Tissue-specific induction of Hsp90 mRNA and plasma cortisol response in Chinook salmon following heat shock, seawater challenge, and handling challenge

In studying the whole-body response of chinook salmon (Oncorhynchus tshawyt scha) to various stressors, we found that 5-hour exposure to elevated tempe rature (mean 21.6 degrees C; + 10.6 degrees C over ambient) induced a marke d increase in Hsp90 messenger RNA accumulation in heart, brain, gill, muscl e, liver, kidney, and tail fin tissues. The most vital tissues (heart, brai n, gill, and muscle) showed the greatest Hsp90-mRNA response, with heart ti ssue increasing approximately 35-fold. Heat shock induced no increase in pl asma cortisol. In contrast, a standard handling challenge induced high plas ma cortisol levels, but no elevation in Hsp90 mRNA in any tissue, clearly s eparating the physiological and cellular stress responses. We saw no increa se either in tissue Hsp90 mRNA levels or in plasma cortisol concentrations after exposing the fish to seawater overnight.