Renal catecholamines and alpha 2-adrenergic receptors in salt-related and genetic hypertension

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 alpha 2-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 alpha 2-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 alpha 2-adrenergic receptors. Increased salt intake elevated blood pressure, decreased renal norepinephrine stores and resulted in renal alpha 2-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 alpha 2-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 alpha 2-adrenergic receptor number. Renal dopamine metabolism was also altered by high-salt diets. These studies demonstrated a relationship between renal NE content and renal alpha 2-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.