Prostate epithelial cells continuously secrete a thin, milky, and slightly acidic fluid known as prostate fluid, with a pH of 6.5 (which can rise to 7.7 during inflammation, making it slightly alkaline). This fluid constitutes 10% to 30% of the ejaculate and contains a variety of components, including lysosomal and secretory acid phosphatase, proteolytic enzymes, fibrinolytic enzymes, maltase, lysozyme, aminopeptidase, plasminogen activators, citrate, lipids, polyamines (such as spermine, spermidine, and putrescine), transfer factors, zinc ions, and prostate concretions of varying sizes. Notably, the protein content in prostate fluid is low, and it contains little to no reducing sugars.
The Role of Zinc in Seminal Fluid
Zinc ions in seminal fluid bind to proteins and distribute on the surface of sperm, protecting the biological membrane. This interaction helps delay lipid peroxidation and maintains sperm motility. Zinc also acts as an antimicrobial factor and a cofactor for enzyme activity. The concentration of zinc in seminal fluid positively correlates with sperm motility and density, making zinc supplements a potential clinical tool to enhance sperm activity in patients.
Enzymes and Their Functions in Prostate Fluid
Prostate fluid contains high concentrations of proteolytic and fibrinolytic enzymes, which play a crucial role in semen liquefaction and cervical mucus hydrolysis. These enzymes also reduce the acidity of the urethra. Abnormalities in semen viscosity or liquefaction often indicate defects in the secretion of these enzyme systems. To avoid interference from endogenous hydrolytic enzymes, clinical protein measurements in semen are best conducted before liquefaction.
Citrate: A Multifunctional Component
Citrate serves as a metal ion chelator, maintaining osmotic balance in seminal fluid. It also binds with calcium to form soluble complexes, preventing calcium salt precipitation. Additionally, citrate plays a role in controlling semen gelation, buffering pH, and protecting the activity of acid phosphatase and hyaluronidase. The prostate is the strongest site of acid phosphatase activity in the body, surpassing organs like the kidney, liver, spleen, and white blood cells.
Acid Phosphatase and Its Significance
Acid phosphatase, an enzyme that hydrolyzes phosphate monoesters in acidic pH ranges, is closely linked to nucleic acid and protein metabolism. Its activity increases with heightened metabolic activity, indicating its role in sperm nutrition. Polyamines in seminal fluid contribute to anti-infection, DNA replication, and cell growth, while their derivatives are responsible for the characteristic odor of semen.
Prostate-Specific Antigen (PSA) and Its Implications
Prostate epithelial cells secrete a glycoprotein called prostate-specific antigen (PSA), which aids in the hydrolysis of semen clots and is associated with male fertility. PSA is also a critical marker for the early diagnosis of prostate cancer. Measuring levels of acid phosphatase, citrate, and zinc in semen can help assess prostate function and detect cancer. Additionally, acid phosphatase testing on clothing or vaginal samples can assist forensic investigations in cases of sexual activity.
The Sequence of Ejaculation
During ejaculation, the initial pre-ejaculate is clear and viscous, containing minimal prostate fluid and few sperm. This portion primarily consists of secretions from the urethral glands (Littre’s glands) and bulbourethral glands, lubricating the urethra to facilitate ejaculation and typically not undergoing coagulation. The main portion of the ejaculate, rich in prostate fluid and epididymal fluid, contains a high concentration of high-quality sperm. This portion coagulates and then liquefies after ejaculation. The final portion, or post-ejaculate, is primarily composed of seminal vesicle and ampullary secretions, with little prostate fluid. It contains fructose and very few sperm, coagulates more rapidly, and liquefies more slowly, resulting in reduced fertilization potential. The order of ejaculation begins with the bulbourethral glands, followed by the prostate, epididymis, ampulla, and seminal vesicles. When collecting semen samples, it is essential to consider this sequence for accurate analysis.
Conclusion
Prostate fluid is a vital component of seminal fluid, contributing to sperm protection, motility, and overall reproductive health. Its complex composition, including enzymes, zinc, citrate, and PSA, plays multifaceted roles in semen function and male fertility. Understanding the biochemical properties and functions of prostate fluid is crucial for diagnosing and treating reproductive disorders, as well as for forensic applications.
