Pathophysiology of pulsatile and copulsatile release of thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, and alpha-subunit.

Under physiological conditions, TSH, LH, FSH, and alpha-subunit are released in discrete pulses. To further characterize their neuroregulation and to investigate possible copulsatile secretion of these glycoprotein hormones, we studied the 24-h pulse profiles of all four hormones in each of four subject groups: young men, young women, postmenopausal women, and subjects with untreated primary hypothyroidism. Gonadotropin pulse properties in euthyroid men and women were similar to those previously reported, and hypothyroid subjects had normal gonadotropin pulse patterns. TSH release was pulsatile in all groups; hypothyroid subjects had increased pulse amplitude, but loss of the usual nocturnal increases in pulse amplitude. alpha-Subunit concentrations were pulsatile in all groups, with minimal circadian variation; postmenopausal and hypothyroid subjects had increased alpha-subunit pulse amplitude. We then tested pulse concordance among the four simultaneous hormone series. alpha-Subunit and the gonadotropins were significantly coreleased (triple coincidence), suggesting that all three hormones are closely linked to processes that regulate GnRH secretion. alpha-Subunit bursts were also significantly coincident with those of TSH in men, postmenopausal women, and hypothyroid subjects. Interestingly, TSH pulses were significantly concordant with those of LH and FSH, and all four hormones were significantly concordant in men, postmenopausal women, and hypothyroid subjects. In conclusion, the present findings imply that an underlying unified signal coordinates pulsatile hormone secretion from both gonadotrophs and thyrotrophs.     

Administration of low dose pulsatile gonadotropin-releasing hormone (GnRH) to GnRH-deficient men regulates free alpha-subunit secretion

Although pharmacological doses of GnRH and TRH stimulate free alpha-subunit (alpha-subunit) secretion from the pituitary, little is known about the pattern and control of alpha-subunit release under physiological circumstances. Euthyroid men with idiopathic hypogonadotropic hypogonadism, a condition of deficient GnRH release, provide a unique opportunity to study alpha-subunit secretion before and during administration of a physiological regimen of GnRH administration. Before GnRH therapy, six euthyroid IHH men with normal endogenous TSH secretion had circulating alpha-subunit levels close to or below assay detection limits, with a mean level less than 0.5 ng/ml. During 12-42 weeks of physiological GnRH replacement, serum alpha-subunit concentrations rose to a mean value of 2.07 +/- 0.3 (+/- SEM) ng/ml (P less than 0.01). After GnRH administration, alpha-subunit was released in a pulsatile pattern following each dose of GnRH and mirrored the secretory pattern of LH. Increases in serum alpha-subunit concentrations during GnRH administration were closely correlated with increases in LH (r = 0.91; P less than 0.01), but not FSH (r = 0.24; P = NS), levels. In addition, a situation in which LH secretion was clearly predominant and FSH levels were barely detectable was created by increasing the frequency of GnRH administration to every 30 min. In this circumstance, free alpha-subunit concentrations increased in conjunction with LH levels in the face of decreased FSH levels. We conclude that replacement of GnRH regulates both the level and pattern of alpha-subunit secretion in GnRH-deficient men, and that there is tight correlation of alpha-subunit with LH, but not with FSH, secretion.     

Pulsatile gonadotropin secretion after discontinuation of long term gonadotropin-releasing hormone (GnRH) administration in a subset of GnRH-deficient men

Normal pituitary and gonadal function can be maintained with long term pulsatile GnRH administration in men with idiopathic hypogonadotropic hypogonadism (IHH), and both pituitary and gonadal priming occur during the process of GnRH-induced sexual maturation. Still, the long term effects of discontinuing GnRH therapy in IHH men have not been examined. Therefore, we evaluated the patterns of gonadotropin and alpha-subunit secretion before and after a prolonged period of pulsatile GnRH administration in 10 IHH men. Before exogenous GnRH stimulation, no patient had any detectable LH pulsations. In 6 of these men, who were typical of most of our IHH patients (group I), no LH pulsations were detectable after cessation of GnRH administration. However, in the other 4 men (group II), LH pulsations were easily detectable despite cessation of exogenous GnRH stimulation, and the amplitude (9.3 +/- 3.5 IU/L) and frequency (13.8 +/- 1.7 pulses/day) of these LH pulses were similar to those in 20 normal men (10.6 +/- 0.7 IU/L and 11.0 +/- 0.7 pulses/day). Three of these 4 men in group II maintained normal serum testosterone levels after discontinuation of GnRH delivery. To determine if there were any characteristics that might be useful in predicting which IHH men could maintain normal pituitary-gonadal function after long term GnRH administration, we evaluated various clinical and hormonal parameters at the time of initial presentation. Mean alpha-subunit levels (P less than 0.01) and alpha-subunit pulse amplitude (P less than 0.02) were significantly higher in the group II than the group I men, suggesting that the group II patients had partial, rather than complete, deficiency of endogenous GnRH secretion. None of the other parameters that were assessed distinguished the two groups. We conclude that gonadotropin and sex steroid levels return to their pretreatment state in the majority of IHH men when long term GnRH administration is discontinued. Normal pituitary-gonadal function can be maintained after discontinuation of long term GnRH administration in a rare subset of IHH men who present with higher levels of alpha-subunit. We hypothesize that these latter IHH men have an incomplete GnRH deficiency and that long term exogenous GnRH administration induces pituitary and gonadal priming, which subsequently enables them to sustain normal pituitary and gonadal function in response to their own enfeebled GnRH secretion.     

Alpha-subunit secretion in men with idiopathic hypogonadotropic hypogonadism

We studied the regulation of glycoprotein hormone alpha-subunit secretion in four men with idiopathic hypogonadotropic hypogonadism due to presumed GnRH deficiency. Immunoreactive alpha-subunit was present at low but usually detectable levels in blood samples drawn at 10- to 20-min intervals for 12-24 h; however, no characteristic pattern of pulsatile alpha-subunit secretion was found. Serum from each man was examined by gel filtration chromatography. Each sample tested contained an immunoreactive alpha-subunit peak with a slightly lower elution volume than [125I]hCG alpha, as we had previously found in serum from normal men. To determine if this peak represented TSH alpha, two men were treated with 0.3 mg L-T4 daily for 7-14 days. Serum TSH levels decreased to less than 1.5 mU/L, and neither TSH nor alpha-subunit levels increased after the iv administration of 500 micrograms TRH. An alpha-subunit peak that eluted before [125I]hCG alpha was again found in the serum of T4-treated men. We conclude that glycoprotein hormone alpha-subunit is present in the serum of men with idiopathic hypogonadotropic hypogonadism in whom TSH secretion is completely suppressed by L-T4. The gonadotrophs represent the most likely source of this alpha-subunit. The finding of more normal alpha-subunit than LH secretion in these men indicates that the production of the gonadotropin subunits is differentially regulated in man and supports the hypothesis that factors in addition to GnRH regulate alpha-subunit gene expression.     

Dopaminergic inhibition of glycoprotein hormone alpha-subunit in normal subjects.

The pituitary glycoprotein hormones thyrotropin (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) consist of two noncovalently linked subunits, alpha and beta. In addition to producing intact hormone, the pituitary releases free alpha-subunit, which is stimulated by gonadotropin-releasing hormone (GnRH) and thyrotropin-releasing hormone (TRH). However, little is known about the dopaminergic regulation of free alpha-subunit in vivo. The effect of dopamine (DA), metoclopramide (MTC), and the specific DA D-1 receptor agonist, fenoldopam, on circulating alpha-subunit levels was studied in normal men and women. Normal women received 4-hour infusions of either glucose (n = 6) or DA at rates of 0.04 (n = 6), 0.4 (n = 6), and 4.0 micrograms/kg.min (n = 6). After 3 hours, 10 mg MTC was administered intravenously (IV). The high dose of DA significantly lowered alpha-subunit levels (P less than .05). No response to MTC was observed in any of the groups. Six women received glucose or DA infusion (4.0 micrograms/kg.min) for 18 hours. DA significantly reduced basal alpha-subunit levels compared with control infusion (P less than .05). MTC administration after 17 hours induced a significant increase in alpha-subunit levels on the day of DA infusion compared with control (P less than .05). In a third study, nine normal males received fenoldopam (0.5 microgram/kg.min) or placebo infusions for 4 hours. Fenoldopam did not affect basal alpha-subunit levels, but the alpha-subunit response to a GnRH/TRH bolus was significantly increased during fenoldopam compared with control (P less than .05). The results suggest that alpha-subunit release may be modulated by the dopaminergic system in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulation of serum inhibin concentrations by gonadotropin-releasing hormone in men with idiopathic hypogonadotropic hypogonadism

Inhibin is a gonadal hormone thought to be important in FSH regulation. We investigated the effects of the hypogonadotropic state and subsequent GnRH-induced increases in gonadotropin levels on inhibin secretion. Serum levels of inhibin, LH, FSH, and testosterone (T) as well as sperm concentrations were measured in 5 men with idiopathic hypogonadotropic hypogonadism (IHH) before (baseline) and during 8 weeks of GnRH therapy (5 micrograms, sc, every 2 h). Baseline and peak inhibin levels were compared to those in a group of 19 normal men. Before GnRH administration, the mean serum inhibin level was significantly lower in the IHH men than in the normal men [166 +/- 56 (+/- SE) vs. 588 +/- 30 U/L; P less than 0.001]. Serum inhibin levels rose after 1 week of GnRH therapy (P less than 0.05) and remained higher than the baseline level thereafter. The mean peak inhibin level during GnRH administration was lower than the mean value in normal men (485 +/- 166 vs. 588 +/- 30 U/L; P less than 0.05). Serum LH and FSH levels rose promptly to the midnormal range or slightly above it. Serum T levels did not significantly increase until 4-5 weeks of GnRH administration and remained in the low normal range. All IHH men were azoospermic throughout the study. These data are consistent with the hypothesis that inhibin is produced by the testis under gonadotropin control. They also suggest the possibility of defective Sertoli and Leydig cell function in men with IHH, since the men's serum inhibin and T levels did not rise to the same extent as did their normalized serum gonadotropin levels during GnRH administration.     

Familial thyroid hormone resistance

Eight patients with thyroid hormone resistance were found in four generations of a kindred containing 19 members. Results of studies in this family are consistent with an autosomal dominant mode of inheritance for this disorder. The affected family members were clinically euthyroid but all had goiters and markedly increased serum thyroid hormone levels: thyroxine (T4) = 21.1 +/- 2.1 microgram/dl; triiodothyronine (T3) = 323 +/- 60 ng/dl; free T4 = 5.4 +/- 0.9 ng/dl; and free T3 = 1,134 +/- 356 pg/dl (mean +/- SD). Serum thyrotropin (TSH) levels were normal or slightly elevated in six patients and responded normally to the administration of thyrotropin-releasing hormone (TRH) and L-triiodothyronine. Two patients who had previously undergone subtotal thyroidectomy had elevated baseline serum TSH levels and exaggerated TSH responses to the administration of TRH suggesting subclinical hypothyroidism despite elevated total and free thyroid hormone levels. The absence of thyrotoxicosis and normal serum TSH levels despite elevated serum free T3 and T4 levels in the untreated members of this family are consistent with resistance of pituitary and peripheral tissues to the actions of thyroid hormones. In addition, the absence of hypothyroidism and normal responsiveness of serum TSH to TRH and L-triiodothyronine administration in untreated family members suggest that the thyroid has compensated for the hormone resistance by increased secretory activity under the control of pituitary TSH secretion.     

The nature of the gonadotropin-releasing hormone stimulus-luteinizing hormone secretory response of human gonadotrophs in vivo

To examine the stimulus-secretion response of human pituitary gonadotrophs in vivo, we applied a new multiple parameter deconvolution technique to analyze (1) exogenous GnRH-stimulated LH secretory responses in 10 men with isolated hypogonadotropic hypogonadism (IHH), and (2) endogenous and exogenous GnRH-stimulated LH secretory responses in 8 normal men. The GnRH-deficient men were given 4 bolus doses of synthetic GnRH (7.5, 25, 75, and 250 ng/kg) iv at 2-h intervals in randomized order after long term pulsatile GnRH administration. The normal men were studied by sampling blood at 10-min intervals for 12 h basally and after 2 consecutive 10-micrograms iv GnRH doses. The serum LH peaks in both groups were subjected to quantitative deconvolution to resolve underlying LH secretory and clearance rates simultaneously. Such analyses revealed that exogenous GnRH-induced LH secretory episodes in GnRH-deficient men with IHH could be modeled as algebraically Gaussian distributions of instantaneous LH secretory rates with a mean half-duration of 14 +/- 2 min. The simultaneously resolved half-life of endogenous LH disappearance was 71 +/- 5 min. The log dose-response relationship for GnRH dose vs. maximal LH secretory rate or vs. calculated mass of LH released per secretory burst was linear. In contrast, varying GnRH doses did not alter the duration of LH secretory bursts, the half-time of LH disappearance, or the latency of LH secretory bursts after iv GnRH injections (viz. 7.6 min). Deconvolution analysis of the spontaneous (endogenous GnRH-stimulated) LH peaks in normal men revealed a mean half-duration of secretory bursts of 9.9 +/- 1.5 min, and a mean half-time of endogenous LH disappearance of 76 +/- 5 min. These values were not significantly different from those in the GnRH-treated normal or GnRH-deficient men. In summary, deconvolution analysis of LH release in men with IHH revealed a significant linear relationship between iv doses of pulsed GnRH and computer-resolved LH secretory rate and/or the mass of LH released per secretory event. In contrast, varying doses of GnRH did not alter the lag time between the GnRH stimulus and the LH secretory burst, the duration of LH secretion, or the calculated half-life of the LH released. We conclude that GnRH exerts dose-dependent effects on specific attributes of the secretory response of human gonadotrophs in vivo.     

The spectrum of abnormal patterns of gonadotropin-releasing hormone secretion in men with idiopathic hypogonadotropic hypogonadism: clinical and laboratory correlations

Several lines of evidence indicate that hypothalamic-pituitary-gonadal activity varies among men with idiopathic hypogonadotropic hypogonadism (IHH). To test the hypothesis that a spectrum of abnormalities of GnRH secretion underlies the syndrome of IHH, we characterized the patterns of GnRH-induced gonadotropin secretion during periods of frequent sampling in 50 consecutive men with IHH and contrasted them with those in 20 normal men. The largest group of IHH patients (n = 42) had no detectable LH or FSH pulsations and could be categorized into 2 subsets according to the presence or absence of evidence of spontaneous puberty. The most severely affected subset (n = 32), who recalled no history of puberty, had testes with a mean volume of 3.3 +/- 0.5 (+/- SEM) ml, with a prepubertal appearance on biopsy, and often were anosmic (n = 17). The second subset of apulsatile IHH men (n = 10) had histories of partial or complete spontaneous sexual development with subsequent isolated loss of sexual function, testes with a mean volume of 13.3 +/- 1.9 ml (P less than 0.01 compared to the first subset), a pubertal or adult appearance of the testes on biopsy, and an intact sense of smell. In a second group of IHH patients (n = 3), LH was secreted predominantly in a nighttime pattern similar to that of normal children during early puberty. These men were aged 18-24 yr, had a mean testicular volume of 10.5 +/- 2.3 ml, pubertal changes on testicular biopsy, and an intact sense of smell. A third group of IHH men (n = 4) had LH pulses of abnormally low amplitude. Only one patient in this group had a history of spontaneous sexual development. The mean testicular volume of these patients was 5.6 +/- 1.9 ml, and the testes appeared prepubertal (n = 3) or pubertal (n = 1) on biopsy. In addition to these groups, another patient had apparent LH pulsations and nearly normal amplitude, but the LH was bioinactive and appeared to consist chiefly of alpha-subunit. Testing of other anterior pituitary hormone functions did not distinguish IHH men from normal men. However, those IHH patients with some evidence of endogenous GnRH secretion had higher basal and stimulated serum PRL levels than IHH men without such evidence (P less than 0.05), suggesting an influence of GnRH on PRL secretion.     

Histamine-induced paradoxical GH response to TRH/GnRH in men and women: dependence on gonadal steroid hormones

A stimulatory GH response to TRH and GnRH occurs frequently in patients with various pathological conditions, but is absent in normal subjects. We have previously shown that histamine induced a paradoxical GH response to TRH in normal men. Since gonadal steroids influence GH secretion, we investigated whether infusion of histamine might induce a GH response to combined administration of TRH (200 micrograms) and GnRH (100 micrograms) in 6 normal women during the early follicular and luteal phase of the same menstrual cycle and in 7 normal men. Histamine had no effect on basal GH secretion in men or in women during the two phases of the menstrual cycle. However, compared with saline, histamine induced a GH response to TRH/GnRH in men (GH peak: 5.5 +/- 1.0 vs 1.4 +/- 0.3 micrograms/l; p less than 0.01) and in women during the luteal phase (GH peak: 5.2 +/- 1.6 vs 1.5 +/- 0.4 micrograms/l; p less than 0.025), but not during the early follicular phase of the cycle (GH peak: 1.7 +/- 0.5 vs 1.6 +/- 0.3 micrograms/l). In luteal-phase women the GH response to TRH/GnRH correlated with the serum estradiol-17 beta level (GH area/E2: r = 0.98; p less than 0.005) and the serum estrone level (GH area/E1: r = 0.81; p less than 0.05). In men the GH response to TRH/GnRH did not correlate with estrogen or androgen levels. We conclude that high physiological levels of estrogens are pertinent to the activation of a histamine-induced GH response to TRH/GnRH in women, whereas the role of androgens and estrogens for the induction of the response in men seems more complex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of pituitary glycoprotein alpha-subunit secretion after administration of a luteinizing hormone-releasing hormone antagonist in normal men.

Pituitary glycoprotein hormones are composed of two different subunits, the alpha- and beta-subunits. The alpha-subunit is common to all FSH, LH, and TSH, while the beta-subunit is specific for each of these hormones. We studied the effects of a potent LHRH antagonist on alpha-subunit and LH secretion in normal men. The LHRH antagonist Nal-Glu, ([Ac-D2Nal1,D4ClPhe2,D3Pal3,Arg5,DGlu6(AA) ,Ala10]LHRH), was given (10 mg daily) as one injection of 5 mg every 12 h. Blood samples were drawn every 24 h, and on days 1 and 7 a day curve was established by drawing hourly blood samples for 26 h. Mean serum alpha-subunit levels decreased progressively (P less than 0.001) from 2.9 +/- 0.49 micrograms/L at baseline to a nadir of 1.4 +/- 0.27 micrograms/L on day 8. In contrast, mean immunoreactive LH (IR-LH) levels decreased rapidly from 3.2 +/- 0.6 U/L at baseline to 0.9 +/- 0.08 U/L on day 2 and remained suppressed (P less than 0.001) throughout the treatment period. On day 1 after the administration of Nal-Glu mean alpha-subunit levels decreased, although not significantly (P = 0.054), from 3.0 +/- 0.6 micrograms/L at baseline to a nadir of 2.0 +/- 0.3 micrograms/L at 17 h. alpha-Subunit remained at this level for the remainder of day 1. On day 7, however, the baseline serum alpha-subunit level was 1.5 +/- 0.3 micrograms/L, significantly suppressed (P less than 0.01) compared to the level on day 1, and no further decrease was seen after administration of Nal-Glu. IR-LH on day 1 before the first injection of 5 mg Nal-Glu was 3.5 +/- 0.8 U/L. Then, IR-LH levels decreased significantly (P less than 0.001) to a nadir of 0.9 +/- 0.1 U/L and remained at this level throughout day 1. IR-LH levels on day 7 were at or below 1.0 U/L throughout the sampling period. These results indicate that alpha-subunit secretion can be partially suppressed after chronic administration of a LHRH antagonist. Furthermore, LH serum levels dissociate from those of pituitary glycoprotein alpha-subunit after administration of LHRH antagonist analogs.     

The relative role of gonadal sex steroids and gonadotropin-releasing hormone pulse frequency in the regulation of follicle-stimulating hormone secretion in men

OBJECTIVE: Our objective was to determine the importance of testosterone (T), estradiol (E(2)), and GnRH pulse frequency to FSH regulation in men. DESIGN: This was a prospective study with four arms. SETTING: The study was performed at the General Clinical Research Center. PATIENTS OR OTHER PARTICIPANTS: There were 20 normal (NL) men and 15 men with idiopathic hypogonadotropic hypogonadism (IHH) who completed the study. Intervention: Medical castration and inhibition of aromatase were achieved using ketoconazole x 7 d with: 1) no sex steroid addback, 2) T addback starting on d 4, and 3) E(2) addback starting on d 4. IHH men in these arms received GnRH every 120 min. In a further six IHH men receiving ketoconazole with no addback, GnRH frequency was increased to 35 min for d 4-7. Blood was drawn every 10 min x 12 h at baseline, overnight on d 3-4 and 6-7. MAIN OUTCOME MEASURES: Mean FSH was calculated from the pool of each frequent sampling study. RESULTS: In NL men FSH levels increased from 5.1 +/- 0.7 to 8.7 +/- 1.3 and 9.7 +/- 1.5 IU/liter (P < 0.0001). T caused no suppression of FSH. E(2) reduced FSH from 12.4 +/- 1.8 to 9.3 +/- 1.3 IU/liter (P < 0.05). In IHH men on GnRH every 120 min, FSH levels went from 6.0 +/- 1.6 to 9.0 +/- 3.0 and 11.9 +/- 4.3 (P = 0.07). T caused no suppression of FSH. E(2) decreased FSH such that levels on d 6-7 were similar to baseline. Increasing GnRH frequency to 35 min had no impact on FSH. CONCLUSIONS: The sex steroid component of FSH negative feedback in men is mediated by E(2). Increasing GnRH frequency to castrate levels has no impact on FSH in the absence of sex steroids. When inhibin B levels are NL, sex steroids exert a modest effect on FSH.     

Endocrine and immunohistochemical studies on thyrotropin (TSH)-secreting pituitary adenomas: responses of TSH, alpha-subunit, and growth hormone to hypothalamic releasing hormones and their distribution in adenoma cells.

Endocrine and immunohistochemical studies were performed in two cases of TSH-secreting pituitary adenomas. The patients had elevated serum TSH and alpha-subunit concentrations despite high serum thyroid hormone levels. In addition, one patient (no. 1) had elevated serum GH levels with clinical evidence of acromegaly. GH-releasing hormone infusion increased serum levels of TSH, alpha-subunit and GH in the two patients. TRH injection increased serum TSH levels in both patients and, concomitantly, serum alpha-subunit and GH levels in patient 1. Basal TSH levels and their responses to TRH changed reciprocally to changes in serum thyroid hormone levels, although TRH-induced GH release did not. The administration of GnRH also increased serum TSH, alpha-subunit, and GH levels in patient 1. In accordance with these in vivo results, pituitary adenoma cells in culture obtained from patient 1 responded to GH-releasing hormone, TRH, or GnRH to secrete TSH, alpha-subunit, and GH. Incubation of cells with dexamethasone resulted in inhibition of TSH and stimulation of GH secretion without a significant change in alpha-subunit secretion. On the basis of light microscopic and electron microscopic double gold immunohistochemistry, the tumor from patient 1 was a bimorphous adenoma composed of two separate cell types: cells with TSH beta-subunit (TSH beta) and alpha-subunit, and those with GH and alpha-subunit. The remainder consisted mainly of cells with TSH beta and alpha-subunit. The coproduction of the unusual combination of two hormones such as GH and alpha-subunit in a single-type of adenoma cell and the coexistence of thyrotrophs and somatotrophs in one pituitary adenoma along with the aberrant responses of TSH beta, alpha-subunit, and GH to multiple hypothalamic hormones suggest the dedifferentiation of pituitary cells to multipotential progenitor cells by neoplastic transformation.     

TRH-induced TSH and prolactin responses in the elderly

Since there are divergencies in the thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) in old age, and since a hypothalamopituitary dysfunction has been suggested in the elderly, we have studied the thyroid function and the TRH responsiveness of TSH and prolactin (PRL) in 56 euthyroid patients over 70 years old, grouped according to age (70-79, 80-89, 90 or more years) and sex. Results were compared to those of 15 postmenopausal women and 11 men. In the elderly patients there was a decrease in plasma tri-iodothyronine (T3) and an increase in reverse T3 (rT3) levels while thyroxine (T4), basal TSH and PRL levels remained normal. The mean TSH and PRL responses to TRH (250 micrograms i.v.) were reduced but there was no age effect within the elderly. Only a sex effect was detected, TSH and PRL responses being appreciably lowered in men. In eight patients without severe disease or malnutrition, the response of TSH was not significant. We conclude that despite an apparent euthyroid status, TSH and PRL responses are blunted in elderly patients, and more in men than in women. These data, consistent with a hypothetical hypothalamopituitary dysfunction, indicate the difficulties of thyroid status assessment in the elderly.     

The relationship of changes in serum estradiol and progesterone during the menstrual cycle to the thyrotropin and prolactin responses to thyrotropin-releasing hormone.

The responses of serum TSH and PRL to TRH (500 microgram) were studied in normal young women in the early follicular, periovulatory, and midluteal phases of the menstrual cycle in order to examine the relationship of these responses to the levels of estradiol relationship of these responses to the levels of estradiol (E2) and progesterone. Each woman was studied twice in each phase in order to assess intraindividual variability. There was no significant difference in either the TSH or PRL responses among the phases of the menstrual cycle nor was either response affected by the periovulatory rise in E2 or by the luteal rise in both E2 and progesterone. Thus, the interpretation of the TSH and PRL responses to TRH in normal women is not affected by the menstrual cycle although both responses are greater in women that in men. Both the peak TSH and peak PRL after TRH were highly correlated with the basal levels of TSH (r = 0.85; P less than 0.01) and PRL (r = 0.67; P less than 0.01), respectively, indicating that the TSH and PRL responses to TRH in women are directly proportionate to the basal levels of the respective hormones, as previously shown for the TSH response in men. The mean intraindividual variability (coefficient of variation) of the TSH response to TRH was 18%, but ranged as high as 56%, while that of the PRL response was 16% and ranged up to 31%; variability was not affected by the phase of the menstrual cycle. The normal range of the peak TSH after TRH in women is 7-33 microU/ml (mean +/- 2 SD); however, because of the variability, a normal woman may sometimes have a peak TSH after TRH as low as 4 microU/ml. Repeating the test will result in a normal value if the woman is truly normal. Similarly, the normal peak PRL after TRH in women is 22-111 ng/ml (mean +/- 2 SD); usually, however, the lower limit is 30 ng/ml with lower values due to intraindividual variation. The data suggest that the higher average level of E2 in women compared to women, but that the cyclic changes in serum E2 or progesterone in women have little or no additional effect.     

Thyrotropin suppression by 3,5-dimethyl-3'-isopropyl-L-thyronine in man.

The thyromimetic activity of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), a nonhalogenated thyroid analog, was studied in adult men using suppression of TRH-induced TSH release to assess this activity. In nine men, aged 30-58 yr, the TSH increment after 500 microgram TRH iv was compared to the TSH response to TRH 24 h after oral administration of 1 mg DIMIT. Eight euthyroid subjects had normal baseline TSH levels of 1.5 +/- 0.2 (SE) microunit/ml that fell significantly to 0.7 +/- 0.2 microunit/ml 24 h after DIMIT (P less than 0.005). Their TSH increments after TRH fell from 15.3 +/- 2.8 to 6.7 +/- 1.6 microunit/ml 24 h after DIMIT (P less than 0.001). One subject with probable Hashimoto's thyroditis had an elevated TSH of 18 microunit/ml, with an exaggerated TSH response to TRH of 72 microunit/ml. His basal TSH fell to 7.6 and his TSH increment fell to 14.3 microunit/ml 24 h after DIMIT. The suppression of TSH was relatively prolonged. In four subjects, the TSH response to TRH was still blunted from 5-12 days after DIMIT. In one subject, the TSH increment returned to normal 15 days after DIMIT. DIMIT had no significant effect on PRL secretion. There was no evidence of toxicity in patients receiving DIMIT. DIMIT has effective thyromimetic activity in man, as shown by its significant and prolonged suppression of TSH secretion.     

Pituitary-thyroid function in spironolactone treated hypertensive women.

Four weeks high dose spironolactone treatment (Aldactone Searle, 100 mg q. i. d.) significantly enhanced the TSH (delta max. 8.5 +/- 4.1 vs. 4.6 +/- 3.1 microunits/ml, P less than 0.05) and T3 (delta max. 32 +/- 27 vs. 11 +/- 16 ng/100 ml, P less than 0.05) responses to an intravenous TRH/LH-RH bolus injection in 6 eumenorrhoeic euthyroid hypertensive women, without affecting basal serum TSH, T3 or T4 levels or the basal and stimulated LH, FSH and prolactin values (P greater than 0.10). The mean serum testosterone, 17-hydroxyprogesterone and oestradiol levels were also similar before and during therapy. Spironolactone, possibly by virtue of its antiandrogenic action, may exert its enhancing effect on pituitary-thyroid function by modulating the levels of receptors for TRH in the thyrotrophs or by altering the T3 receptor in the pituitary permitting a greater response to TRH.     

Bioactive follicle-stimulating hormone responses to intravenous gonadotropin-releasing hormone in boys with idiopathic hypogonadotropic hypogonadism

To test the hypothesis that exogenous pulsatile administration of GnRH will increase serum bioactive FSH (bFSH) levels, we studied four boys with suspected idiopathic hypogonadotropic hypogonadism (IHH). These boys presumably secreted relatively little GnRH. By virtue of their low baseline serum gonadotropin levels yet responsive pituitary gonadotrophs, these boys with IHH proved to be an excellent clinical model to test this hypothesis. Administration of GnRH (0.025 microgram/kg.dose) iv at 1- or 2-h intervals for 3-5 days resulted in an increase in serum bFSH after 91% of the GnRH doses. Serum immunoreactive FSH (iFSH) and LH (iLH) levels increased after 42% and 64% of the GnRH doses, respectively. Ninety percent of the iLH responses were concordant with bFSH responses, but only 33% of the iLH responses were concordant with iFSH responses. The serum bFSH responses occurred consistently within 20 min after GnRH administration and resulted in an increased serum bioactive to immunoreactive FSH ratio. By 60 min, serum bFSH levels had returned to preinjection levels. Serum testosterone and estradiol levels did not change during the period of GnRH administration in three of the four boys. We conclude that pulsatile, low dose iv GnRH administration in boys with IHH elicits significant serum bFSH increases by 20 min; the newly secreted FSH is preferentially enriched with increased in vitro FSH bioactivity, and it is rapidly cleared from serum (60 min). Therefore, serum bFSH measurements may provide a sensitive index of GnRH effects on the gonadotrophs.     

Five-day pulsatile gonadotropin-releasing hormone administration unveils combined hypothalamic-pituitary-gonadal defects underlying profound hypoandrogenism in men with prolonged critical illness.

Central hyposomatotropism and hypothyroidism have been inferred in long-stay intensive care patients. Pronounced hypoandrogenism presumably also contributes to the catabolic state of critical illness. Accordingly, the present study appraises the mechanism(s) of failure of the gonadotropic axis in prolonged critically ill men by assessing the effects of pulsatile GnRH treatment in this unique clinical context. To this end, 15 critically ill men (mean +/- SD age, 67 +/- 12 yr; intensive care unit stay, 25 +/- 9 days) participated, with baseline values compared with those of 50 age- and BMI-matched healthy men. Subjects were randomly allocated to 5 days of placebo or pulsatile iv GnRH administration (0.1 microg/kg every 90 min). LH, GH, and TSH secretion was quantified by deconvolution analysis of serum hormone concentration-time series obtained by sampling every 20 min from 2100-0600 h at baseline and on nights 1 and 5 of treatment. Serum concentrations of gonadal and adrenal steroids, T(4), T(3), insulin-like growth factor I (IGF), and IGF-binding proteins as well as circulating levels of cytokines and selected metabolic markers were measured. During prolonged critical illness, pulsatile LH secretion and mean LH concentrations (1.8 +/- 2.2 vs. 6.0 +/- 2.2 IU/L) were low in the face of extremely low circulating total testosterone (0.27 +/- 0.18 vs. 12.7 +/- 4.07 nmol/L; P < 0.0001) and relatively low estradiol (E(2); 58.3 +/- 51.9 vs. 85.7 +/- 18.6 pmol/L; P = 0.009) and sex hormone-binding globulin (39.1 +/- 11.7 vs. 48.6 +/- 27.8 nmol/L; P = 0.01). The molar ratio of E(2)/T was elevated 37-fold in ill men (P < 0.0001) and correlated negatively with the mean serum LH concentrations (r = -0.82; P = 0.0002). Pulsatile GH and TSH secretion were suppressed (P < or = 0.0004), as were mean serum IGF-I, IGF-binding protein-3, and acid-labile subunit concentrations; thyroid hormone levels; and dehydroepiandrosterone sulfate. Morning cortisol was within the normal range. Serum interleukin-1beta concentrations were normal, whereas interleukin-6 and tumor necrosis factor-alpha were elevated. Serum tumor necrosis factor-alpha was positively correlated with the molar E(2)/testosterone ratio and with type 1 procollagen; the latter was elevated, whereas osteocalcin was decreased. Ureagenesis and breakdown of bone were increased. C-Reactive protein and white blood cell counts were elevated; serum lactate levels were normal. Intermittent iv GnRH administration increased pulsatile LH secretion compared with placebo by an increment of +8.1 +/- 8.1 IU/L at 24 h (P = 0.001). This increase was only partially maintained after 5 days of treatment. GnRH pulses transiently increased serum testosterone by +174% on day 2 (P = 0.05), whereas all other endocrine parameters remained unaltered. GnRH tended to increase type 1 procollagen (P = 0.06), but did not change serum osteocalcin levels or bone breakdown. Ureagenesis was suppressed (P < 0.0001), and white blood cell count (P = 0.0001), C-reactive protein (P = 0.03), and lactate level (P = 0.01) were increased by GnRH compared with placebo infusions. In conclusion, hypogonadotropic hypogonadism in prolonged critically ill men is only partially overcome with exogenous iv GnRH pulses, pointing to combined hypothalamic-pituitary-gonadal origins of the profound hypoandrogenism evident in this context. In view of concomitant central hyposomatotropism and hypothyroidism, evaluating the effectiveness of pulsatile GnRH intervention together with GH and TSH secretagogues will be important.     

Endocrine, biochemical, and morphological studies of a pituitary adenoma secreting growth hormone, thyrotropin (TSH), and alpha-subunit: evidence for secretion of TSH with increased bioactivity

A 40-yr-old man who had acromegaly and hyperthyroidism due to a GH/TSH-secreting pituitary adenoma is described. Serum free T4 was 2.8 ng/dl, free T3 was 1.1 ng/dl, and TSH was 1.2-1.5 microU/ml; the latter was measured in an immunoradiometric assay with a sensitivity of 0.07 microU/ml. Serum TSH was immunologically identical to standard TSH and did not decrease during a T3 suppression test. Serum free alpha-subunit and the molar alpha-subunit to TSH ratio were high (6.1 ng/ml and 31.2, respectively). TRH administration induced significant increases in both GH (+129%) and alpha-subunit (+156%) levels. Conversely, dopamine infusion resulted in a decrease in serum GH (-66%) and alpha-subunit (-43%) levels, and subsequent administration of the dopamine antagonist sulpiride induced significant increases in both GH and alpha-subunit (+393% and +106%, respectively). Similarly, somatostatin infusion inhibited GH (-43%) and alpha-subunit (-61%) secretion. Serum TSH levels were not affected by TRH, dopamine, or somatostatin. The biological to immunological activity ratio of serum TSH purified by immunoaffinity chromatography and measured in an adenylate cyclase assay was significantly increased compared to that in serum from hypothyroid or euthyroid subjects [biological to immunological activity ratio, 6.9 +/- 0.2 (+/- SD) vs. 4.4 +/- 1.1; P less than 0.001]. In gel chromatography, the apparent mol wt of the patient's TSH was smaller than that of the controls. After adenomectomy, all of the altered parameters of pituitary function became normal. Double gold particle immunostaining of the adenomatous tissue showed that all of the cells contained secretory granules positive for GH and alpha-subunit, while very few cells were positive for TSH beta as well as GH and alpha-subunit. These data indicate that in this patient serum TSH had an apparent mol wt smaller than that of normal TSH and an increased biological activity which, along with the autonomous TSH secretion, account for hyperthyroidism in the presence of low normal TSH levels; alpha-subunit originated from the same adenomatous cells that secreted GH but not TSH, thus explaining the in vivo observation that alpha-subunit responses to several agents were dissociated from TSH responses and parallel to GH responses; and TSH and GH were colocalized in a minority of the neoplastic cells.