Population data evidence of interdependence of the limbs of hormonal feedback loops

in Journal of Endocrinology
Authors:
Stephen P Fitzgerald Departments of General Medicine and Endocrinology, The Royal Adelaide Hospital, Adelaide, Australia
The University of Adelaide, Discipline of Medicine, Adelaide Medical School, Adelaide, Australia

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Nigel G Bean School of Mathematical Sciences, University of Adelaide, Adelaide, Australia

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Henrik Falhammar Department of Endocrinology, Karolinska University Hospital, Stockholm, Sweden
Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden

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Rudolf Hoermann Klinikum Lüdenscheid, Paulmannshöherstr, Lüdenscheid, Germany

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Yael Korem Kohanim Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, USA

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Hermann Pohlabeln Department Biometry and Data Management, Leibniz Institute for Prevention Research and Epidemiology – BIPS, Bremen, Germany

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Niels Grote Beverborg Department of Cardiology University Medical Center Groningen, University of Groningen, Groningen, The Netherlands

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Sarah Tomassetti Hematology-Oncology Division, Harbor-UCLA Medical Center, Torrance, California, USA
Health Sciences, UCLA, Los Angeles, California, USA
The Lundquist Institute, Harbor-UCLA Medical Center, Torrance, California, USA

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Correspondence should be addressed to S P Fitzgerald: stephen.fitzgerald2@sa.gov.au
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The fundamental models underlying hormonal physiological regulation and homeostasis remain poorly understood. We aimed to derive quantitative evidence regarding these models from the study of population data of balance points of different parameters and their respective controlling hormones. We studied the slopes of correlations between concentrations of circulating free thyroxine and thyrotropin, calcium and parathyroid hormone, hemoglobin and erythropoietin, and glucose and insulin in such population data, as well as the slopes of the limbs of various feedback loops estimated empirically and by reverse engineering of the population data. We used computer simulations to model the factors that influence the slopes derived from the population data, and then matched these simulations with the empirically derived slopes. Our simulations showed that changes to the population distribution of feedback loop limbs may alter the slopes of correlations within population data in specific ways. Non-random (interdependent) associations of the limbs of feedback loops may also have this effect, as well as producing discrepancies between the slopes of feedback limb loops determined experimentally and the same slopes determined by derivation from population data. Our corresponding empirical findings were consistent with the presence of such interdependence in the free thyroxine/thyrotropin, hemoglobin/erythropoietin, and glucose/insulin systems. The glucose/insulin data provided evidence consistent with increasing interdependence with age in childhood. Our findings therefore provide strong evidence that the interdependence of the limbs of feedback loops is a general feature of endocrine homeostatic regulation. This interdependence potentially bestows evolutionary homeostatic and regulatory advantages.

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