Uptake and clearance of exogenous estradiol-17β and testosterone during the early development of coho salmon (Oncorhynchus kisutch), including eggs, alevins and fry

Abstract

The uptake and clearance of estradiol-17β (E2) and testosterone (T) were examined during the initial stages of development of coho salmon (Oncorhynchus kisutch), including eyed-eggs, newly hatched alevins and first feeding fry. Radiolabeled steroids were administered through the water in tracer amounts with or without their nonradioactive form at 400 μg l(-1). Regardless of developmental stage, saturation levels were invariably attained earlier for T than for E2, thus resulting in a higher incorporation of E2. However, both steroids had similar clearance patterns. Uptake and clearance was clearly stage-dependent, being fastest in fry, intermediate in alevins and slowest in eggs. Furthermore, combined uptake and clearance patterns showed that exposure to steroid was also higher for E2 than for T and stage-dependent, but always markedly highest in alevins. Subsequently, based on the observed elimination of the estrogen, a double immersion in E2 at 400 μg 1(-1), administered 2 days apart to maximize exposure during the alevin stage, was assayed for its effect on sex reversal and found to induce the production of 100% females. We suggest that the yolk, which is present in substantial amounts during the initial stages of development in salmonids, can retain the exogenously administered liposoluble steroids, thus providing developing embryos with an extended supply of, and exposure to, these steroids well after the treatment is finished. Together, these findings help to explain the previously observed high effectiveness of sex steroids administered during early development in regulating gonadal differentiation in salmonids, the higher effectiveness of E2 compared to T, and clarify the localization of the most sensitive period to the action of exogenous steroids at the alevin stage in the coho salmon.

Steroids in chicken egg yolk: Metabolism and uptake during early embryonic development

“…This conversion may explain the rapid decrease in yolk hormone levels within the first days of incubation reported in previous studies (Bowden et al, 2002;Eising et al, 2003;Elf and Fivizzani, 2002). Steroid metabolism by the embryo and the extraembryonic membranes (yolk sac, allantois, amnion, chorion) has been observed in all species studied so far, in fish (Antila, 1984;Piferrer and Donaldson, 1994), amphibians (Antila, 1977), reptiles (Painter and Moore, 2005;Paitz and Bowden, 2008), birds Parsons, 1970) and mammals (Levitz, 1966). Chick blastoderm can metabolise steroid hormones in vitro even within the first 2 days after laying Parsons, 1970), producing both conjugated and free steroids.…”

Estrogen responses in killifish (Fundulus heteroclitus) from polluted and unpolluted environments are site- and gene-specific

“…A possible interpretation is that high ERα expression in progeny of NBH is due to exposure to estrogenic NBH contaminants accumulated in yolk, as previously observed in embryos derived from fish exposed to steroids (Piferrer and Donaldson, 1994; Yeoh et al, 1996). If so, this implies that the ERα autoregulatory loop is operative, and would be predicted to lead to increased expression of other ERα gene targets.…”

Sulfation and uptake of the maturation-inducing steroid, 17α,20β-dihydroxy-4-pregnen-3-one by rainbow trout ovarian follicles

“…Kime et al (1992) noticed significant uptake of radioactive steroids by goldfish ovarian tissue, and Kime and Abdullah (1994) found that, as in the present study, the amount which was taken up was increased, rather than decreased, by the addition of cold steroid. Piferrer and Donaldson (1994) showed that fertilized eggs and alevins of coho salmon were able to take up exogenous testosterone and 17f3-estradiol, and suggested that it was the yolk which was responsible for absorbing the steroids. This is in agreement with the results of the present study which showed that yolkextruded follicles do not take up label.…”