DOWN-REGULATION OF CORTICOSTEROID RECEPTORS IN GILLS OF COHO SALMON DUE TO STRESS AND CORTISOL TREATMENT

The effect of stress and cortisol treatment on corticosteroid receptors (CRs) in the gills of coho salmon (Oncorhynchus kisutch) was examined. Plasma cortisol levels were elevated acutely by intraperitoneal injection of cortisol 21-hemisuccinate and chronically by implanting miniosmotic pumps filled with cortisol or by repeated daily handling stresses. CR concentration and affinity were measured by radioreceptor assay employing H-3-labeled triamcinolone acetonide as ligand. Acute administration of cortisol resulted in a reduction in CR numbers for 72 h with no change in affinity. Chronic cortisol treatment resulted in a decrease in CR concentration and affinity. The change in affinity occurred only while plasma cortisol levels remained elevated, but CR population remained significantly reduced for at least 10 days after cessation of hormone treatment. Repeated handling stresses resulted in a similar reduction in CR numbers but without an apparent change in affinity. The chronic or repeated elevation in plasma cortisol downregulates the sensitivity of the gills to cortisol by a persistent reduction in CR concentration, despite the return to nonstress levels of circulating cortisol.