Possible factors influencing post‐ejaculatory changes of the osmolality of human semen in vitro

The human ejaculate is made up of secretions from the different accessory sex glands that empty in sequence at ejaculation. However, the different secretions only mix completely in vitro when the entire ejaculate is collected in a container and handled in the laboratory. At ejaculation, proteins from the seminal vesicles form a gel in the ejaculate and semen cannot be properly analysed and processed until the gel is liquefied. During and after liquefaction, there is continuous enzymatic activities and an ongoing increase in osmolality. The aim of this study was to investigate possible factors that influence the increase in semen osmolality in vitro. Osmolality was measured by freezing‐point depression. Prostatic secretion was measured as zinc concentration. The presence of spermatozoa neither influenced the actual measurement of semen osmolality, nor the increase in osmolality. Enzymatic inhibitors reduced the increase in osmolality, and semen dilution prevented any increase in semen osmolality. However, the increase in osmolality covaried with the seminal zinc concentration, indicating that the observed increase was related to factors of prostatic origin. A simple and convenient procedure to reduce the risk for osmotic challenges for spermatozoa during handling for assisted reproductive technologies might be early dilution of semen.