Suppression of catechol-O-methyltransferase activity through blunting of α2-adrenoceptor can explain hypertension in dahl salt-sensitive rats

Abstract

Catecholamines have been reported to be involved in the development of salt-sensitive hypertension. We investigated the relation between catechol-O-methyltransferase (COMT) and salt-sensitivity. In the first experiment, Dahl salt-sensitive (DS) rats were given a normal-salt (NS), high-salt (HS), or HS + hydralazine (80 mg/l water) diet for 4 or 13 weeks, and Dahl salt-resistant (DR) rats were given a NS or HS diet. COMT activities in both the kidneys and liver and urinary norepinephrine (NE) and doparnine (DA) excretion were measured. In the second experiment, HepG2 cells were used to investigate the role of NE in regulating COMT activity. In the third experiment, we investigated the reactivity of pre- and postsynaptic a2-adrenoceptor (AR) in DS rats. HS loading significantly suppressed the activities of membrane-bound COMT (MB-COMT) and, consistent with this finding, increased the urinary NE level in DS rats, but not in DR rats. Hydralazine did not restore the MB-COMT activities, which suggested that HS loading rather than elevated blood pressure suppressed the MB-COMT activities. The in vitro experiment using HepG2 cells revealed that NE increased the MB-COMT activity via the α2-AR. However, both the pre- and postsynaptic α2-AR reactivity was decreased by HS loading in DS rats. In conclusion, HS intake suppresses the MB-COMT activities in DS rats, presumably by blunting α2-AR signaling. The suppression of MB-COMT activities, consequent decrease in degradation of NE, and increase in NE release by blunting of α 2-AR function may be involved in the development of salt-sensitive hypertension in DS rats, in whom DA-dependent natriuresis may be suppressed.