Profile Photo of Duncan MacKenzie
Duncan MacKenzie

Associate Professor


Fax: 979-845-2891

3258 TAMU
Biological Sciences Building East
Room 306E

Biological Sciences Building East
Room 306

Joined the Department in 1983

  • B.S., 1975, University of Calfornia, Davis, Zoology.
  • Ph.D., 1980, University of California, Berkeley, Zoology.
  • Postdoctoral research: University of Alberta.

Comparative Endocrinology of Thyroid Function

Hormones secreted by the thyroid gland are of primary importance in the regulation of such fundamental physiological processes as growth, nutrient utilization, and reproduction. In my laboratory we examine the regulation of the secretion of thyroid hormones and their actions in poikilothermic vertebrates in order to understand the evolution of thyroid function. We are presently focusing on the regulation on thyroid hormone secretion and the mechanisms of iodine transport in commercially-important fish species such as the red drum (Sciaenops ocellatus), the channel catfish (Ictalurus punctatus), and even the zebrafish (Danio rerio).

We have discovered that blood thyroxine levels undergo robust daily cycles in the red drum, supporting a role for an endogenous clock in the central control of thyroid hormone production. Current studies are directed towards examining the regulation of thyroid hormone cycles and determining their physiological significance. I am also interested in the specific mechanisms through which nutrient intake influences thyroid hormone secretion and the manner in which thyroid hormone delivery to target tissues is influenced by circulatory factors unique to poikilotherms.  Thyroid hormone studies have led us to an examination of the mechanisms through which euryhaline fish obtain iodine from their environment.  We are currently examining the physiology of iodide transport in fish and hope to integrate it into a better understanding of the maintenance of thyroid homeostasis in variable marine environments.

A comparative perspective is always maintained in my research. Because of their position at the transition to endothermy, reptiles remain an interesting model for the examination of thyroid hormone action. For this reason, I also direct research on endocrine function in reptiles, such as sea turtles, desert tortoises, and alligators. From these animals we gain a broader perspective of the relationship between nutrient intake, temperature, and thyroid hormone production.

This research is aimed at providing new insights into the potentially ancient role of thyroid hormones in nutrient assimilation, as well as elucidating evolutionary trends in the regulation of thyroid function. These studies may serve identify ways in which the pituitary-thyroid axis may be manipulated to enhance aquaculture production or endangered species conservation.