9781934874615-ch14

Methods for Fish Biology, 2nd edition

Chapter 14: Endocrinology

Jennifer D. Jeffrey, Nicholas J. Bernier, and W. Gary Anderson

doi: https://doi.org/10.47886/9781934874615.ch14

The nineteenth century French physiologist Claude Bernard wrote, “The constancy of internal environment has become the condition of the free and independent life” (Bernard 1878). Bernard’s work focused on mammalian physiology, and he is credited by many for being the first to recognize the concept of homeostasis and understand that maintenance of the “milieu intérieur” required constant and careful regulation: that is, endocrine control. Some 15 years later, the first “cause and effect” comparative endocrine paper was published when Bayliss and Starling (1903) demonstrated that pancreatic secretions into the intestine were stimulated by a hormone released into the circulation from enteroendocrine cells lining the duodenum. Unlike Bernard, Bayliss and Starling’s initial studies were truly comparative as they used extracts of dogfish intestine to demonstrate the evolutionary significance of their findings across all vertebrates. At that time the American physiologist, Walter Cannon, was also working on gut function but soon shifted focus to examine the general effects of the adrenal medulla and from these studies was able to develop his thesis of the now well-described “fight or flight” response (Cannon 1914). Cannon’s work laid the foundation for the “general adaptation syndrome” developed by Hans Selye (1936), by which, following exposure to a stressor, an organism’s early physiological and behavioral responses are under endocrine control striving to maintain homeostasis. Most recently, the concept of achieving stability (survival) through change, or allostasis, has been developed to include the impact of exposure to a series of stressors over time with the assumption being that an organism will incur an “allostatic load” through time that may result in increased prevalence to disease and/or reduced fitness as they age (McEwen 2000). These studies serve to track the evolution of our understanding of how exposure to a stressor impacts an organism in the short and long term and how successful coordination by endocrine agents of the physiological and behavioral responses are a cornerstone to the survival of any species. Needless to say, endocrine agents are involved in the regulation of all physiological systems, and while the vast majority of studies are mammalian based, there is remarkable functional conservancy in endocrinology across all vertebrates.