The effects of cortisol on heat shock protein 70 levels in two fish species.

We studied the relationship between heat stress (2 h, +12 degrees ) and increased levels of circulating cortisol (50 microg cortisol/g body weight) on heat shock protein 70 (hsp70) levels in liver and gill tissues of rainbow trout (Oncorhynchus mykiss) and tilapia (Oreochromis mossambicus). The administration of cortisol by intraperitoneal injection (no heat stress) did not alter tissue hsp70 levels compared to sham implanted (no heat stress) trout and tilapia. We found elevated levels of cortisol significantly suppressed the heat stress-induced levels of hepatic hsp70 by 34.2% and 31.0%, 3 and 24 h post-heat stress, respectively, compared to sham implanted trout. Additionally, elevated levels of cortisol significantly suppressed the heat stress-induced levels of gill hsp70 by 66.2% in trout (3 h post stress) and 26.7% in tilapia (4 h post stress), compared to sham implanted fish. These results suggest that cortisol may be mediating hsp70 levels in fish tissues following times of physiological stress, and that the neuroendocrine and cellular stress responses may be functionally related in these two different species of fish. Copyright 2001 Academic Press.