Regional cerebral, ocular and peripheral vascular effects of naloxone and morphine in unanesthetized rabbits

Abstract

Effects of morphine and naloxone were investigated on cerebral, ocular and peripheral blood flow in unanesthetized rabbits. Blood flow measurements were performed with the labeled microsphere method. Cervical sympathotomy was performed on 1 side the day before the flow determination. Naloxone 2 mg/kg b.w. [body wt] i.v. had no consistent effect on cerebral, ocular or peripheral blood flow or on mean arterial blood pressure. Morphine 2 mg/kg b.w. i.v. caused a rise in Pa CO2 [CO2 arterial partial pressure] of 0.9 kPa [kiloPascal] and tended to increase cerebral blood flow in all parts studied. In the hippocampal region, caudate nucleus and colliculi the increase in flow was .apprx. 30% which is more than expected from the rise in PaCO2. Blood flow in the retina increased while the other parts of the eye showed no consistent changes in blood flow. Morphine reduced the blood flow in the duodenum by 60%. Mean arterial blood pressure did not change after morphine. No effect of the cervical sympathotomy was detected on cerebral or ocular blood flow before or after morphine or naloxone. There was no evidence for a tonically operating opioid system controlling cerebral, ocular or peripheral blood flow but exogenously administrated opiate can influence blood flow in these areas.