REGIONAL VASCULAR-RESISTANCE AND HEART-RATE RESPONSES MEDIATED THROUGH H1-HISTAMINE AND H2-HISTAMINE RECEPTORS IN UNANESTHETIZED RABBIT

Abstract

The effects of histamine infusions (10-100 microgram/kg/min) on heart rate and hindlimb, carotid, mesenteric and renal vascular resistance were investigated in unanaesthetised rabbits after "total" autonomic effector block to abolish reflex effects. Histamine caused a rise in heart rate that was predominately due to stimulation of H2-receptors (blocked by metiamide). Hindlimb and carotid vascular resistance did not change significantly during histamine infusion. However, after blocking H2-receptors with metiamide histamine infusions produced dose-related vasoconstriction in these beds while after H1-receptor block with mepyramine histamine caused dose-related vasodilatation indicating that H..