Hormone-secreting glands communicate via intermittent (pulsatile or rhythmic) signal exchange. Signals act upon target glands via implicit (not directly observable) stimulatory and inhibitory dose-response functions. Time delays operate, since secreted hormones do not arrive at or act on responsive cells instantaneously. Neuroendocrine systems are unique examples, therefore, of intermittent time-delayed dose-dependent homeostatic ensembles. Investigating such ensembles thus requires estimating secretion from plasma concentrations, recognizing biological time-delays and reconstructing unobserved feedforward (agonist) and feedback (antagonist) dose-response interfaces as illustrated primarily for the GnRH-LH-T-axis, and secondarily for the corticotropic and somatotropic axes. In this manner, each neuroendocrine system is viewed as a whole, rather than the sum of individual parts.
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