Renal effects of calcitonin

Exploring the relationship between calcitonin, ionized calcium, and bone turnover in cats with and without naturally occurring hypercalcemia

Objectives

This case-control study aimed to evaluate calcitonin response in naturally occurring hypercalcemia in cats and assess the relationships between calcitonin and ionized calcium (iCa) and examine relationships between calcitonin, iCa and bone turnover.

Methods

Hypercalcemic cats (persistently increased iCa concentration [>1.40 mmol/l]) were identified retrospectively via a medical database search; additional hypercalcemic and normocalcemic cats were recruited prospectively. Data regarding routine biochemical and urine testing, diagnostic imaging and additional blood testing were obtained. Serum alkaline phosphatase (ALP) activity was used as a marker of bone turnover. Serum calcitonin concentration was analyzed using a previously validated immunoradiometric assay. Hypercalcemic cats with an increased calcitonin concentration (>0.9 ng/L) were termed responders. Group comparisons were performed using a Mann-Whitney test for continuous variables and a χ2 test for categorical variables. Spearman's correlation coefficient was used to examine the relationships between calcitonin, iCa and ALP.

Results

Twenty-six hypercalcemic and 25 normocalcemic cats were recruited. Only 5/26 (19.2%) of the hypercalcemic cats were identified as responders, and all were diagnosed with idiopathic hypercalcemia. There was no significant correlation between the concentrations of calcitonin and iCa (p = 0.929), calcitonin and ALP (p = 0.917) or iCa and ALP (p = 0.678) in hypercalcemic cats, however, a significant negative correlation was observed between calcitonin and ALP (p = 0.037) when normocalcemic and hypercalcemic cats with an elevated calcitonin concentration were analyzed together.

Discussion

The expected increase in calcitonin concentration was present in only a small subset of hypercalcemic cats; no correlation was found between iCa and calcitonin concentration. The inverse relationship between calcitonin and ALP in cats with increased calcitonin concentrations suggests that the ability of calcitonin to correct hypercalcemia may be related to the degree of bone turnover.

A feline-focused review of chronic kidney disease-mineral and bone disorders - Part 1: Physiology of calcium handling

Mineral derangements are a common consequence of chronic kidney disease (CKD). Despite the well-established role of phosphorus in the pathophysiology of CKD, the implications of calcium disturbances associated with CKD remain equivocal. Calcium plays an essential role in numerous physiological functions in the body and is a fundamental structural component of bone. An understanding of calcium metabolism is required to understand the potential adverse clinical implications and outcomes secondary to the (mal)adaptation of calcium-regulating hormones in CKD. The first part of this two-part review covers the physiology of calcium homeostasis (kidneys, intestines and bones) and details the intimate relationships between calcium-regulating hormones (parathyroid hormone, calcitriol, fibroblast growth factor 23, α-Klotho and calcitonin) and the role of the calcium-sensing receptor.

Hepatic Osteodystrophy-Molecular Mechanisms Proposed to Favor Its Development

Almost all patients with chronic liver diseases (CLD) show altered bone metabolism. Depending on the etiology, this manifests in a severe osteoporosis in up to 75% of the affected patients. Due to high prevalence, the generic term hepatic osteodystrophy (HOD) evolved, describing altered bone metabolism, decreased bone mineral density, and deterioration of bone structure in patients with CLD. Once developed, HOD is difficult to treat and increases the risk of fragility fractures. Existing fractures affect the quality of life and, more importantly, long-term prognosis of these patients, which presents with increased mortality. Thus, special care is required to support the healing process. However, for early diagnosis (reduce fracture risk) and development of adequate treatment strategies (support healing of existing fractures), it is essential to understand the underlying mechanisms that link disturbed liver function with this bone phenotype. In the present review, we summarize proposed molecular mechanisms favoring the development of HOD and compromising the healing of associated fractures, including alterations in vitamin D metabolism and action, disbalances in transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signaling with histone deacetylases (HDACs) as secondary regulators, as well as alterations in the receptor activator of nuclear factor kappa B ligand (RANKL)–osteoprotegerin (OPG) system mediated by sclerostin. Based on these mechanisms, we give an overview on the limitations of early diagnosis of HOD with established serum markers.

Calcitonin Response to Naturally Occurring Ionized Hypercalcemia in Cats with Chronic Kidney Disease

Background

Hypercalcemia is commonly associated with chronic kidney disease (CKD) in cats.

Objectives

To explore the calcitonin response to naturally occurring ionized hypercalcemia in cats with azotemic CKD, and to assess the relationship of plasma calcitonin with ionized calcium, alkaline phosphatase (ALP), and urinary calcium excretion.

Animals

Thirty‐three client‐owned cats with azotemic CKD and ionized hypercalcemia from first opinion practice.

Methods

Cohort study. Calcitonin was measured with an immunoradiometric assay in heparinized plasma. Simple correlations were assessed with Kendall's rank correlation, and the within‐subject correlations of calcitonin with ionized calcium and other clinicopathological variables were calculated with a bivariate linear mixed effects model.

Results

Calcitonin concentrations above the lower limit of detection (>1.2 pg/mL; range, 1.7–87.2 pg/mL) were observed in 11 of 33 hypercalcemic cats (responders). Blood ionized calcium concentration did not differ significantly between responders (median, 1.59 [1.46, 1.66] mmol/L) and nonresponders (median, 1.48 [1.43, 1.65] mmol/L; P = 0.22). No evidence was found for calcitonin and ionized calcium to correlate between cats (τ_b = 0.14; P = 0.31; n = 33), but significant positive correlation was evident within individual responders over time (within‐subject correlation coefficient [r_within], 0.83; 95% confidence interval [CI], 0.63–0.92). Calcitonin correlated negatively over time with plasma ALP (r_within, −0.55; 95% CI, −0.79 to −0.16).

Conclusions and Clinical Importance

Calcitonin does not appear to have an important role in calcium metabolism in cats with CKD.

Plasma Citrate Homeostasis: How It Is Regulated; And Its Physiological and Clinical Implications. An Important, But Neglected, Relationship in Medicine

The homeostatic maintenance of a normal plasma citrate concentration is an important factor in humans and in animals; and is required for many normal physiological activities. Dysregulation of normal plasma citrate presents pathophysiological hypocitricemic or hypercitricemic conditions. This can lead to clinical consequences in many areas of medicine; such as impaired blood clotting, altered acid/base status, impaired neuromuscular/cardiac activities, hypocitraturia and stone formation, bone disorders with loss of bone strength and increased fractures, hypocitricemia of surgical stress. These important implications of citrate relationships have been largely ignored by the contemporary clinical and biomedical community; to the extent that it is not even described in most current textbooks and review papers. This review describes the physiological, endocrine, and metabolic relationships in the normal regulation and maintenance of plasma citrate; and presents some important clinical consequences of its dysfunctional maintenance. The importance of bone, kidney and liver activities in the maintenance of normal plasma citrate is described along with the citricemic roles of parathyroid hormone, calcitonin and vitamin D. These factors and relationships are presented as the contemporary understanding of the integrated regulation of plasma citrate as the basis for its clinical importance in medicine. The exclusion of these citrate relationships leads to misunderstanding and misrepresentation of physiological and clinical conditions in many issues in medicine and paramedicine areas. The intent of this review is to revive the interest and support for research to address the many unknown and speculative issues of plasma citrate regulation and its important clinical implications. This is in the best interest of the medical community and the public-at-large.

Plasma Citrate Homeostasis: How It Is Regulated; And Its Physiological and Clinical Implications. An Important, But Neglected, Relationship in Medicine

The homeostatic maintenance of a normal plasma citrate concentration is an important factor in humans and in animals; and is required for many normal physiological activities. Dysregulation of normal plasma citrate presents pathophysiological hypocitricemic or hypercitricemic conditions. This can lead to clinical consequences in many areas of medicine; such as impaired blood clotting, altered acid/base status, impaired neuromuscular/cardiac activities, hypocitraturia and stone formation, bone disorders with loss of bone strength and increased fractures, hypocitricemia of surgical stress. These important implications of citrate relationships have been largely ignored by the contemporary clinical and biomedical community; to the extent that it is not even described in most current textbooks and review papers. This review describes the physiological, endocrine, and metabolic relationships in the normal regulation and maintenance of plasma citrate; and presents some important clinical consequences of its dysfunctional maintenance. The importance of bone, kidney and liver activities in the maintenance of normal plasma citrate is described along with the citricemic roles of parathyroid hormone, calcitonin and vitamin D. These factors and relationships are presented as the contemporary understanding of the integrated regulation of plasma citrate as the basis for its clinical importance in medicine. The exclusion of these citrate relationships leads to misunderstanding and misrepresentation of physiological and clinical conditions in many issues in medicine and paramedicine areas. The intent of this review is to revive the interest and support for research to address the many unknown and speculative issues of plasma citrate regulation and its important clinical implications. This is in the best interest of the medical community and the public-at-large.

A Role for the Calcitonin Receptor to Limit Bone Loss During Lactation in Female Mice by Inhibiting Osteocytic Osteolysis

During lactation, the large transfer of calcium from the mother to the milk is primarily sourced from the maternal skeleton. To determine whether the calcitonin receptor (CTR) plays a physiological role to protect the skeleton from excessive resorption during lactation, we assessed the maternal skeleton of global CTR knockout (CTRKO) and littermate control mice at the end of lactation (postnatal day 21). Micro-computed tomography analyses showed no effect on trabecular or cortical bone in the distal femur and L1 vertebra of maternal global CTR deletion at the end of lactation in global CTRKO mice compared with that in control mice. Bone resorption, as assessed by osteoclast number and activity at the end of lactation, was unaffected by maternal CTR deletion. Cathepsin K, carbonic anhydrase 2, matrix metalloproteinase 13, and receptor activator of nuclear factor-κB ligand mRNA levels, however, were markedly elevated by 3- to 6.5-fold in whole bone of lactating global CTRKO females. Because these genes have been shown to be up-regulated in osteocytes during lactation when osteocytes resorb their surrounding bone matrix, together with their reported expression of the CTR, we determined the osteocyte lacunar area in cortical bone. After lactation, the top 20% of osteocyte lacunar area in global CTRKO mice was 10% larger than the top 20% in control mice. These data are consistent with an increased osteocytic osteolysis in global CTRKO mice during lactation, which is further supported by the increased serum calcium observed in global CTRKO mice after lactation. These results provide evidence for a physiological role for the CTR to protect the maternal skeleton during lactation by a direct action on osteocytes to inhibit osteolysis.

Hypercalcemia in the Intensive Care Unit: A Review of Pathophysiology, Diagnosis, and Modern Therapy

Hypercalcemia may be seen in a variety of clinical settings and often requires intensive management when serum calcium levels are dramatically elevated. All of the many etiologies of mild hypercalcemia can lead to severe hypercalcemia. Knowledge of the physiologic mechanisms involved in maintaining normocalcemia and basic pathophysiology is essential for making a timely diagnosis and hence prompt institution of etiology-specific therapy. The development of new medications and critical reviews of traditional therapies have changed the treatment paradigm for severe hypercalcemia, calling for a more limited role for aggressive isotonic fluid administration and furosemide and an expanded role for calcitonin and the bisphosphonates. Experimental therapies such as denosumab show promise.

Calcitonin: physiology or fantasy?

Calcitonin, a potent hypocalcemic hormone produced by the C-cells of the thyroid, was first discovered by Harold Copp in 1962. The physiological significance of calcitonin has been questioned, but recent studies using genetically modified mouse models have uncovered additional actions of calcitonin acting through its receptor (CTR) that are of particular significance to the regulation of bone and calcium homeostasis. Mice in which the CTR is deleted in osteoclasts are more susceptible to induced hypercalcemia and exogenous calcitonin is able to lower serum calcium in younger animals. These data are consistent with the hypothesis that calcitonin can regulate serum calcium by inhibiting the efflux of calcium from bone, and that this action is most important when bone turnover is high. Calcitonin has also been implicated in protecting the skeleton from excessive loss of bone mineral during times of high calcium demand, such as lactation. This action may be linked to an intriguing and as yet unexplained observation that calcitonin inhibits bone formation, because deletion of the CTR leads to increased bone formation. We propose several mechanisms by which calcitonin could protect the skeleton by regulating bone turnover, acting within the bone and/or centrally. A new more holistic notion of the physiological role of calcitonin in bone and calcium homeostasis is required and we have highlighted some important knowledge gaps so that future calcitonin research will help to achieve such an understanding.

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.

The calcitonin and glucocorticoids combination: mechanistic insights into their class-effect synergy in experimental arthritis

INTRODUCTION

Previous work reported the anti-arthritic synergy afforded by combining calcitonin (CT) and glucocorticoids (GC). Here we focus on the pairing of elcatonin (eCT) and dexamethasone (Dex), querying whether: i) this was a class-effect action; ii) mechanistic insights could be unveiled; iii) the synergy affected canonical GC adverse effects.

METHODS

Using the rat collagen-induced arthritis model, different combinations of eCT and Dex, were administered from disease onset to peak (day 11 to 18). Macroscopic disease score was monitored throughout, with biochemical and histological analyses conducted on plasma and tissues at day 18. The effect on acute hyperglycaemia and liver enzyme message were also assessed.

RESULTS

Whilst eCT alone was inactive, it synergised at 1 µg/kg with low doses of Dex (7.5 or 15 µg/kg) to yield an anti-arthritic efficacy equivalent to a 4- to 7-fold higher Dex dose. Mechanistically, the anti-arthritic synergy corresponded to a marked attenuation in RA-relevant analytes. CXCL5 expression, in both plasma and joint, was markedly inhibited by the co-therapy. Finally, co-administration of eCT did not exacerbate metrics of GC adverse effects, and rescued some of them.

CONCLUSIONS

We present evidence of a class-effect action for the anti-arthritic synergy of CT/GC combination, underpinned by the powerful inhibition of joint destruction markers. Furthermore, we identify CXCL5 as a marker for the combination therapy with potential diagnostic and prognostic utility. Substantial GC dose reduction, together with the absence of exacerbated adverse effects, indicated a significant clinical potential for this co-therapy in RA and beyond.

Salmon calcitonin in the acute treatment of moderate and severe hypercalcemia in man

The effect of i.v. infusions with salmon calcitonin was evaluated in the treatment of acute hypercalcemia in 12 patients. Clinical improvement and a less critical level of serum calcium were achieved within 24 hours for eight of the patients, for another two after treatment for 48 hours. In malignant conditions (six patients) calcitonin was less effective, which could be evaluated within 24 hours. In addition to rehydration, the rapid onset of action and the lack of side-effects make calcitonin a drug of first choice in the treatment of acute hypercalcemia.

Hormonal regulation and calcium metabolism in the rabbit

Calcium is an important mineral in homeostasis in all vertebrate animals. It is the most abundant mineral in the body, and is the major component of bones and teeth. In addition, calcium is involved in various vital physiologic processes, including blood coagulation, muscle contraction, membrane permeability, nerve conduction, enzyme activity, and hormone release. Calcium metabolism in the rabbit differs in several respects from that of most mammals. This article discusses calcium metabolism and its hormonal regulation in the rabbit, as compared with normal calcium metabolism in other mammalian species. Medical disorders associated with this unique metabolism are introduced briefly.

The effects of salmon calcitonin-induced hypocalcemia on bone metabolism in ovariectomized rats

The ovariectomized rat has proved to be a most useful model for preclinical testing of potential therapies for osteoporosis. We describe the immediate effects of a single treatment with salmon calcitonin (sCT) on calcium homeostasis and bone turnover markers in 6-month-old sham and ovariectomized (ovx) rats at 15 days postovariectomy. Rats were fasted for 24 h prior to and following administration of 0.3 microg/kg body weight sCT. Blood specimens were collected at 0 (pretreatment), 2, 4, and 8 h. Urine samples were collected during the intervening periods. sCT treatment produced a decrease in blood ionized calcium at 2 h posttreatment in sham and ovx rats (P < 0.001), which was exaggerated in the ovx rats (P < 0.001). Increased parathyroid hormone (PTH) levels (P < 0.001) accompanied the hypocalcemia in ovx rats. Furthermore, PTH levels were significantly higher in ovx rats compared with sham rats for the same ionized calcium range of 1.275-1.300 mmol/l (P < 0.05). sCT treatment in sham rats increased urine hydroxyproline (UHyp) at 6 h posttreatment (P < 0.01). In conclusion, the calcitonin-induced hypocalcemia and secondary hyperparathyroidism was more pronounced in the ovariectomized rats, consistent with the actions of calcitonin in states of increased bone turnover induced by estrogen deficiency. This study highlights the importance of considering the actions of PTH and estrogen status when interpreting changes in calcium homeostasis and bone turnover following treatment with calcitonin in rodent models and provides further evidence for a potential role of estrogen in parathyroid function.

Bioavailability and biological efficacy of a new oral formulation of salmon calcitonin in healthy volunteers

Salmon calcitonin (SCT) is a well-tolerated peptide drug with a wide therapeutic margin and is administered parenterally for long-term treatments of bone diseases. Its clinical usefulness would be enhanced by the development of an orally active formulation. In this randomized crossover double-blinded phase I trial, controlled by both a placebo and a parenteral verum, we have tested a new oral formulation of SCT associated with a caprylic acid derivative as carrier. Eight healthy volunteers received single doses of 400, 800, and 1200 microg of SCT orally, a placebo, and a 10-microg (50 IU) SCT intravenous infusion. SCT was reliably absorbed from the oral formulation, with an absolute bioavailability of 0.5-1.4%, depending on the dose. It induced a marked, dose-dependent drop in blood and urine C-terminal telopeptide of type I collagen (CTX), a sensitive and specific bone resorption marker, with the effects of 1200 microg exceeding those of 10 microg intravenously. It also decreased blood calcium and phosphate, and increased the circulating levels of parathyroid hormone (PTH) and, transiently, the urinary excretion of calcium. It was well-tolerated, with some subjects presenting mild and transient nausea, abdominal cramps, diarrheic stools, and headaches. This study shows that oral delivery of SCT is feasible with reproducible absorption and systemic biological efficacy. Such an oral formulation could facilitate the use of SCT in the treatment of osteoporosis and other bone diseases.

Calcitonin and calcitonin receptors: bone and beyond

Calcitonin (CT), a 32 amino acid peptide hormone produced primarily by the thyroid, and its receptor (CTR) are well known for their ability to regulate osteoclast mediated bone resorption and enhance Ca2+ excretion by the kidney. However, recent studies now suggest that CT and CTRs may play an important role in a variety of processes as wide ranging as embryonic/foetal development and sperm function/physiology. In this review article, CT and CTR gene transcription, signal transduction and function are addressed. The effects of CT on the physiology of a variety of organ systems are discussed and the relationship between polymorphisms in the CTR gene and bone mineral density (BMD)/osteoporosis is examined. Recent studies demonstrating the ability of receptor activity modifying proteins (RAMPs) to post-translationally modify the calcitonin receptor-like receptor (CRLR) are detailed and studies employing transgenic mouse technology to determine the temporal and tissue specific transcriptional activity of the CTR gene in vivo are discussed.

Effect of calcitonin on calcium transport by the luminal and basolateral membranes of the rabbit nephron

In the rabbit, calcitonin has been shown to enhance calcium (Ca2+) reabsorption in the early distal tubule. The aim of the present study was to investigate the mechanism of this action, using isolated luminal and basolateral membranes of distal tubules. The tubule suspensions were preincubated in the presence or absence of 10(-7) M calcitonin. The luminal or basolateral membranes were subsequently purified and 45Ca transport through the vesicles was measured using the rapid filtration technique. Results were compared with those obtained from proximal tubule membranes. In the proximal tubules, calcitonin had no effect on Ca2+ uptake by luminal membranes. In the distal tubules, the presence of Na+ in the incubation medium strongly decreased the uptake of Ca2+ by luminal membranes. Preincubation of distal tubules with calcitonin partially restored this uptake. We previously reported a dual kinetics of Ca2+ uptake by the distal luminal membranes. Calcitonin enhanced Ca2+ transport by the low affinity component, increasing the Vmax and leaving the K(m) unchanged. Renal calcitonin receptors usually couple to both adenylate cyclase and phospholipase C. To determine through which messenger(s) calcitonin enhances Ca2+ transport by the distal tubules, we first confirmed that the hormone stimulates cAMP and IP3 release. Incubation of the distal tubules with 10(-7) M calcitonin significantly increased both messengers. In contrast, calcitonin did not influence the IP3 nor the cAMP content of proximal tubules. Therefore, we studied the actions of cAMP and phorbol 12-myristate 13 acetate (PMA) on Ca2+ transport by the distal luminal membranes. Incubation of distal tubule suspensions with dibutyryl cAMP significantly increased Ca2+ uptake by the luminal membranes. However, incubation of these tubules with various concentrations of PMA (10 nM, 100 nM and 1 microM) had no effect on this uptake. Calcitonin also influenced Ca2+ transport by the distal basolateral membrane. Incubation of distal tubule suspensions with 10(-7) M calcitonin activated the Na+/Ca2+ exchanger activity, almost doubling the Na+ dependent Ca2+ uptake. Here again this action was mimicked by cAMP. We conclude that calcitonin increases Ca2+ transport by the distal tubule through two mechanisms: the opening of low affinity Ca2+ channels in the luminal membrane and the stimulation of the Na+/Ca2+ exchanger in the basolateral membrane, both actions depending on the activation of adenylate cyclase.

Primary Hyperparathyroidism: Diagnosis and Management

OBJECTIVE

To review the manifestations of primary hyperparathyroidism and the available treatment strategies.

METHODS

The epidemiologic and pathologic features of this endocrine disorder are outlined. Guidelines for surgical intervention are discussed, and the effectiveness of various medical treatments is summarized.

RESULTS

Primary hyperparathyroidism, a common disorder, is diagnosed on the basis of hypercalcemia in the presence of increased parathyroid hormone levels as measured by immunoassay. Clinical manifestations are variable with many patients being asymptomatic at the time of diagnosis. Patients with severe disease require definitive surgical treatment. Surgical cure rates are high--approximately 95% in experienced hands. Indications for surgery include a serum calcium of more than 2.9 mmol/L (12 mg/dL), osteoporosis, recurrent renal stones, and parathyroid carcinoma. As well, it is recommend in individuals younger than 50 years of age. Patients with mild disease may have a benign natural history and may not have progression to severe disease. Asymptomatic individuals with mild hypercalcemia and close to normal bone mass and renal function may be managed medically, particularly those who are over the age of 50 years. Medical management includes ensuring adequate hydration and avoiding volume depletion. Estrogen therapy is valuable in postmenopausal women without contraindications to hormone replacement. Calcitonin has been shown to decrease serum calcium levels on a short-term basis. Bisphosphonates are also potential treatment options and require further study. Calcium-mimetic agents also may become valuable in the medical management of primary hyperparathyroidism in the near future.

CONCLUSION

As primary hyperparathyroidism is being increasingly detected at an asymptomatic stage, medical therapy is assuming a greater role in the effective management of this common condition.

Drugs used in the treatment of metabolic bone disease. Clinical pharmacology and therapeutic use

Osteoporosis is the most important metabolic bone disease and places an increasing burden on the healthcare system. The condition can be prevented by the early introduction of hormone replacement therapy. The role of bisphosphonates in achieving the same result is being actively explored. The attraction of preventing bone loss is that it preserves the micro-architecture of bone, and therefore its mechanical integrity. The great problem of treating the established condition is that substantial bone loss is accompanied by architectural disintegration. Replacing lost bone may not necessarily restore mechanical integrity and protect against fractures. The management of Paget's disease has been quite revolutionised by the introduction of the bisphosphonates. The condition is a result of a primary increase in osteoclastic bone resorption which can be corrected by bisphosphonates, with considerable symptomatic improvement. The increasing potency and safety margin of the newer agents has meant that the threshold for treatment has fallen. There is now potential for long term control of bone turnover with the hope of preventing late complications. Hypercalcaemia of malignancy is usually the result of both increased bone destruction and decreased urinary calcium excretion. These two components of hypercalcaemia demand different approaches to management. The general availability of an ever-expanding range of increasingly potent bisphosphonates has resulted in a dramatic improvement in the treatment of increased bone resorption associated with malignancy. Many types of tumour, either directly or indirectly, compromise the ability of the kidney to eliminate a calcium load derived from increased bone destruction. Calcitonin is the only agent which is currently available to counter this process.

Comparison of low-dose intramuscular and intravenous salcatonin in the treatment of primary hyperparathyroidism

The treatment of hypercalcaemia with low-dose salcatonin (100 U/d), administered either as a single intramuscular bolus or as a continuous intravenous infusion for five days, was examined in two groups of 10 patients with primary hyperparathyroidism, in a randomized open parallel study. Both the peak (0.31 +/- 0.035 mmol/L v 0.13 +/- 0.034 mmol/L) and overall (0.073 +/- 0.016 mmol/L v 0.018 +/- 0.016 mmol/L) hypocalcaemic responses were greater in the infusion group. The peak reduction in serum calcium occurred on day 2 of treatment after which there was a progressive attenuation of response. All the differences between the two methods of administration wer due to renal rather than bony effects of salcatonin. Possible causes of progressive resistance to treatment included reductions in sodium excretion and serum phosphate. It is concluded that low-dose salcatonin administered as a continuous infusion was more effective than the same dose given as a bolus. The kidney played a pivotal role both in the cause of the hypercalcaemia and in the response to treatment, including the rapid development of resistance which limits the use of salmon calcitonin in primary hyperparathyroidism to short-term reduction of serum calcium.

Evaluation of salmon calcitonin treatment in bone metastases from breast cancer--a controlled trial

Salmon calcitonin 100 MRCU/day or a saline placebo were given in daily injections for at least three months to 49 patients with bone metastases from breast cancer in a randomized double-blind trial. All patients were normocalcemic, and most patients had stable or regressing disease at start of trial. No improvement in general performance or bone pain was detected as measured by a visual analogue scale, the daily duration of pain or consumption of analgetic drugs. Calcitonin had no effect on disease progression as judged by bone scans and radiographs. Calcitonin therapy did not affect serum calcium, alkaline phosphatase, bone gla-protein, or the urinary excretion of calcium and hydroxyproline. Serum phosphate and magnesium decreased significantly during calcitonin treatment (p = 0.01, and 0.00005, respectively). It was concluded that salmon calcitonin in this dosage has no discernible effect on skeletal pain, general performance, bone metabolism or disease progression in patients with breast cancer metastatic to bone. A significant decrease in serum phosphate and magnesium probably indicated an effect of calcitonin on the renal excretion of these ions.

Quantitation of the renal effect of calcitonin in the hypercalcaemia of malignancy

The renal effect of calcitonin (independent of changes due to variations in sodium excretion) was quantitated in malignancy associated hypercalcaemia. There was considerable inter- and intra-patient variability in response but this was unaffected by tumour type. Humoral hypercalcaemia tended to be resistant to control. In responsive patients the renal effects of calcitonin unlike those described in bone did not diminish with time.

Effect of calcitonin on calcium and magnesium transport in rat nephron

Renal calcium and magnesium reabsorption was investigated in young, thyroparathyroidectomized rats receiving synthetic salmon calcitonin. Kidney and tubular function was assessed by clearance and in vivo microperfusion techniques, respectively. Calcitonin reduced urinary calcium and magnesium excretion that was attributed to increased reabsorption within the loop of Henle. This enchanced reabsorption was independent of parathyroid hormone; however, it is contingent on a decline in plasma calcium concentration. Prevention of hypocalcemia by CaCl2 infusion in rats acutely administered calcitonin resulted in loop function comparable to animals not receiving the hormone. Calcitonin had little effect on proximal tubule or distal tubule electrolyte reabsorption. These results are consistent with a transport model for calcium and magnesium in the loop of Henle involving a contraluminal transfer step modulated by absolute extracellular calcium or magnesium. Furthermore, these studies suggest that the discrepancies present in the literature concerning renal effects of calcitonin on electrolyte reabsorption are due to variations in observed hormone action, namely, the effect on plasma calcium concentration.

Early effects of synthetic bovine parathyroid hormone and synthetic salmon calcitonin on urinary excretion of cyclic AMP, phosphate and calcium in man

Bovine synthetic parathyroid hormone infused intravenously in man increased both the urinary excretion of cyclic AMP and the urinary excretion of phosphate whereas a Salmon synthetic calcitonin infusion increased the urinary excretion of phosphate without change in urinary excretion of cyclic AMP. These data are consistent with the hypothesis that different renal mechanisms are involved in the response to each hormone.

Renal effects of calcitonin and parathyroid extract in man. Studies in hypoparathyroidism

To clarify the controversial renal action of calcitonin (CT) and a possible interrelationship between CT and parathyroid hormone, eight patients with untreated surgical hypoparathyroidism were studied. Various calcitonins, i.e. extracted porcine, synthetic porcine, synthetic human, and synthetic salmon CT in doses of 150 Medical Research Council U or 1.5 mg were infused over a 3 hr period. Subsequently, six of the same subjects received 500 USP U parathyroid extract (PTE) (Eli Lilly & Co., Indianapolis, Ind.) in 3 hr and later a combination of CT and PTE. In addition, two patients were given an infusion of ammonium phosphate with the aim of producting a phosphaturia of comparable degree as seen after CT and PTE, thus differentiating hormonal from nonhormonal influences on cation excretion. A protocol of serial clearance (C) studies using the patients as their own controls was followed. Serum and urinary inorganic phosphate (P), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), and creatinine (Cr) were determined and the clearance values calculated. All CT peptides caused a uniform, immediate and significant increase of C(P), C(Na), C(K), C(Ca), and C(Mg), PTE evoked a rise of C(P), C(Na), and C(K), but C(Ca) and C(Mg) were reduced, the Ca and Na figures being not statistically significant. The administration of both CT and PTE resulted in a summation of individual hormone effects on Ca and Mg excretion. Phosphate infusion on the other hand induced an isolated phosphaturia but no concomitant changes of the urinary cations.The hypoparathyroid data demonstrate that calcitonin enhances urinary elimination of P, Na, K, Ca, and Mg independently of parathyroid action, CT and PTE act qualitatively similarly on P, Na, and K excretion, while an antagonism seems to exist for the renal handling of Ca and Mg.

Value of plasma chloride concentration and acid-base status in the differential diagnosis of hyperparathyroidism from other causes of hypercalcaemia

A study is reported of the estimation of plasma chloride concentration and acid-base status in the differentiation of primary hyperparathyroidism from all other causes of hypercalcaemia. In the two groups of patients studied, all of whom had hypercalcaemia, there was complete separation between the two groups on the basis of plasma chloride concentration and acid-base status. In 16 patients with primary hyperparathyroidism the increase in plasma chloride concentration and associated metabolic acidosis could have been accounted for by the known renal tubular effects of parathyroid hormone. In 13 patients with hypercalcaemia due to various other causes the decrease in plasma chloride concentration and associated metabolic alkalosis could be accounted for either by the known effects of an excess of calcium-ion on the renal tubules, or perhaps by suppression of endogenous parathyroid hormone secretion. In patients with hypercalcaemia and hypophosphataemia of ;pseudohyperparathyroidism' associated with non-endocrine tumours it is postulated that the low plasma chloride concentrations and metabolic alkalosis found in these patients were due either to a differing biological activity of the parathyroid-hormone-like polypeptide secreted by the tumour cells, or possibly to simultaneous secretion by these cells of an ACTH-like polypeptide.