Central alpha 2-adrenoceptor responsiveness in borderline hypertensive rats.

Increased dietary NaCl intake increases the responsiveness of central nervous system alpha 2-adrenoceptors which regulate the neural control of renal function in spontaneously hypertensive rats (SHR) but not Wistar-Kyoto (WKY) normotensive rats. The borderline hypertensive rat (BHR) is the first filial offspring of the SHR and the WKY. With increased dietary NaCl intake, the BHR develops hypertension and expresses other characteristics of the hypertensive SHR parent. This investigation sought to determine whether increased dietary NaCl intake in the BHR enhances the responsiveness of central nervous system alpha 2-adrenoceptors. Six weeks of increased dietary NaCl intake (8% versus 1% NaCl) in BHR augmented the depressor, bradycardic, renal sympatho-inhibitory and diuretic responses to intracerebroventricular administration of graded doses (5, 25 and 125 micrograms) of the alpha 2-adrenoceptor agonist, guanabenz. The results suggest that the potential for an increased responsiveness of central nervous system alpha 2-adrenoceptors is genetically transmitted to the BHR by the SHR and may be exposed in the BHR by increased dietary NaCl intake.