Study on the histamine-like activity of guanfacine

Abstract The effects of guanfacine have been studied on guinea-pig isolated atria and diethylstilboestrol-treated rat isolated uterus to determine whether it possesses histamine-like activity. Guanfacine produced a concentration-dependent negative chronotropic effect which was not modified by ranitidine (0.1 μM). In rat isolated uterus contracted by KCl, clonidine (5–5000 μM) produced concentration-dependent relaxation which was blocked by ranitidine (0.1 μM), but guanfacine only produced relaxation at high concentrations (100–1000 μM), and this was not affected by ranitidine (0.1 μM). It is concluded that guanfacine, unlike clonidine, does not produce effects due to activation of H2-recept…