Thyrocalcitonin: stimulation of secretion by pentagastrin

Cholecystokinin expression in tumors: biogenetic and diagnostic implications

Cholecystokinin (CCK) is a classic gut hormone. CCK is also a complex system of peptides expressed in several molecular forms in enteroendocrine I cells, in cerebral and peripheral neurons, in cardiac myocytes and spermatozoa. CCK gene expression has now been found at protein or peptide level in different neuroendocrine tumors; cerebral gliomas and astrocytomas and specific pediatric tumors. Tumor hypersecretion of CCK was recently reported in a patient with a metastatic islet cell tumor and hypercholecystokininemia resulting in a novel tumor syndrome, the cholecystokininoma syndrome. This review presents an overview of the cell-specific biogenesis of CCK peptides, and a description of the CCK expression in tumors and of the cholecystokininoma syndrome. Finally, assays for the diagnosis of CCK-producing tumors are reviewed.

Thyroid C-Cell Biology and Oncogenic Transformation

The thyroid parafollicular cell, or commonly named "C-cell," functions in serum calcium homeostasis. Elevations in serum calcium trigger release of calcitonin from the C-cell, which in turn functions to inhibit absorption of calcium by the intestine, resorption of bone by the osteoclast, and reabsorption of calcium by renal tubular cells. Oncogenic transformation of the thyroid C-cell is thought to progress through a hyperplastic process prior to malignancy with increasing levels of serum calcitonin serving as a biomarker for tumor burden. The discovery that multiple endocrine neoplasia type 2 is caused by activating mutations of the RET gene serves to highlight the RET-RAS-MAPK signaling pathway in both initiation and progression of medullary thyroid carcinoma (MTC). Thyroid C-cells are known to express RET at high levels relative to most cell types; therefore, aberrant activation of this receptor is targeted primarily to the C-cell, providing one possible cause of tissue-specific oncogenesis. The role of RET signaling in normal C-cell function is unknown though calcitonin gene transcription appears to be sensitive to RET activation. Beyond RET, the modeling of oncogenesis in animals and screening of human tumors for candidate gene mutations have uncovered mutation of RAS family members and inactivation of Rb1 regulatory pathway as potential mediators of C-cell transformation. A growing understanding of how RET interacts with these pathways, both in normal C-cell function and during oncogenic transformation, will help in the development of novel molecular-targeted therapies.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Medullary Thyroid Carcinoma

Medullary thyroid carcinoma is a neuroendocrine tumor derived from the C cells of the thyroid gland and accounts for approximately 5% of all thyroid carcinomas. Approximately 30% of the cases are associated with an autosomal dominant syndrome called multiple endocrine neoplasia type 2, and the identification of these individuals is important because affected family members may benefit from an early diagnosis. The treatment of this disease is predominantly surgical, and the impact of radiotherapy and chemotherapy is limited. The identification of the associated molecular events has lead to the development of specific molecular targeted agents that may change the way this disease is treated in the near future.

Comparison of Two Provocative Tests for Calcitonin in Medullary Thyroid Carcinoma: Omeprazole vs Pentagastrin

Background: Provocative tests for calcitonin (CT) are fundamental in the diagnosis and follow-up of C-cell disease and in the detection of hereditary medullary thyroid carcinoma (MTC) carriers with unknown RET mutations. A recent report has proposed omeprazole, which can increase endogenous gastrin (GT), as a new provocative test for MTC.

Methods: We compared the omeprazole test (20 mg twice a day for 4 days) to the pentagastrin test (0.5 μg/kg of body weight) for the diagnosis and management of MTC. Twenty healthy individuals and 20 MTC patients with mildly or moderately increased basal CT serum concentrations underwent the pentagastrin and omeprazole tests.

Results: In MTC patients, the pentagastrin test produced a significantly higher increase in serum CT than did omeprazole. After the pentagastrin injection, several patients reported unpleasant side effects, including substantial tightness in 38 of 40 participants. No adverse effects were observed during the omeprazole test. A significant direct correlation was recorded between CT% (ratio of CT peak to basal value × 100) and GT% (ratio of GT peak to basal value × 100) during the omeprazole test in MTC patients (r = 0.73; P <0.001).

Conclusions: In spite of several adverse effects, pentagastrin remains the best provocative test for the diagnosis of MTC. Omeprazole may be useful when pentagastrin is contraindicated or refused because of the unpleasant side effects, but further validation is needed.

Long-term safety of proton pump inhibitors: risks of gastric neoplasia and infections

After Helicobacter pylori eradication was introduced and largely eliminated the need for maintenance therapy for peptic ulcer disease, gastroesophageal reflux disease (GERD) became the main indication for prolonged gastric acid inhibition. The drug effect on GERD depends on the degree of acid inhibition, thus the efficacious proton pump inhibitors are preferred. The proton pump inhibitors have few immediate side effects, the main concern being the profound hypoacidity and hypergastrinaemia they induce. In short-term, hypergastrinaemia causes rebound hyperacidity, possibly worsening GERD and reducing the efficacy of histamine H(2) blockers. In the long-term, hypergastrinaemia causes enterochromaffin-like cell hyperplasia and carcinoids. Since enterochromaffin-like cells may be important in gastric carcinogenesis, iatrogenic hypergastrinaemia may predispose to carcinoma. Gastric hypoacidity also increases gut bacterial infections, and the barrier function of acid against viral and prion infections requires further assessment.

Personal review: is profound acid inhibition safe?

Inhibitors of gastric acid secretion, particular proton pump inhibitors, are effective drugs in the treatment and prophylaxis of acid-related diseases. Proton pump inhibitors are therefore prescribed widely, often for minor complaints. Gastric acidity kills swallowed microorganisms, and acid secretion must be of biological importance because it is maintained in phylogenesis. Acid secretion is controlled by feedback mechanisms, mainly via gastrin. A decrease in acidity always causes an increase in plasma gastrin. The trophic effect of gastrin leads to hyperplasia and neoplasia of the enterochromaffin-like (ECL) cell. ECL cell derived tumours in man were previously regarded as rare, and also as rather benign. It is now clear that the ECL cell gives rise to a significant proportion of gastric carcinomas. Moreover, ECL cell carcinoids secondary to hypergastrinaemia may develop into highly malignant tumours. Treatment with a proton pump inhibitor is followed by rebound acid hypersecretion and decreased efficiency of H2-blockers, thus such treatment may induce a type of physical dependence. It is therefore reasonable to be cautious and not to treat younger (< 50 years) patients for long periods of time with profound inhibitors of gastric acid secretion. Chromogranin A in the blood is a sensitive marker of the ECL cell mass, and it could be used to survey patients on long-term proton pump inhibitors.

Nuclear receptors for 1,25-dihydroxy-22-oxavitamin D3 (OCT) and 1,25-dihydroxyvitamin D3 in gastric gland neck mucous cells and gastrin enteroendocrine cells

22-Oxacalcitriol the analog with low calcemic effect and the original hormone 1,25(OH)2 vitamin D3 were localized by autoradiography in mouse stomach at different time intervals after intravenous injection. Both compounds showed a distinct nuclear concentration and retention in neck mucous cells of gastric and pyloric glands, and in dispersed endocrine cells in the antrum region. When the nuclear binding of radioactively labelled compound was compared between gastric neck cells and duodenal absorptive cells, binding was low but sustained in neck cells. Peak uptake after the injection was between 8 and 12 h in neck cells, but between 15 min and 30 min in duodenal villous epithelium. In the duodenum, weak nuclear labelling appeared at 8 h and was undetectable at 12 h under the conditions of the experiment. Nuclear labelling of neck cells remained detectable at 12 h and even after 24 h, similarly for both OCT and 1,25(OH)2 vitamin D3. These results suggest that the stomach is an important target tissue for vitamin D and its analog OCT. Regulation of neck cell functions is suggested, such as proliferation and differentiation of surface epithelium and gastric gland epithelium, and neck cell secretion of acidic mucus. Regulation is also indicated of G-cell gastrin secretion associated with gastrin paracrine effects on parietal cell HCl and intrinsic factor secretion, chief cell pepsinogen secretion, neck cell proliferation, as well as endocrine effects on systemic calcium homeostasis.

Detection of calcitonin gene expression in human infant and monkey carotid body chief cells by in situ hybridization

Calcitonin mRNA was detected in human and monkey carotid bodies by in situ hybridization histochemistry, using a 35S-labeled oligonucleotide probe for human calcitonin. In both human and monkey carotid body, moderate to high hybridization signal for calcitonin mRNA was observed in all cases. The hybridization signal in the formalin-fixed, paraffin-embedded samples was comparable to that obtained from frozen paraformaldehyde-fixed tissue. Our observations extend the finding of calcitonin-like immunoreactivity in the carotid body chief cells and indicate that calcitonin is produced in the carotid body, probably in the chief cells.

Calcitriol corrects deficient calcitonin secretion in the vitamin D-deficient elderly

The thyroid calcitonin-producing C cells possess vitamin D receptors and synthesize the vitamin D-dependent calbindin D28K. The present study evaluates the possible direct or indirect influence of vitamin D on calcitonin secretion in the elderly. Serum calcitonin was measured before and after a short calcium infusion (1.5 mg/kg over 10 minutes) in nine normal young adults (30 +/- 4 years, mean +/- SEM) and eight elderly subjects (78 +/- 4 years). The test was repeated 48 h after the last of three intravenous injections of calcitriol (2 micrograms) given every other day. Basal serum calcium did not change, but basal calcitonin of the elderly increased from 7 +/- 1 to 10 +/- 1 pg/ml (p < 0.06), similar to basal values in young adults (11 +/- 1 pg/ml). The increase in calcitonin after calcium infusion increased from 8 +/- 1 to 14 +/- 1 pg/ml (p < 0.001) after calcitriol treatment and approached the increase in young adults (18 +/- 3 pg/ml). These data demonstrate that calcitriol can improve and nearly normalize the impaired calcitonin secretion of the mildly vitamin D-deficient elderly subjects without changes in serum calcium, whereas the inverse situation is observed for parathyroid hormone.

Medullary carcinoma of the thyroid: current diagnosis and management

Medullary thyroid carcinoma (MTC) accounts for 5-10% of thyroid malignancies and occurs in either a sporadic or a familial form. The familial form is inherited in an autosomal dominant pattern, and expressed clinically as multiple endocrine neoplasia (MEN), types IIa and IIb, or as familial MTC alone. This neoplasm is derived from the parafollicular or C-cells, and has the ability to secrete a variety of polypeptide hormones including calcitonin, which serves as a tumor marker for the presence of MTC. The development of a calcitonin radioimmunoassay and the screening of patients at risk for the familial forms of MTC allows the diagnosis of the neoplasm in an occult stage when total thyroidectomy results in virtually 100% cure. We will present our experience with the diagnosis, treatment, and postoperative follow-up of our patients with this interesting neoplasm.

Partial gastrectomy and mineral metabolism: effects on gastrin-calcitonin release

Bone mineral metabolism was studied in 20 male patients, between 8 and 18 years, after surgical treatment for peptic ulcer (ten Billroth 1 and ten Billroth 2 gastrectomies) and in 16 sex- and aged-matched healthy controls. The bone mineral content was statistically reduced only in the Billroth 2 group. Serum 25(OH)D was lower in all patients, but fractional calcium absorption was similar to the control value. This may be due to increases in 1,25(OH)2D and parathyroid activity (particularly in Billroth 2). Serum osteocalcin levels and hydroxyproline excretion were higher than in the controls. A positive linear correlation emerged not only between serum 1,25(OH)2D and PTH levels but also between each of these and serum osteocalcin and urine hydroxyproline. Both PTH and calcitriol were inversely correlated with the bone mineral mass in Billroth 2, confirming a trend observed in Billroth 1. Although calcitonin values were normal, basal gastrin levels were severely impaired in all patients. In response to a mixed meal, increases in gastrin and calcitonin were significantly lower than in the controls. The calcitonin response to intravenous calcium and pentagastrin infusion was not significantly different to the controls. The percentage increase in gastrin and calcitonin responses to oral calcium correlated positively with the reduction in bone mineral content only in the Billroth 2 group, suggesting a reduction in calcitonin release may contribute to gastric surgery osteopenia in these patients.

Effects of rat and chicken calcitonin gene-related peptides (CGRP) upon calcium metabolism in chicks

In vivo effects of intravenously injected chicken(c-) and rat(r-) calcitonin gene related peptide (CGRP) upon plasma total (Cat), ionized (Cai) calcium, inorganic phosphate (Pi) and clearance of an acutely administered 45Ca label have been examined in chicks. Both peptides were hypercalcaemic in fasted chicks, unlike previously reported hypocalcaemic response in mammals. r-CGRP was hypercalcaemic at doses of both 0.26 and 1.31 nmol/100 g body wt, the lower dose produced a significant elevation of Cat one hour after injection into 12-h-fasted chicks, the upper dose had a similar effect at 20 min. Cai was also non-significantly elevated by r-CGRP. Pi was slightly increased by r-CGRP at both doses, 20 and 60 min after injection. c-CGRP produced a dose (0.26-4.17 nmol/100 g body wt) dependent elevation of Cat and Cai in 22-h-fasted chicks. A greater response was however seen in fed animals. Peak responses were observed 45 min after injection. c-CGRP (1.04 nmol/100 g body wt) caused a significant decline in plasma Pi (P less than 0.05) in fasted chicks. Pi was elevated in control fed animals compared with fasted controls. c-CGRP (1.04 nmol/100 g) did not effect plasma Pi in fed chicks. Whilst both peptides elevated plasma Ca, clearance of an acutely administered 45Ca label from plasma was greater in both r-CGRP treated 12-h-fasted chicks and c-CGRP treated 22-h-fasted chicks. In contrast, the rate of 45Ca clearance in fed chicks was not affected by c-CGRP treatment. The differential effects of these peptides upon plasma 45Ca clearance and other plasma parameters of Ca metabolism, suggest a complex mode of action of the peptide upon avian Ca homeostasis, possibly involving direct actions upon kidney and bone.

The calcitonin gene peptides: biology and clinical relevance

The calcitonin/CGRP multigene complex encodes a family of peptides: calcitonin, its C-terminal flanking peptide, katacalcin, and a third novel peptide, calcitonin gene-related peptide (CGRP). The 32-amino acid peptide calcitonin inhibits the osteoclast, thereby conserving skeletal mass during periods of potential calcium lack, such as pregnancy, growth, and lactation. This hormonal role is emphasized by observations that lower circulating calcitonin levels are associated with bone loss and that calcitonin replacement prevents further bone loss. Structurally, CGRP resembles calcitonin and has been implicated in neuromodulation and in the physiological regulation of blood flow. Here we review the molecular genetics, structure, and function of the calcitonin-gene peptides as analyzed in the laboratory and focus on more recent clinical studies relating to disorders and therapeutics.

Cholecystokinins but not gastrin-17 release calcitonin from thyroid C-cells in the rat

Subcutaneous injections of gastrin-17, cholecystokinin-39, cholecystokinin-8 (sulfated and non-sulfated forms), cholecystokinin-4 or pentagastrin induced hypocalcemia in rats. The hypocalcemia was associated with calcitonin release for pentagastrin and the cholecystokinins but not for gastrin-17, even at very high doses. Permanent hypergastrinemia, induced by surgical removal of the acid-producing part of the stomach (fundectomy) or by treatment with high doses of omeprazole, a blocker of acid secretion, was not accompanied by elevated plasma calcitonin. Long-lasting hypergastrinemia is known to cause hyperplasia of gastrin-sensitive endocrine cells in the rat stomach while hypogastrinemia does the reverse. In antrectomized rats, having low serum gastrin, and in fundectomized rats, having high serum gastrin, the serum calcitonin concentration, the thyroid calcitonin content and the number of C-cells remained as in sham-operated controls two months after the operations. We conclude that neither exogenous nor endogenous gastrin stimulates calcitonin secretion in the rat and that long-standing hypo- or hypergastrinemia is without effect on the number of thyroid C-cells. Our results, however, do not exclude the possibility that the cholecystokinins might act as calcitonin secretagogues in the rat although such a role remains to be established.

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.

Vitamin D--soltriol the heliogenic steroid hormone: somatotrophic activator and modulator. Discoveries from histochemical studies lead to new concepts

Evidence from autoradiographic studies with 3H 1,25(OH)2 vitamin D3 (soltriol) about its many sites of nuclear binding and multiple actions suggests that the traditional view of "vitamin D and calcium" is too limited and requires modification. A new concept has been developed which proposes that the skin-derived hormone of sunshine, soltriol, is a somatotrophic activator and modulator that affects all vital systems. Regulation of calcium homeostasis is only one of its many actions. Target tissues for soltriol include not only bone, intestine and kidney, but also brain, spinal cord, pituitary, thyroid, endocrine pancreas, adrenal medulla, enteroendocrine cells, thymus, and male and female reproductive organs. Accordingly, actions of soltriol involve effects on autonomic and endocrine regulation with changes in tissue and blood hormone levels, innervation of skeletal muscle, immune and stress response, digestion, blood formation, fertility, pregnancy and lactation, general energy metabolism, mental processes and mood, and others. The skin-mediated transduction of short-wave sunlight induces a purposeful modulation of growth, reproduction and other biological activities in tune with the conditions of the sun cycle and season. Synthesis and actions of vitamin D3-soltriol are dependent not only on the amount of sunlight, but also on the availability of precursor in the skin and access of sunlight, the rate of hydroxylation in liver and kidney, and the modulation of these events by the endocrine status, in particular growth and reproduction. A concept of a five-level control of soltriol synthesis is proposed, in which the hydroxylation steps provide for a sensitive tuning. Relationships between the heliogenic skin-derived hormonal system and the helioprivic pineal-derived hormonal system are recognized and a comprehensive concept of the "endocrinology of sunlight and darkness" is pointed out.

Pyloric gastrin-producing cells and pyloric sphincter muscle cells are nuclear targets for 3H 1,25(OH)2 vitamin D3. Studied by autoradiography and immunohistochemistry

Autoradiographic studies were conducted to identify and characterize target cells for 1,25(OH)2 vitamin D3 in the pyloric region of rats and mice. After injection of 3H 1,25(OH)2 vitamin D3, nuclear concentration of radioactivity was observed in nuclei of duodenal epithelium and certain cells of pyloric glands, while most of the epithelial cells in the pyloric and gastric glands did not show nuclear labeling. In combined immunohistochemical studies, cells in the pyloric glands that showed nuclear concentration of radioactivity, were stained in their cytoplasm with antibodies to gastrin. Also, cells of the pyloric sphincter muscle showed nuclear labeling, in contrast to cells of the duodenal muscularis, which remained unlabeled under the conditions of the experiments. The results indicate that the cells with nuclear radioactivity contain receptors for 1,25(OH)2 vitamin D3 and suggest that gastrin secretion and pyloric muscle functions are regulated by a direct action of 1,25(OH)2 vitamin D3 on these cells.

Gastric secretion kinetics in chronic renal failure

A dose-response gastric secretion test was performed in 87 nondialyzed patients with chronic renal failure (CRF) and in 87 age- and sex-matched controls without renal disease. Twenty-six of the CRF patients were reexamined, 18 undergoing regular hemodialysis and 8 after successful transplantation. The gastric acidity, acid output, and volume output of the nondialyzed CRF subjects were decreased when compared with those of the controls or of patients in the posttransplant phase. This decrease was more marked with low than with high stimulant doses. The decrease in acid output was significantly greater than that in volume output. Moreover, when compared with the dialysis phase the nondialyzed patients had lowered gastric acidity and acid output, but no decrease in volume output was evident. The results indicate that there is an inhibition of gastric secretion in CRF. This inhibition is dependent on strength of stimulation and is abolished by active treatment of CRF, more clearly by transplantation than by maintenance dialysis. In addition, the inhibition is predominantly on the secretion of acid, the output of gastric juice being less affected.

Sensitivity of gastric acid secretion in patients with chronic renal failure

By means of a dose-response secretion test the sensitivity of gastric acid secretion was investigated in 85 patients with chronic renal failure and in 85 age- and sex-matched controls. The renal patients were also gastroscoped, with biopsy specimens taken from the gastric body. The examinations were repeated on 18 patients undergoing regular dialysis and 8 patients after successful transplantation. The acid secretion sensitivity of the stomach among the non-dialyzed patients was decreased when compared with the controls (p less than 0.01) but tended to normalize during the intermittent dialysis treatment (p less than 0.05) and particularly after transplantation (p less than 0.01). The low secretion responses were independent of gastric body histology and were also seen in patients with normal body mucosa. The maximum theoretic acid output did not differ significantly from that of the controls. It is concluded that there is an inhibition of gastric acid secretion in chronic renal failure. This inhibition depends on the decreased sensitivity to stimulation and is diminished by treatment of renal failure by dialysis or transplantation.

Advances in the diagnosis and treatment of medullary thyroid carcinoma

Medullary thyroid carcinoma accounts for 5 to 10 per cent of all thyroid malignancies and may occur in a familial or a sporadic pattern. This article reviews the authors' experience with 200 patients with medullary thyroid carcinoma and outlines the recent advances made in our understanding of the biochemical properties of these cancer cells and the relationship of different tumor markers to prognosis.

Pathogenesis of early neonatal hypocalcemia: studies of serum calcitonin, gastrin, and plasma glucagon

In 64 maternal-infant pairs, we tested the hypotheses that serum calcitonin, serum gastrin, and plasma glucagon concentrations are elevated in infants at risk for early neonatal hypocalcemia, and that elevated serum gastrin and plasma glucagon result in elevated serum calcitonin and low serum calcium values in neonates. Serum Ca declined significantly in neonates at 24 hours of age, and was inversely correlated with serum calcitonin. Cord serum calcitonin, gastrin, and plasma glucagon concentrations rose significantly at 24 hours of age. Cord calcitonin was significantly higher in preterm compared with term infants, and there was no significant difference between asphyxiated and nonasphyxiated preterm neonates; in term neonates cord calcitonin concentration was inversely correlated with Apgar scores at 1 and 5 minutes. Cord calcitonin was not correlated with cord gastrin or glucagon. Cord and 24-hour gastrin and glucagon values were not related to prematurity; cord glucagon, but not gastrin, was related to birth asphyxia. We conclude that (1) serum calcitonin, gastrin, and plasma glucagon values rise postnatally; cord calcitonin is elevated in preterm and in asphyxiated term infants; serum calcitonin concentration does not correlate with the elevated serum gastrin and plasma glucagon values; and at 24 hours of age, decreased serum Ca is correlated with serum calcitonin, and hence calcitonin might play a role in the pathogenesis of early neonatal hypocalcemia.

Basal and stimulated release of calcitonin gene-related peptide (CGRP) in patients with medullary thyroid carcinoma

Calcitonin gene-related peptide (CGRP) is a recently discovered peptide whose existence was first predicted following sequence analysis of the rat calcitonin gene. In the present study, plasma levels of CGRP were measured in patients with medullary thyroid carcinoma, both basally and following calcium or pentagastrin stimulation. Using a sensitive radioimmunoassay for CGRP, 19 of 21 patients with medullary thyroid carcinoma had elevated plasma levels of immunoreactive CGRP (median value 114 pmol/l) while 23 normal subjects had plasma CGRP levels below the detection limit of the assay (less than 10 pmol/l). Calcium or pentagastrin infusion in medullary thyroid carcinoma patients were potent stimuli to CGRP release, increasing plasma levels two- to five-fold. Chromatographic characterization using high pressure liquid chromatography of the CGRP immunoreactivity in plasma from two patients with medullary carcinoma of the thyroid demonstrated the presence of two molecular forms, neither of which co-eluted with synthetic human CGRP. The role of CGRP in the pathophysiology of medullary thyroid carcinoma is not clear but it may contribute to some of the clinical features associated with the disease. Furthermore, measurement of CGRP in conjunction with calcitonin could help in determining the prognosis of these patients.

Calcium homeostasis in the first days of life in relation to feeding

Determinations of serum calcium (Ca), phosphorus (P), magnesium (Mg), calcitonin (CT) and parathyroid hormone (PTH) were carried out in full term newborn infants during the first 168 h of life. The infants were randomly assigned to two different diets: glucose and breast feeding (BF) only or early formula feeding (F). The Ca serum levels decreased from birth to the 24th h; after that time they increased until the 72nd h. The values of serum Ca at the 48th and 72nd h were significantly lower in the F than in the BF group. In contrast, the P serum levels increased from birth to the 48th h and then they decreased; the values of serum P at the 48th h were significantly higher in F than in the BF group. The CT serum levels increased from birth to the 24th h and then they decreased. No difference between the F and BF groups was found during the first 48 h, while at the 72nd h the F group demonstrated significantly higher values of serum CT. PTH serum levels also increased from birth to the 24th h with significantly higher values at the 72nd h in the F group. The results of this investigation demonstrate that the difference in feeding in the first hours of life affects the calcium homeostasis and the secretion of hormones involved in the regulation of serum Ca levels.

Novel peptides from the calcitonin gene: expression, receptors and biological function

Calcitonin gene products include calcitonin and its carboxyl-terminal flanking peptide (in man PDN-21), and calcitonin gene-related peptide (CGRP). Alternative splicing of the initial gene transcripts results in the production of two distinct messenger RNA encoding precursors of CGRP and of calcitonin. CGRP messenger RNA is the predominant transcription product of the calcitonin gene in neural tissues, but it is also present in the pituitary and the C-cells of normal thyroid glands and in medullary thyroid carcinoma. Immunoreactive CGRP has, moreover, been recognized around blood vessels of the heart. Calcitonin and PDN-21 are cosecreted from thyroid C-cells, but they are also found in the brain and pituitary. CGRP receptors are present in the brain and the heart, and calcitonin receptors in bone and kidney cells and in the hypothalamus. Calcitonin administered peripherally and in vitro inhibits bone resorption and stimulates renal 1.25-dihydroxycholecalciferol production. CGRP used in the same manner has potent cardiovascular effects (vasodilation, hypotension, positive chronotropic and inotropic action in the heart). Intracerebroventricular administration of CGRP raises the blood pressure, and both CGRP and calcitonin inhibit gastric acid secretion and food intake. The distinct but overlapping effects of calcitonin and CGRP raise important regulatory and functional issues.

Multiple endocrine neoplasia syndromes

The multiple endocrine neoplasia (MEN) syndromes are characterized by autosomal dominant inheritance with a high degree of penetrance but varying expression. This review gives a classification of these syndromes and a short summary of the historical background. The pathogenesis of the disease and its possible origin in the APUD cell system are discussed together with the mechanisms underlying normal and ectopic hormone production by MEN tumors on the basis of recent findings in molecular endocrinology. The natural history and the clinical manifestations of the different syndromes are described. The sensitivity and discriminative capacity of the tests used to detect the syndromes in an early stage are compared. The choice of therapy and criteria for the timing and extensiveness of treatment are also considered. Lastly, problems associated with the ethical and legal aspects of screening, central registration, and monitoring of relatives at risk are described.

Calcium absorption in the rat as influenced by highly selective vagotomy with special regard to endogenous gastrin

The effect of HSV (controls: sham), which induces hypergastrinemia, on duodenal Ca absorption was studied in "intact", TPTX, PTX, and TX rats. Ca absorption was estimated by an in vivo loop technique. As this technique increased serum gastrin by the duodenal Ca load, gastrin was also measured in rats not subjected to evaluation of Ca absorption. Following vagotomy gastrin rose significantly in "intact" as well as in TPTX, PTX, and TX rats. Further, intraduodenal Ca increased gastrin both after sham and vagotomy. However, gastrin in vagotomized rats was significantly higher than in sham rats, too. Although duodenal Ca absorption was not altered by vagotomy in "intact" and in TX rats, it was significantly lowered in vagotomized TPTX and PTX rats. Pretreatment of TPTX rats by pentagastrin for 10 days or immediately preceding experiments did not change Ca absorption. In addition, serum parathyroid hormone was unchanged by vagotomy in "intact" rats as compared to sham controls. We conclude that (1) vagotomy does not influence the rate of duodenal Ca absorption in "intact" rats, (2) Ca absorption is lower after vagotomy only in the absence of parathyroid glands, and (3) this vagotomy effect is not mimicked by exogenous pentagastrin and therefore appears unrelated to endogenous postvagotomy gastrinemia.

Calcitonin and phosphate

This report summarizes the relationship of calcitonin to phosphate. The hypocalcemic action of calcitonin is dependent upon phosphate, while the hypophosphatemic action is independent of calcium. Calcitonin moves phosphate into bone cells and bone fluid in contrast to reducing the movement of calcium from bone to blood. Calcitonin acts rapidly and at low doses on the osteocytes and lining cells at bone surfaces. Morphological changes can be identified within 7 min. This action causes the accumulation of an electron-dense material both in bone lining cells and their microenvironment. It is postulated that both the hypocalcemic action of calcitonin and its ability to cause an accumulation of material at bone surfaces may result from the movement of phosphate into these areas. The biochemical action which could produce the phosphate movement is unknown. The possibility is suggested that calcitonin increases phosphate transport into bone cells.

Lack of clinical and physiological relationship between gastrin and calcitonin in man

The clinical and physiological relevance of the relationship between gastrin and calcitonin has been investigated in normal subjects and in patients suffering from gastritis or duodenal ulcer. Basal plasma levels of calcitonin are increased in these patients but there is no significant relationship between calcitonin and gastrin levels. Acute pentagastrin injection in normal male subjects increased significantly (P less than 0.05) plasma calcitonin levels whereas lower doses of pentagastrin which are known to stimulate gastric secretion are without effect on calcitonin levels. Moreover, stimulation of gastrin secretion by a protein test meal and by intragastric administration of a calcium chloride solution is not followed by any significant increase of plasma calcitonin levels. These results suggest that the stimulation of calcitonin secretion by gastrin and its synthetic analogue pentagastrin is a pharmacological rather than a physiological phenomenon.

Hypercalcitonemia in pernicious anemia

Gastrin has been suggested as a natural secretogogue of the hormone calcitonin. We have found hypercalcitonemia in 55% of patients with pernicious anemia, and the gastrin levels, although usually increased, did not correlate.

Effect of early oral calcium supplementation on serum calcium and immunoreactive calcitonin concentration in preterm infants

Oral calcium supplements (80 mg/kg per 24 h) were given to 23 preterm infants, and the course of serum calcium, magnesium, immunoreactive calcitonin, and gastrin was compared with a control group of 23 matched infants. In the supplemented group, serum calcium concentrations remained at the baseline level (2.31 mmol/l +/- 0.18 SD) while a fall (from 2.27 +/- 0.18 to 1.91 +/- 0.24 mmol/l) was observed at 12-16 hours of age in the control group, with 4 values < 1.75 mmol/l. There was no change in serum magnesium concentration in either group. The postnatal rise of serum immunoreactive calcitonin concentrations in the control group (from 171 +/- 135 to 493 +/- 273 pg/ml at 12-48 hours of age) was not found in the supplemented group. There was a negative correlation between serum calcium and immunoreactive calcitonin levels in the control group, but not in the supplemented group. There was no correlation between serum immunoreactive calcitonin and gastrin concentrations. These data show that oral calcium supplementation can prevent early neonatal hypocalcaemia, and suggest that this effect is achieved at least in part through a reduction of the postnatal rise of serum immunoreactive calcitonin.

Calcitonin reduces feeding in man, monkey and rat

It is proposed that calcitonin is a hormonal mediator of the satiety reflex. To test this hypothesis, effects of calcitonin on feeding and drinking were measured in rats and in rhesus monkeys. In monkeys, calcitonin produced severe (90%) and prolonged (3-5 days) reduction in feeding, and smaller decreases in drinking. In rats calcitonin decreased feeding in a dose-related manner over 24 hours, but increased drinking and urine output. A modest loss in body weight (2%) was also observed in psychiatric patients given calcitonin. It is suggested that calcitonin reduces feeding either through its effects on calcium metabolism, or by a direct action on the central nervous system.

Evidence for an important physiological role for calcitonin

We propose that calcitonin, secreted in response to the intake of food, aids in routing calcium, obtained by intestinal absorption, into bone fluid. Here calcium is temporarily stored in combination with phosphate for return to the extracellular fluid (blood) during intervals between oral intakes of calcium. The net result is a conservation of calcium postprandially and a decrease in parathyroid hormone-induced bone destruction during subsequent fasting periods. Evidence for this postulate is provided in the following six sequential steps from the time a calcium-containing meal is consumed until that portion of calcium stored in bone fluid is utilized during fasting periods to aid in plasma calcium maintenance. (i) Calcitonin secretion is stimulated by feeding and subsequent digestive processes. (ii) Postprandial secretion of calcitonin restricts the efflux of calcium from bone fluid to blood, thereby maintaining parathyroid hormone (PTH) secretion. (iii) In thyroid-intact individuals, both PTH and calcitonin are secreted postprandially and act in concert on calcium homeostasis. (iv) Calcitonin actively moves phosphate into bone and prevents its loss from bone fluid to blood. (v) Postprandial storage of calcium with phosphate occurs in bone fluid of thyroid-intact individuals. (vi) This labile storage form of calcium is the first to be utilized during fasting periods. In the absence of partial disruption of this storage mechanism, rapid development of pathological bone conditions would not be expected because PTH action permits the extended utilization of bone calcium for plasma calcium control. However, augmentation of osteopenic conditions could be expected if long-term low calcium intake were accompanied by a malfunction of this calcitonin-induced system for calcium storage.

The role of serum gastrin in the secretion of calcitonin: studies in patients with pernicious anaemia and in healthy subjects

Basal concentrations of serum gastrin and serum calcitonin were measured in 38 patients with pernicious anaemia and in 32 healthy control subjects. The fasting level of serum gastrin was greatly elevated in 32 patients and was within normal range in 6 patients, the difference between pernicious anaemia patients and controls being highly significant (P less than 0.001). No significant difference between fasting serum calcitonin concentrations in patients and healthy subjects was found. Furthermore, these hormones were studied before and after a beef meal in eight of the patients with hypergastrinaemia and in six healthy control subjects. After the meal serum gastrin concentrations increased significantly from basal values in both patients and controls, the peak values being reached 60 and 30 min after the meal, respectively. No significant changes in serum calcitonin concentrations were observed after the meal in either group. In five patients a transient rise in serum calcitonin occurred 5-10 min after ingestion, beginning, however, before any rise in serum gastrin was observed. Our results indicate that serum gastrin is without influence on calcitonin release, either in hypergastrinaemic patients with pernicious anaemia or in healthy subjects.

Medullary thyroid carcinoma: importance of serial serum calcitonin measurement

Thirty-two patients with medullary carcinoma of the thyroid (MCT) were studied before and after therapy. Sixteen patients had familial and 16 had the sporadic type of disease. The groups differed in several features: Patients with sporadic disease were older at diagnosis and presented with enlargements in the thyroid or lymph nodes, and one patient had neuromata; in the familial group the disease was more often bilateral and was associated at times with the MEA syndrome (parathyroid adenoma or pheochromocytomas, or both). The immunoreactive serum calcitonin (CT) level was measured before and after some form of therapy in all 32 patients. Our investigations showed: 1) Delaying treatment was clearly detrimental in this progressive disease; 2) The most effective therapy was surgery, while radiotherapy and chemotherapy were less effective; 3) Postoperatively, the CT level usually fell sharply, when the disease was thought extirpated, but the lowest nadir might be reached at from 1 month to 6 years; 4) In all such patients the CT level eventually rose from the postoperative nadir; 5) Patients with no clinical or radiological evidence of disease, had high CT levels for a mean of 3 years of observation; 6) A marked rise of CT levels in three patients preceded metastases and death; 7) Patients with abdominal, particularly liver disease had the highest CT levels; and 8) Patients who died had relatively high CT levels, corresponding in general with the extent of disease.

Ethanol induced secretion of calcitonin in chronic renal disease

Whisky (25-50 ml) increased plasma levels of immunoreactive calcitonin (iCT) in seventeen of nineteen patients with chronic renal failure. The effect was greater in patients with high levels of iCT than in those with normal levels. Changes in plasma iCT were not related to changes in calcium, phosphate or immunoreactive gastrin, but were inhibited by the prior administration of propranolol.

Comparison of the effects of pentagastrin and meal-stimulated gastrin on plasma calcitonin in normal man

We compared the effects of exogenous pentagastrin and meal-stimulated gastrin on plasma immunoreactive calcitonin (iCT) in various studies of 13 normal adult men. Bolus intravenous injection of pentagastrin (0.5 microgram/kg) produced increases of iCT in 8 of 9 men. There was a linearly increasing response of iCT concentrations to increasing doses of pentagastrin (0.0625, 0.125, 0.25, and 0.5 microgram/kg) and to achieved serum immunoreactive pentagastrin concentrations (r = 0.72, P less than 0.01). To determine the effects of endogenous gastrin upon peripheral iCT concentrations, we measured serum immunoreactive gastrin (iG) and plasma iCT in four men at frequent intervals for 240 min after ingestion of low- (100 mg) and high- (400 mg) calcium meals. Serum iG increased in all subjects, with a peak at approximately 30 min. However, plasma iCT levels were unchanged from basal throughout the study. The increase of pentagastrin (0.3 pmol/ml) which caused a barely detectable increase of iCT was five- to tenfold greater than the mean maximal increases of gastrin after low- and high-calcium meals (0.04 and 0.06 pmol/ml, respectively). These results suggest that increases of plasma iCT concentrations after administration of pentagastrin in man reflect pharmacologic phenomena and that postprandial gastrin secretion may be insufficient to affect peripheral iCT concentrations.