Further evidence for central histamine H2-receptor involvement in the hypotensive effect of clonidine in the rat.
In urethane-anaesthetised rats, the administration of the specific histamine H2-receptor antagonist metiamide intracerebroventricularly (i.c.v.) raised the blood pressure and increased the heart rate. Metiamide (i.c.v.) antagonised the hypotensive effect of clonidine (i.c.v.) in an apparently competitive manner. 4-Methylhistamine i.c.v. did not significantly change the blood pressure. The results are consistent with the concept that the hypotensive effect of clonidine is at least partly due to a stimulation of cerebral H2-receptors. The existence of cerebral H2-receptors mediating hypotensive effects is supported by the hypertensive effect of metiamide but not by the lack of hypotensive effects of 4-methylhistamine.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D003864:Depression, Chemical; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008761:Methylhistamines / Q000494:pharmacology; D008785:Metiamide / Q000494:pharmacology; D051381:Rats; D011968:Receptors, Histamine / Q000502:physiology*; D011970:Receptors, Histamine H2 / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D008761:Methylhistamines; D011968:Receptors, Histamine; D011970:Receptors, Histamine H2; D008785:Metiamide; D003000:Clonidine