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Published on: December 26, 2011
The apparent hysteresis in hormone-agonist relationships
William A Pruett1, Robert L Hester, Thomas G Coleman
1Department of Physiology, Center for Computational Medicine, University of Mississippi Medical Center, Jackson, MS 39216 4505, USA. wpruett@umc.edu
Journal of Theoretical Biology
|December 14, 2011
Summary
Hormone systems exhibit hysteresis due to inherent delays, not gland sensitivity. Mathematical modeling reveals this delay-dependent phenomenon explains over-secretion in hormone-agonist axes.
Area of Science:
- Endocrinology
- Mathematical Biology
- Systems Biology
Background:
- The calcium-parathyroid hormone (PTH) axis and other hormone systems show apparent hysteresis.
- Hysteresis in biological systems can complicate the interpretation of experimental data.
Purpose of the Study:
- To mathematically model a hormone-secretagogue system to explain observed hysteresis.
- To investigate the role of delays and concentration-dependent secretion in generating hysteresis.
Main Methods:
- Developed a simple mathematical model of a hormone and secretagogue system.
- Incorporated concentration-dependent secretion and two distinct time delays.
- Simulated hormone-agonist axis profiles using four experimental protocols.
Main Results:
- Observed delay- and load-dependent hysteresis as a mathematical artifact.
- Identified that delays in the corrective mechanism lead to hormone over-secretion.
- Demonstrated that rate dependence is a result of the corrective mechanism, not gland sensitivity.
Conclusions:
- Apparent hysteresis in hormone systems is primarily an artifact of inherent system delays.
- The secretory mechanism itself is not sensitive to the magnitude of change, but rather the delays influence the observed dynamics.
- Mathematical modeling provides a framework for understanding complex physiological phenomena like hysteresis.
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