A new method for measurements of plasma protein steroid-binding kinetics in human plasma at 37 C

Abstract

The equilibrium kinetics in vivo of free and protein-bound steroid hormone were examined at 37 C. Human plasma was pumped through a 1 m PVC catheter and tritiated steroid hormone continuously added at the inlet. The plasma was collected and rerun through a new catheter 24 h later. A significantly (P<0.05) higher uptake of steroid hormone was observed in the first parts of the catheter during the first passage when compared to the second passage. The results indicate that non-equilibrium conditions existed for testosterone (>10 sec), estradiol (4 sec), estrone (>2 sec), and estriol (>2 sec) while no delay was observed for progesterone. The results indicate that the counter-current transfer between the testicular and ovarian vessels, respectively, may create a physiologically important, temporarily increased concentration of available hormones in the arterial blood supply to the organs.