[The method for the measurement of the binding capacity of androgen binding protein in human semen (author's transl)].

In the present study, the androgen-binding properties of human semen was evaluated by experimenting with incubation and the technique for separating bound from unbound hormones. Some of the properties of a protein in human seminal plasma (SPABP) that has a high affinity and low capacity for binding dihydrotestosterone (DHT) was found and studied. The dissociation constant (Kd) was 1.63 X 10(-9) M and the number of binding sites of 275.3 X 10(-12)M was obtained. The intraassay and interassay coefficient of variation of this assay method was less than 5.6% and 8.4%, respectively. DHT was displaced from the binding protein by testosterone (81%), estradiol (75%) and levonorgestrel (63%). The endogenous level of steroids in human seminal plasma did not interfere with the estimation of DHT binding sites. In order to investigate the binding of DHT to human spermatozoa, the separation of sperm from the incubation mixture was accomplished by low-field centrifugation followed by 3,000 X G for 10 minutes. Using this separation method, the optimal steady-state condition for DHT-binding was found to be an incubation time of one hour. The binding of DHT to spermatozoa was nonspecific in nature, that is, of high capacity and low affinity (Kd greater than 10(-6)M).