The dopaminergic system is able to modulate the central histamine-induced pressor effect in hemorrhage-shocked rats.

I NTRODUCTION: Histamine administered intracerebroventricularly (icv) induces a resuscitating effect in hemorrhage- -shocked rats. Dopamine receptors are present in neuronal pathways involved in central cardiovascular regulation; therefore, the aim of the study was to examine the effects of pre-treatment with dopamine receptor antagonists on histamine-induced cardiovascular effects in hemorrhagic shock. MATERIAL AND METHODS: Male Wistar rats subjected to a reversible hemorrhagic hypotension with mean arterial pressure (MAP) of 30–35 mmHg were anaesthetized with ketamine/xylazine (100 mg/kg + 10 mg/kg, intraperitoneally). Immediately after bleeding terminated, the animals were pre-treated icv with dopamine receptor antagonists or saline; 5 min later they were treated icv with histamine (50 nmol) or saline. RESULTS: Hemorrhagic hypotension was accompanied by decreases in pulse pressure (PP), heart rate (HR), and mesenteric blood flow (MBF). Histamine induced increases in MAP, HR, and MBF, with a decrease in PP as compared to the control group. Pre-treatment with the dopamine D4 receptor antagonist L-745,870 potentiated histamine-induced MAP and MBF changes, with no influence on PP or HR. There were neither the influence of the other dopamine receptor antagonists on histamine-mediated action nor the effects of dopamine receptor antagonists given alone in the control groups. CONCLUSIONS: Dopamine, acting via D4 receptors, is able to modulate the central histamine-induced pressor effect in hemorrhage-shocked rats.