Renal Catecholamines and α2-Adrenergic Receptors in Salt-Related and Genetic Hypertension

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Abstract
Increased dietary salt intake alters renal function which often leads to deleterious cardiovascular consequences. Studies were carried out to characterize the effects of high-salt diets on renal catecholamines and α2-adrenergic receptors. These parameters were evaluated in both genetic and acquired forms of hypertension and also in normotensive rats on high-salt diets. Renal catecholamine content was determined by high-performance liquid chromatography with electrochemical detection. Renal α2-adrenergic receptor-binding studies were performed on whole kidney homogenates using 3H-p-aminoclonidine to label both high- (0.5 nM) and low-affinity (5.0 nM) renal α2-adrenergic receptors. Increased salt intake elevated blood pressure, decreased renal norepinephrine stores and resulted in renal α2-adrenergic receptor up-regulation in deoxycorticosterone acetate salt hypertensive rats, Dahl-S rats and COX-SHR. The decreased renal stores of norepinephrine (NE) appeared to reflect increased renal NE utilization. In contrast, SHR (Charles River) had elevated NE stores and α2-adrenergic receptors while on normal salt diets. Short-term (10–14 days) exposure to high-salt diets had modest effects in normotensive rats or COX-SHR, although it was sufficient to increase low affinity renal α1-adrenergic receptor number. Renal dopamine metabolism was also altered by high-salt diets. These studies demonstrated a relationship between renal NE content and renal α2-adrenergic receptors. The implications of this relationship and other salt-related changes in renal catecholamine metabolism were discussed as they pertained to hypertension and renal function.

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