Characterization of 17 β-estradiol- 3 H Single-Injection Disappearance Curves in Rat Plasma and Red Cells 1

Summary

Tritiated 17 β-estradiol was injected intracardially into rats and blood samples were collected over the succeeding 6-hr period. Subjection of data on radioactivity to a semilog plot revealed that three regression lines could be developed. By mathematical computation the regressions and intercepts on the V-axis showed that a three-pool model fit the data. Three possible solutions of three-pool models were developed. The most acceptable of these on physiological grounds was model I, in which the first pool represented blood and the half-life of approximately 5 min represented mixing, the second pool represented extracellular fluid of the body and the half-life of approximately 30 min represented the utilization rate of estradiol by target tissues, and the third pool represented the major part of the body fluid and the half-life of approximately 700 min represented the movement of metabolites to the blood and then eliminated via an excretory pathway.