Role of acetylcholine, corticoids and opioids in the rostral ventrolateral medulla in stress-induced hypertensive rats.

Hypertension was induced in Sprague-Dawley and Wistar rats by irregular foot shocks combined with a buzzing noise for 2 h twice a day for 1-2 weeks. The plasma catecholamine, corticosterone, angiotensin II, glucose and lipids were found to increase in parallel. The acetylcholine (ACh) and choline acetyltransferase in rostral ventrolateral medulla (rVLM) increased markedly). Microinjection of ACh or cholinergic agonists into rVLM induced a pressor effect, and microinjection of M receptor blockers had a depressor effect. Electrophysiological studies showed that the stress-induced hypertension was closely related to the activation of a cholinergic system in rVLM. Microinjection of corticoids into rVLM had led to a pressor response which could be blocked by Ru38486, spironolactone, cholinergic blockers or verapamil. Microinjection of morphine and mu- or delta-receptor agonists into rVLM caused bradycardia and a reduction of arterial pressure that could be blocked by naloxone.