Intravenous morphine causes hypertension, hyperglycaemia and increases sympatho-adrenal outflow in conscious rabbits

Abstract

1. In conscious rabbits, intravenous morphine (3 mg/kg) caused hypertension, bradycardia, hyperglycaemia and sedation. These changes were accompanied by large increases in plams adrenaline and smaller increases in plasma noradrenaline. 2. These effects of morphine were prevented by intravenous naloxone, demonstrating their dependence on stimulation of opiate receptors. 3. Pretreatment with the antihistamines cimetidine and chlorpheniramine enhanced the morphine-induced rise in blood pressure, excluding a role for histamine release in the hypertensive action of morphine. 4. The centrally acting α2-adrenergic agonist clonidine prevented the morphine-induced hypertension and rise in plasma cate..