ANDROGEN-BINDING IN THE GILLS OF ATLANTIC SALMON, SALMO-SALAR, MATUREMALE PARR, AND IMMATURE MALE SMOLTS

In general, salmonid fishes undergo morphological, physiological, and behavioural changes, known as smoltification, before migrating out to the sea. Among these changes is an increased Na+-K+-ATPase activity in the gills that improves the hypoosmoregulatory ability. Earlier studi es have shown that androgens impair the hypoosmoregulatory ability in salmonids. The aim of the present study was to investigate if this obs erved effect of androgens could result from a direct action at the lev el of the gills. To that extent, the gills of two-summer-old mature ma le Atlantic salmon, Salmo salar, parr or immature smelts, were homogen ized and cytosolic and nuclear fractions were incubated with labelled testosterone (T) or 11-ketotestosterone (11KT) with or without unlabel led steroid added. A receptor like binding for T, but not for 11KT, wa s found in the cytosol and nuclei of mature male pan; with a KD of 1.3 nM in the cytosol and 3.0 nM in the nuclei. The binding of labelled T in the cytosol could be displaced with unlabelled T, 11KT and 5 alpha -dihydrotestosterone but no displacement of labelled T could be detect ed with estradiol, progesterone, cortisol, or with the antiandrogens f lutamide and cyproterone acetate. No significant differences in T rece ptor affinity or capacity could be observed when cytosolic fractions f rom mature male salmon parr or immature male smelts were compared; KD of 1.1 nM, Bmax 103 fmol/mg protein and KD 1.1 nM, Bmax 75 fmol/mg pro tein, respectively. (C) 1997 Wiley-Liss, Inc.