THE DECOMPENSATORY PHASE OF ACUTE HYPOVOLEMIA IN RABBITS INVOLVES A CENTRAL DELTA(1)-OPIOID RECEPTOR

Graded caval occlusion in conscious rabbits caused a biphasic response. Phase I was characterized by a fall in conductance so that arterial pressure was maintained. When cardiac output had fallen to 69 +/- 2% of its baseline level, phase II supervened. During phase II, conductance rose abruptly and arterial pressure fell to a life-threatening level (< 40 mm Hg). Centrally administered delta-opioid receptor antagonists prevented the occurrence of phase II. The relative order of potency was 7-benzyl-idenenaltrexone (BNTX, delta(1)-selective) > N, N-diallyl-Tyr-Aib-Phe-Leu-OH (ICI 174 864) > naltrindole (delta(2)-selective). It is concluded that a central delta(1)-opioid receptor is involved in the onset of the second decompensatory phase of the haemodynamic response to haemorrhage.