Capsaicin treatment in adult Wistar-Kyoto and spontaneously hypertensive rats: effects on substance P contents of peripheral and central nervous system tissues

The effects of s.c. capsaicin treatment on the contents of immunoreactive substance P (ISP) in several peripheral and central nervous system tissues were examined in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Significant differences between vehicle-treated subjects of the WKY and SHR strains were observed in the ISP contents of both superior cervical and celiac sympathetic ganglia. Capsaicin pretreatment significantly reduced the ISP contents of both sympathetic ganglia in both strains. Capsaicin pretreatment significantly elevated the ISP contents of adrenal medullae only in rats of the SHR strain. The effects of s.c. capsaicin administration on the ISP contents of several selected isolated brain nuclei were also examined. No statistically significant strain or treatment differences in the SIP contents of the nucleus tractus solitarii nucleus locus ceruleus and periaqueductal central gray were observed. The ISP contents of the nucleus raphe magnus, periventricular preoptic area, and nucleus amygdaloideus medialis were significantly greater in vehicle-treated SHR rats than in vehicle-treated WKY animals. Capsaicin pretreatment significantly increased the ISP contents of both the periventricular preoptic area and nucleus amygdaloideus medialis in SHR rats. These results indicate that the effects of capsaicin treatment of the ISP contents of nervous systems tissues vary with both the tissues examined and the strain of rat. In addition, the previously reported long-lasting hypotensive effect produced by capsaicin in both the WKY and SHR strains may be related to the significant depletion of the ISP contents in peripheral sympathetic ganglia in both strains.