IL-6 microinjected in the nucleus tractus solitarii attenuates cardiac baroreceptor reflex function in rats

1 Department of Physiology, Wakayama Medical University School of Medicine, Wakayama; 2 Department of Therapeutic Health Promotion, Kansai University of Health Sciences, Osaka, Japan; and 3 Department of Physiology and Pharmacology, Bristol Heart Institute, School of Medical Sciences, University of Bristol, Bristol, United Kingdom Submitted March 26, 2009 ; accepted in final form November 5, 2009 Recent gene array and molecular studies have suggested that an abnormal gene expression profile of interleukin-6 (IL-6) in the nucleus tractus solitarii (NTS), a pivotal region for regulating arterial pressure, may be related to the development of neurogenic hypertension. However, the precise functional role of IL-6 in the NTS remains unknown. In the present study, we have tested whether IL-6 affects cardiovascular control at the level of the NTS. IL-6 (1, 10, and 100 fmol) was microinjected in the NTS of Wistar rats (280–350 g) under urethane anesthesia. Although the baseline levels of arterial pressure and heart rate did not change following IL-6 injections, the cardiac baroreflex in response to increased arterial pressure was dose-dependently attenuated. In addition, IL-6 (100 fmol) microinjections also attenuated L -glutamate-induced bradycardia at the level of the NTS. Immunohistochemical detection of IL-6 in naïve rats demonstrated that it was predominantly observed in neurons within the brain stem, including the NTS. These findings suggest that IL-6 within the NTS may play an important role for regulating cardiovascular control via modulation of input signals from baroreceptor afferents. Whether the abnormal gene expression of IL-6 in the NTS is associated in a causal way with hypertension remains to be resolved. interleukin-6; blood pressure Address for reprint requests and other correspondence: H. Waki, Dept. of Physiology, Wakayama Medical Univ. School of Medicine, 811-1 Kimiidera, Wakayama 641-8509, Japan (e-mail: h-waki{at}wakayama-med.ac.jp ).