Inhibition of the fibrillation of highly amyloidogenic human calcitonin by cucurbit[7]uril with improved bioactivity.

Protein/peptide fibrillation is an important challenge for biotechnological drug development. Salmon calcitonin (sCT) is currently used in the clinical treatment of bone-related diseases such as osteoporosis and hypercalcemia, but it still has the risk of immune responses. Although human calcitonin (hCT) would be a better choice in terms of immunogenicity, it has a strong tendency to irreversibly aggregate in aqueous solutions and form long amyloid fibrils, which significantly reduces its bioavailability and therapeutic potency. Here, we demonstrate that cucurbit[7]uril (CB[7]) can inhibit hCT fibrillation by supramolecular interaction with its aromatic groups (affinity: Phe16 > Tyr12 > Phe19 > Phe22). The hCT-CB[7] complex exhibits low cytotoxicity, even promotes osteoblast proliferation and osteogenic capacity of MC3T3 cells. Meanwhile the hCT-CB[7] complexes shows higher bioactivity compared to hCT in reducing blood calcium levels in rats, and also decreases the immunogenicity of hCT. These results suggest that CB[7] has the potential to improve the therapeutic potency of amyloidogenic protein/peptide drugs such as hCT.

Bisphenol A exposure disturbs the bone metabolism: An evolving interest towards an old culprit.

Bisphenol A (BPA) (2,2,-bis (hydroxyphenyl) propane), a well-known endocrine disruptor (ED), is the exogenous chemical that mimic the natural endogenous hormone like oestrogen. Due to its extensive exposure to humans, BPA is considered to be a major toxicological agent for general population. Environmental exposure of BPA results in adverse health outcomes including bone loss. BPA disturbs the bone health by decreasing the plasma calcium level and inhibiting the calcitonin secretion. BPA also stimulated differentiation and induced apoptosis in human osteoblasts and osteoclasts. However, little is known about the underlying mechanisms of the untoward effect of BPA against bone metabolism. The present review gives an overview on the possible mechanisms of BPA towards bone loss. The previous literature shows that BPA exerts its toxic effect on bone cells by binding to the oestrogen related receptor-gamma (ERγ), reducing the bone morphogenic protein-2 (BMP-2) and alkaline phosphatase (ALP) activities. BPA interrupts the bone metabolism via RANKL, apoptosis and Wnt/ß-catenin signaling pathways. It is, however, still debated on the exact underlying mechanism of BPA against bone health. We summarised the molecular evidences with possible mechanisms of BPA, an old environmental culprit, in bone loss and enlightened the underlying understanding of adverse action of BPA in the society.

[Positioning of headache units in the field of neurology: the importance of OnabotulinumtoxinA and other therapies in the treatment of headaches]. / Posicionamiento de las unidades de cefalea en el ambito de la neurologia: la importancia de la OnabotulinumtoxinA y otras terapias en el tratamiento de la cefalea.

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.

TITLE: Posicionamiento de las unidades de cefalea en el ambito de la neurologia: la importancia de la OnabotulinumtoxinA y otras terapias en el tratamiento de la cefalea.La migraña cronica es una enfermedad que afecta al 0,5-2,5% de la poblacion segun las estadisticas que se analicen y la definicion de migraña cronica que se adopte. Es extraordinariamente incapacitante, ya que no permite realizar las actividades personales, profesionales o sociales programadas, y tiene un gran impacto sobre la calidad de vida de los pacientes, medido en escalas de discapacidad, calidad de vida e impacto en la actividad diaria. Sin embargo, actualmente se dispone de tratamientos que han demostrado eficacia en la migraña cronica, como la OnabotulinumtoxinA. Es un tratamiento bien tolerado y con una tasa de eficacia elevada. Pero no es solo una herramienta terapeutica, sino que ha abierto las puertas en el mundo de la cefalea a la realizacion de tratamientos invasivos, al aprendizaje de tecnicas y, en definitiva, a situar la cefalea en unidades de referencia ubicadas, habitualmente, en hospitales de tercer nivel. Ademas, ha ayudado a eliminar el concepto de que los pacientes con cefalea deben ser atendidos exclusivamente por medicos de atencion primaria o neurologos generales. Esta es una oportunidad que debe aprovecharse para redimensionar el campo del estudio y asistencia de la cefalea. En el futuro, esto va a complementarse con novedosos tratamientos con neuroestimulacion y, probablemente, con anticuerpos monoclonales contra el peptido relacionado con el gen de la calcitonina. Se ha iniciado una revolucion en nuestro conocimiento y capacidad de actuacion. Es nuestro deber darle la importancia y uso que se merecen tanto para nuestros pacientes como para nosotros como especialistas.

Amylin receptor signaling in the ventral tegmental area is physiologically relevant for the control of food intake.

The ability of amylin, a pancreatic ß-cell-derived neuropeptide, to promote negative energy balance has been ascribed to neural activation at the area postrema. However, despite amylin binding throughout the brain, the possible role of amylin signaling at other nuclei in the control of food intake has been largely neglected. We show that mRNA for all components of the amylin receptor complex is expressed in the ventral tegmental area (VTA), a mesolimbic structure mediating food intake and reward. Direct activation of VTA amylin receptors reduces the intake of chow and palatable sucrose solution in rats. This effect is mediated by reductions in meal size and is not due to nausea/malaise or prolonged suppression of locomotor activity. VTA amylin receptor activation also reduces sucrose self-administration on a progressive ratio schedule. Finally, antagonist studies provide novel evidence that VTA amylin receptor blockade increases food intake and attenuates the intake-suppressive effects of a peripherally administered amylin analog, suggesting that amylin receptor signaling in the VTA is physiologically relevant for food intake control and potentially clinically relevant for the treatment of obesity.

Asic3 is a neuronal mechanosensor for pressure-induced vasodilation that protects against pressure ulcers.

Pressure-induced vasodilation (PIV) delays the decrease in cutaneous blood flow produced by local application of low pressure to the skin, a physiologically appropriate adjustment of local vasomotor function. Individuals without a normal PIV response have a high risk of ulceration. Here we demonstrate that acid-sensing ion channel 3 (Asic3) is an essential neuronal sensor for the vasodilation response to direct pressure in both humans and rodents and for protecting against pressure ulcers in mice.

Calcium channel blockers inhibit the hyperglycemic effect of calcitonin.

We studied the effect of Russian preparation of porcine calcitonin (calcitrin, 1 U/100 g) and blockers of Ca(2+) channels nifedipine (1 mg/kg, blocker of chemosensitive Ca(2+) channels) and isoptin (5 mg/kg, blocker of voltage-dependent Ca(2+) channels) on glucose metabolism. Calcitonin produced a pronounced hyperglycemic effect in rats. A close negative correlation was found between glucose level and total calcium content. Injection of calcitonin reduced glucose tolerance in rats. Isoptin and nifedipine reduced plasma calcium level and did not affect significantly the blood glucose levels, did not change the pattern of alimentary hyperglycemia in response to glucose load, completely abolished the hyperglycemic effect of calcitonin, and prevented calcitonin-induced impairment of glucose tolerance.

What procalcitonin brings to management of sepsis in the ICU.

In inflammatory states, particularly in response to infectious stimuli, local procalcitonin (PCT) production rises, and because these tissues cannot further process PCT into calcitonin, serum levels increase. In the critical care setting, PCT should be considered a useful tool to help physicians in some specific, although frequent, situations. Serial measurements of PCT levels may indicate the effectiveness of medical decisions such as the appropriateness of antibiotic therapy, the detection of new infections, and the exclusion of a diagnosis of sepsis. PCT-guided algorithms may also help to decrease the duration of antimicrobial therapy. However, the role of PCT as a prognostic marker in critically ill patients is controversial. In a study by Karlsson and colleagues, PCT concentrations did not differ between hospital survivors and nonsurvivors, but the outcome was better in patients whose PCT concentrations decreased more than 50%. The study of PCT kinetics thus could offer an individual risk assessment in patients with severe sepsis.

Predictive value of procalcitonin decrease in patients with severe sepsis: a prospective observational study.

INTRODUCTION: This prospective study investigated the predictive value of procalcitonin (PCT) for survival in 242 adult patients with severe sepsis and septic shock treated in intensive care. METHODS: PCT was analyzed from blood samples of all patients at baseline, and 155 patients 72 hours later. RESULTS: The median PCT serum concentration on day 0 was 5.0 ng/ml (interquartile range (IQR) 1.0 and 20.1 ng/ml) and 1.3 ng/ml (IQR 0.5 and 5.8 ng/ml) 72 hours later. Hospital mortality was 25.6% (62/242). Median PCT concentrations in patients with community-acquired infections were higher than with nosocomial infections (P = 0.001). Blood cultures were positive in 28.5% of patients (n = 69), and severe sepsis with positive blood cultures was associated with higher PCT levels than with negative cultures (P = < 0.001). Patients with septic shock had higher PCT concentrations than patients without (P = 0.02). PCT concentrations did not differ between hospital survivors and nonsurvivors (P = 0.64 and P = 0.99, respectively), but mortality was lower in patients whose PCT concentration decreased > 50% (by 72 hours) compared to those with a < 50% decrease (12.2% vs. 29.8%, P = 0.007). CONCLUSIONS: PCT concentrations were higher in more severe forms of severe sepsis, but a substantial concentration decrease was more important for survival than absolute values.

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 DeltaSOFA, decreasing DeltaPCT and decreasing DeltaCRP. Survival was directly related to decreasing DeltaPCT with odds ratio (OR) = 5.67 (95% confidence interval 1.78 to 18.03), decreasing DeltaCRP with OR = 3.78 (1.24 to 11.50), decreasing DeltaSOFA 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 DeltaPCT with OR = 4.43 (1.08 to 18.18) and decreasing DeltaCRP with OR = 7.40 (1.58 to 34.73) remained significant. Decreasing DeltaCPIS 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.

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.

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.

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.