Does acute hypoxemia blunt sympathetic activity in hyperthermia

Sympathetic alpha-adrenergic function is depressed by hypoxemia per se; does addition of another sympathoexcitatory stimulus elicit normal responses in other sympathetic effector pathways? We activated by hyperthermia four sympathetic pathways: alpha-adrenergic [norepinephrine (NE) release], beta-adrenergic [plasma renin activity (PRA)], cholinergic (sweating), and peptidergic (active vasodilation). In the first test, five normothermic men were exposed to hypoxemia for 10 min (control), then hypoxemia plus heat for 30 min, and then heat with normoxia for 8–10 min over a continuous 48- to 50-min period. Heating was controlled with a water-perfused suit. Time courses and magnitudes of heat-induced increments in body temperature, forearm blood flow, and sweat rate were normal during hypoxemia and unaffected by switching to normoxia. Hypoxemia exaggerated increases in plasma NE, epinephrine, PRA, and heart rate but had no additional effects on blood pressure. In a second 50-min test (2 men) with normoxic cont...