Immunoreactive calcitonin in the mother, neonate, child and adult

Age-Related Association of Calcitonin with Parameters of Anthropometry, Bone and Calcium Metabolism during Childhood

INTRODUCTION

The thyroid parafollicular hormone calcitonin (CT) shows particularly high blood levels in early childhood, a period of high bone turnover, which decrease with increasing age. Data about the physiological role of CT during infancy, childhood, and adolescence are contradictory or lacking.

OBJECTIVE

We hypothesize that CT demonstrates age-related correlations with parameters of bone growth and turnover as well as with parameters of calcium homeostasis.

METHODS

5,410 measurements of anthropometric data and venous blood samples were collected from 2,636 participants of the LIFE Child study, aged 2 months-18 years. Univariate correlations and multiple regression analysis were performed between serum CT and anthropometric indicators (height standard deviation scores [SDS] and BMI-SDS), markers of calcium (Ca) homeostasis (Ca, parathyroid hormone, 25-OH vitamin D, and phosphate [P]), bone formation (procollagen type 1 N-terminal propeptide [P1NP], osteocalcin), and bone resorption (β-CrossLaps).

RESULTS

CT was significantly associated with Ca (β = 0.26, p < 0.05) and P1NP/100 (β = 0.005, p < 0.05) in children aged 2 months-1.1 years. These relations were independent of age and sex and could not be confirmed in children aged 1.1-8 years. Independent of age, sex, puberty, P, and height SDS CT showed a significant positive relation to Ca (β = 0.26; p < 0.001) in children aged 8-18 years.

CONCLUSIONS

Our findings suggest a unique association between CT and Ca in periods of rapid bone growth and point to a possible involvement of CT in promoting bone formation during the first year of life.

Maternal Mineral and Bone Metabolism During Pregnancy, Lactation, and Post-Weaning Recovery

During pregnancy and lactation, female physiology adapts to meet the added nutritional demands of fetuses and neonates. An average full-term fetus contains ∼30 g calcium, 20 g phosphorus, and 0.8 g magnesium. About 80% of mineral is accreted during the third trimester; calcium transfers at 300-350 mg/day during the final 6 wk. The neonate requires 200 mg calcium daily from milk during the first 6 mo, and 120 mg calcium from milk during the second 6 mo (additional calcium comes from solid foods). Calcium transfers can be more than double and triple these values, respectively, in women who nurse twins and triplets. About 25% of dietary calcium is normally absorbed in healthy adults. Average maternal calcium intakes in American and Canadian women are insufficient to meet the fetal and neonatal calcium requirements if normal efficiency of intestinal calcium absorption is relied upon. However, several adaptations are invoked to meet the fetal and neonatal demands for mineral without requiring increased intakes by the mother. During pregnancy the efficiency of intestinal calcium absorption doubles, whereas during lactation the maternal skeleton is resorbed to provide calcium for milk. This review addresses our current knowledge regarding maternal adaptations in mineral and skeletal homeostasis that occur during pregnancy, lactation, and post-weaning recovery. Also considered are the impacts that these adaptations have on biochemical and hormonal parameters of mineral homeostasis, the consequences for long-term skeletal health, and the presentation and management of disorders of mineral and bone metabolism.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Expression of prolactin receptor and prolactin in normal and malignant thyroid: a tissue microarray study

OBJECTIVE

There is increasing evidence involving prolactin (PRL) and its receptor (PRLR) in the development of different cancers. The aim of the present study was to investigate the expression of PRLR and PRL in human thyroid tissues.

DESIGN AND METHODS

Using tissue microarray (TMA) by immunohistochemical staining, we examined the expression level of PRLR and PRL in 314 specimens from 71 thyroid cancer patients and 15 normal thyroid samples.

RESULTS

Expression of the PRLR was observed in 93.3% of normal thyroid samples and in 76.1% of all thyroid cancers, while expression of PRL was observed in only 10% of medullary thyroid carcinomas and not at all in the other specimens, whether normal or neoplastic. Moreover, results suggested an overexpression of PRLR in 70% of medullary thyroid carcinomas, whereas 53.3% of poorly differentiated thyroid carcinomas showed a negative pattern of staining (p = 0.014 vs normal).

CONCLUSIONS

Present data revealed, for the first time, a widespread expression of PRLR in normal and neoplastic human thyroid tissues as well as a scarce expression of PRL, observed only in a few medullary thyroid carcinomas. Whether the overexpression of PRLR observed in medullary thyroid carcinomas or the underexpression of PRLR observed in poorly differentiated thyroid carcinomas play a contributory role in the oncogenesis of these tumors remains to be determined.

Adapting to the transition between gestation and lactation: differences between rat, human and dairy cow

Adequate blood calcium concentrations are vital for the normal function of mammals. Mechanisms for maintaining normal blood calcium function adequately most of the time; however, occasionally they fail and calcium homeostasis is compromised. Milk fever or periparturient hypocalcemia in dairy cattle is a well-documented example of a breakdown in the mechanisms of calcium homeostasis. This disease occurs at the time of parturition and is unique to adult dairy animals. The disease results from the inability of animals to cope with the sudden demand for calcium in support of colostrum formation. Animals developing the disease become hypocalcemic and require intravenous calcium to survive. The precise metabolic disorder(s) responsible for the onset of milk fever is still being debated. This report will highlight some of the current concepts related to the causes and prevention of milk fever in dairy cattle, as well as contrasting differences in calcium demands that exist between dairy cattle, humans and rats at the onset of lactation.

Calcium, magnesium and phosphorus in the nutrition of the newborn

Several factors have been suggested to contribute to inadequate bone mineralization in infants. Calcium and phosphorus intakes in preterm infants are below the intrauterine accretion rates. Calcium retention is influenced by the types of calcium salts used and by alterations in dietary phosphorus, fat and carbohydrates. Dietary intakes of vitamin D, and modifications in the protein base of infant formula, e.g., soy base vs cow milk base, may impact bone mineralization. The major hormonal mechanisms involved in the regulation of bone mineralization are parathyroid hormone, calcitonin and vitamin D. From recent animal studies, it has been suggested that parathyroid hormone related peptide (PTH-rp) may also play a role in perinatal calcium homeostasis.

Hormonal alterations and osteoporotic syndromes

Hormonal control of skeletal growth, modeling, and remodeling is characterized by a complex interaction between the calciotropic hormones (25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol, parathyroid hormone, and calcitonin), growth, and thyroid hormones in addition to the estrogenic and androgenic gonadal hormones. Although both growth and thyroid hormones are essential skeletal growth and modeling and also can produce detrimental skeletal effects in adults when circulating in excess concentrations, these hormones assume a minor role in the day-to-day bone remodeling of the mature skeleton. Following the attainment of the peak bone mass, bone mineral content begins to decline in the fourth and fifth decades of life, accelerating in females in the first 5-7 years after the menopause as a result of estrogen deficiency. Associated with this age-dependent loss in skeletal mass are decreases in calcitonin reserve primarily in the 5-7 years following the menopause, decreases in circulating 25-hydroxycholecalciferol, intestinal resistance to 1,25-dihydroxycholecalciferol, and a gradual progressive rise in blood parathyroid hormone. These changes in calciotropic hormone profiles, together with poor nutritional habits, anticonvulsant, glucocorticoid, and thyroid medications, diseases such as type I diabetes, immobilization, or decreased physical activity all serve to weaken the aging skeleton. The result is a gradual and subtle change in skeletal anatomy, which progresses to alterations in vertebral structure, such as kyphosis, scoliosis, and pseudospondylolisthesis, and a variety of sciatic and nerve entrapment syndromes. Vertebral, forearm, and hip fractures and edentulism ultimately comprise the syndrome of age-related bone loss, resulting in lifestyle disabilities, extensive morbidity, analgesic drug abuse, hospitalization, and escalating annual health care expenditures.

Multiple endocrine syndrome type IIb in early childhood

A 3-week-old girl who was born with club feet had signs of failure to thrive. On physical examination the child appeared normal; she had no abnormalities in the mucous membranes of the mouth, the eyelids, or in the neck, and her other systems, including heart, chest, abdomen, and neurologic systems, were clinically normal. Radiologically, the gastrointestinal tract was normal, but rectal biopsy showed neuromas. Her serum calcitonin level was measured both at basal and after pentagastrin stimulation at 5 weeks of age and found to be high, but whether it was consistent with the normal level at this early age or was caused by medullary thyroid carcinoma was not clear. At 3 months, the corneal nerves of both eyes were examined and showed considerable thickening, and multiple endocrine syndrome type IIb was suspected. The serum calcitonin level at 8 and 14 months was increased. A total thyroidectomy was done, and C-cell nodular hyperplasia and adenomatosis was found in the isthmus. The postoperative serum calcitonin level decreased to low normal and did not increase after pentagastrin stimulation. To the authors' knowledge, this case represents the youngest patient diagnosed with multiple endocrine syndrome type IIb in the absence of family history of the disease.

Development of endocrine pathways in the regulation of calcium homeostasis

The mammalian fetus is maintained hypercalcaemic relative to its mother by the action of a calcium pump believed to be located at the basement membranes of the epithelial cells of the fetal chorion. It has recently been demonstrated that the activity of this putative pump is stimulated by a new fetal hormone, parathyroid hormone-related protein, described originally as the product of a human BEN cell line which was derived from a lung tumour associated with hypercalcaemia of malignancy. Whereas the circulating level of immunoreactive parathyroid hormone in the fetus is very low, in keeping with the hypercalcaemia, the plasma concentrations of bioactive parathyroid hormone and parathyroid hormone-related protein can be measured using a sensitive cytochemical bioassay and the separate concentrations assessed by pre-incubation with appropriate antisera. The total plasma concentration of both hormones is inversely related to the prevailing calcium ion concentration but the set point of parathyroid hormone-related protein is probably higher than that for parathyroid hormone. Probably as a result of the hypercalcaemia, the circulating concentration of calcitonin is also higher than in maternal plasma and may serve to limit bone resorption to favour net bone accretion as part of the overall growth of the fetus. Vitamin D and its most active metabolite, 1,25(OH)2D, can pass across the placenta in either direction, in contrast to most peptide hormones. In addition to the supply of some 1,25(OH)2D by the mother to her fetus, the fetal placenta and fetal kidneys can all synthesize 1,25(OH)2D. The relative concentrations circulating in maternal and fetal plasma pools vary with the species, presumably as a result of differing importance of the three sources of supply to the fetus and the relative concentrations of vitamin D-binding protein circulating in mother and fetus. The importance of parathyroid hormone-related protein derived from fetal parathyroid glands has been clearly demonstrated in the fetal sheep. Such animals develop rickets following the removal of their parathyroid glands, despite the demonstration of this substance in fetal placental membranes. However, the relative importance of the parathyroid glands versus the placenta and its membranes as the principal source of parathyroid hormone-related protein remains to be elucidated and may vary with species.

Human placental calcitonin receptors

Receptors for the hypocalcaemic hormone, calcitonin (CT), have been identified in a membrane fraction prepared from term human placentae. Binding of 125I-labelled salmon CT (125I-sCT) to the membranes was time- and temperature-dependent, saturable (Bmax. 58 +/- 11 fmol/mg of protein), of high affinity (Kd 80 +/- 21 pM) and poorly reversible. Species-specific CTs and CT analogues competed for 125I-sCT binding with potencies proportional to their known biological potencies. Various unrelated peptide hormones did not compete, indicating that receptor binding was specific for CT. Photoaffinity labelling using a derivatized biologically active sCT analogue, [Arg11,18,3-nitrophenylazide-Lys14]sCT, identified a receptor component of Mr approximately 85,000, comparable with findings in osteoclasts and other target cells. The presence of CT receptors in the human placenta supports other evidence that CT may have a role in the regulation of placental function.

Does testosterone influence the post-stimulatory levels of calcitonin in normal men?

We have analysed the sex difference of calcitonin (CT) levels after combined stimulation with calcium and pentagastrin (Ca-PG) in the normal population, and the relationship of the post-stimulatory CT levels with free testosterone (FT). We have also studied the correlation between CT values and the anthropometric parameters, body mass index (BMI) and body surface area (BS), as well as the relationship between CT levels and calcium. A positive and statistically significant correlation was found between post-stimulatory CT and the increment over the base-line of CT and basal FT, and with the anthropometric parameters. However, the increment of CT and the peak values of CT did not have any significant correlation with the Ca levels (basal or post-stimulation). We conclude that the enhanced CT response found in normal men compared to normal women is at least partially determined by the higher testosterone levels found among normal men.

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.

Absence of evidence for a role of calcitonin in the etiology of femoral neck fracture

Twenty elderly women with fracture of the femoral neck were compared with 10 age-matched women undergoing elective hip surgery. In spite of an equivalent calcium response to intravenous calcium, neither basal nor stimulated calcitonin levels were significantly different between the groups. Parathormone, 25OHD, and 1,25(OHD)2 showed no significant differences between the femoral neck fracture group and control subjects. It is thus unlikely that calcitonin has an important role in the etiology of postmenopausal osteoporosis associated with femoral neck fracture.

Effect of human calcitonin (hCT) on glucose- and arginine-stimulated insulin secretion

Many studies have shown that in normal man salmon and porcine CT administration in bolus inhibits the release of TSH, LH, GH, and glucose- or arginine-induced insulin secretion. In the present study we investigated the effects of human synthetic calcitonin (hCT) on glucose- or arginine-induced insulin secretion in man. Twenty-two subjects were submitted to i.v. administration of hCT during glucose or arginine test. In our opinion, the most interesting results are those observed with arginine plus hCT at two different dosages (25 micrograms and 12.5 micrograms infused in 30 min). In fact arginine plus hCT (25 micrograms in 30 min) administration induced a significant increase of glycemia at 5, 10 and 20 min (p less than 0.01) and at 30 min (p less than 0.05) and a significant decrease of IRI at 5, 10, 20 and 30 min (p less than 0.001) and at 45 min (p less than 0.005). The highest plasma CT levels were observed at 15 and 30 min (490 and 540 pg X ml-1). Arginine plus hCT (12.5 micrograms in 30 min) infusion induced a similar significant increase in plasma glucose at 10, and 20 min (p less than 0.05) and at 30 min (p less than 0.01) and a significant decrease of plasma IRI at 10 min (p less than 0.05) at 20 min and 30 min (p less than 0.005). The highest plasma CT levels were reached at 20 min and 30 min (250 and 270 pg X ml-1, respectively). Our results clearly demonstrate that physiologic doses of hCT are able to inhibit arginine induced insulin secretion in normal man. Since insulin induces hypercalcemia and food ingestion increases both insulin and CT, one could hypothesize that CT inhibits insulin secretion thus controlling post-prandial hypercalcemia by its osteotrophic effect and by its action upon calcium redistributed within the cells.

Effect of calcium supplementation on the vascular sensitivity to angiotensin II in pregnant women

Pregnant women destined to develop pregnancy-induced hypertension lose refractoriness to the pressor effects of infused angiotensin II. The effect of calcium supplementation on the vascular sensitivity to angiotensin II was investigated in pregnant women. We administered orally 600 mg of calcium L-aspartate daily to 22 pregnant women from 20 weeks of gestation to delivery. The values for the effective pressor dose of angiotensin II in the calcium-supplemented women were compared with those in 72 nonsupplemented pregnant women. The vascular sensitivity was significantly decreased after calcium supplementation. The values for the effective pressor dose of angiotensin II in the calcium-supplemented patients were 18.1 +/- 1.2 ng/kg/min at 20 weeks of gestation, 32.2 +/- 2.6 ng/kg/min at the twenty-sixth week, 41.1 +/- 3.4 ng/kg/min at the thirtieth week, and 25.9 +/- 2.9 ng/kg/min at the thirty-sixth week (mean +/- SEM), while those in the nonsupplemented patients were 17.3 +/- 1.2, 17.7 +/- 1.6, 17.6 +/- 1.2, and 15.0 +/- 1.6 ng/kg/min, respectively. Assessment of the changes in the effective pressor dose of angiotensin II in the individual patients indicated that the percentile changes from 20 weeks of gestation in the calcium-supplemented patients were also significantly greater than those in 22 nonsupplemented patients. These findings suggest that calcium supplementation tends to reduce the vascular sensitivity in pregnancy. The present dosage of calcium did not affect the blood chemical parameters and did not reduce the blood pressure. The incidence of pregnancy-induced hypertension in the calcium-supplemented patients was 4.5%, which was smaller than that (21.2%) in the nonsupplemented patients. Although there is no clear explanation of the mechanisms involved in such an effect of calcium, the present results do provide evidence to support the idea that oral calcium intake can prevent the onset of pregnancy-induced hypertension.

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.

Calcium metabolism in pregnancy and the perinatal period: a review

Calcium homeostasis is a complex process involving calcium, other involved ions, and three calcitropic hormones, parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D3. The principal maternal adjustment during pregnancy is an increasing parathyroid hormone secretion which maintains the serum calcium concentration in the face of a falling albumin level, an expanding extracellular fluid volume, an increasing renal excretion, and placental calcium transfer. The placenta transports calcium ions actively, making the fetus hypercalcemic relative to its mother, which in turn stimulates calcitonin release and perhaps suppresses parathyroid hormone secretion by the fetus. A unique extrarenal system for 1 alpha-hydroxylation of 25-hydroxyvitamin D3 exists in the placenta and/or decidua, providing a source of 1,25-dihydroxyvitamin D3 for the fetus. With the abrupt cessation of the placental source of calcium at birth, the neonate's serum calcium level falls for 24 to 48 hours, then stabilizes and rises slightly. Hyperparathyroidism during pregnancy causes complications in both mother and infant and should usually be treated surgically as soon as diagnosed. Maternal hypoparathyroidism can be treated satisfactorily with high doses of supplemental calcium and vitamin D. Osteopenia accompanying long-term heparin administration may respond to 1,25-dihydroxyvitamin D3 (calcitriol) therapy. Diabetes in pregnancy is associated with disturbed neonatal calcium homeostasis, perhaps due to chronic hypomagnesemia. A possible etiologic role of calcium deficiency in pregnancy-related hypertension has been suggested. Dietary deficiency of calcium and/or vitamin D during gestation may lead to several adverse effects in the newborn infant.

Racial differences in calcitonin and katacalcin

Profound racial differences exist in the incidence of osteoporosis, particularly in women. To investigate possible underlying reasons for this, we have measured the circulating levels of calcitonin (iCT), a bone-protecting hormone, and its flanking peptide, katacalcin (iKC), in black Gambian and white British populations. Whilst sex differences in both peptides were observed, with males having higher levels than females, the most striking finding was that white women have the lowest iCT levels. This important observation may explain, at least in part, why osteoporosis is particularly a disease of white, postmenopausal women.

Calcitonin levels in sera of infants and children: relations to age and periods of bone growth

Serum calcitonin levels have been reported to be elevated in premature and newborn infants, a period of maximal rate of bone growth. To determine whether calcitonin remains elevated during the first year of life, a time of rapid extrauterine bone growth, fasting serum calcitonin levels were determined in 31 hospitalized infants and children ages 24 weeks gestation to 6 years. Calcitonin levels were significantly higher in the premature and newborn infants than in the first year of life. However, calcitonin levels in the first year of life were still significantly higher than during the second to sixth years. This fall in serum calcitonin levels parallels the age-related decline in rate of bone growth. One can speculate that the changes in serum calcitonin levels during the first year of life may indicate that it plays a role in bone growth or mineralization. However, the possibility that the changes in calcitonin levels are unrelated to changes in bone growth or mineralization has not been ruled out.

Regulation of calcium-regulating hormones by exogenous sex steroids in early postmenopause

A major function of calcitonin in humans appears to be maintenance of the skeleton. There is a marked sex difference in circulating calcitonin levels: women have much lower levels. This has led to speculation that calcitonin lack may be one factor involved in the pathogenesis of postmenopausal bone loss. We have measured levels of calcitonin and the other major calcium-regulating hormones in healthy women during the early menopause, and studied the effects of reversing their oestrogen deficiency with natural and synthetic oestrogen. The major findings were that calcitonin levels were increased by oestrogen administration (P less than 0.02-less than 0.001) and that the levels of the bone-resorbing hormones, parathyroid hormone and 1,25 dihydroxyvitamin D, were not higher in postmenopausal than in premenopausal women. We suggest that loss of oestrogen at the menopause accelerates the natural age-related decline of calcitonin secretion, thus further decreasing the calcitonin levels. This leads to increased sensitivity of the skeleton to the actions of the bone-resorbing hormones. It seems likely that the well-known effect of oestrogen in preventing postmenopausal bone loss is achieved, at least in part, by enhancement of calcitonin secretion.

Serum calcitonin concentrations in premature infants during the first 12 weeks of life

Twenty-eight premature infants of mean gestation 30.9 +/- 2.5 weeks and mean birth weight 1175 +/- 206 g had repeated serum calcitonin concentrations determined over the first 12 weeks of life. Serum calcitonin concentrations slowly fell but remained elevated even at 12 weeks of age [normal adult = 71 +/- 48, 1 week (N = 15) = 327 +/- 167, 3 week (N = 23) = 270 +/- 129, 6 week (N = 16) = 249 +/- 154, 9 week (N = 13) = 214 +/- 108, 12 week (N = 12) = 174 +/- 11]. Throughout this period, serum total calcium was normal or low (8.4 +/- .8-9.3 +/- 1.0). Serum phosphorus was normal or low (6.0 +/- 1.4-6.5 +/- 1.0), and serum magnesium was normal (1.7 +/- 0.24-1.8 +/- 0.34). The reason for the sustained elevation of serum calcitonin in these very small, sick, premature infants in unclear.

Regulation of calcitonin and parathyroid hormone secretion by oestrogens

Calcitonin is a peptide hormone secreted by C-cells which, in humans, are found mainly in the thyroid gland. It now seems that a major physiological function of this hormone in man is the long-term maintenance of the skeleton achieved by control of bone resorption. A marked sex difference in circulating calcitonin levels normally exists, with a relative deficiency in women as compared to men. It has now been found that oestrogens regulate calcitonin secretion and it appears likely that the loss of ovarian function at the menopause accelerates the natural decline in calcitonin secretion which occurs with age. Thus, post-menopausal women are more markedly calcitonin-deficient. Levels of the bone-resorbing hormones, parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D are not elevated post-menopausally and it seems likely that the increased bone resorption which leads to post-menopausal bone loss is due mainly to the loss of oestrogen and calcitonin secretion.

Immunoreactive calcitonin in maternal milk and serum in relation to prolactin and neurotensin

Maternal milk four days post partum contained immunoreactive calcitonin in concentrations which were 22-89 times higher than those noted in concomitantly sampled maternal sera. Neurotensin-like immunoreactivity was barely detectable in milk. It is suggested that calcitonin may be a prerequisite for the concentration of calcium ions in milk but there is also possibility that it acts locally on the intestinal mucosa.

Interrelations of calcium-regulating hormones during normal pregnancy

Profound changes in calcium metabolism occur during pregnancy. The mother has to make available extra calcium for fetal requirements while ensuring that her plasma and bone calcium concentrations are satisfactorily maintained. In a cross-sectional study plasma concentrations of the major calcium-regulating hormones--namely, calcitonin, parathyroid hormone, 25-hydroxyvitamin D (25-OHD), and 1,25-dihydroxyvitamin D (1,25-(OH)2D)--were measured to establish their interrelations during normal pregnancy. The major changes observed were increases in the circulating concentrations of 1,25-(OH)2D and calcitonin. Concentrations of parathyroid hormone and 25-OHD remained within the normal range. The increased concentrations of 1,25-(OH)2D enable the increased physiological need for calcium to be met by enhancing intestinal absorption of this element. The simultaneous rise in calcitonin opposes the bone-resorbing activities of 1,25-(OH)2D, thereby protecting the integrity of the maternal skeleton. Maternal calcium homeostasis is thus maintained yet the requirements of the fetus are fulfilled.

Calcitonin and the calcium-regulating hormones in postmenopausal women: effect of oestrogens

In man, the major function of calcitonin appears to be prevention of excessive or unwanted bone resorption. There is a striking sex difference in circulating levels, with a relative deficiency in women. Calcitonin secretion in young adults is increased by oestrogens and therefore long periods of oestrogen lack, such as after the menopause, may be associated with a more pronounced calcitonin deficiency. This exaggerated deficiency could be an important factor in the pathogenesis of postmenopausal bone loss, especially since the latter may be due to excessive bone resorption. In a study of the effects of oestrogen treatment on circulating levels of calcitonin, parathyroid hormone, and vitamin-D metabolites in postmenopausal women, the most striking change was a sharp rise in plasma-calcitonin. Oestrogens prevent postmenopausal bone loss, and it is suggested that this effect could be mediated, at least in part, through control of calcitonin secretion. Calcitonin may prove effective in the prevention of postmenopausal bone loss, and it is suggested that this effect could be mediated, at least in part, through control of calcitonin secretion. Calcitonin may prove effective in the prevention of postmenopausal bone loss. Its place in the treatment of postmenopausal osteoporosis warrants further evaluation.

Hypercalcemia in hyperthyroidism. Role of age and goiter type

Hyperthyroidism is often associated with hypercalcemia which is provoked by osteoclastic activity of the thyroid hormones. These data show that hypercalcemia develops with increasing age and in the presence of a special type of hyperthyroid goiter. Total serum calcium, total protein, and albumin as well as different parameters of thyroid function, namely T3 RIA1, T4 test, ETR and TRH test were determined in a group of 147 patients. The ionized calcium level was estimated from total calcium and albumin. 211 measurements were performed. Hyperthyroidism existed in 92 cases. Total calcium was not significantly elevated in hyperthyroidism. Hyperthyroid patients under 61 years of age showed elevated ionized calcium levels in only 2.3% and patients over 60 years of age in 18.8% of cases. Elevated ionized serum calcium levels were observed in 43.8% of hyperthyroid patients with multinodular goiters. The linear correlation between ionized calcium levels and different parameters of thyroid function is much more pronounced in the older group and it was found to be highly significant. 7 of 9 hyperthyroid patients with elevated ionized calcium levels showed multinodular goiters, though no autonomous adenoma. In the hyperthyroid group of patients of over 60 years of age with multinodular goiters the incidence of hypercalcemia was 43.8%. Direct action of thyroid hormone on calcium turnover as well as increasing age and special goiter type seem to be responsible for disturbances in calcium metabolism. A possible calcitonin deficiency in the above mentioned conditions is discussed.

The pathogenesis of infantile malignant osteopetrosis: bone mineral metabolism and complications in five infants

Bone mineral metabolism was studied in five infants aged 8 to 22 months with severe osteopetrosis. There were findings consistent with biochemical osteomalacia. These included hypocalcemia, hypophosphatemia, high serum acid phosphatase and alkaline phosphatase activity, high levels of serum parathyroid hormone, and high urinary cyclic AMP. Serum 1,25(OH)2 vitamin D3 level was high in the one patient tested. Radiographs in all infants revealed rachitic changes in the metaphyses. However, dense bones on radiographs, calcium balance studies, and radio-calcium absorption studies demonstrated markedly positive calcium balance. Iliac crest bone biopsies showed increased quantity of woven bone with abundant numbers of osteoclasts, excessive amounts of osteoid, myelofibrosis, and a decreased number of Howship's lacunae. The wide bands of unmineralized osteoid did not take up tetracycline. In vitro bone resorbing activity due to osteoclast activating factor from cultured stimulated leukocytes was normal. Bone turnover however, was now as evidenced by low urinary hydroxyproline levels. We interpret these findings as indicating there is decreased bone remodeling and resorption in spite of increased humoral stimuli and osteoclasts. Since calcitonin levels were normal for age, the most likely cause of the impaired bone remodeling sequence was defective osteoclast function. We postulate that there may be a common genetic defect in phagocyte cells, including monocytes, neutrophils and osteoclasts, which accounts for the abnormalities of mineral metabolism and previously reported hematologic, neurologic, and infectious complications.

Perinatal parathyroid hormone, vitamin D metabolites, and calcitonin in man

Plasma levels of calcium and of parathyroid hormone (PTH) were comparable in the mothers at delivery and in nonpregnant controls; magnesium was decreased (P < 0.001) in maternal blood; and phosphate (P < 0.001), 1,25-dihydroxyvitamin D (1,25(OH)2D) (P < 0.001), and calcitonin (CT) (P < 0.01) were raised. Cord levels of calcium (P < 0.01), magnesium (P < 0.05), and CT (P < 0.01) were higher, and PTH (P < 0.01) was lower than in the maternal blood. Levels of 25(OH)D, 1,25(OH)2D, and 24,25(OH)2D lower in fetal than in maternal blood (P < 0.01) and significant linear correlations between the vitamin D metabolites examined in mothers and neonates (P < 0.001) are consistent with a diffusion barrier across the placenta and/or different affinities of binding proteins. Plasma levels of 25(OH)D and 24,25(OH)2D were significantly related (P < 0.01), suggesting precursor product type, relationships. Levels of 1,25(OH)2D higher in arterial than in venous umbilical blood (P = 0.06, sign test; P < 0.005, paired t test) suggest that the fetus participates in the synthesis of 1,25(OH)2D. Maternal PTH was significantly related to the arteriovenous difference of 1,25(OH)2D levels (P < 0.01) in cord blood, and it possibly enhances the synthesis of 1,25(OH)2D during the final stage of fetal development.

Chemistry, physiology, and therapeutic applications of calcitonin

The chemistry and physiology of calcitonin are reviewed with particular emphasis on the evolution of the hormone and its modern role in humans. It seems likely that the relative deficiency of calcitonin in women may be important in postmenopausal bone loss. A major therapeutic application of calcitonin is in the treatment of Paget's disease of bone, and current recommendations for therapy are presented.

Calcitonin secretion in congenital nongoitrous cretinism

Plasma calcitonin (CT) was measured in the basal state and/or during provocative tests of hormone secretion in 11 children with congenital non-goitrous cretinism (CNC), in 1 girl with a lingual thyroid, and in 11 normal children. Basal and stimulated CT concentrations were significantly lower in the patients with CNC than in the normal subjects. Mean basal CT (+/- SE) was 41 +/- 4 pg/ml in the normal children, 24 +/- 3 pg/ml in the children with CNC, and 20 +/- 2 pg/ml in the patient with the lingual thyroid. The mean incremental CT responses to calcium infusion were 7.0 +/- 2 pg/ml in the children with CNC, 6.0 pg/ml in the patient with the lingual thyroid, and 146 +/- 47 pg/ml in the normal children. The children with CNC also demonstrated a significant delay in the return of the total serum calcium to basal level after the calcium infusion. The mean incremental CT response after infusion of pentagastrin was 7.6 +/- 2 pg/ml in the children with CNC, 10.0 pg/ml in the child with the lingual thyroid, and 34.4 +/- 11 pg/ml in the normal children. These data indicate that CT deficiency is present in children with CNC and suggest that the deficiency is a consequence of the defective embryologic development of the thyroid gland.