THE PLASMA DISAPPEARANCE OF INTRAVENOUSLY ADMINISTERED COBALT58 VITAMIN B12*

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Abstract
The disappearance of a 0.043 [mu]g dose in control subjects was initially rapid followed by a slow phase of loss. Less than 20% remained in 1 hour. Pre-injection plasma binding of 0.007 - 0.012 [mu]g doses did not alter the disappearance pattern. Large amounts of nonradioactive vitamin produced only minor changes in the disappearance of the labeled vitamin. The rapidly removed vitamin was not excreted and was not detected in extracellular fluids. It was detected in various tissues. The plasma disappearance, plasma binding, and tissue distribution appeared to be controled by processes more complex than a simple addition of the vitamin to unsaturated plasma binding sites.