Pituitary-thyroid responses to 4-hour constant infusions of thyrotropin releasing hormone in man

Serum thyrotropin responses to thyrotropin-releasing hormone in Korsakoff's syndrome

Eleven patients with DSM-III-R Korsakoff's syndrome were studied as were 11 patients with alcohol dependence syndrome (without Korsakoff's syndrome and abstinent for at least 3 years) and 11 healthy controls. All subjects underwent a thyroid-releasing hormone and thyroid-stimulating hormone stimulation test. Forty-five percent of the Korsakoff's syndrome patients had a blunted response and 18% of the chronic abstinent alcoholic group were similarly blunted. None of the controls had an attenuated response. The possible reasons for the high level of blunting are discussed.

Influence of partial sleep deprivation on the secretion of thyrotropin, thyroid hormones, growth hormone, prolactin, luteinizing hormone, follicle stimulating hormone, and estradiol in healthy young women

The influence of partial sleep deprivation during the second half of the night on the secretion of thyroid stimulating hormone (TSH), thyroxin (T4), free T4 (fT4), triiodothyronine (T3), prolactin (PRL), growth hormone (GH), luteinizing hormone (LH), follicle stimulating hormone (FSH), and estradiol (E2) was investigated in 10 healthy young women. Blood samples were drawn at hourly intervals over a 64-hour period (i.e., 3 consecutive days and nights). During night 2, all subjects were awakened at 1:30 a.m. During partial sleep deprivation, TSH concentrations increased significantly and remained elevated throughout the following day. Levels of T4, fT4, and T3 were enhanced during the partial sleep deprivation hours only, and changes in these hormones seemed to be independent of TSH. PRL levels decreased, LH and E2 concentrations increased, and GH and FSH secretion remained unchanged during partial sleep deprivation. This pattern of change of different endocrine axes during partial sleep deprivation resembles those seen after total sleep deprivation, suggesting that similar neurochemical changes are induced by both forms of antidepressant therapy. The late evening GH peak occurred almost exclusively before the onset of sleep. Partial sleep deprivation did not influence the chronobiological profiles of any of the hormones investigated. The chemical changes underlying these alterations are speculated to involve enhancement of central norepinephrine and dopamine activity with a concomitant increase in the activity of the sympathetic nervous system.

Pulsatile TSH secretion during 48-hour continuous TRH infusions

Thyroid-stimulating hormone (TSH), like other anterior pituitary hormones, is normally secreted in a series of pulses over 24 h. However, the factors that control TSH pulse generation are unknown. We investigated the potential role of thyrotropin-releasing hormone (TRH) in TSH pulse generation by measuring TSH pulses during constant TRH infusions. Two groups of subjects were studied: five healthy subjects and five subjects with treated primary hypothyroidism and normal TSH levels. Each subject underwent four separate studies: (1) TSH levels were measured every 15 min over 24 h (baseline study). (2) TSH levels were measured every 15 min over 48 h during TRH infusions at 0.1 microgram/min (low dose TRH study). (3) TSH levels were measured every 15 min over 48 h during TRH infusion at 0.5 microgram/min (medium dose TRH study). (4) TSH levels were measured every 15 min over 48 h during TRH infusions at 1.0 microgram/min (high dose TRH study). TSH pulses were located by cluster analysis. We found that constant TRH infusions at any of the doses utilized did not alter TSH pulse frequency in normal or treated hypothyroid subjects, although pulse amplitude increased. Normal subjects had lower TSH pulse amplitude than treated hypothyroid subjects at all TRH doses, perhaps due to slightly higher serum T3 levels. This suggests that, at least acutely, pulsatile input of TRH to the pituitary gland does not determine pulsatile TSH release. However, TRH may modulate TSH pulse amplitude.

Circadian changes in pulsatile TSH release in primary hypothyroidism

OBJECTIVE

We evaluated pulsatile and circadian TSH secretion in primary hypothyroidism.

DESIGN

In a prospective study, blood was sampled every 10 minutes during 24 hours for assay of TSH (IRMA). Thyroid hormones and TSH responsiveness to TRH were then measured.

SUBJECTS

Nine patients with overt primary hypothyroidism, seven patients with subclinical hypothyroidism and 16 healthy controls.

MEASUREMENTS

Computer-assisted analysis by the Desade and Cluster programs.

RESULTS

Both computer-assisted programs revealed an increased TSH pulse amplitude in both overt and subclinical hypothyroidism versus controls (Desade: 36.9 +/- 31.4 (mean +/- SD) (P < 0.001) and 2.8 +/- 1.9 (P < 0.001) vs 0.4 +/- 0.2 mU/l; Cluster: 25.6 +/- 25.1 (P < 0.001) and 2.4 +/- 1.4 (P < 0.001) vs 0.4 +/- 0.2 mU/l). TSH pulse frequency remained unchanged with approximately 10 pulses/24 hours. A highly significant correlation was found between the mean 24-hour TSH concentration and the TSH pulse amplitude in all controls and patients but not to TSH pulse frequency. The nocturnal TSH surge was absent in six out of nine patients with overt primary hypothyroidism. The deficient nocturnal rise of TSH in primary hypothyroidism vs controls (22 +/- 51 vs 82 +/- 41%, P < 0.001), was associated with a loss of the usual nocturnal increase in TSH pulse amplitude and frequency.

CONCLUSIONS

Mean 24-hour TSH pulse amplitude is increased in primary hypothyroidism, but TSH pulse frequency remains unchanged. The decrease of the nocturnal TSH increase in primary hypothyroidism is associated with a loss of the usual nocturnal increase in TSH pulse amplitude and frequency.

Nocturnal cortisol, thyroid stimulating hormone, and growth hormone secretory profiles in depressed adolescents

Twelve depressed adolescents and 12 controls matched for age, sex, Tanner stage, time of menstrual cycle (females), weight, and time of year assessed were studied over 3 nights. Measurements for cortisol, thyroid stimulating hormone, and growth hormone were made on serum collected at 10 P.M., 12 midnight, 1 A.M., 2 A.M., 3 A.M., 4 A.M., and 6 A.M. in eight pairs and every 20 minutes from 8 P.M. to 7 A.M. in four pairs. Cortisol secretion did not significantly differentiate the groups. Thyroid stimulating hormone secretion was significantly elevated in the depressed group at one time point. Growth hormone secretion significantly differentiated the two groups at most time points, and the depressed adolescents significantly hypersecreted growth hormone (area under the curve). Implications for the diagnosis, etiology, and treatment of adolescent depression are discussed.

Serum thyrotropin responses to thyrotropin-releasing hormone in alcohol-dependent patients with and without depression

Forty-one patients with DSM-III alcohol dependence syndrome were studied, as were 30 patients with major depression and 20 healthy controls. Nineteen of the alcohol-dependent patients had depressive symptoms. All subjects underwent a TRH/TSH stimulation test. Fifty percent of the alcohol-dependent patients without depression had a blunted response, while 52% of patients with depression were similarly blunted. The overall rate of blunting in the non-alcoholic major depressives was 26%. Blunting in the alcoholics was not associated with a personal or family history of affective disorder. Furthermore the blunted response in recently detoxified alcoholics was of no prognostic significance.

TRH: behavioral and endocrine effects in man

1. The tripeptide TRH exerts a spectrum of biological activities in both animals and man. Some of these activities have been extensively studied, particularly in psychiatric patients. 2. Behaviorally, TRH appears to increase the sense of well-being, motivation, relaxation, and coping capacity in both normal subjects and patients with psychiatric and neurologic disease. These effects are not disease-specific; attempts to use TRH as a treatment tool have thus been disappointing. 3. Endocrinologically, administration of TRH stimulates the response of TSH; this response has been reported to be blunted in approximately 30% of patients with major depression. However, TSH blunting is not specific for depression, it has also been observed in a variety of other psychiatric conditions. 4. The relevance of these effects for psychiatry in general, and for psychoneuroendocrinology especially, is discussed in this review.

Controlled acute trial of a thyrotrophin releasing hormone analogue (RX77368) in motor neuron disease

Twenty five patients with motor neuron disease completed a double blind randomised cross over trial of RX77368, a stabilised TRH analogue, iv over 2 hours against saline. Temporary improvement in bulbar symptoms including speech, respiratory parameters, tongue movements and swallowing were seen. Fasciculations increased and spasticity decreased. Change in muscle force with drug was different from placebo but both increase and decrease in force were seen and did not result in detectable changes in function. Side effects were clinically significant in 50% of the patients and cleared within 12 hours. Prolonged rise of thyroxine and an increase in plasma levels of prolactin, thyroid stimulating hormone and growth hormone were seen and followed characteristic patterns.

Biphasic effect of thyrotropin-releasing factor (TRH) on alpha-melanotropin secretion from frog intermediate lobe in vitro

The kinetics of alpha-MSH secretion induced by prolonged TRH infusion were studied using perfused frog neurointermediate lobe (NIL). During a 2 h administration of TRH (10(-8) M), the secretion rate of alpha-MSH displayed two phases. During the first phase, secretion of alpha-MSH increased rapidly reaching a maximum within 20 min and then, despite continued TRH infusion, this secretion slowly declined. The second phase was characterized as plateau of elevated release (relative to basal secretion); within this second phase there was often a small peak of released alpha-MSH occurring at about 100 min. Exposure of NIL to another TRH (10(-8) M) pulse 90 min later induced a normal stimulation of alpha-MSH secretion, thus demonstrating the viability of tissue in perifusion. Continuous infusion of cycloheximide (10(-5) M) during a 5 h period totally inhibited the biosynthetic activity of NIL but did not influence TRH-induced alpha-MSH secretion. In particular, cycloheximide had no effect on the second phase of the response to prolonged infusion of TRH. Similarly, during continuous infusion of the monovalent carboxylic ionophore monensin (10(-6) M), the biphasic response to prolonged infusion of TRH (10(-8) M) was still observed. Administration of a short pulse of TRH (10(-7) M) during the declining part of the first phase or during the second phase of prolonged TRH (10(-8) M) infusion induced a significant enhancement of alpha-MSH stimulation. From these results we conclude that prolonged TRH infusion causes alpha-MSH release in a biphasic manner; attenuation of the secretory response to continuous TRH administration does not result from exhaustion of the releasable pool of alpha-MSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of thyrotrophin releasing hormone and the enkephalin analogue DAMME on pituitary hormone secretion

Because TRH counteracts the inhibitory effect of opiate peptides on LH secretion in cultured cells from normal pituitaries, six normal postmenopausal women were studied to determine whether TRH interacts in vivo with opioid peptides in the regulation of pituitary hormone secretion. At two different times a constant 3 h infusion of either saline or TRH (5 micrograms/min) was initiated. At 60 min a 250 micrograms bolus of the opiate agonist peptide D-Ala2-MePhe4-met-enkephalin-0-ol (DAMME) was injected in one of the two saline and TRH infusion tests. The four treatments, i.e. saline infusion alone, saline infusion with a DAMME bolus, TRH infusion alone; and TRH infusion with DAMME bolus were given at random with an interval of at least 7 d. Blood samples were taken every 15 min during the 3 h study. DAMME induced a significant fall (P less than 0.05) in serum LH (from 35 +/- 8.5 to 18.3 +/- 5.1 mIU/ml) (mean +/- SEM) without significantly affecting FSH levels (from 29 +/- 11.2 to 26.9 +/- 12.4 mIU/ml). These changes were not antagonized by the continuous infusion of TRH. PRL had a monophasic response pattern to continuous isolated TRH infusion; the basal levels increased from 4.2 +/- 1.2 to 24.5 +/- 6.8 ng/ml at 30 min and then slowly decreased with a plateau from 90 min until the end of the study. DAMME administration at 60 min induced a significant second peak of PRL secretion (44 +/- 6.5 ng/ml) 30 min later (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin response to exercise, metoclopramide and other provacative agents in children

Metoclopramide (MCP), a derivative of procainamide was compared with exercise, arginine, insulin and thyrotropin releasing hormone (TRH) as a prolactin (PRL) releaser in children. The peak response of plasma PRL after oral administration of MCP was greater than that after strenuous exercise and after i.v. administration of pharmacodynamic agents. Normal PRL and TSH responses were observed after TRH administration in all subjects. Variable PRL responses were seen after exercise and after i.v. administration of arginine and insulin, despite significant growth hormone (GH) release following the administration of these agents. MCP produced no increase in plasma TSH. Metoclopramide may be useful for dynamic testing of PRL release in children. It can be taken orally and is free of side-effects.

TRH-induced hyperprolactinemia and pituitary-ovarian function

To elucidate the role of prolactin in the control of pituitary-ovarian function, eight healthy women were given 80 mg of synthetic thyrotropin-releasing hormone (TRH) orally on two consecutive days during the luteal phase of their menstrual cycle. TRH elevated serum prolactin to a mean concentration of 43.8 ng/ml on the first day and to 15.5 ng/ml on the second day. The reduced response to the second TRH dose was statistically significant (p < 0.05). Accompanying changes in concentrations of gonadotropins or ovarian steroids were not consistent. Short-term oral administration of TRH and/or the temporary hyperprolactinemia induced by its use do not modify the pituitary-ovarian function during the luteal phase of the menstrual cycle.

Gonadotropin-releasing hormone receptor binding in bovine anterior pituitary

Synthetic gonadotropin-releasing hormone (GnRH) was monoiodinated at a high specific radioactivity with 125I. The iodinated hormone retained full biological activity as assessed by the release of luteinizing hormone in vitro from bovine anterior pituitary tissue slices. Specific binding of 125I-labeled gonadotropin-releasing hormone of high affinity and low capacity was obtained using dispersed bovine anterior pituitary cells. The binding had sigmoid characteristics, compatible with the presence of more than one binding site. The subcellular fraction responsible for binding was identified with the plasma membranes. However, significant binding also occurred in the secretory granules fraction. The plasma membranes were solubilized with sodium dodecyl sulfate. Using gonadotropin-releasing hormone covalently coupled to a solid phase, a protein was purified by an affinity technique from the solubilized plasma membrane preparation which possessed similar binding propperties as plasma membranes, both intact and solubilized. The protein migrated as a single component on polyacrylamide gel in sodium dodecyl sulfate and the estimated molecular weight was 60 000. The character of the gonadotropin-releasing hormone concentration dependence binding as well as association kinetics were multiphasic and suggested the presence of more than one binding site. When analyzed by the Hill plot, the Hill coefficient of all binding curves was always greater than one which is compatible with positive cooperativity. This was further supported by the dissociation studies where the dissociation rate was inversely proportionate to both the gonadotropin-releasing hormone concentration and the time interval during which the gonadotropin-releasing hormone-gonadotropin-releasing hormone receptor protein complex was formed. Using difference chromatography, aggregation of the purified gonadotropin-releasing hormone receptor protein was demonstrated to occur upon its exposure to gonadotropin-releasing hormone. The formed macromolecular complexes bound preferentially 125I-labeled gonadotropin-releasing hormone. It is concluded that a single receptor protein is responsible for gonadotropin-releasing hormone binding in the bovine anterior pituitary. It is a part of the plasma membranes. Its interaction with gonadotropin-releasing hormone provokes transitions of the protein into different allosteric forms and this may be related to the biological effect of gonadotropin-releasing hormone on gonadotropin secretion.

Serum T3 and T4 determinations during the TRH test as a complement to improved discriminatory power in suspect hyperthyroidism

The aim of the study was to determine whether the addition of T3 and T4 determination in connection with a routine TRH-test could increase the discriminatory power of the test. Thus, forty-one patients with suspect hyperthyroidism were examined and samples for T3 and T4 and TSH determinations were drawn prior to the administration of TRH and at 20 and 60 min thereafter. The results showed that the addition of these thyroid hormone estimations did not increase the clinical value of the TRH-test.

The effect of oral thyrotropin-releasing hormone on thyroid function and the composition of breast milk in puerperal women

To determine the effect of oral administration of thyrotropin-releasing hormone (TRH) on the thyroid function and on the composition of breast milk in the early puerperium, six lactating women were treated with a single dose of 40 mg of synthetic TRH and six women were treated with placebo. Serial serum samples taken before and between one and 25 hours after TRH administration were assayed with specific radioimmunoassays for thyrotropin (TSH), triiodothyronine (T3) and total thyroxine (T4). Milk samples were collected three times a day and their major fatty acids were determined by gas-liquid chromatography and were compared with those obtained from normal lactating women. A statistically significant TSH elevation was observed between one and six hours after TRH administration, with a peak value of 23.7 +/- 10.6 mU/liter at three hours. The T3 concentration rose between three and nine hours after TRH administration, with a peak of 6.3 +/- 1.2 nmole/liter at six hours. The T4 elevation was statistically significant between six and 12 hours after TRH administration. The fatty acid content of milk samples from women treated with TRH did not differ from the normal series. A single daily dose of oral TRH thus caused a temporary thyroid stimulation. It is doubtful whether this could lead to hyperthyroidism since the levels of thyroid hormones became normal within ten hours after TRH administration.

Dopamine is a physiological regulator of thyrotrophin (TSH) secretion in normal man

Using a sensitive and precise radioimmunoassay for human TSH we have demonstrated significant elevations in serum TSH levels in euthyroid volunteers following administration of the dopamine receptor blocking drug metoclopramide when compared with placebo. The degree of TSH response is significantly greater in females than in males and is sustained over a 3-hour period after a single oral 10 mg dose of metoclopramide. The degree of TSH release after metoclopramide is inversely related to the basal TSH level suggesting that dopamine is a determinant of low daytime TSH levels and is thus implicated in the circadian rhythm of TSH secretion. Pretreatment with 10 mg of metoclopramide orally, one hour before TRH administration leads to significant enhancement of the TSH response to TRH. Our findings provide further evidence for the physiological inhibitory role of dopamine in the contol of TSH secretion in normal man. The possible mode of action of dopamine and the clinical implications of this neuroregulatory pathway are discussed.

Increases in serum concentrations of follicle-stimulating hormone (FSH) during thyrotrophin-releasing hormone (TRH) infusions in normal men

Increases in serum FSH values to approximately 50% above basal concentrations were found during TRH infusions of 2.0 microgram/min into normal men (n = 10). These increases could not be explained by cross-reactivity of thyrotrophin (TSH) in the FSH assay. No significant change was found in serum concentrations of FSH during saline infusions (n = 4) nor in LH concentrations during either TRH or saline infusions. Many previous studies using single injections of TRH have failed to demonstrate changes in serum FSH concentrations. It is possible that prolonged infusions of TRH, as used in this study, are more likely to lead to non-specificity of the effects of this tripeptide on pituitary hormone secretion.