MULTIPLE RESPONSE PATTERNS TO OESTROGENIC STIMULATION IN THE AVIAN LIVER

Abstract

The response patterns of vitellogenin, very low density lipoprotein-apoprotein B (apo VLDL-B), and serum albumin were examined following oestrogen administration to roosters. Vitellogenin synthesis was not detectable in the absence of hormone treatment, but increased to a maximum within 3-6 days following oestrogen treatment. The hormone-stimulated increase in vitellogenin synthesis was paralleled by the accumulation of vitellogenin mRNA. In contrast to the complete oestrogen-dependence of vitellogenin synthesis, an appreciable level of apo VLDL-B synthesis was seen in the absence of exogenous hormone treatment. Following oestrogen treatment, the hepatic synthesis of apo VLDL-B increased to an extent similar in magnitude to the increase in vitellogenin synthesis. In the case of apo VLDL-B, oestrogen appears to modulate the expression of a gene which is expressed to a significant extent in the absence of the hormone. In contrast to the positive effects of oestrogen on vitellogenin and apo VLDL-B, the hepatic content of serum albumin mRNA was seen to decrease following hormone treatment. Comparison of the response patterns of these proteins suggests that oestrogen may exhibit multiple modes of control over the expression of different genes within the same cell.