No effect of naloxone or morphine on plasma catecholamines during hemorrhage in rat.

Awake rats were bled 2.5 per cent of their body weight during 15 min. This caused a 50-fold increase of plasma adrenaline and a 15-fold increase of plasma noradrenaline after 90 min. Treatment with naloxone or morphine did not significantly affect blood pressure or plasma catecholamine levels. The results suggest that the action of naloxone in hemorrhagic hypotension is not mediated via the sympatho-adrenal system.