CLEARANCE RATE OF EXOGENOUS 3H‐THYMIDINE FROM THE PLASMA OF PREGNANT RHESUS MONKEYS

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Abstract
The plasma clearance rate of 3H‐TdR was determined by thin‐layer chromatography of samples from pregnant rhesus monkeys who had received a single intravenous injection of 3H‐TdR. At 10 min after the injection the circulating levels of 3H‐TdR had fallen to less than 0.2% of the initial theoretical distribution of the label. In general the plasma clearance rate can be described by a ‘double exponential’curve with half‐lives of 1 min and 20 min. Thus, 3H‐TdR disappears from the circulation of the pregnant monkey more rapidly than it does from the bloodstream of rodents, which correlates with previously detected interspecies differences in autoradiographic labeling of neurons. This means (1) that higher doses of 3H‐TdR must be used for autoradiographic labeling of monkey tissues and (2) that the monkey may be useful for studying cell kinetics because it has a short pulse labeling of the DNA.