Analog Computer Model for the ACTH-Glucocorticoid System

A closed-loop analog computer model for corticosterone dynamics in the male rat is presented in an attempt to examine some existing experimental evidence which suggests contradictory characteristics of the ACTH-glucocorticoid system. First-order compartmental kinetics model the removal of ACTH and corticosterone from the blood. Nonlinear models are used to describe the release of corticosterone by the rat adrenal cortex in response to ACTH in blood, and for the release of ACTH by the anterior pituitary in response to corticotrophin-releasing factor (CRF) in the hypophyseal portal system. Curve-fitting techniques are used for each system function to adjust the analog to obtain good agreement with laboratory data. The gross characteristics of the neurosecretion of CRF and the resulting ACTH secretion are identified by using portions of the model to simulate various physical experiments.