Limitations of a sensitive assay for thyrotropin in managing patients with thyroid disease.
Explore the source record for details and available documents.
Humans↗
Biomedical subjects
M C Sheppard
Publications and source records attributed to M C Sheppard.
Aspiration cytology of the thyroid.
Explore the source record for details and available documents.
Biopsy, Needle↗
A comparison of the effects of bromocriptine and somatostatin on growth hormone gene expression in the rat anterior pituitary gland in vitro.
The effects of the dopamine agonist bromocriptine (BCR) have been compared with those of somatostatin (SS) on growth hormone (GH) synthesis and secretion by rat anterior pituitary cells in vitro. Both BCR and SS produced a dose-related reduction in GH release. Cytoplasmic GH mRNA levels were unchanged by BCR treatment and this finding was associated with an increase in total intracellular GH content. The reduction in GH release seen following SS treatment was accompanied by a fall in cytoplasmic GH mRNA levels and no significant change in intracellular GH content. These results suggest that the effects of BCR are predominantly on GH release mechanisms, whereas SS appears not only to regulate hormone release but also to regulate GH gene expression at a pre-translational level.
Animals↗
Mechanisms of TSH release: studies with forskolin, phorbol ester and A23187.
We have investigated the interactions of intracellular messenger systems which may regulate thyrotrophin (TSH) release in primary cultures of rat anterior pituitary cells. Calcium ionophore A23187 was used to raise intracellular free calcium, the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) to activate protein kinase C, and forskolin to activate adenylate cyclase. Each of these agents stimulated TSH secretion in a dose-dependent manner, but the effect of forskolin was delayed for at least 6 h. The combined effects of A23187 and TPA on TSH secretion were simply additive, but forskolin synergistically enhanced the effect of A23187 and 55 mM potassium, but not that of TPA. Co-incubation of cells with 1 microM A23187 caused parallel upward shift of the TPA dose-response curve, and the further addition of 10 microM forskolin led to further upward shift. These results suggest that calcium mobilization and adenylate cyclase activation may interact synergistically to modulate TSH secretion. Raised cellular cyclic AMP content may amplify further the TSH release stimulated by the combination of protein kinase C activation and raised intracellular free calcium.
Adenylyl Cyclases↗
Serial serum thyroglobulin measurements in the management of differentiated thyroid carcinoma.
Serum thyroglobulin (Tg) was measured on repeated occasions in 416 patients with differentiated thyroid cancer for up to 7 years after initial therapy. All patients had thyroidectomy and/or ablative 131I therapy and all measurements were done while patients were receiving T4 replacement. Tg was measured using a double-antibody radioimmunoassay. Overall correlation between serum Tg concentration and presence or absence of cancer was 95.9%. At the time of initial measurement 295 patients had serum Tg less than 5 micrograms/l, and in latest analysis only 1.7% of these patients showed evidence of disease. Initially there were 19 patients of a total of 121 with serum Tg greater than 5 micrograms/l in whom no cancer was apparent. In eight of these 19 subjects recurrent or metastatic disease has been diagnosed up to 3.5 years after the first measurement indicating that in these cases serum Tg values were 'predictive'. Serum Tg appears to be a sensitive and specific means of detecting residual, recurrent or metastatic thyroid cancer and in most situations can replace routine, expensive and inconvenient radioactive thyroid scans; these should be performed when serum Tg values are elevated or when there is clinical evidence suggesting recurrence.
Biomarkers, Tumor↗
Amiodarone and thyroid hormone effects on anterior pituitary hormone gene expression.
Amiodarone therapy results in marked changes in circulating thyroid hormone and TSH concentrations in man. In the present study we have demonstrated that amiodarone treatment of the rat increases serum TSH and pituitary cytoplasmic concentrations of TSH beta and alpha subunit messenger RNAs (mRNAs) and reduces PRL mRNA as measured by cytoplasmic dot hybridization with specific complementary (c) DNA probes. The fall in circulating TSH and TSH mRNA resulting from thyroid hormone treatment was less marked in animals receiving amiodarone in addition to T3 and T4. In contrast, in the hypothyroid state, increases in serum TSH, TSH beta and alpha mRNA, and reductions in PRL and GH mRNA were less marked in rats treated with amiodarone. In studies of rat anterior pituitary cells in primary monolayer culture we demonstrated a direct effect of amiodarone on PRL gene expression which was antagonized by T3. Changes in circulating thyroid hormone concentrations and deiodination of T4 and T3 induced by amiodarone in vivo may be important in the regulation of pituitary hormone gene expression but we have, in addition, shown a direct interaction between amiodarone and T3 effects on the anterior pituitary cell.
Amiodarone↗
Evaluation of a sensitive chemiluminescent assay for TSH in the follow-up of treated thyrotoxicosis.
We have studied 21 patients treated for thyrotoxicosis to evaluate a highly sensitive chemiluminescent thyrotrophin (TSH) assay in the assessment of changing thyroid status. Serum TSH was generally suppressed with high serum thyroid hormone concentrations and invariably rose when free T4 and T3 fell substantially below the normal range. However TSH values in 14 of the 21 patients remained undetectable or subnormal for variable periods despite normal or even slightly subnormal free T4 and T3 values. The level of free T4 and T3 at which TSH concentrations rose was highly variable, suggesting differing degrees of hypothalamo-pituitary suppression. Sensitive TSH assays are likely to provide useful information regarding physiological regulation of TSH secretion in man, but our data indicate that in certain circumstances these assays used alone will be inadequate for biochemical assessment of thyroid status.
Adult↗
Effect of hypothyroidism and thyroid hormone replacement in vivo on pituitary cytoplasmic concentrations of thyrotropin-beta and alpha-subunit messenger ribonucleic acids.
We have studied the influence of hypothyroidism and thyroid hormone replacement in vivo on rat pituitary cytoplasmic concentrations of TSH beta and alpha-subunit mRNA, measured by cytoplasmic dot hybridization, as well as circulating TSH and pituitary TSH content. Cytoplasmic concentrations of GH, PRL, and LH beta-subunit mRNA were measured in parallel. Marked increases in serum TSH and TSH beta and alpha mRNA were found in hypothyroidism; these changes reversed 72 h after beginning T3 replacement. A more marked effect of hypothyroidism on TSH beta mRNA than on alpha mRNA was evident, suggesting differential control of regulation of the TSH genes. In contrast to a rapid fall in serum TSH after T3 administration, an increase in TSH beta and alpha mRNA was evident at 1 and 6 h, followed by a later fall in TSH mRNA to euthyroid values. Pituitary cytoplasmic concentrations of GH and PRL mRNA were reduced in hypothyroidism and increased after administration of T3; LH beta mRNA was unaffected by hypothyroidism or T3 replacement. The differential effects of thyroid status on TSH, GH, PRL, and LH mRNA indicate specificity of regulation of these anterior pituitary hormone genes.
Animals↗
The effect of thyroid hormones on growth hormone gene expression in vivo in rats.
Thyroid hormones are important regulators of GH synthesis and secretion. In this study we have made a detailed examination of the time-course of the effects of hypothyroidism and tri-iodothyronine (T3) replacement in the intact rat on GH gene expression in the anterior pituitary gland. Changes in pituitary cytoplasmic GH messenger (m)RNA levels were compared with total pituitary GH content and serum GH concentration during the development of hypothyroidism and following short-term T3 replacement in vivo. Hypothyroidism was associated with a fall in pituitary GH mRNA levels. Treatment of hypothyroid animals with T3 rapidly stimulated GH mRNA levels to values above those seen in euthyroid controls. The reduction in GH mRNA levels seen during the development of hypothyroidism was accompanied by a fall in serum GH and pituitary GH content, both of which were partially restored by T3 replacement. Thus thyroid hormone replacement in hypothyroidism rapidly stimulates GH mRNA synthesis, which is followed by the gradual restoration of pituitary GH stores and serum GH concentration.
Animals↗
Modulation by oestrogen of thyroid hormone effects on thyrotrophin gene expression.
The role of oestrogen in the regulation of TSH gene expression is unclear. We have examined the effect of administration of oestrogen in the rat on serum TSH, pituitary TSH content and pituitary cytoplasmic concentrations of mRNA encoding the TSH beta and alpha subunits, thus deriving measures of hormone release and synthesis. In addition, we have examined the effect of oestrogen on the binding of tri-iodothyronine (T3) to nuclear receptors in the anterior pituitary. Administration of oestrogen did not affect serum concentrations of TSH in euthyroid or untreated hypothyroid rats, but did augment the effects of T3 (1 and 2 micrograms) on serum TSH in hypothyroid animals 6 h after injection of T3. No influence of oestrogen or of thyroid status on pituitary content of TSH was seen. A marked increase in the concentrations of TSH beta and alpha mRNA in pituitary cytoplasm was found in hypothyroidism, compared with those in the euthyroid state. No effect of oestrogen on TSH mRNA was seen in euthyroid animals but concentrations of TSH beta and alpha mRNA were lower in hypothyroid animals than in vehicle-treated controls. A stimulatory influence of T3 on TSH mRNA was seen 6 h after injection of T3; this stimulation was absent in oestrogen-treated rats. No effect of oestrogen on the action of T3 was evident 72 h after beginning treatment with T3. In addition to effects on serum TSH and TSH mRNA, an increase in the number of pituitary nuclear receptors for T3 was seen after oestrogen treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Thyroid status affects the regulation of prolactin mRNA accumulation by tri-iodothyronine and thyrotrophin-releasing hormone in cultured rat anterior pituitary cells.
The effects of tri-iodothyronine (T3) and TRH on prolactin mRNA accumulation in monolayer pituitary cell cultures prepared from both euthyroid and hypothyroid rats were investigated. Basal prolactin mRNA concentrations and prolactin release into culture medium were increased in hypothyroid cultures, the increase being related to the duration of hypothyroidism in vivo. The inhibitory effects of T3 seen in euthyroid cells were preserved in cells derived from hypothyroid animals, and the degree of inhibition was greater in cells from the most severely hypothyroid rats. However, the stimulation of prolactin synthesis and secretion induced by TRH in euthyroid cultures was not found in the hypothyroid cells. Hypothalamic and anterior pituitary TRH content were measured in similarly hypothyroid and euthyroid rats. A large hypothalamic pool of TRH was found, which was unchanged in hypothyroidism, whereas anterior pituitary TRH content was increased in the hypothyroid rats. The consequent down-regulation of anterior pituitary TRH receptors may explain the poor response of prolactin to TRH seen in vitro.
Animals↗
Elevation of free thyroxine measurements in patients without thyrotoxicosis.
The recent development of single step analogue assay techniques to measure free thyroxine in serum has meant that this estimation has become widely used as a first line test of thyroid function. However these assays are subject to in-vitro interference in two ways: where there is a variant serum albumin in familial dysalbuminaemic hyperthyroxinaemia, or where there are circulating thyroid hormone binding antibodies. In both these situations a spuriously high result for free thyroxine is obtained. This may have serious implications for patient management and we describe 10 patients in whom the finding of a misleadingly high free thyroxine concentration led to confusion in diagnosis and, in eight of the 10, to inappropriate antithyroid treatment. Clinicians should be aware of these technical problems and where a result for the free thyroxine concentration seems inappropriate to the patient's clinical state then measurement of thyrotrophin (TSH) by a sensitive immunometric method should be performed. If the results remain confusing the presence of a variant serum albumin or thyroid hormone binding antibodies should be sought.
Adult↗
Fine needle aspiration cytology in the management of euthyroid goitre.
The role of fine needle aspiration cytology was examined in a series of 115 euthyroid patients referred with thyroid enlargement presenting consecutively to a joint medical and surgical thyroid clinic from April 1985 to December 1986. Needle aspiration was performed at first clinic attendance and repeated two to six months later in 39 subjects. Patients were classified according to cytological features of the thyroid aspirate. A diagnosis of benign colloid goitre was made in 59 patients, lymphocytic thyroiditis in 11, thyroid cyst in 32 and in addition there were 13 reports of suspicious or malignant cytological features. Malignancy was confirmed histologically in six patients in this group and five more had follicular adenomata. There were two false positive reports of 'suspicious' cytological features. During a median period of observation of 11.4 months one false negative cytological diagnosis has emerged in a further patient with follicular adenoma. Accuracy in the diagnosis of thyroid neoplasia of 97 per cent has thus been achieved. Fine needle aspiration cytology has replaced isotope and ultrasound scanning in our practice. The number of 99mTc scans performed in the investigation of goitre fell from 77 in 1984 to three in 1986. Neoplastic tissue was removed at operation in 40 per cent of cases proceeding to surgery (20 subjects), compared with a predicted rate of 9.6 per cent if all solitary nodules had been removed. Aspiration cytology performed at first clinic attendance has led to improved selection of patients for surgery and hence economy in their management.
Adolescent↗
Hormonal regulation of thyrotrophin synthesis and secretion.
We have examined the effects of triiodothyronine treatment on serum TSH and pituitary cytoplasmic TSH alpha and beta mRNA levels in the hypothyroid rat. Serum TSH and the cytoplasmic levels of the TSH alpha and beta subunit mRNAs rose concomitantly in hypothyroidism. Treatment of hypothyroid animals with triiodothyronine resulted in a fall in serum TSH but an initial increase in subunit mRNAs, followed by a reduction to euthyroid levels. We have also studied the modulation of these responses by oestrogen and testosterone administration. Treatment with oestradiol during the development of hypothyroidism gave rise to lower levels in alpha and beta subunit mRNAs compared with hypothyroid animals not receiving the oestrogen. Oestrogen also abolished the early rise in subunit mRNA levels seen following triiodothyronine replacement. Testosterone administration during the development of hypothyroidism had a similar effect to that of oestrogen in that subunit mRNA levels were lower in the androgen-treated hypothyroid animals than in hypothyroid animals receiving no exogenous androgen. These data suggest that gonadal steroids render the pituitary thyrotroph cell more sensitive to thyroid hormone.
Animals↗
Clinical application of a sensitive non-isotopic immunometric assay of thyrotropin.
We have evaluated an immunometric assay of thyrotropin (TSH) based on enhanced chemiluminescence signal; its detection limit is 0.06 milli-int. unit/L. Values in 101 clinically euthyroid subjects with normal thyroid hormone concentrations ranged from 0.39 to 6.83 milli-int. units/L. TSH in 15 hypothyroid patients ranged from 10.3 to greater than 200 milli-int. units/L, whereas in 31 hyperthyroid subjects with increased concentrations of free thyroxin and free triiodothyronine, TSH was undetectable serum of all but one subject. Of 32 clinically and biochemically euthyroid patients with goiter, two had undetectable serum TSH and six had values below the normal range. In 19 clinically euthyroid patients from an intensive-care unit, TSH was undetectable in two and below the normal range in another two. This immunometric chemiluminescence assay distinguishes thyrotoxic from euthyroid subjects, but caution is required in interpreting TSH values alone in subjects with goiter or nonthyroidal illness.
Adolescent↗
The use of a multiwire camera for the detection of 3H labelled cDNA/mRNA hybrids.
We have investigated the use of a multiwire camera for the rapid direct quantitation of 3H labelled cDNA/mRNA hybrids. Growth hormone (GH) complementary DNA (cDNA) probes were labelled with either 3H or 32P and used in dot-blot hybridization assays of pituitary cytoplasmic samples. The results were assessed either by counting in the multiwire camera (3H) or by autoradiography and scanning densitometry (32P). Results obtained by both methods were comparable over a similar range of pituitary cytoplasmic dilutions. The use of a multiwire camera may have several advantages over conventional methods for the detection of radioisotopically labelled cDNA/mRNA hybrids and has great potential for use in this field of endocrine research.
Animals↗
Glycosylation of human thyroglobulin and characterization by lectin affinity electrophoresis.
Thyroglobulin, a 660 kDa glycoprotein, is the major product of protein synthesis in the thyroid gland. It has been suggested that modifications of thyroglobulin glycosylation occur in various thyroid disorders. In order to study possible changes in glycosylation of tissue thyroglobulin associated with thyroid disease, we have developed a lectin affinity electrophoresis system which allows characterization of small (less than 1 microgram) quantities of thyroglobulin. Human thyroglobulin was extracted and purified. Agarose gels were cast containing concanavalin A, Ricinus communis agglutinin, L-phytohaemagglutinin and pokeweed mitogen at various concentrations. Purified human thyroglobulin was serially diluted, loaded onto lectin gels and electrophoresed. Concanavalin A, R. communis agglutinin and phytohaemagglutinin all bound thyroglobulin in a concentration-dependent manner. Pokeweed mitogen did not bind thyroglobulin. Purified thyroglobulin was treated with neuraminidase and endoglycosidase H. Two-dimensional immunoelectrophoresis revealed the migration of thyroglobulin to be modified by neuraminidase but not by endoglycosidase H. Lectin affinity electrophoresis of purified human thyroglobulin with and without enzyme treatment indicated the presence of: oligomannose structures as shown by concanavalin A reactivity and modification by endoglycosidase H, and complex oligosaccharides as shown by affinity for R. communis agglutinin and modification by neuraminidase. These structures are in keeping with the proposed patterns of glycosylation of human thyroglobulin and indicate suitability of the method for characterizing the glycosylation of small quantities of thyroglobulin.
Acetylglucosaminidase↗
Does growth hormone releasing factor desensitize the somatotroph? Interpretation of responses of growth hormone during and after 10-hour infusion of GRF 1-29 amide in man.
It is unclear whether growth hormone releasing factor (GRF) administration in vivo may desensitize the somatotroph. To investigate this possibility we have examined the effects of 10-h infusion of the equipotent 1-29 amide analogue of hpGRF on serum GH levels and on the subsequent GH response to a bolus dose of GRF (1-29). Four normal adult males received an intravenous infusion of 1-29 GRF (1 microgram/kg/h) from 0800 to 1800 h, with blood samples taken at 10 min intervals. A 100 micrograms intravenous bolus dose of GRF was given at 1800 h, and sampling continued for a further 90 min. GH levels were near or below the limit of detection (0.5 mU/l) throughout the control 10 h period. During GRF infusion there was increased GH release with pulses of irregular frequency and amplitude (up to 80 mU/l) continuing throughout the entire infusion period. There was no apparent reduction in total GH released towards the latter part of the infusion. On the control day, 100 micrograms GRF bolus increased mean (+/- SEM) GH from 0.82 +/- 0.21 mU/l to a peak of 59.0 +/- 44.8 mU/l (P less than 0.002). Following 10-GRF infusion, responses to bolus injection of GRF were reduced, but variable. In two subjects a small rise in GH levels occurred (basal 6.4 and 7.2 rising to peak values of 11.2 and 23.0 mU/l respectively). In the other two subjects, GH levels fell but in these the GRF bolus had coincided with a GH peak. The loss of GRF responsiveness after GRF infusion may be due to 'desensitization'.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗