Immunoreactive calcitonin in the intermediate lobe of the pituitary gland

Analgesia with Epidural Calcitonin in Cancer Patients

We evaluated the analgesic effect of salmon calcitonin (sCT) on 14 patients with intractable cancer pain. The drug was administered by epidural infusion (4–8 bolus administrations in 48 h); the dosage was 100 IU/48 h in 5 patients and 400 IU/48 h in 9 patients. Significant, although limited, pain relief and nocturnal pain relief were obtained; the requirement for conventional analgesic drugs was substantially reduced. The treatment was well tolerated and no side effect was recorded. However, only in 3/14 patients did pain relief result in improvement of mobility, with two patients becoming able to ambulate; no patient experienced absence of pain. In general, the treatment produced only limited benefit and subsequent morphine treatment was required in all instances. Widespread use of epidural sCT in intractable cancer pain is not justified as a routine procedure and more substantial evidence is required to support the clinical utility of such an approach.

60 YEARS OF POMC: Purification and biological characterisation of melanotrophins and corticotrophins

The remarkable conservation of the primary structures and anatomical location of dogfish α-melanocyte-stimulating hormone (MSH), corticotrophin-like intermediate lobe peptide (CLIP) and adrenocorticotrophic hormone (ACTH) compared with mammals reinforced the tissue-specific processing hypothesis of ACTH peptides in the pituitary gland. The cloning of dogfish pro-opiomelanocortin (POMC) led to the identification of δ-MSH and simultaneously revealed the high conservation of the γ-MSH sequence during evolution. These studies have also shown that β-MSH is much less conserved during evolution and in some species is not even processed from β-LPH. Human pro-γ-MSH potentiates the corticosteroidogenic activity of ACTH and peptides generated from its N-terminal, in particular big-γ-MSH, appear to have adrenal mitogenic activity. Human big-γ-MSH (from the zona intermedia) may also cause the adrenache. The review finishes with a cautionary note with regard to the misdiagnosis of the ectopic ACTH syndrome in which partial processing of ACTH can result in large concentrations of α-MSH and CLIP, which can interfere in the performance of two-site immunoassays, and the problem of the correct disulphide bridge arrangement in synthetic N-POMC peptides is also discussed.

Biological role of the pars intermedia in lower vertebrates

The most obvious function of the pars intermedia in lower vertebrates is the secretion of melanocyte-stimulating hormone (MSH) for the purpose of pigmentary control. In some amphibia, elasmobranchs and teleosts, the histological study of the pars intermedia, the radioimmunoassay of pituitary and plasma MSH and the effects of hypophysectomy and of MSH injection suggest that the activity of the pars intermedia is regulated to satisfy the needs of cryptic colour change. MSH secretion is associated with dispersion of melanin granules and with melanogenesis. However, in other teleost species, both the evidence from pituitary cytology and the failure to respond to MSH injection suggest that pigmentary change is not regulated by changes in the plasma titres of MSH. Results discussed here indicate that MSH alone may be inadequate for pigmentary control. Evidence for non-pigmentary functions of the pars intermedia is circumstantial and fragmentary. It is based on cytological observations of altered pars intermedia activity under certain conditions, and on observations of physiological changes that accompany increased melanotropic activity. Such function include effects of plasmas titres of cortisol in teleosts, resistance to adrenaline-induced hyperglycaemia in toads, and effects on neural activity in fish and amphibia. Evidence for pars intermedia involvement in osmoregulation is briefly discussed.

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.

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.

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

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

Calcitonin and beta-endorphin secretion

Calcitonin is a peptide hormone secreted by the C-cells of the thyroid gland. This hormone mainly acts in preventing bone resorption. Furthermore, calcitonin is involved in other biological actions, and in particular it is able to relieve pain independently of its peripheral effects on bone. Here, we examine the possible mechanisms of calcitonin-induced analgesia, with particular regard to the opioid system involvement. Several studies in animals and in humans demonstrate that calcitonin increases plasma beta-endorphin levels, acting at the hypothalamic and/or at the pituitary level, either directly or indirectly, through monoaminergic neurotransmitters. However, this calcitonin-induced beta-endorphin release has not always been observed. These different results are discussed, and a possible implication of sex and/or calcitonin dose employed has been examined. We conclude that the analgesic effects of calcitonin are multifactorial, and beta-endorphin plays its own specific role.

Immunoreactive "calcitonin-like" material in heroin addicts: varying reactivity with different antibodies

High levels of immunoreactive calcitonin (iCT) in the blood of heroin addicts were previously reported. As it is well known that multiple forms of calcitonin exist in the blood and in tissues, the purpose of the present study was to investigate the immunological nature of the CT-like immunoreactive material found in the blood of these subjects. We investigated 25 addicts, who had been using heroin for more than one year and were hospitalized for a 2 week detoxication program. Blood samples were drawn at the start of the program (when the subjects were still on heroin) and after 5 and 12 days of abstinence from heroin. Twenty-five healthy subjects served as controls. We used 2 commercial RIA kits, calibrated against the same reference material (WHO 70-234), but employing different antisera. One antiserum substantially confirmed the previous findings of increased levels of calcitonin during heroin use, but the other seemed to exclude any change in the hormone concentrations. This suggests that the "calcitonin like" material found in heroin addicts contains some epitopes similar to those found in the calcitonin standard which are detected by the first antiserum. However it lacks other epitopes which are also present in calcitonin standard and which are recognized by the second antiserum. Therefore, this substance seems to be different from the standard human calcitonin 1-32. A possible involvement of a calcitonin analogue (precursor or metabolite) in the biochemical changes occurring during chronic opiate use is suggested.

Intranasal salmon calcitonin. A review of its pharmacological properties and potential utility in metabolic bone disorders associated with aging

Salmon calcitonin, a polypeptide hormone secreted by the parafollicular C cells of the thyroid gland, lowers serum calcium levels by decreasing bone resorption and renal tubular calcium reabsorption. An analgesic action, possibly mediated via beta-endorphins, is also evident. In the past, parenteral formulations of salmon calcitonin have been used in the management of metabolic bone disorders, but their routine use has been limited by the inconvenience of this route of administration and by poor tolerability. The development of an intranasal preparation of salmon calcitonin will provide a more convenient means of administering the drug. In clinical trials published to date intranasal salmon calcitonin has been effective and well tolerated in small numbers of recently postmenopausal women at risk of developing osteoporosis, and in patients with established osteoporosis, Paget's disease, or osteoporosis secondary to corticosteroid usage, multiple myeloma or ovariectomy. For periods of up to 2 years the drug reduces bone resorption and improves bone architecture, relieves pain and increases functional status. Further research is needed to confirm longer term efficacy (in particular, effects on fracture rate), optimal dosage schedules and the role of intermittent and combination treatment regimens.

Subarachnoid and epidural calcitonin in patients with pain due to metastatic cancer

Nine patients with metastatic cancer who had pain refractory to traditional treatments received a subarachnoid injection of salmon calcitonin. Eight of the nine patients reported pain relief after subarachnoid injection varying from 1 hr to 5 days. Four of the responding patients subsequently received an epidural injection of salmon calcitonin, and two of these patients reported pain relief. Although many patients experienced pain relief, nausea and vomiting appeared to be a significant side effect, occurring in seven out of nine patients.

Salmon calcitonin given by nasal spray or by injection does not increase beta-endorphin levels in normal men

It has been suggested that the analgesic action of calcitonin (CT) might involve a stimulation of beta-endorphin (beta-EP) release. To verify whether salmon CT modifies the circulating levels of beta-EP, and whether the route of administration plays any role in this response, we have studied 10 healthy male volunteers, aged 30-40 yr. Each of them was studied on 4 different days, after administration of placebo or salmon CT (100 UI) by the intravenous, intramuscular and nasal route, in random order. Ionized calcium tended to decrease, especially after intravenous CT, but there was no change in plasma beta-EP levels, regardless of the route of administration. It is therefore unlikely that circulating beta-EP mediates any biological effect of CT.

Antagonistic behavioral effects of calcitonin and amphetamine in the rat

Using an automated testing apparatus, the hypermotility induced by amphetamine had previously been found to be inhibited by intracerebroventricular (ICV) administration of salmon calcitonin (CT). The present study used a computer-supported direct observational method to characterize further the interactions of CT and amphetamine. After treatment with amphetamine (1.5 mg/kg, IP), the incidence of rearing, nose poking, and locomotion was reduced in rats that were pretreated with 85 pmol salmon CT ICV; the incidence of sniffing and grooming remained unchanged. CT-induced dyskinesia, a unique consequence of central CT treatment, was attenuated but not abolished by administration of amphetamine. These results support the premise that a compound with receptor recognition characteristics similar to those of salmon CT may act as a neurotransmitter-modulator in the central nervous system.

Motor effects of calcitonin administered intracerebroventricularly in the rat

In rats treated with salmon calcitonin (CT) administered intracerebroventricularly (i.c.v., 85 or 8.5 pmol), spasmodic body movements, hopping and tail jerks, collectively termed dyskinesia, appeared within 1 h of administration and persisted for at least 24 h. In addition, spontaneous grooming, rearing and locomotion occurred less often in CT-treated rats than in vehicle-injected animals, while the incidence of both sniffing and nose poking remained essentially unchanged. The CT failed to displace either [3H]dopamine or [3H]spiperone from striatal membranes, and the behavioral effects were not blocked by haloperidol or SCH 23390, suggesting that the peptide did not directly affect dopamine receptors. The dyskinesia was not blocked by scopolamine, atropine, muscimol, diazepam or ketanserin. These data are consistent with the hypothesis that a compound with recognition characteristics similar to those of salmon CT may function as a neurotransmitter-modulator in the central nervous system.

Immunoreactive calcitonin in brain regions and pituitary of sheep

In this study we have investigated the presence of immunoreactive calcitonin in the central nervous system and pituitary of sheep. The calcitonin concentrations were determined radioimmunologically by two different antibodies. We have demonstrated calcitonin in extracts of areas of the central nervous system, whole pituitary, thyroid gland and plasma of 21 sheep. The concentrations were (ng/g wet weight, mean values +/- SE): thyroid 16.0 +/- 4.4, pituitary 2.03 +/- 0.34, reticular formation 1.64 +/- 0.25, substantia nigra 1.53 +/- 0.46, dentate nucleus 1.11 +/- 0.27, putamen 1.05 +/- 0.35, hippocampus 0.97 +/- 0.17, fornix 0.96 +/- 0.15, anterior thalamus 0.92 +/- 0.28, mammillary body 0.88 +/- 0.12, cerebellum 0.86 +/- 0.09, caudate nucleus 0.84 +/- 0.11, posterior hypothalamus 0.83 +/- 0.19, epiphysis 0.75 +/- 0.25, thalamus centralis 0.71 +/- 0.10, almond nucleus 0.69 +/- 0.16, medulla oblongata 0.67 +/- 0.15, anterior hypothalamus 0.66 +/- 0.20, precentral gyrus 0.66 +/- 0.16, globus pallidus 0.63 +/- 0.31, postcentral gyrus 0.36 +/- 0.08 and plasma (ng/ml) 0.058 +/- 0.013. Our results demonstrate that immunoreactive calcitonin is present in the central nervous system (CNS) of sheep, compatible with a neurotransmitter function for this hormone.

Alternative RNA processing events in human calcitonin/calcitonin gene-related peptide gene expression

Two mRNAs generated as a consequence of alternative RNA processing events in expression of the human calcitonin gene encode the protein precursors of either calcitonin or calcitonin gene-related peptide (CGRP). Both calcitonin and CGRP RNAs and their encoded peptide products are expressed in the human pituitary and in medullary thyroid tumors. On the basis of sequence comparison, it is suggested that both the calcitonin and CGRP exons arose from a common primordial sequence, suggesting that duplication and rearrangement events are responsible for the generation of this complex transcription unit.

A preliminary study on the use of calcitonin in clinical psychopathology

After having reviewed the properties of calcitonin (Ct), a hormone involved in calcium-phosphate metabolism and bone turnover, mention is made of the effects of Ct at the level of the CNS and its role as a neuromediator interfering with endorphins, prolactin, dopamine and the Ca concentration of the CSF. Overall's rating scale was used to evaluate the effects of synthetic salmon Ct in nine subjects with severe depression syndromes refractory to normal therapy. The study demonstrated statistically significant improvements of the major symptoms (behavioural excitation, depression, agitation, anxiety and affectivity). The favourable results justify broader and more detailed studies involving the relationship between Ct and psychopathology.

Production of a novel neuropeptide encoded by the calcitonin gene via tissue-specific RNA processing

Alternative processing of the RNA transcribed from the calcitonin gene appears to result in the production of a messenger RNA in neural tissue distinct from that in thyroidal 'C' cells. The thyroid mRNA encodes a precursor to the hormone calcitonin whereas that in neural tissues generates a novel neuropeptide, referred to as calcitonin gene-related peptide (CGRP). The distribution of CGRP-producing cells and pathways in the brain and other tissues suggests functions for the peptide in nociception, ingestive behaviour and modulation of the autonomic and endocrine systems. The approach described here permits the application of recombinant DNA technology to analyses of complex neurobiological systems in the absence of prior structural or biological information.

Pituitary immunoreactive calcitonin-like material: lack of evidence for cross-reactivity with pro-opiomelanocortin

In mammals, calcitonin (CT) is synthesized, stored, and secreted by intrathyroidal C cells. Several reports have suggested the presence of immunoreactive CT in the pituitary gland. We have studied the rat pituitary gland using a radioimmunoassay for CT and have also found immunoreactive CT-like material. Assay of extracts of whole rat pituitary glands was performed using a radioimmunoassay for human CT, which gave identical dilution curves with synthetic human CT (hCT), synthetic rat CT (rCT), and mouse and rat thyroid extracts, but not with a variety of other pituitary and hypothalamic peptides. Immunoreactive CT (iCT) content of extracts of whole pituitary glands ranged from 6 to 72 pg/mg wet weight of tissue (60-840 pg/whole pituitary gland), whereas iCT was not measureable (less than 5 pg/mg tissue) in similar extracts of hypothalamus and cerebral cortex. Gel filtration studies of pituitary extracts showed a peak of iCT, which eluted with 125I-rCT and diluted in parallel with rCT. To investigate whether the pituitary iCT was related to pro-opiomelanocortin, extracts of ACTH-producing AtT20/D16 cells from mice, which contain the ACTH precursor in large quantities, were examined and no iCT was found. Immunohistochemical studies of rat pituitary glands with peroxidase-antiperoxidase and immunofluorescent techniques showed positive staining for CT in cells in the pars anterior, but not in the pars intermedia of pars nervosa; this staining was not eliminated when the antiserum was absorbed with CT under conditions that completely obliterated staining of rat thyroid glands. Double staining demonstrated essentially two distinct populations of cells, one positive for CT and another positive for ACTH, with less than 1% of the cells positive for both ACTH and CT. Immunoreactive CT-like material was present in the pituitary glands of rats thyroparathyroidectomized 18 days before they were killed, but was diminished. Biosynthetic labeling in vitro of rat pituitary glands with 3H-leucine showed incorporation into prolactin; there was no incorporation into CT. No in vitro secretion of iCT by whole rat pituitary glands either basally or after high K+ stimulation was observed. We conclude that: (1) a substance that has certain immunologic and size characteristics of CT is present in minute amounts in the pituitary gland of rats; (2) this material is not a part of the ACTH precursor; and (3) positive immunohistochemical staining in pituitary glands may not be specific for authentic CT.

Extraction of a substance with calcitonin-like immunoreactivity from pituitary glands of intact and thyroidectomized rats

We have previously demonstrated the presence of calcitonin (CT)-like immunoreactivity in the pituitary glands of a number of vertebrate species. Subsequent work by ourselves and others has confirmed this finding by immunohistology and radioimmunoassay (RIA) of pituitary extracts. However, no data have been reported on the site of biosynthesis of the CT-like pituitary peptide, or the relationship of pituitary levels of the substance to experimental alterations of systemic CT levels. In the present study, we measured the content of CT-like peptide in rat pituitaries by using gel filtration chromatography and an RIA, which recognizes rat and human calcitonin. The CT-like peptide has an elution position on gel filtration similar to that of rat and human calcitonin. Its RIA binding appears indistinguishable from that of rat thyroidal CT. Various conditions for extraction were evaluated, and homogenization in acetic acid at 100 degrees C gave the best results. The CT-like content of rat pituitaries was generally 75-125 pg/gland. Presence of CT-like peptide in rat pituitaries was not abolished by prior thyroidectomy. We conclude that the CT-like pituitary peptide is not synthesized in the thyroid, but is similar to thyroidal CT in the characteristics studied.

Simultaneous immunohistochemical localization of gastrin releasing peptide (GRP) and calcitonin (CT) in human bronchial endocrine-type cells

Formalin-fixed paraffin-embedded sections of fetal and adult human lungs were examined for the localization of gastrin releasing peptide (GRP) and calcitonin (CT) in bronchial endocrine-type cells with the indirect immunoperoxidase method. In fetal lungs, the appearance of CT was much later than that of GRP, and CT-containing cells were less frequent than GRP-containing cells which, in later fetal life, formed "neuroepithelial bodies (NEB)". NEB revealed little CT immunoreactivity. The serial section technique demonstrated that all CT immunoreactants in fetal and neonatal lungs were present within GRP-containing cells. An increase of CT immunoreactivity in GRP-containing cells was observed in perinatal lungs. The lung of a neonate who died of hyaline membrane disease contained the most abundant CT immunoreactants. In adult lungs, CT immunoreactivity was identified in some GRP-containing cells but cells containing only GRP or CT were also present. Cells containing both hormones occasionally formed hyperplastic foci in the bronchi of fibrotic lungs. Most cells of pulmonary tumorlets consistently showed GRP immunoreactivity, but the number of CT immunoreactive cells in them varied greatly.

Does calcitonin modulate anterior pituitary hormone secretion?

In a group of 5 healthy subjects salmon CT (sCT) infusion was unable to induce significant variations on basal secretory levels of LH, FSH, PRL and TSH. In a second group of 5 normal subjects, GnRH and TRH tests were performed both during sCT and saline infusion; a clear inhibition of TSH-stimulated levels and of PRL area was documented, while gonadotropin secretion was not significantly affected by sCT infusion. These results suggest that CT effect might be attributed to a change in intracellular calcium of pituitary cells; however the different behavior between TRH-and GnRH-stimulated hormones might be due to a different hormonal release mechanism. Furthermore the widespread recognition of CT-like immunoreactivity in adenohypophysis and in portions of the central nervous system suggests that CT may be a neurotransmitter or paracrine regulator.

Ability of calcitonins to alter food and water consumption in the rat

Synthetic salmon calcitonin (sCT) given SC (30 MRC U/kg) or ICV (1.4 U, 300 ng) inhibited 24-hr food consumption in the rat by 50-100%. Furthermore, ICV doses of sCT ranging from 75 ng (0.35 U) to 300 ng (1.4 U) lowered both food and water intake in a dose-dependent manner. Use of various forms of CT give an apparent order of potency of salmon greater than porcine greater than or equal to human with sCT being at least 40 fold more potent than the mammalian forms. Measurement of food and water intake over a brief (30-90 min) period showed that ICV sCT was effective in reducing food and water consumption regardless of whether it had been given 1, 12, or 23 hr previously. Daily administration of sCT for 5 days caused marked suppression of food and water intake for 2 days; thereafter, consumption returned toward normal, becoming equivalent to vehicle injected controls by day 3 or 4 despite continued daily injections of sCT. The results show that CT can act centrally to modify certain types of behavior and are of special interest since CT-like peptides have been described in the pituitary and hypothalamus and since CT receptors have been reported in hypothalamic and other brain regions.

Response of rat brain to calcitonin alteration

Endogenous calcitonin was altered in rats by thyroparathyroidectomy, followed by supplementation with thyroxine and calcium. As a result, a reduction in the content of 5-hydroxytryptamine in the brain together with an increase in the concentration of tryptophan in the plasma were observed. The changes were accompanied by a diminution in the activity of both choline acetyltransferase and acetylcholinesterase in the cerebral hemispheres. The results are consistent with those produced by exogenous hormone and suggest that calcitonin probably plays a role in the regulation of 5-hydroxytryptamine levels in the brain.

Concomitant secretion of calcitonin, beta-endorphin and ACTH from medullary thyroid carcinoma in vivo and in vitro

The present study was performed to investigate the possible synthesis of a common precursor molecule for calcitonin (CT), adrenocporticotropin (ACTH) and beta-lipotropin (beta-LPH)/ beta-endorphin (beta-EP) by the human medullary thyroid carcinoma (MTC). In a patient with MTC but without Cushing's syndrome, the response of plasma CT, ACTH and cortisol levels to a calcium infusion, lysine vasopressin (LVP) and dexamethasone were measured. A parallel increase of these hormones in response to calcium and LVP was seen, while there was a paradoxical increase of CT during dexamethasone infusion. Incubation of MTC fragments obtained at surgery showed a significant correlation of the secretion of CT, ACTH and beta-LPH/ beta-EP in response to calcium, LVP and dexamethasone. The concomitant release of these hormones in vivo and in vitro could be compatible with the synthesis of a common precursor molecule for CT, ACTH and beta-LPH/ beta-EP in MTC, although this was not substantiated by gel-chromatography of the tumor extract. Corticotropin releasing factor, a regulator of the normal processing of pro-opiococorticoid precursor molecule in the anterior pituitary gland, is also able to activate ACTH, beta-LPH/ beta-EP and calcitonin secretion from the malignant C-cell of the thyroid.

Presence of immunoreactive calcitonin in the hypothalamus and pituitary lobes of rats

We have found calcitonin-like immunoreactive material in extracts of hypothalami from six-month old, male rats. The level of this immunoreactivity, 0.21 ng/hypothalamus, is substantial considering out lower limit of detection of 0.006 ng of rat calcitonin. However, the hypothalamus contains less calcitonin-like immunoreactive material than either the anterior lobe (1.16 ng) or neurointermediate lobe (0.81 ng) of the pituitary. Taken together these three sources of calcitonin-like immunoreactive material contain less than one thousandth the immunoreactivity found in the thyroid. The exact nature of the calcitonin-like immunoreactive material found in these extrathyroidal sites and its physiological role, if any, remain to be discovered. The recent report of the occurrence of calcitonin receptors in the hypothalamus and other brain regions in conjunction with our finding of calcitonin-like immunoreactivity in the hypothalamus suggests that calcitonin-like molecules may be active within the brain.

Immunoreactive calcitonin in the central nervous system of the pigeon

To determine whether calcitonin (CT) is present in avian central nervous system (CNS), as it has been recently found in the CNS of other species, we studied extracts of pigeon (Columbia livia) brain by immunochemical methods. A sensitive and specific radioimmunoassay for salmon CT was used together with gel filtration and high performance liquid chromatography (HPLC). Extracts of hypothalamus contained 31.5 +/- 9.65 ng/g wet weight as salmon CT-like immunoreactivity while extracts of midbrain and brain stem contained 17.0 +/- 5.00 and 2.85 +/- 2.1 ng/g wet weight respectively. Extracts of whole pituitary gland, other areas of the CNS and vazrious peripheral tissues were below the detection limits of our assay, but salmon CT-like immunoreactivity was present in ultimobranchial gland (UBG), thyroid gland and lung tissue extracts. On Sephadex G-50 chromatography extracts of hypothalamic, midbrain, UBG and thyroid gland gave an immunoreactive peak which co-eluted with synthetic salmon CT. However, on HPLC the material in pigeon hypothalamus, midbrain, UBG and thyroid gland eluted in an identical manner when compared to each other but the major peak was 2 ml after that of synthetic salmon CT. These results clearly show that a salmon CT-like immunoreactive molecule is present in pigeon hypothalamus and midbrain, in addition to its main locations in the UBG and thyroid gland.

The endocrinology of the opiates and opioid peptides

Since the isolation of the enkephalins five yr ago, there has been an explosive increase in knowledge concerning the effects of the opiates and opioid peptides. This review deals with the interactions of opiates with the endocrine system in rat and man. The opioid peptides have been demonstrated to exert a variety of effects on pituitary hormone secretion in rat and man. In the rat, opiates stimulate growth hormone, prolactin and ACTH release and inhibit the release of the glycoprotein hormones. In man, the physiologic role of the endogenous opiates appears to be involved predominantly in ACTH and gonadotrophin regulation. Opiate effects are mainly exerted at the level of the hypothalamus but further modulating effects may occur at the pituitary and at end-organs. Opiate-induced hormonal effects appear to be mediated through dopaminergic and/or serotonergic mechanisms. Recent studies have also suggested a possible local neuromodulatory role for the opioid peptides in the control of carbohydrate metabolism and reproductive processes.

Chemistry and biosynthesis of pro-opiomelanocortin. ACTH, MSH's, endorphins and their related peptides

Studies of lipotropins, melanotropins and endorphins on one hand, and of adrenocorticotropin on the other, has given rise to the concept of a multipotent precursor molecule recently renamed proopiomelanocortin. The preferential sites of cleavage of the precursor to produce its biologically active components are made of pairs of basic amino acid residues as described for the biosynthesis of beta-MSH and pro-insulin. Such structural feature is also found in other pro-hormone molecules. Pulse chase experiments and secretory studies carried out in both anterior and intermediate lobes of rat pituitary glands revealed the transformation of different forms of the precursor into different end-products, the anterior lobe producing preferentially ACTH and beta-LPH while the intermediate produces mainly the alpha-MSH and beta-endorphin. The multiple forms of precursors seem to differ in their carbohydrate content although at least two different gene products are still possible. The presence of similar peptides in the hypothalamus makes it highly probable that neuropeptides are biosynthesized with similar process. Thus the model of beta-LPH precursor, proposed as early as in 1967, is now applicable to the biosynthesis of all other neuropeptides. Major advances in this field are expected in the 1980s.

Immunoreactive calcitonin in cerebrospinal fluid of man

We have detected immunoreactive calcitonin (iCT) in the cerebrospinal fluid (CSF) of normal individuals. Using an antibody with midportion recognition, the mean +/- S.D. of the cerebrospinal iCT in 27 normal subjects was 28 +/- 14 pg/ml. The mean serum iCT was 89 +/- 68 pg/ml, the CSF/serum distribution ratio being 0.31. There were no significant correlations between CSF iCT or serum iCT and the calcium, magnesium, phosphate, sodium, potassium or chloride in the CSF or serum. Although there was a trend for serum iCT values to be related to CSF iCT values, it did not attain statistical significance. The demonstration that the CSF contains iCT may have important physiologic implications, and its measurement offers a useful parameter to study its effects on calcium metabolism and/or other aspects of brain function.

Immunoreactive calcitonin in the rat anterior pituitary gland and its localization in thyrotrophs

The distribution of those cells in the anterior pituitary gland of the rat which stain immunohistochemically with rabbit anti-human calcitonin serum has been examined. Immunoreactive cells were confined primarily to the ventral surface of the gland and possessed both a distribution and morphology distinct from the corticotrophs. Staining of serial thin sections with rabbit anti-rat TSH-subunit serum resulted in an immunoreaction in those cells that stained for calcitonin. However, not all the thyrotrophs gave a positive immunoreaction for calcitonin. It is concluded from this study that it is inappropriate to attribute calcitonin as being part of the 31K-dalton precursor for adrenocorticotropin, a hypothesis that was proposed earlier. In the immunohistochemical reaction with anti-calcitonin serum, it was found that relatively high concentrations of antigen (500 micrograms/ml) were required in absorption experiments in order to inhibit staining. Furthermore, the staining of thyrotrophs with the anti-calcitonin serum was inhibited after preadsorption of the primary antiserum with excess rat beta-TSH (1000 micrograms/ml). Because of these immunochemical characteristics, it is questionable whether the calcitonin-like material observed in the rat pituitary gland is chemically identical to that of thyroidal calcitonin.

Reactivity of ACTH and synthetic ACTH peptides with antisera to human calcitonin

We studied reactivity of highly purified pituitary hormones in our human calcitonin (hCT) radioimmunoassay (RIA) which can detect 1 pg of hCT. ACTH at doses of greater than 1 microgram of peptide per RIA tube reacted in the hCT assay, as did beta-endorphin (beta EPH) at a dose of 10 micrograms per tube. No reactivity was observed with comparable concentrations of all other known pituitary hormones. ACTH also reacted at doses greater than 1 microgram per tube with 7 other hCT antisera which recognized differing antigenic determinants in the calcitonin molecule but it was not reactive with 2 antisera against porcine calcitonin or 2 antisera against salmon calcitonin. This slight degree of cross-reactivity of hACTH and beta EPH in the hCT RIA cannot account for the presence of immunoreactive CT in pituitary glands. Nevertheless, antisera used for the localization of peptides must be rigorously tested for the existence of cross-reactivities with other possible substances, especially if such antisera detect the peptide in unexpected tissues.

Elevation of calcitonin immunoreactivity in the pituitary and thyroid glands of genetically obese rats (fa/fa)

This paper contains the first demonstration of quantitative changes in the levels of calcitonin-like immunoreactivity in the pituitary. The concentration of calcitonin-like material in lean Zucker rats (?/+) was 0.42 +/- 0.09 ng/mg wet weight of pituitary. The pituitaries of obese rats (fa/fa) contained significantly greater levels (1.56 +/- 0.56 ng/mg wet weight). This 271% increase represents the first indication that pituitary calcitonin-like material may have a physiological role in genetically obese rats. Thyroidal calcitonin also elevated in the obese (111%). These large elevations in the calcitonin content of the glands of obese rats were not accompanied by significant elevations of calcitonin in the blood. This suggests that obese rats have problems with mechanisms for the release of calcitonin into the blood and might not be able to combat hypercalcemia as effectively as leans. However, this hypothesis remains to be tested.