Gila Monsters
Field Site

Team DeNardo

Carol (Christel) Hurst

BA. Biology 2000, Lewis and Clark College
Ph.D. Biology, 2006, Arizona State University

Doctoral Research Interest

My work focused on the endocrinology of feeding and digestion in Gila Monsters, and how this physiological aspect has influenced their natural history.


Dissertation Work

My research on Gila Monsters, Heloderma suspectum, combined endocrinology and metabolism with ecological life history. More specifically, I was interested in the role of exendin-4 in Gila Monsters. Exendin-4 is a recently identified peptide hormone isolated from the saliva of the Gila Monster. Research on exendin-4 has focused primarily on its glucose-lowering activity in mammals, which is similar to that associated with glucagon-like peptide 1 (GLP-1). Much of this research is directed towards using exendin-4 as an anti-diabetic agent, and currently synthetic exendin-4 is being tested in clinical trials. While these clinical trials have assessed the efficacy to which exendin-4 achieves a targeted physiological goal, the overall activity of exendin-4 remains poorly understood. This deficiency may result in missed potential implications for biomedical use, missed untoward side-effects, or a missed opportunity for a greater understanding of the physiological mechanisms of glucose homeostasis.

To address this lack of information on exendin-4, I studied this protein hormone in Gila Monsters. Exendin-4 is found only in this species, which raises several questions as to its role and evolution. My dissertation experiments were designed to describe the function of exendin-4 in Gila Monster physiology with these basic questions in mind:

1) Where is exendin-4 acting?
2) What triggers the release of exendin-4?
3) What affect does exendin-4 have on Gila Monster metabolism?
4) Why and how might this protein hormone have evolved?

By using a captive Gila Monster population, I measured endogenous exendin-4 levels in response to food, exogenous exendin-4, and anti-exendin-4 treatments. Further experimentation included exploration into the molecular and cellular mechanisms by which exendin-4 exerts its effect on glucose homeostasis as well as exploration into additional effects on other body systems. The results from my research gave us an idea of how exendin-4 acted in its native organism and also provided insight on the evolution of metabolic control mechanisms.

Past Research

As an undergraduate at Lewis and Clark College, I worked with Dr. Kenneth Clifton investigating the foraging ecology of shorebirds within coastal wetlands.


Publications from work while in the DeNardo lab

Christel, C. M., Secor, S. M., and DeNardo, D. F. (2007) Metabolic and digestive response to food ingestion in a binge-feeding lizard, the Gila monster (Heloderma suspectum). Journal of Experimental Biology 210: 3430-3439.

Christel, C. M., and DeNardo, D. F. (2007) Absence of exendin-4 effects on postprandial glucose and lipids in the Gila monster, Heloderma suspectum, Journal of Comparative Physiology B. 177: 129-134.


Christel, C. M., DeNardo, D. F. (2006) Release of exendin-4 is controlled by mechanical action in Gila Monsters, Heloderma suspectum. Comparative Biochemistry and Physiology, Part A 143: 85–88.

© 2005 DeNardo Lab. All elements contained within this web site are the exclusive copyright of ASU and/or its authors and may not be used or reproduced for any purpose without express written permission.