Kinetics of avian vitellogenin messenger RNA induction. Comparison between primary and secondary response to estrogen.

Following either primary or secondary stimulation of cockerels with 17beta-estradiol, vitellogenin mRNA begins to accumulate in the liver after about 30 min, reaches a maximum in 3 days, and decays thereafter with a half-life of 30 h. During primary induction, accumulation of vitellogenin mRNA begins at a low rate (50 nucleotides/s/nuclear equivalent of DNA) and after 4 h, shifts to a higher rate (340 nucleotides/s/nuclear equivalent of DNA). In contrast, during secondary induction (administration of estrogen several weeks after the primary response has ceased), accumulation of vitellogenin mRNA begins at the rate of 350 nucleotides/s/nuclear equivalent of DNA and subsequently increases by about 40%. These accumulation rates result in a maximal level of vitellogenin mRNA that is approximately 1.5 times higher during secondary stimulation than that found during primary stimulation. This difference is sufficient to explain the anamnestic response to secondary hormonal stimulation that results in higher levels of circulating vitellogenin in the plasma of the rooster.