Histamine is not involved in pentagastrin-induced gastric mucosal vasodilation in the rat

The effects of histamine and its role in the gastric mucosal vascular response to pentagastrin were studied in anesthetized rats. Blood flow was measured with laser-Doppler flowmetry (LDF) and with red blood cell velocity measurements in the superficial mucosal microcirculation. Acid secretion was determined by titration of the saline covering 0.8 cm2 of the fundic mucosa. Pentagastrin (40 micrograms.kg-1 x h-1 i.v. induced a blood flow increase (+40%), which was not significantly altered by ranitidine (H2-receptor antagonist, 2 mg/kg iv bolus), whereas the stimulated acid output was abolished. In experiments in which the H1-receptor antagonist pyrilamine (2.5 mg/kg i.v. bolus) was administered before pentagastrin stimulation, pentagastrin still increased blood flow by approximately 60%. Intravenous histamine (4 mg.kg-1 x h-1) induced a blood flow reduction in parallel with the reduction in blood pressure (vascular resistance unchanged). Even during intra-arterial (thoracic aorta) infusion of histamine (1 or 4 mg.kg-1 x h-1), gastric vascular resistance was unchanged. In animals pretreated with pyrilamine, histamine (4 mg.kg-1 x h-1 i.v.) left the gastric blood flow and blood pressure unchanged. These results indicate that the pentagastrin-induced increase in the rat gastric blood flow is not dependent on histamine.