[Positioning of headache units in the field of neurology: the importance of OnabotulinumtoxinA and other therapies in the treatment of headaches]

Chronic migraine is a disease that affects 0.5-2.5% of the population, depending on the statistics that are analysed and the definition of chronic migraine that is used. It is extraordinarily disabling, since it does not allow the sufferer to carry out any of their scheduled personal, professional or social activities, and it has a great impact on the patients' quality of life, as measured on disability, quality of life and impact on daily activities scales. Yet, nowadays there are treatments that have proven to be effective in cases of chronic migraine, such as OnabotulinumtoxinA. It is a treatment that is well tolerated and with a high rate of efficacy. Yet it is not only a therapeutic tool, but in the world of headaches it has also opened up the doors to invasive treatments, to the learning of techniques and, in short, to placing headaches in referral units that are usually located in tertiary care hospitals. Furthermore, it has also helped to overcome the idea that patients with headache should be visited exclusively by primary care physicians or general neurologists. This is an opportunity to redefine the field of study and the care for headaches that must be seized. In the future, this is going to be complemented by novel treatments with neurostimulation and probably with monoclonal antibodies against the calcitonin gene-related peptide. A revolution has begun in our knowledge and capacity to act. It is our duty to give it the importance and usage it deserves both for our patients and for us as specialists.

Olcegepant, a non-peptide CGRP1 antagonist for migraine treatment

Olcegepant is the first potent and selective non-peptide antagonist of the calcitonin gene-related peptide 1 (CGRP1) receptor, a key modulator in neurogenic inflammatory pain. Under development by Boehringer Ingelheim GmbH, olcegepant is an intravenously formulated treatment for acute attacks of migraine. In preclinical studies, olcegepant attenuated arterial dilation induced by CGRP or electrical stimulation. In a phase II clinical trial, olcegepant reduced the severity of headache in 60% of migraine sufferers and met secondary endpoints including headache-free rate and rate of sustained response. Only mild-to-moderate transient adverse events were observed, with no adverse cardiovascular symptoms reported. The compound appears to be an effective anti-migraine medication that is well tolerated and does not display the vasoconstrictive effect that precludes the use of triptans and dihydroergotamine in certain patients. For a successful marketing of olcegepant, larger clinical trials and the development of an effective oral formulation will be necessary.

The RET Kinase Inhibitor NVP-AST487 Blocks Growth and Calcitonin Gene Expression through Distinct Mechanisms in Medullary Thyroid Cancer Cells

The RET kinase has emerged as a promising target for the therapy of medullary thyroid cancers (MTC) and of a subset of papillary thyroid cancers. NVP-AST487, a N,N'-diphenyl urea with an IC(50) of 0.88 mumol/L on RET kinase, inhibited RET autophosphorylation and activation of downstream effectors, and potently inhibited the growth of human thyroid cancer cell lines with activating mutations of RET but not of lines without RET mutations. NVP-AST487 induced a dose-dependent growth inhibition of xenografts of NIH3T3 cells expressing oncogenic RET, and of the MTC cell line TT in nude mice. MTCs secrete calcitonin, a useful indicator of tumor burden. Human plasma calcitonin levels derived from the TT cell xenografts were inhibited shortly after treatment, when tumor volume was still unchanged, indicating that the effects of RET kinase inhibition on calcitonin secretion were temporally dissociated from its tumor-inhibitory properties. Accordingly, NVP-AST487 inhibited calcitonin gene expression in vitro in TT cells, in part, through decreased gene transcription. These data point to a previously unknown physiologic role of RET signaling on calcitonin gene expression. Indeed, the RET ligands persephin and GDNF robustly stimulated calcitonin mRNA, which was blocked by pretreatment with NVP-AST487. Antagonists of RET kinase activity in patients with MTC may result in effects on plasma calcitonin that are either disproportionate or dissociated from the effects on tumor burden, because RET kinase mediates a physiologic pathway controlling calcitonin secretion. The role of traditional tumor biomarkers may need to be reassessed as targeted therapies designed against oncoproteins with key roles in pathogenesis are implemented.

Decreases in procalcitonin and C-reactive protein are strong predictors of survival in ventilator-associated pneumonia

Introduction

This study sought to assess the prognostic value of the kinetics of procalcitonin (PCT), C-reactive protein (CRP) and clinical scores (clinical pulmonary infection score (CPIS), Sequential Organ Failure Assessment (SOFA)) in the outcome of ventilator-associated pneumonia (VAP) at an early time point, when adequacy of antimicrobial treatment is evaluated.

Methods

This prospective observational cohort study was conducted in a teaching hospital. The subjects were 75 patients consecutively admitted to the intensive care unit from October 2003 to August 2005 who developed VAP. Patients were followed for 28 days after the diagnosis, when they were considered survivors. Patients who died before the 28th day were non-survivors. There were no interventions.

Results

PCT, CRP and SOFA score were determined on day 0 and day 4. Variables included in the univariable logistic regression model for survival were age, Acute Physiology and Chronic Health Evaluation (APACHE) II score, decreasing ΔSOFA, decreasing ΔPCT and decreasing ΔCRP. Survival was directly related to decreasing ΔPCT with odds ratio (OR) = 5.67 (95% confidence interval 1.78 to 18.03), decreasing ΔCRP with OR = 3.78 (1.24 to 11.50), decreasing ΔSOFA with OR = 3.08 (1.02 to 9.26) and APACHE II score with OR = 0.92 (0.86 to 0.99). In a multivariable logistic regression model for survival, only decreasing ΔPCT with OR = 4.43 (1.08 to 18.18) and decreasing ΔCRP with OR = 7.40 (1.58 to 34.73) remained significant. Decreasing ΔCPIS was not related to survival (p = 0.59). There was a trend to correlate adequacy to survival. Fifty percent of the 20 patients treated with inadequate antibiotics and 65.5% of the 55 patients on adequate antibiotics survived (p = 0.29).

Conclusion

Measurement of PCT and CRP at onset and on the fourth day of treatment can predict survival of VAP patients. A decrease in either one of these marker values predicts survival.

Insights into interactions between the alpha-helical region of the salmon calcitonin antagonists and the human calcitonin receptor using photoaffinity labeling

Fish-like calcitonins (CTs), such as salmon CT (sCT), are widely used clinically in the treatment of bone-related disorders; however, the molecular basis for CT binding to its receptor, a class II G protein-coupled receptor, is not well defined. In this study we have used photoaffinity labeling to identify proximity sites between CT and its receptor. Two analogues of the antagonist sCT(8-32) containing a single photolabile p-benzoyl-l-phenylalanine (Bpa) residue in position 8 or 19 were used. Both analogues retained high affinity for the CT receptor and potently inhibited agonist-induced cAMP production. The [Bpa(19)]sCT(8-32) analogue cross-linked to the receptor at or near the equivalent cross-linking site of the full-length peptide, within the fragment Cys(134)-Lys(141) (within the amino terminus of the receptor, adjacent to transmembrane 1) (Pham, V., Wade, J. D., Purdue, B. W., and Sexton, P. M. (2004) J. Biol. Chem. 279, 6720-6729). In contrast, proteolytic mapping and mutational analysis identified Met(49) as the cross-linking site for [Bpa(8)]sCT(8-32). This site differed from the previously identified cross-linking site of the agonist [Bpa(8)]human CT (Dong, M., Pinon, D. I., Cox, R. F., and Miller, L. J. (2004) J. Biol. Chem. 279, 31177-31182) and may provide evidence for conformational differences between interaction with active and inactive state receptors. Molecular modeling suggests that the difference in cross-linking between the two Bpa(8) analogues can be accounted for by a relatively small change in peptide orientation. The model was also consistent with cooperative interaction between the receptor amino terminus and the receptor core.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Calcitonin gene-related peptide-induced suppression of atrial natriuretic peptide release through receptors for CGRP1 but not for calcitonin and amylin

Calcitonin gene-related peptide (CGRP), a 37-amino acid neuropeptide, is found in the central nervous system as well as in the heart. CGRP shows high sequence homology with amylin, salmon calcitonin, and adrenomedullin. This study aimed to investigate the effect of CGRP on atrial hemodynamics and atrial natriuretic peptide (ANP) release by using isolated perfused beating left atria and to identify its receptor subtypes. Rat alpha-CGRP (0.1, 1, 10, or 100 nM) increased atrial contractility and suppressed the release of ANP in a concentration-dependent manner. However, cys-CGRP (1 microM), a CGRP(2) receptor agonist, slightly decreased ANP release without positive inotropism. Human alpha-CGRP (1 nM) showed an effect on ANP release similar to that of rat alpha-CGRP with potent positive inotropism. However, salmon and rat calcitonin (1 microM) caused a slight decrease or no change in ANP release. Pretreatment with a receptor antagonist for CGRP(1) [rat alpha-CGRP-(8-37)] blocked rat alpha-CGRP-induced suppression of ANP release and positive inotropism, whereas the antagonists for salmon or amylin did not. Therefore, we suggest that rat alpha-CGRP causes a suppression of ANP release with positive inotropism through the receptor for CGRP(1) but not that for calcitonin and amylin.

New therapeutic target in primary headaches - blocking theCGRP receptor

The primary headaches are among the most prevalent neurological disorders, afflicting up to 16% of the adult population. The associated pain originates from intracranial blood vessels that are innervated by sensory nerves storing several neurotransmitters. In primary headaches, there is a clear association between the headache and the release of calcitonin gene-related peptide (CGRP), but not other neuronal messengers. The specific purpose of this review is to describe CGRP in the human cranial circulation and to elucidate a possible role for a specific antagonist in the treatment of primary headaches. Acute treatment with administration of a 5-HT(1B/1D) agonist (triptan) results in alleviation of the headache and normalisation of the CGRP level. The mechanism of action of triptans involves vasoconstriction of intracranial vessels and a presynaptic inhibitory effect of sensory nerves. The central role of CGRP in migraine and cluster headache pathophysiology has led to the search for small-molecule CGRP antagonists, which are predicted to have fewer cardiovascular side effects in comparison to the triptans. The initial pharmacological profile of such a group of compounds has recently been disclosed. These compounds have high selectivity for human CGRP receptors and are reportedly efficacious in the relief of acute attacks of migraine.

Somatostatin, but not somatostatin receptor subtypes 2 and 5 selective agonists, inhibits calcitonin secretion and gene expression in the human medullary thyroid carcinoma cell line, TT

Somatostatin (SRIH) analogs are commonly used to treat symptoms in medullary thyroid carcinoma (MTC), that expresses SRIH receptors (SSTR1 to SSTR5), as does the human MTC cell line TT. The aim of this work was to evaluate whether SRIH, SSTR2 and SSTR5-selective agonists influence calcitonin (CT) secretion and gene expression in the TT cell line. CT secretion was evaluated by chemiluminescence, and gene expression was analyzed by Northern blot. TT cell line proliferation was also assessed by [(3)H] thymidine ([(3)H]thy) incorporation and viable cell number count. SRIH significantly (p < 0.05) reduced [(3)H]thy incorporation (approx. 50 %), viable cell number (approx. 20 %), CT secretion (-30 %) and CT gene expression (approx. 2-fold). Exposure to the SSTR2-selective agonist, BIM-23 120, and to the SSTR5-selective agonist, BIM-23 206, did not modify CT secretion and mRNA levels in TT cells. Thus, SRIH inhibits DNA synthesis, cell proliferation, CT secretion and CT gene expression in the TT cell line, while SSTR2 and 5 selective agonists, although influencing DNA synthesis and cell proliferation, do not modify CT gene expression, suggesting that SRIH may influence gene expression acting through SSTRs other than subtypes 2 and 5. Furthermore, these findings may explain the erratic response of MTC patients in terms of CT plasma levels to treatment with SRIH analogs, like octreotide and lanreotide, which interact mainly with SSTR2 and 5.

Calcitonin-induced impairment in conditioning is antagonized by chronic antidepressant drug treatment

The purpose of this study was to test the effect of calcitonin, when injected into the lateral ventricle, on conditioning behaviour and to see whether antidepressant drug treatment can antagonize calcitonin-induced impairment of this behaviour. Conditioned response by conditional stimulus (CS) was compared in control rat (CO) and in rats that received intraventricular perfusion of calcitonin (CA), acute antidepressant drug treatment (ADa), acute antidepressant drug treatment + calcitonin (ADa + CA), chronic antidepressant drug treatment (21 days) + calcitonin the day after (ADc + CA). Control rats acquired easily the conditioned response, the CA group and ADa + CA had problems in making the correlation between CS and unconditional stimulus (US), and consequently did not acquire a conditioned response, but in the ADc + CA group, rats exhibited more conditioned responses. The results indicate that calcitonin disrupts conditioning processes and chronic but not acute antidepressant drug treatment can reverse the effects of calcitonin.

Protein kinase C antagonizes pertussis-toxin-sensitive coupling of the calcitonin receptor to adenylyl cyclase

The calcitonin receptor is known to couple to Gs and Gq, activating adenylyl cyclase and phospholipase C, respectively. The observation of pertussis-toxin-sensitive responses to calcitonin suggests that the receptor is capable of coupling to Gi/o as well. However, the calcitonin-dependent activation of adenylyl cyclase in HEK-293 cells that stably express the cloned rabbit calcitonin receptor, as in many other cells that express calcitonin receptors, shows little pertussis toxin sensitivity. Calcitonin treatment of these cells stimulates protein kinase C, which is reported to antagonize the receptor-dependent activation of Gi. The possibility that protein kinase C could be antagonizing Galphai-adenylyl cyclase coupling was tested by examining the effects of protein kinase C inhibitors (chelerythrine chloride and sphingosine) or of chronic treatment with phorbol ester to deplete protein kinase C. All three treatments led to a reduction of calcitonin-induced adenylyl cyclase activity that was reversed by pertussis toxin. Inhibiting or depleting protein kinase C had no effect on the activation of adenylyl cyclase by cholera toxin, indicating that Gs and adenylyl cyclase were not affected by these treatments. Calcitonin treatment of HEK-293 cells, that stably express a myc-tagged rabbit calcitonin receptor, induced the formation of complexes of the receptor and Galphai subunits, confirming that the calcitonin receptor interacts with Gi. Thus, the calcitonin receptor can couple to Gi, but the inhibition of adenylyl cyclase by Galphai is negatively regulated by protein kinase C.

Effects of amylin and salmon calcitonin on beta-endorphin-induced growth hormone and prolactin secretion in the rat

In this study we examined the possible interplay of amylin (AMY) and salmon calcitonin (sCT) in the central control of growth hormone (GH) and prolactin (PRL) secretion in male rats. For this purpose we first compared effects of central intracerebroventricular (i.c.v.) admininstration of various doses of AMY (2.5-2,500 ng/rat) and sCT (2.2-220 ng/rat) on beta-endorphin (beta-END, 0.5 microg/rat)-induced GH and PRL secretion. AMY and sCT dose-dependently inhibited beta-END-induced GH secretion, whereas only sCT was able to inhibit beta-END-induced PRL secretion. To examine whether the GH inhibitory effect of AMY was due to the possible cross-reactivity of AMY and sCT on the same receptors in the CNS, we pretreated some rats with the AMY antagonist (AMY8-37, 2. 5 microg/rat, i.c.v.). AMY8-37 significantly enhanced the GH-stimulatory action of beta-END. AMY8-37, administered prior to AMY and sCT, significantly removed the inhibitory effect of both AMY and sCT on beta-END-induced GH release, suggesting that both peptides mediate their response on GH through a common receptor. In vitro competition binding studies on rat hypothalamic membranes have shown that both AMY and sCT compete with [125I]rAMY binding with half inhibition (IC50) values of 3.6 x 10(-11) and 1.6 x 10(-10) M, respectively. Binding of [125I]sCT was inhibited by sCT with an IC50 of 1.09 x 10(-10) M and to a lesser extent by AMY with an IC50 of 1. 3 x 10(-6) M. Thus it is possible that the two peptides recognize a common hypothalamic receptor but with different affinities (sCT > AMY). Overall these data indicate that AMY behaves as a mimic of sCT in the central control of GH secretion. The failure of AMY, at variance with sCT, to modify the PRL-releasing activity of beta-END indicates that different receptor subtypes for sCT are involved in the endocrine effects of sCT and only those mediating the modulatory action of GH respond to AMY.

Mortality is increased by procalcitonin and decreased by an antiserum reactive to procalcitonin in experimental sepsis

OBJECTIVES

Procalcitonin (ProCT), the precursor to the calcitonin hormone, is abnormally increased in experimental and clinical systemic inflammation, including sepsis. Initially, we investigated the effects of supraphysiologic amounts of ProCT administered to animals with septic peritonitis. Subsequently, we evaluated the efficacy of prophylactic and therapeutic immune blockade of ProCT in this lethal model of sepsis.

DESIGN

Prospective, experimental, controlled study.

SETTING

Animal research laboratory approved by the American Association for the Accreditation of Laboratory Animal Care at a Veterans Affairs Medical Center.

SUBJECTS

Young male Golden Syrian hamsters, weighing 90 to 120 g.

INTERVENTIONS

In the first study, serum ProCT concentrations were measured in animals at 0, 3, 6, 12, and 24 hrs after induction of sepsis by intraperitoneal implantation of pellets containing Escherichia coli (5 x 10(8) colony-forming units/pellet). In the second study, with mortality as the end point, 30 microg/kg of isolated, purified human ProCT in 10% hamster serum (experimental) or an equal volume of 10% hamster serum (control) were administered intravenously at the time of the E. coli peritoneal implantation. In the third study, experimental animals received intraperitoneal injections of a multiregion-specific goat antiserum reactive to hamster ProCT 1 hr before and 24 hrs after E. coli implantation, while control animals received nonimmune goat serum at the same time points. In the final study, the same antiserum was administered in five divided doses during the 24 hrs after the insertion of E. coli.

MEASUREMENTS AND MAIN RESULTS

In the initial study, ProCT concentrations were increased shortly after induction of sepsis and peaked at 12 hrs. Administration of exogenous ProCT to septic animals significantly increased mortality compared with control animals (93% vs. 43%, p=.02). Prophylactic blockade of ProCT almost completely protected the animals from the lethal effects of sepsis: the 102-hr mortality rate in the experimental group was 6% compared with 62% in the control group (p < .003). In the therapeutic trial, the 102-hr mortality rate was 54% in experimental animals compared with 82% in control animals (p < .045).

CONCLUSIONS

These results demonstrate that increased ProCT exacerbates mortality in experimental sepsis, whereas neutralization of ProCT increases survival. Thus, ProCT, in addition to being an important marker of severity of systemic inflammation and mortality, is an integral part of the inflammatory process and directly affects the outcome.

Calcitonin is a physiological inhibitor of prolactin secretion in ovariectomized female rats

Calcitonin (CT) inhibits secretion of PRL when administered intravenously in rats and humans. It also inhibits PRL release from cultured rat anterior pituitary (AP) cells. Recent evidence suggests that CT-like immunoreactive peptide is synthesized and released from the AP gland. However, its physiological role in the regulation of PRL secretion has not been understood. Present studies tested the role of endogenous pituitary CT (pit-CT) in the regulation of PRL secretion in vivo by passive immunization. In the first group of experiments, ovariectomized (ovx) adult female rats were administered either preimmune or anti-salmon CT (sCT) serum, and their serum PRL levels were analyzed at various time points up to 3 h. A second group of experiments examined the effects of anti-sCT serum and dopamine on PRL release from cultured rate AP cells. In the next group of experiments, the regional distribution of pit-CT secretion was examined in different sections of the AP gland. In the last set, CT-like activity of AP extract was tested in neonatal rat kidney cells, which respond to CT with an increase in cAMP accumulation. These experiments also tested whether anti-sCT serum reduces AP extract-induced increase in cAMP accumulation. The results suggest that anti-sCT serum dramatically increased serum PRL levels (by 5-fold) of ovx rats within 30 min of administration. The serum PRL levels declined gradually after the peak. However, a significant increase in serum PRL levels was maintained by the anti-sCT serum for the duration of the experiment. The anti-serum also induced a significant increase in PRL release from cultured AP cells when added to the presence or absence of dopamine. The distribution profile of pit-CT within the AP gland suggests that the release of pit-CT immunoreactivity was significantly greater in the inner sections, and anti-sCT serum also caused greater increase in PRL release in these sections. Finally, AP extract and sCT stimulated cAMP accumulation in neonatal rat kidney cells, and anti-sCT serum significantly reduced AP extract-induced cAMP accumulation. These results demonstrate that pit-CT is an important regulator of tonic PRL secretion in female rats and can potently inhibit PRL secretion even in the presence of dopamine.

Effect of CGRP antagonist, alpha-CGRP 8-37, on acid secretion in the dog

The recently synthesized calcitonin gene-related peptide (CGRP) antagonist, human alpha-CGRP 8-37, was used to study its effects on gastric acid secretion. Four dogs with gastric fistula were used to measure the antagonist's physiologic effects in the stomach. All dogs received a bactopeptone dextrose meal (intragastric titration to pH 5.5) with either continuous CGRP 8-37 (1000 pmol/kg/hr) or saline (control). Additionally, intravenous bombesin (75-600 ng/kg/hr) and bethanechol (12.5-100 micrograms/kg/hr) was tested in the presence of the antagonist. Plasma gastrin levels also were measured via radioimmunoassay (RIA) in control and CGRP 8-37-stimulated animals. Gastric acid secretion increased by 100% with infusion of 1000 pmol/kg/hr CGRP 8-37 when compared to the control. Acid output increased 98% with both intravenous antagonist and 600 ng/kg/hr bombesin when compared to bombesin alone. However, no augmentation of acid secretion by CGRP 8-37 was shown with 25 micrograms/kg/hr bethanechol. RIA of plasma gastrin demonstrated no effect with the antagonist when given alone and did not increase bombesin-stimulated gastrin release. We conclude that CGRP 8-37 blocks native CGRP inhibitory effects on gastric acid secretion. Our findings of potentiation of acid secretion by bombesin as well as no change in gastrin levels in the presence of the antagonist is likely due to a blockage in a noncholinergic neuron to the somatostatin cell. Furthermore, CGRP 8-37 did not increase bethanechol-stimulated acid secretion, most likely due to bethanechol's (acetylcholine) nearly ubiquitous positive effects on acid secretion.

Inhibition of the calcitonin-induced outward current in identified Aplysia neurons by interleukin-1 and interleukin-2

1. The effects of bath-applied recombinant human interleukin-1 (rhIL-1) and interleukin-2 (rhIL-2) on the calcitonin (CT)-induced outward current recorded from identified neurons (R9-R12) of Aplysia kurodai were investigated with conventional voltage-clamp and pressure ejection techniques. 2. Micropressure ejection of CT onto the soma of the neuron induced a slow outward current [Io(CT); 4-6 nA in amplitude, 30-40 sec in duration] associated with a decrease in input membrane conductance. 3. Io(CT) was increased by hyperpolarization. 4. The extrapolated reversal potential was +10 mV. Additionally, Io(CT) was sensitive to changes in (Na+)o but not to changes in (K+)o, (Ca2+)o, and (Cl-)o. 5. Micropressure-ejected forskolin produced a slow outward current similar to that induced by CT. 6. Bath-applied rhIL-1 and rhIL-2 (10-40 U/ml) reduced the CT-induced current in identified Aplysia neurons without affecting the resting membrane conductance or the holding current. 7. The inhibitory effects of both cytokines on the current were completely reversible. Heat-inactivated rhIL-1 and rhIL-2 were without effect. 8. These results suggest that the immunomodulators, IL-1 and IL-2, can modulate the CT-induced outward current associated with a decrease in Na+ conductance in the nervous system of Aplysia. Therefore, the study suggests that these cytokines may also serve as neuromodulators.

N-terminal truncation of salmon calcitonin leads to calcitonin antagonists. Structure activity relationship of N-terminally truncated salmon calcitonin fragments in vitro and in vivo

Structural requirements for binding to the bone calcitonin (CT) receptor and for CT bioactivity both in vitro and in vivo were assessed for a series of N-terminally truncated, N alpha-acetylated, fragments of salmon calcitonin (sCT). Sequential deletion of amino acid residues from the amino-terminus of [Ala7]sCT-(2-32) peptide amide first led to partial agonists and, upon deletion of residues 1 to 7, to a high affinity antagonist, N alpha-acetyl-sCT-(8-32)-NH2. The presence of two separate domains within the sCT sequence is proposed: (I) a binding domain comprising residues 9-32 and (II) an activation domain requiring residues 3 to 6. N alpha-acetyl-sCT-(8-32)-NH2, in several bioassays including plasminogen activator release from LLC-PK1 cells (pA2 = 7.31), cAMP production in UMR-106-06 cells (pA2 = 7.81) and in the fetal rat long bone resorption assay showed potent antagonistic properties.

Antagonism of calcitonin-induced anorexia by chronic, but not acute, tricyclic antidepressants in the rat

Intraperitoneal or intracerebral injections of calcitonin in the rat produce several behavioral and hormonal effects which have some analogies with the human depressive syndrome. To determine if calcitonin effects are sensitive to antidepressant drugs, the ability of antidepressants and other psychotropic drugs to interact with calcitonin-induced anorexia was tested. The results show that chronic treatments (21 days) with tricyclic, or with tetracyclic, antidepressants significantly tend to neutralize the anorectic effect of calcitonin. Other antidepressants and other psychotropic drugs had no significant effect. The acute administration (24 h) of clomipramine did not antagonize the effect of calcitonin, and even significantly enhanced it. These results allow the author to propose the effects of calcitonin in the rat as a new animal model of depression, and to raise the hypothesis that a possible mechanism of action of tricyclic antidepressant treatments is to counteract the effects of certain brain peptides.

Inhibitory role of somatostatin on calcitonin secretion

Calcitonin (CT) secretion is not exclusively controlled by calcemia, but the secretory tonus is maintained by the beta-stimulatory adrenergic system Somatostatin (SMS) plays a neuromodulatory role with the reduction of CT secretion by its interference at the central and peripheral level of the beta adrenergic receptors. The experiments were carried out on groups of rats in which the effect of SMS on CT content of the thyroid gland was followed up. Thus, SMS administered i.c.v. significantly reduced the basal CT secretion without blocking the stimulatory effect of calcium. The results were comparable with those obtained after the blockade of the sympatho-adrenergic system by chemical sympathectomy with 6HODA or propranolol. Central blockade of alpha receptors with phentolamine determined a significant rise of CT. This effect was annihilated by SMS. The i.v. administration of SMS did not induce a change in CT content of the thyroid, but blocked the stimulatory action of hypercalcemia. The results are identical with those obtained by blocking the beta-receptors with propranolol. SMS also blocked the stimulatory effects of isoproterenol on CT secretion. The data obtained revealed the fact that SMS lowers CT secretion by the central and peripheral interference of the sympatho-adrenergic path, maintaining the secretory tonus of the thyroid C cells.

Selective antagonism of calcitonin-induced osteoclastic quiescence (Q effect) by human calcitonin gene-related peptide-(Val8Phe37)

Exposure of isolated rat osteoclasts to calcitonin (CT) leads to an abrupt cessation of cell motility (Q effect) followed by cell retraction (R effect). We have previously shown that these effects are mediated by two G proteins that appear to activate separate post-receptor pathways. The present study demonstrates that the Q but not the R effect of CT (0.006 microM) is abolished in the presence of human calcitonin gene-related peptide (CGRP)-(Val8Phe37) (0.5 microM), a fragment analogue of human CGRP. This selective antagonism suggests that the Q effect could result from an action of CT upon a site that is distinct from that producing the R effect. The former site ('amylin site') also appears to interact with related peptides, amylin and CGRP, whilst the latter site ('CT site') specifically interacts with CT.

Treatment with pertussis toxin does not prevent central effects of eel calcitonin

To determine whether or not the CNS inhibitory activity of eel calcitonin (eCT) on adenylyl cyclase is the endocellular mechanism underlying the antinociceptive effect of the peptide, as shown for morphine analgesia, we administered Bordetella pertussis toxin (PTX) by intracerebroventricular (ICV) injection (0.5 microgram/rat) to block the receptor-mediated inhibition of adenylyl cyclase. In PTX-treated rats there was no change in eCT (2.5 micrograms/rat, ICV)-induced antinociceptive activity (hot-plate test) nor in eCT (100 ng/rat, ICV) inhibition of gastric acid secretion (Shay test) whereas morphine (5 micrograms/rat, ICV) analgesia was significantly reduced. In vitro studies showed no reduction of eCT binding in the CNS of rats treated with PTX in vivo. Moreover, PTX treatment did not change the inhibitory effect of eCT on adenylyl cyclase in isolated membranes from rat striatum in contrast with opiates (DAME and morphine) whose effects were lost. As PTX is known to inactivate the guanidine binding inhibitory protein Gi, these data suggest that a G protein, distinct from the Gi protein involved in the coupling of opiate receptors into a functional response, could be responsible for regulating the intracellular pathways resulting in eCT-induced antinociceptive effect and inhibition of gastric acid secretion.

Pertussis toxin pretreatment affects opiate/nonopiate and stress-induced analgesia differently

Intracerebroventricular injection of pertussis toxin (PTX, 1 microgram/rat) six days before the hot plate test abolished analgesia induced by central morphine. The toxin did not affect analgesia evoked by central neurotensin or ASU 1-7 eel calcitonin. PTX pretreatment also attenuated footshock-induced analgesia (FSIA) delivered to all four paws. When the shock was restricted to the front paws, PTX consistently lowered postshock tail flick latencies, but did not reduce analgesia resulting from shock delivered to the hind paws. It thus appears that PTX-sensitive G-proteins are an essential transduction step needed to initiate the molecular events underlying opiate analgesia evoked by either morphine or shock. In contrast, the signal transduction mechanism subsequent to the stimulation of neurotensin or calcitonin receptors, and to the nonopiate FSIA, appears not to involve PTX-sensitive G-proteins.

Calcitonin causes a sustained inhibition of protein kinase c-stimulated bone resorption in contrast to the transient inhibition of parathyroid hormone-induced bone resorption

Calcitonin is a well known inhibitor of osteoclastic bone resorption, both in vivo and in vitro. However, it is also known that calcitonin has only a transient inhibitory effect on bone resorption. The mechanism for this so-called "escape from inhibition" phenomenon is not clear. In the present study, the inhibitory effect of calcitonin on phorbol ester-induced bone resorption was examined in cultured neonatal mouse calvaria. Bone resorption was assessed as the release of radioactivity from bones prelabelled in vivo with 45Ca. Two protein kinase C-activating phorbol esters, phorbol-12-myristate-13-acetate and phorbol-12,13-dibutyrate, both stimulated 45Ca release in 120-h cultures at a concentration of 10 nmol/l. Calcitonin (30 nmol/l) inhibited phorbol ester-stimulated bone resorption without any "escape from inhibition". This was in contrast to the transient inhibitory effect of calcitonin on bone resorption stimulated by parathyroid hormone (10 nmol/l), prostaglandin E2 (2 mumol/l), and bradykinin (1 mumol/l). Our results suggest that activation of protein kinase C produces a sustained inhibitory effect of calcitonin on bone resorption.

Uncoupling of receptor-mediated cellular responses by ionic lithium

The propensity of ionic lithium to interfere with the coupling of receptors to guanine nucleotide binding proteins (G-proteins) has only recently been investigated using rat cortical membranes. In the present study we have used intact isolated osteoclasts to investigate lithium-induced uncoupling of the receptor-mediated actions of calcitonin. All actions of calcitonin on the osteoclast were abolished by ionic lithium. We believe that the cation prevents signal transduction by inhibiting G protein-receptor interaction, the first step in intracellular signalling.

Relationships between the effects of peripherally administered salmon calcitonin on calcaemia and brain biogenic amines

The effects of s.c. administered salmon calcitonin on the biogenic amine neurotransmitters and metabolites were studied in discrete brain sections in order to evaluate the relationships between these central effects and the fall of serum calcium and to investigate the mechanisms of calcitonin-induced behavioral changes. The biogenic amines and metabolites were simultaneously determined by high-performance liquid chromatography with electrochemical detection in tissue samples obtained from rats treated with 10-80 MRC U/kg of the peptide. Some rats were pretreated with calcium lactate to inhibit the calcitonin-induced hypocalcaemia. Most of the effects, consisting of signs of serotonergic system activation, have been observed in the hypothalamus, accounting for some behavioral effects of the peripherally administered salmon calcitonin. It was speculated that the activation of the brain serotonergic system could result from two indirect and separate mechanisms: the first, which would involve enhanced serotonin synthesis, seemed to be facilitated by calcium availability. A second possible mechanism, which would involve enhanced serotonin release from the neurons, seemed to be mediated by the fall of calcium levels in the blood.

PTHrP secretion is stimulated by CT and inhibited by CgA peptides

We studied the regulation of the secretion in vitro of the parathyroid hormone-related protein (PTHrP) associated with the hypercalcemia of malignancy by Chromogranin A (CgA)-derived peptides and by human calcitonin (CT) in the BEN human lung tumor cell line. The amino terminal peptide of CgA, CgA1-40, inhibited the secretion of PTHrP, whereas other peptides had no such effect. Human CT stimulated the secretion of PTHrP, whereas other hormones had no such effect. Both effects occurred in a dose-dependent manner. These studies reveal novel regulatory pathways among peptides and proteins that are commonly associated with each other and can have paracrine interactions. CgA may be processed at its multiple dibasic sites to peptides that regulate the secretion of its co-resident hormones, in this case PTHrP. In addition to a paracrine effect, CT may be clinically useful as a provocative agent for PTHrP secretion. Complex interactions are present among the calcium-regulating hormones and their associated proteins.

Effects of calcitonin, calcitonin analogues, and calcitonin gene-related peptide on basal in vitro renin secretion

We investigated the relation of calcitonin as a calcium-active hormone to its more recently described effects on peripheral vascular tone. Basal renal renin secretion in vitro in rat kidney slices was studied in the presence of salmon calcitonin (SCT, 4400 U/mg), amino acid substituted analogues of SCT, 16-alanine SCT (6200 U/mg) and 12,16,19 tri-alanine SCT (350 U/mg), and of rat calcitonin gene-related peptide (rCGRP). All calcitonin species at the same hypocalcemic activity (1 U/mL) modestly but significantly suppressed renin secretion from control levels (9.79 +/- 0.44 to 7.51 +/- 0.53, 7.70 +/- 0.72, and 7.78 +/- 0.90 Goldblatt units/g/h for SCT, 16-ala SCT, and tri-ala SCT, P less than .05 for all calcitonins v control), whereas rCGRP had no effect. Thus, on a molar basis, the renin suppressing effects of the various calcitonin species paralleled their bioassay-defined calcium sequestering activity, 16-ala SCT greater than SCT much greater than tri-ala SCT. Lower concentrations of SCT (10(-2) U/mL and 10(-4) U/mL, approximately 6 X 10(-10) and 6 X 10(-12) mol/L, respectively) had virtually identical effects. Moreover, verapamil (5 X 10(-6) mol/L) blocked the SCT-induced suppression of renin secretion (9.79 +/- 0.44 v 9.36 +/- 1.05 GU/g/h, P = NS). We conclude that the juxtaglomerular apparatus is a calcitonin-responsive system, in which calcitonin and its analogues act to suppress basal renin secretion in vitro. This effect seems to depend on and may be mediated by modulating cellular calcium uptake, and suggests a wider, calcium-related role for calcitonin than had previously been suspected.

Prostaglandins promote osteoclastlike cell formation by a mechanism involving cyclic adenosine 3',5'-monophosphate in mouse bone marrow cell cultures

We have developed a mouse bone marrow culture system in which multinucleated osteoclast (OC)-like cells are formed within 8 days. Using this culture system, we examined the effect of prostaglandins (PGs), potent bone-resorbing agents, on OC-like cell formation. Four PGs (PGE1 and PGE2 at 10(-8)-10(-5) M, 6-keto-PGF1 alpha at 10(-5) M, and PGF2 alpha at 10(-6)-10(-5) M) significantly stimulated the formation of OC-like cells. The potency of the PGs in inducing OC-like cell formation was the highest in PGE1 and PGE2, followed by PGF2 alpha and 6-keto-PGF1 alpha in that order, and the order was highly correlated with the order of the potency in increasing the production of cyclic adenosine 3',5'-monophosphate (cAMP) in bone marrow cells. Addition of dibutyryl-cAMP also induced OC-like cell formation. Moreover, isobutylmethylxanthine (IBMX), a potent inhibitor of phosphodiesterase, potentiated the OC-like cell formation induced by PGE2, whereas salmon calcitonin greatly inhibited it. Calcitonin induced cAMP production in cultures treated with PGE2, but not in cultures with vehicle. When bone marrow mononuclear cells were cultured on dentine slices in the presence of PGE2, multinucleated OC-like cells were similarly formed and they resorbed calcified dentine, resulting in so-called Howship's lacunae. These results suggest that PGs stimulate resorption of calcified tissues by promoting osteoclast formation. The activity of PGs in inducing OC-like cell formation is considered mediated mainly by a mechanism involving cAMP.

Hormonal regulation of biliary calcium excretion in rats: inhibition of calcitonin action by alpha 1-adrenergic stimulation

The effect of synthetic [Asu1,7] eel calcitonin (CT) and other hormones on biliary calcium excretion was investigated in rats cannulated bile duct. Administration of CT (80 mU/100 g body weight) produced a significant increase in liver calcium and a corresponding elevation of bile calcium content. The increase in bile calcium content was also caused by administration of insulin (0.1 U/100 g), epidermal growth factor (10 micrograms/100 g), glucagon (10 micrograms/100 g), epinephrine (10 micrograms/100 g), norepinephrine (10 micrograms/100 g), 4 beta-phorbol 12-myristate-13-acetate (10 micrograms/100 g) and ATP (1.0 mg/100 g), suggesting that this increase may be a receptors-mediated response. Of these hormones and drugs, norepinephrine, a alpha-receptor mediator, clearly prevented CT effect on biliary calcium excretion. Moreover, phenylephrine, a alpha 1-receptor agonist, caused an inhibition of the CT effect, while the agonist significantly increased biliary calcium excretion. The present study clearly demonstrates that biliary calcium excretion is stimulated by various hormones which increase calcium influx into liver cells, and suggests that the CT action may be inhibited by alpha 1-adrenergic stimulation.

Inhibition by phenytoin of in vitro secretion of calcitonin from rat thyroid glands and cultured rat C cells

Baby rat thyroid glands and cultured rat medullary carcinoma C cells were incubated acutely with phenytoin (38-100 microM), and the calcitonin (CT) secreted into the serum-free medium was measured by radioimmunoassay (RIA). Phenytoin did not alter CT release from glands or C cells incubated in 1 mM Ca, but, when Ca was raised to 1.75 or 2.5 mM, a marked inhibitory effect of phenytoin was apparent. The inhibitory effect could be negated by including 10 microM BAY-K-8644 in the medium. Inhibitory effects on CT release also were obtained with 100 microM trifluoperazine or 100 microM nitrendipine, and these inhibitory effects also were counteracted by 10 microM BAY-K-8644. The results show that clinically relevant amounts of phenytoin can inhibit CT release, perhaps by interfering with C-cell Ca channels or by inhibiting calmodulin-dependent processes.

Influence of the interaction of calcitonin and 1,25(OH)2-vitamin D3 on prolactin secretion

Calcitonin inhibits and 1,25(OH)2-Vitamin D3 (1,25(OH)2D3) stimulates prolactin and thyrotropin secretion. During concurrent administration of calcitonin and 1,25(OH)2D3 the action of the two calciotropic substances on thyrotropin secretion antagonizes each other. In the submitted investigation the effect of a single dose of synthetic salmon calcitonin on the prolactin secretion at rest and TRH-induced secretion was compared in untreated healthy subjects and in subjects given for four days previously 1,25(OH)2D3 in doses which have a stimulating effect on prolactin secretion (3 micrograms/d). Calcitonin, 50 U, administered by the i.v. route by infusion inhibited the secretion of prolactin at rest (p less than 0.05) and the TRH-stimulated secretion during the 20th, 30th, 40th and 60th minute after TRH administration (p less than 0.01 at all time intervals) in untreated subjects but also the secretion at rest (p less than 0.01) and TRH - stimulated secretion at times 20, 30, 40 and 60 mins following TRH administration (p less than 0.01, p less than 0.05, p less than 0.05 and p less than 0.05, respectively) in subjects pretreated with 1,25(OH)2D3. Compared with the thyrotropic system, the inhibiting effect of calcitonin on the lactotropic system is not cancelled by the administration of 1,25(OH)2D3. It is assumed that differences in the response of the lactotropic and thyrotropic system to the concurrent administration of calcitonin and 1,25(OH)2D3 are conditioned by the different ratio of the number of receptors for calcitonin and 1,25(OH)2D3 in the lactotropic and thyrotropic cell.

Effects of calcitonin, 1,25(OH)2 vitamin D3 and trifluoperazine on thyrotropic secretion and their mutual interactions

The effects of pharmacological doses of calcium ionophores, calcitonin and 1,25 (OH2)D3, and of the calmodulin inhibitor, trifluoperazine, on thyrotropin secretion at rest and TRH stimulated secretion were investigated as well as their mutual interactions in five groups of clinically healthy volunteers. The thyrotropic secretory response to TRH was inhibited by a single intravenous dose of 50 U synthetic salmon calcitonin or trifluoperazine administered by mouth seven days prior to the TRH test, 6-12 mg/day, and stimulated by 1,25(OH)2D3 administered by mouth four days before the TRH test -3 micrograms/day. The stimulating action of 1,25(OH)2D3 was abolished by calcitonin, administered by the intravenous route - 50 U - closely before the TRH test but not by the concomitant administration of trifluoperazine. The author expressed the hypothesis, that calcitonin and 1,25(OH)2D3 but not trifluoperazine and 1,25(OH)2D3 are mutual antagonists which act at the same subcellular level of the thyrotropic cell and that synthesis and activation of calmodulin is not the trigger of thyrotropic secretion after stimulation with 1,25(OH)2D3. An altered thyrotropin secretion must be foreseen during the therapeutic administration of the investigated calciotropic substances, the mutual interactions of which could be used in practice.

Monomeric serum calcitonin and bone turnover during anticonvulsant treatment and in congenital hypothyroidism

Decreased basal and calcium-stimulated calcitonin serum levels have been found in children with congenital hypothyroidism and in those receiving anticonvulsant drugs. The purpose of our investigation was to confirm these results using a new technique for calcitonin measurement and to study the effect on bone turnover. Calcitonin serum levels were measured with two different antibodies before and after a low-dose Ca infusion in patients receiving phenytoin, primidone, carbamazepine, or valproate and in patients with congenital hypothyroidism receiving L-thyroxine. In comparison with control values, basal and Ca-stimulated extractable calcitonin, representing the monomeric and biologically active form of the hormone, were moderately decreased in patients with epilepsy receiving phenytoin and primidone, and severely decreased in patients with hypothyroidism. Ca and bone metabolism were normal, except for an elevated renal threshold for phosphate (indicating phosphate conservation) in patients receiving phenytoin and primidone, and increased fasting urinary excretion of Ca and hydroxyproline (indicating increased bone resorption) in patients with hypothyroidism. The secretory capacity of the C cells for monomeric calcitonin is decreased in children receiving treatment with some, but not all, anticonvulsant drugs, and lacking in patients with hypothyroidism. Patients with calcitonin deficiency may be prone to osteopenia if the tendency to increased osteoclastic activity is aggravated by secondary hyperparathyroidism in patients with epilepsy receiving phenytoin and primidone or by inappropriate thyroid replacement therapy in patients with hypothyroidism.

Inhibition by prostaglandin E2 of renal effects of calcitonin in rats

To investigate the possible role of prostaglandin E2 (PGE2) in modulating the actions of PTH and calcitonin (CT) in the kidney, the effects of PGE2 were examined on the in vivo conversion of [3H]25-hydroxyvitamin D3 to [3H]1,25-dihydroxyvitamin D3 ([3H]1,25-(OH)2D3) in vitamin D-deficient thyroparathyroidectomized (T-PTX) rats and on the urinary excretion of phosphate (Pi) in vitamin D-replete T-PTX rats in the presence of either PTH or CT. Plasma accumulation of [3H] 1,25-(OH)2D3 increased from 12.2 +/- 0.6 pmol/100 ml in controls to 19.5 +/- 1.1 (P less than 0.01) by 20 micrograms/h PGE2 to 29.8 +/- 1.8 (P less than 0.001) by 7.5 U/h PTH, and to 23.3 +/- 0.7 (P less than 0.01) by 500 mU/h CT. Administration of PGE2 inhibited CT-stimulated accumulation of 1,25-(OH)2D3 to levels not different from those by PGE2 alone (17.8 +/- 1.0 pmol/100 ml). In contrast, PGE2 had no effect on PTH-stimulated 1,25-(OH)2D3 accumulation. PTH and CT caused an increase in urinary Pi excretion and a decrease in plasma Pi levels. PGE2 abolished the effects of CT, but not of PTH, on both urinary Pi excretion and plasma Pi levels. Administration of PGE2 alone caused no significant changes in plasma Pi levels and only minimal increase in urinary Pi excretion. PGE2 did not suppress urinary cAMP excretion stimulated by CT. These results demonstrate that PGE2 specifically suppresses the effects of CT to stimulate synthesis of [3H]1,25-(OH)2D3 from [3H]25-hydroxyvitamin D3 and to inhibit tubular reabsorption of Pi without affecting urinary cAMP excretion. Since CT appears to stimulate 1 alpha-hydroxylase and inhibit Pi reabsorption in proximal tubules, nephron segments devoid of CT-sensitive adenylate cyclase, these data suggest that PGE2 modulates the actions of CT, but not of PTH, on proximal tubular functions.

Hypocalcemia during restraint stress in rats. Indication that gastric ulcer prophylaxis by exogenous calcium interferes with calcitonin release

The influence of restraint stress on serum calcium (Ca) and phosphate was studied in normal and thyroidectomized rats. In addition the response of gastric stress ulcer index, blood gastrin and glucagon to exogenous Ca was investigated. In intact as well as in thyroidectomized animals serum total, ionised and previously injected radioactive Ca decrease during an 8h stress period, whereas inorganic phosphate increases. Together with a constant specific activity these findings are consistent with hypoparathyroidism and calcitonin independent hypocalcemia during stress. Intragastric infusion of 45 mg/kg Ca-gluconate per 8h proves to be a potent anti-stress ulcer regimen in intact and neck-sham operated, but not in thyroidectomized rats without and with additional adrenal demedullation. Gastrin and glucagon were not correlated with calcemia during either stress alone or stress combined with intragastric Ca infusion. It is suggested that the development of gastric stress ulcerations can be prevented by a Ca-mediated release of endogenous calcitonin.

Influence of methyl xanthine treatment on calcitonin effect

The presented results clearly demonstrate that theophylline, caffeine and theobromine have a blocking action on calcitonin effect as determined by the elevation of serum calcium level, although different degree of potency was found with each drugs. There is no difference in respect of the serum calcium elevation after a single dose of methyl xanthines or after a 9-10 day lasting treatment. The castration had no additional enhancing effect of the calcitonin resistance of methyl xanthine treated animals. The administration of androgens simultaneously with the methyl xanthine treatment failed to produce improvement of calcitonin sensitivty preventing the elevation of serum calcium after calcitonin injection. So the calcitonin resistance of methyl xanthine treated animals appears to be different to the calcitonin resistance of sex hormone deprived conditions because the latter could be abolished by androgen administration. Theophylline treatment resulted in a slightly but significantly elevated serum calcium comparing to controls without exogeneous calcitonin. This magnitude of elevation remains between the normocalcaemic limits.

Evidence for interference of 25 (OH) vitamin D3 with phosphaturic action of calcitonin

The present study evaluated the effect of 25(OH)vitamin D3[25(OH)vit D3] on the phosphaturic action of calcitonin in anesthetized parathyroidectomized rats. In group 1, calcitonin was given intravenously over six clearance periods. In group 2, after three periods of calcitonin given intravenously, 25(OH)vit D3 was added and given together with calcitonin for three additional periods. During calcitonin infusion, Cp/CIn 0.18 +/- 0.02 (mean +/- SE) in group 1 was not different from the corresponding Cp/CIn 0.18 +/- 0.03 in group 2; but when 25(OH)vit D3 was added, Cp/CIn 0.12 +/- 0.01 in group 2 was lower (P less than 0.001) than the corresponding Cp/CIn 0.26 +/- 0.02 in group 1. With intravenous calcitonin the urinary excretion of cycle AMP (UcAMP) 97 +/- 29 in group 1 did not differ from the corresponding UcAMP 86 +/- 27 pmol/min in group 2, but when 25(OH)vit D3 was added UcAMP 41 +/- 12 in group 2 was lower (P less than 0.001) than the corresponding UcAMP 131 +/- 14 pmol/min in group 1. This study demonstrated that 25(OH)vit D3 blocks the phosphaturic action of calcitonin. The associated fall in Uctamp suggests that25 (OV)vit D3 acts possibly by inhibiting the calcitonin-induced activation of adenylate cyclase in the kidney. However, other alternative mechanisms of action have not been excluded.

Effects of oestrogen on thyrocalcitonin activity in male and female rabbits

Thyrocalcitonin is an effective hypocalcaemic agent in both the male and female Dutch Belted rabbit. In this strain of rabbit, a level of oestradiol (1 μg/kg of body weight) which is not hypercalcaemic and levels of oestradiol that are hypercalcaemic can effectively block the action of thyrocalcitonin in both the male and female.

Influence of gonadal hormones on the action of calcitonin in the rat

The influence of short-term and long-term treatment with gonadal hormones on the response to calcitonin was investigated in the rat. Oestrogen-treatment, short-term as well as long-term, resulted in a reduced responsiveness to calcitonin. Long-term treatment with androgens enhanced the hypocalcaemic effect of calcitonin in castrated rats of either sex, but reduced the effect in intact animals. No sex differences could be registered in the sensitivity to calcitonin, when intact animals were compared according to age, while marked differences were observed, when the animals were compared according to weight. There was a linear decrease in the response to calcitonin with increasing age in rats of both sexes. An intraperitoneal calcium load was followed by an acute rise in the serum calcium levels. The adult animals counteracted the hypercalcaemia more slowly than the young ones. Significant differences also occurred between male and female rats, the rise in the serum calcium concentration being much more pronounced in the latter group. The hypocalcaemic activity of thyroid tissue from rats of both sexes and of various ages showed considerable variations, but no differences correlated to age or sex.