Capsaicin treatment in adult Wistar-Kyoto and spontaneously hypertensive rats: effects on nociceptive behavior and cardiovascular regulation.

Effects of s.c. capsaicin pretreatment on nociception, mean systemic arterial blood pressure, and dose-response curves for depressor effects of substance P (SP) and pressor effects of angiotension II (AII) and norepinephrine (NE) were examined in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Capsaicin pretreatment significantly elevated hot plate and tail flick latencies in SHR subjects but was without effect in WKY rats. Capsaicin pretreatment significantly reduced mean systemic arterial blood pressure in rats of both strains. Both vehicle- and capsaicin-treated WKY subjects exhibited greater depressor responses than did subjects of the corresponding SHR groups after i.v. SP administration. Vehicle-treated SHR subjects exhibited greater pressor responses to both AII and NE than did rats of the vehicle-treated WKY group. Capsaicin treatment decreased the sensitivity of WKY rats to the pressor effects of both AII and NE. Strain differences involving nociception, cardiovascular regulation, and responses to capsaicin may underly the results reported.