Immunoreactive calcitonin in cerebrospinal fluid of man

Calcitonin gene-related peptide and calcitonin in the CSF of patients with dementia and depression: possible disease markers

Cerebrospinal fluid (CSF) was obtained from 32 patients with dementia, 19 healthy controls that were age-matched with the dementia patients, and 29 DSM-IV major depression patients and calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) and calcitonin-like immunoreactivity (CT-LI) measured by RIA. CGRP-LI was lower in the dementia group compared to both the controls and depressed patients (P<.01) after covarying out sex and age. CT-LI was decreased in the dementia and depressed patients (P<.05) compared to the controls. A positive relationship between CGRP-LI and CT-LI was found in dementia. A logistic discriminant analysis with calcitonin gene-related peptide (CGRP) and log calcitonin (CT) predicting diagnosis (three classes) revealed a significant overall fit (chi2 = 18.08, P = .0011), with an effect test showing contributions of both independent variables: CGRP (chi2 = 10.03, P<.007), log CT (chi2 = 8.63, P = .013). In dementia, both CGRP-LI and CT-LI were decreased and their concentration ratio did not differ from that in controls, likely reflecting a general neuronal loss. Alternatively and more speculatively, but theoretically possible, expression of the alpha-CGRP/CT gene may be affected in dementia. In contrast, in depression, CT-LI but not CGRP-LI was decreased and the CGRP/CT concentration ratio was increased, which is consistent with a possibility of an altered splicing process favoring CGRP mRNA.

Physiological neuroendocrinology of peptides, steroids and other hormones in cerebrospinal fluid

Cerebrospinal fluid acts as a conduit in neuroendocrine regulation. Valid assessment of normal cerebrospinal fluid levels of peptides, steroids and other hormones requires clarification of reference concentrations in control patients and normal volunteers. Awareness of factors which may alter neuronal activity and, in turn, the relative composition of cerebrospinal fluid constituents is essential to the accurate sampling and hormonal analysis of cerebrospinal fluid.

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.

Calcitonin-immunoreactive cells are present in the brains of some cyclostomes

In the brains of four species of cyclostomes (two species each of lampreys and hagfishes), immunoreactive calcitonin-producing cells (iCT cells) were located immunohistochemically by the peroxidase-antiperoxidase method using anti-salmon calcitonin antiserum. In the case of both the adults and the ammocoetes of the brook lamprey (Lampetra reissneri) which lives in freshwater throughout its life, iCT cells were found in two distinct areas: in the pars ventralis hypothalami of the diencephalon and in the torus semicircularis of the mesencephalon. The iCT cells in the diencephalon are classified as bipolar nerve cells, and those in the mesencephalon are classified as multipolar nerve cells. In both the anadromous and catadromous arctic lamprey (Lampetra japonica), iCT cells were present only in the diencephalon, and those were bipolar nerve cells. There seemed to be no differences in the numbers and the immunostainability of the iCT cells, despite the different environments inhabited by the lampreys. In the hagfishes (Eptatretus burgeir and Paramyxine atami) that inhabit seawater throughout their lives, iCT cells were also found only in the diencephalon, although they were very few in number and exhibited poor immunostainability.

Intracerebroventricular administration of calcitonin enhances glucose-stimulated release of insulin

Intracerebroventricular (i.c.v.) administration of salmon calcitonin (500 ng) augmented glucose-stimulated release of insulin in rats. Vagotomy increased this enhancement effect of i.c.v. calcitonin significantly, whereas peripheral atropine treatment did not change it. Adrenal catecholamines did not participate in the centrally mediated insulinotropic effect of calcitonin since acute adrenalectomy did not modify the enhancement effect of i.c.v. calcitonin. Destruction of the sympathetic ganglia by neonatal treatment with 6-hydroxydopamine abolished the enhancement effect of i.c.v. calcitonin, which suggests that the sympathetic nervous system participates in the central action of calcitonin to enhance glucose-stimulated release of insulin.

Pituitary cells secrete calcitonin in the reverse hemolytic plaque assay

Rat pituitary cells were evaluated in the reverse hemolytic plaque assay for calcitonin (CT) secretion. The secretion of CT could be demonstrated by the formation of hemolytic plaques around single pituitary cells when a specific CT antibody was used. Approximately 0.1 percent of the cells secreted CT in the basal state. Phorbol stimulated CT secretion by up to 25-fold. The diameter of the hemolytic plaques around pituitary cells from genetically obese (Zucker) rats was significantly greater than normal rats (24 versus 37 microns). This study demonstrates that pituitary cells secrete CT and that the secretion may be regulated by pharmacological agents (phorbol) and physiological signals (obesity).

Calcitonin as a feeding suppressant: localization of central action to the cerebral III ventricle

Calcitonin suppresses food and water intake. To further study this effect of calcitonin, rats were subjected to various intra-cerebroventricular (ICV) applications of calcitonin. The results show: (1) Intra-third ventricular (III-ICV) infusion of calcitonin dose-dependently decreased food intake with short- and long-term effects; (2) Potency was decreased by using non-siliconized materials; (3) Potency decreased with age of rats; (4) Infusion into the aqueduct and cisterna magna decreased short- and long-term food intake less than III-ICV administration; (5) Aqueduct obstruction did not affect feeding suppression by III-ICV calcitonin. Aqueduct obstruction did not affect dipsogenic response to III-ICV infusion of angiotensin II; (6) Results of water intake and food to water intake ratios suggest a greater calcitonin effect on food intake than on water intake. The evidence suggests that the hypothalamus is a main locus for suppression of food intake by ICV administered calcitonin.

Tumor markers in patients with lung cancer

The most examined tumor markers in lung cancer patients are CEA, hormonal peptides, and some neurogenic enzymes in small cell carcinoma. Calcitonin, ACTH, ADH, CEA, neurophysin, oxytocin, beta-endorphin, neuron-specific enolase, and CK BB are elevated in serum specimens in 25-75% of cases of small cell carcinoma. The level of these markers is related to the stage of the disease in groups of patients; elevated pretreatment levels decrease with tumor regression. Marker levels are not valid in defining the tumor load and the presence of disease in the individual patient. It has not yet been documented that the markers can be used for clinical decisions on antineoplastic therapy. A recent development is the finding that measurement of CSF and plasma concentrations of ADH, calcitonin, CK BB, bombesin, and neuron-specific enolase may contribute in the diagnosis of CNS metastases including meningeal carcinomatosis.

Calcitonin-induced anorexia in rats: evidence for its inhibitory action on lateral hypothalamic chemosensitive neurons

Effects of a synthetic derivative of eel calcitonin, [Asu1,7]ECT on feeding behavior, and its direct action on the neuronal activity of lateral hypothalamic area (LHA) were studied in rats. Food intake was significantly reduced in a dose-dependent manner after intra-third ventricular injection of [Asu1,7]ECT (0.2-1.0 U/rat). The neuronal activity of LHA neurons, especially the glucose-sensitive neurons, was inhibited by electrophoretic application of [Asu1,7]ECT. The inhibition was accompanied by a hyperpolarization of the membrane by about 5-7 mV with an increase in the membrane resistance (5.0-8.7%). This effect was also shown to be independent of noradrenergic or serotonergic mechanisms. Phosphodiesterase inhibitors, such as 3-isobutyl-1-methylxanthine and papaverine augmented the inhibitory response, whereas nicotinic acid blocked it. These results suggest that the anorexia caused by [Asu1,7]ECT is mediated through a direct inhibition of chemosensitive neuronal activity in the LHA, caused by an increase in the intracellular level of cyclic 3',5'-adenosine monophosphate.

Effects of calcitonin and CGRP alone or in combination on food intake and forestomach (reticulum) motility in sheep

The effects of intracerebroventricular (ICV) and intravenous (IV) administration of calcitonin and calcitonin gene-related peptide (CGRP) on feeding behavior and reticular motility were investigated in sheep. ICV calcitonin at a dose of 2 to 200 mU/kg reduced, in a dose-related manner, the immediate (0-60 min) food intake. The daily food intake was also significantly (p less than 0.05) decreased for doses up to 20 mU/kg, and the frequency of reticular contractions during the first hour of eating was decreased by 27.9%. Calcitonin at the highest IV dose (200 mU/kg) did not affect feeding behavior or reticular motility. In contrast, CGRP given ICV did not affect the first 3 hour period of food intake, while a significant increase (27.8%) in daily food intake was observed at a dose of 20 ng/kg despite immediate inhibitory effects on reticular frequency. No effect on feeding behavior and forestomach motility was noticed for a 25 times higher dose IV administered. Furthermore, CGRP given ICV (100 ng/kg) did not antagonize the immediate anorectic effects of calcitonin (200 mU/kg), although it delayed commencement of rumination and partially restored the daily food intake. These results suggest that calcitonin and CGRP play opposite roles in the central control of food intake in sheep, probably by acting on different brain structures, yet have a similar effect on reticular motility.

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.

Inhibitory effects of intrahypothalamic injection of calcitonin on TRH-stimulated gastric acid secretion in rats

Effects of the peripheral and central administration of porcine (PCT) and salmon (SCT) calcitonin on the gastric acid secretion stimulated by various secretagogues were studied in the perfused stomach of anaesthetized rats. The intraperitoneal administration of PCT and SCT inhibited gastric acid secretion stimulated by thyrotropin-releasing hormone (TRH) and 2-deoxy-D-glucose, but neither bethanechol nor tetragastrin. The intracerebroventricular PCT and SCT blocked TRH-induced acid secretion. The intrahypothalamic injection of PCT and SCT reduced the acid secretion stimulated by the intrahypothalamic administration of TRH. The present study indicates that PCT and SCT may in part suppress gastric acid secretion due to an interaction with TRH in the hypothalamus.

Central effects of growth hormone-releasing factor (GRF) on intestinal motility in dogs: involvement of dopaminergic receptors

The effects of intracerebroventricular (ICV) and intravenous (IV) administration of human pancreatic growth hormone-releasing factor (hpGRF) on gastro-intestinal motility were examined in fasted and fed conscious dogs equipped with chronically implanted strain-gauges on the antrum and the jejunum. During the fasted state, hpGRF injected ICV at 0.1 micrograms . kg-1 or IV at 0.5 micrograms . kg-1 did not affect the cyclic occurrence of the migrating motor complex (MMC). This pattern was normally disrupted for 8-10 hours by a daily standard meal. Injected ventricularly (0.1 micrograms . kg-1) but not intravenously (0.5 micrograms . kg-1) 10-15 min after the daily meal, hpGRF significantly reduced (p less than 0.01) the duration of the jejunal fed pattern (2.0 +/- 1.4 vs. 8.4 +/- 1.1 hours for control) but not that of the stomach. This effect persisted when hpGRF (0.1 micrograms . kg-1 ICV) was administered after indomethacin (2 mg . kg-1 IM), naltrexone (0.1 mg . kg-1 IV) or domperidone (1 mg . kg-1 IV) but was abolished by a previous IV injection of metoclopramide (1 mg . kg-1). It was concluded that hpGRF is able to act centrally to control the pattern of jejunal motility in fed but not in fasted dog, its effect being probably mediated through dopaminergic pathways.

Permeability of the blood-brain barrier to neuropeptides: the case for penetration

Evidence that peptides can cross the blood-brain barrier (BBB) is reviewed. Penetration is suggested by the observations that blood levels correlate with cerebrospinal fluid levels for many peptides and that peripheral administration of peptides results in effects on the CNS. Passage is confirmed by experiments involving administration of a peptide (immunoactive or radioactive) in one compartment and identification of its appearance in the other, supported by such methods as selective labeling, cross-reactivity with highly specific antibodies, and chromatography. The degree of passage varies among peptides and their analogs. The major route of passage is probably by a non-competitive, non-saturable mechanism, wih the physicochemical characteristics of the peptide (e.g. lipophilicity, charge, molecular weight, and protein binding) determining the degree of passage. A competitive transport mechanism also exists for some peptides. Penetration of the BBB via large pores or by pinocytosis does not appear to be of major importance for peptides. Permeability of the BBB to peptides, but not to the larger iodinated albumin, is affected by intraperitoneal administration of aluminum, apparently by an increase in the permeability of the membrane to lipophilic materials.

Pentagastrin promotes prolactin release in patients with medullary carcinoma of the thyroid

Both calcitonin and gastrin have been found in the mammalian central nervous system, including the pituitary. Following a pentagastrin infusion in several patients with medullary carcinoma of the thyroid, we noted a coincident increase in plasma calcitonin and prolactin (PRL) levels. In order to evaluate further the influence of pentagastrin on human PRL release, a pentagastrin infusion was administered to 13 patients with active medullary carcinoma of the thyroid (MTC), eight subjects with inactive MTC, eight family members without MTC, and ten normal subjects. Plasma mean +/- SE PRL levels were significantly (P less than 0.01) increased in the active MTC patients from 7.6 +/- 0.5 to 12 +/- 1.4 ng/mL by 15 minutes post pentagastrin. Plasma mean +/- SE calcitonin levels increased in parallel with the plasma PRL levels from 0.28 +/- 0.1 to a peak of 1.9 +/- 0.9 ng/mL at 5 minutes post pentagastrin. A significant (P less than 0.05) correlation was found between the percentage increase in plasma calcitonin concentrations and plasma PRL levels at five and ten minutes post pentagastrin stimulation in this group of active MTC patients. Significant increases in serum calcitonin levels in the other groups post pentagastrin were of lesser magnitude and were not associated with a significant increase in PRL release. This latter observation suggested that neither the stress of the infusion nor the multiple endocrine neoplasia type 2 nor the pentagastrin was responsible for the observed increase in plasma PRL levels in the active MTC patients. These findings suggest, but do not prove, that calcitonin is a PRL-releasing factor in humans.

CSF-plasma relationships for DSIP and some other neuropeptides

The relationships between CSF and plasma hormonal levels of several peptides were studied in the same samples of simultaneously obtained plasma and CSF. A significant correlation existed between CSF and plasma levels of DSIP as well as gastrin. Preliminary results also showed a correlation between CSF and plasma levels of NT, but not VIP or calcitonin. CSF/plasma ratios and the effect of BBB disruption also varied from peptide to peptide. These diverse CSF/plasma relationships are not easily explained by models of nonspecific passage but may indicate individual systems or axes that could be involved in the central effects of peripherally administered peptides.

Hormones and feed intake

During the several decades that hormones have been considered for roles in the control of feeding, certain ones have gained special attention, although the role assigned to any one hormone has varied from time to time. Three classes of hormones have been considered in this review: gastrointestinal, brain, and pancreatic. Of these classes, two have obtained the most compelling evidence for a physiological role in the control of feeding. CCK, an intestinal and brain hormone, appears to be involved in satiety. Glucagon of pancreatic origin appears also to play an important role in satiety. These hormones, when sequestered by a specific antibody, cause a delay in satiety and thus increase food intake. Insulin, another pancreatic hormone, has been considered for several roles in the control of feeding. Recently, attention has been given to the possibility that insulin of the CSF provides an integrated link between the metabolic state of the adipose tissue and the brain structures concerned with the control of feeding. Thus, insulin may be a primary hormone involved in the maintenance of energy balance or of body-weight. Finally, brain opiate peptides, e.g. dynorphin, are very likely involved in the transmission of information concerned with the interaction of feeding and maintenance of energy balance. Clearly, hormones play primary roles in the control of feeding behaviour and the regulation of energy balance, but much remains to be done to establish their specific actions or components of the associated physiological systems.

Calcitonin--C.N.S. action to control the pattern of intestinal motility in rats

Synthetic calcitonin injected into the lateral ventricles (ICV) of rats at picomolar concentration restores the "fasted' motility pattern of the small intestine in fed rats at doses as low as 0.083 picomoles. This effect which appeared in less than 5 min and persisted at least 2 hours for 0.83 picomole, was blocked by a previous intraventricular administration of 10 micrograms/ of calcium gluconate. At 0.83 picomole ICV, calcitonin also suppressed the disruption of the "fasted' pattern induced by intravenous infusion of Pentagastrin (6 micrograms.kg-1.h-1) but not that induced by insulin (0.5 U.kg-1). These findings support the hypothesis that calcitonin acts centrally to control the pattern of intestinal motility by inhibiting the digestive influences responsible for the "fed' pattern. All of these peripheral influences are mediated by a Ca++ sensitive central structure.

Peptides in the cerebrospinal fluid of neuropsychiatric patients: an approach to central nervous system peptide function

This review highlights that essentially all of the recently discovered putative central nervous system (CNS) peptides and other peptide substances are measurable in human cerebrospinal fluid (CSF). Preliminary evidence also suggests that peptides in CSF may have an active regulatory role in relation to CNS function and behavior. Even if this is not the case, CSF peptides may prove to be a useful indirect marker of CNS peptide function and metabolism. Alterations in peptides have been reported in neurological and psychiatric illness, pain symptoms and their treatment, symptoms such as anxiety, and following treatment with CNS active drugs such as carbamazepine. CSF methodologies provide a strategy for the study of the interaction of classical neurotransmitters and peptide substances and their relationship to neural function and behavior in man. Assessment of peptides in CSF may supplement post mortem studies of peptide levels and receptor distribution and help lead to new diagnostic and treatment approaches in neuropsychiatric disorders.

Neuropeptides and cerebrospinal fluid

Neuropeptides are present in brain tissue as well as in cerebrospinal fluid. Studies from a variety of disciplines have demonstrated that neuropeptides have neuromodulatory activities. Such activities are apparent in the involvement of neuropeptides in the regulation of adaptive, autonomic, and endocrine functions of the brain. Neuropeptides exert their neuromodulating influences by acting as neurotransmitters or as neurohormones. The neurotransmitter function of neuropeptides is associated with their synthesis in situ in brain and anatomical distribution via neuropeptidergic fibre systems. The presence of such neuropeptides in cerebrospinal fluid may be due primarily to drainage into the cerebrospinal fluid compartments, their levels being a reflection of cellular processes such as biosynthesis, release, and metabolism. On the other hand, neuropeptides functioning as neurohormones may be actively delivered into the cerebrospinal fluid from central or peripheral sources. They employ the pathways of cerebrospinal fluid circulation as avenues of transport, and their cerebrospinal fluid levels may be functionally related to neurohormonal activity. In either case the cerebrospinal fluid levels are informative on the neuropeptide climate in brain; thus their determination is meaningful. The methodology for the sensitive and specific determination of neuropeptides is becoming available. Determination of neuropeptides may well be of diagnostic value in clinical practice.

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

Immunoreactive calcitonin (CT), indistinguishable from human CT-(1-32) and its sulfoxide, has been identified in extracts of the hypothalamus, the pituitary, and the thyroid obtained from human subjects at autopsy. DCT concentrations were highest in a region encompassing the posterior hypothalamus, the median eminence, and the pituitary; intermediate in the substantia nigra, the anterior hypothalamus, the globus pallidus, and the inferior colliculus; and low in the caudate nucleus, the hippocampus, the amygdala, and the cerebral and cerebellar cortices. Specific CT binding measured with 125I-labeled salmon CT was highest in homogenates of the posterior hypothalamus and the median eminence, shown to contain the highest concentrations of endogenous CT in the brain; CT binding was less than 12% of hypothalamic binding in all of the other regions of the brain examined and was negligible in the pituitary. Half-maximal binding was achieved with 0.1 nM nonradioactive salmon CT-(1-32), and the binding was directed to structural or conformational sites, or both, in the COOH-terminal half of salmon CT. The rank order of the inhibition of the binding by CT from different species and analogues of the human hormone was the same as in receptors on a human lymphoid cell line (Moran, J., Hunziker, W. & Fischer, J. A. (1978) Proc. Natl. Acad. Sci. USA 75, 3984-3988). The functional role of CT and of its binding sites in the brain remains to be elucidated.

Intraventricular calcitonin inhibits gastric acid secretion

Parenteral and intracerebroventricular administration of calcitonin in rats resulted in the suppression of gastric acid secretion. This suppression also occurred in rats with insulin-induced hypoglycemia and after the administration of thyrotropin-releasing hormone. Intracerebroventricularly administered calcitonin was 1000 times more effective than parenterally administered calcitonin in suppressing gastric acid secretion. Calcitonin also inhibited the development of stress-induced ulcers in rats.

Reduction of feeding in rats by calcitonin

Administration of parenteral and intracerebroventricular calcitonin resulted in suppression of stress-induced and spontaneous eating in rats. Calcitonin also reversed calcium chloride-induced eating and reduced 45Ca2+-uptake in a hypothalamic explant system. The mechanism of calcitonin-induced food suppression may be related to an alteration in calcium flux by neuronal tissue.