Based on an assembly of experimental observations in the rat, sheep, horse and human, the stress-responsive corticotropic-adrenal axis can be viewed as a dynamically adaptive feedback system supervised by key brain (hypothalamic) regulatory centers. The latter secrete episodic bursts of ACTH (adrenocorticotropic hormone)-releasing hormone (CRH) and arginine vasopressin (AVP). Hypophyseal-portal venous CRH and AVP signals act individually and jointly to stimulate ACTH synthesis, accumulation and secretion by the anterior pituitary gland. Systemic ACTH concentrations in turn drive adrenal cortisol secretion via a time-lagged feedforward dose-response function. Blood cortisol inhibits brain CRH/AVP production via both rapid rate-sensitive (differential) and time-delayed concentration dependent (integral) feedback mechanisms. Cortisol also represses corticotrope ACTH secretion via differential feedback and pituitary ACTH synthesis and storage via integral feedback control. While this connectionistic concept reasonably reflects available observations in the human and animal, precisely how the ensemble corticotropic axis maintains effectual homeostasis and reacts time-dependently to internal stress (disease) and external (environmental) demands is not known. To begin to formalize the key mechanisms that govern the time-evolving reactivity of this integrated network, the present goal is to: (a) frame and validate a new biomathematical formalism to encapsulate multivalent, nonlinear, time-lagged combined feedforward and feedback signaling; and (b) implement selected interventional experiments in the human and horse to further elucidate axis dynamics. To this end, we pose four specific aims: (1) to formalize a preliminary biomathematical construct that embodies the major physiological connections and dose-response interfaces within this life-supporting axis; (2) to test specific a priority clinical hypotheses of mechanisms linking 24-h (circadian) rhythmicity and ultradian (pulsatile) output; (3) to evaluate the mechanisms of homeostatic adaptation of CRH/AVP and ACTH release driven by acute cortisol withdrawal and repletion in the human and horse; and (4) to begin to estimate endogenous CRH/AVP-ACTH-cortisol dose-response properties in corresponding human and animal models. We believe that the foregoing unique marriage of clinical, experimental and biomathematical strategies will further enhance understanding of the complex and dynamic mechanisms underlying pathophysiological control of conjoint CRH/AVP-ACTH-cortisol secretion, and thus clarify new issues in the diagnosis, treatment and prevention of stress-related disease and disability.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
7R01DK060717-02
Application #
6620413
Study Section
Pharmacology A Study Section (PHRA)
Program Officer
Sato, Sheryl M
Project Start
2002-03-01
Project End
2006-02-28
Budget Start
2002-07-01
Budget End
2003-02-28
Support Year
2
Fiscal Year
2002
Total Cost
$208,348
Indirect Cost
Name
Mayo Clinic, Rochester
Department
Type
DUNS #
City
Rochester
State
MN
Country
United States
Zip Code
55905
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Veldhuis, Johannes D; Iranmanesh, Ali; Mielke, Kristi et al. (2006) Ghrelin potentiates growth hormone secretion driven by putative somatostatin withdrawal and resists inhibition by human corticotropin-releasing hormone. J Clin Endocrinol Metab 91:2441-6
Veldhuis, Johannes D; Keenan, Daniel M; Roelfsema, Ferdinand et al. (2005) Aging-related adaptations in the corticotropic axis: modulation by gender. Endocrinol Metab Clin North Am 34:993-1014, x-xi
Liu, Peter Y; Takahashi, Paul Y; Roebuck, Pamela D et al. (2005) Age-specific changes in the regulation of LH-dependent testosterone secretion: assessing responsiveness to varying endogenous gonadotropin output in normal men. Am J Physiol Regul Integr Comp Physiol 289:R721-8
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Liu, Peter Y; Pincus, Steven M; Keenan, Daniel M et al. (2005) Joint synchrony of reciprocal hormonal signaling in human paradigms of both ACTH excess and cortisol depletion. Am J Physiol Endocrinol Metab 289:E160-5
Keenan, Daniel M; Chattopadhyay, Somesh; Veldhuis, Johannes D (2005) Composite model of time-varying appearance and disappearance of neurohormone pulse signals in blood. J Theor Biol 236:242-55

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