Effect of 17β estradiol and progesterone on the conformation of the chromatin of the liver of female Japanese quail during aging

Plasma levels of 17β estradiol and progesterone were measured by radioimmunoassay in immature, adult and old female Japanese quails. The levels of progesterone and the progesterone/estradiol ratio were maximum in adult, egg laying birds. Conformation of the chromatin of the liver of birds of various ages before and after administration of steroid hormones was studied by digesting the nuclei with micrococcal nuclease (MNase) and pancreatic deoxyribonuclease I (DNase I) followed by electrophoretic resolution of the DNA fragments. The pattern of bands shows that the chromatin of the adult is more sensitive to DNase I and MNase than that of young and old birds. Administration of 17β estradiol and progesterone enhances the digestion of the chromatin by DNase I and MNase in old birds. Such enhancement does not occur in adult birds as the chromatin is already in relaxed and open conformation due to the high levels of the hormones already present at this age.