Effects of L-citrulline diet on stress-induced cold hypersensitivity in mice
Yoshinori Kobayashi1, Kazuki Narita1, Kotaro Chiba1, Hiroaki Takemoto1, Masahiko Morita2, Koji Morishita2
1 Laboratory of Pharmacognosy, School of Pharmaceutical Sciences, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo, 108-0861, Japan
2 Healthcare Products, Development Center, Kyowa Hakko Bio Co., Ltd, 2, Miyukigaoka, Tsukuba, Ibaraki, 305-0841, Japan
School of Pharmaceutical Sciences, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641
Source of Support: The Ministry of Education, Science, Sports and Culture
Grant-in-Aid for Scientific Research, Conflict of Interest: None
Background: L-citrulline is an amino acid discovered in watermelon (Citrullus lanatus, Cucurbitaceae) and is a known component of the nitric oxide (NO) cycle that plays an important role in adjusting blood circulation and supplying NO and a key component of the endothelium-derived relaxing factor. Objective: The objective of this study is to evaluate the effect of L-citrulline on a newly established stress-induced cold hypersensitivity mouse model. Materials and Methods: When normal mice were forced to swim in water at 25°C for 15 min, their core body temperature dropped to 28.9°C, and then quickly recovered to normal temperature after the mice were transferred to a dry cage at room temperature (25°C). A 1-h immobilization before swimming caused the core body temperature to drop to ca. 24.1°C (4.8°C lower than normal mice), and the speed of core body temperature recovery dropped to 57% of the normal control. We considered this delay in recovery from hypothermia to be a sign of stress-induced cold hypersensitivity. Similar cold hypersensitivity was induced by administration of 50 mM L-NG-nitroarginine methyl ester, a NO synthesis inhibitor. Results: In this study, we showed that recovery speed from the stress-induced hypothermia remarkably improved in mice fed a 1% L-citrulline-containing diet for 20 days. Furthermore, the nonfasting blood level of L-arginine and L-citrulline increased significantly in the L-citrulline diet group, and higher serum nitrogen oxide levels were observed during recovery from the cold. Conclusions: These results suggested that oral L-citrulline supplementation strengthens vascular endothelium function and attenuates stress-induced cold hypersensitivity by improving blood circulation.