Sensitive time-resolved fluoroimmunoassay of salmon calcitonin

A two-site assay was developed by use of the "dissociation and enhancement lanthanide fluoroimmunoassay" (DELFIA) technique for determination of salmon calcitonin (SCT) in serum after administration to osteoporotic patients. Polyclonal antibodies were produced in rabbits immunized with SCT coupled to ovalbumin. After affinity purification, the antibodies were used both as immobilized capture antibodies and as Eu-chelate-labeled signal antibodies. A sensitive assay with a detection limit of 1.1 pmol/L was achieved, and no cross-reaction with human calcitonin was observed. The intra- and interassay CVs were < 12% (n = 10) and < 15% (n = 4), respectively. Analytical recovery of SCT added to serum was 91% +/- 3% (mean +/- SD, n = 4). SCT was measurable in all the samples from eight osteoporotic patients after subcutaneous SCT administration. We conclude that this new sensitive and specific two-site DELFIA can reliably measure SCT in serum.

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)

Calcium homeostasis in normal pregnancy and puerperium. A longitudinal study

Calcium homeostasis was longitudinally followed in serum and urine throughout normal pregnancy and the puerperium in 23 healthy women. From the 14th week of gestation, samples were obtained every fourth week until the 38th week. Post partum samples were obtained on the fifth day and after eight weeks. In the serum the total calcium decreased continuously during pregnancy. The ionized calcium and phosphate levels remained unchanged and within the reference interval for non-pregnant women. The alkaline phosphatase level progressively increased and high levels were found at term. The magnesium and hematocrit values remained below, whereas the calcitonin level remained just above the reference interval throughout pregnancy. The parathyroid hormone was low initially and increased towards term but within the reference interval. The urine excretion of calcium was constantly high, close to the upper reference limit, and renal function was slightly improved. At the last sampling eight weeks after delivery, all values were within normal limits for non-pregnant women. Calcium homeostasis is considerably changed during pregnancy and non-pregnant reference limits are not often valid.

Blood sampling procedures influence serum calcitonin concentrations in rats

The aim of this study was to determine whether serum calcitonin (S-CT) in rats is influenced by the method of taking blood samples. Sampling during halothane anaesthesia, after repeated administration of anaesthesia after a 14-day interval, and sampling without the use of anaesthetics (i.e. after the rats were made unconscious by stunning), resulted in different S-CT values (P < or = 0.001), whereas Ca2+ levels were not affected. In thyroidectomized rats, the S-CT values after stunning were not significantly different whereas those in sham-operated rats were different (P < or = 0.01). The possibility that anaesthesia may suppress stunning-induced changes in S-CT was explored in three other groups of rats subjected to halothane anaesthesia, stunning and stunning under halothane anaesthesia respectively. Although the S-CT level was highest after stunning and lowest in halothane-anaesthetized rats (P < or = 0.001), anaesthesia did not suppress the effect of stunning on S-CT. In conclusion the effect of sampling procedures must be considered in studies on the levels of S-CT in rats.

Parathyroid hormone-related protein is produced by cultured endothelial cells: a possible role in angiogenesis

Parathyroid hormone-related protein (PTHrP) is produced by various normal and neoplastic tissues. Even if the physiological function(s) of PTHrP is unclear, evidence suggests that the protein may participate in the local regulation of smooth muscle contractility. We show here that PTHrP is produced in endothelial cells cultured from human umbilical veins as demonstrated both at the mRNA and protein level. The expression of PTHrP can be upregulated by the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate, which is known to stimulate endothelial cell differentiation and angiogenesis in vitro. Unlike smooth muscle cells, the endothelial cells do not express the parathyroid hormone (PTH)/PTHrP receptor mRNA, nor could specific binding of the protein be detected. We therefore suggest that PTHrP produced by endothelial cells acts on smooth muscle cells and may be of importance for the growth and development of new vasculature.

Plasma calcitonin, IGF-I levels and vertebral bone mineral density in hyperprolactinemic women during bromocriptine treatment

Hyperprolactinemia is associated with decreased bone mineral density, which may be caused by the hypogonadism and hypoestrogenicity noticed in patients with hyperprolactinemia. Since calcitonin inhibits the bone resorption, and insulin-like growth factor I (IGF-I) has important anabolic effects on the skeleton, lack of one or both peptides may contribute to the development of osteopenia. We therefore measured the plasma calcitonin and IGF-I levels in nine women with hyperprolactinemia caused by a prolactin-producing pituitary tumor. The calcium-stimulated C-cell reactivity was studied by measuring calcitonin in plasma during a calcium clamp before and after normalization of serum prolactin during treatment with bromocriptine. Basal CT levels were measurable but lower than in healthy controls. Basal IGF-I levels and calcium-stimulated plasma calcitonin were normal in the hyperprolactinemic state and similar to the calcitonin and IGF-I levels during bromocriptine treatment. The serum prolactin levels decreased (p < 0.001) and the serum estradiol levels increased (p < 0.001). The bone mineral density of the lumbar spine increased significantly during treatment. Thus, basal plasma CT levels are slightly reduced in hyperprolactinemic women. However, the reversible osteopenia in hyperprolactinemic women is less likely to be caused by inhibited IGF-I secretion or by deficient CT levels since the CT response to calcium is normal. In addition, bromocriptine treatment with normalization of prolactin levels is beneficial for the bone mineral content in this condition.

Influence of smoking and snuff use on electrolytes, adrenal and calcium regulating hormones

Little is known about the effects of snuff use on health. We have investigated electrolyte levels, adrenocortical and calcium regulating hormones in three groups of healthy young men, including 18 non-tobacco users, 21 snuff users and 19 smokers with similar age and body mass index. Smoking and snuff use was positively associated with alcohol and coffee consumption and inversely related to physical activity. Compared to non-tobacco users, smokers had significantly increased levels of serum sodium and magnesium, plasma calcitonin, urinary cortisol and potassium levels and decreased serum sex hormone-binding globulin as well as serum and urinary creatinine values. However, only decreased sexual hormone-binding globulin and urinary creatinine and increased serum phosphate and urinary potassium levels were seen in snuff users. Among tobacco users we noted that smokers differed from snuff users in that they had higher serum sodium (1.4 mmol/l, p < 0.01), plasma calcitonin (3.3 pmol/l, p < 0.05) and urinary cortisol (41 nmol/24 h, p < 0.05) but lower serum creatinine (5.8 mumol/l, p < 0.01). We conclude that chronic snuff use appears to have less influence on hormone and electrolyte balance than does smoking, and that some of the abnormalities seen in smokers do not seem to be mediated by nicotine.

Parathyroid hormone-related peptide, measured by a midmolecule radioimmunoassay, in various hypercalcaemic and normocalcaemic conditions

The diagnosis of humoral hypercalcaemia of malignancy often presents considerable clinical problems. We have studied parathyroid hormone-related peptide (PTHrP) in serum from patients with humoral hypercalcaemia of malignancy (N = 22), hypercalcaemia of malignancy with skeletal metastases (17), histologically confirmed primary hyperparathyroidism (21) and hypercalcaemic patients with various benign diseases (9). PTHrP measurements were also made in normocalcaemic patients with various malignancies (23), endocrine diseases (13), sarcoidosis (22) and chronic renal failure (17). PTHrP was measured by a novel radioimmunoassay using rabbit antibodies directed towards the midregion of the molecule. Immuno- or silica cartridge extraction of serum before radioimmunoassay enabled us to measure PTHrP in all samples, which may add further information about circulating forms of PTHrP. PTHrP was clearly elevated in patients with humoral hypercalcaemia of malignancy (5.0 +/- 4.7 pmol/l) (mean +/- SD, N = 12) and when the kidney function was impaired (4.0 +/- 0.9 pmol/l) (N = 15) (silica cartridge extraction), whether the subject was hypercalcaemic or not. Some patients with endocrine diseases, including two with primary hyperparathyroidism, had slightly elevated serum PTHrP concentrations, while they were normal in sarcoidosis. In healthy subjects the levels were 1.1 +/- 0.5 pmol/l (N = 15) after immunoextraction and 0.8 +/- 0.2 pmol/l (N = 33) after silica cartridge extraction.

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.

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.

Salmon calcitonin treatment by nasal spray in primary hyperparathyroidism

The hypocalcemic and hypophosphatemic effect of salmon calcitonin (sCT) given by intranasal (i.n.) spray to 12 patients with histological confirmed primary hyperparathyroidism (1 degree HPT) was studied. The concentration of ionized calcium in whole blood (B-Ca++), serum phosphate (S-P), magnesium (S-Mg), plasma sCT (Pl-sCT), and endogenous CT (hCT) was followed during five 24-hour periods with at least three days between. After period I (control day), 100 IU sCT was given intramuscularly (i.m.) in period II. In periods III-V, either 110, 200, or 400 IU of sCT were given intranasally (i.n.) in randomized order. Although B-Ca++ decreased from the baseline value with all four sCT treatments and at 4.5 hour on the control day (p less than 0.05-0.001), the i.n. sCT treatments had no significant hypocalcemic effect, as the change of the area under the B-Ca++ curve (delta AUC B-Ca++) for the three i.n. treatments was not significantly different from the control period (p less than 0.001, ANOVA). Only the i.m. injection of calcitonin had a calcium-lowering effect (p less than 0.001, ANOVA). Three subjects were considered nonresponders with a decrease in B-Ca++ less than 0.06 mmol/L. S-P decreased within three hours after 200 IU sCT i.n. and 100 IU i.m., but the S-Mg levels showed no consistent changes. The area under the curve for the Pl-sCT levels did not correlate with delta AUC B-Ca++ except for i.m. given sCT.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma calcitonin levels in patients with cystic fibrosis

Plasma levels of calcitonin were investigated in patients with cystic fibrosis and compared with age- and sex-matched healthy controls. About forty per cent of the cystic fibrosis patients had plasma calcitonin levels that were markedly higher than normal. Elevated levels were found predominantly in female patients. In general, patients with marked pulmonary involvement had high plasma calcitonin levels. Immunoextraction and gel chromatography, carried out on plasma of one of the patients demonstrated monomer-like forms of calcitonin similar to those found in the healthy subjects.

Serum calcitonin levels in anesthetized rats

In order to determine whether a short period of general anesthesia influences the levels of serum calcitonin (CTs) and whole blood ionized Ca2+ and pH, 10 rats were sequentially anesthetized at 5-day intervals by halothane, ether, or CO2/O2, respectively, and retroorbital blood samples were collected during anesthesia. We noticed significant differences of serum calcitonin but the role of the anesthetics remains unclear, since other factors also could have accounted for the observed variations. Blood pH was strongly decreased by CO2/O2. Whole blood ionized calcium exhibited marked changes, but no correlation was found between whole blood ionized calcium and serum calcitonin.

Postmenopausal osteoporosis: response of immunoextracted calcitonin to a calcium clamp

Fourteen postmenopausal females with osteoporosis (PMO) and 14 healthy postmenopausal females (PMF) were studied by means of the calcium clamp-technique. Plasma was collected before start and during the 1 hour calcium clamp. Calcitonin (CT) was immunoextracted from plasma with antiserum No. 1 directed against the mid- and carboxyterminal portion of CT. Thereafter radioimmunoassay was performed on the extracts with antiserum No. 2 directed against the carboxyterminal of CT. The detection limit of the assay was 0.8 pg/tube. There was no difference between patients and controls in the basal CT values and CT was detectable in all samples after immunoextraction. Plasma CT increased significantly during the calcium clamp in osteoporotic patients as well as in controls and the CT response did not differ between the groups. The results do not support the hypothesis of a diminished CT secretion as a contributing factor to the development of osteoporosis.

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)

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.

Immunoextracted calcitonin in milk and plasma from totally thyroidectomized women. Evidence of monomeric calcitonin in plasma during pregnancy and lactation

The level of immunoreactive calcitonin in the first produced breast milk was in totally thyroidectomized (TX) women 713 +/- 307 pg-eq/ml (mean +/- SD, N = 7) and in control women 772 +/- 329 pg-eq/ml (N = 33), i.e. about 45 times higher than in plasma (see below). On gel chromatography of immunoextracted milk from TX women, immunoreactive calcitonin appeared as high molecular weight forms in the same pattern as in milk from healthy women when the same antiserum was used for immunoextraction and radioimmunoassay (RIA). In another series of experiments, a new antiserum raised in rabbits was used for measurement of immunoreactive calcitonin after immunoextraction with 1. Plasma levels of immunoreactive calcitonin in the TX women during pregnancy were 16 +/- 6 pg-eq/ml (N = 6) and during lactation 14 +/- 7 pg-eq/ml (N = 5). Immunoreactive calcitonin was undetectable (less than 8 pg/ml) in plasma from those TX women in whom lactation had stopped (N = 5). Immunoextraction and gel chromatography of plasma collected during pregnancy and lactation from the TX women showed that the immunoreactive calcitonin present eluted in the region of monomeric calcitonin with both antiserum 1 and 2. In conclusion, high concentrations of high molecular weight forms of of immunoreactive calcitonin have been demonstrated in milk from TX patients, most probably devoid of any calcitonin-producing thyroid C-cells. This points to a local production site in the mammary gland.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Plasma calcitonin response to a calcium clamp in endogenous Cushing's syndrome

Basal and calcium (Ca) stimulated plasma CT concentrations have been studied in 6 premenopausal females with Cushing's disease and 3 premenopausal females with Cushing's syndrome due to an adrenocortical adenoma. Thirteen healthy premenopausal females served as a reference group. A standardized Ca-stimulus was applied to all subjects by means of the 'calcium clamp' technique. Plasma immunoreactive CT (iCT) was determined by RIA using a carboxyl terminal antiserum with 8 pg-eq/ml as detection limit. The patients with Cushing's disease had normal basal plasma iCT levels and their iCT response during the 2 h calcium clamp was within the reference range in 5 out of 6 patients, the remaining patient showed a slightly exaggerated response. The patients with adrenal adenoma had elevated plasma iCT levels in the basal state but a normal response during the calcium clamp. It is therefore less likely that the bone resorption often seen in Cushing's syndrome is due to CT deficiency.

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

A radioimmunoassay (RIA) was developed for immunoreactive calcitonin (iCT) in human plasma. Antibodies against synthetic human calcitonin (hCT) coupled to bovine serum albumin (BSA) were raised in rabbits and were directed against the carboxy terminal part of CT. The detection limit of the assay was 8 pg/ml. In 7 males the iCT response to a calcium-clamp was studied. Blood was collected at 0, 30 and 60 min after the start of the calcium infusion. iCT was measured directly in plasma and in extracts obtained after purification of plasma iCT by means of immobilized CT antibodies. There was a good correlation between iCT in plasma samples and extracts, r = 0.993, n = 14 (P less than 0.001). Dilution curves of extracts and plasma were parallel with the hCT standard curves. Gel chromatography of the extracts on Sephadex G-50 and G-75 disclosed heterogeneity of iCT in normal plasma during basal conditions as well as during calcium stimulation. Thirty min after the start of the calcium clamp all molecular forms, most likely constituting monomeric and dimeric CT and larger forms, were increased, while after 60 min iCT seemed to constitute predominantly forms larger than monomeric CT. Basal levels of unextracted iCT in healthy males (n = 44, 37 +/- 10 years) were 15 +/- 9 pg-equivalents/ml (mean +/- SD) which was higher than in females (n = 40, 32 +/- 9 years) 11 +/- 4 pg-equivalents/ml (P less than 0.05).

Plasma calcitonin response to a calcium clamp. Influence of sex and age

The influence of sex and age on basal and calcium stimulated immunoreactive plasma calcitonin (iCT) were studied in 36 healthy subjects. An identical calcium stimulus, "calcium clamp", was applied to 10 young males, 13 premenopausal females of similar ages and 13 postmenopausal females. A significantly greater iCT response was found in males compared with both female groups. No age correlation in basal or calcium stimulated iCT levels was observed despite 35 years difference in mean age between the pre- and postmenopausal groups. A positive correlation between the induced change in whole blood ionized calcium (B-Ca++) and the iCT response, recorded after 15 min, was seen in young subjects of both sexes. Basal iCT and B-Ca++ were similar in all three groups. No correlation between basal iCT and basal B-Ca++, or between basal iCT and age was found. The total amounts of infused calcium per kg body weight were equal. The results indicate that male subjects have a greater secretory capacity of the thyroid C-cell than females. No reduction of the secretory capacity was observed with increasing age in females, neither was any difference found between pre- and postmenopausal females of the iCT-response.