Abstract
Summary
Blood obtained from anesthetized rats by cardiac puncture, severance of the tail tip, or decapitation, was analyzed for serum Na+ and K+. The lowest, least variable, and hence most reliable serum K+ values were obtained from heart blood. Tail-blood samples gave serum K+ values which, while often in a plausible range, were substantially higher. Trunk blood collected from decapitates gave inordinately high serum K+ and low Na+ values. These, while obviously inaccurate, could still be used to demonstrate the hypokalemic effects of mineralocorticoid hormone. If accuracy is essential, cardiac puncture is the only reliable method among those used for obtaining serum K+.
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