DOWN-REGULATION OF ALPHA-2 ADRENOCEPTORS IN VENTROLATERAL MEDULLA OF SPONTANEOUSLY HYPERTENSIVE RATS

The binding of [H-3]idaxazon to imidazole sites and [H-3]rauwolscine to alpha-2 adrenoceptors of neuronal membranes prepared from cerebral cortex and ventrolateral medulla of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [H-3]idaxazon bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [H-3]idaxazon in ventrolateral medulla and cerebral cortex was found to be similar in SHR and WKY rats. [H-3]Rauwolscine bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [H-3]rauwolscine in the cerebral cortex was found to be similar in SHR and WKY rats. However, in the ventrolateral medulla [H-3]rauwolscine binding was found to be significantly lower in SHR as compared to WKY rats. The decreased binding was due a decrease (32 %) in the B(max) value in SHR rats as compared to WKY rats. The K(d) values were similar in SHR and WKY rats. It is concluded that imidazole binding sites are not affected while, alpha-2 adrenergic binding sites are decreased in the ventrolateral medulla of SHR rats and may be contributing to the regulation of blood pressure.