4, total T3 and T4/TBG ratio. Concentrations of free T4 or free T3 were below the normal range in more than half (9 out of 17) of the high TSH group suggesting that these measurements are more sensitive indices of thyroid failure than measurement of total hormones or T4/TBG ratio.

Humans↗

The effect of neurotensin on pituitary secretion of thyrotrophin and prolactin in vitro.

The effects of neurotensin on thyrotrophin (TSH) and prolactin (Prl) release were studied in two in vitro systems - anterior pituitary cells in culture and perifused anterior pituitary fragments. Neurotensin significantly reduced basal secretion of both TSH and Prl (P less than 0.001) from cultured pituitary cells, and abolished thyrotrophin releasing hormone (TRH)-stimulated TSH thyrotrophin releasing hormone (TRH)-stimulated TSH TSH and Prl release (P less than 0.02) from perifused pituitary fragments. These data indicate that neurotensin has a direct inhibitory effect on TSH and Prl secretion by the anterior pituitary.

Animals↗

The hypothalamic-pituitary-thyroid axis in type 1 diabetes: influence of diabetic metabolic control.

The influence of diabetic metabolic control on indices of thyroid function was studied in 9 euthyroid, insulin-dependent (Type 1) diabetics. During chronic poor metabolic control (mean fasting blood glucose 13 mmol/l and HbA1 concentrations 14.7%) serum T3 concentrations were low (P less than 0.01) while serum T4 and basal TSH concentrations were normal. After 6-8 weeks of improved metabolic control, mean HbA1 concentrations had fallen to 10.7% (P less than 0.01) and serum T3 concentrations had increased into the normal range. Serum T4 and basal TSH concentrations were unchanged. The serum TSH response to iv TRH remained normal throughout the study. In Type 1 diabetics, with chronic poor metabolic control, the serum T4 concentration and the TSH response to TRH are therefore appropriate indicators of thyroid function.

Adult↗

Desensitization of rat anterior pituitary gland to thyrotrophin releasing hormone.

We have studied the secretion of TSH and prolactin from perifused rat anterior pituitary glands in vitro in response to single pulses of thyrotrophin releasing hormone (TRH) and KCl after prior exposure to TRH. Anterior pituitary fragments were incubated in normal medium or in medium containing 28 nmol TRH/1 for 20 h before perifusion. Thyrotrophin releasing hormone (28 nmol/l), administered as a 3-min pulse, stimulated TSH and prolactin release from control tissue to a peak value four or five times that of basal. After exposure of the pituitary tissue to TRH for 20 h, the subsequent response of TSH to a 3-min pulse of TRH was, however, markedly reduced; in contrast, the prolactin response was not significantly reduced. In a similar series of experiments KCl (60 mmol/l) was administered to both control and TRH-'treated' pituitary tissue as a 3-min pulse; no significant differences in TSH responses or prolactin responses were observed. These data indicate that TRH desensitizes the pituitary thyrotroph to a subsequent TRH stimulus but has very little effect on prolactin secretion.

Animals↗

Control of thyroglobulin secretion from the rat thyroid gland.

Serum thyroglobulin (Tg), measured by radioimmunoassay, was high in 6-propylthiouracil (PTU)-treated rats but low in thyroxine (T4)-treated animals compared with euthyroid controls. Thyroid-stimulating hormone (TSH) stimulated Tg release in vitro from enzymatically dispersed normal rat thyroid cells in a dose-dependent manner. Thyroid cells prepared from T4-treated animals behaved similarly to cells from control rats, whereas in vitro basal release of Tg from thyroid cells prepared from PTU-treated animals was high and the response to TSH was lost. Our data confirm the TSH dependency of Tg release in vivo and in vitro and our system provides a means of studying the control of Tg secretion in vitro.

Animals↗

Stimulation of prolactin secretion by oestradiol in the rat is associated with increased hypothalamic release of thyrotrophin-releasing hormone.

We have studied the effect of oestradiol (OE2) on secretion of prolactin and TSH by rat pituitary glands and correlated this with changes in hypothalamic content and release of thyrotrophin-releasing hormone (TRH). Ovariectomized Wistar rats received s.c. silicone elastomer implants of OE2 at a dose known to give pro-oestrous OE2 levels. After 1 week rats were decapitated, blood was collected for assay of prolactin and TSH, blocks of hypothalamus were dissected out and pituitary glands were removed and bisected. Medium bathing hemipituitary glands was collected for measurement of prolactin and TSH after a 30-min incubation. Immunoreactive TRH was measured in medium removed from hypothalami and in extracts of homogenized hypothalami. Serum prolactin was higher in OE2-treated than in control animals (59.3 +/- 19.5 (S.E.M.) vs 9.4 +/- 1.5 micrograms/l; P less than 0.05) and this was associated with a threefold increase in pituitary prolactin in the medium. By contrast, TSH concentrations in serum and pituitary incubation medium were not significantly different in the two groups. There was no difference between the groups in hypothalamic content of TRH but TRH release in the incubation medium was increased by OE2 (30.2 +/- 6.5 vs 10.0 +/- 1.3 pg/mg protein per 30 min; P less than 0.01). In summary, physiological levels of OE2 stimulated prolactin secretion without change in TSH and this was associated with a threefold increase in hypothalamic release of TRH. These findings suggest that the stimulating effect of OE2 on prolactin secretion may, in part, be mediated by hypothalamic TRH.

Animals↗

Neurotensin regulation of TSH secretion in the rat.

Tri-iodothyronine stimulates neurotensin secretion from rat hypothalami in vitro. Propylthiouracil treatment of rats is associated with a decrease in anterior pituitary neurotensin content, an increase in hypothalamic content and an impaired release of peptide from hypothalami in vitro. In addition neurotensin has a direct inhibitory effect on TRH-stimulated TSH release from anterior pituitary in vitro. These observations suggest a physiological role for neurotensin in the control of TSH secretion in the rat.

Animals↗

Serum free thyroxine concentrations in normal euthyroid subjects and ones with high serum thyroxine binding globulin concentration.

Serum free thyroxine (fT4) was assayed by a commercial fT4 method in 30 normal euthyroid subjects, 19 pregnant females, 13 euthyroid subjects with high thyroxine binding globulin (TBG) and three with low or undetectable serum TBG concentration. In a number of these fT4 was also calculated on the basis of the application of the law of mass action to the binding situation. In states in which TBG was altered for congenital reasons both the experimentally determined and calculated fT4 were not significantly different from their respective means in the normal euthyroid population. Pregnant females had both lower experimental and theoretical free T4 concentrations. It is inferred from these data that TBG concentration per se is without effect on serum fT4 concentration.

Blood Proteins↗

The effect of diet on intermediary metabolite concentrations in Type 2 (non-insulin-dependent) diabetes mellitus.

The metabolic response to a standard meal was studied in six Type 2 (non-insulin-dependent) diabetic patients at diagnosis and following 4-6 weeks of dietary treatment. The fall in blood glucose concentration following treatment was accompanied by significant reductions in circulating concentrations of lactate, pyruvate, alanine and glycerol. Blood 3-hydroxybutyrate concentrations also fell with treatment.

3-Hydroxybutyric Acid↗

Thyroid hormones in non-insulin-dependent diabetes before and after dietary treatment.

In a group of 8 moderately obese non-insulin-dependent diabetics, both serum total T3 and T4 concentrations and serum free T3 and T4 concentrations were significantly lower than control values. Serum TBG levels did not differ. Five patients demonstrated an apparently successful response to dietary treatment with loss of symptoms and glycosuria and fall in post-prandial blood glucose and HbA1. Serum concentrations of thyroid hormones and TBG, however, were not significantly altered. These abnormalities may be unrelated to hyperglycaemia and may reflect the nutritional status of the patients.

Adult↗

Recurrent insulinoma syndrome with metastatic glucagonoma.

A case is reported of a patient who presented with symptomatic hypoglycaemia and who had three pancreatic tumours resected over the ensuing eight years. Immunocytochemistry demonstrated two of these to be insulinomas and the third to be a glucagonoma. In addition metastatic spread of cells positive for glucagon had occurred to a lymph node and multiple nodules staining positively for glucagon were present in the remainder of the pancreas.

Adenoma, Islet Cell↗

The effect of thyroid hormones in vitro and in vivo on hypothalamic neurotensin release and content.

Neurotensin (NT) is a hypothalamic peptide which inhibits TSH secretion when administered intraventricularly to the rat. We have studied the effects of TRH, TSH, T3, and rT3 on the release of immunoreactive NT (iNT) from incubations of freshly dissected sections of whole hypothalamic tissue removed from male rats. The effects of T4 or propylthiouracil administration in vivo on hypothalamic iNT content and release was examined as well. T3 (10(-7) M) stimulated iNT release in vitro [45.3 +/- (SE) 1.8 vs. 32.0 +/- 1.9 pg/hypothalamus 30 min-1, P less than 0.005] and a dose-dependent response was observed from 10(-9) M to 10(-7) M; rT3, TRH, and TSH were without effect. T4 administration in vivo caused a reduction in hypothalamic iNT content (5.77 +/- 0.24 vs. 6.57 +/- 0.37 ng/mg protein, P less than 0.05) whereas the induction of hypothyroidism with propylthiouracil and 131I resulted in an increase in iNT content (8.25 +/- 0.27 ng/mg protein, P less than 0.001). Basal release of hypothalamic iNT was similar in all three groups but 58 mM KCl-induced release from hypothyroid hypothalami was impaired. These results indicate a positive influence of T3 on hypothalamic iNT release and have led us to the hypothesis that T3 exerts a negative feedback effect on its own secretion via inhibition of TSH release by NT.

Animals↗

Neurotensin release from rat hypothalamus in vitro.

Neurotensin is a hypothalamic peptide which inhibits secretion of TSH in the rat in vivo. We have demonstrated a calcium-dependent release of neurotensin from incubated rat hypothalamus in response to depolarizing stimuli, as well as a dose-dependent stimulatory effect of tri-iodothyronine (T3) on neurotensin secretion. We suggest that part of the neuroendocrine control of TSH secretion involves the interaction of T3, neurotensin and TSH; the presence of neurotensin in extracts of anterior pituitary gland is further evidence for its hypophysiotrophic role.

Animals↗

Therapeutic progress--review VII. The medical treatment of Paget's disease.

The presentation of Paget's disease varies from a painful or deforming skeletal affliction to an asymptomatic disorder diagnosed on routine biochemical or radiological assessment. When involvement of the peripheral skeleton by Paget's disease is extensive, the clinical diagnosis is usually clear. Affected bones are thickened and deformed and the overlying skin is warm. Bone pain is sometimes severe and malignant change rarely occurs. The new bone formed is structurally abnormal and is consequently liable to deformity and fractures. Serum alkaline phosphatase concentrations and urinary hydroxyproline excretion are raised. Characteristic X-ray changes are seen. Paget's disease should be treated when it causes skeletal pain and tenderness, or when there are neurological symptoms, fractures, marked deformities, or other complications. New therapeutic agents offer both symptomatic relief and some control of the basic disease process. Simple analgesics should be tried before proceeding to the anti-osteoclastic agents, calcitonin, diphosphonates and mithramycin. All are effective in relieving bone pain and improving biochemical indices. The major advantage of the diphosphonates lies in their oral usage and thus, the number of patients who nowadays require calcitonin is small. The majority of patients should be commenced on a course of diphosphonate therapy (EHDP in most instances), but if clinical response is unsatisfactory calcitonin should be tried. Mithramycin should be reserved for special indications e.g. an elderly patient with severe disabling pain.

Calcitonin↗

Free triiodothyronine and free thyroxin in sera of pregnant women and subjects with congenitally increased or decreased thyroxin-binding globulin.

Concentrations of free thyroxin (T4) and free triiodothyronine (T3) were measured in sera from pregnant women, in subjects with congenitally increased or decreased thyroxin-binding globulin (TBG), and in euthyroid controls. Measured free hormone concentrations were compared with calculated values for free hormone derived from concentrations of total T4, total T3, and binding proteins. Measured and calculated concentrations of free T4 and free T3 were below normal in the pregnant subjects but were normal in subjects with congenital increases of TBG. The low concentrations of free hormone in pregnancy are at variance with the euthyroid status of these subjects. Measured free T4 was normal, but concentrations of free T3 were less in the euthyroid congenitally low-TBG group.

Adolescent↗

Characterization of immunoreactive somatostatin released from rat nervous system in vitro.

There is considerable evidence that somatostatin is released from nerve terminals throughout the central nervous system in response to presynaptic stimulation, thus suggesting a neuromodulator role for the peptide. We here report the partial characterization of immunoreactive somatostatin released from rat nervous system in vitro (hypothalamus, spinal cord and hypothalamic, cortical, thalamic and striatal synaptosomes). Serial dilutions of released somatostatin immunoreactivity showed parallelism with dilutions of synthetic somatostatin standard. Somatostatin immunoreactivity released from all tissue areas coeluted with synthetic tetradecapeptide on Sephadex G-25 (fine grade) gel chromatography; more than 85% of this immunoreactivity bound to Sepharose-anti-somatostatin-serum immunoaffinity columns. In addition, immunoreactive material released from hypothalamus, spinal cord and hypothalamic and cortical synaptosomes inhibited somatotropin (growth hormone, 'STH', 'GH') release from perifused anterior pituitary in a dose-related manner, indicating biological similarity to synthetic somatostatin.

Animals↗

A radioimmunoassay for neurotensin.

A specific radioimmunoassay for neurotensin has been developed with a sensitivity of 40 pg/ml. Neurotensin-like immunoreactivity in human plasma shows characteristics similar to synthetic neurotensin on Sephadex G-25 (f) gel chromatography.

Animals↗