Interactions between dopamine and prostaglandins on vascular reactivity to noradrenaline: Dopamine inhibits the action of PGE1

Interactions between dopamine and responses to noradrenaline as modulated by prostaglandins (PGs) were studied in the perfused rat mesenteric vascular bed. When perfused alone dopamine up to a concentration of 10⁻⁷M neither changed baseline pressure nor modified the pressor response to noradrenaline. Dopamine at 10⁻⁹ to 10⁻⁷M significantly inhibited responses to noradrenaline which had been enhanced by the presence of 10⁻¹⁰ to 10⁻⁸ M PGEI. In preparations in which vascular responses to noradrenaline had been abolised by indomethacin and restored by adding PGEI, 10⁻⁹ to 1⁻⁷M dopamine significantly inhibited the restored responses. Dopamine also attenuated the inhibitory effects of prostacyclin on pressor responses to noradrenaline but it did not change the actions of either PGE2 or PGF2 alpha. Pimozide, a mainly centrally acting dopamine antagonist, did not interfere with these peripheral actions of dopamine. The dopamine effects were blocked by another dopamine antagonist, metoclopramide. Dopamine can inhibit the effects of PGEI and prostacyclin in the rat mesenteric vascular bed, possibly by interacting with specific dopamine receptors.