Hypoxia attenuates the renin response to hemorrhage.

We studied hypoxia and hypotensive hemorrhage in conscious female goats. After control, goats continued an experimental period in normoxia or hypoxia [fractional inspired oxygen concentration (FIO2) = 0.10] for 120 min. After 60 min in the experimental period, a hemorrhage (0.5 ml.kg-1.min-1 for 30 min) was initiated (normoxic hemorrhage, NH; hypoxic hemorrhage, HH). Heart rate (HR) increased 51 +/- 18 beats/min with NH after 30 min of hemorrhage. HR increased 40 +/- 10 beats/min after hypoxic gas introduction, with no further increase during HH. Mean arterial blood pressure (MABP) was reduced 23 +/- 7 mmHg 30 min after completion of blood loss with normoxia but was reduced 23 +/- 7 mmHg at 20 min of HH. Arginine vasopressin (AVP) was increased to 2.60 +/- 2.08 and 160.40 +/- 49.74 microU/ml after 10 and 20 min of HH, respectively, and was only increased after 30 min (87.33 +/- 67.18 microU/ml) of NH. Unexpectedly, plasma renin activity (PRA) increased in parallel in both groups and was doubled at 30 min of hemorrhage. Atrial natriuretic factor was reduced to 8.8 +/- 1.6 pg/ml by 10 min of NH and to 11.4 +/- 3.3 pg/ml at 30 min of HH. Thus hypoxia leads to an earlier development of hypotension and increase in AVP with blood loss but may attenuate the PRA response to blood pressure reduction.