Ergometrine and apomorphine as selective antagonists of dopamine in the canine renal vasculature.

1 Increases in renal blood flow were produced by intra-arterial injections of dopamine (5-50 mug) in anaesthetized dogs pretreated with alpha- and beta-adrenoceptor antagonists.2 Intra-arterial administration of ergometrine (0.5 mg) or apomorphine (1 mg) produced a depression of the renal dilator responses to dopamine, without affecting renal dilatations in response to intra-arterial acetylcholine (0.1-1 mug) or histamine (2-50 mug).3 The depression of dopamine responses lasted 10-15 min, and was greater with ergometrine than with apomorphine.4 It is concluded that both ergometrine and apomorphine can be used as specific blocking agents at vascular dopamine receptors. Ergometrine is the preferred drug for this purpose.