ESTRADIOL REGULATION OF ALPHA(1B)-ADRENOCEPTOR MESSENGER-RNA IN FEMALE RAT HYPOTHALAMUS-PREOPTIC AREA

Estradiol treatment for 48 h increases the density of alpha(1B)-adreno ceptors in the hypothalamus-preoptic area of ovariectomized female rat s by five- to six-fold. Present studies tested the hypothesis that est radiol elevation of hypothalamus-preoptic area alpha(1b)-adrenoceptor density is correlated with increased levels of mRNA for this receptor. We developed a semiquantitative reverse transcriptase-polymerase chai n reaction (RT-PCR) protocol for measuring brain alpha(1b)-adrenocepto r mRNA. The primers chosen yielded the predicted 409 base pair PCR pro duct when used to amplify authentic alpha(1b)-adrenoceptor cDNA. The i dentity of the RT-PCR products from rat brain was confirmed by restric tion digest analysis and sequencing. Moreover, there was a good correl ation between the levels of alpha(1b)-adrenoceptor mRNA measured by RT -PCR in liver, whole brain and cerebellum with previous measurements u sing Northern blots and RNAse protection assays. We then performed RT- PCR on total RNA from hypothalamic-preoptic area tissue taken from ova riectomized control rats and from ovariectomized rats injected once or twice with 2 mu g of estradiol benzoate at 24 or 24 and 48 h before s acrifice. Exposure to estradiol for either 24 or 48 h significantly in creased levels of alpha(1b)-adrenoceptor mRNA by 86-110% in the hypoth alamus-preoptic area of ovariectomized female rats when compared to oi l-treated controls. We also examined whether estradiol regulates alpha (1b)-adrenoceptor mRNA in the cortex. Cortical alpha(1b)-adrenoceptor mRNA levels were reduced to approximately 20% of control levels when m easured 24 h after hormone injection. A similar decrease in cortical a lpha(1b)-adrenoceptor mRNA was observed 48 h after estrogen administra tion. In summary, estradiol treatment significantly increases the leve l of alpha(1b)-adrenoceptor mRNA in the hypothalamus-preoptic area, a brain region involved in the control of reproductive function. In the cortex, a brain region with relatively few estrogen receptors, the sam e estrogen treatment reduces alpha(1b)-adrenoceptor mRNA levels.