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Department of Physiology, Queen's University, Kingston, Ontario, Canada K7L 3N6
We tested
the hypothesis that angiotensin II (ANG II) contributes to ventilatory
and acid-base adaptations during 3-4 h of hypoxia (partial
pressure of O2 in arterial blood
43 Torr) in the conscious dog. Three protocols were carried out
over 3-4 h in five dogs: 1) air
control, 2) 12%
O2 breathing, and
3) 12% O2 breathing with ANG II receptors
blocked by infusion of saralasin (0.5 µg · kg
1 · min
1).
After 2 h of hypoxia, expired ventilation and alveolar ventilation progressively increased, and the partial pressure of
CO2 in arterial blood and the
difference between the arterial concentrations of strong cations and
strong anions ([SID]) decreased. When the hypoxic chemoreceptor drive to breathe was abolished transiently for 30 s with
100% O2, the resultant central
apneic time decreased between 0.5 and 2.5 h of hypoxia. All these
adaptive responses to hypoxia were abolished by ANG II receptor block.
Because plasma ANG II levels were lower during hypoxia and hypoxic
release of arginine vasopressin from the pituitary into the plasma was
prevented by ANG II receptor block, the brain renin-angiotensin system
was likely involved. It is possible that ANG II mediates ventilatory and acid-base adaptive responses to prolonged hypoxia via alterations in ion transport to decrease [SID] in brain extracellular
fluid rather than acting by a direct neural mechanism.
adaptation to hypoxia; brain angiotensin II; angiotensin receptor block; arginine vasopressin; strong ion difference
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