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

Exploring FDA-Approved Frontiers: Insights into Natural and Engineered Peptide Analogues in the GLP-1, GIP, GHRH, CCK, ACTH, and α-MSH Realms

Peptides continue to gain significance in the pharmaceutical arena. Since the unveiling of insulin in 1921, the Food and Drug Administration (FDA) has authorised around 100 peptides for various applications. Peptides, although initially derived from endogenous sources, have evolved beyond their natural origins, exhibiting favourable therapeutic effectiveness. Medicinal chemistry has played a pivotal role in synthesising valuable natural peptide analogues, providing synthetic alternatives with therapeutic potential. Furthermore, key chemical modifications have enhanced the stability of peptides and strengthened their interactions with therapeutic targets. For instance, selective modifications have extended their half-life and lessened the frequency of their administration while maintaining the desired therapeutic action. In this review, I analyse the FDA approval of natural peptides, as well as engineered peptides for diabetes treatment, growth-hormone-releasing hormone (GHRH), cholecystokinin (CCK), adrenocorticotropic hormone (ACTH), and α-melanocyte stimulating hormone (α-MSH) peptide analogues. Attention will be paid to the structure, mode of action, developmental journey, FDA authorisation, and the adverse effects of these peptides.

Complex Regional Pain Syndrome: Practical Diagnostic and Treatment Guidelines, 5th Edition

There have been some modest recent advancements in the research of Complex Regional Pain Syndrome, yet the amount and quality of the work in this complicated multifactorial disease remains low (with some notable exceptions; e.g., the recent work on the dorsal root ganglion stimulation). The semi-systematic (though in some cases narrative) approach to review is necessary so that we might treat our patients while waiting for "better research." This semi-systematic review was conducted by experts in the field, (deliberately) some of whom are promising young researchers supplemented by the experience of "elder statesman" researchers, who all mention the system they have used to examine the literature. What we found is generally low- to medium-quality research with small numbers of subjects; however, there are some recent exceptions to this. The primary reason for this paucity of research is the fact that this is a rare disease, and it is very difficult to acquire a sufficient sample size for statistical significance using traditional statistical approaches. Several larger trials have failed, probably due to using the broad general diagnostic criteria (the "Budapest" criteria) in a multifactorial/multi-mechanism disease. Responsive subsets can often be identified in these larger trials, but not sufficient to achieve statistically significant results in the general diagnostic grouping. This being the case the authors have necessarily included data from less compelling protocols, including trials such as case series and even in some instances case reports/empirical information. In the humanitarian spirit of treating our often desperate patients with this rare syndrome, without great evidence, we must take what data we can find (as in this work) and tailor a treatment regime for each patient.

The effect of salmon calcitonin against glutamate-induced cytotoxicity in the C6 cell line and the roles the inflammatory and nitric oxide pathways play

Recent evidence has shown that salmon calcitonin (sCT) has positive effects on the nervous system. However, its effect and mechanisms on glutamate-induced cytotoxicity are still unclear. The current experiment was designed to examine the effect of sCT on glutamate-induced cytotoxicity in C6 cells, involving the inflammatory and nitric oxide stress pathways. The study used the C6 glioma cell line. Four cell groups were prepared to evaluate the effect of sCT on glutamate-induced cytotoxicity. The control group was without any treatment. Cells in the glutamate group were treated with 10 mM glutamate for 24 h. Cells in the sCT group were treated with various concentrations (3, 6, 12, 25, and 50 µg/mL) of sCT for 24 h. Cells in the sCT + glutamate group were pre-treated with various concentrations of sCT for 1 h and then exposed to glutamate for 24 h. The cell viability was evaluated with an XTT assay. Nuclear factor kappa b (NF-kB), tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), neuronal nitric oxide synthase (nNOS), nitric oxide (NO), cyclic guanosine monophosphate (cGMP), caspase-3, and caspase-9 levels in the cells were measured by ELISA kits. Apoptosis was detected by flow cytometry method. sCT at all concentrations significantly improved the cell viability in C6 cells after glutamate-induced cytotoxicity (p < 0.001). Moreover, sCT significantly reduced the levels of NF-kB (p < 0.001), TNF-α, and IL-6 levels (p < 0.001). sCT also decreased nNOS, NO, and cGMP levels (P < 0.001). Furthermore, it decreased the apoptosis rate and increased the live-cell rate in the flow cytometry (P < 0.001). In conclusion, sCT has protective effects on glutamate-induced cytotoxicity in C6 glial cells by inhibiting inflammatory and nitric oxide pathways. sCT could be a useful supportive agent for people with neurodegenerative symptoms.

The effects of salmon calcitonin on epileptic seizures, epileptogenesis, and postseizure hippocampal neuronal damage in pentylenetetrazole-induced epilepsy model in rats

Epilepsy is one of the most common neurological disorders that severely affect the life quality of many people worldwide. Excitatory-inhibitory mechanisms, oxidative stress, and also inflammation systems have been implicated in the pathogenesis of epilepsy. Recent studies have shown that salmon calcitonin (sCT) has positive effects on the nervous system. However, its relation with epilepsy is still unclear. This study aimed to investigate the effect of sCT on epileptic seizures, epileptogenesis, and postseizure hippocampal neuronal damage in pentylenetetrazole (PTZ)-induced epilepsy model in rats. The study was performed in two steps. In the first step, the effect of sCT on epileptic seizures was evaluated by using electroencephalography (EEG) in fully kindled rats. In the second step, the effect of sCT on epileptogenesis was evaluated by using the kindling process. Glutamate and gamma-aminobutyric acid (GABA), thiobarbituric acid reactive substance (TBARS), superoxide dismutase (SOD), catalase (CAT), tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1 β), and interleukin 6 (IL-6) were measured in the second group in the brain and serum. Hippocampal regions were stained with hematoxylin-eosin and toluidine blue to evaluate hippocampal neuronal damage histopathologically. Salmon calcitonin showed an antiepileptic effect in fully kindled rats and also prevented the development of epileptogenesis in the kindling process. Besides, sCT decreased glutamate and increased GABA levels. Furthermore, it reduced TBARS levels and increased SOD and CAT levels. On the other hand, it decreased TNF-α levels, IL-1 β levels, and IL-6 levels. Histopathologically, sCT decreased neuronal damage in all hippocampal regions. Our findings are the first preclinical report to show the positive effect of sCT on epileptic seizures and epileptogenesis. Further investigation is required to answer the questions raised about the probable mechanisms involved.

[Calcitonin as an analgesic agent: review of mechanisms of action and clinical applications]

BACKGROUND AND OBJECTIVES

Calcitonin is a polypeptide hormone regulating the metabolism calcium in the body. For many years calcitonin has been used to maintain and improve bone mineral density and to reduce the fracture rate. Many studies showed that calcitonin had analgesic role in several painful circumstances. This pain-ameliorating effect is irrelevant to its osteoclastic inhibitory effect and mechanisms like altering Na+ channel and serotonin receptor expression or hypothesis including the endorphin-mediated mechanism were used to explain this effect. In this study we performed a thorough review on the role of calcitonin as an analgesic agent in different scenarios and investigated the fact that calcitonin can be a feasible medication to relieve pain.

METHOD

Many studies focused on the analgesic effect of calcitonin in several painful circumstances, including acute pains related to vertebral fractures, metastasis, migraine and reflex sympathetic dystrophy as well as neuropathic pains related to spinal injuries or diabetes, and phantom pain. Also, calcitonin was showed to be a useful additive to local anesthesia in the case of controlling postoperative pain or trigeminal neuralgia more effectively. However we faced some contradictory data for conditions like lumbar canal stenosis, complex regional pain syndrome, phantom pain and malignancies.

CONCLUSION

This study showed that calcitonin could be helpful analgesic agent in different painful situations. Calcitonin can be considered an eligible treatment for acute pains related to vertebral fractures and a feasible alternative for the treatment of the acute and chronic neuropathic pains where other medications might fail.

Calcitonin as an analgesic agent: review of mechanisms of action and clinical applications

Background and objectives

Calcitonin is a polypeptide hormone regulating the metabolism of calcium in the body. For many years calcitonin has been used to maintain and improve bone mineral density and to reduce the fracture rate. Many studies showed that calcitonin had analgesic role in several painful circumstances. This pain-ameliorating effect is irrelevant to its osteoclastic inhibitory effect and mechanisms like altering Na+ channel and serotonin receptor expression or hypothesis including the endorphin-mediated mechanism were used to explain this effect. In this study we performed a thorough review on the role of calcitonin as an analgesic agent in different scenarios and investigated the fact that calcitonin can be a feasible medication to relieve pain.

Method

Many studies focused on the analgesic effect of calcitonin in several painful circumstances, including acute pains related to vertebral fractures, metastasis, migraine and reflex sympathetic dystrophy as well as neuropathic pains related to spinal injuries or diabetes, and phantom pain. Also, calcitonin was showed to be a useful additive to local anesthesia in the case of controlling postoperative pain or trigeminal neuralgia more effectively. However we faced some contradictory data for conditions like lumbar canal stenosis, complex regional pain syndrome, phantom pain and malignancies.

Conclusion

This study showed that calcitonin could be helpful analgesic agent in different painful situations. Calcitonin can be considered an eligible treatment for acute pains related to vertebral fractures and a feasible alternative for the treatment of the acute and chronic neuropathic pains where other medications might fail.

Combining naproxen and a dual amylin and calcitonin receptor agonist improves pain and structural outcomes in the collagen-induced arthritis rat model

Background

Pain is a debilitating symptom of rheumatoid arthritis (RA), caused by joint inflammation and cartilage and bone destruction. Nonsteroidal anti-inflammatory drugs (NSAIDs) are used to treat pain and inflammation in RA, but are not disease-modifying and do not prevent joint destruction when administered alone. KBPs (Key Bioscience peptides) are synthetic peptides based on salmon calcitonin and are expected to inhibit bone resorption and to be chondroprotective. In this study, we investigated if combining a standard of care NSAID (naproxen) with a KBP resulted in improvement in pain scores, as well as disease activity and structural damage in a rat model of RA.

Methods

Collagen-induced arthritis (CIA) was induced in 40 female Lewis rats by immunization with porcine type II collagen; 10 rats were given sham injections. CIA rats were treated with KBP and/or naproxen. Health scores and joint scores were evaluated daily. Mechanical and cold allodynia tests and burrowing tests were used to assess pain-like behaviors. Blood samples were collected for biomarker testing, and paws were collected for histology and microcomputed tomography.

Results

Naproxen monotherapy increased the time until humane endpoints was reached, and improved health score, pain assessments, and trabecular thickness, while KBP monotherapy did not result in improvements. Combination therapy had improved efficacy over naproxen monotherapy; combination therapy resulted in improved health scores, and importantly reduced mechanical and cold allodynia assessment. Furthermore, protection of articular cartilage structure and preservation of bone structure and bone volume were also observed.

Conclusions

This study demonstrates that combining KBP and naproxen may be a relevant therapeutic strategy for RA, resulting in improvements to the overall health, pain, inflammation, and joint structure.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1819-9) contains supplementary material, which is available to authorized users.

The complex regional pain syndrome

Complex regional pain syndrome (CRPS) is the current consensus-derived name for a syndrome usually triggered by limb trauma. Required elements include prolonged, disproportionate distal-limb pain and microvascular dysregulation (e.g., edema or color changes) or altered sweating. CRPS-II (formerly "causalgia") describes patients with identified nerve injuries. CRPS-I (formerly "reflex sympathetic dystrophy") describes most patients who lack evidence of specific nerve injuries. Diagnosis is clinical and the pathophysiology involves combinations of small-fiber axonopathy, microvasculopathy, inflammation, and brain plasticity/sensitization. Females have much higher risk and workplace accidents are a well-recognized cause. Inflammation and dysimmunity, perhaps facilitated by injury to the blood-nerve barrier, may contribute. Most patients, particularly the young, recover gradually, but treatment can speed healing. Evidence of efficacy is strongest for rehabilitation therapies (e.g., graded-motor imagery), neuropathic pain medications, and electric stimulation of the spinal cord, injured nerve, or motor cortex. Investigational treatments include ketamine, botulinum toxin, immunoglobulins, and transcranial neuromodulation. Nonrecovering patients should be re-evaluated for neurosurgically treatable causal lesions (nerve entrapment, impingement, infections, or tumors) and treatable potentiating medical conditions, including polyneuropathy and circulatory insufficiency. Earlier impressions that CRPS represents malingering or psychosomatic illness have been replaced by evidence that CRPS is a rare complication of limb injury in biologically susceptible individuals.

Roles of osteoclasts in the control of medullary hematopoietic niches

Bone marrow is the major site of hematopoiesis in mammals. The bone marrow environment plays an essential role in the regulation of hematopoietic stem and progenitor cells by providing specialized niches in which these cells are maintained. Many cell types participate to the composition and regulation of hematopoietic stem cell (HSC) niches, integrating complex signals from the bone, immune and nervous systems. Among these cells, the bone-resorbing osteoclasts (OCLs) have been described as main regulators of HSC niches. They are not limited to carving space for HSCs, but they also provide signals that affect the molecular and cellular niche components. However, their exact role in HSC niches remains unclear because of the variety of models, signals and conditions used to address the question. The present review will discuss the importance of the implication of OCLs focusing on the formation of HSC niches, the maintenance of HSCs in these niches and the mobilization of HSCs from the bone marrow. It will underline the importance of OCLs in HSC niches.

Complex regional pain syndrome: practical diagnostic and treatment guidelines, 4th edition

OBJECTIVE

This is the fourth edition of diagnostic and treatment guidelines for complex regional pain syndrome (CRPS; aka reflex sympathetic dystrophy).

METHODS

Expert practitioners in each discipline traditionally utilized in the treatment of CRPS systematically reviewed the available and relevant literature; due to the paucity of levels 1 and 2 studies, less rigorous, preliminary research reports were included. The literature review was supplemented with knowledge gained from extensive empirical clinical experience, particularly in areas where high-quality evidence to guide therapy is lacking.

RESULTS

The research quality, clinical relevance, and "state of the art" of diagnostic criteria or treatment modalities are discussed, sometimes in considerable detail with an eye to the expert practitioner in each therapeutic area. Levels of evidence are mentioned when available, so that the practitioner can better assess and analyze the modality under discussion, and if desired, to personally consider the citations. Tables provide details on characteristics of studies in different subject domains described in the literature.

CONCLUSIONS

In the humanitarian spirit of making the most of all current thinking in the area, balanced by a careful case-by-case analysis of the risk/cost vs benefit analysis, the authors offer these "practical" guidelines.

Additive inhibitory effects of calcitonin and capsaicin on voltage activated calcium channel currents in nociceptive neurones of rat

Calcitonin, a peptide hormone expressed in C-cells of the thyreoid gland, as well as capsaicin, isolated from chili, both, modify intracellular signalling in nociceptive neurones. The pathways triggered by the activation of either of these receptors results in a modulation of the intracellular calcium ([Ca(2+)](i)) concentration. While the regulation of [Ca(2+)](i) depends on many factors, voltage activated calcium channels (VACCs) are a major gate for the calcium entry into neurones. Here we describe the changes of voltage gated calcium channel currents (I(Ca(V))) induced by calcitonin and/or capsaicin. Currents were recorded using adequate solutions and voltage protocols with the whole cell patch-clamp technique. When the channels were opened by a depolarisation to 0 mV, both substances reduce the peak I(Ca(V)) (calcitonin (10nM): 29.3 ± 3.9%; capsaicin (0.5 μM): 41.1 ± 7.7%). While the effect of calcitonin was voltage dependent, capsaicin shifted the largest current to the more hyperpolarizing range (peak current from -10 to -20 mV). A subsequent co-application of either of the two substances (with a pre-application of either 3 min or 60 min) results in an additive reduction of the currents, and prevents the capsaicin-induced shift of the current-voltage relation. Therefore, we hypothesize, that the activation of either of the two receptors reduces I(Ca(V)) by different cellular binding sites of the channel protein triggering channel opening. These findings may be useful to understand cellular mechanisms of pain modulation and might help to find better treatments for neuropathic pain.

Inhibition of Behcet's disease by calcitonin

Behcet's disease (BD) is a chronic, multisystem inflammatory disorder characterized by relapsing oral aphthous and genital ulcers, ocular inflammation, erythemanodosum and folliculitis-like lesions of the skin, arthritis, and central nervous system involvement. Its pathogenesis has not been fully elucidated but the etiology is accepted to be multifactorial, therefore the treatment of Behcet's disease continues to be a major therapeutic challenge. The identification of novel therapeutic agents for the treatment of these disorders is important. Calcitonin (CT), a peptide hormone secreted in response to hypercalcemia, has the dual effect of inhibiting osteoclast recruitment as well as their resorptive activity. A number of reviews have concluded that salmon calcitonin is safe and effective in the treatment of osteoporosis. Calcitonin abrogated the stimulating effect of RANKL or prednisolone; similar results were obtained with OPG. Additionally, the analgesic activity of salmon calcitonin has been shown in several controlled prospective double-blind studies to improve pain. Exogenous calcitonin is thought to cross the blood-brain barrier and to accumulate slowly in the brain, inducing analgesia once sufficient receptors are occupied. Since CT could antagonize resorptive and analgesic activity by competitively binding to CTR and has been considered as a specific antagonist, we postulate that the CT could function as a novel agent to inhibit BD. In our opinion, if the hypothesis proved to be practical, CT could be widely used in clinical settings to treat BD.

Calcitonin: a drug of the past or for the future? Physiologic inhibition of bone resorption while sustaining osteoclast numbers improves bone quality

Postmenopausal osteoporosis results from a continuous imbalance between bone resorption and bone formation, favoring bone resorption. An increasing number of treatments for osteoporosis are in development and on the market. A range of differences and similarities are found between these treatment options, and these need to be carefully evaluated before the initiation of treatment. This article summarizes data from in vitro and animal studies, as well as clinical trials, on the effect of calcitonin on bone turnover. Calcitonin was found to exert its antiresorptive effects via directly reducing osteoclastic resorption, and thus leads to an increase in bone mineral density and bone strength. Furthermore, calcitonin appears to mainly target the most active osteoclasts, and in contrast to most other antiresorptive agents it does not reduce the number of osteoclasts. Finally, in humans, while attenuating resorption, calcitonin treatment does not interfere markedly with bone formation, in contrast to other currently available antiresorptive agents. Thus, we speculate that calcitonin treatment will lead to a continuously positive bone balance in contrast with other antiresorptive agents currently on the market and thereby, in a physiologic manner, result in improved bone quality. Calcitonin is currently only available in injectable and nasal formulations. An oral formulation may, however, improve patient acceptance and compliance. Currently, several different routes are being pursued to identify an optimal oral formulation, of which the technology based on 5-CNAC is the most advanced. There are promising clinical data available for this formulation from both osteoarthritis and osteoporosis clinical trials, although the antifracture efficacy is not yet known.

Could calcitonin be a useful therapeutic agent for trigeminal neuralgia?

Trigeminal neuralgia (TN) has been recognized as one of the most common neurovascular syndromes caused by the vascular contact of the trigeminal nerve in its root entry zone (REZ) with a branch of the superior or anterior inferior cerebellar arteries, leading to a demyelinization of trigeminal sensory fibers within either the nerve root or, less commonly, the brainstem. There is a lack of certainty regarding the aetiology and pathophysiology of TN, therefore the treatment of trigeminal neuropathic pain disorders continues to be a major therapeutic challenge. The identification of novel therapeutic agents for the treatment of these disorders is important. Calcitonin (especially intranasal) provides an interesting analgesic effect in a series of painful conditions including reflex sympathetic dystrophy syndrome, adhesive capsulitis, ankylosing spondylitis, rheumatoid arthritis, vertebral crush fractures and metastasis, phantom limb pain, etc. Exogenous calcitonin is thought to cross the blood-brain barrier and to accumulate slowly in the brain, inducing analgesia once sufficient receptors are occupied. We hypothesize that calcitonin may has anti - trigeminal neuralgia properties. From the clinical point of use, the analgesic effect of calcitonin will be beneficial throughout the whole period of medical treatment of trigeminal neuralgia patients.

Advances in treatment of complex regional pain syndrome: recent insights on a perplexing disease

PURPOSE OF REVIEW

The paper is a critical appraisal of recent advances in the treatment of complex regional pain syndrome. Rapidly changing concepts related to the pathophysiology of this disease has transformed its current management and necessitates an updated review of the literature.

RECENT FINDINGS

Chronic regional pain syndrome is a perplexing disease that continues to challenge researchers with respect to its cause and treatment. Recent modification to diagnostic criteria has enabled clinicians to diagnose this disease in a more consistent fashion. Emerging data indicate a possible role of inflammation in the overall pathophysiology and have led to treatment trials with newer anti-inflammatory medications. Certain 'conventional' interventional techniques have been recently scrutinized. A few novel therapeutic options like graded imagery are also outlined.

SUMMARY

Enhanced insight into the pathophysiology of chronic regional pain syndrome has modified current clinical practice and the focus of research. Certain 'standard' therapeutic options for chronic regional pain syndrome have failed the test of time while others have prevailed. New options have recently been evaluated and have shown promising early results. Knowledge of recent advances in chronic regional pain syndrome will help pain physicians provide optimal care to these patients.

Calcitonin is involved in cartilage homeostasis: is calcitonin a treatment for OA?

OBJECTIVE

Osteoarthritis (OA) is the most common form of degenerative joint diseases and a major cause of disability and impaired quality of life in the elderly. Recent observations suggest that calcitonin may act on both osteoclasts and chondrocytes. The present review was sought to summarize emerging observations from the molecular level to the preliminary clinical findings of possible chondroprotective effects of calcitonin.

METHOD

This review summarizes peer-reviewed articles found using pre-defined search criteria and published in the PubMed database before January 2006. In addition, abstracts from the OsteoArthritis Research Society International (OARSI) conferences in the time period 2000-2005 have been included in the search.

RESULTS

Ample evidence for the effect of calcitonin on bone resorption was found. Support for direct effects of calcitonin on chondrocytes on matrix synthesis and inhibition of cartilage degradation have been published. In addition, clinical evidence for the effect of calcitonin on cartilage degradation is emerging.

CONCLUSION

Several independent lines of evidence suggest a direct chondroprotective effect of calcitonin in addition to the well-established effect on bone resorption. Given the currently limited availability of chondroprotective agents, much expectation regards the ongoing clinical assessment of calcitonin therapy for the prevention and treatment of OA.

Calcitonin therapy in osteoporosis

Osteoporosis is the most prevalent metabolic bone disease and is characterized by diminished bone strength predisposing to an increased risk of fracture. Its incidence is particularly high in postmenopausal women but it can also affect other groups, such as men and patients receiving corticosteroid therapy. Calcitonin is a naturally occurring peptide which acts via specific receptors to strongly inhibit osteoclast function. It has been used in the treatment of osteoporosis for many years. Historically, calcitonin was administered as a parenteral injection, but the intranasal formulation is now the most widely used because of its improved tolerability. New approaches are currently being investigated to enhance the bioavailability and effects of calcitonin, including oral, pulmonary, and transdermal routes of administration, and novel allosteric activators of the calcitonin receptor. Several controlled trials have reported that calcitonin stabilizes and in some cases produces a short-term increase in bone density at the lumbar spine level. The most relevant clinical trial to evaluate the effect of calcitonin in the prevention of fractures was the Prevent Recurrence of Osteoporotic Fractures (PROOF) study, a 5-year double-blind, randomized, placebo-controlled trial showing that salmon calcitonin nasal spray at a dosage of 200 IU/day can reduce the risk of vertebral osteoporotic fractures by 33% (relative risk [RR] = 0.67; 95% CI 0.47, 0.97; p = 0.03). However, the 100 and 400 IU/day dosages did not significantly reduce vertebral fracture risk. Effects on nonvertebral fractures were not significant (RR = 0.80; 95% CI 0.59, 1.09; p = 0.16). There is mounting evidence to show that calcitonin diminishes bone pain in osteoporotic vertebral fractures, which may have clinical utility in vertebral crush fracture syndrome. A recent study suggests that nasal salmon calcitonin appears to be a promising therapeutic approach for the treatment of men with idiopathic osteoporosis, although long-term trials are necessary to confirm these results and evaluate fracture rate as an endpoint in men. The role of calcitonin in corticosteroid-induced osteoporosis remains controversial, hence it can only be considered a second-line agent for the treatment of patients with low bone mineral density who are receiving long-term corticosteroid therapy.

Consequences of Inadequate Postoperative Pain Relief and Chronic Persistent Postoperative Pain

Inadequately controlled pain has undesirable physiologic and psychologic consequences such as increased postoperative morbidity, delayed recovery, a delayed return to normal daily living, and reduced patient satisfaction. Importantly, the lack of adequate postoperative pain treatment may lead to persistent pain after surgery, which is often overlooked. Overall, inadequate pain management increases the use of health care resources and health care costs. This article reviews the physiologic and psychologic consequences of inadequately treated pain, with an emphasis on chronic persistent postoperative pain.

Calcitonin: physiological actions and clinical applications

Calcitonin (CT) was first reported as a hypocalcemic principle, initially thought to originate from the parathyroid gland, a view subsequently corrected to an origin from parafollicular C-cells. Human CT is a 32 amino acid peptide with an N-terminal disulphide bridge and a C-terminal prolineamide residue, shown to potently inhibit bone resorption. More recent studies have demonstrated that this may take place through a direct osteoclastic action. A number of osteoclast CT receptors have subsequently been characterized and particular receptor regions necessary for ligand binding and intracellular signaling identified. Its potent anti-resorptive effect has led to its use in treating Paget's bone disease, osteoporosis, hypercalcaemia and osteogenesis imperfecta. This review summarises some key aspects of its synthesis, structure and its actions at the cellular and molecular levels, and leads on to its therapeutic uses that have emerged since its discovery as well as possibilities for future clinical applications.

No tolerance to the antinociceptive action of calcitonin in rats and mice

The involvement of a central opioid mechanism in the antinociceptive effect of calcitonin is still a matter of controversy. Since a major characteristic of the effects of opioids is tolerance to repeated treatments, we investigated the effects of acute and chronic (over 7 days) calcitonin injections on pain sensitivity in rats and mice. We examine the effect of single and repeated intraventricular (0.15 UI) and intraperitoneal (2.5, 5 and 20 IU/kg) injection of salmon calcitonin using respectively a tail flick test in rats and the writhing test in mice. The results showed that repeated injection of calcitonin produces a stronger antinociceptive effect than the single injection effect. The antalgic effect, evaluated in the writhing test, is dose-dependent. In both tail-immersion and writhing tests, repeated administration of calcitonin produced a long-lasting antinociceptive effect. These data suggest therefore that the tolerance does not develop after repeated treatment with calcitonin in both rat and mouse. These results support the hypothesis that an important component of the antinociceptive effects of calcitonin is not mediated by an opioid mechanism.

Complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a heterogeneous disorder that falls in the spectrum of neuropathic pain disorders. It is maintained by abnormalities throughout the neuraxis (the peripheral, autonomic, and central nervous systems). The pathophysiology of CRPS is not fully known. There are no scientifically well-established treatments. The diagnostic criteria for CRPS at this time are purely clinical, and the use of diagnostic tests has not been demonstrated. The most appropriate management of CRPS uses a multidisciplinary approach, with the inclusion of medical and psychologic intervention, and physical and occupational therapy. The key is gradual, persistent, functional improvement. The rational use of pain therapies must be grounded in a thorough knowledge of the neurobiology of pain, its endogenous modulation, and the clinical presentation. Potential peripheral pathophysiologic targets (and possible treatments) include increased spontaneous firing and responsiveness of peripheral afferent fibers mediated by inflammatory and other algogenic substances (somatosensory blocks, corticosteroids), altered levels of expression and functioning of multiple ion channels (local anesthetics, calcium channel blockers, anticonvulsants), abnormal interneuronal communication, and increased peripheral expression of adrenergic receptors and sympathetic excitation (sympathetic blocks, alpha-adrenergic antagonists, alpha-2 agonists). CRPS is also perpetuated by central mechanisms, with pathophysiologic targets (and possible treatments) including reorientation of dorsal horn terminals (desensitization techniques), functional reduction in inhibitory interneuron activity (tricyclic antidepressants, gabapentin, opioids), central sensitization and increased central excitability (gabapentin, topiramate, spinal cord stimulation, somatosensory blocks), impaired descending nociceptive inhibition (tricyclic antidepressants, opioids), and adaptive changes in the cortical centers underlying the sensory-discriminative and affective-motivational dimensions of pain (psychologic, physical, and occupational therapies). The treatment choices should be aimed at remodulating, normalizing, disrupting, or preventing the progression of abnormalities in pain processing. Sympathetic nerve blocks should be performed at least once to assess if sympathetically maintained pain is present. To the extent that peripheral somatosensory nerve blocks can diminish nociceptive input to the central nervous system, these techniques may help reduce the nociceptive sensitization of spinal neurons. Pain relief, however it is achieved and however temporary it is, is intended to facilitate participation in functional therapies to normalize use and to improve motion, strength, and dexterity. Psychologic therapies, such as biofeedback and cognitive-behavioral techniques targeting pain, stress, and mood disorders, are valuable adjunctive treatments for pain control and can facilitate functional improvement.

Calcitonin in reflex sympathetic dystrophy syndrome and other painful conditions

Salmon calcitonin (especially intranasal) provides an interesting analgesic effect in a series of painful conditions including reflex sympathetic dystrophy syndrome, adhesive capsulitis, ankylosing spondylitis, rheumatoid arthritis, vertebral crush fractures and metastasis, phantom limb pain, etc. In addition, in preliminary series, calcitonin shows an unexpected benefit to vasomotor changes and peptic ulcer. Yet the experience in these conditions is limited and needs confirmation. By comparison with the injectable, the intranasal route seems particularly interesting because of less undesirable effects, and a more rapid and probably more powerful analgesia.

Possible mechanisms of the analgesic action of calcitonin

The analgesic activity of calcitonin is well established, both through clinical observation and specific experimental investigation. The mechanism involved, however, is still unclear, and the hypotheses that have been proposed range from a simple peripheral antiinflammatory action to a direct action on specific receptors in the central nervous system. The various hypotheses are briefly reviewed and some of the supporting evidence is presented. The conclusion is that the principal mechanism of calcitonin's analgesic effect is probably a direct central action, but that this is further supported by peripheral mechanisms that may also improve bone status locally.

Forty years of calcitonin--where are we now? A tribute to the work of Iain Macintyre, FRS

Calcitonin was discovered as a hypocalcemic principal that was initially thought to originate from the parathyroid gland. This view was corrected subsequently, and an origin from the thyroid C cells was documented. The purification and sequencing of various calcitonins soon followed. Calcitonin is a 32-amino-acid-long peptide with an N-terminal disulfide bridge and a C-terminal prolineamide residue. The peptide was shown to potently inhibit bone resorption; however, a direct osteoclastic action of the peptide was confirmed only in the early 1980s. Several osteoclast calcitonin receptors have subsequently been cloned and sequenced. Specific regions of the receptor necessary for ligand binding and intracellular signaling through cyclic AMP and calcium have been identified through systematic deletion mutagenesis and chimeric receptor studies. Calcitonin's potent antiresorptive effect has led to its use in treating Paget's disease of bone, osteoporosis, and hypercalcemia. This review retraces key aspects of the synthesis and structure of calcitonin, its cellular and molecular actions, and its therapeutic uses as they have emerged over the 40 years since its discovery. The review also examines the implications of these findings for future clinical applications as a tribute to early workers to whom credit must be given for creation of an important and expanding field. Notable are the new approaches currently being used to enhance calcitonin action, including novel allosteric activators of the calcitonin receptor, modulation of the release of endogenous calcitonin by calcimimetic agents, as well as the development of oral calcitonins.

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.

Side-chain lactam-bridge conformational constraints differentiate the activities of salmon and human calcitonins and reveal a new design concept for potent calcitonin analogues

We have recently reported the potent hypocalcemic effects of side-chain lactam-bridged analogues of human calcitonin (hCT) (Kapurniotu, A.; et al. Eur. J. Biochem. 1999, 265, 606-618). To extend these studies, we have now synthesized a new series of (Asp(17), Lys(21)) and (Asp(17), Orn(21)) side-chain bridged salmon calcitonin (sCT) and hCT analogues. The affinities of these analogues for the human calcitonin receptor, hCTR(I1)(-), and for rat-brain membrane receptors were assayed in competitive binding assays, and agonist potencies at the hCTR(I1)(-) receptors were assessed, using a cAMP-responsive gene-reporter assay. The bridged sCT analogues had activities similar to sCT itself. In contrast, an (Asp(17), Orn(21)) side-chain bridged hCT analogue, cyclo(17-21)-[Nle(8), Phe(12), Asp(17), Orn,(21) Tyr(22))-hCT, was 80 and 450 times more active than hCT in the hCTR(I1)(-) and rat-brain receptor binding assays, respectively, and was 90 times more potent than hCT and 16 times more potent than sCT in initiating receptor signaling. An uncyclized, isosteric analogue of this peptide was also more potent than hCT, demonstrating that the cyclization constraint and these single-residue substitutions enhance the activities of hCT in an additive fashion. This study demonstrates that the potency-enhancing effects of lactam-bridge constraints at hCT residues 17-21 are not transferable to sCT. We also show that, in comparison to the hCT analogues, sCT and its analogues are less potent agonists than expected from their hCTR(I1)(-) affinities. This suggests that it may be possible to preserve the efficient signal transduction of hCT while introducing additional receptor affinity-enhancing elements from sCT into our potent lactam-bridged hCT analogue, thereby creating new super-potent, hCT-based agonists.

Treatment of reflex sympathetic dystrophy (CRPS type 1): a research synthesis of 21 randomized clinical trials

A blinded meta analysis was performed on randomized clinical trials (RCT) on the medicinal treatment of reflex sympathetic dystrophy (complex regional pain syndrome type I) to assess the methodological quality and quantify the analgesic effect of treatments by calculating individual and summary effect sizes. The internal validity of 21 RCTs was investigated and the quality weighted summary effect size was calculated using a fixed effect model (Glass Delta). The methodological quality ranged from moderate to good (average 46%). Differences were found between the trials in inclusion/exclusion criteria, treatment methods, duration of treatments and trials, and measurement instruments. Statistical analysis was possible for four subgroups; one evaluating the analgesic effects of sympathetic suppressors in general (n = 12), one subgroup concerning the analgesic effects of guanethidine (n = 6), one investigating the analgesic effect of intravenous regional sympathetic blocks (n = 9), and one subgroup (n = 5) evaluating the analgesic effect of calcitonin. Except for the calcitonin subgroup (P = 0.002), the quality-weighted summary effect size of these subgroups were not significant. No significant analgesic effect by sympathetic suppressing agents could be established. Calcitonin seems to provide effective pain relief in reflex sympathetic dystrophy patients. The results of the present study show that weighting methodological quality influences the magnitude of the effect sizes of specific treatment methods. Future studies should control for methodological quality.

Heroin-induced rhabdomyolysis as a cause of reflex sympathetic dystrophy

Reflex sympathetic dystrophy is an excessive or abnormal response of the sympathetic nervous system in an extremity to an injury or other condition. The authors describe a 37-year-old man who experienced constant pain and vasomotor instability in both feet after nontraumatic rhabdomyolysis secondary to smoking heroin. Three-phase bone scintigraphy was performed and revealed significantly increased blood-flow, blood-pool, and delayed-phase radioactivity. The follow-up three-phase bone scinitigram showed less radiotracer uptake that was consistent with a good response to calcitonin therapy. Heroin-induced rhabdomyolysis should be added to the list of precipitating conditions that can induce this syndrome.

Neurotensin inhibits neuronal Na+,K+-ATPase activity through high affinity peptide receptor

Neurotensin is a peptide present in mammalian CNS and peripheral tissues, which may play a major role in neurotransmission or neuromodulation, subserving diverse physiological functions. We studied the effect of added neurotensin on ATPase activities in synaptosomal membranes isolated from rat cerebral cortex. Neurotensin at 3 x 10(-8)-3 x 10(-6) M concentration decreased 20-44% Na+,K+-ATPase activity but failed to modify Mg2+-ATPase activity; lower neurotensin concentrations (3 x 10(-14)-3 x 10(-10) M) had no effect on enzyme activities. This inhibitory effect was abolished by neurotensin heating, by enzyme preincubation with neurotensin during periods exceeding 10 min, or by adding 1 x 10(-6) M SR 48692, a high affinity neurotensin receptor antagonist. Levocabastine, which blocks low affinity neurotensin receptor, failed to alter enzyme inhibition by the peptide. It is suggested that the sodium pump may be a target for neurotensin effects at neuronal level involving the participation of high affinity neurotensin receptor.

Calcitonin in phantom limb pain

PLP is a challenging disorder that is often difficult to treat. Like all other types of pain, PLP is a tremendous source of morbidity and should be treated aggressively. Though evidence is very limited, one or two doses of intravenous salmon calcitonin 200 IU may be an effective treatment. The minor adverse effects reported in the literature would seem to indicate the relative safety of this regimen; however, clinicians should be aware of the rare but severe hypersensitivity reactions that can occur with salmon calcitonin. Intranasal calcitonin appears to be similar in efficacy to the parenteral formulation, at least in pain associated with vertebral crush fractures. Long-term studies using intranasal calcitonin for relief of PLP are warranted given the ease of administration of this dosage form.

Prevention and treatment of osteoporosis in the elderly

Due to age-associated bone losses, all elderly are prone to osteoporosis, which often leads to fractures. Fractures frequently result in dependency and institutionalization, as well as physical deformities that may lead to respiratory and cardiovascular problems. Currently, no drugs exist to promote new bone formation. Thus care of the elderly focuses primarily on lifestyle modification and increased dietary intake of calcium and vitamin D; decreased intake of caffeine, phosphates, and alcohol; smoking cessation; increased exercise; and drugs. Drugs for preventing osteoporosis include supplemental calcium and vitamin D, hormone replacement therapy, and alendronate. Drugs that enhance bone loss or increase the likelihood of falls should be eliminated, if possible, or the dosages adjusted. Making residences safer will also help to minimize the potential for falls. Drugs for treating osteoporosis include hormone replacement therapy, alendronate, and nasal calcitonin. The prevention and treatment plan is individualized for each patient, taking into account personal preferences, risk factors for osteoporosis and fracture, concomitant diseases and drug therapies, efficacy and tolerance of osteoporosis therapy, quality of life, life expectancy, finances, and health insurance coverage.

Osteoporosis in women: prevention and treatment

OBJECTIVE

To review osteoporosis, its pathophysiology, lifestyle and dietary factors that influence osteoporosis, and treatments to prevent and treat the disease in women.

DATA SOURCES

MEDLINE using the search term osteoporosis and individual therapies and interventions for 1974-1988.

STUDY SELECTION

English-language studies in humans were reviewed. Prospective clinical trial data were selected when available; epidemiologic data were used when prospective clinical trials were not available.

DATA SYNTHESIS

Pharmacists should initiate discussions with women of all ages to help prevent, recognize, and treat osteoporosis. Assessing and modifying calcium, vitamin D, caffeine, alcohol, and phosphate intake, increasing exercise, and minimizing falls can help prevent osteoporosis and fractures. The risks and benefits of hormone replacement therapy should be presented to women so they can make an informed decision. Hormone replacement therapy is the treatment of choice for preventing and treating osteoporosis; it also reduces cardiovascular morbidity and mortality. The benefits must be put into the proper perspective with adverse effects, events such as vaginal bleeding and the risk of breast cancer, that prevent women from taking estrogen. As not every woman is willing or able to take estrogen, alternatives should be discussed. Raloxifene prevents osteoporosis, has beneficial lipid effects, and does not stimulate breast or endometrial tissue. Alendronate is a safe and effective for the prevention and treatment of osteoporosis when administered properly. Calcitonin is approved for treatment of osteoporosis and provides analgesic effects for fractures.

CONCLUSION

Pharmacists should initiate discussions with women of all ages to help prevent, recognize, and treat osteoporosis. Assessing and modifying calcium and vitamin D, caffeine, alcohol, and phosphate intake, increasing exercise, and minimizing falls can help prevent osteoporosis and fractures.

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.

A chelate theory for the mechanism of action of aspirin-like drugs

Two hundred years after the discovery of the pharmaceutical usefulness of aspirin, it and aspirin-like drugs, a family with an ever-increasing number of members, are an indispensable part of modern life. However, the question as to how these drugs work in the body has remained unsettled. It is postulated here that this group of drugs may exert their therapeutic (and adverse) effects by chelating various physiologically important metallic cations in the body. The chelate theory is supported by the vast majority, if not all, of the observations on these drugs made in the past.

A study of calcitonin effect on synaptosomal membrane enzymes

Calcitonin is a hormone peptide produced by the thyroid gland, whose best described role is to prevent bone reabsorption. It also participates in other biological functions, even at central nervous system level. We studied the effect of added calcitonin on ATPase and acetylcholinesterase activities in synaptosomal membranes isolated from rat cerebral cortex. Calcitonin at 10(-7) - 10(-5)M concentration decreased 20-40% Na+, K(+)-ATPase and 15-25% K(+)-p-nitrophenylphosphatase activities, and at 10(-6)-10(-5)M reduced 20-30% Mg(2+)-p-nitrophenylphosphatase activity. However, this peptide failed to modify Mg(2+) - and Ca(2+)-ATPase or acetylcholinesterase activities. Results suggest that the sodium pump may be a target for calcitonin effects at neuronal level. Thus, calcitonin inhibition of sodium/potassium transport through synaptic membranes supports a regulatory role of this peptide on neurotransmission.

Antinociceptive effects of repeated systemic injections of calcitonin in formalin-induced hyperalgesic rats

Calcitonin (CT) produces long-lasting analgesia in patients suffering from painful diseases following repeated systemic injections, but there have been only a few contradictory reports on the antinociceptive action of systemic injections of CTs in animal experiments. This study was conducted to elucidate an antinociceptive action of systemic CT in rats. An injection of dilute formalin induced hyperalgesia for about 2 h. Single topical injections of 0.12 and 1.2 U, but not 0.012 U, of [Asu1.7] eel CT (eCT) into the same site of formalin injection inhibited the hyperalgesia. Repeated systemic injections of eCT (4 and 40, but not 0.4, U kg-1 day-1) for 7 days inhibited the hyperalgesia, while the single injection was without effects at doses tested. Although the highest dose of eCT (40 U kg-1 day-1) inhibited an increase in body weight following repeated injections, lower doses (0.4 and 4 U kg-1 day-1) were without effects. The suppression of hyperalgesia following repeated systemic injections of eCT (4 U kg-1 day-1) lasted for at least 24 h, and subsided by 3 days following the last eCT injection. These results indicate that the repeated systemic injections of eCT produce a long-lasting inhibition of formalin-induced hyperalgesia in rats. This inhibitory effect is similar to CT analgesia in human subjects in terms of a necessity for repeated administration, effective dose and long-lasting effects.

Intranasal salcatonin (salmon calcitonin). A review of its pharmacological properties and role in the management of postmenopausal osteoporosis

Osteoporosis is a common problem among postmenopausal women and is associated with significant morbidity, mortality and costs primarily resulting from osteoporotic fractures. Salcatonin (salmon calcitonin) inhibits osteoclastic bone resorption and is approximately 40 to 50 times more potent than human calcitonin. In most randomised trials in which intranasal salcatonin (usually 50 to 200 IU/day plus oral calcium supplements) was administered for 1 to 5 years to postmenopausal women for prevention of osteoporosis, bone mineral density or content of the lumbar spine increased by approximately 1 to 3% from baseline. In contrast, postmenopausal women receiving only oral calcium supplements typically had reductions in bone mineral density or content of about 3 to 6%. The difference between treatment groups was statistically significant in essentially all studies. Although changes in bone mineral density or content were broadly similar in studies of postmenopausal women with established osteoporosis to those in postmenopausal women receiving therapy for prevention of the disease, studies in women with established osteoporosis did not usually demonstrate statistically significant differences between treatment groups. Also in postmenopausal women with established osteoporosis, intranasal salcatonin reduced pain and/or analgesic consumption in some trials and, in a limited number of studies of relatively short duration (i.e. < or = 2 years), the incidence of osteoporotic fractures. A large multicentre 5-year study with adequate statistical power to confirm the effect of intranasal salcatonin on reducing osteoporotic fracture rates in postmenopausal women is currently under way. The intranasal formulation of salcatonin offers a more convenient and better tolerated alternative to the parenteral formulation of the drug which is administered by regular subcutaneous or intramuscular injections. Adverse events associated with the intranasal formulation are generally mild and transient, usually involving local reactions such as nasal discomfort, rhinorrhoea or rhinitis. Thus, for postmenopausal women unable or unwilling to tolerate long term hormone replacement therapy, intranasal salcatonin is an attractive alternative for the management of osteoporosis.

A mechanism for sympathectomy-induced bone resorption in the middle ear

BACKGROUND

Recent investigations have demonstrated a link between sympathectomy and osteoclast-mediated bone resorption. The exact nature of this link, however, is unknown. We hypothesize that substance P, a potent vasoconstrictive neuropeptide found in peripheral sensory fibers, including those innervating bone, is the mediator of this phenomenon. To test this theory, the effects of substance P on in vitro calcium release from cultured neonatal mouse calvaria were assessed. In addition, an in vivo study was conducted whereby gerbils were injected with capsaicin to eliminate substance P-containing fibers before sympathectomy with 6-hydroxydopamine. If the effects of 6-hydroxydopamine were eliminated by prior administration of capsaicin, the role of sensory nerves in sympathectomy-induced resorption would be strongly implicated.

IN VITRO STUDY

Substance P at 10(-8) mol/L was incubated with eight newborn Swiss-Webster mouse hemicalvarial explants and compared with explants incubated in control media alone. The neonatal mice were euthanized at day 3, and their hemicalvaria were preincubated in 2 ml of stock media without treatment for 24 hours at 36.5 degrees C as a stabilization period. After the stabilization period, the stock media were replaced with 2 ml of fresh control media or media containing substance P at 10(-8) mol/L. A similar experiment was performed with the addition of indomethacin at 5 x 10(-7). The explants were then incubated for 72 hours with gassing every 12 hours with a mixture of O2, N2, and CO2. At the end of the 72-hour period, the media were analyzed for calcium content by atomic absorption spectrophotometry and compared by one-way analysis of variance with Bonferroni-corrected post hoc tests.

IN VIVO STUDY

Forty-eight Mongolian gerbils were placed into four groups: group 1 received intraperitoneal injections of 6-hydroxydopamine at 75 micrograms/gm body weight on days 1, 2, 6, 7, and 8; group 2 received identical injections of hydroxydopamine, but 12 hours after receiving subdermal injections of capsaicin at 50 micrograms/gm body weight; group 3 received only subdermal injections of capsaicin; and group 4 received only saline injections to serve as controls. Seven days after treatment, the animals were euthanized, and the ventral wall of each animal's right bulla was resected and quantified for osteoclast number and surface with a computer-based histomorphometry system. Analysis was then made by one-way analysis of variance with Bonferroni-corrected post hoc tests.

RESULTS

The results of the in vitro study revealed that substance P at 10(-8) mol/L (11.05 +/- 3.37 micrograms/ml) induced significant calcium release from cultured neonatal mouse calvaria when compared with control bone incubated in base media alone (0.92 +/- 2.85 micrograms/ml, p < 0.01). The process was completely inhibited by 5.0 x 10(-7) indomethacin. The results of the in vivo study showed 6-hydroxydopamine treatment significantly increased both the osteoclast number (NOc/TL = 3.14 +/- 1.33/mm) and the osteoclast surface (OcS/BS = 16.04% +/- 6.95%) of bone when compared with bone from saline-treated controls (NOc/TL = 1.77 +/- 0.79/mm, p < 0.01; OcS/BS = 8.88% +/- 4.15%, p < 0.01). These 6-hydroxydopamine-induced increases were eliminated, however, in animals pretreated with capsaicin before sympathectomy (NOc/TL = 1.86 +/- 0.68/mm, p > 0.05; OcS/BS = 9.92 +/- 3.73, p > 0.05), whereas treatment with capsaicin alone had no effect when compared with bone from saline-treated controls (NOc/TL = 2.02 +/- 0.50/mm, p > 0.05; OcS/BS = 10.28% +/- 2.62%, p > 0.05). Substance P has thus been shown to induce calcium release from membranous bone in vitro, whereas capsaicin, a substance P-specific sensory neurolytic chemical, eliminates the in vivo osteoclast-inductive effects of 6-hydroxydopamine when given 12 hours before treatment. The results indicate that substance P is capable of inducing resorption and that substance P-containing sensory ne