Adaptation to periodic high-altitude hypoxia inhibits baroreflex vagal bradycardia in rats.

A 3-week course of adaptation to high-altitude hypoxia (4500 m above sea level) inhibited baroreflex vagal bradycardia induced by a rapid rise of systemic blood pressure in conscious rats. Bradycardic responses to electrical stimulation of peripheral end of the right vagus nerve and methacholine (M(2) muscarinic receptor agonist) in hypoxia-adapted rats did not differ from the control. It is concluded that hypoxia inhibits baroreflex vagal bradycardia by acting on a central element of the baroreceptor reflex arch.