Pharmacological responses to acute morphine administration in normotensive Wistar-Kyoto and spontaneously hypertensive rats

The effect of acute administration of morphine on analgesia, hyperthermia, hypothermia and catalepsy was determined in spontaneously hypertensive (SH) rats and normotensive Wistar-Kyoto (WKY) rats. A greater analgesic and hyperthermic response to morphine was observed in SH rats than in WKY rats. A dose of morphine (50 mg/kg ip) which produced hypothermia in WKY rats produced pronounced hyperthermia in SH rats. The cataleptic response to morphine was lower in SH rats. The cataleptic response to morphine was lower in SH rats than in WKY rats. The brain and plasma levels of morphine in SH rats were significantly lower as compared to the WKY rats at any dose of morphine used but the ratio of brain to plasma did not differ. It is concluded that SH rats exhibit altered sensitivity to morphine in comparison with their normotensive counterparts.