Plasma levels of five androgens and 17α-hydroxy-20β-dihydroprogesterone in immature and mature male Baltic salmon (Salmo salar) parr, and the effects of castration and androgen replacement in mature parr

Abstract

During the spawning period, the plasma levels of the androgens 11-ketotestosterone, testosterone, 11β-hydroxytestosterone, 11β-hydroxyandrostenedione, 11-ketoandrostenedione, and of the progestin 17α-hydroxy-20β-dihydroprogesterone were higher in mature compared with immature male Baltic salmon parr. 11-Ketotestosterone was always found to be the predominant androgen in the plasma of mature male parr and mature anadromous males. Mature male parr and large mature anadromous males had similar androgen profiles during the main spawning period, although 11-ketotestosterone tended to be higher in the mature anadromous males and testosterone was always higher in the mature male parr. At the time of the main spawning period, plasma levels of 17α-hydroxy-20β-dihydroprogesterone rose sharply in mature male parr, these levels being similar to those found in the plasma of large mature anadromous males. All measured androgens were low or nondetectable in castrated parr. Treatment of castrated parr with Silastic capsules containing 11-ketoandrostenedione resulted in high plasma 11-ketoandrostenedione levels and even higher levels of 11-ketotestosterone, indicating an extratesticular site of androgen conversion.