Transient hyperkalaemia immediately after acute haemorrhage in rats.

The effect of haemorrhage on plasma potassium concentration was studied in Sprague-Dawley rats, Brattleboro (BDI) rats and the parent strain Long-Evans (LE) rats. Haemorrhage induced an increase in plasma potassium within 10 min in all rats studied; 20 and 30 min later, plasma potassium was back to prehaemorrhage level. Changes in plasma sodium concentration were not statistically significant. When haemorrhage (1.0% of body weight) was repeated in the same animal preparation, there was a further significant increase in plasma potassium, but a fall in plasma sodium concentration. When vasopressin was injected intravenously, plasma potassium concentration did not change significantly (-0.21 +/- 0.21 mmol/l) in LE rats, whilst it increased significantly (0.69 +/- 0.20 mmol/l, p less than 0.001; paired t-test) in the BDI rats. The results suggest that haemorrhage-induced hyperkalaemia is unrelated to vasopressin, despite the fact that it increases plasma potassium concentration in the BDI rats when injected.