Changes In Calcium Homeostasis Research Articles

Cellular calcium homeostasis changes in lymphoma-induction by ATP iron complex

An in vivo comparative study of 45Ca-uptake and lipid peroxidation in tissues of mice treated with ATP complex of iron and sodium salt of ATP shows that only the iron complex produces a sustained increase of intracellular calcium on the organs susceptibles to develop lymphomas. A paralled study of 59Fe-uptake from 59Fe-iron complex of ATP presents a coincidental increase of iron uptake in those organs. To prove the involvement of the calcium homeostasis change in lymphoma-induction we have studied it with the lanthanum complex of ATP. Lanthanum is a well known cellular calcium entry modifier. Based on the results, the increased and sustained entry of extracellular calcium ion appears as the cause of lymphoma-induction by the iron complex. The effects of the calcium-overload in proliferation and neoplastic transformation of lymphocytes, as well as in reducing the immuno-response induced by thymus is discussed.

Resistance to NMDA toxicity correlates with appearance of nuclear inclusions, behavioural deficits and changes in calcium homeostasis in mice transgenic for exon 1 of the huntington gene.

Transgenic Huntington's disease (HD) mice, expressing exon 1 of the human HD gene (lines R6/1 and R6/2), are totally resistant to striatal lesions caused by the NMDA receptor agonist quinolinic acid (QA). Here we show that this resistance develops gradually over time in both R6/1 and R6/2 mice, and that it occurred earlier in R6/2 (CAG-155) than in R6/1 (CAG-115) mice. The development of the resistance coincided with the appearance of nuclear inclusions and with the onset of motor deficits. In the HD mice, hippocampal neurons were also resistant to QA, especially in the CA1 region. Importantly, there was no change in susceptibility to QA in transgenic mice with a normal CAG repeat (CAG-18). R6/1 mice were also resistant to NMDA-, but not to AMPA-induced striatal damage. Interestingly, QA-induced current and calcium influx in striatal R6/2 neurons were not decreased. However, R6/2 neurons had a better capacity to handle cytoplasmic calcium ([Ca2+]c) overload following QA and could avoid [Ca2+]c deregulation and cell lysis. In addition, basal [Ca2+]c levels were increased five-fold in striatal R6/2 neurons. This might cause an adaptation of R6 neurons to excitotoxic stress resulting in an up-regulation of defense mechanisms, including an increased capacity to handle [Ca2+]c overload. However, the increased level of basal [Ca2+]c in the HD mice might also disturb intracellular signalling in striatal neurons and thereby cause neuronal dysfunction and behavioural deficits.

Diabetes-induced changes in calcium homeostasis and the effects of calcium channel blockers in rat and mice nociceptive neurons.

Distal neuropathy is the most common complication of diabetes mellitus, making it important to reveal the cellular mechanisms leading to its development, one of which might be the alteration in intracellular calcium homeostasis in primary and secondary nociceptive neurons. We aimed to investigate these possible changes. Control and streptozotocin-treated diabetic rats and mice were used. Changes in intracellular free calcium concentrations ([Ca(2+)]i) were measured fluorometrically in primary nociceptive neurons from dorsal root ganglia and in secondary nociceptive neurons from substantia gelatinosa of spinal dorsal horn slices. Measurements of [Ca(2+)]i increases induced in dorsal root ganglion and dorsal horn neurons by membrane depolarization did not show any substantial difference in their peak amplitudes in control and diabetic animals. However, a definite prolongation of the decay phase of the transients was observed under diabetic conditions. Caffeine application to dorsal root ganglion and dorsal horn neurons induced a transient elevation of [Ca(2+)]i which was less prominent in cells from diabetic animals. Short-term application of a calcium channel blocker nifedipine showed a substantial amplification of its action in diabetic neurons. However, chronic administration of nimodipine induced a clear increase in the peak values of transients in dorsal root ganglion neurons of diabetic animals compared with those of untreated animals. The described changes of calcium signalling in nociceptive neurons could be the reason for the development of distal polyneuropathy and its symptoms in the early stages of diabetes mellitus.

A subpopulation of mitochondria prevents cytosolic calcium overload in endothelial cells after cold ischemia/reperfusion.

Calcium represents a key mediator of cold ischemia/reperfusion (CIR) injury presumably by affecting mitochondrial function. In this study, we investigated cellular and mitochondrial changes of calcium homeostasis in sublethally damaged human endothelial cells. Changes in cellular and mitochondrial calcium concentrations were studied after cold ischemia in University of Wisconsin solution for 12 hr and reperfusion in ringer solution. Cytosolic-free calcium concentration ([Ca2+]c) and mitochondrial-free calcium content ([Ca2+]m) were analyzed by fura-2 and rhod-2 fluorescence, respectively. Pretreatment of cells with ruthenium red (RR) or a H+-ionophore was used to inhibit mitochondrial calcium uptake. Mitochondrial membrane potential (DeltaPsim) was measured by 5,5',6,6'-tetrachloro- 1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide and 3,3'-dihexyloxacarbocyanine iodide fluorescence. Twelve-hr cold ischemia did not induce apoptosis in endothelial cells. In such sublethally damaged cells, [Ca2+]c rose from approximately 20 nmol/L after cold ischemia to approximately 120 nmol/L during reperfusion. Pretreatment with RR leads to an approximately 5-fold rise in [Ca2+]c. Image analysis revealed a significant increase of [Ca2+]m in a subpopulation of mitochondria during reperfusion. This was not the case in RR-pretreated cells. DeltaPsim decreased significantly during cold ischemia and was sustained during reperfusion. The loss of DeltaPsim can be related to a reduced portion of mitochondria exhibiting high DeltaPsim. Our results suggest that cytosolic calcium influx during CIR is buffered by a selective portion of mitochondria in human umbilical vein endothelial cells. These mitochondria protect cells against cytosolic calcium overload and probably against subsequent cell injury.

Local and systemic effects of Na+/K+ATPase inhibition.

The positive inotropic and electrophysiological effects of cardiac glycosides on cardiac muscle are mediated through inhibition of Na+/K+ ATPase by binding to a specific extracytoplasmic site of the a-subunit of this enzyme. The inhibition of Na+/K+ ATPase affects ionic flux and produces direct local effects on cardiac contractility, electrical excitability and conduction, but also profound systemic effects mainly as a result of haemodynamic changes. These effects are responsible for beneficial therapeutic as well as toxic effects. Inhibition of Na+/K+ ATPase results in potentiation of K+ loss from cells and Na+ entry into cells, so consequently affects action potential generation and propagation. This also underlines the potentiation of certain effects of cardiac glycosides by hypokalemia and hypomagnesaemia, and the effects of changes in calcium homeostasis on the cardiac glycoside pharmacodynamics. Furthermore, inhibition of Na+/Ca++ exchange enhances Ca++ mobilization and promotes contractility. These effects (locally and systemically) differ greatly, depending on the haemodynamic status and myocardial oxygen supply. Cardiac glycosides have less affinity for Na+/K+ ATPases at other sites (e.g. skeletal muscle), but some extracardiac effects (vascular effects, effects on colour vision, CNS and autonomic effects, renal effects) may be related to Na+/K+ ATPase inhibition.

Local and systemic effects of Na+/K+ ATPase inhibition

The positive inotropic and electrophysiological effects of cardiac glycosides on cardiac muscle are mediated through inhibition of Na+/K+ ATPase by binding to a specific extracytoplasmic site of the a‐subunit of this enzyme. The inhibition of Na+/K+ ATPase affects ionic flux and produces direct local effects on cardiac contractility, electrical excitability and conduction, but also profound systemic effects mainly as a result of haemodynamic changes. These effects are responsible for beneficial therapeutic as well as toxic effects.Inhibition of Na+/K+ ATPase results in potentiation of K+ loss from cells and Na+ entry into cells, so consequently affects action potential generation and propagation. This also underlines the potentiation of certain effects of cardiac glycosides by hypokalemia and hypomagnesaemia, and the effects of changes in calcium homeostasis on the cardiac glycoside pharmacodynamics. Furthermore, inhibition of Na+/Ca++ exchange enhances Ca++ mobilization and promotes contractility. These effects (locally and systemically) differ greatly, depending on the haemodynamic status and myocardial oxygen supply.Cardiac glycosides have less affinity for Na+/K+ ATPases at other sites (e.g. skeletal muscle), but some extracardiac effects (vascular effects, effects on colour vision, CNS and autonomic effects, renal effects) may be related to Na+/K+ ATPase inhibition.

Age-dependent effects of Aroclor 1254 R on calcium uptake by subcellular organelles in selected brain regions of rats

Earlier reports from our laboratory have indicated that polychlorinated biphenyls (PCBs) affect signal transduction mechanisms in brain, including Ca 2+ homeostasis, phosphoinositol hydrolysis, and protein kinase C (PKC) translocation in mature neurons and adult brain homogenate preparations. Present studies were designed to investigate whether there were any brain region-, gender-, or age-dependent effects of PCBs on 45Ca 2+-uptake by two subcellular organelles, microsomes and mitochondria. We have studied in vitro effects of a widely studied commercial PCB mixture, Aroclor 1254 R, on 45Ca 2+-uptake by microsomes and mitochondria in cerebellum, frontal cortex and hippocampus of postnatal day (PND) 7, 21, and 90–120 (adult) male and female Long–Evans (LE)-rats. In general, microsomal and mitochondrial 45Ca 2+-uptake in selected brain regions increased with age; PND 7<PND 21≤adults. Among three brain regions, hippocampus had relatively lower microsomal 45Ca 2+-uptake than cerebellum and frontal cortex throughout the development. Mitochondrial 45Ca 2+-uptake was comparable in three brain regions of PND 7 and adult animals, but in PND 21 rats, the cerebellum had much higher activity than frontal cortex and hippocampus. No gender-related differences were seen in 45Ca 2+-uptake by either microsomes or mitochondria in selected brain regions throughout development. Inhibition of 45Ca 2+-uptake by Aroclor 1254 in a concentration-dependent manner was observed throughout the study. However, the degree of inhibition of microsomal 45Ca 2+-uptake in these brain regions by Aroclor 1254 increased with age, PND 7<PND 21≤adults (IC 50s=21–34, 8–20 and 10–14 μM, respectively). Brain region-specific differential sensitivity to Aroclor 1254 on the inhibition of microsomal 45Ca 2+-uptake was not seen in PND 7 and adult animals but in PND 21 rats, hippocampus was more sensitive than the other selected brain regions. There were no age-, gender- or brain region-specific differential effects of Aroclor 1254 on mitochondrial 45Ca 2+-uptake. These results indicate that a commercial PCB mixture, Aroclor 1254, inhibited 45Ca 2+-uptake by both microsomes and mitochondria uniformly in selected brain regions of males and females during development. However, the inhibition of microsomal 45Ca 2+-uptake by Aroclor 1254 increased with age. The age- and gender-related differential sensitivity to Aroclor 1254 may be attributed to the changes in calcium homeostasis in various brain regions during development.

The Role of Insulin-Like Growth Factor I in Age-Related Changes in Calcium Homeostasis in Men

The Role of Insulin-Like Growth Factor I in Age-Related Changes in Calcium Homeostasis in Men

Perception of environmental signals by a marine diatom.

Diatoms are a key component of marine ecosystems and are extremely important for the biogeochemical cycling of silica and as contributors to global fixed carbon. However, the answers to fundamental questions such as what diatoms can sense in their environment, how they respond to external signals, and what factors control their life strategies are largely unknown. We generated transgenic diatom cells containing the calcium-sensitive photoprotein aequorin to determine whether changes in calcium homeostasis are used to respond to relevant environmental stimuli. Our results reveal sensing systems for detecting and responding to fluid motion (shear stress), osmotic stress, and iron, a key nutrient that controls diatom abundance in the ocean.

Seasonal changes in calcium homeostasis affect the incidence of postoperative tetany in patients with Graves' disease

Background: We have found that postoperative tetany occurs in patients with Graves' disease who have secondary hyperparathyroidism caused by a deficiency in calcium and vitamin D concomitant with transient hypoparathyroidism after surgery. There are seasonal variations in serum 25-hydroxyvitamin D (25[OH]D) concentrations. The purpose of this study was to investigate the effects of seasonal changes in calcium homeostasis on the incidence of postoperative tetany in patients with Graves' disease who undergo subtotal thyroidectomy. Patients and Methods: A prospective study was carried out to investigate sequential changes in serum levels of intact parathyroid hormone (iPTH), calcium and other electrolytes, 25(OH)D, and 1,25-dihydroxyvitamin D (1,25[OH] 2D) in female patients with Graves' disease who underwent subtotal thyroidectomy during the summer (n = 89) and during the winter (n = 89). Results: The serum levels of calcium, magnesium, and 25(OH)D were significantly higher, but iPTH levels and 1,25(OH) 2D levels were lower in summer than in winter. The percentage of vitamin D deficiency (25(OH)D < 25nmol/L) was 23% in summer and 62% in winter (P < .001). iPTH was below the detection limit on the first postoperative day in 15 patients (13.8%) in summer and in 13 patients (11.4%) in winter. In summer, tetany developed in only 4 of 15 patients and in one patient whose iPTH level was below normal (incidence of tetany, 5.6%). In winter, however, tetany developed in 6 of 13 patients and in 4 patients whose iPTH level was below normal (incidence of tetany, 11.2%). Conclusions: Patients with Graves' disease are more susceptible to calcium and vitamin D deficiency during the winter than during the summer, resulting in the tendency toward a higher incidence of postoperative tetany in winter. (Surgery 2000;127:377-82.)

Alcohol dependence at the cellular level: effects of ethanol on calcium homeostasis of IM-9 human lymphoblast cells.

Increased intracellular calcium level ([Ca2+]i) was previously observed in peripheral blood mononuclear cells of alcoholic patients under withdrawal. To determine whether this change in [Ca2+]i is due to direct effect of ethanol on blood cells and shows adaptation of these cells to alcohol, we examined the effect of alcohol on IM-9 human lymphoblast cultures. [Ca2+]i of IM-9 lymphoblasts. after acute and chronic alcohol treatment as well as alcohol withdrawal, was measured fluorometrically using Quin2 as a Ca2+-indicator. Acute ethanol treatment induced a rapid, transient increase in intracellular calcium concentration in a dose-dependent manner. During chronic ethanol (50mM) administration, after the first 24 hours, basal [Ca2+]i was significantly lower (44 +/- 8% of control, p < .025), whereas from the fifth day [Ca2+]i was significantly higher (415 +/- 59% of control on the sixth day, p < .01) compared with untreated cells. After a 3-day ethanol (50OmM or 100mM) treatment, elimination of alcohol from the medium caused elevation in [Ca2+]i. After 24-hour ethanol withdrawal, the addition of alcohol decreased the elevated [Ca2+]i of alcohol-adapted cells to the resting level of control cells. Similar results were observed when verapamil, diazepam or haloperidol were applied. Moreover, when ethanol or these agents were administered at the beginning of alcohol withdrawal, they could prevent the increase in [Ca2+]i. These results suggest that alcohol dependence can develop at the cellular level, and that changes in calcium homeostasis, likely due to direct effects of ethanol on ion channels, may play a central role in processes leading to adaptation of cells to alcohol.

Natural polyphenols-iron interaction: its biological importance.

The iron-binding capacity of different fractions of natural polyphenols extracts was determined by chromatographic and electrophoretic methods. Their effects on iron-induced calcium homeostasis changes in liver tissue suspension showed that mate tea and green tea extracts provoke a very significant inhibition of the iron effects, whereas it is much less significant with red wine extract. The biological importance of this phenomenon is discussed.

Age-related alterations in caffeine-sensitive calcium stores and mitochondrial buffering in rat basal forebrain

The properties of caffeine- and thapsigargin-sensitive endoplasmic reticulum calcium stores were compared in acutely dissociated basal forebrain neurons from young and aged F344 rats by ratiometric microfluorimetry. The ability of these stores to sequester and release calcium resembles that observed in other central neurons, with an important role of mitochondrial calcium buffering in regulating the response to caffeine. An age-related reduction in the filling state of the stores in resting cells appears to be mediated by increased rapid calcium buffering, which reduces the availability of calcium for uptake into the stores. An age-related decrease in the amplitude of maximal caffeine-induced calcium release was attributed to increased mitochondrial buffering. There were no age-related differences in the sensitivity to caffeine or in the calcium sequestration/release process at the level of the endoplasmic reticulum per se. These findings demonstrate the importance of interactions between cellular calcium buffering mechanisms and provide details regarding age-related changes in calcium homeostasis which have been thought to occur in these and other neurons associated with age-related neuronal dysfunctions.

Electromechanical Effects of Protamine and Verapamil in Rat Papillary Muscle

The electromechanical effects of protamine sulfate and the calcium channel blocker verapamil on rat cardiac and skeletal muscles were studied using isolated left ventricular papillary muscle and phrenic nerve-hemidiaphragm preparations. Protamine produced significant decreases in isometric force in the cardiac tissue and contracture developed at concentrations of 40 and 80 mg·L−1. Isometric force also decreased significantly with verapamil at concentrations of 0.757 and 7.57 mg·L−1. Both drugs caused significant decreases in the contractile force of hemidiaphragm muscle when the tissue was stimulated indirectly. Protamine and verapamil caused the resting membrane potential and the amplitude of the action potential to decrease in cardiac tissue and overshoot failed to develop with 80 mg·L−1 of protamine or 7.57 mg·L−1 of verapamil. These bioelectrical changes developed in a dose-dependent manner. It was concluded that protamine had a similar effect to that of calcium channel blockers and it may act through a reduction of cellular calcium. This effect on cardiac tissue may be mediated through the sarcolemmal ion pumps or channels, leading to changes in calcium homeostasis.

The effect of in vitro exposure to white spirit on [Ca2+i] in synaptosomes from rats exposed prenatally to white spirit.

Female rats were exposed to white spirit (400 and 800 ppm for 6 hr/day) at day 7-20 during pregnancy. Thirty-five days after birth all female offspring were sacrificed, the brains removed, and the synaptosomal fractions prepared for in vitro studies. The cytosolic calcium concentration was measured using the FURA-2 technique. The results show that cytosolic calcium was increased in synaptosomes from rats exposed to white spirit prenatally compared to synaptosomes from unexposed rats. When synaptosomes were exposed to white spirit in vitro, the cytosolic calcium concentration changes were identical in all groups of rats. The membrane leakage measured as FURA-2 leakage from the synaptosomes identical in all three groups of animals. The results suggest that prenatal exposure to white spirit induces long-lasting and possibly irreversible changes in calcium homeostasis in the rat nervous system.

The calcium response of human T lymphocytes is decreased in aging but increased in Alzheimer’s dementia

Background: A significant increase in the [Ca 2+] i response of single T lymphocytes to mitogenic stimulation with phytohemagglutinin is reported for 27 Alzheimer patients compared with 27 healthy gender- and age-matched control subjects, regardless of gender. Methods: The [Ca 2+] i signals of T lymphocytes were assessed using the Fura-2-AM method. Results: In Alzheimer’s disease (AD) the reaction pattern is similar to that seen in a group of 27 young healthy control subjects who exhibited a marked [Ca 2+] i rise after stimulation. During normal aging the reaction pattern of T cells is significantly attenuated in comparison to that found in young subjects. In healthy control subjects differences in age-related changes in calcium homeostasis are highly significant among women, young women showing the most intense cell response. Conclusions: The elevation of [Ca 2+] i appears to be a prerequisite for apoptosis, which is suggested to be involved in the neuronal death occurring in AD. An increased [Ca 2+] i in AD is consistent with processes leading to neurodegeneration in AD.

Severe Deficiency of 1,25-Dihydroxyvitamin D3 in Human Immunodeficiency Virus Infection: Association with Immunological Hyperactivity and Only Minor Changes in Calcium Homeostasis

Severe Deficiency of 1,25-Dihydroxyvitamin D3 in Human Immunodeficiency Virus Infection: Association with Immunological Hyperactivity and Only Minor Changes in Calcium Homeostasis

Severe deficiency of 1,25-dihydroxyvitamin D3 in human immunodeficiency virus infection: association with immunological hyperactivity and only minor changes in calcium homeostasis.

The serum level of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D], the biologically most potent metabolite of vitamin D, is tightly regulated within narrow limits in human healthy adults. 1,25-(OH)2D deficiency is rare and is associated with disturbances in calcium and bone metabolism. We have previously reported a marked decrease in serum levels of 1,25-(OH)2D in human immunodeficiency virus (HIV)-infected patients. The present study was designed to further examine the causes and consequences of severe 1,25-(OH)2D deficiency in these patients. The design was a prospective cohort study. Fifty-four HIV-infected patients clinically classified according to the revised criteria from Centers for Disease Control and Prevention and healthy controls were studied. Parameters related to vitamin D and calcium metabolism as well as immunological and nutritional status were determined. Twenty-nine of the patients (54%) had serum levels of 1,25-(OH)2D below the lower reference limit, and 18 of these had undetectable levels. In contrast, HIV-infected patients had normal serum levels of 25-hydroxyvitamin D and vitamin D-binding protein. HIV-infected patients as a group had modestly depressed serum calcium and PTH levels. There were, however, no correlations between these parameters and serum levels of 1,25-(OH)2D. There were no differences in serum calcium or PTH levels or nutritional status when patients with severe 1,25-(OH)2D deficiency were compared to other patients, but patients with undetectable 1,25-(OH)2D had significantly elevated serum phosphate levels. Furthermore, patients with undetectable 1,25-(OH)2D levels were characterized by advanced clinical HIV infection, low CD4+ lymphocyte counts, and high serum levels of tumor necrosis factor-alpha (TNFalpha). We conclude that inadequate 1alpha-hydroxylation of 25-hydroxyvitamin D seems to be the most likely cause of 1,25-(OH)2D deficiency in HIV-infected patients, possibly induced by an inhibitory effect of TNFalpha. The low 1,25-(OH)2D and high TNFalpha levels observed may impair the immune response in HIV-infected patients both independently and in combination and may represent an important feature of the pathogenesis of HIV-related immunodeficiency. Markedly depressed 1,25-(OH)2D serum levels are also present in certain other disorders characterized by immunological hyperactivity. Thus, the findings in the present study may not only represent a previously unrecognized immune-mediated mechanism for induction of 1,25-(OH)2D deficiency in human disease, but may also reflect the importance of adequate serum levels of 1,25-(OH)2D for satisfactory performance of the immune system in man.

Analysis of the mechanisms underlying the age-related impairment in long-term potentiation in the rat.

The process of ageing is common to all organisms but despite its universality, understanding of the cellular and molecular changes which accompany ageing is poor. With the increase in the ageing population, the need for systematic study of the process becomes a priority but the development of a systematic approach to the problem requires the development of a testable theory of ageing. While several theories of ageing have been proposed /336/, between which there is at least some overlap, no generally-accepted theory has been identified. In relation to the brain, four interrelated theories of ageing have received significant attention; these are (1) the membrane hypothesis, (2) the free radical hypothesis, (3) the calcium hypothesis and (4) the glucocorticoid theory. The overlap between these hypotheses is such that a causal relationship between them is very likely with age-related changes in membrane composition triggered by changes in free radical production, while changes in membrane composition are likely to account for changes in membrane function including age-related changes in calcium homeostasis. The glucocorticoid theory could equally well be termed the stress hypothesis of ageing, which in the hippocampus at least, might trigger age-related changes in free radical production. This review is not intended to be a balanced appraisal of each theory but emphasizes aspects of the membrane hypothesis of ageing and discusses some relevant aspects of the other hypotheses. Attention is focussed on analysis of the biochemical changes which might underlie age-related changes in hippocampal function, particularly maintenance of long-term potentiation (LTP), and these changes are discussed in the context of the four hypotheses of ageing.

Polyethylene glycol-induced calcium appetite.

Polyethylene glycol (PEG) has been used to investigate the physiological basis of sodium intake because it sequesters sodium from the extracellular fluid (ECF) and causes rats to drink concentrated NaCl solutions. To test the hypothesis that PEG also depletes ECF calcium and thus activates calcium intake, male Sprague-Dawley rats received two-bottle tests with a choice between a taste solution and water. Relative to intakes after control injections, rats injected with PEG (5 ml of 30% wt/wt sc) drank significantly greater volumes of several calcium solutions (0.1, 1, 10, or 32 mM CaCl2 or 10 or 100 mM calcium lactate). They also drank more 10 mM SrCl2, 300 mM NaCl, and 100 mM KHCO3, drank less 10 mM sodium saccharin, and did not alter intakes of 10 or 100 mM KCl, 32 mM NH4Cl, 10 mM AlCl3, 10 mM FeCl2, 100 mM CaCl2, or 1,000 mM NaCl. Thus PEG treatment produced an appetite that was specific to low and moderate concentrations of calcium, sodium, and perhaps bicarbonate. The physiological basis for this appetite was explored. At 24 h after PEG injection, plasma total calcium concentrations were either unaltered or increased, but plasma ionized calcium concentrations were reduced. Concentrations of parathyroid hormone and calcitonin but not 1 alpha, 25-dihydroxyvitamin D3 were elevated. Perhaps one or more of these changes in calcium homeostasis is responsible for the increased calcium intake. Whatever the mechanism, it is clear that PEG treatment induces an appetite for calcium in addition to the well-known appetite for sodium.