Lack of an effect of estrogen on endogenous RNA polymerase II in guinea pig brain

An early action of estrogen in peripheral target tissues is to increase endogenous RNA polymerase II activity which precedes changes in protein synthesis. Previous reports have indicated that estrogen causes a similar increase in polymerase activity in rat brain regions containing high affinity receptors for this hormone. The present series of experiments was designed to test whether a similar action of estrogen on polymerase activity occurs in guinea pig brain, with the expectation being that this enzyme might prove to be a useful marker for the early actions of estrogen. Injections of 25 or 100 μg estradiol-17β in an ethanol-saline vehicle failed to induce significant changes in polymerase II activity in the basal hypothalamus, preoptic area-septum or cortex 1, 2, 6, 13 or 24 h after hormone administration. It is concluded that the modification of RNA polymerase II activity by estrogen is not a good marker for estrogen action in the brain. This may be due to the intrinsic heterogeneity of the tissue resulting possibly in (1) increased activity in some cells and decreased activity in other cells with no net change in overall polymerase activity after estrogen treatment (2) only a small percentage of the cells responding to the steroid with altered polymerase activity with this change not detectable when whole tissue is measured or (3) only a few genes within the cells being altered in transcription by the steroid.