Changes in plasma levels of vitellogenin in the black-tailed gull, Larus crassirostris, after treatment with estradiol-17beta

Abstract Lipovitellin (Lv), the major vitellogenin (Vg)-derived yolk protein, was purified from egg yolk of the black-tailed gull, Larus crassirostris, by hydroxylapatite column chromatography followed by gel filtration. The apparent mass of native Lv was -280 kDa, while its corresponding subunit mass estimated by SDS-PAGE was -100kDa. A specific antiserum against purified gull Lv (a-gLv) was generated in a rabbit. In Western blotting. a-gLv specifically reacted with a polypeptide (-220 kDa) present in blood plasma of female and estrogen-treated male gulls, but not nornal males, suggesting that this polypeptide represents the primary subunit of gull Vg. A single radial immunodiffusion (SRID) assay was developed for gull Vg using the a-glove. The assay was specifically targeted to gull Vg and plasma levels of Vg could be expressed as relative concentrations equivalent to Lv, when purified gull Lv was used as the assay standard. The time-course of changes in plasma Vg levels was assessed for up to 60 hours after a single injection of estradiol-17v (E sub 2) was administered to male gulls. The effect of E2 concentrations on plasma Vg induction appeared dose-dependent. Plasma Vg reached its maximum level (61.7 mg/ml) at 60 hr after E sub 2 administration (50 mg/kg body weight), while lower E sub 2 doses (O.05, 0.5 mg/kg body weight) resulted in earlier peak Vg levels (24 hr after injection). These results indicated that production of gull Vg was induced directly by estrogen within 24 hours. These developments in biochemical characterization of Lv and Vg, along with establishment of the SRID assay for Vg and knowledge of the endocrine regulation of Vg synthesis in the black-tailed gull, set the stage for the survey of endocrine disruption of avian reproduction in the wild.