Factors affecting angiotensin II-induced hypothermia in rats.
Systemic administration of angiotensin II (AII) to the rat has previously been shown to induce a dose-dependent, hypothermic response manifested by a fall in colonic temperature (CT), a decrease in heat production and an increase in tail skin temperature (TST). The factors mediating AII-induced hypothermia and their site of action were the subjects of the present investigation. To this end, intracerebroventricular administration of 1 microgram of AII induced a 0.4 degrees C reduction in CT and a 2.4 degrees C increase in TST. In contrast, SC administration of 200 micrograms angiotensin III/kg induced a slight increase in CT but had no affect on TST. Pretreatment with the AII-receptor antagonist, saralasin, at either 1 or 10 micrograms/kg, SC did not affect either the fall in CT or the increase in TST induced by administration of 200 micrograms AII/kg, SC. However, the administration of 100 micrograms saralasin/kg, SC attenuated both the fall in CT and the increase in TST induced by either 100 or 200 micrograms AII/kg. Since both the presynaptic alpha adrenoceptor agonist, clonidine, and the opioid antagonist, naloxone, modulate the pressor and dipsogenic responses to AII, their effects on AII-induced hypothermia were tested. Both clonidine (25 micrograms/kg, SC) and naloxone (1 mg/kg, IP) enhanced the fall in CT. Clonidine lengthened the duration of the increase in TST while naloxone had no effect. Pretreatment with the presynaptic adrenoceptor antagonist, yohimbine (300 micrograms/kg, SC), did not alter the hypothermic response to administration of AII. To determine whether vasodilation of the tail of the rat was mediated by AII-induced prostaglandin release, indomethacin (4 and 6 mg/kg) was administered.(ABSTRACT TRUNCATED AT 250 WORDS)
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology; D003106:Colon; D005260:Female; D007036:Hypothermia, Induced; D007213:Indomethacin / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012504:Saralasin / Q000494:pharmacology; D012881:Skin Temperature / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
D000804:Angiotensin II; D015016:Yohimbine; D009270:Naloxone; D012504:Saralasin; D003000:Clonidine; D007213:Indomethacin