High resolution ¹H NMR spectroscopic studies on dynamic biochemical processes in incubated human seminal fluid samples

High resolution 600 MHz NMR spectroscopy was used to investigate the changes in biochemical composition of whole human seminal fluid (SF) and an artificial mixture of prostatic (PF) and seminal vesicle fluid (SVF). A variety of time-related biochemical changes were monitored simultaneously and non-invasively in SF, including enzymatic hydrolysis of phosphorylcholine to choline and polypeptides to amino acids. The fastest NMR-observable reactions in SF were the conversion of phosphorylcholine to choline (t1/2≅9 min) and uridine-5′-monophosphate (UMP) to uridine (t1/2<2 min). UMP has not previously been detected in SF because of its rapid hydrolysis. Artificial mixtures of separately obtained prostatic and SVF showed very similar biochemical changes to those observed in whole SF. Addition of EDTA to SF incubated for 2 min post ejaculation strongly inhibited peptide hydrolysis. Zn²⁺, present in whole SF was shown to be non EDTA-chelatable 2 min after ejaculation, whereas after 7 min, a singlet signal from the ethylenic protons of the Zn-EDTA²⁻ complex was clearly observed which remained constant after 7 min. This indicates that soon after ejaculation (<5 min) Zn²⁺ is immobilised in a macromolecular complex which is rapidly broken down by proteolytic enzymes, the released Zn²⁺ then being free to react with EDTA. Mg- and Ca-EDTA²⁻ complexes were observed at 2 min and remained constant (at 1.4 and 2.1 mM, respectively) throughout the entire time course of the experiment. These studies cast new light on the time-related biochemical changes occurring in the post-ejaculatory SF which may have an important role in reproductive function.