The Early Disappearance of Extracellular Tracers from Plasma After Intravenous Injection

Abstract

Summary

The early disappearance from plasma of extracellular tracers ³H-mannitol and ¹⁴C-para-aminohippurate was studied after intravenous injection in nonnephrectomized and nephrectomized rats. The amount of each tracer remaining in the plasma was studied between 30 sec and 32 min after injection and was expressed as a percentage of the dose remaining in plasma relative to a simultaneously injected ^113mindium-transferrin plasma tracer internal standard. Approximately 80% of the ³H-mannitol and ¹⁴C-para-aminohippurate disappeared from plasma in the first minute in both nonne-phrectomized and nephrectomized groups. The effects of nephrectomy became clearly evident only after the first minute when blood plasma and extracellular fluid equilibration was nearly complete. This initial disappearance from plasma of both tracers with a T _1/2 less than 30 sec is probably representative of many polar solutes not appreciably bound to plasma proteins and having minimal affinity for general cell surfaces.

The authors acknowledge the helpful suggestions of S. Z. Oldendorf and technical assistance of Shigeyo Hyman and Leon Braun.