Effects of pollutants on interrenal steroidogenesis:mechanisms underlying species differences in vulnerability

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Recognition and reaction to stressful stimuli is a physiological response that occurs in all vertebrates, including teleost fish. Secretion of cortisol is activated during acute exposures to stressors, including pollutants, and the increase in blood cortisol is believed to be beneficial. However overactivation of the stress response can be detrimental and there is new evidence that the interrenal tissue itself can be a target of pollutants. Thus the role of cortisol in the physiological response to pollutants in teleosts is not entirely clear.   Our research program is focused on interrenal steroidogenesis, synthesis of cortisol by steroidogenic cells found, with other cell types, in the interrenal tissue of teleosts. The objective of the proposed research program is to determine the cellular characteristics and the mechanisms underlying species-specific differences in the cortisol stress response and in vulnerability of the steroidogenic cells to pollutants. Working with rainbow trout (highly sensitive to pollutants) and fathead minnow (less sensitive), we will use an in vitro approach, with either the whole interrenal tissue or steroidogenic cells purified with Percoll gradients, in combination with in vivo exposures of whole fish. The effects of test pollutants (Cd-non essential metal; Se-essential metal; Roundup-pesticide) on the functional integrity of the steroidogenic cells (basal and ACTH-stimulated cortisol and cAMP production, cell viability), their oxidative status  (catalase, GSH/GSSG, SOD) and intracellular calcium homeostasis will be assessed in vitro and in vivo in the two fish species. The role of cortisol during in vivo exposures to the toxicants will be investigated using metyrapone and RU-486, a blocker of cortisol receptors. Effects of temperature on the responses to the toxicants will be also assessed, an issue of importance given climate change and the gradual warming of our aquatic ecosystems. Comparison of rainbow trout and the minnow will provide data to help us understand the cellular characteristics that make organisms and their tissues vulnerable to pollutants. This knowledge can be used in setting up of water quality guidelines that will protect our aquatic species and in management of our fisheries.