Pressor responsiveness to intravenous quinpirole is blunted in malnourished, conscious rats: central vs. peripheral and spinal mechanisms.

Abstract

In conscious rats, intravenous treatment with the dopamine D2-like receptor agonist quinpirole, elicited a pressor effect, which is attributed to central dopamine D2 receptor-mediated activation of sympathetic outflow associated with arginine vasopressin release. This prominent central effect is opposed to peripheral sympathoinhibitory and spinal depressor effects. The present study investigated the effects of pre- and postnatal undernutrition on the central pressor responsiveness to quinpirole. Malnourished (MalN) rats were obtained by feeding dams a multideficient diet (providing 8% protein) during pregnancy and nursing. At 90 days of age, MalN rats weighed significantly less than control (CNT) rats born to dams fed standard commercially diet (23% protein) during pregnancy and nursing. Baseline mean arterial pressure and heart rate in MalN rats were comparable to those of CNT. Intravenous treatment with quinpirole (0.3 mg/kg) in MalN conscious rats induced a pressor effect, which was significantly reduced in both magnitude and duration, when compared with CNT rats. In both groups studied, pressor response to quinpirole was fully abolished by the peripheral and central dopamine D2 receptor antagonist, metoclopramide (5 mg/kg, i.v.) whereas was significantly enhanced after pretreatment with either intravenous (0.5 mg/kg) or intrathecal (40 microg per rat at T9-T10 level) domperidone, a dopamine D2 receptor antagonist that does not cross the blood-brain barrier. However, even under peripheral and spinal dopamine D2 receptor blockade, maximum pressor effect of quinpirole remained significantly reduced in MalN when compared with CNT rats. Neither the maximum pressor nor the bradycardiac responses to intravenous phenylephrine or arginine vasopressin differed between CNT and MalN rats. This study shows that undernutrition imposed during fetal life and suckling blunted the pressor response to quinpirole in conscious rats. This blunted response appears mainly related to desensitization of brain dopamine D2 receptors rather than enhanced peripheral and/or spinal dopamine D2 receptor-mediated depressor effect or vascular hyporesponsiveness to alpha1-adrenoceptor and vasopressin receptor stimulation.