Plasma atrial natriuretic factor and subarachnoid hemorrhage

Hyponatremia is common following aneurysmal subarachnoid hemorrhage and has been linked to the syndrome of inappropriate secretion of antidiuretic hormone. However, the demonstration of volume depletion and natriuresis in some patients has suggested that salt wasting is a more likely etiology. Atrial natriuretic factor appears to play a role in both central and peripheral regulation of sodium homeostasis. To investigate the behavior of circulating atrial natriuretic factor following subarachnoid hemorrhage, we studied 25 patients with intracranial aneurysms: 21 after acute subarachnoid hemorrhage and four without evidence of recent rupture. Atrial natriuretic factor was measured by radioimmunoassay of extracted plasma (normal value, 20.8 ± 24.6, mean ± 3 SD). Mean ± SEM plasma atrial natriuretic factor concentration was elevated to 84 ± 25 pg/ml on Day 1, rose to 134 ± 29 pg/ml on Day 3, and fell to 86 ± 17 pg/ml by Day 7 after subarachnoid hemorrhage (p<0.01). In two patients (9.5%) who developed hyponatremia after aneurysm rupture, plasma concentrations were no different from that in the group as a whole; concentrations in patients with no evidence of recent subarachnoid hemorrhage were not elevated. Neither fluid administration nor timing of surgery could account for the elevated concentrations. We conclude that concentrations of circulating atrial natriuretic factor are elevated after subarachnoid hemorrhage but do not solely account for the accompanying hyponatremia.