A decrease in angiotensin receptor binding in rat brain nuclei by antisense oligonucleotides to the angiotensin AT1 receptor

Intracerebroventricular (i.c.v.) injections of antisense oligonucleotides against mRNA of the angiotensin type 1 (AT1) receptor have been shown to reduce blood pressure in spontaneously hypertensive (SHR) rats and angiotensin II-induced drinking in both SHR and Sprague-Dawley (SD) rats. The present investigation was designed to quantify the effect of i.c.v. injections of antisense oligonucleotides to the AT1 receptor mRNA on brain angiotensin receptors using membrane binding and autoradiographic analysis. Control injections contained sense or scrambled oligonucleotides or saline. Three daily injections of antisense oligonucleotides into the third ventricle of SD rats decreased the AT1 receptor number significantly by 25% in a hypothalamic tissue block. AT2 receptors were not altered. Autoradiography showed a decrease in angiotensin receptor number in hypothalamic nuclei and in the anteroventral region of the third ventricle (AV3V) after antisense treatment. AT2 receptors were not reduced indicating the AT1 antisense oligonucleotides were specific. In a second series of experiments, single injections of antisense oligonucleotides into the lateral ventricle of SHR rats were tested. Antisense oligonucleotides produced a significant decrease in receptor number in the same hypothalamic area. Sense and scrambled oligonucleotides did not decrease the receptor numbers significantly. The decreases observed after injection of antisense oligonucleotides were between 15 and 30%. These changes may be sufficient to account for the physiological effects of i.c.v. injections of antisense oligonucleotides to AT1 receptor mRNA.