Soy and phytoestrogens. Their effects on vitellogenesis and steroid endocrinology in the rainbow trout and in the Siberian sturgeon. In vivo and in vitro approaches.

The development of a new sex determination test of Siberian sturgeon based on vitellogenin (VTG) detection in plasma led to identify this complex fact or in plasma from male, female and immature fish of this species. The hypot hesis of an estrogenic contamination from an environmental origin was confi rmed by a test based on the feeding of fish on different diets. In control fish fed with a casein-based diet free of any estrogenic compound, VTG disa ppeared from the plasma within 15 weeks. With a fish meal-based diet as wel l as with a soy-based diet, the plasma VTG levels raised significantly. Lat er, an estrogenic effect of soy orally administrated was demonstrated in vi vo in the rainbow trout although it is lower than that observed in sturgeon . Soya is known to contain phytoestrogens which were demonstrated to be estro genic when injected in vivo in yearling Siberian sturgeon. These compounds were then tested in vitro in hepatocyte culture obtained from rainbow trout . Results were shown to be different between male and female at the onset o f vitellogenesis. This difference is explained, up to now, by a difference in the initial levels of estradiol receptor available between males and fem ales and between very young fish and fish undergoing their gametogenesis. In vitro, in the rainbow trout equol, one of the major phytoestrogens was f ound to have an inhibitory effect on the ovarian aromatase activity. This c ompound can also bind to the rainbow trout Steroid Binding Protein (SBP) wh ereas in sturgeon at least two compounds namely equol and genistein can com pete for SEP with testosterone. In vivo tests realised in the rainbow trout recently showed that all vegeta ble crude matter are not equivalent in terms of phytoestrogens contents and it seems to us crucial to set up a new assay of these compounds to be able to correlate doses in diets and effects recorded in fish.