Investigation of the central sites at which morphine acts to cause hypertension in conscious rabbits

Abstract

In conscious rabbits intracerebroventricular (i.c.v.) morphine (10 and 50 μg kg-1) caused a dose-related increase in plasma noradrenaline and adrenaline, respiratory depression and sedation. The increase in sympatho-adrenal outflow resulted in hypertension accompanied by bradycardia and the increase in adrenaline secretion caused hyperglycaemia. Morphine (1 μg kg-1 i.c.v.) and i.c.v. saline had no effect. The same doses of morphine given intracisternally (i.c.) caused bradycardia and a similar degree of respiratory depression to i.c.v. morphine, but no significant increase in blood pressure and only a small, gradual rise in plasma adrenaline. Intravenous naloxone (1 mg kg-1) did not block th..