The present study investigated the hypotensive responses to intravenous (i.v.) treatment with the
essential oil of Alpinia zerumbet (EOAZ) and its main constituent,
terpinen-4-ol (Trp-4-ol), in the experimental model of
deoxycorticosterone-
acetate (
DOCA)-
salt hypertensive rat. In both
DOCA-
salt hypertensive and uninephrectomized, normotensive rats, i.v. bolus
injections of EOAZ (1-20 mg/kg) or Trp-4-ol (1-10 mg/kg) decreased mean aortic pressure (MAP) in a dose-related manner. However, hypotensive responses to Trp-4-ol were significantly greater than those evoked by the same doses of EOAZ (1-10 mg/kg). Treatment with
DOCA-
salt significantly enhanced the maximal percentage decreases in MAP evoked by EOAZ or Trp-4-ol. Likewise, both maximal percentage and absolute decreases in MAP elicited by i.v. injection of the
ganglion blocker,
hexamethonium (30 mg/kg), were significantly greater in
DOCA-
salt hypertensive than in control rats. In
DOCA-
salt hypertensive rats, neither
hexamethonium (30 mg/kg, i.v.) nor
methylatropine (1 mg/kg, i.v.) pretreatment affected the enhancement of EOAZ-
induced hypotension. These results show that i.v. treatment with either EOAZ or Trp-4-ol dose-dependently decreases blood pressure in conscious
DOCA-
salt hypertensive rats, and this action is enhanced when compared with uninephrectomized controls. This enhancement could be related mainly to an increase in EOAZ-induced vascular smooth muscle relaxation rather than to enhanced sympathetic nervous system activity in this hypertensive model. The data further support our previous hypothesis that hypotensive effects of EOAZ are partially attributed to the actions of Trp-4-ol.