Changes in the alpha-adrenoceptors in the medulla oblongata including nucleus tractus solitarii of spontaneously hypertensive rats

摘要

The nucleus tractus solitarii (NTS) is a brain stem center mediating depression of blood pressure. In order to elucidate a possible mechanism for the central regulation of blood pressure, we studied noradrenergic indices in the medulla oblongata, a region including the NTS, in spontaneously hypertensive rats (SHR) as compared with normotensive controls of the Wistar Kyoto strain (WKY) at 12 weeks of age. The medulla oblongata was the only brain region showing a significantly low noradrenaline level in the SHR as compared with WKY rats; the level is also significantly decreased at 8 weeks of age. The alpha 1-adrenergic binding sites, as measured with 2-(2′, 6′-dimethoxy) phenoxyethylamine-methylbenzodioxan 3HWB4101 showed significant increases inKDandBmaxvalues in medulla oblongata homogenates from rats of both strains from 4–12 weeks after birth, with no significant interstrain difference. On the other hand, theKDandBmaxof the alpha 2-sites, measured by 3Hyohimbine binding, were reduced in SHR as compared to WKY animals, even at 4 weeks after birth when hypertension was not yet apparent. As expected, the relatively selective alpha 2-antagonist, clonidine, was a potent inhibitor of 3Hyohimbine binding but not of 3HWB4101 binding in these homogenates. The results suggest that some genetic disorder in the alpha 2-adrenergic transmission system in the NTS region may be involved in the development of hypertension in the SHR