抄録
In Spontaneously Hypertensive Rats (SHR), the pain reaction threshold tends to be much higher than that in normotensive rats. This insensitivity in SHR is considered to be attributed to chronic hypertension. Then, using naloxone to make the pain reaction threshold decrease we examined changes in the level of blood pressure in SHR. The present study consists of two sessions : l) measurement of pain threshold by hot-plate method and 2) that of blood pressure. Fourteen male SHRS and 14 normotensive Wistar-Kyoto strain rats (WKY) were used in the pain-threshold session. Each group of the two strains was divided into two subgroups of 7 rats each to make the drug effect clear; one of the subgroups was injected with naloxone (0.2mg/kg, IP) and the other with saline (1.0ml/kg, IP). For the blood-pressure measurement 10 male SHRs and WKYs were used; here too each group was divided into two subgroups. The result showed that the pain reaction thresholds in the SHR rats were significantly higher than in the WKY rats at pre-injection periods; twenty minutes after the injection the thresholds of naloxone-injected SHRS Were significantly decreased while those of saline-injected SHRS little changed. This indicated that naloxone could be effective in heightening the sensitivity of heat stimulation. Blood-pressure levels in the SHR rats were significantly higher than the WKY rats at pre-injection periods. After the injection of naloxone the blood pressure levels remained unchanged in naloxone-injected SHRs. Thus, naloxone had no effect on the blood pressure level in the SHRs. The chronically-generated insensitivity in SHRS is probably related to the action of endogenous opiate system within the brain rather than of blood pressure regulation system.
