Immunoreactive and bioactive isoforms of human thyrotropin.

Isoforms of intrapituitary human TSH were separated by gel isoelectrofocusing, and their immunoreactivity analyzed by subsequent immunoblotting using polyclonal and monoclonal antibodies. Under these conditions, TSH polymorphism could be resolved as seven major isoforms (pI 8.6, 8.3, 8.0, 7.5, 7.0, 6.5, and 6.0) by both silver staining of the gels and binding to anti-TSH polyclonal antibodies. The distribution pattern of these forms appeared totally distinct from that of individual TSH alpha (pI 8.8, 8.4, 8.2, 7.6, 7.4, 6.8, 6.6, 5.8, and 5.4) and TSH beta (pI 8.7, 8.1, 7.2, 6.8, 6.2, and 5.8) subunits. While most anti-TSH polyclonal antibodies recognized neutral and alkaline isoforms of TSH (pI 8.6, 8.3, 8.0, 7.5, 7.0, 6.5, and 6.0) through beta determinants, they displayed a variable potency to bind acidic forms of the hormone (pI 5.8, 5.5, 4.8, and 4.5), in contrast to anti-TSH alpha antisera, which enlighted the broadest spectrum of isoforms. Monoclonal antibodies of various specificities largely reproduced this distribution, indicating that at least five distinct epitopes are coexpressed in the neutral and alkaline forms of TSH, but only two are expressed in the acidic ones. All of the forms were found to induce cAMP production and stimulate growth of FRTL-5 rat thyroid cells, although neutral forms proved to be definitely less potent than the others. We therefore, conclude that TSH isoforms differ in the expression of both their immunoreactive and bioactive domains and that the bioactive/immunoreactive ratio is not an accurate index for the biopotency of the hormone.

Glycoprotein hormone alpha-subunit response to growth hormone (GH)-releasing hormone in patients with active acromegaly. Evidence for alpha-subunit and GH coexistence in the same tumoral cell.

Basal serum concentrations of glycoprotein hormone alpha-subunit and its response to GH-releasing hormone (GHRH) were studied in 22 acromegalic patients and in normal subjects. Four out of 22 patients had a basal alpha-subunit concentration (1.2-3.5 ng/ml) clearly above the upper limit of the normal range. GHRH injection (1 microgram/kg body weight, bolus dose iv) produced a clear alpha-subunit response [mean % increase: 120 +/- 37 (SD)] in the 4 patients with elevated basal alpha-subunit levels. No increase in serum glycoprotein hormones (TSH, LH, and FSH) occurred. Selective adenomectomy in 2 patients resulted in normalization of both serum GH and alpha-subunit levels, as well as disappearance of the abnormal alpha-subunit response to GHRH. In in vitro studies, only these 2 adenomas secreted alpha-subunit in large amounts (534 and 388 ng/mg protein . 30 min) and was it further stimulated by GHRH (% increase: 83 and 126). Morphological studies done with protein A-gold particle immunotechnique demonstrated that in these adenomas the great majority of the cells contained secretory granules positive for both GH and alpha-subunit. We conclude that: 1) alpha-subunit hypersecretion is present in some acromegalic patients (about 20%), 2) GHRH stimulates alpha-subunit release both in vivo and in vitro only in patients with elevated basal alpha-subunit levels, and 3) in these patients alpha-subunit derives from a common adenomatous cell secreting both alpha-subunit and GH molecules.

Hyperthyroidism due to a pituitary adenoma composed of two different cell types, one secreting alpha-subunit alone and another cosecreting alpha-subunit and thyrotropin.

A 37-yr-old female presented with clinical signs and symptoms of mild hyperthyroidism, high serum levels of free T4 (24.2 pmol/L), free T3 (11.7 pmol/L), and sex hormone-binding globulin (157 nmol/L) as well as measurable (by immunofluorometric assay) serum TSH concentrations (1.9 mU/L) in the absence of any known methodological interference. The above finding indicated the presence of hyperthyroidism due to inappropriate secretion of TSH, whose neoplastic origin was documented by computed tomographic scan showing a 1-cm pituitary adenoma. The diagnosis was confirmed by elevated alpha-subunit levels (9.2 micrograms/L) and alpha-subunit/TSH molar ratio (25.2) as well as absent TSH suppression after T3 administration. TRH injection (200 microgram, iv) caused impaired TSH (from 3.0 to 4.8 mU/L) and unexpectedly exaggerated alpha-subunit (from 8.8 to 18.2 micrograms/L) responses. Such a discrepancy was also observed after other dynamic tests. Double gold particle immunostaining of the adenomatous tissue removed at surgery showed that all of the cells contained secretory granules positive for alpha-subunit, while very few cells were positive for TSH beta and alpha-subunit. In conclusion, the present study demonstrates the existence of TSH-induced hyperthyroidism due to a pituitary adenoma composed of two different cell types: one secreting alpha-subunit alone and another cosecreting alpha-subunit and TSH.

Sex hormone-binding globulin measurement in patients with inappropriate secretion of thyrotropin (IST): evidence against selective pituitary thyroid hormone resistance in nonneoplastic IST.

The differential diagnosis of the various forms of inappropriate secretion of TSH (IST), i.e. generalized thyroid hormone resistance (GRTH), selective pituitary resistance [non-neoplastic IST (nnIST)], and tumoral pituitary TSH hypersecretion [neoplastic IST (nIST)], mainly rests on clinical observation, skull imaging, and measurement of several parameters assessing peripheral thyroid hormone effects. Clinically, patients with GRTH usually display compensated hypothyroidism, while those with nnIST or nIST are hyperthyroid. Since sex hormone-binding globulin (SHBG) measurement has been shown to be a reliable parameter in distinguishing between euthyroid and hyperthyroid states, we evaluated serum SHBG levels in 39 patients with IST (7 with GRTH, 15 with nnIST, and 17 with nIST). The results were compared to those in 68 normal subjects, 76 hyperthyroid patients, and 31 hypothyroid patients. SHBG levels in patients with either GRTH or nnIST were similar to those in controls or hypothyroid patients [GRTH, 40.5 +/- 11.8 (+/- SD) nmol/L (range, 26.4-57.5); nnIST, 29.7 +/- 12.8 nmol/L (range, 6.8-46.8); controls, 36.7 +/- 21.7 nmol/L (range, 5.4-96.5); hypothyroid, 30.8 +/- 14.4 nmol/L (range, 10.4-63.3)]. On the contrary, SHBG levels in patients with either overt hyperthyroidism or nIST were significantly higher than those in the above groups [hyperthyroid, 149 +/- 111 nmol/L (range, 48-557); nIST, 99.5 +/- 54.7 nmol/L (range, 21.6-259)]. The apparent overlap of SHBG values between hyperthyroid patients and controls almost completely disappeared when comparisons were made with control groups matched for age and sex. Additional indices of peripheral thyroid hormone action (basal metabolic rate, cardiac systolic time intervals, and Achilles' reflex time) were normal in patients with GRTH, while they were in the hyperthyroid range in patients with nnIST and nIST. After successful treatment of hyperthyroidism, SHBG levels normalized in patients with nIST, but they did not change in patients with nnIST. In conclusion, the measurement of SHBG in patients with IST is useful in differentiating the neoplastic form from that due to thyroid hormone resistance, but it fails to distinguish between generalized and pituitary resistance to thyroid hormone action. Moreover, the present data suggest that the resistance to thyroid hormone action in patients with nnIST is not selective at the thyrotroph cell level, but also involves the hepatic SHBG-synthesizing cells, thus supporting the view that the various forms of thyroid hormone resistance could represent a continuum of the same defect with variable expression in different tissues.

Treatment of hyperthyroidism due to inappropriate secretion of thyrotropin with the somatostatin analog SMS 201-995.

The management of hyperthyroidism due to inappropriate secretion of TSH (IST) includes agents that selectively suppress TSH hypersecretion both in patients with TSH-secreting tumor [neoplastic IST (nIST)] in whom pituitary surgery was unsuccessful and in those with selective pituitary resistance to thyroid hormone action [nonneoplastic IST (nnIST)]. Among such agents, somatostatin administration has proven to be effective in blocking TSH hypersecretion, but its short plasma half-life prevented its use in long term therapeutic trials. The recent availability of a potent and long-acting analog of somatostatin (SMS 201-995, Sandostatin) prompted us to study its effects on serum TSH, alpha-subunit, and free thyroid hormone (FT4 and FT3) concentrations in five patients with nIST and three patients with nnIST. During short term SMS 201-995 administration (100 micrograms, sc, three times daily for 5 days) both serum TSH and alpha-subunit levels decreased in all patients with nIST (mean decrements, -86% and -85%, respectively), with concomitant normalization of serum FT4 and FT3 concentrations. In the three patients with nnIST, this treatment lowered serum TSH levels less well (mean decrement, -47%), although serum FT4 and FT3 levels normalized in one patient. Chronic SMS 201-995 (100 micrograms, sc, every 12 h for 1-7 months) treatment in four hyperthyroid patients (two with nIST and two with nnIST) resulted in a steady euthyroid state in both patients with nIST, with restoration of normal visual fields in one patient. In contrast, in both patients with nnIST, escape occurred after 2 weeks of therapy. We conclude that SMS 201-995 administration is effective treatment for patients with nIST, able to suppress TSH hypersecretion from the adenomatous thyrotrophs and, consequently, to restore clinical and biochemical euthyroidism in such patients. On the contrary, the inhibitory effects of SMS 201-995 on TSH secretion in patients with nnIST are weaker and transient.

Maturation of hypothalamic-pituitary-gonadal function in normal human fetuses: circulating levels of gonadotropins, their common alpha-subunit and free testosterone, and discrepancy between immunological and biological activities of circulating follicle-stimulating hormone.

The recent availability of both cordocentesis, a low risk and effective technique for fetal blood sampling, and ultrasensitive/highly specific two-site immunofluorometric assays (IFMA) for pituitary and chorionic glycoprotein hormone (I-LH, I-FSH, and I-CG) measurement prompted us to study the maturation of hypothalamic-pituitary-gonadal function in 114 normal human fetuses (49 females and 65 males) from 17-40 weeks gestation. The subjects were selected from 216 consecutive cordocenteses carried out for rapid karyotyping and diagnosis of fetal infection or hematological disorders. In addition, FSH bioactivity (B-FSH) was measured by rat Sertoli cell aromatase induction assay, glycoprotein hormone alpha-subunit (alpha-SU) by RIA, and circulating free testosterone (fT) by direct analog technique. No significant cross-reactions were recorded in the different measurement methods. In particular, alpha-SU did not interfere in any IFMA, and CG cross-reactivity in LH IFMA was 0.5%. Circulating I-LH, I-FSH, and B-FSH levels at 17-24 weeks gestation were significantly higher in female than in male fetuses (I-LH, 48 +/- 4 vs. 6.3 +/- 0.7 U/L; I-FSH, 35 +/- 2 vs. 0.7 +/- 0.1 U/L; B-FSH, 131 +/- 17 vs. 43.4 +/- 5.4 U/L). During the last weeks of gestation, a significant decrease in I-LH and I-FSH levels was seen in both female and male fetuses (I-LH, 0.24 +/- 0.05 and 1.0 +/- 0.3 U/L; I-FSH, 0.45 +/- 0.1 and 0.5 +/- 0.1 U/L), while serum B-FSH remained elevated, but the previously recorded difference between sexes disappeared (54.3 +/- 7.2 and 58.7 +/- 7.3 U/L). Circulating I-CG and alpha-SU levels at midgestation were elevated in both female and male fetuses (I-CG, 117 +/- 29 and 191 +/- 44 U/L; alpha-SU, 143 +/- 16 and 105 +/- 9 micrograms/L, respectively) and decreased thereafter (I-CG, 42 +/- 9 and 26 +/- 6 U/L; alpha-SU, 60 +/- 15 and 37 +/- 6 micrograms/L). Serum fT levels at midgestation were significantly lower in females than in males (4.3 +/- 0.9 vs. 10.0 +/- 0.8 pmol/L) and increased until term, when the difference between sexes disappeared (16.2 +/- 1.8 vs. 17.6 +/- 1.6 pmol/L).(ABSTRACT TRUNCATED AT 400 WORDS)

Dual activity of human pituitary thyrotrophin isoforms on thyroid cell growth.

Alkaline (pI 8.6-7.5) and neutral (pI 7.0-6.0) isoforms of human TSH have been isolated from a highly purified intrapituitary preparation by isoelectric focusing and compared for their respective actions on thyroid cell proliferation. Both TSH isoforms displayed the same ability to bind to porcine thyroid membranes as the original hormone preparation, indicating a similar recognition at the receptor sites. Alkaline forms showed a higher potency in inducing either cyclic AMP (cAMP) production or [3H]thymidine incorporation in FRTL-5 cells (half-maximal effective doses (ED50 values) = 0.25 and 0.29 nM respectively) compared with their neutral counterparts (ED50 values = 0.66 and 0.70 nM respectively). Increasing the concentration of alkaline forms in the presence of a half-maximal concentration of neutral TSH resulted in a profound inhibition of cell growth without a significant change in cAMP. Conversely, increasing the amount of neutral forms in the presence of a half-maximal dose of alkaline TSH resulted in an additive response for cAMP production but not in cell proliferation. To assess whether glycosylation might be responsible for the variation in hormone action, both alkaline and neutral TSH isoforms were tested for recognition of their carbohydrate chains by concanavalin A (Con A) and ricin. No major difference was found in binding to Con A, indicating that the contribution of carbohydrates to changes in hormone pI was not related to core branching. Very few galactose residues were accessible in either hormone fraction since little binding to ricin was observed. Isoelectric focusing of TSH forms before and after neuraminidase treatment revealed that neutral forms had a higher sialic acid content than alkaline TSH. In conclusion, the current findings show that TSH isoforms differentially affect cAMP production and cell growth. TSH fractions with a high sialic acid content and a low mitogenic activity behave as antagonists to the more active forms for cell proliferation. It is suggested that physiological control of TSH action at the thyroid gland may reside in the respective amounts of various TSH forms which, once bound to their receptor, can induce variable activation of post-receptor events while controlling cell proliferation.

Differential effect of glycosylation on the expression of antigenic and bioactive domains in human thyrotropin.

Enzymatic deglycosylation of human thyroid-stimulating hormone (hTSH) was shown to result in a mixture of partially and fully deglycosylated forms of the hormone by gel electrophoresis, silver staining and immunoblotting. Radioiodination of the enzymatic digest, followed by gel filtration and concanavalin A-Sepharose chromatography allowed to separate two different forms of partially deglycosylated [125I]hTSH and a fully deglycosylated hormone. The final recovery was of approx. 60% for [125I]hTSH deglycosylated in its beta-subunit, of 30% for [125I]hTSH missing the oligosaccharide in beta and one in alpha but only of 10% for [125I]hTSH deglycosylated in both the alpha- and beta-subunits. Gel electrophoresis under non-denaturing conditions showed that each form migrated distinctly from free subunits and reverse-phase high performance liquid chromatography after reduction and carboxymethylation identified the presence of the two subunits. Mapping of [125I]hTSH derivatives with polyclonal, monoclonal and anti-peptide antibodies allowed to identify two novel glycosylation-independent epitopes preserved in deglycosylated hTSH while the main immunogenic determinant was lost. When assayed in a bioassay with FRTL-5 cells, the hormone deprived of its beta-linked carbohydrate chain was found to be as effective as the native hormone on cAMP production and cell growth. In contrast, the fully deglycosylated derivative proved to stimulate cAMP release but appeared to be definitely less potent on thyroid cell growth. Our findings thus demonstrate that glycosylation of the alpha-subunit but not that of the beta-subunit is essential to express the domains involved in hTSH immunoreactivity as well as those controlling the post-receptor biological activity of the hormone.

Inappropriate secretion of thyrotropin by the pituitary.

Inappropriate secretion of thyrotropin (IST) is characterized by elevated serum free thyroid hormone and unsuppressed thyrotropin (TSH) levels, and results from either a TSH-secreting pituitary tumor (nIST) or a selective resistance to thyroid hormone action (nnIST). Although in most patients TSH levels are definitely high, in a quarter of the cases they are within the 'normal range'. In some of these cases, TSH had an elevated biologic activity and an apparent molecular weight smaller than in normals. The current availability of ultrasensitive TSH immunoradiometric assay, able to distinguish suppressed from unsuppressed TSH levels enables the recognition of the disease. The distinction between nnIST and nIST rests on clinical, neuroradiological, and biochemical criteria, the most useful of which are the alpha-subunit:TSH molar ratio (increased in nIST), and the evaluation of the TSH responses to thyrotropin-releasing hormone and high doses of 3,5,3'-triiodothyronine, both qualitatively normal in nnIST, while absent in nIST. The therapy of choice for patients with nIST is pituitary surgery, followed by irradiation in case of surgical failure. Chronic administration of bromocriptine is effective in a minority of cases. The long-acting somatostatin analogue SMS 201-995 has given promising results in 2 patients. In nnIST, bromocriptine is frequently uneffective, while small doses of 3,5,3'-triiodothyronine or 3,5,3'-triiodothyroacetic acid, a thyroid hormone derivative with a strong inhibitory effect on TSH secretion but poor thyromimetic activity on peripheral tissues, are effective in controlling TSH hypersecretion.

Thyrotropin alpha- and beta-subunit responses to thyrotropin-releasing hormone and domperidone in normal subjects and in patients with microprolactinomas.

Microprolactinoma is a particular pathological situation characterized by the presence of increased hypothalamic dopaminergic tone reactive to tumoral hyperprolactinemia. Since dopamine (DA) is a physiological regulating factor of the secretion of thyroid-stimulating hormone (TSH), we investigated the responses of serum TSH (holo-TSH) and its subunits (alpha-subunit: alpha-sub, and TSH-beta) to thyrotropin-releasing hormone (TRH) and domperidone (DOM; an antidopaminergic drug acting outside the blood-brain barrier) in 36 euthyroid subjects (20 controls and 16 patients with microprolactinoma) in order to evaluate the possible in vivo effects of DA excess on TSH subunit secretion. No significant difference in serum TSH increase after TRH (200 micrograms i.v.) was observed between patients with microprolactinoma and controls (TSH net incremental area under the curve, nAUC: 146 +/- 9, mean +/- SE, and 143 +/- 7.7 micrograms/l/60 min, respectively), while serum alpha-sub and TSH-beta responses were markedly reduced in patients with microprolactinoma as compared to those found in normals (alpha-sub nAUC: 3.0 +/- 0.5 vs. 19.8 +/- 2.2 micrograms/l/60 min, p less than 0.001; TSH-beta nAUC: 5.0 +/- 0.8 vs. 9.5 +/- 0.9 micrograms/l/60 min, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Precocious puberty in a boy with a PRL-, LH- and FSH-secreting pituitary tumour: hormonal and immunocytochemical studies.

The case of a 7-year-old boy affected with precocious puberty and a large intra- and suprasellar pituitary tumour is described. He had hyperprolactinemia and elevated serum LH, FSH and testosterone concentrations. Pre-operative dynamic hormonal studies showed a rise of PRL, LH and FSH levels after TRH (200 micrograms iv) and a rise of LH and FSH after GnRH (100 micrograms iv). Dopamine infusion (4 micrograms.kg-1.min-1 for 180 min) did not affect gonadotropins and greatly reduced serum PRL. GnRH analogue (buserelin, 0.5 mg sc t.i.d. for 10 days) administration inhibited both LH and FSH, but did not affect PRL concentration. Serum LH and FSH increased after ethinyl-estradiol (0.5 mg orally) administration, and were not affected by bromocriptine (5-7.5 mg/day for 10 days), which decreased serum PRL levels. The patient underwent transfrontal neurosurgery and a large tumour mass was completely removed. Morphological study of the excised tumour, by electron microscope double label immunotechnique, revealed that a large number of tumour cells (70-85%) were positive for PRL, LH and FSH, co-localized in the same secretory granule. After neurosurgery, serum PRL, LH, FSH and testosterone levels fell to within the normal limits. Two months later the patient was well and signs of precocious puberty had partially regressed; hormone levels were in the normal range and MR imaging control did not demonstrate any residual lesion in the sellar region.

Biological and immunochemical characterization of recombinant human thyrotrophin.

Recombinant human thyroid-stimulating hormone (recTSH) has recently been engineered to detect metastatic lesions in patients operated on for thyroid cancer. In this report, we have compared the microheterogeneity, carbohydrate (CHO) content, mitogenic potency and immunoreactivity of the biotechnology product to those of human TSH of pituitary origin (pitTSH). Compositional analysis revealed that recombinant (rec) TSH produced in Chinese hamster ovary cells was overglycosylated compared with the native hormone (21 and 14%, respectively) with a higher amount of sialic acid and lack of N-acetylgalactosamine. Electrofocusing followed by immunoblotting resolved recTSH into six glycoforms with pIs ranging from 6.0 to 8.6, which were converted to a major species of pI 8.9 by sialidase treatment. pitTSH contained five main isoforms of pI 6.5-8.2 distinct from those of recTSH and partially resistant to sialidase. Binding activity of both human TSHs to porcine thyroid membrane receptors was found to be similar, but recTSH appeared to be 20% active compared to pitTSH in eliciting cAMP production and cell growth in rat FRTL-5 cells. Immunoreactivity of the recombinant hormone was investigated using polyclonal and monoclonal antibodies raised against the native hormone or synthetic peptide sequences of its subunits. While rec- and pitTSH were recognized to a similar extent by anti-protein antibodies, they exhibited a different binding pattern to antipeptide antibodies. Serial dilution of anti-alpha 1-25, anti-alpha 26-51, anti-beta 96-112 antisera bound recTSH to a greater extent than pitTSH, while anti-beta 31-51 and anti-beta 53-76 displayed similar recognition toward both preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymorphism of thyrotropin and alpha subunit in human pituitary adenomas.

To understand better why patients with TSH-secreting pituitary tumors exhibit variable degree of hyperthyroidism, we analyzed the various isoforms of TSH and alpha-subunit secreted by 4 TSH-secreting adenomas in primary culture. All patients had macrodenomas clinically associated with hyperthyroidism with normal to elevated TSH plasma levels. The in vivo molar alpha/TSH ratio ranged from 18.4 to 3.8. The hormone material secreted over 4 to 48 h in culture was separated by gel isoelectrofocusing, eluted and estimated by immunoassays. The release of free alpha-subunit was noticeably different among adenomas. Three tumors were found to release an homogeneous and acidic (pI = 5.4-4.5) species totally unrelated to the alpha-subunit dissociated from intrapituitary TSH (5 isoforms, pI = 8.8-5.8) while another was more heterogeneous (pI = 8.8, 8.4, 7.6, 6.8, 5.8, 5.4-4.5). Tumoral TSH exhibited at least six detectable isoforms (pI = 8.6, 8.3-8.0, 7.5, 7.0, 6.5, 6.0) very similar to those present in a purified intrapituitary hormone preparation. While intrapituitary TSH was composed of 70% of alkaline (pI = 8.6-7.5), 25% of neutral (pI = 7.0-6.0) and 5% (pI = 5.8-4.5) of acidic forms, these species were found to be more evenly distributed in adenomatous secretion (43%/42%/15%). The TSH-secreting tumors thus appeared to relase preferentially neutral and acidic forms of TSH than alkaline components but for one tumor, this ratio could be modified by chronic incubation with TRH. When assayed for their capacity to stimulate 3H-thymidine incorporation in FRTL-5 cells, neutral TSH appeared definitely less potent than the alkaline and acidic isohormones. Altogether, these data show that pituitary adenomas synthesize normal forms of TSH but release them in variable amount in the medium. When circulating in the blood, the ratio between active and inactive isoforms of TSH may thus be responsible for the variable stimulation of the thyroid gland observed in the patients.

Treatment of inappropriate secretion of thyrotropin with somatostatin analog SMS 201-995.

Inappropriate thyrotropin secretion (IST) may originate from either neoplastic disease (nIST) or non-neoplastic resistance to thyroid hormone (nnIST). An inhibitory effect of somatostatin on TSH secretion has been documented. In an attempt to elucidate the possible therapeutic effect of this peptide on nIST and nnIST, a study was conducted in 7 such patients. Sandostatin (SMS 201-995) was administered in daily doses of 100 micrograms for several days to 1 month. Four patients with nIST responded with a fall in circulating TSH as well as alpha-subunit with concomitant normalization of free thyroxine and clear symptomatic improvement. In the 3 nnIST patients this effect was considerably less apparent and a partial TSH escape was observed on long-term treatment in 2 cases. The importance of somatostatin and its analogs in the management of thyroid malignancy is stressed.

Pituitary glycoprotein hormones in chronic renal failure: evidence for an uncontrolled alpha-subunit release.

Chronic renal failure affects the secretion of pituitary glycoprotein hormones by mechanism(s) that are still unknown. In this study, we evaluated serum concentrations of TSH, free thyroid hormones (FT4, FT3), LH, FSH, testosterone (T), and alpha-subunit (alpha-SU) in 25 uremic patients (19 males and 6 females), both in basal conditions and after stimulatory and inhibitory tests. Basal TSH levels were in the normal range, while FT4 and FT3 were significantly lower than in controls. Basal LH and FSH levels were clearly elevated. The LH levels measured by RIA were significantly higher than those measured by a "two-site" IRMA (48.9 +/- 16.5 vs 18.0 +/- 8.6 U/L) due to alpha-SU cross-reactivity in RIA. FSH bioactivity was normal in all patients. Serum T was normal in all but 3 males, without any correlation with LH and FSH levels. Serum alpha-SU concentrations were significantly elevated (5.5 +/- 3.0 vs 0.4 +/- 0.2 microgram/L). Of 17 patients, the TSH response to TRH was normal in 9 and impaired in 8, whereas alpha-SU response was normal in 5 and impaired in 12. In 8 male patients, TRH plus GnRH caused a normal LH and FSH response in 4 patients, while the increase of alpha-SU was normal in only one patient and significantly lower than expected in subjects with comparable basal alpha-SU levels in the remaining 7. In 2 patients, the combined suppression test with T undecanoate and T3 completely blocked TSH secretion and reduced both LH and FSH release by 30%, while serum alpha-SU levels did not change.(ABSTRACT TRUNCATED AT 250 WORDS)