Gel chromatography of immunoextracted plasma calcitonin in response to the calcium clamp in healthy males

Calcitonin as Biomarker for the Medullary Thyroid Carcinoma

Calcitonin (CTN) is a polypeptide hormone consisting of 32 amino acids with a disulfide bridge between position 1 and 7 that is mainly produced by the C-cells of thyroid gland. The measurement of CTN concentrations in blood reflects C-cell activity and is performed in general by immunoassay methods. However, there are analytical, physiological, pharmacological, and pathological factors that can influence results of serum CTN values. Due to the influence of these factors, there is a high variability in assay-dependent cutoffs used to discriminate between MTC, C-cell hyperplasia (CCH), and the absence of the pathological impairment of C-cells. There is a lot of evidence that the measurement of serum CTN concentrations in patients with thyroid nodules can lead to an earlier diagnosis of MTC or CCH than the exclusive use of imaging procedures and/or fine-needle aspiration cytology. Basal CTN concentrations higher than 60-100 pg/mL are highly indicative for the diagnosis MTC. In the range between cutoff and 60 pg/mL CTN, both MTC and HCC may be a relevant diagnosis. PCT and CTN appear to have a comparable diagnostic capability to diagnose MTCs. However, "positive" PCT values of more than 50 pg/mL may be reached also in subclinical infections and will lead, therefore, to an overdiagnosis of the tumor. Pentagastrin- or calcium-stimulated serum CTN concentrations higher than cutoff values might improve diagnostics of MTC, but the non-availability of the first and the lacking of relevant cutoff values for the second tool favors the use of only basal values currently.

Measurement of calcitonin by immunoassay analyzers

BACKGROUND

Since Nichols Institute Diagnostics (NID) ended production of their automated calcitonin immunoassay, evaluation of an alternative calcitonin assay was necessary.

METHODS

Calcitonin measured by the NID procedure was compared with a test from Diagnostic Products Corporation (DPC). Calcitonin was also measured by assays from DiaSorin (DS) and Scantibodies (SC).

RESULTS

In 187 samples, detection failed either by NID (39%) or DPC (96%) assay; in 35% of samples, the tests agreed for non-measurable calcitonin. The regression line DPC=0.78 x NID-0.3 (r=0.998) fitted results from 236 samples with detectable calcitonin. A linear relationship, albeit with scattering at low concentrations, was observed. Importantly, stimulation by pentagastrin above basal calcitonin concentrations yielded similar results with both assays. Comparisons (DPC=0.80 x DS-3.4 and DPC=0.81 x SC-1.1) confirmed an aberrant calibration of the DPC test. To overcome the method bias, we propose a multiplication factor of 0.8 to convert NID to DPC results.

CONCLUSIONS

Apparently due to non-specific effects, the DS and SC assays produced calcitonin results in samples from completely thyroidectomized patients, while the DPC assay correctly failed to detect calcitonin. Thus, the DPC assay on an Immulite 2000 analyzer may be used as a more accurate substitute for NID if the different calibration is noted.

Evidence that peroral calcium does not activate the gastrin-ECL-cell axis in the rat

The ECL cells are histamine- and pancreastatin-secreting endocrine cells in the oxyntic mucosa, thought to release a blood Ca2+-lowering peptide hormone upon stimulation by gastrin. Previously, we have shown that the ECL cells do not respond to perturbations in blood Ca2+. In the present study, we examine if Ca2+ in the gastric lumen will affect the activity of the gastrin-ECL-cell axis. Freely fed or food deprived (48 h) rats were given an oral load of CaCl2 (or NaCl), and the blood Ca2+ concentration was monitored. The serum gastrin concentration at sacrifice, 3 h after ingestion of CaCl2, was measured together with two parameters of ECL cell activity: the oxyntic mucosal histidine decarboxylase (HDC) activity and the serum pancreastatin concentration. The circulating concentrations of calcitonin and parathyroid hormone (PTH) were also measured. Oral CaCl2 raised the blood Ca2+ in a dose-dependent manner. The two highest doses (which caused damage to the oxyntic mucosa) raised the serum gastrin concentration and the HDC activity in both fed and fasted rats; the serum pancreastatin concentration remained unaffected. Oral CaCl2 raised the serum calcitonin concentration and lowered the serum PTH concentration. The effects of high doses of oral CaCl2 on the serum gastrin concentration and on the oxyntic mucosal HDC activity could be reproduced by a high dose of NaCl. Thus the effects are probably not due to Ca2+ per se. We conclude that the gastrin-ECL-cell axis in the rat does not respond to peroral Ca2+. Since the ECL cells do not respond to either circulating or peroral Ca2+ they are unlikely to secrete a calciotropic hormone.

Effect of acute endurance and strength exercise on circulating calcium-regulating hormones and bone markers in young healthy males

Physical activity plays a role in the maintenance of the skeleton but the mechanical, metabolic and hormonal mechanisms involved are largely unknown. The influence of acute endurance and strength exercise on circulating levels of calcitonin, parathyroid hormone (PTH), PTH-related peptide (PTHrP), osteocalcin, carboxyterminal cross-linked telopeptide of type I collagen (ICTP) and ionized calcium (Ca2+) was therefore evaluated. Eight healthy young males performed three exercise bouts on separate occasions: endurance exercise, i.e. cycling on a cycle ergometer for 45 min at 55% of Vo2max (E55%) and 15 min at 85% of Vo2max (E85%) and strength exercise at 85% of three repetitions maximum using a leg-press device (STR). Control experiments included the same subjects with the same time schedule but without exercise. Blood samples were taken before, immediately after exercise and during the recovery period. Hormones and bone markers were measured by use of various immunoassays. There was no obvious influence on calcitonin and PTHrP levels, whereas PTH was increased after strength exercise. ICTP and osteocalcin levels correlated positively at all times and showed regular variations. In comparison with the controls, ICTP levels showed a more pronounced decrease following physical activity whereas osteocalcin followed the same pattern as the controls except for after prolonged endurance exercise when a decrease was abolished. In conclusion, an increase in PTH after strength exercise and a pronounced decrease in ICTP after all exercise together with a relative increase in osteocalcin after prolonged endurance exercise might reflect some mechanisms involved in the positive effect of physical activity on bone mass.

Expression of the calcitonin gene family in medullary thyroid carcinoma

The regulatory peptide calcitonin was discovered in 1962. During the last decade it has been demonstrated to be part of a gene family. Calcitonin is synthesized in the parafollicular cells (C cells) of the thyroid gland. These cells give rise to an endocrine tumor, medullary thyroid carcinoma (MTC), which is found in a sporadic and an inherited form. Calcitonin is used as a tumor marker for MTC. The calcitonin gene was demonstrated in 1981 to give rise to an alternative peptide product, alpha-CGRP, and a second gene encoding a very similar peptide, beta-CGRP, has also been identified. A third CGRP-like peptide, amylin, was identified in 1986. This article summarizes the present knowledge about gene structure, regulation of gene expression, and expression of the calcitonin gene family in MTC and in MTC-derived cell lines. The methods employed for detection of gene expression and for measurement and characterized of peptide products are described, and finally the relevance of biochemical tumor markers is discussed in relation to the new diagnostic methods for inherited MTC based on molecular biological techniques.

Perturbations in blood Ca(2)+ do not affect the activity of rat stomach enterochromaffin-like cells

BACKGROUND

Gastrin stimulates uptake of Ca(2)+ into bone and causes transient hypocalcemia, possibly by releasing a peptide hormone from enterochromaffin-like (ECL) cells, which are histamine- and peptidehormone-producing cells in the acid-producing part of the stomach. However, if ECL cells secrete a calciotropic hormone, it is to be expected that their activity is affected by the serum Ca(2)+ concentration.

METHODS

Food-deprived male rats were infused with human (Leu)15-gastrin-17 and/or ethylenediamine-tetraacetic acid and CaCl(2). The blood Ca(2)+ level was monitored throughout the experiments (3 h), and the serum concentrations of gastrin, parathyroid hormone, and calcitonin were measured at death. The activity of the ECL cells was assessed by measuring the histidine decarboxylase (HDC) activity.

RESULTS

Gastrin produced the expected increase in HDC activity, but neither hyper- nor hypo-calcemia affected the RDC activity of either hypo- or hyper-gastrinemic rats.

CONCLUSION

Perturbations in blood Ca(2)+ do not seem to affect ECL cells, which is at odds with the view that ECL cells harbor a calciotropic hormone.

Circulating monomer-like calcitonin in osteoporotic patients

Physiological concentrations of monomeric calcitonin can inhibit osteoclastic bone resorption in vitro. We therefore investigated the circulating molecular forms, including monomer-like calcitonin, and their concentrations in 9 men and 9 women with established osteoporosis. Calcitonin was immunoextracted from serum by the use of rabbit calcitonin antibodies coupled to Sepharose 4B. The lyophilized extracts were incubated with 6 M urea overnight and gel chromatographed in a fast protein liquid chromatography (FPLC) system; calcitonin was measured by radioimmunoassay in the fractions. FPLC disclosed immunoreactive calcitonin of three different molecular sizes in the patients. The two largest forms were approximately 30 and 10 kDa and one eluted at the same position as monomeric calcitonin (3.4 kDa). After extraction and FPLC we found slightly higher calcitonin concentrations in osteoporotic women than previously reported levels in age-matched healthy women. Male patients had higher levels than female patients. None of the osteoporotic patients lacked monomer-like calcitonin. There was no significant correlation between the extracted total or monomer-like calcitonin and bone mineral density of the femoral neck. It is concluded that the circulating calcitonin in both male and female patients comprises three different molecular forms and that there is no deficiency of the monomer-like form. The calcitonin levels in the female patients were slightly higher than in a previous control group.

Serum calcitonin forms and concentrations in young and elderly healthy females

To further investigate the role of calcitonin (CT) in normal physiology we studied circulating forms and the secretion after "calcium clamp" in young and elderly healthy females. Heterogeneity of CT in serum was disclosed after immunoextraction, fast protein liquid chromatography, and radioimmunoassay in young (27 +/- 3 years; mean +/- SD, n = 6) and elderly females (69 +/- 6 years, n = 11). Three distinct molecular forms appeared with approximate mol wt of 30, 10, and 3-4 kDa. All young women studied had considerable amounts of circulating monomer-like CT whereas several elderly had undetectable or low levels. The influence of age on basal and calcium stimulated, immunoextracted CT in serum was also studied in young (26 +/- 4 years; mean +/- SD, n = 13) and elderly (63 +/- 6 years; n = 12) healthy females. The calcium stimulation was carried out by means of the standardized calcium clamp method, where calcium was kept on a presettled level at 1.45 mmol/liter (+/- 2%) for 60 minutes. CT was immunoextracted from serum in all series of experiments with a polyclonal antiserum directed against the mid- and carboxyterminal region of the CT molecule, and the amount of extracted CT was determined by radioimmunoassay using another polyclonal antiserum against the carboxyterminal portion. After calcium infusion, the increase in CT was significantly higher in young women than in elderly (P < 0.05). At basal conditions, the CT levels were not significantly different but slightly higher in young than in elderly females. In conclusion, several elderly women lack monomer-like calcitonin in serum in contrast to young women.(ABSTRACT TRUNCATED AT 250 WORDS)

Pronounced elevation in circulating calcitonin in critical care patients is related to the severity of illness and survival

OBJECTIVE

To study circulating levels of calcitonin in critically ill patients in relation to the severity of illness and survival.

DESIGN

Cross-sectional and prospective.

SETTING

The ICU in Gävle hospital, a secondary non-teaching hospital.

PATIENTS

37 consecutive ICU patients.

MEASUREMENTS AND RESULTS

Serum calcium and immunoreactive calcitonin (iCT) were measured and the Apache II and the Multiple Organ Failure (MOF) scores were recorded during the first 24 h in the ICU. Patients were followed for hospital survival. Profound increase in circulating iCT was seen (mean 591, median 184, range 8-3445 pg/ml) in the studied sample and only 11% of the patients showed normal levels (< 40 pg/ml). iCT was higher in septic than nonseptic patients (p < 0.004) and was correlated to two indices of severity of illness (r = 0.50, p < 0.006 versus the Apache II score and p = 0.55, p < 0.003 versus the MOF score). Furthermore, iCT was correlated to the length of stay in the intensive care unit (r = 0.56, p < 0.001) and was elevated in the patients who did not survive when compared to survivors (p < 0.03). iCT was not significantly related to the degree of serum calcium (mean 2.22 +/- 0.15 SD mmol/l). Gel chromatography in a fast protein liquid chromatography (FPLC) system of serum from 4 patients with elevated iCT disclosed that a majority of the measured CT was not due to monomeric CT, but high molecular CT.

CONCLUSIONS

Pronounced elevations in circulating iCT were seen during the first 24 h critically ill patients. As the major part of the iCT consisted of high molecular weight CT this would not induce hypocalcemia. Rather, the elevated iCT would be regarded as a part of the metabolic responses to illness.

Polyamines regulate human medullary thyroid carcinoma TT-cell proliferation and secretion of calcitonin and calcitonin gene-related peptide

The significance of polyamines for the neoplastic proliferation and secretion of calcitonin (CT) and calcitonin-gene-related peptide (CGRP) by the human medullary thyroid carcinoma TT cell line was investigated. TT cells were cultured in vitro for 6 days with or without additions of pathway inhibitors of polyamine biosynthetic enzymes. Treatment of the cells with 1 mM of the specific L-ornithine decarboxylase (ODC) inhibitor DL-alpha-difluoromethylornithine (DFMO) resulted in a 97% decrease in ODC activity, lowered contents of putrescine (96%) and spermidine (85%) and cell proliferation rates (90%) along with a compensatory 15-fold increase in S-adenosyl-L-methionine decarboxylase (SAMDC) activity. DFMO treatment also led to a decrease in cellular content of CT (33%) and CGRP (26%), while the drug enhanced secretion of CT (31%) but depressed that of CGRP (26%), and elevated the ratio of CT to CGRP secreted into the medium by 74%. Ethylglyoxal bis(guanylhydrazone) (EGBG), a SAMDC inhibitor, at 100 microM evoked a similar reduction of cell proliferation and lowered the content of spermine by 81%. Furthermore, EGBG treatment caused a 34-fold increase in ODC activity and a subsequent 35-fold build-up of putrescine, but also seemed to stabilize SAMDC as evidenced by a highly enhanced SAMDC activity (approximately 200-fold) during enzyme assays in the absence of the inhibitor. EGBG exposure resulted in an increase in cellular CT content (110%) and secretion of the hormone (82%), while not affecting CGRP content or release.2+ EGBG effects were partially counteracted by DFMO.(ABSTRACT TRUNCATED AT 250 WORDS)

A new highly sensitive radioimmunoassay for human calcitonin useful for physiological studies

A highly sensitive and specific radioimmunoassay (RIA) for human calcitonin-like immunoreactivity (CT-LI) has been developed. The assay is performed directly without extraction and may be used for measurements in plasma or serum as well as buffer solutions. The detection limit of the assay is < 0.4 pmol/l, intra- and interassay variations 5 and 10%, respectively when calculated from a control sample within the range of normal concentrations. The recovery of calcitonin (CT) varied between 87 and 118% in the concentration range 10-130 pmol/l. Measurements of CT-LI in sera from 70 normal individuals, showed significantly lower concentrations in women as compared to men, 7.4 pmol/l +/- 2.1 pmol/l and 9.1 pmol/l +/- 2.2 pmol/l, respectively (mean +/- S.D.), P < 0.005. The chromatographic profile of immunoreactive CT in normal serum was investigated by gel chromatography and high pressure liquid chromatography (HPLC) and showed heterogeneity of circulating CT-LI, but with the majority eluting corresponding to the elution position of synthetic human CT. The study of physiological variations in CT levels has so far been hindered by the limitations in assay sensitivity. It is hoped that the significantly improved sensitivity of the presently described assay may contribute towards the elucidation of the physiological functions of CT.

Calcium homeostasis in pregnancy during long-term heparin treatment

OBJECTIVE

To investigate the effect of subcutaneous heparin treatment on calcium homeostasis in pregnancy.

DESIGN

A longitudinal case-control observational study.

SETTING

Department of Obstetrics and Gynaecology, Karolinska Hospital, Stockholm, Sweden.

SUBJECTS

36 pregnant women with previously verified thromboembolic complications and 23 healthy pregnant control women similar in age, parity, weight, and smoking habit.

INTERVENTIONS

Thromboprophylaxis during pregnancy and 6 weeks post partum was given with subcutaneous heparin twice daily to the 36 women with a history of thromboembolic complications, 16 received an average dose of 24,500 IU/day and 20 a mean dose of 17,300 IU/day. Venous blood and urine samples were obtained every 4 weeks.

MAIN OUTCOME MEASURES

Serum concentrations of total calcium, ionized calcium, calcitonin and urinary calcium.

RESULTS

Women on high-dose heparin treatment showed significantly higher concentrations of total and ionized calcium and of calcitonin in serum and significantly lower concentrations of calcium in urine than did 23 normal pregnant controls. The differences were most pronounced in the third trimester. The results obtained in the low-dose heparin group were between those in the high-dose and the control groups. At 8 weeks postpartum there were no significant differences between the heparin-treated women and the controls. No significant differences were found during pregnancy in haematocrit, liver or renal function, serum levels of albumin, phosphate, magnesium, alkaline phosphatase, parathyroid hormone or urinary cyclic AMP.

CONCLUSIONS

Heparin treatment during pregnancy results in changes in calcium homeostasis and a dose-dependent response is suggested.

Parathyroid hormone-related peptide in human milk measured by a mid-molecule radioimmunoassay

Several peptide hormones and growth factors have been found in human milk, and we present here the results of measurements of parathyroid hormone-related peptide (PTHrP). A radioimmunoassay (RIA) using a polyclonal antiserum against the mid-region of the molecule has been developed. In milk collected during the first 6 days after parturition, the PTHrP concentrations showed large interindividual variations ranging from 0.3 to 13.7 nmol-Eq/L (0.5 to 24.4 ng-Eq/mL) (n = 67) and increased between days 3 and five postpartum. PTHrP also increased during the first 4 collecting days when measured in milk from the same mother during a prolonged period. On fast-protein liquid chromatography (FPLC), the bulk of PTHrP eluted with a molecular weight of approximately 10 to 12 kd after treatment with urea. After mid-molecule immunoaffinity extraction of PTHrP from milk, higher levels were obtained by the mid-molecule RIA than by an aminoterminal assay, indicating that all fragments did not contain the aminoterminal. Parts of immunoextracted milk PTHrP stimulated cyclic adenosine monophosphate (cAMP) production in rat osteosarcoma cell line, UMR-106. In conclusion, we have found PTHrP-like immunoreactivity in human milk using a mid-region RIA. Parts of the immunoextracts also contained the aminoterminal and possessed PTH-like bioactivity. Whether PTHrP in human milk plays a physiological role in the maternal breast or in the newborn gastrointestinal tract is unknown, but the present observations demonstrate that a portion of the PTHrP is at least potentially biologically active.

Effect of calcitonin deficiency on bone density and bone turnover in totally thyroidectomized patients

To investigate the influence of calcitonin deficiency on bone turnover and density we studied 25 premenopausal female and 12 male patients (age 23 to 49 years) who had undergone total thyroidectomy for differentiated thyroid cancer 1 to 15 years previously. Basal and calcium stimulated extractable calcitonin, representing the monomeric, biologically active form of the hormone, was lacking or markedly decreased in all patients. There was a relative increase of urine hydroxyproline excretion (an index of osteoclastic bone degradation) in relation to serum osteocalcin (an index of osteoblastic bone formation) indicating an imbalance of bone turnover with a tendency to increased degradation in all patients. Total and trabecular bone density, measured with quantitative computed tomography at the distal forearm were significantly decreased in the male and normal in the female patients, without a relation to the duration of the calcitonin deficiency. The study indicates that patients with calcitonin deficiency, suppressive thyroid hormone treatment, or both may have a higher risk of increased bone degradation and osteopenia. Whether the effect is more due to calcitonin deficiency or thyroid hormone therapy, cannot be concluded from this study design. The fact that only the male patients had a decreased bone density may be due to a lower parathyroid activity in our female patients and the greater thyroidectomy-induced decrement of monomeric calcitonin in our male patients compared with male controls.

A rapid extraction method for serum calcitonin

A rapid, simple and reliable extraction method for calcitonin from serum has been developed. 2 volumes of acidic ethanol and 1 volume of serum were mixed, centrifuged, and the supernatant was evaporated to dryness. The extracts were reconstituted in assay buffer before radioimmunoassay was performed. Basal concentrations of calcitonin after extraction were 5.4 +/- 3.0 pg-equivalents/ml (mean +/- SD), females, n = 48 and 8.8 +/- 5.5 pg-equivalents/ml, males, n = 42. Calcitonin was detectable in serum from all males and from 90% of the females. The concentrations in males were significantly higher (P less than 0.001). There was a more pronounced calcitonin response in males (n = 12) than in females (n = 12) to a calcium clamp (P less than 0.01). Gel chromatography of serum from patients with medullary thyroid carcinoma on a Sephadex G-75 column and a TSK G 2000 SW column in a fast protein liquid chromatography system, disclosed that the ethanol extraction excluded the high mol mass forms of calcitonin. We propose the acidic ethanol extraction as a convenient method for routine measurements of calcitonin.

Immunoextracted calcitonin in human gastric secretion

Immunoreactive calcitonin (iCT) has been demonstrated in human gastric juice after immunoextraction with immobilized antibodies and subsequent radioimmunoassay. The basal levels were 4.5 +/- 3.1 (mean +/- SD) pg-Eq/ml gastric juice; range 1.2-9.1 pg-Eq/ml; n = 7, and after stimulatory gastric secretion test with pentagastrin 0.3 +/- 0.2 pg-Eq/ml; range 0.1-0.7 pg-Eq/ml; n = 7 (p less than 0.01). The main fraction of iCT from gastric juice eluted in the same region as synthetic human calcitonin (hCT) on Sephadex G-75 gel chromatography. Reverse phase chromatography in a fast protein liquid chromatography (FPLC) system revealed a slightly less hydrophobic character of the iCT from gastric juice compared to synthetic monomeric hCT. The results were further confirmed by using an additional antiserum. In plasma, the calcitonin (CT) levels were after immunoextraction at the basal state 6.6 +/- 1.7 pg-Eq/ml (mean +/- SD); range 5.1-10.1 pg-Eq/ml; n = 7 and after pentagastrin stimulation 9.4 +/- 5.4 pg-Eq/ml; range 6.3-18.5 pg-Eq/ml; n = 7.

Evidence for precursors of calcitonin/PDN 21 in human milk

Large amounts of immunoreactive PDN-21 (iPDN -21) were found in human milk in concentrations similar to those of immunoreactive calcitonin (iCT): 187 +/- 73 pM (mean +/- S.D.) vs 210 +/- 83 pM. (n = 17). Calcitonin (CT) was immunoextracted from milk by means of CT antibodies coupled to Sepharose 4B, and the extracts were gel-chromatographed on Sephadex G-75 after treatment with 6 M guanidine HCl. iCT and iPDN-21 in the fractions were determined with radioimmunoassay. The main part of iCT eluted as high molecular weight forms and these fractions also contained iPDN-21. Enzymatic cleavage of immunoextracted milk CT by trypsin demonstrated that iPDN-21 could be split apart from the high molecular weight forms and be recovered at the position of synthetic human PDN-21 on gel chromatography. iCT was eluted in the region of monomeric CT and as larger forms. Since PDN-21 constitutes the carboxyterminal of preprocalcitonin, our results indicate that human milk contains precursors of calcitonin.

The influence of sex steroid hormones on plasma calcitonin response to the calcium clamp in normal subjects

The influence of sex steroid hormones on plasma calcitonin levels in healthy subjects was studied in 15 males and 10 premenopausal (PREMF) and 12 postmenopausal females (PMF). A standardized ionized calcium stimulus was achieved by means of the calcium clamp technique, and a sensitive RIA was used to determine immunoreactive CT (iCT) in plasma. Plasma iCT levels increased in response to the calcium clamp with an initial peak at 15 or 30 min. The iCT levels then declined but remained at an elevated level for the rest of the 180-min infusion period in all three groups. In males a positive correlation was found between the serum testosterone levels at 0 min and the estimates for initial iCT response, i.e., the change between 0 and 15 min (r = 0.80, n = 11, p less than 0.01), between 0 and 30 min (r = 0.56, n = 15, p less than 0.05) and between 0 and the maximum value (r = 0.68, n = 15, p less than 0.01). In the two female groups no such correlation was found. Serum 17 beta-estradiol or dehydroepiandrosterone sulfate concentrations were not correlated either to basal iCT levels or to the iCT response to the calcium clamp. PMF had lower levels of 17 beta-estradiol than PREMF (p less than 0.001), while the testosterone levels were similar. The iCT levels and response to the calcium clamp showed no significant difference in the two groups. The results indicate that sex difference in the plasma CT levels may be related to different testosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Monomeric serum calcitonin and bone turnover during anticonvulsant treatment and in congenital hypothyroidism

Decreased basal and calcium-stimulated calcitonin serum levels have been found in children with congenital hypothyroidism and in those receiving anticonvulsant drugs. The purpose of our investigation was to confirm these results using a new technique for calcitonin measurement and to study the effect on bone turnover. Calcitonin serum levels were measured with two different antibodies before and after a low-dose Ca infusion in patients receiving phenytoin, primidone, carbamazepine, or valproate and in patients with congenital hypothyroidism receiving L-thyroxine. In comparison with control values, basal and Ca-stimulated extractable calcitonin, representing the monomeric and biologically active form of the hormone, were moderately decreased in patients with epilepsy receiving phenytoin and primidone, and severely decreased in patients with hypothyroidism. Ca and bone metabolism were normal, except for an elevated renal threshold for phosphate (indicating phosphate conservation) in patients receiving phenytoin and primidone, and increased fasting urinary excretion of Ca and hydroxyproline (indicating increased bone resorption) in patients with hypothyroidism. The secretory capacity of the C cells for monomeric calcitonin is decreased in children receiving treatment with some, but not all, anticonvulsant drugs, and lacking in patients with hypothyroidism. Patients with calcitonin deficiency may be prone to osteopenia if the tendency to increased osteoclastic activity is aggravated by secondary hyperparathyroidism in patients with epilepsy receiving phenytoin and primidone or by inappropriate thyroid replacement therapy in patients with hypothyroidism.

Melatonin, cortisol, prolactin, and calcitonin secretion in primary hyperparathyroidism before and after surgery

The aim of the present study was to determine the diurnal secretion of melatonin, cortisol, prolactin, and calcitonin during chronic parathyroid hormone-dependent hypercalcemia. Eight women, aged 40-76 years, with primary hyperparathyroidism (PHPT) were studied before and after surgical removal of a parathyroid adenoma. The hormone concentrations in blood were determined at 08, 12, 16, 22, 02, 04, and 06 h. Concomitantly, the excretion of melatonin and cortisol in urine between 07-19 h and 19-07 h, and the clearance of calcium and creatinine were measured. Nyctohemeral serum prolactin and calcitonin were unaffected by moderate parathyroid hormone-dependent hypercalcemia. In contrast, serum cortisol and melatonin were significantly higher during active disease than after surgical cure. Mean 24-h variation of serum cortisol was 349 +/- 34 nmol/liter vs. 223 +/- 17 nmol/liter and mean serum melatonin was 0.13 +/- 0.04 nmol/liter vs. 0.06 +/- 0.02 nmol/liter. Endogenous creatinine clearance was similar before and after surgery, while the clearance of melatonin and cortisol significantly increased after surgery, indicating an increased tubular reabsorption of both hormones during active disease. Fasting morning glucose concentrations were also significantly decreased after successful surgery, 6.1 +/- 0.6 vs. 5.2 +/- 0.5 mmol/liter. It is suggested that the relative hypercortisolism may be the cause of the glucose intolerance in primary hyperparathyroidism. Three to 4 months after surgical cure the serum melatonin levels were significantly lower than those seen in age-matched controls, indicating a melatonin insufficiency in patients successfully treated for PHPT. The meaning of this finding is not yet understood but might be of importance in the development of primary hyperparathyroidism.

Large forms of immunoreactive calcitonin in human seminal fluid exhibit PDN-21 immunoreactivity

Semen samples were obtained from 4 healthy males on two occasions. One of the samples was liquefied at room temperature for 20 min while the other was diluted immediately with buffer to suppress proteolysis. A pool of immunoextracted calcitonin from liquefied and diluted samples, respectively, was subjected to gel chromatography in a separate experiment. In lyophilized samples the majority of immunoreactive calcitonin (CT) had an approximate molecular weight (Mr) of 10 kilodaltons (Kd) and immunoreactive PDN-21 was also present in the fractions. In diluted ejaculates CT was composed of larger species as well as the 10 Kd form. PDN-21 was present in fractions containing the 10 Kd form but could not be detected in the peaks of larger molecular weight, probably because of lower sensitivity of the PDN-21 assay compared to the CT assay. Our finding of CT and PDN-21 in the same fractions after immunoextraction with CT antibodies suggests the presence of proforms of CT in human seminal fluid.

Immunoextracted calcitonin from human seminal plasma constitutes different forms

Levels of immunoreactive calcitonin (iCT) in human seminal plasma were studied after extraction with immobilized antibodies. Immunoextraction of semen was necessary to abolish the high concentrations of proteolytic enzymes that can interfere in radioimmunoassay (RIA). Since proteolysis occurs already during semen liquefaction, iCT levels and chromatographic properties were compared in extracts from liquefied ejaculates, and samples were the proteolysis was suppressed by immediate dilution of the ejaculates with buffer. The levels in the two groups were 81 +/- 43 pg-equivalents ml-1 seminal plasma (mean +/- SD, n = 6) in liquefied samples and 120 +/- 42 pg-equivalents ml-1 (n = 7) in diluted samples, which is about ten times the iCT levels in extracted blood plasma from healthy males. Extracted liquefied seminal plasma from two vasectomized men contained 93 and 107 pg-equivalents of iCT ml-1 seminal plasma, respectively. Gel chromatography of undiluted semen samples disclosed that iCT was composed of forms larger than monomeric CT, the major part with an approximate molecular weight (MW) of 10,000. Two of the six subjects had a smaller amount of iCT eluting with a MW of about 40,000. In diluted samples, iCT seemed to be more heterogenous with approximate molecular weights ranging from 40,000 to fragments smaller than monomeric CT. In some ejaculates, monomeric CT seemed to be present. Undiluted samples from vasectomized men contained iCT with the same chromatographic pattern as in normal men.