Differential responsiveness of avian vitellogenin I and vitellogenin II during primary and secondary stimulation with estrogen.

Avian vitellogenin consists of two major species, VTG I and VTG II, which show major differences in structure and immunological properties suggesting that VTG I and VTG II are distinct gene products. During primary stimulation with estrogen, VTG I was found to accumulate in plasma much more slowly than VTG II. At 1 day after hormone treatment VTG I was only 1-3% of VTG II, but by day 5 VTG I increased to approximately 25% of VTG II. Measurements of hepatic vitellogenin synthesis confirmed the slower induction and reduced expression of VTG I. A further difference was noted in the amnestic or memory response to secondary estrogen treatment. Measurements of VTG I and VTG II accumulation and synthesis after primary and secondary estrogen treatment showed that the memory response occurs to a much greater extent for VTG I than VTG II. These differences indicate that the inductions of VTG I and VTG II are not tightly coupled.