Agonistic actions of DPI (2-(3,4-dihydroxyphenylimino)-imidazolidine) on alpha-adrenoceptors and dopamine receptors.

Some of the pharmacological actions of 2-(3,4-dihydroxyphenylimino)-imidazolidine (DPI) were studied in vivo and vitro. DPI (1 nM-100 micro M) had a similar affinity but a lower intrinsic activity on alpha-adrenoceptors in rabbit aortic strips to noradrenaline (1 nM-10 micro M). DPI did not affect the uptake of [3H]noradrenaline in guinea-pig isolated atria. The effects of DPI on dopamine receptors were examined in the dog coronary and renal vasculature and in the rat isolated, perfused kidney. In the dog coronary vasculature DPI (0.005-10 micrograms, i.a.), like dopamine (5-50 micrograms, i.a.), caused an increase in coronary blood flow which was antagonized by the dopamine receptor antagonist, ergometrine. In the renal vasculature of both the rat and the dog, dopamine (5-50 micrograms, i.a.) caused vasodilatation but there was no evidence of an effect of DPI on dopamine receptors. It appears that DPI is a selective agonist for dopamine receptors in the coronary vasculature.