British Journal of Nutrition

Research Article

Effect of a γ-aminobutyric acid-enriched dairy product on the blood pressure of spontaneously hypertensive and normotensive Wistar–Kyoto rats

Kazuhito Hayakawaa1 c1, Masayuki Kimuraa1, Keiko Kasahaa1, Keisuke Matsumotoa1, Hiroshi Sansawaa1 and Yukio Yamoria2

a1 Yakult Central Institute for Microbiological Research, 1796 Yaho, Kunitachi-shi, Tokyo 186-8650, Japan

a2 International Center for Research on Primary Prevention of Cardiovascular Diseases, 86-2 Shimobara-cho Jodoji,Sakyo-ku, Kyoto 606-8413, Japan

Abstract

We investigated the blood-pressure-lowering effects of γ-aminobutyric acid (GABA) and a GABA-enriched fermented milk product (FMG) by low-dose oral administration to spontaneously hypertensive (SHR/Izm) and normotensive Wistar–Kyoto (WKY/Izm) rats. FMG was a non-fat fermented milk product produced by lactic acid bacteria, and the GABA contained in FMG was made from the protein of the milk during fermentation. A single oral dose of GABA or FMG (5 ml/kg; 0·5 mg GABA/kg) significantly (P>0·05) decreased the blood pressure of SHR/Izm from 4 to 8 h after administration, but did not increase that of WKY/Izm rats. The hypotensive activity of GABA was dose-dependent from 0·05 to 5·00 mg/kg in SHR/Izm. During the chronic administration of experimental diets to SHR/Izm, a significantly slower increase in blood pressure with respect to the control group was observed at 1 or 2 weeks after the start of feeding with the GABA or FMG diet respectively (P>0·05) and this difference was maintained throughout the period of feeding. The time profile of blood-pressure change due to administration of FMG was similar to that of GABA. FMG did not inhibit angiotensin 1-converting enzyme. Furthermore, an FMG peptide-containing fraction from reverse-phase chromatography lacked a hypotensive effect in SHR/Izm rats. The present results suggest that low-dose oral GABA has a hypotensive effect in SHR/Izm and that the hypotensive effect of FMG is due to GABA.

(Received October 22 2003)

(Revised April 29 2004)

(Accepted May 11 2004)

Correspondence:

c1 *Corresponding author: fax +81 42 577 3020, Email kazuhito-hayakawa@yakult.co.jp

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