Ga3+ inhibits parathyroid hormone release without interacting with the Ca2+ receptor of the parathyroid cell

Gallium nitrate is an antihypercalcemic agent with established actions on bone. The effects of Ga(NO3)3 on parathyroid hormone (PTH) release, cytoplasmic Ca2+ concentration ([Ca2+]i) and cAMP production of enzymatically dispersed parathyroid cells from bovine as well as normal and pathological human parathyroid glands have now been studied. Ga3+ at 200 microM inhibited PTH release whereas 600 microM NO3- had no effect. The inhibition was additive to that obtained by elevating extracellular Ca2+. Unlike Ca2+, Ga3+ failed to increase [Ca2+]i or reduce cAMP formation. The results indicate that Ga3+ inhibits PTH release by a mechanism other than activation of the cation receptor of the parathyroid cells. This mechanism may contribute also to inhibition by other cations.

Fluoride interactions with stimulus-secretion coupling of normal and pathological parathyroid cells

Effects of the GTP binding protein (G-protein) activator NaF on parathyroid hormone (PTH) release, cytoplasmic Ca2+ concentration ([Ca2+]i) and cAMP content of bovine as well as normal and pathological human parathyroid cells were studied using precautions to avoid CaF2 precipitation. In 0.5 mM external Ca2+, NaF inhibited PTH release and lowered the cAMP content by 50-70% of the effects attained with 3.0 mM Ca2+. The NaF-induced increase of [Ca2+]i was considerably smaller than that obtained with rise of external Ca2+. It seems likely that NaF activates the inhibitory G1-protein involved in the regulation of cAMP generation. However, it is unclear whether the sluggish rise of [Ca2+]i induced by NaF is due to a direct effect of a G-protein on Ca2+ entry, or somehow related to the G-protein mediated formation of inositol 1,4,5-trisphosphate, which is part of the signal transduction pathway normally initiated by Ca2+ binding to its receptor on the parathyroid cell surface. Inhibition of PTH release by NaF probably results from the combined effects on [Ca2+]i and cAMP content. In hyperparathyroidism (HPT) the actions of NaF were not markedly affected despite severe impairments of Ca(2+)-inhibited PTH release and Ca2+ triggered increase of [Ca2+]i. Consistent with observations of down regulation of the parathyroid Ca2+ receptor in HPT, the present results indicate that the disease perturbs signal transduction at a level proximal to the site of action for NaF.

Causes of failed primary exploration and technical aspects of re-operation in primary hyperparathyroidism

Hypercalcemia was corrected in 62 (90%) of 69 patients after re-operation for primary hyperparathyroidism during a mean follow-up of 6.3 years. Failed primary exploration was mainly due to inadequate visualization of the pathological parathyroid glands, often in association with misleading or absent peroperative histology. Other causes included seeding of parathyroid adenoma tissue, truly recurrent adenomas, and recurrent hyperplasia, especially in patients with multiple endocrine neoplasia type 1. A considerable number of parathyroid glands missed at the primary operations were subsequently found in essentially normal positions. Ectopic superior glands were most frequently positioned para-esophageally or retro-esophageally, while abnormally placed inferior glands were generally situated within or close to the thymus. Glands in 3 patients were dissected from around the large vessels in the mediastinum. Concomitant thyroid procedures during the primary operation yielded few abnormal parathyroids and made the re-exploration considerably more difficult. We suggest a semilateral approach and caudal identification of the recurrent laryngeal nerve to reduce the hazards of difficult parathyroid re-operations. Mediastinal exploration may require total removal of the thymus and careful dissection of the middle mediastinum.

Dynamics of parathyroid hormone release and serum calcium regulation after surgery for primary hyperparathyroidism

Analysis of 14 patients with primary hyperparathyroidism (HPT) prior to and during the first year after parathyroid surgery disclosed that the operation was associated with rapid reductions of intact serum parathyroid hormone (PTH) and total serum and ionized plasma calcium values. A decreased urinary calcium excretion, a gradual elevation of renal calcium reabsorption, a transient reduction of serum calcitriol, and a late increase in 25-hydroxycholecalciferol values were also noted. Dynamic tests of parathyroid function by EDTA infusion and an oral calcium load revealed a sigmoidal relationship between serum PTH and calcium levels, and that parathyroid surgery induced considerable changes in both the position and slope of the dose-response curve. It was also apparent that PTH release was submaximally stimulated event at periods of hypocalcemia. The findings substantiate that adjustments of PTH release to acute alterations of serum calcium occur along the prevailing dose-response relationship, while stimuli being maintained for longer periods of time induce compensatory shifts in the position and slope of this curve. It is further suggested that unknown factors with PTH-like function may participate in the calcium regulation after surgery for primary HPT.

Regulation of parathyroid hormone release in normal and pathological parathyroid cells exposed to modulators of protein kinase C

Effects of the protein kinase C activating phorbol ester 12-O-tetradecanoyl phorbol 13-acetate and the inhibitor 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7) on parathyroid hormone (PTH) release were studied in normal bovine and pathological human parathyroid cells. An increase of extracellular Ca2+ from 0.5 to 3.0 mmol/l inhibited PTH release by 60% in the bovine cells with half maximal effect (ED50) at 1.31 mmol/l. This inhibition reached less than 50% in the cells from patients with primary and uremic hyperparathyroidism, and the ED50 values were 1.49 and 1.42 mmol/l, respectively. The phorbol ester (0.1 mumol/l) made secretion insensitive to changes of extracellular Ca2+, an action counteracted by H-7 (50 mumol/l) in the bovine cells, whereas H-7 alone had no effects. The phorbol ester and H-7 had opposite actions on regulation of PTH release also from cells from patients with hyperparathyroidism. However, in pathological cells H-7 alone improved Ca2+ inhibition of secretion by stimulating release in low Ca2+ concentrations and decreasing the ED50 values. The magnitude of changes in ED50 values by H-7 increased with the severity of the secretory disturbance of the pathological cells. The results indicate that increased protein kinase C activity may be a factor of importance in the pathophysiology of hyperparathyroidism.

Capsaicin pretreatment of rats does not prevent tissue extravasation of albumin from intra-abdominal trauma

Intra-abdominal surgery causes a loss of plasma into tissues within and around the abdomen, predisposing to a decreased tissue viability and postoperative complications. In a rat model of intra-abdominal trauma, we investigated whether neuropeptides released from thin afferent nerve endings may contribute to this extravasation. Newborn male Wistar rats were pretreated with capsaicin 50 mg/kg s.c., leading to a lifelong degeneration of thin afferents. The same animals, when adult, were subjected to experiments under chloralose anesthesia in which tissue clearances of radiolabelled albumin were determined by a double isotope technique. Non-pretreated animals served as controls. In non-traumatized animals, pretreated rats had a higher loss of labelled albumin in calf muscle. In animals subjected to the standardized intra-abdominal trauma, the pretreatment did not decrease the trauma-induced loss of albumin. In neck skin, the loss of protein was higher in pretreated animals, possibly due to a decreased trauma-induced sympathetic activation. In conclusion, degeneration of thin afferent fibers may alter the autonomic reflex response to intra-abdominal trauma, but neuropeptide release from afferents apparently plays no role in the relocation of albumin.

Immunoelectron microscopical evidence of a calcium receptor function in parathyroid, placenta and kidney

The parathyroid, kidney and placenta have been investigated for ultrastructural signs of immunostaining with a murine monoclonal IgG 1-antibody denoted E11. Dispersed cells and tissue sections revealed a finely granular, electron dense precipitate after fixation with periodate-lysine-paraformaldehyde and indirect immunoperoxidase staining with the native or biotinylated antibody. This precipitate was confined to the surface membrane of parathyroid chief cells of normal and adenomatous human glands as well as the bovine and rat parathyroid parenchyma, preferentially the brush border membrane of proximal tubular cells in the human, rat and mouse kidney, cytotrophoblast cells of the human placenta, and trophoblast cells lining fetal blood vessels in the rat placenta. Since the E11 antibody recognizes a large glycoprotein regulating intracellular calcium mobilization and cation fluxes across the cell membrane, the present findings suggest the existence of a similar calcium receptor function on cells involved in different aspects of the calcium homeostasis within a variety of species.

Parathyroid-like regulation of parathyroid-hormone-related protein release and cytoplasmic calcium in cytotrophoblast cells of human placenta

Immunohistochemical staining of human placenta revealed intense reactivity for amino terminal and midregional parathyroid-hormone-related protein (PTHrp) in the cytotrophoblast cells and weaker staining in the syncytiotrophoblasts. The cytotrophoblasts also displayed conspicuous surface staining with the monoclonal antibodies E11 and G11, which recognize a Ca2+ receptor mechanism regulating hormone release of parathyroid cells. Cytotrophoblasts enriched on Percoll gradients or by linking surface-bound E11 to magnetic beads revealed biphasic elevation of cytoplasmic Ca2+ ([Ca2+]i) upon a stepwise rise of external Ca2+ from 0.5 to 3.0 mM, with a half-maximal effect at 1.75 mM. Individual cytotrophoblasts identified by their E11 reactivity disclosed a temporary increase of [Ca2+]i upon elevation of external Mg2+, while Mn2+ triggered both a [Ca2+]i transient and an influx of itself. These effects were efficiently blocked by the G11 antibody. Depolarization with K+ or addition of the voltage-dependent Ca2+ channel blocker verapamil had only marginal effects on [Ca2+]i. Raised extracellular calcium inhibited release of PTHrp from the cells, and this inhibition was blocked by the G11 antibody. The virtually parathyroid-identical Ca2+ regulation of [Ca2+]i may mediate feedback control of PTHrp release from the cytotrophoblasts and thereby participate in the regulation of placental Ca2+ transport.

Neomycin interacts with Ca2+ sensing of normal and adenomatous parathyroid cells

Effects of the polyvalent cationic antibiotic neomycin on regulation of the cytoplasmic Ca2+ concentration ([Ca2+]i) were studied in normal and adenomatous human, and bovine parathyroid cells. Parathyroid hormone (PTH) release was also measured in the bovine cells. Elevation of extracellular Ca2+ from 0.5 to 3 mM caused biphasic increase of [Ca2+]i and inhibition of PTH release. In low external Ca2+ neomycin inhibited PTH release and virtually only triggered the [Ca2+]i transient. In contrast [Ca2+]i was lowered and PTH release stimulated by neomycin in the presence of 3.0 mM Ca2+ or 7 mM Mg2+. These actions of Ca2+ and neomycin on [Ca2+]i were qualitatively similar but less pronounced in the adenomatous than normal human parathyroid cells. Some effects of neomycin were thus similar to those induced by other cationic agents interacting with the Ca2+ receptor mechanism on the parathyroid cell surface, whereas others may involve phospholipase C inhibition, protein kinase C activation or a direct reduction of the Ca2+ influx.

Histological and clinical features of non-familial primary parathyroid hyperplasia

Relations between histopathological characteristics and clinical data were retrospectively investigated in patients with sporadic primary hyperparathyroidism due to hyperplasia. The study comprised 100 patients with chief cell hyperplasia and nine with hyperplasia of the water-clear cell type operated on during the period of 1959-1989. The chief cell hyperplasia was associated with a renal stone disorder as the predominant symptom in 41 patients, psychiatric/neuromuscular manifestations in 26 patients, while 23 patients were apparently asymptomatic. The remaining ten patients had miscellaneous symptoms. Patients with renal stones were more frequently of the male sex and generally had lower serum calcium values and less marked increments in total parathyroid glandular weights than patients with other symptoms or those who were overtly asymptomatic. Two main morphological patterns, diffuse and nodular hyperplasia, were encountered in chief cell hyperplasia. Diffuse hyperplasia was usually found in moderately enlarged glands, with a less variable size and morphology. It was also more prevalent among young patients having moderate hypercalcaemia and either recurrent renal stones or neuromuscular/psychiatric symptoms. The glands affected by nodular hyperplasia were asymmetric in size with a variable cellular arrangement and a high proportion of oxyphil cells. Nodular hyperplasia was irrespective of symptoms more frequent in the elderly patients. Water-clear cell hyperplasia was not encountered during the last decade of the study and until then it was an occasional finding in patients with marked hypercalcaemia. In this histological entity the glands were greatly and asymmetrically enlarged.

Cellular physiology and pathophysiology of the parathyroid glands

This report provides insight into parathyroid gland physiology and the pathophysiology of hyperparathyroidism (HPT). Increases in the extracellular calcium concentration constitute the primary physiological signal for inhibition of parathyroid hormone (PTH) release. Transduction of the external signal into a cellular response involves activation of a cation receptor mechanism on the plasma membrane with rapid rise in the cytoplasmic calcium concentration of the cells. This recently discovered parathyroid calcium receptor has been characterized as a glycoprotein of unusually high molecular weight, which may play a key role in calcium homeostasis since it is also expressed in the kidney and placenta. Binding of external calcium to the receptor is associated with mobilization of intracellular calcium as well as calcium influx into the cells and phosphoinositol hydrolysis. These events rapidly interfere with the release process through essentially unknown mechanisms and probably also at sustained stimulation inhibit PTH gene transcription. The relative calcium insensitivity of the PTH release in HPT is associated with a deranged regulation of cytoplasmic calcium within pathological parathyroid cells. The molecular basis for this disturbance comprises down regulation of the cation receptor, whereby external calcium is translated into abnormally low levels of cytoplasmic calcium and insufficient inhibition of PTH release. Studies on expression of the functionally important cation sensing glycoprotein and its associated cellular signal systems may provide novel means for interference with the pathophysiological derangements of HPT.

The role of the pathologist in diagnosis and surgical decision making in hyperparathyroidism

Hyperparathyroidism has been diagnosed with increasing frequency in recent decades. The concomitant awareness that the disease may be the cause of a concealed morbidity and even an increased mortality has resulted in more liberal indications for surgery. Many patients currently undergo surgery on the grounds of only mild hypercalcemia and in the absence of any apparent clinical symptoms. This policy of early surgical treatment has emphasized the importance of a histopathological parathyroid diagnosis, since many of these patients exhibit chief cell hyperplasia and minimal glandular enlargement. Light microscopic examination of frozen sections stained with hematoxylin-eosin and with stains for demonstration of cytoplasmic fat in the parathyroid chief cells, and appropriate weight estimates of the parathyroid glands, constitute the conventional, intra-operative basis for the diagnosis. The use of specific antiparathyroid antibodies is an important new tool in the histopathological parathyroid examination, mainly because of the ability to demonstrate the cause of increased parathyroid hormone release from the pathological parathyroid tissue. A careful histopathological examination in combination with gross inspection of the parathyroid glands by an experienced eye should contribute to adequate surgical treatment and minimize errors in operative management in patients with hyperparathyroidism.

Distribution of monoclonal antiparathyroid antibody E11 in mice grafted with human parathyroid adenoma and carcinoma

One hundred six immunoincompetent mice grafted with human parathyroid adenoma or carcinoma were used to evaluate distribution of the murine monoclonal antibody E11, which recognizes a calcium sensor of high molecular weight on the parathyroid cell surface. The subcutaneous parathyroid grafts were infiltrated with murine fibrous tissue, which seemed to increase with the duration of transplantation and the size of inserted tissue pieces. Intraperitoneal injection of biotinylated or 125I-labeled E11 antibody indicated time- and dose-dependent antibody accumulation, as well as the presence of unoccupied binding sites in the transplanted parathyroid tissue. The iodinated intact immunoglobulin G and Fab fragment of the E11 antibody demonstrated low radioactivity in the lung, liver, spleen, kidney, and intestine for up to 14 days, except for the Fab fragment, which was rapidly accumulated and cleared from the kidney. The peak radioactivity ratio in the adenoma tissue versus blood averaged 2.8 for the intact antibody and 5.3 for the Fab fragment, whereas the corresponding values for the carcinoma tissue were 8.6 and 8.8, respectively. These ratios increased considerably, especially for the adenoma specimens, when weights of the excised grafts were adjusted for the calculated content of parathyroid tissue. The results support that the E11 antibody may localize even minute amounts of human parathyroid adenoma and carcinoma tissue.

Primary hyperparathyroidism: epidemiology, diagnosis and clinical picture

Primary hyperparathyroidism (HPT) is a common disorder that mainly afflicts elderly women. It can be diagnosed in at least 1% of all postmenopausal females and autopsy studies indicate an even higher frequency. Although the widespread use of automated serum calcium analyses has increased the awareness of HPT, only 10% of all cases seem to be identified. The diagnosis relies on the demonstration of an inappropriately elevated serum concentration of parathyroid hormone (PTH) relative to the serum calcium value, which need not be markedly raised. Measurements of intact PTH with immunometric methods have considerably improved the diagnostic precision but it is still difficult to evaluate patients with only marginal hypercalcemia. Few patients with diagnosed HPT are completely without symptoms. Symptoms commonly encountered are psychiatric and neuromuscular disturbances. Subclinical bone disease might be relevant but there is insufficient information about its importance in otherwise asymptomatic individuals. Various cardiovascular risk factors appear more commonly in patients with HPT and untreated disease is associated with an increased risk of premature death.

Longitudinal studies of mild primary hyperparathyroidism

In 1969, a health survey was offered to all inhabitants of a town district in Sweden. A clinical examination was carried out, and among other variables, a measurement was made of serum calcium. The same procedure was repeated in 1971. From these two investigations a cohort of 176 individuals (1.1%) with sustained hypercalcemia was identified who could be followed during the subsequent 15 years. Comparisons were made with an age- and sex-matched control group from the same health survey. Survival was significantly lower in the hypercalcemic cohort than in the control group. This reduction was related to the degree of hypercalcemia and apparently mainly due to diseases of the circulatory organs. There was no marked deterioration of renal function, and although there was in some patients a moderate progression of the hypercalcemia, none developed a hypercalcemic crisis during 15 years of follow-up. In consecutively referred patients with primary hyperparathyroidism, psychiatric disturbances of mainly a depressive character were found upon detailed analysis within a majority of the patients, and parathyroid surgery resulted in a clear improvement in mental health.

Multiple endocrine neoplasia type 1: a 10-year prospective screening study in four kindreds

A total of 80 individuals in 4 kindreds with multiple endocrine neoplasia type 1 (MEN 1) have been subjected to repeated biochemical screening during a 10-yr period with the principal aim being to analyze characteristics of the developing pancreatic lesion. Age at presentation of the MEN 1 trait averaged 18 yr in 7 previously unaffected individuals, and this effect of the screening procedure represented a lowering by almost 2 decades. Pancreatic endocrine involvement was recognized at a mean age of 25 yr and constituted the presenting lesion in a majority of the patients. A standardized meal test and basal values of serum pancreatic polypeptide, insulin, proinsulin, and gastrin were the most efficient markers for the pancreatic lesion and preceded signs of pancreatic tumors upon radiological examinations by a mean of 3.5 yr. A 75% penetrance of the islet cell disease and 90% for primary hyperparathyroidism within the affected individuals equalled the prevalences reported in autopsy studies. Two of the kindreds showed signs of intrafamilial homogeneity with respect to the profile of peptide excess (P less than 0.05) and considerable discrepancy in the malignant potential of the pancreatic lesions. The results of early detection and surgical intervention of the pancreatic tumors in MEN 1 suggested an impact on morbidity, while any effect on the mortality of these individuals remains to be clarified.

Hypertension in primary hyperparathyroidism in relation to histopathology

Hypertension in primary hyperparathyroidism (HPT) was previously attributed to hypercalcemia per se or to impaired kidney function. Of 441 consecutive patients operated on for HPT over 24 years, 57% were hypertensive. Preoperative blood pressure remained fairly constant during the study period, despite otherwise markedly changing clinical picture with, latterly, more asymptomatic patients. The preoperative systolic blood pressure (SBP) was significantly correlated to both serum calcium (p less than 0.001) and serum creatinine (p less than 0.05), but not when the influence of age was taken into account in a multiple regression analysis. Other pathogenetic factors in hypertension were therefore probable. When the statistical analysis was adjusted for differences in age and serum calcium, blood pressure was lower in the HPT patients with parathyroid hyperplasia than in those with adenoma (153 +/- 31/90 +/- 14 vs. 163 +/- 29/91 +/- 14 mmHg, p less than 0.01 for SBP). The concept that parathyroid hyperplasia represents a mild (early) form of HPT that may precede adenoma formation is corroborated by our observations, which also indicate that there is no simple cause-and-effect relationship accounting for hypertension in primary HPT.

Disturbance of basal and stimulated serum levels of intact parathyroid hormone in primary hyperparathyroidism

In patients with primary hyperparathyroidism, measurements were made of basal and stimulated levels of intact parathyroid hormone (PTH). The basal PTH values were elevated in all but six of 89 patients and provided clear separation towards normal individuals (n = 75) and patients with hypercalcemia of other origin (n = 34). The PTH value correlated with the serum calcium concentration in hyperparathyroidism and with the weight of excised parathyroid adenomas but not with that of chief cell hyperplasias. A constant ethylenediaminetetraacetic acid infusion during 60 minutes of induced essentially linear reductions of plasma-ionized calcium concentrations, averaging 0.02 mmol/L/10 minutes, which were associated with swift, curvilinear, elevations of PTH levels that reached a plateau after 10 to 20 minutes. The increment in serum PTH level correlated with the basal PTH value both in patients with hyperparathyroidism and controls. However, in proportion to the much greater glandular mass in the patients with hyperparathyroidism, the secretion of PTH was relatively reduced. The findings support the value of the intact PTH assay in the differential diagnosis of hypercalcemia and show that PTH secretion in vivo is extremely sensitive to hypocalcemic stimulation, that the pathological parathyroid tissue in hyperparathyroidism is characterized by a reduction of hormone release per unit weight, and that the hormone secretion in hyperparathyroidism operates closer to its maximal capacity than under normal circumstances.

Skeletal responsiveness to parathyroid hormone in healthy females: relationship to menopause and oestrogen replacement

In order to directly evaluate the role of parathyroid hormone (PTH) and its interaction with oestrogens for postmenopausal bone loss, studies were performed where synthetic human (1-38) PTH was infused s.c. over 24 h in 15 healthy females. Measurements were made of serum electrolytes, PTH and biochemical indices of bone turnover: serum osteocalcin and alkaline phosphatase and fasting urinary hydroxyproline and calcium. During the infusion of PTH there were significant increases of serum calcium (15%), fasting urinary calcium (55%) and hydroxyproline (80%) but a reduction of the serum osteocalcin concentrations (15%). There were significant relations between the calcaemic response and the increases of urinary calcium and hydroxyproline and the two latter were also closely related. There was, however, no correlation between the responses to PTH for the formative vs the resorptive indices. Postmenopausal women displayed greater increases of serum calcium and fasting urinary hydroxyproline indicating greater skeletal sensitivity to exogenous PTH. Following treatment with oestrogens the indices of skeletal responsiveness were reversed towards the premenopausal values. The findings demonstrate that during short-term infusion of PTH there is a dissociation between bone resorption and formation and, furthermore, that the menopause is associated with an enhanced skeletal sensitivity for PTH.

Tissue extravasation of albumin from intraabdominal trauma in rats

Intraabdominal surgery tends to lower circulating plasma volume by mechanisms unrelated to bleeding and evaporation. In chloralose-anesthetized rats, the tissue clearance of radiolabelled albumin was determined by a double isotope method. Animals were subjected to a standardized abdominal trauma, eliciting minimal bleeding and evaporation, and others served as controls. The trauma significantly increased tissue albumin extravasation in abdominal skin, abdominal wall, pancreas, small intestine, colon, mesentery and diaphragm. Considering the mass of the respective tissues, a substantial portion of the albumin extravasation took place in the abdominal wall. No increased albumin clearance was found in extra-abdominal tissues. It is suggested that abdominal surgery decreases plasma volume by extravasation in the operation field.

Abdominal surgery in patients with midgut carcinoid tumors

In patients with midgut carcinoid tumors a curative, radical tumor removal should be attempted when possible. As these tumors are generally malignant, irrespective of size, the radical surgery implies that intestinal resection for excision of a primary tumor should be combined with an extended mesenteric resection. When the patients present with the carcinoid syndrome the disease is, with few exceptions, too advanced for curative surgery. However, surgery often has to be performed also in patients with the advanced carcinoids. Patients with more extensive disease may thus benefit from surgical debulking of large mesenteric or hepatic metastases. Moreover, when the patients present with abdominal symptoms it is important to exclude a threatening major abdominal complication, such as intestinal obstruction or ischemia. As these complications may cause malnutrition and deterioration, it is important to treat them properly, sometimes by repeated surgery.