High blood cortisol levels and low cortisol receptor affinity: Is the chub, Leuciscus cephalus, a cortisol-resistant teleost?

In contrast to the relatively minor intra- and interspecies differences in blood cortisol levels reported for salmonid species, there is a more pronou nced distinction between cortisol levels among the Salmonidae and the Cypri nidae, with both basal and stress-induced cortisol levels markedly higher i n the latter. This study shows that in the chub, Leuciscus cephalus, a wide ly distributed European cyprinid, mean blood cortisol levels during stress (1500 ng mL(-1)) exceeded those reported for most other species of fish and , even in unstressed chub, cortisol levels (50-100 ng mL(-1)) were within t he range known to cause immunosuppression, growth retardation, and reproduc tive dysfunction in salmonid fish. The chub appears to be atypical only wit h respect to plasma cortisol levels; the levels of plasma glucose and plasm a lactate in unstressed and stressed chub are similar to those reported for other species. Plasma levels of 11-ketotestosterone in males and: 17 beta -estradiol in females are lower than those reported for salmonids but simil ar to those reported for other cyprinid species and display clear stress-in duced reduction. Comparative analysis of the binding characteristics of the trout and chub gill cortisol receptor revealed that the total number of bi nding sites in gill tissue for each species was similar (B-max; similar to 50-100 fmol mg(-1) protein). However, the affinity of the binding site for cortisol displayed an eightfold difference between the species (rainbow tro ut: K-d similar to6 nM; chub: K-d similar to 50 nM). Therefore, the potenti ally adverse effects of high circulating levels of cortisol found both at r est and under conditions of stress in chub may be offset by the lower affin ity of the cortisol receptor, rather than the abundance of target-tissue re ceptor sites. This strategy is similar to that reported for some glucocorti coid-resistant rodents and New World primates. (C) 2000 Academic Press.