Target organs for androgens in two teleost fishes, Atlantic salmon, Salmo salar, and three-spined stickleback, Gasterosteus aculeatus

Abstract: The major androgen in male teleost fishes is 11-ketotestosterone (11KT) and not testosterone (T) as in mammals. 11KT has often been found to be more effective than T in stimulating teleost male secondary sexual characters (SSC's). The main aim of this thesis was to investigate how androgens, in particular 11KT, act on target organs in teleost fishes.Androgen binding was studied in three sexually dimorphic androgen target organs in teleosts, the kidney in the male three-spined stickleback, Gasterosteus aculeatus, which hypertrophies during the breeding season and produces a glue used in the building of a nest, the skin in male salmon, which increases in thickness during breeding season and finally the salmon heart, which increases in size during the breeding season. Binding of 11KT was detected in both the kidney and skin, two androgen dependent SSC's where 11KT has been found to be more effective than T. In contrast, only specific binding of T was found in the salmon heart, although 11KT and T are equally effective in stimulating heart growth. Thus, different androgen dependent target organs in fish appear to be controlled via different mechanisms.Specific binding of 11KT was detected in both tissue pieces and membrane fractions from the kidney of the stickleback and in the skin from Atlantic salmon, Salmo salar. The localisation of 11KT binding to membrane fractions suggests a different mechanism of action for 11KT than via traditional intracellular receptors.A specific binding of 11KT was found in the salmon brain membrane fraction, where tritiated 11KT could be displaced by unlabelled T and less effectively by 11KT. A specific binding of tritiated T was also detected in the brain membrane fraction, with T again being more effective than 11KT in displacement. T and 11-ketoandrostenedione (11KA, which is known to be extratesticulary converted to 11KT) administration can be to have similar effects on secretion of follicle stimulating hormone in summer. All these results are consistent with a shared action site for T and 11KT in the brain.Specific binding of T but not of 11KT could be detected in Atlantic salmon gill cytosolic and nuclear fractions. This suggests that the previously known impairment of androgens on salmon seawater adaptability could be due to a direct effect of androgens on the gills.The stickleback nest building glue was characterised and found to consist almost entirely of a major protein with an apparent molecular size of 203 kDa. It was named spiggin after the Swedish name for stickleback, spigg. Spiggin production could be induced by 11KT treatment and is so far the only protein known to be induced by 11KT.