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

Abstract

1. In conscious rabbits intracerebroventricular (i.c.v.) morphine (10 and 50 micrograms 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 microgram kg-1 i.c.v.) and i.c.v. saline had no effect. 2. 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. 3. Intravenous naloxone (1 m..