Decapitation increases plasma sodium and potassium in the rat

Sodium, potassium, and osmolality were measured in plasma obtained from conscious and decapitated rats. The sodium and potassium content of plasma derived from blood taken from decapitated rats via arterial cannulae or free-flowing trunk blood was significantly greater than that in conscious animals or animals killed by an overdose of pentobarbital. Plasma osmolality was not different. Hemoglobin was present in the plasma of decapitated rats, suggesting hemolysis. Hemolysis and subsequent release of intracellular potassium may be the cause of the elevated plasma potassium. The cause of the elevated sodium is unclear. This study points out the importance of considering the method of obtaining blood in determinations of plasma levels of biologic substances.