Parathyroid Hormone Secretion After Operative Bone Trauma

Skeletal trauma in man (operations for scolioses and femoral shortening) results in a significant increase in parathyroid hormone secretion beginning the day after the operation and lasting for more than 1 week. A concurrent decrease in serum calcium, dependent on the postoperative lowering of serum albumin, was also observed.     

Long-Term Effect of Different Dialysate Calcium Concentrations on Parathyroid Hormone Levels in Hemodialysis Patients

The appropriate dialysate calcium concentration (D[Ca]) for hemodialysis (HD) therapy has not yet reached a consensus. We have conducted a prospective control study for five years on the effects of different D[Ca] on serum intact parathyroid hormone (iPTH) levels. Patients were divided into three groups receiving different D[Ca] therapies: the low-Ca (D[Ca]?=?2.5 mEq/L; N?=?96), mid-Ca (D[Ca]?=?3.0 mEq/L; N?=?121), and high-Ca (D[Ca]?=?3.5 mEq/L; N?=?82) groups. After five years' study, only 41 patients in the low-Ca group, 34 in the mid-Ca group, and 32 in the high-Ca group completed the study. The results demonstrated that serum corrected calcium concentrations were significantly lower in the low-Ca group compared with other groups in years 3 and 4, although the products of corrected calcium time phosphate did not show difference between each group.^Δserum alkaline phosphatase (^ΔAlk-p) to baseline levels increased significantly after the fourth year in all three groups (p < 0.05). Serum ^Δ iPTH only increased significantly after the fourth year in the low-Ca group (p < 0.05) but not in the other groups. There were no significant differences in the extent of ^ΔAlk-p and ^ΔiPTH between the groups. Cox proportional methods also showed no difference in cumulative survival between the groups. In conclusion, our results demonstrate that compared with the other two groups of D[Ca], long-term use of D[Ca] of 2.5 mEq/L was associated with relatively lower serum calcium concentration. Perhaps this was related to a greater extent of iPTH concentration elevation after five years.     

Parathyroid Hormone and Bone Marker Levels in Patients with Morbid Obesity Before and After Biliopancreatic Diversion

Background Scopinaro biliopancreatic diversion (BPD) is associated with malabsorption of calcium and vitamin D, which manifests as a secondary hyperparathyroidism (SHP) and may lead to osteopenia. Methods 96 morbidly obese patients were studied (age 19–60 years, 23 men and 73 women, with mean initial BMI 53) following intervention by Scopinaro BPD. The change in iPTH levels, urine DPD, Pyrilinks-D of DPC and serum CTx were studied at 0, 3, 6, 12, 18 and 24 months after surgery. Postoperatively, they were given supplements of calcium and vitamin D3. The control group consisted of 67 non-obese women and 10 men. Results The iPTH levels gradually increased after BPD, with a substantial difference compared to presurgery levels at month 6. In spite of the calcium and vitamin D supplements, 77% of the patients with presurgery SHP did maintain high levels of iPTH after 2 years.The percentage of SHP among the patients with normal pre-surgery iPTH was 58%. The basal figures of DPD/cre were significantly higher than in the control group, 9.06 (4.6–13.5) nM/mMcre vs 3.9 (2.8–5.6) in men and 6.75 (5.4–7.9) vs 7.67 (3.3–11.6) in women, but not CTx, 0.24 (0.02–0.89) vs 0.22 (0.07–0.55). After the operation, there was a noticeable increase which persisted at 2 years. There was a lack of correlation between the levels of iPTH and the bone resorption markers, i.e. the first ones decreased from month 6 in men and from month 12 in women, while the levels of iPTH continued to increase. Conclusion In obese patients, we found no correlation between iPTH levels and BMI. Supplements of calcium and vitamin D did not prevent the appearance of SHP following BPD. The patients with high pre-surgery iPTH levels have a higher risk of malabsorption of calcium and vitamin D. Following malabsorptive bariatric surgery, there is an increase in bone resorption, which results in DPD and CTx increase. Those markers do not correlate with iPTH, and this may suggest that there is a phenomenon of bone reshaping parallel to the loss of weight.     

Preoperative Localization of Parathyroid Adenomas Using 99mTc-MIBI Scintigraphy in Patients with Hyperparathyroidism

Background Technetium (Tc) 99m methoxyisobutyl isonitrile (_99mTc-MIBI) has recently been introduced for parathyroid imaging, as well as for myocardial imaging. We studied the usefulness of _99mTc-MIBI scintigraphy for preoperative localization of abnormal parathyroid glands.
Methods The usefulness of _99mTc-MIBI scintigraphy for detection of hyperfunctional parathyroid lesions was evaluated in 5 patients with primary hyperparathyroidism. The results of localizing the abnormal glands by using _99mTc-MIBI were compared with those obtained by using thallium (Tl) 201-technetium (Tc) 99m (_2ulTI-_99mTc) subtraction scintigraphy, computed tomography, and ultrasonography.
Results The delayed (2 hours) imaging of _99mTc-MIBI scintigraphy was highly useful for accurate localization of the abnormal parathyroid lesions. The diseased glands were detected in all cases where _99mTc-MIBI scintigraphy was used, and using _99mTc-MIBI scintigraphy provided more information than did computed tomography, ultrasonography, or ₂₀₁Tl-_99mTc subtraction scintigraphy. Conclusion: This method is simple and essential for detecting hyperfunctioning parathyroid glands, especially those with small or ectopic lesions. This technique should be widely applied as a localizing diagnostic method for hyperparathyroidism.     

腔镜下甲状旁腺全切联合部分甲状旁腺组织前臂移植治疗继发性甲状旁腺亢进

目的探讨腔镜下甲状旁腺全切（endoscopic total parathyromectomy,ETP）联合部分甲状旁腺组织前臂移植（parathyroid tissue autotranspIantafion,PTA）治疗继发性甲状旁腺亢进（secondary hyperparathyroidism,SHPT）的安全性、可行性。方法2004年6月-2009年6月72例SHPT经胸前路径行腔镜下全部甲状旁腺切除,同时将20枚1-1．5mm。大小的健康甲状旁腺组织移植于患者前臂肌膜下。结果71例ETP联合PTA顺利完成,无术中及围手术期死亡。手术时间平均119．9rain（85-155rain）,术中出血量平均39．7ml（10-60m1）,下床时间平均1．2d（0．5-2．0d）,住院时间平均4．7d（3-8d）。1例因术中出血中转开放手术,术后发现声音嘶哑,经保守治疗后缓解。术后临床症状明显改善,生化检查（甲状旁腺激素、碱性磷酸酶、血钙、血磷等指标）恢复正常或明显改善。72例随访10个月-5年,平均3．8年,2例术后甲状旁腺亢进症状复发,二次手术后痊愈。结论ETP联合PTA治疗SHPT安全、可行,疗效满意。     

The PTH-calcium curve and the set point of calcium in primary and secondary hyperparathyroidism.

BACKGROUND: The regulation of PTH secretion by calcium is altered in patients with primary hyperparathyroidism (HPT). A similar abnormality may occur in secondary HPT, but comparisons of PTH secretion in normal subjects and those with secondary HPT have given contrasting results. Differences in baseline serum ionized calcium (ICa) may partly account for these conflicting results. The aim of the present study was to evaluate whether the regulation of PTH secretion by calcium differs from normal in patients with primary and secondary HPT and to determine whether serum calcium concentration per se can affect the set point of calcium and the PTH-calcium relationship. METHODS: The PTH-ICa relationship and the set point of ICa were evaluated in 19 patients with primary HPT (1-HPT), 16 normocalcaemic patients with secondary HPT (2-HPT; PTH 344+/-191 pg/ml), 19 hypercalcaemic patients with secondary HPT (3-HPT; PTH 806+/-254 pg/ml) and 14 healthy volunteers, by inducing hypocalcaemia and hypercalcaemia in order to maximally stimulate or inhibit PTH secretion. In five 1-HPT patients the PTH-ICa curve was restudied after normalization of serum ICa by pamidronate. Parathyroid gland volume was determined by measuring gland size at parathyroidectomy or by means of high-resolution color Doppler ultrasonography. RESULTS: In 1-HPT patients the PTH-ICa curve, constructed using maximal PTH secretion induced by hypocalcaemia as 100%, was shifted to the right, the set point of ICa was increased, and the slope of the curve was reduced when compared to normal subjects. After normalization of baseline serum ICa by pamidronate, a shift of the PTH-ICa curve towards normal and a reduction in the set point of ICa was observed. However, basal PTH and maximal PTH secretion induced by hypocalcaemia increased, minimal PTH secretion induced by hypercalcaemia remained increased and the slope of the curve did not change significantly. The alterations in the PTH-ICa relationship in hypercalcaemic patients with secondary HPT were similar to those found in 1-HPT patients. In normocalcaemic patients with secondary HPT baseline PTH, maximal and minimal PTH secretion and parathyroid gland size were reduced compared to 3-HPT patients. Compared to normal subjects, 2-HPT patients showed greater calcium-induced minimal PTH secretion. The increase in non-suppressible PTH secretion resulted in a rightward shift of the PTH-ICa curve and an increase in the set point of ICa. A strong correlation was found, in both primary and secondary HPT, between the set point of ICa and baseline serum ICa, and between parathyroid gland size and baseline PTH, maximal PTH and minimal PTH. Multivariate regression analysis showed that baseline serum ICa was the main determinant of the set point of ICa in both primary and secondary HPT. CONCLUSIONS: (i) The regulation of PTH secretion by calcium is abnormal in secondary as well as in primary HPT. (ii) Parathyroid gland enlargement in secondary HPT is associated with reduced sensitivity to serum ICa and resistance of parathyroid gland to calcium-mediated PTH suppression, resulting ultimately in PTH hypersecretion, despite hypercalcaemia. (iii) The set point of calcium is strongly dependent on baseline serum calcium, and the PTH-ICa relationship can be affected by variations in serum ICa concentrations. Thus, when the set point of calcium and the PTH-ICa relationship are evaluated, possible differences in baseline serum ICa concentration among the patients should be taken into account.     

Intraoperative total serum calcium levels,unlike intraoperative intact PTH levels,do not correlate with cure of hyperparathyroidism

BACKGROUND: Intraoperative intact parathyroid hormone (iPTH) monitoring is useful in the operative management of hyperparathyroidism. Recent studies suggest that measurement of intraoperative total serum calcium (TSC) levels may be a more cost effective and readily available method of intraoperative guidance during neck dissection than iPTH levels, the gold standard. We compared the accuracy of intraoperative TSC to iPTH in predicting surgical cure during parathyroidectomy. PATIENTS AND METHODS: From September 1, 2001 to October 31, 2002, 88 parathyroidectomies were performed. iPTH and TSC were measured at the start of the operation, and at 5 and 10 min after gland removal. Data were compared, and trends were analyzed with respect to removal of abnormal parathyroid tissue as confirmed by pathology. One-way analysis of variance was used to determine if decreases in TSC were significant. RESULTS: The mean baseline iPTH level (418 +/- 610 pg/ml) dropped by 70% 5 min after removal of the abnormal glands (86 +/- 102 pg/ml) and by 85% at 10 min (39 +/- 39 pg/ml). The mean baseline TSC level (10.0 +/- 0.8 mg/dl) dropped by 4% at 5 min after removal of the abnormal glands (9.6 +/- 0.9 mg/dl) and remained at 4% at 10 min (9.6 +/- 0.8 mg/dl). iPTH dropped by > or =50% in 73 patients (83%) at 5 min and in 87 patients (99%) at 10 min after gland resection. TSC decreased below baseline at 5 min and remained below baseline at 10 min in only 47 patients (54%). In the remaining patients, intraoperative TSC changes were less predictable and did not respond consistently to resection of abnormal glands. CONCLUSIONS: The decreases in TSC during parathyroidectomy, if present, are minimal. Unlike iPTH levels, TSC levels do not consistently decrease at 5 and 10 min after gland resection. While attractive in terms of cost and availability, intraoperative TSC levels are not clinically reliable in confirming removal of abnormal parathyroid tissue.     

Intact PTH assay overestimates true 1-84 PTH levels after maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism.

BACKGROUND: Although the so-called intact parathyroid hormone (iPTH) assay detects not only true 1-84 PTH (1-84PTH) but also large C-terminal PTH fragments, it remains inconclusive whether the 1-84PTH assay is more useful in clinical practice. Previous studies have shown that the results of these two PTH assays in dialysis patients are closely correlated. METHODS: Chronic dialysis patients whose plasma iPTH levels were >400 pg/ml were selected for inclusion in the present study. Following a 4 week wash-out time during which all vitamin D administration was halted, maxacalcitol was intravenously injected at the end of dialysis sessions three times per week for 24 weeks, at an initial dosage of 10 micro g. RESULTS: Ninety-seven patients with secondary hyperparathyroidism were included in our analysis. Their serum calcium levels were elevated from the start levels while phosphate levels remained unchanged. The plasma 1-84PTH levels constantly declined throughout the 24 weeks. Although the patients' plasma 1-84PTH and iPTH levels were closely correlated with each other both at the beginning of the study and after 24 weeks of maxacalcitol therapy, the ratio of 1-84PTH/iPTH consistently decreased throughout the study period (P<0.01). The changes in the ratio were significantly correlated with changes in serum calcium levels. CONCLUSIONS: Twenty-four weeks of intravenous maxacalcitol injection therapy significantly reduced the 1-84PTH/iPTH ratio. Estimated 1-84PTH levels from iPTH levels using a conversion formula obtained before the treatment were 21.0+/-20.4% higher than measured 1-84PTH levels after the therapy. Thus, iPTH measurement has a potential risk to overestimate 1-84PTH levels when evaluating the efficacy of maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism.     

Parathyroid function in end-stage penal failure

To clarify the degree of parathyroid dysfunction in end-stage renal failure, sigmoidal relationship between serum Ca²⁺ and intact-PTH was evaluated in vivo in 47 hemodialysis (HD) patients including 12 diabetics. Patients were divided into 3 groups, 9 who had been just introduced to HD (0 years), 31 who were on maintenance HD for 2.5 to 16.2 years without significant secondary hyperparathyroidism (2nd HPT), and 7 who suffered from severe 2nd HPT for 8.5 to 15.3 years on HD. Additional 4 patients who were treated with HD or hemodiafiltration because of acute hepatic failure with normal renal function were selected for control. Sigmoidal curve (SC) in patients with non-diabetics on 0 years on HD was significantly deviated to upper and right direction. Similarly, the set point of calcium (SP) in non-diabetics was deviated to the right (higher calcium level). These abnormalities were more pronounced as the length of HD duration increased. However, these parathyroid dysfunction was not obvious in diabetic patients. In severe 2nd HPT, SC and SP were remarkably deranged. Mean SP in these patients was 1.22 mmol/l, and 1.26 mmol/l in 3 patients who required parathyroidectomy after the study. These results indicate that the earlier treatment to prevent 2nd HPT would be necessary from conservative stage of renal failure in non-diabetic population.     

The Relationship between Apelin and Parathyroid Hormone in Hemodialysis Patients

Both apelin and parathyroid hormone (PTH) are endogenous ligands for G-protein-coupled receptors. Apelin acts as a mitogenic agent for osteoblasts, and metabolic bone abnormalities are frequently seen in hemodialysis (HD) patients because of hyperparathyroidism. The aim of this study was to analyze plasma apelin levels in HD patients and to determine whether they are related to PTH concentrations. A total of 23 HD patients [15 men and 8 women, with a mean (SD) age of 54.2 (4.4) years and a mean body mass index (BMI) of 25.0 (4.1) kg/m²] were studied and compared with 15 healthy subjects [6 men and 9 women, with a mean (SD) age of 51.3 (13.6) years and a BMI of 27.0 (4.3) kg/m²]. Plasma apelin-36 was measured using an enzyme immunometric assay method and PTH was measured by ELISA. There was no significant difference in apelin levels between the patients [0.80 (0.6) ng/mL] and the healthy subjects [0.83 (0.23) ng/mL]. There was a positive correlation between apelin and PTH (r = 0.66, p = 0.0001). The patients with PTH >300 pg/mL had significantly higher plasma apelin levels [1.17 (0.7) ng/mL] compared with the patients with PTH <300 pg/mL [0.50 (0.15) ng/mL] (p = 0.003). In conclusion, HD patients with secondary hyperparathyroidism have high plasma apelin levels, which suggest that apelin may protect bone in HD patients by acting as an osteoblastic factor.     

High Parathyroid Hormone Level and Osteoporosis Predict Progression of Coronary Artery Calcification in Patients on Dialysis

Coronary artery calcifications (CACs) are observed in most patients with CKD on dialysis (CKD-5D). CACs frequently progress and are associated with increased risk for cardiovascular events, the major cause of death in these patients. A link between bone and vascular calcification has been shown. This prospective study was designed to identify noninvasive tests for predicting CAC progression, including measurements of bone mineral density (BMD) and novel bone markers in adult patients with CKD-5D. At baseline and after 1 year, patients underwent routine blood tests and measurement of CAC, BMD, and novel serum bone markers. A total of 213 patients received baseline measurements, of whom about 80% had measurable CAC and almost 50% had CAC Agatston scores>400, conferring high risk for cardiovascular events. Independent positive predictors of baseline CAC included coronary artery disease, diabetes, dialysis vintage, fibroblast growth factor-23 concentration, and age, whereas BMD of the spine measured by quantitative computed tomography was an inverse predictor. Hypertension, HDL level, and smoking were not baseline predictors in these patients. Three quarters of 122 patients completing the study had CAC increases at 1 year. Independent risk factors for CAC progression were age, baseline total or whole parathyroid hormone level greater than nine times the normal value, and osteoporosis by t scores. Our results confirm a role for bone in CKD–associated CAC prevalence and progression.     

Higher Incidence of Cholelithiasis in Chronic Renal Failure Patients with Secondary Hyperparathyroidism Undergoing Peritoneal Dialysis

Background. In this study, we endeavored to determine whether the incidence of cholelithiasis (CL) was increased in chronic renal failure (CRF) patients with secondary hyperparathyroidism on a peritoneal dialysis (PD) program. We also evaluated the factors that might have some influence on the development of CL. Methods. A total of 59 CRF patients undergoing PD were included in the study. We studied the following groups to determine whether parathyroid hormone (PTH) levels were increased in CRF-PD patients: twenty patients with secondary hyperparathyroidism (group 1) and 39 patients with normal PTH levels (group 2). PTH levels were maintained at three times the upper limit of normal. Biochemical parameters were obtained for each CRF-PD patient. All patients underwent abdominal ultrasonography to screen for the presence of cholelithiasis. For statistical analysis, χ², t test, and logistic regression analysis were used; p < 0.05 was considered as significant. Results. We found an almost ten times higher incidence (25% vs. 2.6%) of CL in group 1 patients with statistical significance (p = 0.007). When the incidence of CL according to sex, creatinine, and PTH levels were considered, female gender, creatinine, and PTH levels were higher in group 1, which was also significant statistically. No significant relationship was detected between gallbladder stone formation and the other analyzed biochemical parameters. Conclusions. We found that the incidence of CL in CRF-PD patients with secondary hyperparathyroidism was higher than CRF-PD patients with normal PTH levels. It was also detected that female gender, high creatinine levels, and elevated PTH levels might influence the development of CL in CRF-PD patients.     

Water-Clear Cell Parathyroid Adenoma Causing Primary Hyperparathyroidism in a Patient with Neurofibromatosis Type 1: Report of a Case

Water-clear cell parathyroid adenoma is an exceedingly rare tumor, composed exclusively of tumor cells with abundant foamy cytoplasm. A combination of hyperparathyroidism and neurofibromatosis type 1 (NF1) is also a rare phenomenon. We report an 18-year-old woman with primary hyperparathyroidism caused by water-clear cell parathyroid adenoma in association with NF1. She had renal stones, hypercalcemia, and an elevated plasma level of intact parathyroid hormone. Physical examination revealed a palpable tumor in the right neck, and café-au-lait spots distributed over her entire body. An ultrasound examination showed an isoechoic mass in the right thyroid lobe. Thallium–technetium subtraction scintigraphy showed high thallium accumulation in the right thyroid lobe area. A surgical exploration revealed the palpable mass to be a parathyroid tumor. The pathological features were consistent with water-clear parathyroid adenoma. This is the first reported case of water-clear cell parathyroid adenoma associated with NF1.     

Relationship between parathyroid gland size and responsiveness to maxacalcitol therapy in patients with secondary hyperparathyroidism.

BACKGROUND: Although vitamin D has been reported to be useful in the treatment of patients with secondary hyperparathyroidism, it is not effective in some of them. The goal of this study was to see whether a relationship could be found between maxacalcitol responsiveness and parathyroid gland size. METHODS: Parathyroid gland size was measured by ultrasonography in 25 patients with secondary hyperparathyroidism [serum intact parathyroid hormone (PTH) >300 pg/ml, 58.1 +/- 2.8 years old, 15 males and 10 females], who were treated with maxacalcitol. Patients were divided into two groups according to the mean value of the maximum diameter of the glands: group S with a diameter <11.0 mm and group L with a diameter >or =11.0 mm. Between the two groups there were no significant differences in serum intact PTH, calcium or phosphate level or duration of haemodialysis. RESULTS: Mean (+/- SE) maximal diameter of detectable parathyroid glands was 11.0 +/- 0.7 mm before treatment. At 4-24 weeks after administration of maxacalcitol, intact PTH concentrations decreased significantly in group S (from 546 +/- 39 to 266 +/- 34 pg/ml at 24 weeks; P < 0.01), but did not significantly change in group L (from 481 +/- 39 to 403 +/- 49 pg/ml at 24 weeks). At 24 weeks after maxacalcitol administration, the number of detectable parathyroid glands was significantly decreased in group S (from 2.2 +/- 0.3 to 1.8 +/- 0.4; P < 0.05), but not in group L. Serum calcium increased significantly in group L (from 9.6 +/- 0.2 to 10.2 +/- 0.3 mg/dl; P < 0.05), but not in group S. There was a significant correlation between reduction in PTH and parathyroid gland size (r = -0.42, P < 0.05). CONCLUSIONS: These results indicate that the responsiveness to maxacalcitol therapy of secondary hyperparathyroidism is dependent on parathyroid gland size and that the simple measurement of maximum parathyroid gland diameter by ultrasonography may be useful for predicting responsiveness to maxacalcitol treatment.     

Coexistent Thyroid Pathologies and High Rate of Papillary Cancer in Patients with Primary Hyperparathyroidism: Controversies About Minimal Invasive Parathyroid Surgery

Thyroid carcinoma and benign thyroid diseases associated with primary hyperparathyroidism (PHPT) may cause difficulties in the diagnosis, localization and therapy of PHPT. In this study, we analysed coexistent thyroid pathologies in 51 patients who underwent neck exploration with a diagnosis of PHPT between 1999-2002. Five hundred thirteen patients who underwent thyroidectomy for nodular thyroid disease without a parathyroid pathology in histopathological examination served as controls. In patients with PHPT there were 43 cases (84.3%) of coexistent thyroid pathology. Nine patients (17.6 %) had coexistent papillary thyroid cancer. Nine patients (17.6 %) had lymphocytic thyroiditis, two (3.9%) had benign thyroid adenoma and 24 (47%) had nodular hyperplasia. In one patient (2%), there was intrathyroidal metastasis from a parathyroid cancer. One patient had coexistent lymphocytic thyroiditis and multifocal papillary cancer. One of the two cases with thyroid adenomas was Hürthle cell type. In the control group only 28 patients (5.5%) had thyroid malignancy (27 papillary cancer and one follicular cancer). In conclusion, the coexistent thyroid pathologies are highly prevalent in patients with PHPT and pre-and intra-operative thyroid examination should be performed to avoid overlooking important thyroid pathologies.     

The calcitonin-calcium relation curve and calcitonin secretory parameters in renal patients with variable degrees of renal function

Increased calcitonin (CT) levels have been reported in chronicrenal failure, even before the uraemic phase and in the absenceof hypercalcaemia. Furthermore, a sigmoidal CT-calcium relationshipwas recently observed in rats and haemodialysed patients. We carried out the present investigation in order to assess:(a) whether the sigmoidal CT-calcium relationship is also evidentin renal patients with a variable degree of renal failure andin normal subjects; (b) whether the four secretory parametersalready described for the PTH-calcium relation curve might bedescribed for CT too; (c) whether any change in some, if any,of these secretory parameters could be found at a variable degreeof renal insufficiency. We studied 33 renal patients (RP), with a variable degree ofrenal failure (creatinine clearance ranging from 16 to 164ml/min),and 10 normal subjects (C). All RP and C were submitted to abasal evaluation including the assessment of (1) basal concentrationsof 1,25(OH)₂ vitamin D, 25(OH) vitamin D, mono-meric CT, intactPTH; (2) GFR by Cr⁵¹EDTA clearance. On the 2 subsequent days,a hypocalcaemic test (Na₂-EDTA about 37 mg/kg of body-weight/2h) and a hypercalcaemic test (Ca gluconate giving 8 mg/kg body-weight/2h of Ca element) were carried out for the assessment of bothCT and PTH secretory parameters. According to GFR values, theRP were divided into three groups: group RP1 (GFR > 70 ml/minper 1.73 m²; n = 10), group RP2 (GFR between 30 and 70 ml/minper 1.73 m²; n=15), group RP3 (GFR < 30 ml/min per 1.73 m²;n = 8). In most, but not all, RP and C a sigmoidal CT-calcium relationshipwas evident, opposite in direction to the PTH-calcium relationcurve. In these RP and C the four secretory parameters, characteristicfor the PTH-calcium secretion curve, were calculated for CTtoo. When pooled RP and C were considered, both minimal (9.0± 6.4 pg/ml) and maximal CT levels (71.8 ± 56.2pg/ml) significantly differed from basal levels (24.3±18 pg/ml; P<0.001). The CT set point (CT SP) and sensitivity(CT SENS) values were significantly higher and lower than thecorresponding PTH secretory parameters (CT SP 1.39 ±0.08 mmol/1, PTH SP 1.23 ± 0.05 mmol/1,P<0.001) (CTSENS 243 ± 67%/mmol, PTH SENS 598 ± 329%, P<0.001).However, the CT SP values were strictly correlated with PTHSP values (r = 0.78, P<0.001). When CT secretory parameterswere considered separately in the RP groups, increased levelsof basal (36.1±28.6pg/ml), minimal (17.9±10.4),and maximal (139.9 ± 39.7) CT levels were found in theRP3 group, when compared with both the other RP groups and C.No significant difference was found as regards the CT SP andCT SENS values between RP and CT. These results suggest that (1) CT secretion is homeo-staticallycontrolled by calcium changes in the same range of the PTH-calciumsystem; (2) a sigmoidal CT-calcium relationship is demonstrablein most (but not all) RP and C; in these subjects it is possibleto calculate the CT secretory parameters as for PTH; (3) theincrease in CT levels in the course of chronic renal failureis quite similar to the already known increase of PTH, and ischaracterized by the increase of basal, minimal and maximalCT values, suggesting that an increased secretion of CT by thethyroid C-cells (rather than CT retention due to a decreasein renal function), is responsible for these findings.