Modification of clonidine-induced pressor responses in morphine-dependent and hypophysectomised rats.
Pressor responses to successive doubling doses of clonidine were examined in anaesthetised normotensive (NT) and spontaneously hypertensive rats (SHR). The slope of the dose-response curves was similar in both strains of rat, but the average response to the same concentrations of clonidine was less in the SHR. Naloxone (2 mg/kg i.v.) did not alter the dose-response curve in either strain. However, in NT and SHR made morphine-dependent (3 X 75 mg morphine pellets s.c.) and in hypophysectomised rats the increase in blood pressure was significantly reduced compared to the untreated or sham operated control groups, with a decrease in both the slope of the dose-response curve and a decrease in the average response. These results suggest that opioid peptide systems can modify vascular reactivity although not via circulating peptides. The specificity of the effects remains to be established.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006973:Hypertension / Q000503:physiopathology; D007016:Hypophysectomy; D008297:Male; D009021:Morphine Dependence / Q000503:physiopathology*; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR
D009270:Naloxone; D003000:Clonidine