Calcitonin: regional distribution of the hormone and its binding sites in the human brain and pituitary

Evolutionary origin of the chordate nervous system revealed by amphioxus developmental trajectories

The common ancestor of all vertebrates had a highly sophisticated nervous system, but questions remain about the evolution of vertebrate neural cell types. The amphioxus, a chordate that diverged before the origin of vertebrates, can inform vertebrate evolution. Here we develop and analyse a single-cell RNA-sequencing dataset from seven amphioxus embryo stages to understand chordate cell type evolution and to study vertebrate neural cell type origins. We identified many new amphioxus cell types, including homologues to the vertebrate hypothalamus and neurohypophysis, rooting the evolutionary origin of these structures. On the basis of ancestor-descendant reconstruction of cell trajectories of the amphioxus and other species, we inferred expression dynamics of transcription factor genes throughout embryogenesis and identified three ancient developmental routes forming chordate neurons. We characterized cell specification at the mechanistic level and generated mutant lines to examine the function of five key transcription factors involved in neural specification. Our results show three developmental origins for the vertebrate nervous system: an anterior FoxQ2-dependent mechanism that is deeply conserved in invertebrates, a less-conserved route leading to more posterior neurons in the vertebrate spinal cord and a mechanism for specifying neuromesoderm progenitors that is restricted to chordates. The evolution of neuromesoderm progenitors may have led to a dramatic shift in posterior neural and mesodermal cell fate decisions and the body elongation process in a stem chordate.

Effects of intracerebroventricular administration of calcitonin gene-related peptide (CGRP) on sex hormones and sperm quality in rats

Background

Therapeutic strategies with calcitonin gene-related peptide (CGRP) or its receptor have been investigated, but there are few studies regarding the possible harmful effects of CGRP in other body organs.

Objective

This study aimed to investigate the effect of intracerebroventricular (ICV) injection of CGRP on sex hormones and sperm quality in rats.

Methods

Twelve male rats were divided into two groups (n=6 per group). The first group (control) rats were injected with 5 µl artificial cerebrospinal fluid intra-ICV; the second group rats, 5 µl (1.5 nmol) CGRP. The levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone were measured. Epididymal sperms were used to determine the sperm parameters.

Results

The levels of testosterone, LH and FSH in CGRP group was significantly lower than in artificial cerebrospinal fluid (ACSF) group (P<0.05). The concentration and motility of sperm in CGRP group was significantly lower than in ACSF group (P<0.05). In CGRP group live spermatozoa and intact acrosome significantly reduced compared to the ACSF group (P<0.05). In addition, in CGRP group dead spermatozoa and lose acrosome significantly increased compared to the ACSF group (P<0.05).

Conclusion

ICV injection of CGRP may reduce sperm quality, probably through induction of an imbalance in FSH and LH production as well as testosterone.

Building the case for the calcitonin receptor as a viable target for the treatment of glioblastoma

Researchers are actively seeking novel targeted therapies for the brain tumour glioblastoma (GBM) as the mean survival is less than 15 months. Here we discuss the proposal that the calcitonin receptor (CT Receptor), expressed in 76-86% of patient biopsies, is expressed by both malignant glioma cells and putative glioma stem cells (GSCs), and therefore represents a potential therapeutic target. Forty-two per cent (42%) of high-grade glioma (HGG; representative of GSCs) cell lines express CT Receptor protein. CT Receptors are widely expressed throughout the life cycle of organisms and in some instances promote apoptosis. Which of the common isoforms of the CT Receptor are predominantly expressed is currently unknown, but a functional response to cell stress of the insert-positive isoform is hypothesised. A model for resistant malignancies is one in which chemotherapy plays a direct role in activating quiescent stem cells for replacement of the tumour tissue hierarchy. The putative role that the CT Receptor plays in maintenance of quiescent cancer stem cells is discussed in view of the activation of the Notch-CT Receptor-collagen V axis in quiescent muscle (satellite) stem cells. The pharmacological CT response profiles of four of the HGG cell lines were reported. Both CT responders and non-responders were sensitive to an immunotoxin based on an anti-CT Receptor antibody. The CALCR mRNA exhibits alternative splicing commonly associated with cancer cells, which could result in the atypical pharmacology exhibited by CT non-responders and an explanation of tumour suppression. Due to the inherent instability of CALCR mRNA, analysis of CT Receptor protein in patient samples will lead to improved data for the expression of CT Receptor in GBM and other cancers, and an understanding of the role and activity of the splice variants. This knowledge will aid the effective targeting of this receptor for treatment of GBM.

Clinical efficacy of calcitonin compared to diclofenac sodium in chronic nonspecific low back pain with type I Modic changes: a retrospective study

Background

The objective of this study was to compare the efficacy of calcitonin with diclofenac sodium in the treatment of patients with nonspecific low back pain (LBP) and type I Modic changes (MC1).

Patients and methods

The study was a retrospective observational study with 109 patients who had nonspecific LBP and MC1 that appeared as bone marrow lesions on magnetic resonance imaging (MRI). Between October 2013 and March 2016, 62 patients were injected intramuscularly with calcitonin 50 IU once daily and 47 patients were treated with diclofenac 75 mg once per day for 4 weeks for the treatment of LBP associated with MC1 on MRI. Visual analog scale (VAS) (0–10) and Oswestry Disability Index (ODI) (0–100) questionnaires were acquired from clinical records to evaluate LBP perception and degree of disability. Imaging data were also collected before and after treatment.

Results

Significant improvements were found in VAS and ODI at posttreatment compared with baseline in both groups (P < 0.05). Meanwhile, there was a significant difference between calcitonin group and diclofenac group at both 4 weeks and 3 months of follow-up (4 weeks: VAS 4.46 ± 1.58 vs 5.08 ± 1.50, ODI 20.32 ± 9.64 vs 24.35 ± 7.95; 3 months: VAS 3.70 ± 1.74 vs 4.51 ± 1.67, ODI 16.67 ± 9.04 vs 21.18 ± 9.56; P < 0.05 for all). Moreover, the proportion of patients with a significant change in LBP scales was higher in the calcitonin group (4 weeks: VAS 50.00% vs 23.40%, ODI 54.83% vs 25.53%; 3 months: VAS 58.06% vs 38.29%, ODI 59.67% vs 38.29%; P < 0.05 for all). According to MRI, 43.54% patients in the calcitonin group showed improvement compared with 21.27% patients in the diclofenac group (P < 0.05).

Conclusion

There was greater short-term efficacy of calcitonin compared with diclofenac in patients with LBP and MC1 on MRI.

Prolonged calcitonin receptor signaling by salmon, but not human calcitonin, reveals ligand bias

Salmon calcitonin (sCT) and human calcitonin (hCT) are pharmacologically distinct. However, the reason for the differences is unclear. Here we analyze the differences between sCT and hCT on the human calcitonin receptor (CT_(a)R) with respect to activation of cAMP signaling, β-arrestin recruitment, ligand binding kinetics and internalization. The study was conducted using mammalian cell lines heterologously expressing the human CT_(a) receptor. CT_(a)R downstream signaling was investigated with dose response profiles for cAMP production and β-arrestin recruitment for sCT and hCT during short term (<2 hours) and prolonged (up to 72 hours) stimulation. CT_(a)R kinetics and internalization was investigated with radio-labeled sCT and hCT ligands on cultured cells and isolated membrane preparations from the same cell line. We found that sCT and hCT are equipotent during short-term stimulations with differences manifesting themselves only during long-term stimulation with sCT inducing a prolonged activation up to 72 hours, while hCT loses activity markedly earlier. The prolonged sCT stimulation of both cAMP accumulation and β-arrestin recruitment was attenuated, but not abrogated by acid wash, suggesting a role for sCT activated internalized receptors. We have demonstrated a novel phenomenon, namely that two distinct CT_(a)R downstream signaling activation patterns are activated by two related ligands, thereby highlighting qualitatively different signaling responses in vitro that could have implications for sCT use in vivo.

Expression profile and localization of mouse calcitonin (CT) sense/antisense transcripts in pre- and postnatal tissue development

Calcitonin (CT) has been shown to have various functions including osteoclast activity and calcium and phosphorus metabolism in mammals. In the present study, we measured the amounts of CT mRNA in the mouse brain, liver, kidney, heart and testis at various development stages, 14 days post-coitum (dpc), 17-dpc, newborn, 1 week and 8 weeks (adult), using real-time PCR. In the brain and kidney, the amount of CT mRNA decreased with development. In the testis, elevated amounts were observed at 17-dpc and 8 weeks. In the liver, the amount increased from the 14 dpc embryo to newborn stage and then decreased. In the heart, elevated amounts were observed at 17-dpc. Additionally, the CT antisense transcript was determined using a modified RT-PCR and nucleotide sequencing in the present study. Organs with high mRNA expressions were examined for localization of transcripts using in situ hybridization. The CT sense and antisense transcripts in the 14 dpc brain were mainly localized in the mesencephalon. In the pre- and postnatal stages, sense and antisense transcripts were shown to exist rather uniformly in the kidney, heart, liver and testis. In the 17-dpc rib and thyroid lobe and the adult ovary, the sense and antisense transcripts were found to be densely localized.

Salmon calcitonin: a review of current and future therapeutic indications

Salmon calcitonin, available as a therapeutic agent for more than 30 years, demonstrates clinical utility in the treatment of such metabolic bone diseases as osteoporosis and Paget's disease, and potentially in the treatment of osteoarthritis. This review considers the physiology and pharmacology of salmon calcitonin, the evidence based research demonstrating efficacy and safety of this medication in postmenopausal osteoporosis with potentially an effect on bone quality to explain its abilities to reduce the risk of spine fracture, the development of an oral salmon calcitonin preparation, and the therapeutic rationale for this preparation's chondroprotective effect in osteoarthritis.

The role of calcitonin and alpha-calcitonin gene-related peptide in bone formation

The Calca gene encodes two polypeptides, calcitonin (CT) and alpha-calcitonin gene-related peptide (alpha-CGRP), generated through alternative splicing. While CT, a hormone mainly produced by thyroidal C cells, has been described as a major regulator of bone resorption, alpha-CGRP, a neuropeptide expressed in the cells of the central and peripheral nervous system, is mostly known as a regulator of vascular tone. Surprisingly, the generation and skeletal analyses of two mouse deficiency models has recently uncovered a physiological function for both peptides in the regulation of bone formation. In the first model, where the replacement of exons 2-5 of the Calca gene resulted in the combined deficiency of CT and alpha-CGRP, an increased bone formation rate (BFR) was observed, whereas decreased BFR was found in the second model, where the introduction of a translational termination codon into exon 5 of the Calca gene resulted in the specific absence of alpha-CGRP.

A novel promoter regulates calcitonin receptor gene expression in human osteoclasts

The calcitonin receptor (CTR) is expressed in a wide variety of tissues and cell types. In bone, its expression is restricted to osteoclasts, the cells that mediate bone resorption. The human CTR (hCTR) gene has a complex structural organization that exhibits similarity to the porcine (pCTR) and mouse (mCTR) CTR genes. In these species, alternative splicing of a single gene generates multiple CTR isoforms that are distributed in both tissue-specific and species-specific patterns. However, the structural organization of the 5' putative regulatory region and transcriptional mechanisms responsible for tissue-specific expression of the different CTR isoforms are not fully defined. The present studies were undertaken to characterize the structural organization of the 5'-region of the hCTR and identify the regulatory regions involved in osteoclast-specific transcriptional activation. Analysis of mRNA prepared from human osteoclasts using reverse transcription-polymerase chain reaction (RT-PCR) and transient transfection of hCTR promoter-luciferase reporter constructs identified two regions in the 5'-flanking sequence of the hCTR gene that regulated CTR gene expression in osteoclasts. Both of these putative promoters were responsive to the osteoclast-inducing cytokine, receptor activator of NF-kappaB ligand (RANKL) and demonstrated trans-activation by the RANKL-induced transcription factor nuclear factor of activated T cells (NFATc1), consistent with a role in regulating CTR gene expression in osteoclasts.

A synthetic peptide derived from mouse pituitary calcitonin cDNA sequence exhibits potent inhibition of prolactin secretion and prolactin mRNA abundance in primary mouse pituitary cells

We have shown that gonadotrophs synthesize and secrete immunoreactive calcitonin (CT)-like peptide, and CT is a potent inhibitor of prolactin (PRL) secretion and gene transcription. CT cDNA cloned from LssT2 cells (pit-CT cDNA) exhibits 99% homology with mouse CT cDNA sequence, but exhibits four mismatches in the coding region of CT peptide (347-485 bp) with consequent changes in the amino acids at positions 5 and 17 of mouse CT. We have synthesized a putative 23 amino acid pit-CT peptide based on pit-CT cDNA sequence, and tested its effect on PRL secretion and mRNA abundance in primary mouse pituitary cells. The results suggest that synthetic pit-CT attenuates PRL mRNA abundance and inhibits PRL release from mouse anterior pituitary cells. Moreover, pit-CT is remarkably more potent than salmon (S)CT in attenuating PRL mRNA abundance. These results raise a possibility that this endogenous pituitary peptide may potentially serve as a therapeutic molecule for the treatment of prolactinomas.

The influence of phospholipid membranes on bovine calcitonin peptide's secondary structure and induced neurotoxic effects

The peptide hormone, calcitonin, which is associated with medullary carcinoma of the thyroid, has a marked tendency to form amyloid fibrils and may be a useful model in probing the role of peptide-membrane interactions in beta-sheet and amyloid formation and amyloid neurotoxicity. Using bovine calcitonin, we found that, like other amyloids, the peptide was toxic only when in a beta-sheet-rich, amyloid form, but was non-toxic, when it lacked an amyloid structure. We found that the peptide bound with significant affinity to membranes that contained either cholesterol and gangliosides. In addition, incubation of calcitonin with cholesterol-rich and ganglioside-containing membranes resulted in significant changes in peptide structure yielding a peptide enriched in beta-sheet and amyloid content. Because the cholesterol- and ganglioside-rich phospholipid systems enhanced the calcitonin beta-sheet and amyloid contents, and peptide amyloid content was associated with neurotoxicity, we then investigated whether depleting cellular cholesterol and gangliosides affected calcitonin neurotoxicity. We found that cholesterol and ganglioside removal significantly reduced the calcitonin-induced PC12 cell neurotoxicity. Similar results have been observed with other amyloid-forming peptides such as beta-amyloid (A beta) of Alzheimer's disease and suggest that modulation of membrane composition and peptide-membrane interactions may prove useful in the control of amyloid formation and amyloid neurotoxicity.

Williams syndrome: an historical perspective of its evolution, natural history, and etiology

This review examines the Williams syndrome (WS) from an historical perspective, beginning with the early descriptions of idiopathic infantile hypercalcemia (IIH) and ending with some speculative ideas about a possible causative function of a recently discovered neuropeptide. The earliest reports of WS individuals are probably those which describe a "severe" subgroup of IIH and separate it from the epidemic of milder IIH reported in Post-WWII Great Britain and Europe. Most of these latter cases apparently resulted from hypervitaminosis D produced by excessive supplementation of government-supplied infant foods. With more extensive recognition and reporting of this "severe" subgroup, the diagnostic constellation of IIH, mental deficiency, elfin face, and supravalvular aortic stenosis (SVAS) evolved as WS. More of these reports emphasized the physical and behavioral manifestations as the key diagnostic features, and the frequency of occurrence and relative importance of SVAS and IIH in WS decreased. Despite the diminished consequence of hypercalcemia, calcium and vitamin D have continued to dominate the investigation of the cause of infantile hypercalcemia and led to the proposal and confirmation of deficient calcitonin secretion in individuals with WS. Though calcitonin is probably pertinent only to infantile hypercalcemia, its alternative gene product, calcitonin-gene-related product, is an important neuropeptide with physiological effects in the central nervous system and cardiovascular systems which raise the possibility that it may be responsible for some of the manifestations of WS.

The influence of phospholipid membranes on bovine calcitonin secondary structure and amyloid formation

Calcitonin, a peptide hormone associated with medullary carcinoma of the thyroid, has the potential to form amyloid fibrils and may be a valuable model for investigating the role of peptide-membrane interactions in beta-sheet and amyloid formation. Via a new model peptide system, bovine calcitonin, we found that the exposure of peptide to phospholipid membranes altered its structure relative to the structures formed in aqueous solutions. Of particular relevance to the amyloidoses, incubation of calcitonin with cholesterol-rich and ganglioside-containing membranes resulted in significant enrichment in the beta-sheet and amyloid content of the peptide. The formation of amyloid was also accelerated in these systems. A correlation between the phospholipid-induced structural alterations and calcitonin binding affinities to phospholipid membranes was evident. Bovine calcitonin has considerably higher binding affinity for the phospholipid systems that enhanced its beta-sheet and amyloid structure. Electrostatic forces were not the governing forces behind the observed behavior, as supported by the fact that the ionic strength did not affect the peptide structures or binding affinities. A Van't Hoff analysis of the temperature-dependent peptide binding affinities indicated that binding led to an increase in enthalpy and possibly an increase in entropy of the peptide-membrane systems. Experiments with other amyloid-forming peptides such as beta-amyloid of Alzheimer's disease have also shown similar results and may indicate the need to manipulate peptide-membrane interactions in order to control amyloid formation and its associated disease.

Effect of nanomolar concentrations of sodium dodecyl sulfate, a catalytic inductor of alpha-helices, on human calcitonin incorporation and channel formation in planar lipid membranes

Human Calcitonin (hCt) is a peptide hormone which has a regulatory action in calcium-phosphorus metabolism. It is currently used as a therapeutic tool in bone pathologies such as osteoporosis and Paget's disease. However, due to its amphiphilic property tends to form a gelatinous solution in water which consists of fibrils that limits its therapeutic use. Here we show that sodium dodecyl sulfate (SDS), an anionic detergent able to induce and stabilize alpha-helices in polypeptides, at a monomeric concentration ranging between 0.26 mM-5 pM (all concentrations are below the CMC), increases the rate and number of hCt channel formation in planar lipid membranes, at both high and low hCt concentrations, with a maximum increase at a molecular hCt/SDS ratio of 1000:1. This effect could be interpreted as a counteraction to the fibrillation process of hCt molecules by removing molecules available for aggregation from the fluid; furthermore, this action, independently of channel formation in the cell membrane, could improve the peptide-receptor interaction. The action of SDS could be attributable to the strength of the sulfate negative charge and the hydrophobic chain; in fact, a similar effect was obtained with lauryl sarcosine and not with a neutral detergent such as n-dodecyl-beta-D-maltoside. The very low molecular ratio between SDS and peptide is suggestive of a possible catalytic action of SDS that could induce alpha-helices, the appropriate structures for interacting with the membrane. Moreover, in the experimental conditions investigated, the addition of SDS does not modify the membrane's electrical properties and most of the channel properties. This finding may contribute to the knowledge of environment-folding diseases due to protein and peptides.

Biomarkers of endometrial receptivity--a review

Implantation is a phenomenon that involves an interaction between the embryo and maternal endometrium. There is, in the menstrual cycle, a short and precise period of time in which the maternal-embryonic interaction is optimal and culminates with adhesion and invasion of the blastocyst into the progesterone-induced secretory endometrium. This period is called nidation or implantation window. In the implantation window changes occur in endometrial epithelial morphology, characterized by the appearance of membrane projections called pinopodes. Pinopodes are progesterone-dependent organelles, that look like apical cellular protrusions appearing between days 20 and 21 of the natural menstrual cycle. There are many factors that regulate the changes typical of the implantation window and the appearance of the pinopodes. The embryonic and maternal expression of growth factors and cytokines, calcitonin, HOX genes and cell adhesion molecules might all play a major role in the phenomenon of implantation. The cytokines function as chemical messengers and can serve as biomarkers of uterine receptivity. Understanding the function of these biomarkers and their role in determining the implantation window in women, will help us to diagnose and treat infertile couples more efficiently.

Calcr, a brain-specific imprinted mouse calcitonin receptor gene in the imprinted cluster of the proximal region of chromosome 6

Expressed sequence tags (ESTs) in the human chromosome 7q21-q31 region were recently used to screen for allelic expression bias in monochromosomal hybrids retaining a paternal or maternal human chromosome 7. Six candidate imprinted genes were identified. In this study, we investigated parent-of-origin-specific expression profiles of their mouse homologues in the proximal region of chromosome 6. An imprinting analysis, using F1 mice from reciprocal crosses between the B6 and JF strains, demonstrated that the mouse calcitonin receptor gene ( Calcr) was expressed preferentially from the maternal allele in brain, whereas no allelic bias was detected in other tissues. Our results indicate that Calcr is imprinted in a tissue-specific manner, with a predominant expression from the maternal allele in the brain.

Tissue-specific activity of the proximal human calcitonin receptor promoter is mediated by Sp1 and an epigenetic phenomenon

To identify cis-acting sequences transcriptionally regulating the human calcitonin receptor (hCTR) gene, hCTR promoter/luciferase gene constructs were transiently or stably transfected into hCTR-positive and -negative cell lines. Luciferase assays demonstrated that the proximal hCTR promoter (hCTRP1) was transcriptionally active in all cell lines tested. High-level hCTRP1 activity depended on an 11 bp Sp1/Sp3 binding site. Electrophoretic mobility shift assay showed that this region bound the transcription factors Sp1 and Sp3. We further showed that hCTRP1 was strongly activated by the 11 bp Sp1/Sp3 binding site in hCTRP1/luciferase-, Sp1-transfected Drosophila S2 cells. Bisulphite-mediated sequencing of genomic DNA from hCTR-expressing and -non-expressing cell lines demonstrated that the endogenous hCTRP1 was hypomethylated in all cell lines tested. These results suggest that the hCTRP1 is activated by the tissue-ubiquitous transcription factor Sp1 and that an epigenetic process unrelated to CpG methylation represses its activity in hCTR-negative tissues.

Calcitonin inhibits prolactin promoter activity in rat pituitary GGH3 cells: evidence for involvement of p42/44 mitogen-activated protein kinase in calcitonin action

Previous findings from our laboratory have shown that pituitary calcitonin-like peptide (pit-CT) is synthesized and released by gonadotrophs and inhibits prolactin (PRL) release, synthesis, and lactotroph proliferation. To investigate further the regulation of PRL gene transcription by CT, we examined the effect of CT on rat PRL (rPRL) promoter activity in rat pituitary GGH3 cells. GGH3 cells were transiently transfected with rPRL promoter- luciferase and control plasmids. Thirty-six hours later, the cells were treated with CT or other agents and their effect on luciferase activity was examined. The effect of CT and/or thyrotropin-releasing hormone (TRH) on p42/44 mitogen-activated protein kinase (MAPK) activity was also investigated. CT inhibited basal rPRL promoter activity in a dose-dependent fashion, with an approximate IC(50) of 3 nM. The maximal inhibition occurred 1 h after the CT addition, and the peptide was equipotent in inhibiting 600 and 2500 rPRL promoter constructs. CT also inhibited TRH-, Bay K 8644-, and ionomycin-induced rPRL promoter activity. CT mimicked the actions of MEK inhibitors U0126 and PD 980089. However, CT could not inhibit rPRL promoter activity in GGH3 cells expressing constitutively active ERK1 or ERK2. CT markedly attenuated phospho-MAPK immunoreactivity in untreated as well as TRH-treated GGH3 cells. These results suggest that CT inhibits rPRL promoter activity by antagonizing Ca(2+) and ERK1/2-mediated signaling events. They also demonstrate that CT is a potent inhibitor of early events associated with PRL gene activation and may play an important role in regulation of lactotroph function.

Calcitonin expression in rat anterior pituitary gland is regulated by ovarian steroid hormones

Gonadotroph-derived calcitonin-like peptide (pit-CT) is a potent inhibitor of lactotroph function. We investigated the effect of ovarian hormones on pit-CT mRNA expression in the anterior pituitary (AP) gland of cycling female rats. Levels of mRNAs for pit-CT, CT receptor, prolactin (PRL), and beta-LH during 4-d estrous cycle were determined. In a second study, the effects of estrogens and progesterone on pit-CT and PRL mRNA levels were investigated. In a third group, the effect of estrogen or progesterone depletion on pit-CT mRNA expression was studied. In a fourth group, the effect of passive pit-CT immunization on PRL and LH mRNA expression was examined. Pit-CT mRNA levels varied during estrous cycle. They were highest in diestrus, but lowest in the evening of proestrus. CT-receptor mRNA levels displayed smaller fluctuations. Estrogen repletion caused a decline in pit-CT mRNA expression in ovariectomized rats, but progesterone produced a marked increase. ICI 182,780 prevented the decline of pit-CT mRNA levels during late proestrus-estrus, but RU 486 attenuated pit-CT mRNA levels. Passive CT immunization in diestrus altered PRL and LH mRNA expression, and advanced the estrus cycle. These results suggest that pit-CT mRNA expression is regulated by ovarian hormones, and depletion of pit-CT advances their estrous cycle.

Calcitonin immunostaining in monkey uterus during menstrual cycle and early pregnancy

Calcitonin has been shown to be a progesterone-regulated potential marker of the receptive endometrium in the rat and human. The present study was undertaken to immunohistochemically investigate the changes in calcitonin in the monkey uterus during the menstrual cycle and periimplantation period. Calcitonin immunostaining was primarily localized in the glandular epithelium on d 16, 20, and 25 of the menstrual cycle. During early pregnancy, calcitonin immunostaining was strongly observed in the glandular epithelium only on d 9 of pregnancy, the day before implantation. Since the high level of calcitonin immunostaining in the glandular epithelium during the luteal phase of the menstrual cycle and periimplantation period matched the high level of maternal progesterone during this period, the expression of calcitonin in monkey endometrium may be under the regulation of maternal progesterone.

Analgesic effect of calcitonin in osteoporosis

Bone pain is the most common symptom in osteoporotic patients. To date, there is mounting evidence that calcitonin significantly reduces bone pain in osteoporosis, and that the analgesic effect can be evident as soon as the second week of treatment. The limitations to the use of calcitonin, which are parenteral administration and side effects, can now be overcome by the availability of the nasal spray preparation. At present, controlled studies have demonstrated the analgesic activity of calcitonin given by nasal spray in patients with vertebral crush fractures and bone pain. The mechanism for the analgesic effect of calcitonin is yet to be clarified. In humans, similarities between calcitonin and morphine-induced analgesia, and reports of calcitonin-induced elevation of plasma beta-endorphin levels, suggest the possible involvement of the endogenous opiate system in mediating the analgesic action of calcitonin. However, the demonstration of calcitonin binding sites in areas of the brain involved in pain perception and a series of animal studies have raised the possibility that calcitonin may directly modulate nociception in the central nervous system. In support of this hypothesis are some observations of an analgesic effect obtained by direct epidural or subaracnoidal injection of calcitonin in humans.

Channel formation by salmon and human calcitonin in black lipid membranes

In this study we investigated the interaction of salmon and human calcitonin (Ct) with artificial lipid bilayer membranes. Both peptides were able to form either transient or permanent channels in the model membranes. The channels formed by salmon Ct at concentration (125 nM) had, on average, a single-channel conductance of 0.58 +/- 0.04 nS in 1M KCl (+10 mV), which is voltage-dependent at lower voltages. Human Ct forms at the same concentration channels with a much lower probability, and high voltages of up to +150 mV were needed to initiate channel formation. The estimated single-channel conductance formed under these conditions was approximately 0.0119 +/- 0.0003 nS in 1 M KCl. Both salmon and human Ct channels were found to be permeable to calcium ions. The possibility is discussed that the superior therapeutic effect of salmon Ct as a tool to treat bone disorders, including Paget disease, osteoporosis, and hypercalcemia of malignancy, rather than human Ct is related to the lack of the fibrillating property of salmon Ct. Preliminary data indicate that also eel and porcine Ct and carbocalcitonin form channels in model membranes.

Role of steroid hormone-regulated genes in implantation

The endometrium acquires the ability to implant the developing embryo within a specific time window, termed the "receptive phase." During this period, the endometrium undergoes pronounced structural and functional changes induced by the ovarian steroids, estrogen and progesterone, which prepare it to be receptive to invasion by the embryo. These steroid-induced molecules, when identified, may serve as useful markers of uterine receptivity. In this article, we provide a brief description of one such molecule that has emerged as candidate marker of steroid hormone action in rats and humans during implantation.

Calcitonin potentiates oxygen-glucose deprivation-induced neuronal death

Calcitonin is a hormone that decreases plasma calcium through inhibition of osteolysis. It is used in the treatment of osteoporosis and other bone disorders. Salmon calcitonin is typically utilized in individuals for whom use of estrogen is contraindicated, for example, women at high risk for breast cancer. In addition to actions on bone, calcitonin may have effects on the central nervous system. Receptors for calcitonin are present on central neurons, and salmon calcitonin has been shown to alter neuronal activity. Since salmon calcitonin is used clinically, and it can have actions on neurons, the present studies were designed to determine whether salmon calcitonin could alter death of cortical neurons. The effects of salmon calcitonin on neuronal death induced by exposure of murine cortical cultures to serum deprivation, staurosporine, oxygen-glucose deprivation, kainate, and NMDA were tested. Salmon calcitonin had no effect on apoptotic cell death in cortical cultures. However, acute treatment with salmon calcitonin (1-1000 nM) caused significant potentiation of neuronal death induced by oxygen-glucose deprivation. Similarly, salmon calcitonin potentiated cell death induced by exposure to kainate. In contrast, it did not potentiate cell death induced by exposure to NMDA. In fact, addition of a high concentration (1000 nM) of salmon calcitonin attenuated NMDA toxicity. These results indicate that calcitonin is not a survival factor for cortical neurons; however, it can alter excitotoxic cell death. The most interesting, and disturbing, effect is the ability of low concentrations of salmon calcitonin to potentiate oxygen-glucose deprivation-induced cell death.

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.

Transgenic mice reveal novel sites of calcitonin receptor gene expression during development

To characterize the tissue and developmental-specific transcriptional activity of the human calcitonin receptor (hCTR) gene in vivo, transgenic mice containing a 4.9-kb hCTR promoter/beta-galactosidase (lacZ) construct were generated. Between 8.5 and 10.5 days of development, lacZ-positive cells were observed on the lateral side of cervical and occipital level somites and in the lateral myotome. LacZ-positive cells also appeared to be migrating from the dermomyotome into the adjacent limb buds, suggesting that the hCTR promoter is active in hypaxial muscle progenitors. By 11.5-16 days of development, novel hCTR expression sites were identified that included limb buds, cornea, retina, skin, intercostal muscles, muscles of the limbs, face, and dorsal root ganglion. hCTR promoter activity in a number of these tissues was repressed at adult stages of development. RT-PCR demonstrated endogenous mCTR mRNA in all lacZ-positive tissues assayed. The developmental regulation of hCTR gene expression in the above tissues suggests that CTRs are likely to play an important role in their morphogenesis.

Multiple promoters regulate human calcitonin receptor gene expression

To initiate studies on the transcriptional regulation of the human calcitonin receptor (hCTR) gene, a 4.9-kb hCTR promoter fragment was cloned and hCTR transcriptional initiation sites were mapped in human osteoclasts, kidney, and breast cancer cell line T47D. RT-PCR detected additional hCTR transcripts initiating at least 1 kb 5' to the transcripts mapped above, demonstrating that the hCTR gene is regulated by at least two separate promoters (hCTRP1 and hCTRP2). Transcripts initiating from the upstream promoter (hCTRP2) have a novel 5' untranslated region (5' UTR). Transfection of T47D breast cancer cells with hCTR promoter/luciferase deletion constructs demonstrated that the cloned 4.9-kb hCTR promoter fragment contains both hCTRP1 and hCTRP2 promoters. Fine deletion mapping of the more transcriptionally active hCTRP1 promoter demonstrated that only 97 bp of the hCTRP1 5' flanking region is required for the majority of its transcriptional activity.

Calcitonin modifies ligand binding to muscarinic receptor in CNS membranes

Calcitonin (CT) is a peptide produced by the thyroid gland, whose best described role is to prevent bone reabsorption, though it also participates in other biological functions through both central and peripheral mechanisms. CT is able to inhibit brain Na(+), K(+)-ATPase activity (Rodríguez de Lores Arnaiz, López Ordieres, Peptides 1997;18:613-5) and a relationship between such enzyme activity and cholinergic function has been suggested. Accordingly, we tested CT effect on [(3)H]-quinuclidinyl benzilate ([(3)H]-QNB) binding to rat CNS membranes to determine whether the peptide is able to modify the cholinergic muscarinic receptor as well. It was found that 1x10(-7)-1x10(-5) M CT decreased 20-70% ligand binding to hippocampal, cerebellar, cortical and striatal membranes. Scatchard analysis of saturation curves showed that 5x10(-6) M CT significantly modified binding kinetic constants, thus it increased roughly 220% K(d) values and decreased 20-36% B(max) values in cerebral cortical and cerebellar membranes. Since the peptide decreases affinity ligand binding and reduces the number of binding sites, CT may well be acting as a cholinergic modulator through a decrease in muscarinic receptor functionality.

Continuous subcutaneous administration of high-dose salmon calcitonin in bone metastasis: pain control and beta-endorphin plasma levels

This prospective nonrandomized trial was performed to evaluate the efficacy of salmon calcitonin (sCT) in controlling pain related to bone metastasis in cancer patients and the relation of sCT's analgesic efficacy with beta-endorphin blood levels. The study group consisted of 22 cancer patients with bone metastases (male 13 and female 9, age range 38-77 years). Pain control was first achieved by continuous subcutaneous (s.c.) morphine administration. The next increase in pain was managed with continuous s.c. administration of 400 IU/day sCT. Beta-endorphin blood levels were measured before and during sCT administration. The first measurement was taken before sCT administration; subsequent measurement occurred at 12, 24, and 48 hours and 7 days after the commencement of treatment. Pain scores were monitored by a visual analogue scale. A complete blood count and a biochemical screening profile were taken before the administration of calcitonin and also on the seventh and the fifteenth day of the administration. The results showed a satisfactory analgesic effect. The mean pain score before the calcitonin administration was 4.43 and the score on the seventh day was 1.17. The gradual reduction of pain score was associated with an increase in beta-endorphin blood levels (increase to 147.2% of baseline on the seventh treatment day). In three cases, no satisfactory analgesic effect was obtained and pain control was achieved by increasing the continuous s.c. morphine dosage. No significant side effects were observed. These data suggest that sCT in high doses may be a useful adjuvant analgesic when combined with low doses of morphine in continuous s.c. administration for the management of metastatic bone pain.

A novel calcitonin receptor gene in human osteoclasts from normal bone marrow

The calcitonin receptor (CTR) gene in human osteoclasts formed in a human bone marrow cell culture system was examined by reverse transcription-polymerase chain reaction (RT-PCR). The RT-PCR results indicated that the 5'-untranslated region (5'UTR) was different between CTR mRNAs in human osteoclasts and in a mammary tumor cell line, MCF-7 cells. We isolated the 5'UTR of the CTR gene from human osteoclasts, whose sequence had only 28.6% identity with that of other CTR genes reported until now. In a radioligand binding assay, COS-1 cells transfected with the osteoclast CTR gene bound to [125I]human CT (hCT). These results provided evidence that the CTR gene cloned from human osteoclasts was expressed functionally and its coding protein was identical to MCF-7 cell CTR.

Calcitonin inhibits anterior pituitary cell proliferation in the adult female rats

Previous studies have shown that CT-like immunoreactive peptide(s) (pit-CT) is synthesized by the anterior pituitary (AP) gland, and exogenously added salmon(s) CT inhibits PRL release and PRL gene transcription in cultured AP cells. Anti-sCT serum, which immunoreacts with pit-CT, stimulates PRL secretion, suggesting pit-CT is a physiologically relevant PRL-inhibiting hormone. Using proliferating cell nuclear antigen (PCNA) staining and 5-bromo-2'deoxyuridine (BrdU) incorporation into newly replicated DNA, the effect of calcitonin (CT) on cellular proliferation in the rat anterior pituitary gland (AP) was examined. CT significantly attenuated PCNA-immunopositive as well as BrdU-positive AP cell populations in dispersed rat AP cells. A second series of experiments tested the effects of CT on AP cell proliferation in vivo. OVX + E2 rats were injected with 200 microg CT (iv), the rats killed at various time points, and the APs were processed for BrdU staining. CT inhibited BrdU incorporation at all time points up to 15 h after the injection, and this inhibitory effect was reversed at later time points. The effect of CT was concentration dependent, and a maximal inhibition was observed 10 h after the CT injection. Subsequent experiments identified CT-responsive AP cell populations using double immunofluorescence for BrdU and either PRL or FSH. The number of BrdU-labeled lactotropes in the AP gland declined by 74% in the CT-treated rats. Neutralization of endogenous pit-CT by passive immunization with anti-sCT serum caused a 2-fold increase in AP cell proliferation. These results suggest an important role for the endogenous pit-CT in regulation of lactotrope population of the AP gland.

Inhibition of salmon calcitonin on secretion of progesterone and GnRH-stimulated pituitary luteinizing hormone

The effects of salmon calcitonin (sCT) on the production of progesterone and secretion of luteinizing hormone (LH) were examined in female rats. Diestrous rats were intravenously injected with saline, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. Ovariectomized (Ovx) rats were injected with saline or sCT. In the in vitro experiments, granulosa cells and anterior pituitary glands (APs) were incubated with the tested drugs. Plasma LH levels of Ovx rats were reduced by sCT injection. Administration of sCT decreased the basal and hCG-stimulated progesterone release in vivo and in vitro. 8-Bromo-cAMP dose dependently increased progesterone production but did not alter the inhibitory effect of sCT. H-89 did not potentiate the inhibitory effect of sCT. Higher doses of 25-hydroxycholesterol and pregnenolone stimulated progesterone production and diminished the inhibitory effects of sCT. sCT did not decrease basal release of LH by APs, but pretreatment of sCT decreased gonadotropin-releasing hormone (GnRH)-stimulated LH secretion. These results suggested that sCT inhibits progesterone production in rats by preventing the stimulatory effect of GnRH on LH release in rat APs and acting directly on ovarian granulosa cells to decrease the activities of post-cAMP pathway and steroidogenic enzymes.

The porcine calcitonin receptor promoter directs expression of a linked reporter gene in a tissue and developmental specific manner in transgenic mice

We have investigated the transcriptional regulation of the porcine calcitonin (CT) receptor (pCTR) promoter in transgenic mice. A construct containing 2.1 kb pCTR 5' flanking region, fused to a beta-galactosidase (lacZ) gene, was employed for the production of transgenic mice. At 11.5 days of development lacZ expression was observed in the embryonic brain and spinal cord. By 15.5 days post fertilization, lacZ expression was detected in the developing mammary gland, external ear, cartilage primordium of the humerus, and anterior naris (nostril). RT-PCR on RNA from these fetal tissues showed endogenous mouse CTR (mCTR) expression. In neonatal and adult transgenics, lacZ expression was silenced, except in brain, spinal cord, and testis (adults only). Endogenous mCTR gene expression and pCTR promoter activity were corepressed in the same tissues from adult mice. No pCTR promoter activity was detected in the kidney or bone of transgenic animals. This suggests that additional DNA sequences may be required for pCTR promoter activity in these tissues. From these results, we conclude that the pCTR promoter is active only in tissues expressing endogenous mCTR. Many of the these tissues represent previously unknown sites of CTR gene expression. Finally, the developmental regulation of pCTR/mCTR in tissues such as breast and cartilage primordium suggests that CTRs may play a role in the morphogenesis of these tissues.

Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human

During the last decade, the GH axis has become the compelling focus of remarkably active and broad-ranging basic and clinical research. Molecular and genetic models, the discovery of human GHRH and its receptor, the cloning of the GHRP receptor, and the clinical availability of recombinant GH and IGF-I have allowed surprisingly rapid advances in our knowledge of the neuroregulation of the GH-IGF-I axis in many pathophysiological contexts. The complexity of the GHRH/somatostatin-GH-IGF-I axis thus commends itself to more formalized modeling (154, 155), since the multivalent feedback-control activities are difficult to assimilate fully on an intuitive scale. Understanding the dynamic neuroendocrine mechanisms that direct the pulsatile secretion of this fundamental growth-promoting and metabolic hormone remains a critical goal, the realization of which is challenged by the exponentially accumulating matrix of experimental and clinical data in this arena. To the above end, we review here the pathophysiology of the GHRH somatostatin-GH-IGF-I feedback axis consisting of corresponding key neurotransmitters, neuromodulators, and metabolic effectors, and their cloned receptors and signaling pathways. We propose that this system is best viewed as a multivalent feedback network that is exquisitely sensitive to an array of neuroregulators and environmental stressors and genetic restraints. Feedback and feedforward mechanisms acting within the intact somatotropic axis mediate homeostatic control throughout the human lifetime and are disrupted in disease. Novel effectors of the GH axis, such as GHRPs, also offer promise as investigative probes and possible therapeutic agents. Further understanding of the mechanisms of GH neuroregulation will likely allow development of progressively more specific molecular and clinical tools for the diagnosis and treatment of various conditions in which GH secretion is regulated abnormally. Thus, we predict that unexpected and enriching insights in the domain of the neuroendocrine pathophysiology of the GH axis are likely be achieved in the succeeding decades of basic and clinical research.

Calcitropic peptides: neural perspectives

In mammals and higher vertebrates, calcitropic peptides are produced by peripheral endocrine glands: the parathyroid gland (PTH), thyroid or ultimobranchial gland (calcitonin) and the anterior pituitary gland (growth hormone and prolactin). These hormones are, however, also found in the neural tissues of lower vertebrates and invertebrates that lack these endocrine organs, suggesting that neural tissue may be an ancestral site of calcitropic peptide synthesis. Indeed, the demonstration of CNS receptors for these calcitropic peptides and their induction of neurological actions suggest that these hormones arose as neuropeptides. Neural and neuroendocrine roles of some of these calcitropic hormones (calcitonin and parathyroid hormone) and related peptides (calcitonin gene related peptide, stanniocalcin and parathyroid hormone related peptide) are thus the focus of this review.

Purification of calcitonin-like peptides from rat brain and pituitary

Accumulating evidence supports the existence of nonthyroidal calcitonin (CT)-like peptides, more similar to fish CTs, which may act as endogenous regulators of CT receptors in brain and other tissues. In this study, we have carried out large-scale extractions from Sprague-Dawley rat brain diencephalon and pituitary, and purified a novel, biologically active, CT-like peptide from pituitary. Monitoring of the calcitonin-like activity of the peptides from rat brain and pituitary required different detection systems. While the brain CT cross-reacted with C-terminally directed salmon CT-specific antisera, the pituitary CT did not. However, the pituitary CT was biologically active, exhibiting specific interaction with CT receptors to activate adenylate cyclase. Conventional chromatographic techniques were employed to purify the CT-like peptides. Although the brain CT was not purified to homogeneity, size exclusion chromatography revealed the presence of multiple molecular weight forms of immunoreactive CT. Of these, only the lowest molecular weight form was biologically active. Purification from the pituitary resulted in the isolation of a biologically active peptide with a mass of 3267 Da. This mass differs from the mass of both salmon and thyroid-derived rat CT. Initial amino acid sequencing of the pituitary CT indicated that it was N-terminally blocked. Following aminopeptidase digestion, a unique six amino acid sequence, EKSQSP, was identified. Elucidation of the amino acid composition provided supporting evidence that the peptide was novel and was consistent with a full length peptide of approximately 30 amino acids. These data support the existence of novel, nonthyroidal, CTs which are potential regulators of CT receptor-mediated functions.

Differential expression of calcitonin and parathyroid hormone/parathyroid hormone-related protein receptors in P19 embryonic carcinoma cells treated with retinoic acid

Mouse embryonic carcinoma P19 cell aggregates treated with retinoic acid (RA) sequentially differentiate into neurons and astrocytes, whereas attached cells develop a mesodermal phenotype. The expression of calcitonin (CT) and PTH/PTH-related protein (PTHrP) receptors was investigated in embryonic cells, and during neural and mesodermal differentiation. In embryonic P19 cells, specific binding of [125I]salmon (s) CT(1-32) ([125I]sCT(1-32)) was 56 fmol/mg protein, and of [125I]chicken (ch) [Tyr36]PTHrP(1-36) amide ([125I]chPTHrP(1-36)) < 0.5 fmol/mg protein. Correspondingly, cAMP was maximally stimulated 47-fold by sCT(1-32) (EC50 0.05 nM) and 3-fold by chPTHrP(1-36) (EC50 1.3 nM). Receptor autoradiography revealed specific binding of [125I]sCT(1-32) to the undifferentiated P19 cells, but not to RA induced neurons and astrocytes. At the same time, [125I]sCT(1-32) binding and cAMP accumulation by sCT were gradually decreased. But, specific binding of [125I]chPTHrP(1-36) was raised at least 6-fold compared with embryonic cells to 3 fmol/mg protein, in parallel with a 10-fold higher maximal cAMP accumulation. A similar, but delayed suppression of CT and stimulation of PTH/PTHrP receptor expression was observed during mesodermal cell differentiation. The results indicate that CT receptors are associated with undifferentiated P19 cells, whereas PTH/PTHrP receptors are expressed in RA induced neural and mesodermal cells.

Calcium intake by rats: influence of parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D

We examined the contribution of the primary hormones of calcium homeostasis to the control of calcium intake in the rat. Male Sprague-Dawley rats with 50 mM CaCl2 solution as their only source of calcium received subcutaneous hormone infusions for 13 days. Parathyroid hormone (PTH; 40, 80, or 160 ng/h) produced sustained dose-related decreases in CaCl2 intake. High doses of calcitonin (CT; 32 or 64 ng/h) increased CaCl2 intake transiently, and low doses (4, 8, or 16 ng/h) had no effect. 1,25-Dihydroxyvitamin D [1,25(OH)2D] in doses > 1 ng/h initially increased CaCl2 intake, but the effects of moderate doses (2 or 4 ng/h) tended to dissipate, and the sustained effect of high doses (8 or 16 ng/h) was to reduce CaCl2 intake. Infusions of combinations of the hormones had effects consistent with their individual actions: there was no evidence for synergy. Based on changes in plasma hormone concentrations, it appeared that most of the infusions had effects within the physiological range. Consistent with hypotheses that calcium appetite is mediated by circulating calcium, PTH and CT infusions produced reciprocal changes in plasma calcium concentrations and CaCl2 intake. However, the finding that 1,25(OH)2D elevated both plasma calcium concentrations and CaCl2 intake raises the possibility that one or more of the hormones may mediate calcium appetite directly.

Tissue-specific mRNA expression of a calcitonin receptor-like receptor during fetal and postnatal development

The distribution of calcitonin receptor-like receptor (CRLR) mRNA in developing rats was investigated by in situ hybridization. Signals were found in the piriform cortex, the central and basolateral amygdala and the amygdalostriatal transition area. Among peripheral organs, the CRLR was predominantly expressed in the lung. mRNA expression in blood vessels, liver, midgut, rectum and urethra was restricted to gestational days 16 and/or 20. The CRLR was thought to be a calcitonin gene-related peptide (CGRP) type 1 receptor (Aiyar et al., J. Biol. Chem., 271 (1996) 11325-11329). This contrasts with previously reported evidence that the CRLR is an orphan receptor with no identifiable interactions with CGRP and other related ligands (Flühmann et al., Biochem. Biophys. Res. Commun., 206 (1995) 341-347). In situ hybridization signals have not been detected in the cerebellum and the spleen known to present a high density of CGRP binding sites. The different regional distribution of CGRP receptor binding sites and CRLR mRNA implies the latter encoding a different CGRP receptor subtype.

Expression of two human skeletal calcitonin receptor isoforms cloned from a giant cell tumor of bone. The first intracellular domain modulates ligand binding and signal transduction

Two distinct calcitonin (CT) receptor (CTR)-encoding cDNAs (designated GC-2 and GC-10) were cloned and characterized from giant cell tumor of bone (GCT). Both GC-2 and GC-10 differ structurally from the human ovarian cell CTR (o-hCTR) that we cloned previously, but differ from each other only by the presence (GC-10) or absence (GC-2) of a predicted 16-amino acid insert in the putative first intracellular domain. Expression of all three CTR isoforms in COS cells demonstrated that GC-2 has a lower binding affinity for salmon (s) CT (Kd approximately 15 nM) than GC-10 or o-hCTR (Kd approximately 1.5 nM). Maximal stimulatory concentrations of CT resulted in a mean accumulation of cAMP in GC-2 transfected cells that was greater than eight times higher than in cells transfected with GC-10 after normalizing for the number of receptor-expressing cells. The marked difference in maximal cAMP response was also apparent after normalizing for receptor number. GC-2 also demonstrated a more potent ligand-mediated cAMP response compared with GC-10 for both human (h) and sCT (the EC50 values for GC-2 were approximately 0.2 nM for sCT and approximately 2 nM for hCT; EC50 values for GC-10 were approximately 6 nM for sCT and approximately 25 nM for hCT). Reverse transcriptase PCR of GCT RNA indicated that GC-2 transcripts are more abundant than those encoding for GC-10. In situ hybridization on GCT tissue sections demonstrated CTR mRNA expression in osteoclast-like cells. We localized the human CTR gene to chromosome 7 in band q22. The distinct functional characteristics of GC-2 and GC-10, which differ in structure only in the first intracellular domain, indicate that the first intracellular domain of the CTR plays a previously unidentified role in modulating ligand binding and signal transduction via the G protein/adenylate cyclase system.

Calcitonin inhibits testosterone and luteinizing hormone secretion through a mechanism involving an increase in cAMP production in rats

Effects of calcitonin peptides, including human calcitonin (hCT), salmon calcitonin (sCT), and calcitonin gene-related peptide (CGRP), on the secretion of testosterone and luteinizing hormone (LH) in male rats were studied. Male rats were injected intravenously with human chorionic gonadotropin (hCG), calcitonin peptides, or hCG plus calcitonin peptides. Blood samples were collected at several intervals following hormone challenge. In an in vitro experiment, testis blocks were incubated with hCG (0, 0.05, 0.5, or 5 IU/ml) or hCG (0.5 IU/ml) plus calcitonin peptides (0-10(-9) or 10(-6) M) at 34 degrees C for 30 minutes. Both medium and plasma samples were extracted by ether and analyzed for testosterone by radioimmunoassay (RIA). The concentration of calcium in each plasma sample was measured by an automatic calcium analyzer. The anterior pituitary gland (AP) was incubated with or without calcitonin peptides (0-10 nM) at 37 degrees C for 30 minutes. They were then incubated with gonadotropin releasing hormone (GnRH, 10 nM) for a further 30 minutes. The concentration of LH in AP medium was measured by RIA. The accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in both testicular tissues and APs were measured by RIA. A single intravenous injection of calcitonin peptides decreased the basal and hCG-stimulated levels of plasma testosterone gradually from 60 to 180 or 360 minutes after challenge. The plasma calcium was not altered by the injection of calcitonin peptides and/or hCG. Administration of calcitonin peptides in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of salmon calcitonin on the tail-biting and scratching behavior induced by substance P and three excitatory amino acids

We have examined the effects of salmon calcitonin (SCT), injected into the cerebral ventricle (i.c.v.), on the tail-biting and scratching behavior induced by the intrathecal injection of different types of nociceptive agents, i.e., substance P, N-methyl-D-aspartate (NMDA), kainate (KA), and quisqualate (Quis). Tail-biting and scratching behavior induced by the 4 substances was significantly inhibited by SCT (i.c.v.) in the same manner: the dose-response curves were U-shaped, and the most effective dose was 0.1 IU/mouse in all cases. SCT did not, however, completely inhibit tail-biting and scratching behavior. At its most effective dose, the percent inhibition of substance P-, NMDA-, KA- and Quis-induced behavior were 77.9%, 40.2%, 49.4%, and 52.9%, respectively. These results suggest that SCT has the inhibitory effects of substance P- and glutamate receptor agonists-induced nociceptive response in vivo.

Calcitonin and its antinociceptive activity: animal and human investigations 1975-1992

Calcitonin (CT) is a polypeptide hormone produced in the thyroid gland that regulates, blood calcium levels and bone calcium metabolism. The unexpected finding of binding sites for calcitonin in several areas of the brain oriented attention to activities of CT in the central nervous system and also to its antinociceptive action. The first report of this last effect was in 1975, and the many different experimental and clinical data on this topic reported since then are reviewed here. The heterogenous findings have been organized according to the logical classification of animal and human studies. For each of these headings, subheadings such as acute and chronic pain, different kinds of administration and different procedures used to record the results, are considered. The several proposed mechanisms of action, involving serotoninergic, catecholaminergic, Ca2+ fluxes, protein phosphorylation, beta-endorphin production, cyclooxygenase inhibition and histamine interference are also reviewed. Calcitonin, neurotensin, substance P, VIP and, recently, CGRP are some of the non-opioid peptides that have been reported to interfere with pain and that open up a new, alternative way of investigating antinociceptive drugs different than opioid or opioid-like agents. An examination of the state-of-investigation of calcitonin's antinociceptive activity in the last 17 years shows that many experimental studies indicate the existence of this effect, including studies in humans, and this opens up perspectives for therapy with a new class of antinociceptive agents.

In vitro autoradiographic localization of calcitonin binding sites in human medulla oblongata

In this study we examined the distribution of calcitonin (CT) binding sites in the human medulla oblongata by in vitro autoradiography. In competition studies, the rank order of potency for calcitonins competing for 125I-salmon CT binding was salmon CT > porcine CT > human CT, which is consistent with physiologically relevant CT receptors in other systems. For the determination of CT binding in the human medulla, 20-micron cryostat sections were incubated with 125I-salmon CT in the presence or absence of 10(-6) M unlabelled salmon CT to map specific CT binding sites. Punctate binding was observed over discrete nuclei of the medulla. High binding densities were seen over subnuclei of the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, the intermediate reticular zone, the gigantocellular and dorsal paragigantocellular nuclei, and the raphe obscurus nucleus. Moderate levels of binding were observed over the lateral paragigantocellular nucleus and the rostral extent of the epiolivary nucleus. The cuneate and gracile nuclei and the fiber tracts did not contain detectable binding, while the inferior olivary nucleus had moderate levels of nonspecific binding. The localization of calcitonin binding sites in the human presents similarities but also important differences to the distribution in rat and cat. The most notable difference is the extreme binding densities in the intermediate reticular zone of the human. The location of binding sites suggests involvement of calcitonin in regulation of autonomic function.