Plasma concentrations of ovarian steroids in the freshwater European silver eel (Anguilla anguilla L.): effects of hypophysectomy and transfer to sea water.
Intact and hypophysectomized freshwater (FW) silver eels were transferred to tanks of FW or artificial sea water (SW; salinity = 0.60 osmol/l) which were simultaneously renewed twice a week. Fish were killed 2 months after transfer and plasma was assayed for ovarian steroids. In all fish, 5 alpha-androstane-3 beta,17 beta-diol was present, while 5 alpha-dihydrotestosterone and 5 alpha-androstane-3 alpha,17 beta-diol were undetectable. In intact FW eels, plasma levels of testosterone, 5 alpha-androstane-3 beta,17 beta-diol and oestradiol-17 beta were approximately 0.15 nmol/l. In intact SW eels, no change in plasma levels of testosterone and 5 alpha-androstane-3 beta,17 beta-diol was found, whereas the concentration of oestradiol-17 beta was increased significantly (P less than 0.01), indicating stimulation of aromatase activity. In hypophysectomized compared with intact FW fish, plasma levels of testosterone and 5 alpha-androstane-3 beta,17 beta-diol were decreased (P less than 0.05) and there was a slight but significant (P less than 0.01) augmentation of the plasma concentration of oestradiol-17 beta which may have involved the removal of pituitary-dependent inhibition of aromatase activity, possibly by 5 alpha-reduced compounds. In hypophysectomized compared with intact SW fish, plasma levels of testosterone, 5 alpha-androstane-3 beta,17 beta-diol and oestradiol-17 beta were decreased (P less than 0.05); in the case of oestradiol-17 beta, this may have reflected the diminished ovarian synthesis of testosterone, its precursor. The plasma level of oestradiol-17 beta was, however, higher in SW than in FW fish, even in hypophysectomized eels. This suggests that extra-pituitary mechanisms mediate, at least partly, the effects of transfer to SW on aromatase activity.
Quérat
B
B
Laboratoire de Physiologie Générale et Comparée, Muséum National d'Histoire Naturelle, Paris, France.
Nahoul
K
K
Hardy
A
A
Fontaine
Y A
YA
Leloup-Hâtey
J
J
D000728:Androgens / Q000097:blood; D000811:Anguilla / Q000502:physiology*; D000818:Animals; D004958:Estradiol / Q000097:blood; D005260:Female; D006854:Hydrocortisone / Q000097:blood; D007016:Hypophysectomy; D010053:Ovary / Q000502:physiology*; D011374:Progesterone / Q000097:blood; D012623:Seawater; D013974:Thyroxine / Q000097:blood
D000728:Androgens; D011374:Progesterone; D004958:Estradiol; D013974:Thyroxine; D006854:Hydrocortisone