Vasopressin, ACTH, and blood pressure during hypoxia induced at different rates

We decreased arterial PO2 at three different rates and measured blood pressure (BP), vasopressin (AVP), ACTH, and corticosteroid levels in nonsurgically stressed, anesthetized, paralyzed dogs. PaO2 was lowered to 28 Torr in 2 (fast), 10 (moderate), and 20 min (slow). The fast dPO2/dt produced a large spike in BP. Increases in AVP, ACTH, and corticosteroids were similar regardless of the dPO2/dt. When the spike in BP during the fast dPO2/dt was prevented with nitroprusside, hormone levels increased more quickly and were higher during the first 20-30 min of hypoxia. By 60 min, hormone levels were not different between experiments. The data suggest that 1) faster decreases in PO2 produce larger increases in BP, 2) increases in AVP, ACTH, and corticosteroids are primarily sensitive to the level of steady-state PaO2, and 3) increases in BP inhibit stress-induced increases in AVP and ACTH.