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A M Perault-Staub

Publications and source records attributed to A M Perault-Staub.

At least 19 recordsLinked to original sources
PubMed1992

Modelling of in vivo calcium metabolism. I. Optimal cooperation between constant and rhythmic behaviours.

The relevance of nonlinear dynamics to calcium metabolism led us to reevaluate the role of Ca-regulating hormones in Ca homeostasis. We suggest that, firstly, the main Ca metabolic functions in rat-bone and gut--are organized as dynamic entities able to generate various temporal expressions, including self-oscillating patterns and, secondly, Ca homeostasis results from interaction between both metabolic and hormonal oscillators. Following this schema, a major role for the hormonal system, with its circadian pattern, could be to act directly on metabolic functions or indirectly through feeding behaviour, in order to optimize, coordinate and synchronize the Ca fluxes at ECF level.

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PubMed1992

Modelling of in vivo calcium metabolism. II. Minimal structure or maximum dynamic diversity: the interplay of biological constraints.

The temporal behaviour of the nonlinear compartmental model we have developed for rat calcium metabolism is discussed with respect to the theoretical properties of the self-oscillating autocatalytic subunit around which the model is constructed. Depending on the approximations made, this subunit is described by a minimal two-variable model, SU2, or by a three-variable one, SU3. The diversity of the theoretical dynamic behaviours possible with SU2 is greatly increased with SU3. But the identification of SU3 parameter values in three different experimental situations reveals that biological constraints efficiently preserve a simple circadian rhythm for bone metabolism. This analysis indicates the significant contribution of the available bone crystal pool to the dynamic organization of this tissue, and hence to extracellular calcium homeostasis.

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PubMed1990

Regulation of plasma calcium and phosphate in calcitonin-infused rats.

The effects of long-term constant infusion of moderate doses (2-32 ng/h) of salmon calcitonin (sCT) on plasma Ca (and its radionuclide 45Ca), Pi, Mg, and on endogenous rat CT (rCT) metabolism were investigated in the rat. Daily variations were included. 1) The plasma concentrations of Ca and Pi fell and that of Mg increased transiently during infusion, with the duration of responses (1-3 days) depending on the sCT dose. Rats infused with 8 ng/h sCT remained sensitive to CT after 7 and 14 days, as indicated by the effects of minipump removal and of a bolus injection of exogenous sCT on plasma mineral concentrations. 2) In contrast to control rats, the well-established daily variations in plasma Ca and Pi levels were no longer observed after 7 and 14 days of sCT infusion (8 ng/h), but normal variations persisted for plasma Mg, circulating rCT, rCT mRNA, and rCT thyroid content. 3) Statistical analysis of plasma mineral data, collected at five sequential times during days 7 and 14, showed that the means were not significantly different and that the daily variations were essentially identical on days 7 and 14 in control rats. In contrast, the variability of measurements for plasma Ca and Pi, but not for Mg, increased significantly between days 7 and 14 in infused rats, and the mean differences were significantly lower in infused rats on day 7 than in control rats. These results are consistent with a transitory loss of the daily variations for Ca and Pi (day 7) and the later (day 14) spontaneous recovery of some variations in these parameters, although the individuals remain unsynchronized.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1989

A physiological view of in vivo calcium dynamics: the regulation of a nonlinear self-organized system.

Our aim is neither to re-evaluate the term homeostasis, nor to summarize the conventional concepts in the field of calcium metabolism and its regulation, nor even to comment on their advantages and their limitations (excellent recent reviews have been published). This paper is rather a position article and references to the current literature will be made only if they contribute to a better understanding of our proposals; in contrast, emphasis will be placed on a literature which has, until now, remained unfamiliar to the field of calcium metabolism. The text is organized around three related features which are largely dictated by the characteristics of our recently published compartmental self-oscillatory model for rat calcium metabolism: (a) The circadian behavior associated with calcium dynamics in vivo may be viewed as a "key" temporal behavior for investigating the spatiotemporal organization of calcium metabolism in the normal rat. Within the bone, a large part of this circadian behavior should stem from the physico-chemical properties of the transformations of calcium-phosphate associations at the extracellular fluid (ECF)/mature bone interface; (b) an important part of the maintenance of a nearly constant plasma calcium concentration (homeostasis) results from interaction between nonlinear oscillators belonging to both calcium metabolism and calcium-regulating hormones. This implies that: firstly, calcium metabolism, like any biological system, is a complex dynamic system which has evolved over a long period and whose metabolic components--gut, kidney, bone--are organized as dynamic entities, adapted to periodic relationships with the external environment. The intrinsic nature of the circadian behavior of bone calcium efflux proposed here is a sufficient demonstration of this. Secondly, the existence of rhythmic variations in the main calcium regulating hormones, parathyroid hormone (PTH), calcitonin (CT) and vitamin D (VitD), are in agreement with this argument. As developed below, fascinating properties emerge from interaction between oscillators (hormones and target organs) which provide a new perspective on calcium regulation; and (c) one of the striking properties of the kind of nonlinear dynamic system required for this representation of calcium metabolism is that periodicity is only one of many temporal expressions. Thus, qualitative diversity in the temporal expression of calcium metabolism can be expected with varying experimental situations and different modes of temporal regulation of calcium metabolism might be physiologically effective, depending on the species studied.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1988

Calcium metabolism in the rat: a temporal self-organized model.

Based on consideration of rat plasma Ca and 45Ca concentrations, we analyze the circadian behavior of Ca metabolism of the rat as the temporal expression of a self-organized system. We present a self-oscillatory model M for rat Ca metabolism based on a compartmental formalism, which includes a second-order autocatalytic process. M describes the entire mass of Ca as made up of eight compartments and predicts a distinction between 1) the amount of Ca deposited in zones of rapid bone growth and reutilized during bone maturation and 2) the amount of Ca in mature bone subdivided into four compartments. Two of these compartments, largely self-oscillating, may represent Ca-P associations at bone liquid/solid interface and are subject to osteoblast-osteocyte control. The other two compartments can be thought of as made up of a large expanding pool of hydroxyapatite (HA) crystals, which are largely unavailable as such, and a small pool or more available HA crystals. Bone Ca influx and rhythmic efflux play a major role in the regulation of Ca in extracellular fluid but must be dissociated from bone accretion and resorption. Application to Ca deficiency was analyzed. Conceptual consequences of the connection of Ca metabolism to a self-regulated system are discussed.

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PubMed1985

Circadian variations in plasma calcium and calcitonin: effect of calcium deficiency and fasting.

Circadian fluctuations of plasma calcium and immunoassayable calcitonin levels were studied in normal and calcium-deficient 2-month-old rats. The relationship between these parameters was also studied in animals which had been fasted for short periods. The plasma calcium rhythm persisted and was even amplified in rats placed on a 4-week calcium-deficient diet. In these rats, as in normal rats, the plasma calcium concentration diminished during the dark period. Calcitonin levels increased at the onset of the feeding period in normal rats but, in calcium-deficient rats, the pattern changed completely, with a major peak at the end of the light period and remaining at a low level during the dark feeding period. This modification of calcitonin rhythmicity appeared to be dependent on the degree of calcium deficiency. Fasting had little effect on calcitonin rhythms in either normal or calcium-deficient rats. It is concluded that the calcitonin rhythm is relatively independent of feeding per se and that there appears to be no simple relationship between plasma calcium and calcitonin concentrations. It is suggested that the results may best be interpreted as reflecting the presence of rhythmic endogenous phenomena which are intrinsic to calcium metabolism and its regulation in the rat.

Animals↗
PubMed1979

Endogenous nature of circadian rhythms in calcium metabolism.

Rats studied when the lights are on from 0600 to 1800 daily and fed only in the dark period displayed circadian rhythms in plasma calcium (ionized and total) and 45Ca concentrations, 6 and 8 days after 45Ca administration. In rats fed a calcium-deficient diet, the amplitude of daily variation of plasma ionized and total calcium increased markedly whereas plasma 45Ca daily fluctuation remained essentially unchanged. In the calcium-deficient rats, significant correlations between plasma calcium and 45Ca and between plasma calcium and magnesium were observed throughout the 24 h; circadian periodicity of calcium metabolism persisted in rats fasted overnight, regardless of the illumination schedule. Normal daily fluctuations in plasma 45Ca, lost after thyroparathyroidectomy (TPTX), were restored by feeding the TPTX rats a high-calcium diet. These results demonstrate clearly that circadian rhythms of calcium metabolism occurred irrespective of the light-dark schedule, the calcium supply through intestines and the thyroparathyroid system. An attractive suggestion is that circadian rhythmicity originates as a result of dynamic properties involving nonlinear processes of calcium metabolism.

Animals↗
PubMed1979

[Regulation of calcium metabolism ; its rhythmic variations].

In rats fed a calcium-deficient diet, the amplitude of daily variation of plasma ionized and total calcium increased markedly whereas plasma 45Ca daily fluctuation remained essentially unchanged. Normal daily fluctuations in plasma 45Ca, lost after thyroparathyroidectomy, were restored by feeding rats a high-calcium diet. A suggestion is that circadian rhythmicity originates as a result of dynamic properties involving nonlinear processes of calcium metabolism.

Animals↗
PubMed1972

Diurnal variation of plasma calcium and calcitonin function in the rat.

1. These experiments were designed to investigate the normal physiological role of calcitonin in the control of blood calcium.2. The rat can be adapted to an artificial cycle of alternating 12-hr periods of light and darkness. Since rats eat only in the dark, calcium absorption is confined to the dark period.3. In rats thus adapted, the plasma calcium and phosphate levels show cyclic variation related, among other factors, to the calcium intake.4. The variation observed is modified by the removal of the thyroid gland. This cannot be attributed to deprivation of thyroxine and triiodothyronine because these experiments were carried out within 2 days of thyroidectomy.5. Thyroidectomy raises the plasma calcium and phosphate levels, but only if performed during the dark-fed period. This suggests the existence of a diurnal rhythm in endogenous calcitonin function.6. The magnitude of the falls in plasma calcium and phosphate, produced by exogenous calcitonin, also varies with the time of day. This shows that the rat's responsiveness to calcitonin also varies diurnally.

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