Modulation of the Plasma Ghrelin Level by Intraventromedial Hypothalamic Microinjection of D2 Receptors Agonist and Antagonist

Dopamine is well recognized to regulate feeding via hypothalamic circuits in the brain.However, the mechanism by which dopamine controls food intake through hypothalamic pathways remains largely unknown. Recent findings propose that metabolic circuit and especially peripheral orexigenic/anorexigenic signals may play a critical role in the regulation of food intake. Therefore, in the present study, we hypothesized that ghrelin might modulate the orexigenic effect of ventromedial hypothalamic (VMH) dopamine receptors. To address this issue, we assessed the effects of intraventromedial administration of dopamine D2 receptors agonist, Quinpirrole, and anatagonist, Sulpiride, on plasma levels of ghrelin in 20-h fasted rats. Results showed that the pharmacological activation of D2 receptors increases the plasma ghrelin level persisted over 1h. This stimulatory effect of dopamine receptor activation on ghrelin was reduced by D2 receptors blockade in the VMH. In some experiments, atropine (cholinergic antagonist; 1 mg ⁄ kg s.c.) was administered 30 min before drug or saline injections which resulted in a marked suppression of fasted and stimulated ghrelin secretion. Together, our novel data implicates ghrelin in the orexigenic action of VMH D2 receptors signaling with a possible functional role of vagal pathway in the control of dopamine-evoked appetite (ghrelin) induction.