G. Milhaud

Diurnal variations 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.

Distribution of calcitonin gene-related peptide and calcitonin-like immunoreactivity in trout.

Radioimmunoassay and chromatography were used to study the occurrence of calcitonin gene-related peptide in various tissues of the rainbow trout, Salmo gairdnerii. The highest concentrations of the peptide were found in gill (1.68 +/- 0.09 ng/mg protein) and in intestine (1.06 +/- 0.4 ng/mg protein). Significant concentrations were also found in heart and stomach. The level in brain was very low. In trout, the plasma concentration accounted for 283 +/- 82 pg/ml. Chromatographic analysis of the calcitonin gene-related peptide (CGRP)-like immunoreactivity occurring in gills showed that two molecular forms cross-reacted with the anti-human CGRP antibody, one co-eluting with the synthetic human CGRP. In addition, calcitonin in fish is not confined to the ultimobranchial organ but is also present in organs as heart, intestine, kidney, spleen and stomach. The evidence of CGRP in fish emphasizes the role of this hormone in evolution and leads us to investigate its physiological role in this species.

Predicted secondary structure of calcitonin in relation to the biological activity

Abstract The secondary structure of the natural analogues of calcitonin have been predicted using the methods of Burgess et al., Chou and Fasman, and Lim. The predicted structures were similar in the N-terminal part of the chain, but were variable in other regions of the molecules. The higher hypocalcaemic potency of ultimobranchial calcitonins as compared to thyroidal calcitonins may be related to the higher potential for helical structure in the former.

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)

Binding sites of calcitonin gene related peptide (CGRP) to trout tissues

We localized specific binding sites for human calcitonin gene related peptide (hCGRP) in different organs of the trout using labelled human CGRP. Maximal binding was observed in gill and spleen membranes. The binding of 125I-hCGRP was time and temperature dependent. Scatchard analysis of binding data for the spleen and the gills disclosed two binding sites. The constants for the site of high affinity and low capacity (KAM-1 and Bmax (fmol/mg of proteins] were 2.9 x 10(9) for the spleen and 70 and 3.5 x 10(9) for the gill. Salmon calcitonin (sCT) inhibited the binding of 125I-hCGRP to spleen membranes with the same order of potency as hCGRP. In contrast sCT was less effective than hCGRP in suppressing the specific binding of 125I-hCGRP to gill membranes.

Immunoreactive salmon calcitonin-like molecule in crustaceans: High concentrations in Nephrops norvegicus

A salmon calcitonin (CT)-like peptide was characterized in various crustaceans by radioimmunological and radioreceptor assays. The highest levels of the molecule were found in the anterior part of the gut and the hepatopancreas of the Norway lobster: Nephrops norvegicus. Molecular sieving of this molecule suggested an apparent molecular weight of 4500 Da, that is higher than that of calcitonin. This peptide can be referred to as crustacean calcitonin as it inhibits the binding of labeled salmon CT to rat kidney membranes. The high concentration found in crustaceans suggested that this molecule could have an important role in this class of arthropods.

CALCITONIN GENE-RELATED PEPTIDE STIMULATES ADENYLATE CYCLASE ACTIVITY IN TROUT GILL CELL MEMBRANES

The physiological significance of calcitonin gene-related peptide (CGRP) was investigated by assessing the CGRP stimulated adenylate cyclase activity in various tissues of trout. The highest enzyme concentration was found in gill and stomach membranes. The maximal activity (190% of the basal value) was observed for a concentration of 53.3 nM CGRP I or II. In the presence of 58 nM sCT, the maximal enzyme activity represented 120% of the basal value. No additive effect was observed; this suggests that both CGRP and sCT activities are mediated through the same receptor. The present data are in favour of a role for this neuropeptide operating in branchial cell functions such as calcium transfer from the external to the internal milieu.

Calcitonin and calcitonin gene-related peptide in the shrimp, Palaemon serratus: Variations during the molt cycle

Abstract 1. 1. The presence of both salmon calcitonin (CT) and human calcitonin gene-related peptide (CGRP) was investigated in tissues of Palaemon serratus. 2. 2. The variation of these two molecules was studied as a function of the molt cycle. 3. 3. The highest salmon CT concentration was found in the eyestalks and heart whereas CGRP was mainly concentrated in the heart, gills and eyestalks. 4. 4. In the eyestalk, both CT and CGRP-like immunoreactivity were maximal at the B stage. In the haemolymph, the calcium fall observed in the B stage was correlated with the CT increase. No correlation appeared between the circulating calcium and the CGRP concentration.

Calcitonin variations in male and female trout, Salmo gairdneri, during the annual cycle

Calcitonin (CT) levels in the ultimobranchial body and in plasma were radioimmunoassayed in rainbow trout, Salmo gairdneri, as a function of the annual cycle. In male and female, there was an important increase in the CT levels in the ultimobranchial body and in plasma. These variations in CT levels in both male and female suggest that sexual maturity influences the synthesis and the secretion of calcitonin in fishes. A positive correlation was observed between plasma and ultimobranchial CT levels and the gonadosomatic index in both sexes, suggesting that CT has a role in the processes involved in gonadal development.

Epitopes of the 44–68 human parathyroid hormone fragments: The importance of specific hydrophilic peptide sequences

Several pentapeptides included in the 44-68 sequence of human parathyroid hormone (hPTH) were synthesized simultaneously on benzhydrylamine and m-nitrobenzhydrylamine resins. The first polymer gave the free peptide and the second the peptidyl-resin complex. An ELISA test carried out with each peptidyl-resin complex showed that all the anti-44-68 hPTH antibodies raised in different animal species are directed against the same hPTH pentapeptidic sequence. This sequence is very hydrophilic and is specific to the hormone. This study demonstrates the importance of specific peptide chains in an epitope.