Actions of dopamine and apomorphine on the vasoconstrictor responses of perfused mesenteric arteries of mouse, rat and rabbit.

Dopamine (10(-7)--10(-6) M) and apomorphine (5 x 10(-7)--5 x 10(-6) M) inhibited the vasoconstrictor responses of the perfused mesenteric artery preparations of rat, rabbit and mouse to adrenergic nerve stimulation but did not affect responses to added noradrenaline. The inhibitory effects of both dopamine and apomorphine were prevented by haloperidol (3 x 10(-7) M) but not by yohimbine (3 x 10(-8) M) in rat and rabbit mesenteric artery preparations. In contrast, yohimbine (3 x 10(-8) M), but not haloperidol, antagonized the inhibitory effect of dopamine and apomorphine in mouse mesenteric artery preparations. In higher concentrations, dopamine (10(-6)--10(-4) M) produced a direct vascoconstrictor effect, which involved post-junctional alpha-adrenoceptors in all three species. However, in preparations contracted with 10(-7) M 5-hydroxytryptamine and in the presence of phentolamine (3 x 10(-7) M) and propranolol (10(-6) M), dopamine (10(-6)--10(-4) M) produced a direct relaxant effect in rabbit mesenteric artery preparations but not in those of rat and mouse. It is suggested that inhibition of neurogenic vasoconstrictor responses, by dopamine and apomorphine, may be mediated through a specific prejunctional inhibitory dopamine receptor in the mesenteric artery of rat and rabbit whereas in the mouse they involve activation of alpha-adrenoceptors.