Several studies have shown that green tea improves lower urinary tract (LUT) symptoms in humans. Although green tea contains various constituents, most such studies have focused on the antioxidant effects of (-)-epigallocatechin gallate. Few studies have examined the effects of other constituents of green tea on LUT dysfunction (LUTD). We therefore focused on L-theanine, one of the amino acids mainly derived from green tea. L-theanine is a known source of flavonoid antioxidants and promotes relaxation. We investigated the effects of L-theanine on LUTD in spontaneously hypertensive rat (SHR).

Adult (12-week-old) SHRs were divided into two groups (controls, n=7; L-theanine, n=10).  The control group was allowed free access to food and tap water. The L-theanine group was allowed free access to food and L-theanine solution (78 µg/mL). After 6 weeks, voiding behavior studies and cystometric studies were performed in both groups. After cystometric study, bladder tissue was harvested for pharmacological studies, histological examinations and protein expression analysis. Contractile responses to 80-mM KCl, electrical field stimulation, 1-mM ATP and carbachol (Cch) in organ baths were recorded. Malondialdehyde(MDA), a biomarker for oxidative stress, was assessed by immunohistochemical staining and Western blotting. A Values of p<0.05 were considered statistically significant.

Body and bladder wet weights did not differ significantly control and L-theanine groups (body weight: 356 ± 16 g vs 355 ± 9 g, p=0.70; bladder wet weight: 0.194 ± 0.027 g vs 0.181 ± 0.024 g, p=1.00). The voiding behavior study showed that micturition frequency was lower in the L-theanine group (21.3 ± 5.5) than in controls (16.3 ± 3.6, p<0.05). Urine output did not differ between the L-theanine group (14.6 ± 3.53 g/day) and controls (13.1 ± 3.03 g/day, p=0.06). Cystometric studies showed micturition intervals were significantly smaller in controls (6.07 ± 1.23 min) than in the L-theanine group (8.13 ± 1.79 min, p<0.05). Although no significant differences were evident, cystometric capacity tended to higher in the L-theanine group (1.34 ± 0.35 g) than in controls (1.03 ± 0.25 g, p=0.11). No significant differences among groups were evident in maximal detrusor pressure, post-void residual or bladder compliance. Contractile responses of bladder strips to KCl, electrical field stimulation, Cch and ATP were significantly higher in the L-theanine group than in controls. MDA was obviously expressed in the urothelium of controls compared with the L-theanine group on immunohistochemistry. In addition, Western blotting analysis showed that expression of MDA was decreased in bladder tissue of the L-theanine group.

Our results suggest that L-theanine is effective in preventing LUTD in SHRs. Several studies have showed that oxidative stress plays an important role in hypertension-related bladder dysfunction. L-theanine seems to reduce oxidative stress, protecting LUT function in SHR.

These results imply that LUTD in SHR is ameliorated by L-theanine in Japanese green tea.