The effects of dopexamine on the cardiovascular system of the dog

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Abstract
The cardiovascular effects of dopexamine and dopamine were compared in the anaesthetized and conscious dog by the use of intravenous infusions over the dose range 3 × 10−9 − 10−7 mol kg−1 min−1. In the anaesthetized dog, dopexamine produced a dose‐related fall in blood pressure due to peripheral vasodilatation and a small rise in heart rate and contractility. By contrast, dopamine did not significantly reduce blood pressure but produced a larger dose‐related increase in contractility. At the highest infusion rate (10−7 mol kg−1 min−1) blood pressure and heart rate were increased by dopamine. Dopexamine dilated the renal and mesenteric vascular beds with a potency similar to that of dopamine. Femoral vascular responses produced by both agents were inconsistent but the highest infusion rate of dopamine did produce vasoconstriction. With the aid of selective receptor antagonists (haloperidol, propranolol and bulbocapnine) the vasodepressor activity of dopexamine was shown to be mediated by stimulation of DA2‐, β‐ and DA1‐receptors. The cardiac stimulation and renal vasodilatation produced by both compounds were due to stimulation of β‐adrenoceptors and DA1‐receptors respectively. In the conscious dog, intravenous infusion of dopexamine caused a dose‐related fall in blood pressure, renal vasodilatation and an increase in cardiac contractility and heart rate. Dopamine also increased cardiac contractility, and renal blood flow due to renal vasodilatation but without affecting heart rate. At the highest infusion rate, blood pressure was increased. Dopexamine and dopamine produced a similar incidence of panting and repetitive licking at 3 × 10−8 mol kg−1 min−1 and emesis at 10−7 mol kg−1 min−1, due to stimulation of dopamine receptors in the chemoreceptor trigger zone. Dopexamine produces a different cardiovascular profile from dopamine in the anaesthetized and conscious dog. Both compounds reduce renal vascular resistance, but in contrast to dopamine, dopexamine reduces afterload and produces only mild inotropic stimulation. These differences reflect contrasting activity at adrenoceptors.