Endothelium‐dependent And‐independent Relaxation by Dopamine in the Rabbit Pulmonary Artery

Abstract

1. The relaxing response of dopamine (DA) was studied in the rabbit pulmonary artery. DA caused concentration-related relaxation in helically cut strips of the artery contracted with prostaglandin F2 alpha in the presence of prazosin. 2. The DA-induced relaxation in endothelium-denuded strips was reduced to about 40% compared with that in endothelium-intact strips. 3. Methylene blue and haemoglobin, inhibitors of endothelium-dependent relaxation, reduced the DA-induced relaxations in endothelium-intact strips to the level of endothelium-denuded strips. These results indicate that the DA-induced relaxation is partially mediated or modified by the release of endothelium-derived relaxing factor (EDRF). 4. Apomorphine, as a DA agonist, caused concentration-dependent relaxation in endothelium-intact strips. Bromocriptine, a DA2 agonist, produced only a little relaxation at higher concentration. 5. In endothelium-intact strips, haloperidol, a DA antagonist, and the DA1 antagonists, fluphenazine and SCH 23390 inhibited DA-induced relaxations. On the other hand spiperone and domperidone, DA2 antagonists, were inactive. 6. In endothelium-denuded strips, fluphenazine and SCH 23390 inhibited DA-induced relaxations, but domperidone was inactive. 7. These results indicate that the DA-induced relaxation is mediated by DA receptors, and that DA1 receptors are involved in both endothelium-dependent and -independent relaxation in the rabbit pulmonary artery.

Dopamine D 1 Receptor Augmentation of D 3 Receptor Action in Rat Aortic or Mesenteric Vascular Smooth Muscles

“…38,39 The vasorelaxant effect of dopamine in the rabbit pulmonary artery has been reported to be endothelium-dependent and endothelium-independent. 40 However, in our studies, despite the presence of D 3 receptors in the intima, the vasodilatory effects of the D 1 and D 3 receptor agonists are endothelium independent. The function of the D 3 receptor in endothelial cells is not clear, but D 3 receptors have cellprotective properties.…”

The dopaminergic system in hypertension

“…For example, a D 1 -like receptor agonist increases the vascular tone of the rat tail artery [66]; in other vessels, including the renal artery, D 1 -like receptors are vasodilatory [34,36,65,67,68]. The vasorelaxant effect of dopamine in the rabbit pulmonary artery has been reported to be both endothelium-dependent and -independent [69]. However, in the mesenteric artery, we have found that the vasodilatory effect of the D 1 receptor agonist is endothelium-independent.…”

Localization of Dopamine Receptors in the Rabbit Lung Vasculature

“…Localization of DA Dy-like re ceptors in the tunica adventitia of some vascular beds reported by autoradiography is consistent with a prejunc tional role of this DA receptor subtype [4,5], High concentrations of DA have been found in rabbit pulmonary artery' [6] and a dopaminergic innervation of the guinea pig lung has been suggested [7]. In isolated human and rabbit pulmonary arteries, a DA Di-like receptor-mediated relaxation has been demonstrated by functional studies [8][9][10], This DA-mediated vasorelaxa tion is by about 60% endothelium-dependent and by about 40% endothelium-independent [10]. Pharmacolog ical studies have characterized DA receptors mediating the endothelium-dependent and -independent vasorelax ation of the pulmonary artery' as DA D r like receptors.…”