Effects of morphine and naloxone on cerebral blood flow and metabolism in experimental subarachnoid hemorrhage

OBJECTIVE: Naloxone is reported to improve the clinical condition of patients with subarachnoid hemorrhage (SAH). If this effect is vascular determined is unknown, wherefore the influence of morphine and naloxone on cerebral blood flow (CBF) and metabolic rate of oxygen (CMRO2) after SAH was evaluated.

MATERIAL AND METHODS: Two groups of 8 rats each with SAH and 2 corresponding groups of controls were investigated. CBF was calculated by the intracarotid 133Xenon method and CMRO2 as the product of CBF and the difference between systemic arterial and cerebral venous oxygen content.

RESULTS: In controls morphine, 1 mg/kg administered intravenously, decreased CBF by 25% (P < 0.001) without changing the CBF/CMRO2 ratio. In animals with SAH CBF was decreased by 32% (P < 0.001) and CBF/CMRO2 ratio by 38% (P < 0.01). Naloxone, 40 micrograms/kg administered intravenously neither influenced CBF nor the CBF/CMRO2 ratio in the 2 groups.

CONCLUSION: The reported clinical effect of naloxone after SAH can, according to our results, not be explained by changing the relationship between CBF and metabolism.