Summary
Semen contains enzymes and inhibitors of the haemostatic system as well as the high
molecular weight seminal vesicle (HMW-SV) proteins. The former may have roles in seminal
clotting and in liquefaction through “fibrinolytic” activity, which may ultimately
affect fertility. Although a limited number of studies have addressed the subject,
the role of clotting and fibrinolytic factors in semen remains poorly understood.
The liquefaction time and the distribution of components vary across split ejaculates.
This may have an important bearing on the way clotting/fibrinolytic factors in semen
are assessed. Semen contains tissue factor (TF, Thromboplastin, CD142), which originates
from the prostate and is associated with prostasomes. The function of TF (and prostasomes)
in semen is still a matter for speculation. Recently the presence of minute amounts
of factor VII in semen has been demonstrated but its importance is uncertain. Semen
also contains a thrombin-like enzyme, prothrombin fragments 1 and 2 (F1+2), D-dimer
(DD) and thrombin-antithrombin (TAT) complexes. The presence of several fibrinolytic
factors has been demonstrated in semen but few questions about their potential impact
on semen quality have been raised. Factors found include tissue plasminogen activator
(t-PA), urinary plasminogen activator (u-PA) and plasmin. There are also traces of
fibrinogen, plasminogen, plasminogen activator inhibitor-1 (PAI-1), factorVIII coagulant
activity (VIII:c) and fibrin monomers. The co-ordinate expression of both TF and PAI-1
by decidual cells of the endometrium is believed to be important in maintaining haemostasis
during endovascular trophoblast invasion. Kallikrein-like serine protease inhibitors
including prostate specific antigen (PSA) are known to be present in semen at high
concentrations. In semen PSA is also found in a complex form with protein C inhibitor
(PCI) with mutually inhibitory consequences. A better understanding of the spectrum
of coagulating and liquefaction agents in semen to include classical haemostatic processes
and the pathogenesis resulting from any imbalances between or within either system
may provide the basis for the development of more selective and efficient agents affecting
global fertility. Here we review aspects of male reproductive physiology in the light
of recent findings concerning conventional clotting/fibrinolytic systems in human
semen with a view to stimulating further research.
Keywords
Human seminal plasma - haemostasis - fertilization - implantation - prostasomes -
semen quality - review