Effect of green tea rich in γ-aminobutyric acid on blood pressure of Dahl salt-sensitive rats

γ-Aminobutyric acid (GABA) is known to be involved in the regulation of blood pressure by modulating the neurotransmitter release in the central and peripheral sympathetic nervous systems. This study investigated the antihypertensive effect of green tea rich in GABA (GABA-rich tea) in young and old Dahl salt-sensitive (S) rats. GABA-rich tea was made by fermenting fresh green tea leaves under nitrogen gas. In experiment 1, 21 11-month-old rats, fed a 4% NaCl diet for 3 weeks, were given water (group W), an ordinary tea solution (group T), or a GABA-rich tea solution (group G) for 4 weeks. The average GABA intake was 4.0 mg/rat per day. After 4 weeks of the treatment, blood pressure was significantly decreased in group G (176 ± 4; P< .01) compared with group W (207 ± 9) or group T (193 ± 5 mm Hg). Plasma GABA levels were more elevated in group G (111 ± 54) than in group W (not detectable) or group T (14 ± 8 ng/mL; P< .01 v G). In experiment 2, 21 5-week-old rats, fed a 4% NaCl diet, were divided into groups W, T, and G. The average GABA intake was 1.8 mg/rat per day. Body weight or chow and beverage consumption did not differ significantly among the three groups. After 4 weeks of the treatment, although blood pressure was comparable in groups W and T (165 ± 3 v 164 ± 5 mm Hg, mean ± SE), it was significantly lower in group G (142 ± 3 mm Hg) than in the other groups (P< .01). Plasma aldosterone concentration was increased in group G compared to the other groups. Thus, GABA-rich tea seems not only to decrease the established high blood pressure but to prevent the development of hypertension in Dahl S rats fed a high salt diet.