High-affinity, low-capacity estradiol-17?? (E2) binding is present in rainbow trout scale. The K(d) and B(max) of the scale E2 binding are similar to those of the liver E2 receptor (K(d) is 1.6 ?? 0.1 and 1.4 ?? 0.1 nM, and B(max) is 9.1 ?? 1.2 and 23.1 ?? 2.2 fmol x mg protein-1, for scale and liver, respectively), but different from those of the high-affinity, low-capacity E2 binding in plasma (K(d) is 4.0 ?? 0.4 nM and B(max) is 625.4 ?? 63.1 fmol x mg protein-1). The E2 binding in scale was displaced by testosterone, but not by diethylstilbestrol. Hence, the ligand binding specificity is different from that of the previously characterized liver E2 receptor, where E2 is displaced by diethylstilbestrol, but not by testosterone. The putative scale E2 receptor thus appears to bind both E2 and testosterone, and it is proposed that the increased scale resorption observed during sexual maturation in both sexes of several salmonid species may be mediated by this receptor. No high-affinity, low-capacity E2 binding could be detected in rainbow trout gill or skin. (C) 2000 Academic Press.
Additional Publication Details
The presence of high-affinity, low-capacity estradiol-17?? binding in rainbow trout scale indicates a possible endocrine route for the regulation of scale resorption