Dopexamine hydrochloride is a new analog of dopamine that lowers systemic vascular resistance and has positive inotropic and chronotropic properties, but lacks the α-adrenoceptor agonist activity of dopamine. The effects of dopexamine on hypoxic pulmonary vasoconstriction (HPV) are not known. We investigated this using an isolated, blood-perfused, and ventilated rat lung model. To study HPV, the ventilating gas was changed from an FIO2 of 0.21 to 0.03 and dopexamine hydrochloride was added. At blood concentrations of 100, 200, and 300 ng/ml, dopexamine caused a significant decrease in HPV of 22 ± 3%, 31 ± 4%, and 58 ± 4% (mean ± SEM, p <.05), respectively. This effect was blocked completely by pretreatment of the preparation with propranolol (0.5 mg/kg, p <.05). Dopexamine also induced significant (p <.05) vasodilation of the pulmonary circulation preconstricted under normoxic conditions with prostaglandin F2α, suggesting that the effects of the drug were not specific to hypoxia. We conclude that dopexamine inhibits HPV and vasodilates the pulmonary circulation by stimulation of β2 adrenoceptors. (Crit Care Med 1990; 18:520)
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