EFFECTS OF HISTAMINE BOLUS INJECTIONS AND CONTINUOUS INFUSIONS ON THE H1‐ AND H2‐RECEPTORS IN THE HINDLIMB VESSELS OF THE RABBIT

Abstract

1. Hindlimb vascular resistance (HVR) was continuously measured after pharmacological block of the autonomic effectors in unanaesthetized rabbits with previously implanted Doppler ultrasonic flowmeters. 2. Histamine bolus injections caused a dose‐related short lived fall in HVR followed by a more sustained rise. The fall was due to H2‐receptor stimulation (blocked by burimamide or metiamide) and the rise to H1‐receptor stimulation (blocked by mepyramine). At the doses of histamine tested the magnitude of the H1‐mediated vasocoiistriction had a larger peak effect than the H2‐mediated vasodilatation. 3. Histamine infusions up to 200 μg kg−1 min−1 did not alter HVR significantly but both increa..