Kinetics of primary and secondary stimulation of the mRNA for APOVLDL-II, a major yolk protein, in the cockerel liver by estrogen

ApoVLDL-II, the major very low density lipoprotein (VLDL) apoporotein, is also a major yolk protein in the chicken. The response of apoVLDL-II mRNA to estrogen treatment in 5-week-old cockerels was studied by hybridization to a nick-translated probe from cloned apoVLDL-II DNA. Following either primary or secondary stimulation (9 days after primary stimulation) of cockerels with 17 beta-estradiol (5 mg/kg), apoVLDL-II mRNA concentration increased from basal levels of 0.5 and 3.7 molecules/nuclear DNA equivalent respectively by 500- to 1000-fold within 3 h. The concentration of apoVLDL-II mRNA after 3 h during the secondary stimulation reached a level (1800 molecules/cell) 3.6-fold higher than that attained by primary stimulation (500 molecules/cell) at the same time point. Plasma 17 beta-estradiol concentrations following primary and secondary hormone treatment were similar during this time.