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

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Abstract
Arterial PO2 [O2 partial pressure] was decreased at 3 different rates and blood pressure (BP), vasopressin (AVP), ACTH and corticosteroid levels were measured 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 1st 20-30 min of hypoxia. By 60 min, hormone levels were not different between experiments. Apparently, faster decreases in PO2 produce larger increases in BP, increases in AVP, ACTH and corticosteroids are primarly sensitive to the level of steady-state PaO2 and increases in BP inhibit stress-induced increases in AVP and ACTH.