Immunoreactive Thyrotropin Research Articles

Immunoreactive thyroid stimulating hormone (TSH): Association with synaptosomally-rich fractions in the rat hypothalamus

The subcellular compartmentalization of brain thyroid stimulating hormone (TSH) in the hypothalamus of the rat was investigated using differential and discontinuous sucrose density gradient centrifugation. When the mitochondrial fraction (P 2) was layered on a discontinuous sucrose density gradient (0.32–1.4 M) and centrifuged for 60 min at 72,000 g, TSH recovered from the gradient was found, by double antibody radioimmunoassay, to be associated preferentially with the synaptosomally-rich layers. The separation was monitored by electron microscopic examination of all fractions obtained throughout the procedure. The addition of a large excess of either [ 125I]-labeled or unlabeled pituitary TSH at the time of homogenization did not influence the amount of immunoreactive TSH associated with the synaptosome-rich fractions, and both the unlabeled and labeled hormone were recoverable in the final supernatant indicating that the simple addition of peptide to hypothalamic homogenates did not result in any preferential association to any particular subcellular fraction. The apparent association of this brain-based pituitary peptide was not, therefore, an artifact of the homogenization process. It is concluded that an association exists between immunoassayable TSH and brain-based synaptosomes in homogenates of the rodent hypothalamus.

Reversed-phase high-performance liquid chromatography of human thyroid-stimulating hormone

Human pituitary thyroid-stimulating hormone (TSH) has been analysed by reversed-phase high-performance liquid chromatography on Aquapore RP-300, a 300-Å pore-size short-alkyl-chain silica packing, in sodium chloride-containing buffers. At pH 2.0, two clearly resolved peaks were observed corresponding in retention time to α and β subunit of TSH. With increasing pH, the resolution between these peaks was lost. At pH 7.0 a single major peak was observed, co-eluting with immunoreactive TSH, which could be resolved from β-subunit. In vivo TSH bioactivity was recovered at pH 7.0 in 58% yield. High-performance liquid chromatography of a sample of hypothyroid serum yielded a major peak of TSH immunoreactivity corresponding in retention time to that observed for purified TSH.

Release of immunoreactive thyroid stimulating hormone from the rat hypothalamus in vitro.

Thyroid stimulating hormone (TSH) has been identified in the hypothalamus and other brain areas of the rat. However, the alteration of the release of brain TSH has not been demonstrated. Therefore, we examined the release of immunoreactive TSH (IR-TSH) in vitro from hypothalamic tissue obtained from hypophysectomized, thyroidectomized and intact control rats. Whereas TRH (10(-5) M) and PGE2 (10(-4) M) did not alter hypothalamic IR-TSH release, depolarizing concentrations of potassium (60 mM) or veratridine (5 mM) stimulated the release of IR-TSH from hypothalamic tissue from all groups. These data suggest that IR-TSH synthesized in the hypothalamus is stored in a releasable form.

Variant forms of immunoreactive thyrotropin in aged rats

Immunoreactive thyrotropin, extracted by affinity chromatography from the serum of Fischer 344 male rats and fractionated by gel filtration, is more polymorphic (in terms of molecular weight) in 22- and 30-month-old rats than in younger animals (3- and 12-month-old). Changes in hormonal levels with age involve thyrotropin and thyroxine but not triiodothyronine, serum thyrotropin being significantly decreased at 30 months and thyroxine at 22 and 30 months. Low serum thyroxine levels and increased thyrotropin polymorphism may suggest an impaired pituitary-thyroid axis in aged rats.

Endocrinology and metabolism: an annotated bibliography of recent literature. References to journal articles and other papers.

Endocrinology and metabolism: an annotated bibliography of recent literature. References to journal articles and other papers.

Characterization of immunoreactive thyrotropin releasing hormone in human fetal cerebellum.

High concentrations (411 +/- 30 pg/mg protein; mean +/- S.E., n = 12) of immunoreactive TRH (TRHi) were detected in extracts of human fetal cerebellum (13-26 weeks gestation). The TRHi in the cerebellar extracts, when subjected to gel filtration and high performance liquid chromatography (HPLC), co-migrated with synthetic TRH. In each instance, no TRHi was detected which did not share identical chromatographic mobilities with synthetic TRH. Like synthetic TRH, the TRHi in extracts of fetal cerebellum and hypothalamus was insoluble in diethyl ether and was efficiently degraded when incubated at 37 degrees C with adult rat serum. No significant degradation of TRHi occurred when the incubation was conducted at 0 degrees C or when the extracts were incubated with rat serum that had been preheated at 60 degrees C for 20 min. Neither synthetic TRH nor TRHi in extracts of fetal cerebellum of hypothalamus was degraded when incubated with human umbilical cord serum at 37 degrees C or 0 degrees C. The results of this study are supportive of the view that the TRHi in extracts of human fetal cerebellum is identical to TRH.

Thyrotropin secretion in patients with central hypothyroidism: evidence for reduced biological activity of immunoreactive thyrotropin.

TSH concentration was measured in plasma before and after TRH administration (200 micrograms, iv) in 89 patients with documented hypothyroidism consequent to various hypothalamic-pituitary disorders. Basal plasma TSH was less than 1.0 microI/ml in 34.8%, between 1.0-3.6 microU/ml in 40.5% and slightly elevated (3.7-9.7 microU/ml) in 24.7% of the cases. The plasma TSH response to TRH was absent in 13.5%, impaired in 16.8%, normal in 47.2%, and exaggerated in 22.5% of the cases, with delayed and/or prolonged pattern of response in 65% of the cases. The dilution curves of several plasmas drawn before and after TRH were parallel to those obtained with TSH standard preparation. After gel filtration, the elution pattern of TRH-stimulated plasmas from 4 patients did not show any major difference from that of pooled plasmas from normal subjects given TRH or from that of patients with primary hypothyroidism. Plasma TSH values determined by cytochemical bioassay on both basal and TRH-stimulated samples of 5 patients were markedly lower than those obtained by RIA. The serum T3 response to TRH was absent or low in 40 out of 53 patients in whom it was evaluated. The administration of T3 (100 micrograms/day for 3 days) or dexamethasone (3 mg/day for 5 days) respectively suppressed or reduced both basal and TRH-induced plasma TSH levels. Two patients became hypothyroid shortly after pituitary surgery in spite of basal and TRH-induced plasma TSH levels similar to or higher than those before surgery. Though thyroid atrophy due to chronic understimulation could explain the low T3 response to TRH in secondary hypothyroidism, it is difficult to reconcile thyroid understimulation with normal or increased plasma TSH unless the immunoreactive material has low biological activity. Present data suggest that several patients with hypothyroidism consequent to hypothalamic-pituitary diseases secrete a material which is immunologically similar to pituitary standard TSH and responds to stimulatory and suppressive agents in a manner similar to normal TSH but has low or absent biological activity. Thus, hypothyroidism due to insufficient TSH stimulation can be termed central hypothyroidism and can be due 1) to pituitary insufficiency (secondary hypothyroidism), 2) to a hypothalamic defect (tertiary hypothyroidism), or 3) to the secretion of biologically inactive TSH.

Gel filtration profile of immunoreactive thyrotropin and subunits of human pituitaries.

Pituitary extracts from five patients with atrophic asymptomatic thyroiditis and from five subjects without any endocrine disease, matched for sex and age, were passed through gel filtration columns and the collected fractions were analyzed in three different radioimmunoassays (hTSH-anti-hTSH; hTSHbeta-anti-pTSH; hLHAlpha-anti-LHalpha). In the alpha subunit system, every profile showed a first peak corresponding to the elution position of the intact hTSH molecule and second peak, often more important, of free alpha chain. In the beta subunit system, a high molecular weight immunoreactive protein (big hTSHBeta) was found in seven pituitary extracts; cross-reacting intact hTSH molecule was eluted as a second peak and free Beta chain was detected in all the extracts. Free alpha chain was generally found in greater amount than free Beta. In the hTSH system, every elution pattern showed a peak of intact hTSH and another in the subunit area. In six pituitary extracts (5 thyroiditis, 1 control), a high mol wt protein was eluted (big hTSH). Its predominant presence in thyroiditis extracts seems important in view of the already described immunological heterogeneity of pituitary hTSH.

Metabolism of thyrotropin releasing factor in two clonal cell lines of nervous system origin

Immunoreactive thyrotropin releasing factor (TRF) was detected in homogenates of two clonal cell lines, BN1010-1 and BN1010-3, derived from a rat central nervous system tumor. TRF was present in logarithmically-growing cells; daily medium changes with slightly acid culture medium (pH 6.8) greatly increased the TRF content of these cells. In contrast, TRF could not be detected in stationary phase cells. TRF peptidases were <1% as active in homogenates of BN1010 cells as those in homogenates of guinea pig brain or hypothalamus. It is expected that these cells will provide an excellent model system for the study of various aspects of TRF metabolism.

Nocturnal secretory patterns of FSH, GH, LH and TSH.

The nocturnal secretory patterns of follicle-stimulating hormone (FSH), growth hormone (GH), luteinizing hormone (LH) and thyroid-stimulating hormone (TSH) were studied in 1 female and 4 male volunteers. Immunoreactive FSH, GH, LH and TSH in serum were assayed by a radioimmunosorbent technique. Non-conjugated 11-hydroxycorticosteroids in plasma were also measured in the male volunteers by a fluorimetric method. Blood samples were taken half hourly from 10 p.m. to 8 a.m. Polygraphic monitoring of sleep stages was performed. In all the subjects a marked elevation of serum GH occurred within 60 minutes after the onset of sleep and additional, isolated GH peaks were observed in 3 subjects. The serum concentrations of FSH, LH and TSH also fluctuated, but the variations were small compared with the fluctuations of GH. The serum levels of FSH, LH and TSH respectively were not correlated with the depth or stages of sleep. The observed fluctuations, in the serum levels of all hormones assayed, are larger than coul...

Plasma thyroid-stimulating hormone response in anticipation of muscular exercise in the human.

Small but consistent plasma immunoreactive thyroid-stimulating hormone (TSH) responses were observed in 8 out of 8 normal young men during a 20-min interval immediately prior to participating in an exhausting exercise session for the first time. The increase in mean levels from 3.1 to 4.0 μU/ml is statistically significant. The findings in this experiment are compared with control data and those in other experiments involving anticipation of milder degrees of exercise in which such consistent hormonal changes were not observed. These observations lend support to the conclusion that psychological stimuli can stimulate pituitary-thyroid activity in man.

TSH response to synthetic thyrotropin-releasing hormone in human protein-calorie malnutrition.

In 8 of 24 children with proteincalorie malnutrition, basal serum immunoreactive thyrotropin (TSH) is elevated, and the TSH response to synthetic thyrotropin-releasing hormone, while prompt, is exaggerated and sustained, showing a delayed peak in 8 of 19 tests. After 3 weeks of treatment, basal TSH in most cases drops towards normal, peak TSH responses are lower (yet remain exaggerated in 4 instances), but the sustained TSH secretion returns to normal in all patients. In all of 5 cases tested, exogenous triiodothyronine suppresses basal TSH. This suggests a minor impairment of thyroid function in some children with protein-calorie malnutrition. TSH reserve, however, appears normal.

Thyrotropin releasing hormone (TRH) studies in patients with thyroid cancer.

ABSTRACT The effects of iv thyrotropin-releasing hormone (TRH) on serum immunoreactive thyrotropin (TSH) level, 131I uptake, serum resinsponge uptake of triiodothyronine (T3), and total serum thyroxine (T4) were studied after withdrawal of thyroid replacement in six patients with metastatic differentiated thyroid cancer. IV injections of 500 mcg of TRH were given every eight hr for the first two days and once on the third day. TSH levels were measured before and after TRH administration. Body scans were done on day 1 and days 5 or 7, both before and after the TRH. Basal levels of serum TSH were high before TRH (122 ± 9 μU/ml vs 4 ± 1 μU/ml in 8 normal subjects) and decreased on days 2 and 3 (89 ± 18 and 86 ± 20 μU/ml). The peak level after TRH was given was 356 ± 47 μU/ml at 20 min on day 1, as compared with 180 ± 31 and 136 ± 30 μU/ml on days 2 and 3. Body scans showed no significant change in 131I uptake, T3 or T4. One of the above patients plus one other patient were also studied at a later date during...

THYROID FUNCTION IN THE PRETERM FETUS

Measurements of serum total thyroxine (T4), free thyroxine (FT4), and/or immunoreactive thyrotropin (TSH) were conducted on 14 pairs of maternal and cord blood specimens obtained at the time of elective therapeutic abortion of 11- to 18-week pregnancies and on 21 paired maternal and fetal cord blood specimens collected at the time of spontaneous, premature delivery of 22- to 34-week pregnancies. T4 concentrations were elevated in all maternal samples to levels characteristic of pregnancy; mean values were similar at 11 to 18 and at 22 to 34 weeks and did not differ from the mean level reported previously at term. Mean maternal TSH concentrations also were similar at 11 to 18 weeks, 22 to 34 weeks, and at term. The mean FT4 concentration in maternal serum between 11 and 18 weeks was significantly higher than the level reported previously at term. Fetal serum T4 and FT4 concentrations were low between 11 and 18 weeks and increased progressively between 22 weeks and term. Fetal serum TSH concentrations were low between 11 and 18 weeks of pregnancy but seemed to increase abruptly between 18 and 22 weeks to levels characteristic of term infants. These data suggest that the maternal concentration of FT4 is higher early in pregnancy than at term, perhaps because of the higher blood levels of human chorionic thyrotropin in early pregnancy. They also indicate autonomous function of the fetal hypothalamic-pituitary control system as early as 12 weeks' gestation. The abrupt increase in fetal serum TSH between 18 and 22 weeks suggests rapid maturation of the fetal hypothalamic-pituitary unit during this period. The subsequent progressive increase in fetal FT4 concentration indicates an increasing thyroidal response to the TSH stimulus.