Primary Hyperparathyroidism Group Research Articles

Ultrasound evaluation of carotid artery in primary hyperparathyroidism.

Patients with primary hyperparathyroidism (PHPT) have an increased cardiovascular morbidity and mortality. Elevated serum calcium and/or PTH may directly contribute to vascular tissue damage, but the role of classic factors for atherosclerosis has not fully been evaluated in this disease. The aim of our study was to dissect the potential effect of hypercalcemia and/or high PTH from that of major cardiovascular risk factors (i.e. diabetes mellitus, hyperlipidemia, hypertension, obesity, smoking habit) on the carotid artery structure of patients with PHPT. Twenty-six consecutive patients with PHPT [subdivided into two groups according to the absence (n = 10) or the presence (n = 16) of one or more risk factors] and 15 normocalcemic healthy subjects as controls were studied. At ultrasonography, a significant increase (P < 0.001) of carotid mean and maximum intima-media thickness, as well as a significant reduction of lumen diameter (P < 0.05) were found in the PHPT group with risk factors, compared with the other two groups. This suggests that hypercalcemia and/or PTH elevation per se are not determinant of carotid atherosclerosis in PHPT, and that increased cardiovascular mortality and morbility in this disease is attributable to the combined presence of classic cardiovascular risk factors.

Microstructure of the trabecula and cortex of iliac bone in primary hyperparathyroidism patients determined using histomorphometry and node-strut analysis.

The purpose of this study was to use histomorphometry to compare the microstructure of trabecular and cortical bone in patients with primary hyperparathyroidism (PH) with that seen in osteoporosis. Histomorphometric and node-strut analyses of iliac bones were performed on 11 female patients with PH (61.3 +/- 8.0 years old) and 61 age-matched female patients with involutional osteoporosis (OP) (63.6 +/- 5.6 years old). Cancellous bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), and wall thickness (W.Th) were not significantly different in these two groups. The bone formation rate (BFR) tended to be higher in the PH group than in the OP group. The number of nodes (N.Nd/TV) and node-to-node strut length (Nd.Nd/TV) were significantly higher in the PH group than in the OP group. The number of termini (N.Tm/TV) and terminus-to-terminus strut length/total strut length (Tm.Tm/TSL) were significantly lower in the PH group; cortical porosity was significantly higher in the PH group than in the OP group. No correlation was found between age and N.Nd in the PH group, but there was a negative correlation between age and N.Nd in the OP group. Our results show that trabecular connectivity was maintained while cortical porosity deteriorated in patients with PH compared with OP. These results suggest that there are microstructural differences between PH and OP in cancellous and cortical bone that result from the bone remodeling sequence in humans.

Lack of relationship between BsmI vitamin D receptor polymorphism and primary hyperparathyroidism in a Spanish female population.

The role of vitamin D receptor (VDR) gene polymorphisms in the pathogenesis of hyperparathyroidism is uncertain. Controversial results have been reported. The aim of this study was to explore the relevance of BsmI VDR gene polymorphism in patients with primary hyperparathyroidism (PHPT) due to adenomas. For this purpose, 36 postmenopausal patients with PHPT, mean age 64 years, were compared with a normal age-matched female population (n = 81). BsmI polymorphism distribution in PHPT group was as follows: Bb 50% (18/36); BB 22% (8/36); bb 28% (10/36). In the control group, the distribution was Bb 49% (40/81); BB 16% (13/81); bb 35% (28/81). No statistical differences were found between the two groups. In the PHPT group, no statistical associations were found between different allelic distribution and age, creatinine, hematocrit, phosphorus, alkaline phosphatase (ALP), total calcium, serum parathyroid hormone (PTH), or gland weight. By contrast, levels of serum calcium and iPTH values positively correlated with the PT weight (r = 0.421 and 0.599, respectively, P = 0.0001). Our data suggest that at least in this group, BsmI VDR gene polymorphism appears to be of minor relevance in clinical presentation and possibly, tumorigenesis in PHPT due to adenomas.

Characteristics of Biochemical Markers in Patients with Metabolic Bone Disorders.

Biochemical markers of bone turnover are expected to have some different characteristics among bone metabolic disorders. We compared bone formation markers: serum total alkaline phosphatase (s-Alp), serum osteocalcin (s-OC) and serum carboxy-terminal propeptide of type I collagen (s-PICP); and bone resoiption markers: serum carboxy-terminal telopeptide of type I collagen (s-ICTP), urinary pyridinoline (u-Pyr) and urinary deoxypyridinoline (u-Dpyr) to examine which marker is the most suitable and reliable to evaluate bone turnover in patients with osteoporosis (n = 29), osteomalacia (n = 10), primary hyperparathyroidism (n = 6) and renal osteodystrophy (n = 21). The value of s-Alp in the osteomalacia group was significantly higher than those in the normal control group and the osteoporosis group (p<0.001), and T-score of s-Alp was significantly higher than those of s-OC and s-PICP in the osteomalacia group. The values of u-Pyr and u-Dpyr in the primary hyperparathyroidism group were significantly higher than those in the other groups (p < 0.001). S-PICP, which are not dependent upon renal function, was much higher in the renal osteodystrophy group man in all other groups. In the osteoporosis group, T-score of s-ICTP was significantly higher than those of s-OC. Thus, s-Alp was a good marker in osteomalacia, u-Pyr and u-Dpyr in primary hyperparathyroidism, s-PICP in renal osteodystrophy, and s-ICTP in osteoporosis.

Accelerated bone loss in post-menopausal women with mild primary hyperparathyroidism.

Osteopenia is regarded as an indication for parathyroidectomy in primary hyperparathyroidism. However, uncertainty exists as to the extent and degree of the skeletal effects in those with mild disease. We sought to determine whether mild primary hyperparathyroidism affects the rate of bone loss in postmenopausal women. Prospective 2-year comparison of rates of bone loss throughout the skeleton in 17 post-menopausal women with untreated mild asymptomatic primary hyperparathyroidism, and 48 age-matched, eucalcaemic controls. The women with primary hyperparathyroidism had a greater annual rate of loss of bone mineral density (BMD) of the total body (mean +/- SE, primary hyperparathyroidism -1.15 +/- 0.31%, controls -0.39 +/- 0.10%; P = 0.04) and its spine subregion (primary hyperparathyroidism -2.08 +/- 0.88%, controls 0.04 +/- 0.35%; P = 0.02). Lumbar spine BMD tended to decline in the primary hyperparathyroidism group (-0.35 +/- 0.33%) in contrast to the control group (+0.28 +/- 0.22%) (P = 0.10). There were no significant differences between the groups in rates of changes of BMD in the legs or the proximal femur. In the primary hyperparathyroidism group, the rate of total body bone loss in the eight women known at study entry to have had long-standing (> 5 years) primary hyperparathyroidism was -1.52 +/- 0.61%/year, similar to that of the whole group. Primary hyperparathyroidism is associated with an increased rate of loss of total body bone mineral density in post-menopausal women. Prolonged disease duration is therefore likely to be associated with an increasing risk of osteopenia, such that skeletal surveillance and interventions designed to reduce bone loss should be considered.

Acute effects of intravenous 1α-hydroxycholecalciferol on parathyroid hormone, osteocalcin and calcitriol in man

The acute effects of a single intravenous injection of 2 micrograms of 1 alpha-hydroxycholecalciferol (alfacalcidol) were studied for a 24-h period in six normal males (mean age 33 years), six women with primary hyperparathyroidism (mean age 72 years) and six women with established osteoporosis (mean age 63 years). In all three groups, serum calcitriol levels rose to a peak 2-3 h after administration of alfacalcidol. Basal levels were highest in the primary hyperparathyroidism group at (mean +/- SEM) 81 +/- 2 vs 62 +/- 12 (normal males) (p < 0.05) and 56 +/- 5 pmol/l (osteoporosis) (p < 0.01). Highest peak levels were found also in the primary hyperparathyroidism group at 150 +/- 15 vs 114 +/- 15 (normal males) (p < 0.05) and 127 +/- 15 pmol/l (osteoporosis) (p < 0.01). The rise in calcitriol was higher in the primary hyperparathyroidism group than either the normal males or osteoporotic patients (p < 0.05). No significant differences were evident in basal serum calcidiol concentrations among the three treatment groups. As might be expected, highest basal concentrations of parathyroid hormone (PTH), serum calcium and serum osteocalcin were noted in the primary hyperparathyroid group (PTH: 17.1 +/- 7.7 vs 1.9 +/- 0.5 (normal males) (p < 0.01) and 2.1 +/- 0.3 pmol/l (osteoporosis) (p < 0.01); calcium: 3.06 +/- 0.08 vs 2.50 +/- 0.02 (normal males) (p < 0.01) and 2.43 +/- 0.02 mmol/l (osteoporosis) (p < 0.01); osteocalcin: 1.10 +/- 0.08 vs 0.56 +/- 0.16 (normal males) (p < 0.05) and 0.53 +/- 0.21 nmol/l (osteoporosis) (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Primary hyperparathyroidism: Iliac crest trabecular bone volume, structure, remodeling, and balance evaluated by histomorphometric methods

Iliac bone biopsies from 69 patients (48 females, 21 males; median age 58 years; range 17–79 years) with primary hyperparathyroidism (PHP) were examined, and static histomorphometric parameters compared to 30 age- and sexmatched normal controls. The control group for the dynamic parameters constituted 20 sex-matched younger normal controls. Fractional volume of trabecular bone was normal, but the trabeculae were thinner ( p < 0.05) in PHP. The structural parameters marrow space star volume, intertrabecular distance, and mean trabecular plate density were not significantly different in PHP patients compared to normal controls, but the age-related increase, for females, in marrow space star volume and decrease, for both sexes, in mean plate density observed in the controls were not noticed in the PHP group. Trabecular bone remodeling was found significantly increased in the PHP patients reflected by increased extension of eroded ( p < 0.001), osteoid ( p < 0.001), and labeled surfaces ( p < 0.05). The activation frequency was increased by approximately 50% ( p < 0.001). Neither PHP patients nor controls showed age-related decrease in trabecular thickness, and accordingly in both groups the bone balance per remodeling cycle was very close to and not significantly different from zero. Normal postmenopausal women (age ≥ 50 yr) had lower trabecular bone volume ( p < 0.001) and higher intertrabecular distance than normal pre-menopausal women (age < 50 yr). This difference was not found for PHP women, indicating that PHP women in some way seem to be protected from the accelerated bone loss seen in normal women in connection with the menopause. It was concluded that due to an enhanced activation frequency, trabecular bone remodeling was increased in PHP. Except for a slight thinning of trabeculae, no changes in trabecular bone structure were found, and the study displayed no indications of an accelerated bone loss. On the contrary, the data suggested conservation of bone volume with aging in PHP.

Immunoreactivity of plasma parathyrin-related peptide: three region-specific radioimmunoassays and a two-site immunoradiometric assay compared

We measured parathyrin (parathyroid hormone)-related peptide (PTHRP) in plasma by three region-specific RIAs and compared them with an established two-site immunoradiometric assay (IRMA) of PTHRP1-86 in samples from control subjects and from patients with primary hyperparathyroidism (PH) and humoral hypercalcemia of malignancy (HHM). The two direct RIAs of PTHRP1-34 and PTHRP37-67 were specific for regions 9-18 and 52-61, respectively. In the extraction RIA of PTHRP1-34 we used an affinity gel containing a monoclonal antibody specific for the 17-27 sequence; cross-reacting PTHRP species eluted from the gel were assayed by the RIA of PTHRP1-34. PTHRP1-86 plasma concentrations by IRMA were less than 0.23 pmol/L in control subjects and patients with PH, and were significantly increased in patients with HHM (mean 6.1 pmol/L, P less than 0.001). In contrast, plasma PTHRP1-34 concentrations were not significantly different in the three groups; in HHM patients, the mean was 190 pmol/L. Plasma PTHRP37-67 concentrations were similar in control and PH groups and, although significantly increased in HHM patients (mean 440 pmol/L, P less than 0.002), showed poor diagnostic discrimination. PTHRP1-34 concentrations after affinity extraction of plasma were also significantly higher in HHM patients (mean 10.7 pmol/L, P less than 0.001), but showed incomplete diagnostic discrimination. We conclude that the diagnostic utility of the direct RIAs for quantifying PTHRP is markedly inferior to the IRMA of PTHRP1-86.

Immunohistochemical Studies on the Thyroid C-cells in Primary Hyperparathyroidism

This study was conducted in order to establish whether C cells, which are responsible for secretion of calcitonin within the thyroid gland, change either in volume or morphology under conditions of chronic hypercalcemia in primary hyperparathyroidism. Out of 106 primary hyperparathyroid patients undergoing surgery, in 11 cases the thyroids were excised and examined for changes in the C cell. As a control group we used thyroids removed in another 14 cases undergoing thyroidectomy or laryngectomy. Calcitonin in the C cell was observed by optical microscope after immuno staining using the indirect peroxidase-labeled antibody technique. C cells are not evenly distributed within the thyroid. However, there is excellent positive correlation (p less than 0.001) between the C-cell index, which is the average of two tissue samples excised from the area at the border between the upper 1/3 and middle 1/3 of the thyroid lobe (the area where most C cells are found), and the total number of C cells. The C-cell index can thus be used as an indicator of the total number of C cells in the thyroid. The number of C cells decreased (p less than 0.01) as the level of calcium in serum increased. In patients with primary hyperparathyroidism, this decrease in C cells was significantly greater (p less than 0.025) than in the controls. Focal C cell hyperplasia and diffuse C cell hyperplasia were present in both the control group and primary hyperparathyroid group, but there was no significant difference between the two groups as to the frequency of occurrence. For both these conditions the rate of occurrence was considered within normal ranges for C cell morphology. We concluded that the decrease in C-cell count in primary hyperparathyroidism patients with chronic hypercalcemia is due to consumption of calcitonin in the C cell.

Blood pressure, left ventricular mass and intracellular calcium in primary hyperparathyroidism

1. Blood pressure, left ventricular mass and platelet cytosolic free calcium concentrations were measured in 23 patients with untreated primary hyperparathyroidism, 30 normotensive control subjects and 23 control subjects matched for age, sex and blood pressure. In 12 patients measurements were repeated after parathyroidectomy. 2. Patients with primary hyperparathyroidism had significantly elevated blood pressures (139 +/- 6/86 +/- 3 mmHg, mean +/- SEM) compared with control subjects (125 +/- 2/78 +/- 1 mmHg), but high values persisted after hypercalcaemia was corrected. 3. Despite chronic extracellular hypercalcaemia, intracellular free calcium levels were lower in patients with hyperparathyroidism than in controls matched for age, sex and blood pressure (median concentrations 81.5 nmol/l vs 93 nmol/l, 95% confidence interval 0.1 to 20.1; P less than 0.05) and values tended to increase after parathyroidectomy. 4. Left ventricular mass index was increased in the primary hyperparathyroid group as compared with control subjects matched for age, sex and blood pressure (123 g/m2 vs 100 g/m2, 95% confidence interval -36.1 to -3.1; P = 0.03). Parathyroidectomy resulted in a small reduction of the left ventricular mass index (123.5 g/m2 vs 104 g/m2, 95% confidence interval 46.5 to 2.5; P = 0.1) but no change in blood pressure. 5. Hypertension and left ventricular hypertrophy in primary hyperparathyroidism are associated with relatively low levels of free calcium in platelets.

Natural History of Treated Primary Hyperparathyroidism

A follow-up study of patients operated on for primary hyperparathyroidism revealed that recurrent hypercalcemia is uncommon in patients with solitary adenoma, but common in patients with multiglandular disease. The result of parathyroidectomy on the different symptoms of primary hyperparathyroidism is good. On the other hand, even after successful surgery, patients with primary hyperparathyroidism have poorer health than controls, and they also have a higher mortality rate. Most of the deaths in the primary hyperparathyroidism group are caused by cardiovascular disease. The effect of the preoperative serum calcium level on the later state of health is evident.

Possibility of elevated parathyroid function in patients with calcium-containing nephrolithiasis as compared with normal controls.

109 patients with calcium-containing nephrolithiasis and 10 normal controls underwent oral calcium load test. After thorough examination, 6 of the 109 patients were diagnosed as having primary hyperparathyroidism (PHPT) and the remainder as having normocalcemic nephrolithiasis without PHPT. Following the oral calcium load test, the latter were operationally divided into 3 groups - normocalciuric nephrolithiasis (NN), n = 78; absorptive hypercalciuria (AH), n = 10, and renal hypercalciuria (RH), n = 15 - according to the criteria reported by Pak et al. Before the oral calcium load test, nephrogenous adenosine 3',5'-monophosphate (NcAMP), urinary adenosine 3'-5'-monophosphate (urinary cAMP), and plasma immunoreactive parathyroid hormone (iPTH) were determined to evaluate parathyroid function. This function, as assessed by mean basal NcAMP in the NN, AH and RH groups as well as the PHPT group, was significantly increased as compared with that in the normal controls. Within the NcAMP-elevated 4 groups, the mean basal NcAMP was highest in the PHPT group followed by the RH, AH and NN groups. In view of the mean basal NcAMP, disregarding the PHPT group, the NN and AH groups seemed to be intermediate types between the normal controls and the RH groups. Similar, but less distinctive results were obtained in the determination of urinary cAMP and plasma iPTH. On the other hand, when leaving the PHPT group out, the mean basal urinary calcium creatinine ratio (Ca/Cr) was highest in the RH group followed by the AH and NN groups, and lowest in normal controls, suggesting that the NN and AH groups were intermediate between normal controls and the RH group. The mean basal urinary Ca/Cr ratio in the PHPT group was moderately elevated but not remarkable. Almost similar tendencies were observed in 24-hour urinary calcium excretions on a calcium-restricted diet. A weakly positive correlation (r = 0.232, p less than 0.05) between basal NcAMP and basal urinary Ca/Cr ratio was observed in accumulated cases of the NN, AH and RH groups, whereas a negative correlation (r = -0.664, p less than 0.05) was obtained in normal controls. It is concluded that a possible abnormal calcium metabolism is suggested in stone formers without PHPT. Additionally, it is speculated that 'relative hypercalciuria' in NN and hypercalciuria in AH and RH might be accounted for in a single line of a primary renal leak of calcium.

Trabecular bone remodeling and balance in primary hyperparathyroidism

The total remodeling sequences in 19 primary hyperparathyroid patients and 16 approximately age-matched and sex-matched controls were reconstructed from histomorphometric analyses of bone specimens obtained after intravital tetracycline double labeling. In the primary hyperparathyroid group the total amount of work performed by resorptive cells was reduced, as indicated by the significantly lower three-dimensional mononuclear and preosteoblast-like cell resorption depths (35.8 μm vs 44.5 μm in normals, P < 0.01 and 45.3 μm vs 56.6 μm in normals, P < 0.01, respectively). The active resorption period (i.e., the function period for osteoclasts and mononuclear cells) was reduced to 19 days compared to 29 days in normals ( P < 0.05), but no difference with respect to bone resorption rates could be demonstrated between the two groups. The median bone formation period (Sigma f) in primary hyperparathyroid patients was not different from the value obtained in normals (172 days vs 134 days, respectively), and the matrix appositional rate (A ma), as well as the mineralization lag time (t m), were also unchanged. The initial mineralization rate (A mi(i)) was not significantly different from the value obtained in normals, but averaged over the total bone formation period, a reduced mineralization rate could be demonstrated (0.32 μm 3 μm 2 per day vs 0.46 μm 3 μm 2 per day in normals, P < 0.01). The measured final three-dimensional thickness of bone formed during Sigma f (mcwT m) was reduced in the primary hyperparathyroid group (51.1 μm vs 55.9 μm in normals, P < 0.02). The balance between resorption and formation was analyzed using measured as well as growth curve-based estimates for mean thickness of completed walls (mcwT m and mcwT c, respectively). Dependent on the values used, a zero to slightly positive balance between resorption and formation was calculated. The birth rate of new remodeling cycles (μ), defined as the frequency by which a given point on the trabecular surface undergoes new remodeling, was increased in the group of primary hyperparathyroid patients (19 × 10 −4 days −1 vs 12 × 10 −4 days −1 in normals, P < 0.05).

Decreased plasma calcitonin response to a calcium clamp in primary hyperparathyroidism.

In order preoperatively to evaluate the calcium induced plasma calcitonin (CT) response in patients with mild primary hyperparathyroidism (PHPT), 7 postmenopausal (PM) females with PHPT and 14 PM healthy subjects underwent a 2 h calcium infusion. The infusions were performed by means of the 'calcium clamp' technique previously described by us in order to obtain an identical calcium stimulus in all subjects. Immunoreactive calcitonin (iCT) was determined by means of a sensitive RIA utilizing rabbit antibodies directed against the carboxy-terminal amino acid sequence of the CT molecule. All patients with PHPT had normal basal plasma iCT levels: 10 +/- 5 pg-eq/ml (mean +/- SD) as a group and not different from the control group: 13 +/- 5 pg-eq/ml. In the control group significantly increased plasma iCT was seen at 30, 60, 90 and 120 min in contrast to that of the PHPT group where a blunted response was observed. The results indicate a diminished CT reserve in these patients which may imply an impaired defence against the PTH mediated bone resorption seen in patients with PHPT.

Effect of acute cimetidine administration on indices of parathyroid hormone action in healthy subjects and patients with primary and secondary hyperparathyroidism.

To evaluate the acute effect of histamine H2-receptor blockade with cimetidine on PTH concentrations and its endogenous biological activity, we studied the effect of iv administration of cimetidine (50-mg bolus followed by 500 mg/60 min infusion) in normal subjects and patients with primary and secondary hyperparathyroidism. No significant changes in serum concentrations of calcium, phosphate, or immunoreactive C-terminal PTH were found in any group. However, the control group had decreased calciuria, increased phosphaturia, and decreased tubular reabsorption of phosphate, while the primary hyperparathyroid group had increased phosphaturia, increased nephrogenous cAMP excretion, and decreased tubular reabsorption of phosphate. In both of these groups, the finding suggest an increase in PTH-like biological activity. These findings suggest that cimetidine is not useful in the diagnosis or medical management of hyperparathyroidism. In fact, the changes in renal calcium and phosphorous excretion indicative of PTH-like biological activity along with a decrease in creatinine clearance in the primary hyperparathyroid group suggest a relative contraindication to the use of this drug in these patients.

The Pathogenesis of Idiopathic Hypercalciuria: Evidence for Parathyroid Hyperfunction

We studied the effect of calcium deprivation and loading in 17 healthy subjects and 76 patients with renal calculi. Five had primary hyperparathyroidism with an elevated plasma ionised calcium and detectable plasma parathyroid hormone. Forty-nine had idiopathic hypercalciuria, defined by a urine calcium greater than 7 mmol/day on a free diet. Twenty-two were normocalciuric. Fasting plasma calcium, corrected for albumin, was higher in the patients with idiopathic hypercalciuria (2.40 +/- 0.10 mmol/l) than in controls (2.28 +/- 0.05 mmol/l, p less than 0.005). Plasma calcium was intermediate in the normocalciuric stone formers (2.35 +/- 0.08 mmol/l) and elevated in the patients with primary hyperparathyroidism (2.62 +/- 0.07 mmol/l). Nephrogenous cyclic adenosine monophosphate (cAMP) and parathyroid hormone levels were highest in the primary hyperparathyroid group and did not differ significantly within the other groups. Nephrogenous cAMP correlated positively with plasma calcium in the patients with primary hyperparathyroidism and negatively in controls; there was no correlation in the idiopathic hypercalciuria group. Following an oral calcium load, plasma calcium rose and nephrogenous cAMP fell similarly in all groups. Fasting urinary calcium and its increase after load were greatest in the idiopathic hypercalciuria and primary hyperparathyroid groups, with intermediate results in the normocalciuric patients. Neither the initial metabolic patterns nor the response to thiazide fitted with the previously described patterns of absorptive and renal hypercalciuria. Increased parathyroid gland activity is the most probable cause of idiopathic hypercalciuria.

Parathormone and cyclic AMP production in human cryopreserved parathyroids

To compare the in vitro response of cryopreserved parathyroid cells from patients with primary and secondary hyperparathyroidism (HPT), immunoreactive parathormone (i-PTH) and cyclic AMP (i-cAMP) were measured at low (0.5 m M) and high (3.0 m M) calcium concentrations in a cell dispersion preparation. The in vitro suppressibility of i-PTH was 23 ± 4% in the primary HPT group and 50 ± 5% in the secondary HPT group ( P < 0.01). The suppressibility of i-cAMP production in patients with primary and secondary HPT was 50 ± 2 and 19 ± 6%, respectively ( P < 0.01). Evaluation of i-cAMP production by β-adrenergic (isoproterenol) stimulation in both primary and secondary HPT revealed a suppressibility similar to the isoproterenol-free group. This study demonstrated, in vitro, that cryopreserved parathyroid cells from primary HPT are less suppressible by calcium than those from secondary HPT, and that an abnormal calcium-regulated adenylate cyclase-c-AMP system may be an important factor in altered PTH secretion of neoplastic parathyroid tissue.