| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
From the * Department of Urology, Southampton
University Hospitals, Southampton, United Kingdom; and
American Diagnostica Inc, Stamford,
Connecticut.
| Correspondence to: Dr Bashir A. Lwaleed, Department of Urology, Central Block, Level E, West Wing, Mail-point 67, Southampton University Hospitals NHS Trust, Southampton, Tremona Road, SO16 6YD, United Kingdom (e-mail: bashir{at}soton.ac.uk). |
| Received for publication July 7, 2004; accepted for publication September 12, 2004. |
 |
Abstract |
|---|
 Top Abstract Materials and MethodsResultsDiscussionReferences |
|---|
Key words: Fertility, novel finding.
-carboxyglutamic residues; the first 9 are responsible for the
calcium-dependent phospholipid membrane binding
(Astermark et al, 1991;
Freedman et al, 1995). Factor
IXa is composed of N-terminal light chain and a C-terminal heavy chain linked
via a disulphide bond (Brandstetter et al,
1995). It is activated to a multidomain protein, FIXa
(Yoshitake et al, 1985; Brandstetter et al, 1995)
Tissue Factor (TF):FVII complex FVIIa
(Østerud and Rapaport,
1977) and FXIa (DiScipio et
al, 1978). Factor IXa activates FX to supplement FXa initially
generated by TF:FVII/FVIIa complex. This is essential to sustain FX
activation, since TF: FVII/FVIIa activity is temporally limited in a
FXa-dependent fashion by a stoichiometric inhibitor of blood coagulation,
Tissue Factor Pathway Inhibitor (TFPI)
(Broze, 1992;
Rapaport and Rao, 1992).
Independently, FIXa has little activity on its natural substrate FX. However,
complex formation with its co-factor FVIIIa (FIXa:FVIIIa) causes a dramatic
increase in FX activation. Similarly, FVIIIa alone has no proteolytic effect
on FX (Neal and Chavin, 1979).
The interaction between FIXa and FVIIIa is calcium mediated but lipid
independent. In vivo, however, this reaction occurs on the surface of the
endothelial cells or activated platelets
(van Dieijen et al, 1981),
where a suitable membrane phospholipid is provided. Mutations in FIXa can
affect FVIIIa binding by at least two mechanisms
(Bajaj, 1999). Men are considered to have normal semen parameters when the ejaculated semen has a volume of 2-6 mL, a sperm concentration of more than 20 x 106/mL, a normal sperm morphology of greater than 15%, above 40% of the total sperm population is motile, and a sperm progression of 2.5 or more, with 4 being the maximum level of progression (World Health Organization [WHO], 2000). Fifteen percent of all married couples with normal semen parameters are involuntarily childless. Thus, not all subjects with high counts are fertile and not all subjects with low counts are infertile in practice. However, infertility could equally be caused by male or female factors (Schwarzstein, 1983). Failure in the liquefaction process of semen has often been seen in male infertility patients having low sperm count and/or motility (Matsuda et al, 1994). The coagulation and subsequent liquefaction of human semen occurs within 5 minutes of ejaculation in vivo (Sobrero and MacLeod, 1962) and is prolonged by up to 30 minutes in vitro at room temperature (Amelar, 1962). The predominant structural proteins of coagulated human semen are those that are secreted by the seminal vesicles—the High Molecular Weight Seminal Vesicle (HMW-SV) proteins (Lilja, 1985). The interaction between the seminal vesicle and prostate components leads to the liquefaction of the seminal coagulum (Mandal and Bhattacharyya, 1986). Human ejaculates vary in their degree of coagulation as well as in their liquefaction time (Mandal and Bhattacharyya, 1986).
Seminal coagulum is also composed of fibrin-like material (Polak and Daunter, 1989). The procoagulant activity of human seminal plasma added to blood plasma was first recognized in 1942 (Huggins and Neal, 1942). Seminal plasma diluted up to 10 000-fold significantly decreased the recalcification clotting time of blood plasma (Huggins and Neal, 1942). However, the molecular basis for this observation remains uncertain. In the present study we report on seminal FIX and FIXa, which might provide further evidence for the presence of a functioning clotting system in human semen.
|
Materials and Methods |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Stratification of Subjects
A total of 119 subjects, aged 20-64 years were studied. We followed the
classification of the fourth edition of the WHO guidelines on semen analysis
(World Health Organization,
2000): subfertile subjects have sperm counts of less than 20
x 106/mL (n = 18), normal fertility implies sperm counts that
are greater than or equal to 20 and less than 60 x 106/mL (n
= 34). Fertile subjects suitable for semen donation (labeled below as
"fertile donors") in Southampton University Hospitals have sperm
counts of greater than or equal to 60 x 106/mL (n = 27).
Vasectomy subjects were also studied (n = 40). A further classification was
defined with all semen parameters normal according to the WHO criteria (volume
of 2-6 mL, a sperm concentration of more than 20 x 106/mL, a
normal sperm morphology of more than 15% normal forms, above 40% of the total
sperm population motile, and sperm progression of 2.5 or more, 4 being the
maximal progression value). This we term "pooled normal semen
parameters."
Processing of Semen Samples
Seminal plasma was prepared by differential centrifugation. Fresh semen
samples were placed in 1.5-mL Eppendorf tubes after liquefaction and spun at
2000 x g for 10 minutes at room temperature in Heraeus Biofuge
28 RS centrifuge. This low-speed supernatant constitutes the plasma fraction.
The supernatants from this spin were transferred into new 1.5-mL Eppendorf
tubes and were deep-frozen at -72°C for batchwise measurement.
Semen Analysis
Conventional seminal fertility parameters were measured according to the
WHO guidelines as described in the WHO "golden" laboratory manual
for the examination of human semen and sperm-cervical mucus interaction
(World Health Organization,
2000).
Factor IX and IXa Assays
Factor IX Assay—
Factor IX activity was measured by a 1-stage factor assay based on PT/APTT
using ACL 300R analyzer (Instrumentation Laboratory, Warrington, United
Kingdom). The standard curve was reproducible (n = 4; r = 0.991;
P < .001; Figure
1a). Samples giving values higher than the top standard were
diluted, reassayed, and the reading corrected for the dilution factor.
|
Factor IXa Assay— Factor IXa was measured using spectrozyme fIXa (American Diagnostica Inc, Stamford, Conn) according to the manufacturer's instructions. A standard curve was constructed using recombinant FIXa (American Diagnostica). This was also very reproducible (n = 4; r = 0.995; P < .001; Figure 1b). Background activation without the substrate spectrozyme fIXa was (0.079 reaction rate) against (0.334 reaction rate) in the presence of spectrozyme fIXa.
Statistical Analysis
Results were entered into a database and analyzed by the
STAT-GRAPHICSTM statistical software system. Summary statistics were
expressed as medians and interquartile ranges. Differences between two groups
were assessed by Mann-Whitney U test. Correlations were determined
using the Pearson correlation test. Factor IX and FIXa were log-transformed;
hence the choice of test. All assay results are expressed per original sample
volume for FIX (IU/dL) and FIXa (ng/mL), respectively.
|
Results |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
|
Seminal Viscosity and Liquefaction Time
Only FIXa levels were positively and significantly correlated with semen
liquefaction time (n = 62; r = 0.23; P < .05). There was
a positive but not significant association between FIX or FIXa levels and
semen viscosity (data not shown).
Days of Abstention, Semen Volume, Sperm Count, Motility, and Progression
No significant findings were achieved. The direction of weak trends
observed was reversed between FIX and FIXa for motility and progression
(Tables 1 and
2) but not for counts, volume,
and abstention (data not shown).
|
|
Sperm Morphology
Slight increases of FIX and FIXa were observed with abnormal sperm
morphology; however, no significant difference between the normal or abnormal
morphology groups was observed for the two factors (data not shown).
Seminal Agglutination
Higher level of FIX and FIXa levels were seen in semen showing many clumps.
For FIXa levels, the differences between the high and the low clump group were
statistically significant (P < .05;
Table 3).
|
Anti-Sperm Antibodies
Subjects with anti-sperm antibodies had high levels of FIX, but
statistically, no significant difference was observed between the two groups
(Table 4). No such trend was
seen for FIXa (Table 4).
|
|
Discussion |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Semen is known to contain a potent procoagulant activity that was shown to be dependent on FX and Ca++, indicating the presence of FX activator (Fernández et al, 1997). About 90% of the activity was found in the seminal plasma (Carson and De Jonge, 1998). This procoagulant activity was neutralized by monoclonal antibodies to human TF and FVII (Fernández et al, 1997), indicating the presence of TF (Fareed et al, 1995; Ohta et al, 2002). Indeed, evaluation of seminal TF activity in an infertility context showed 16-fold variation, and no relationship was found between TF and number of days of abstinence before sampling, pH, sperm counts, or sperm motility (Carson and De Jonge, 1998). In the light of this finding and the published reports on seminal FXa (Matsuda et al, 2002) and the current, unpublished data by our group demonstrating quantitative levels of clotting factors V, VII, VIIa, VIII, vWF, IX, IXa, Xa, XI, and XII, as well as TFPI, in human semen, we propose the presence of a complete set of blood coagulation factors in semen, bar thrombin—and even in this case prothrombin degradation products (prothrombin fragment 1.2 [F1.2]), thrombin-like enzyme, anti-thrombin III, and thrombin anti-thrombin III complex are present (van Wersch et al, 1992, 1993; Park et al, 1997). Fibrin monomer has also been detected in human semen (van Wersch et al, 1992). In blood plasma, however, when fibrin is formed it is known to provoke fibrinolysis by stimulating tissue plasminogen activator activity, which is present in a rather high concentration in semen (Christ and Binder, 1989). The result is the formation of D-Dimer degradation products, which can only originate from previously formed cross-linked fibrin (covalent). D-Dimer was found in semen in readily measurable concentrations that even permitted the formation of the D-Dimer/thrombin anti-thrombin III complex in seminal plasma (van Wersch et al, 1992, 1993). In addition, semen contains several other fibrinolytic factors, including tissue and urinary plasminogen activators, fibrinogen/fibrinogen-like substance, and plasmin, as well as detectable levels of Plasminogen and Plasminogen Activator Inhibitor-I (PAI-1) (van Dreden et al, 1991; van Wersch et al, 1992; Park et al, 1997). Vitronectin, a regulator of coagulation and fibrinolysis, is also found in semen (Bronson and Preissner, 1997). It protects thrombin from a rapid heparin-dependent inactivation by anti-thrombin III and inhibits the fibrin clot-induced activation of plasminogen by tissue type plasminogen activator. Vitronectin also binds to PAI-1 and stabilizes its inhibitor activity (Schvartz et al, 1999). Taken together, these reports indicate that semen contains a functioning clotting system and that seminal coagulum is at least partly composed of fibrin (van Wersch et al, 1992).
In the present study, however, we discuss our findings with respect to seminal clotting FIX and FIXa and their possible role in male fertility. Concentrations of FIXa were of the same order as the range conventionally accepted for blood plasma (van Hylckama Vlieg et al, 2000). Both FIX and FIXa were measurable at slightly higher concentrations in semen from normal, nonfertile, and vasectomized subjects. We observed a wide variation in FIX and FIXa levels within these groups; as a result, no statistically significant difference could be demonstrated. Wide variation also occurs in peripheral blood. In healthy subjects, individual plasma FIX activity and antigen levels also varied between 50% and 150% of a pooled plasma value (Reiner and Davie, 1994). However, the semen available for assay (from fertility clinics) had inevitably already coagulated and had also subsequently liquefied. This is not directly analogous to plasma, or even serum. Overall, there is substantially more FIXa than FIX in semen. The fertile donor group showed the lowest seminal FIX value, whereas the vasectomy group showed the highest median value (Figure 2a). While the median values for seminal FIXa were lowest in the nonfertile group, all the other medians were similar (Figure 2b). A positive significant correlation was observed between seminal FIX and FIXa levels (n = 36; r = 0.51; P < .05; Figure 3). This is indicative of a functional presence, as both TF and FVII/VIIa, which activates FIX directly, are also found in semen (Carson and De Jonge, 1998). Both FIX and FIXa showed a positive but insignificant correlation with seminal TFPI (n = 119, r = 0.2, P > .05; n = 68, r = 0.22, P > .05, respectively, for FIX and FIXa). Attempts to find associations between concentrations of FIX or FIXa and conventional correlates of fertility encountered limited success. The difference between the high and the low sperm-clump groups was only significant for FIXa levels (FIXa in clumped semen is greater than that for nonclumped semen, P < .05), and days of abstention correlated with FIXa levels (n = 63; r = 0.3; P < .05). This paucity of strong correlations may reflect difficulties in obtaining a numerical index for male fertility in practice. Very large studies would be required to determine whether any of the less-than-significant trends observed were in fact true associations and even if so, the distinction between small significant changes and pathophysiologically meaningful differences is another step further removed.
|
The mere presence of clotting and fibrinolytic factors in semen could reflect transudation from blood plasma. However, in the context of this article, the levels of FIXa obtained in semen, which necessarily must have both coagulated and liquefied before it can be measured, are on the same order of magnitude as those of blood plasma. This is a high proportion for a large molecule, considering that only about 1% of the much smaller albumin and immunoglobulin G molecules, are recovered in seminal plasma after transudation from the prostate (Rümke, 1974). Factor IX product can be localized immunohistochemically in the prostate, but in situ hybridization studies have not yet been undertaken to assess whether there is mRNA present.
Congenital deficiencies of the coagulation factors are rare disorders, and FIX deficiency in particular is less common. In most cases it is a mild bleeding disorder, autosomally inherited (Bolton-Maggs and Pasi, 2003). Severe hemophilia B may become mild and then may show a normal concentration of FIX activity (Bolton-Maggs and Pasi, 2003). For instance, FIX activity changes significantly with age in individuals with mutations in the promoter sequence of the gene such as "hemophilia B Leyden" (Briet et al, 1982; Reitsma et al, 1988; Giannelli, 1997) but not in "hemophilia B Brandenburg," which, in addition to disrupting the binding site of the transcription factor LF-A1/HNF4, also disrupts the androgen responsive elements that overlap the LF-A1/HNF4 site (Crossley et al, 1992). More than 2100 mutations in the FIX gene have been identified (www.kcl.ac.uk/ip/petergreen/haemBdatabase.html). Studies on seminal FIX in subjects with congenital defects in FIX synthesis or function whom are at risk of developing a severe bleeding diathesis would be interesting; in particular, the influence of FIX gene mutations on seminal product levels should be studied.
While we propose that the seminal clotting system may be functional and that it may somehow be involved in seminal coagulum formation, we suggest that one possible way through which this could be achieved is by the interaction with the established HMW-SV proteins and the Prostate Specific Antigen (PSA) system (Lwaleed et al, 2004), which is currently believed to be the sole system responsible for seminal coagulation and liquefaction. For instance, activated Protein C Inhibitor (PCI), a heparin binding serine protease inhibitor (serpins) that has broad protease specificity, acts as an anti-coagulant, anti-anti-coagulant, anti-fibrinolytic, and anti-anti-fibrinolytic factor, complexes with PSA, and partially inhibits its activity (Laurell et al, 1992). PCI is present in semen at a relatively high concentration in both high and low molecular mass form (160 ± 20 µg/mL, mean ± SD). This is more than 30-40 times the concentration of PCI found in blood plasma (5 µg/mL) (España et al, 1991, 1993; Laurell et al, 1992; Christensson and Lilja, 1994). During coagulum dissolution in freshly ejaculated semen, approximately 40% of immunodetected PCI becomes complexed to PSA (Christensson and Lilja, 1994). In semen, complexes between PCI and PSA are detected at levels that correspond to an inactivation of up to 5% of the PSA activity in the ejaculate (Christensson and Lilja, 1994).
In conclusion, studies to date on the seminal coagulation factors are limited to a few reports. An important result of this work is that both FIX and FIXa are quantifiable in human semen. This brings us a step closer toward identifying a functional clotting system in human semen and strengthens the suggestion of a link between the coagulation system in semen and seminal coagulum formation. It is becoming increasingly clear that seminal coagulum formation may be in some measure mediated through the conventional factors of the normal coagulation process. Further studies on the role and functions of seminal clotting factor and its relationship to the HMWSV proteins in the pathophysiology of male fertility are warranted. Evaluation of the seminal clotting/fibrinolytic proteins could also be useful in assessing the secretory function of the accessory genital glands in fertile and infertile men.
|
Acknowledgments |
|---|
|
References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Astermark J, Bjork I, Ohlin AK, Stenflo J. Structural requirements
for Ca2+ binding to the gamma-carboxyglutamic acid and epidermal growth
factor-like regions of factor IX. Studies using intact domains isolated from
controlled proteolytic digests of bovine factor IX. J Biol
Chem. 1991; 266:2430-2437.
Bajaj SP. Region of factor IXa protease domain that interacts with factor VIIIa: analysis of select hemophilia B mutants. Thromb Haemost. 1999; 82:218-225.[Medline]
Bolton-Maggs PH, Pasi KJ. Haemophilias A and B. Lancet. 2003; 361:1801-1809.[Medline]
Brandstetter H, Bauer M, Huber R, Lollar P, Bode W. X-ray structure
of clotting factor IXa: active site and module structure related to Xase
activity and hemophilia B. Proc Natl Acad Sci U S A. 1995; 92:9796-9800.
Briet E, Bertina RM, van Tilburg NH, Veltkamp JJ. Hemophilia B Leyden: a sex-linked hereditary disorder that improves after puberty. N Engl J Med. 1982; 306:788-790.[Medline]
Bronson RA, Preissner KT. Measurement of vitronectin content of human spermatozoa and vitronectin concentration within seminal fluid. Fertil Steril. 1997; 68:709-713.[Medline]
Broze GJ. The role of tissue factor pathway inhibitor in a revised coagulation cascade. Semin Hematol. 1992; 29:159-169.[Medline]
Carson SD, De Jonge CJ. Activation of coagulation factor X in human
semen. J Androl. 1998; 19:289-294.
Christ G, Binder BR. Components of the fibrinolytic system in spermatozoa and seminal plasma of fertile and infertile men. Thromb Haemost. 1989; 62:396.
Christensson A, Lilja H. Complex formation between protein C inhibitor and prostate-specific antigen in vitro and in human semen. Eur J Biochem. 1994; 220:45-53.[Medline]
Crossley M, Ludwig M, Stowel KM, de Vos P, Olek K, Brownlee GG.
Recovery from hemophilia B Leyden: an androgen-responsive element in the
factor IX promoter. Science. 1992; 257:377-379.
DiScipio PG, Hermodson MA, Yates SG, Davie EW. A comparison of human prothrombin, factor IX (Christmas factor), factor X (Stuart factor), and protein S. Biochemistry. 1977; 16:698-706.[Medline]
DiScipio RG, Kurachi K, Davie EW. Activation of human factor IX (Christmas factor). J Clin Invest. 1978; 61:1528-1538.
España F, Estelles A, Fernández PJ, Gilabert J, Sanchez-Cuenca J, Griffin JH. Evidence for the regulation of urokinase and tissue type plasminogen activators by the serpin, protein C inhibitor, in semen and blood plasma. Thromb Haemost. 1993; 70:989-994.[Medline]
España F, Gilabert J, Estellés A, Romeu A, Aznar J, Cabo A. Functionally active protein C inhibitor/plasminogen activator inhibitor-3 (PCI/PAI-3) is secreted in seminal vesicles, occurs at high concentrations in human seminal plasma and complexes with prostate-specific antigen. Thromb Res. 1991; 64:309-320.[Medline]
Fareed J, Callas DD, Hoppensteadt D, Bermes EW. Tissue factor antigen levels in various biological fluids. Blood Coag Fibrinol. 1995; 6:32-36.
Fernández JA, Heeb MJ, Radtke K-P, Griffin JH. Potent blood coagulant activity of human semen due to prostosome-bound tissue factor. Biol Reprod. 1997; 56:757-763.[Abstract]
Freedman SJ, Furie BC, Furie B, Baleja JD. Structure of the
metal-free gamma-carboxyglutamic acid-rich membrane binding region of factor
IX by two-dimensional NMR spectroscopy. J Biol Chem. 1995; 270:7980-7987.
Giannelli, F. The genetics of blood coagulation and haemostasis. In: Rizza CR, Lowe GDO, eds. Haemophilia and Other Inherited Bleeding Disorders. London: Saunders; 1997 :43-86.
Huggins C, Neal W. Coagulation and liquefaction of semen.
Proteolytic enzymes and citrate in prostatic fluid. J Exp
Med. 1942; 76:527-541.
Katayama K, Ericsson LH, Enfield DL, Walsh KA, Neurath H, Davie EW,
Titani K. Comparison of amino acid sequence of bovine coagulation Factor IX
(Christmas Factor) with that of other vitamin K-dependent plasma proteins.
Proc Natl Acad Sci U S A. 1979; 76:4990-4994.
Kurachi K, Kurachi S. Regulatory mechanism of the factor IX gene. Thromb Haemost. 1995; 73:333-339.[Medline]
Laurell M, Christensson A, Abrahamsson PA, Stenflo J, Lilja H. Protein C inhibitor in human body fluids. Seminal plasma is rich in inhibitor antigen deriving from cells throughout the male reproductive system. J Clin Invest. 1992; 89:1094-1101.
Lilja H. A kallikrein-like serine protease in prostatic fluid cleaves the predominant seminal vesicle protein. J Clin Invest. 1985; 76:1899-1903.
Lwaleed BA, Greenfield R, Stewart A, Birch B, Cooper AJ. Seminal clotting and fibrinolytic balance: a possible physiological role in the male reproductive system. Thromb Haemost. 2004; 92:752-766.[Medline]
Mandal A, Bhattacharyya AK. Grouping of human ejaculates according to the degree of coagulation and the relationship to the levels of choline and cholinesterase. Int J Androl. 1986; 9:407-415.[Medline]
Matsuda Y, Oshio S, Yazaki T, Umeda T, Akihama S. The effect of
some proteinase inhibitors on liquefaction of human semen. Hum
Reprod. 1994; 9:664-668.
Matsuda Y, Shimokawa K, Katayama M, Shimizu H, Umeda T, Oshio S, Chiba R. Blood coagulation factor X (FX) in human seminal plasma. Arch Androl. 2002; 48:295-300.[Medline]
Neal GG, Chavin SI. The role of factors VIII and IX in the activation of bovine blood coagulation factor X. Thromb Res. 1979; 16:473-484.[Medline]
Ohta S, Wada H, Gabazza EC, Nobori T, Fuse H. Evaluation of tissue factor antigen level in human seminal plasma. Urol Res. 2002; 30:317-320.[Medline]
Østerud B, Rapaport SI. Activation of factor IX by the
reaction product of tissue factor and factor VII: additional pathway for
initiating blood coagulation. Proc Natl Acad Sci U S
A. 1977; 74:5260-5264.
Park JY, Yoshimara Y, Nozawa S, Umeda T, Akihama S, Matsuda Y. Fibrinogen-like substance and thrombin like enzyme in human seminal plasma: coagulation of human semen. Arch Androl. 1997; 38:29-36.[Medline]
Pavlovsky A. Contribution to the pathogenesis of hemophilia.
Blood. 1947; 2:185-191.
Polak B, Daunter B. Seminal plasma biochemistry. IV: enzymes involved in the liquefaction of human seminal plasma. Int J Androl. 1989; 12:187-194.[Medline]
Rapaport SI, Rao LV. Initiation and regulation of tissue factor-dependent blood coagulation. Arterioscler Thromb. 1992; 12:1111-1121.[Medline]
Reiner AP, Davie EW. The physiology and biochemistry of factor IX. In: Bloom AL, Thomas DP, eds. Haemostasis and Thrombosis. 3rd ed. Edinburgh: Churchill Livingstone; 1994 :309-324.
Reitsma PH, Bertina RM, van Amstel JKP, Reimans A, Briet E. The
putative factor IX gene promoter in hemophilia B Leyden.
Blood. 1988; 72:1074-1076.
Rümke P. The origin of immunoglobulins in semen. Clin Exp Immunol. 1974; 17:287-297.[Medline]
Schvartz I, Seger D, Shaltiel S. Vitronectin. Int J Biochem Cell Biol. 1999; 31:539-544.[Medline]
Schwarzstein L. Male Reproduction and Fertility. New York: Raven Press; 1983.
Sobrero AJ, MacLeod J. The immediate postcoital test. Fertil Steril. 1962; 13:184-189.[Medline]
Taran LD. Factor IX of the blood coagulation system: a review. Biochemistry (Mosc). 1997; 62:685-693.[Medline]
van Dieijen G, Tans G, Rosing J, Hemker HC. The role of
phospholipid and factor VIIIa in the activation of bovine factor X.
J Biol Chem. 1981; 256:3433-3442.
van Dreden P, Gonzalez J, Poirot C. Human seminal fibrinolytic activity: specific determinations of tissue plasminogen activator and urokinase. Andrologia. 1991; 23:29-33.[Medline]
van Hylckama Vlieg A, van der Linden IK, Bertina RM, Rosendaal FR.
High levels of factor IX increase the risk of venous thrombosis.
Blood. 2000; 95:3678-3682.
van Wersch JW, De Vries-Hanje JC, Ubachs JM. Coagulation and fibrinolysis markers in seminal plasma of patients under evaluation for involuntary childlessness. Eur J Clin Chem Clin Biochem. 1992; 30:467-471.[Medline]
van Wersch JW, Ubachs JH, Delaere KP. Fibrinolysis and coagulation markers in seminal plasma before and after vasectomy. Fibrinolysis. 1993; 7:135-138.[Medline]
World Health Organization. WHO Laboratory Manual for the Examination of Human Semen and Semen-Cervical Mucus Interaction. 4th ed. Cambridge, United Kingdom: Cambridge University Press; 2000 :1-128.
Yoshitake S, Schach BG, Foster DC, Davie EW, Kurachi K. Nucleotide sequence of the gene for human factor IX (antihemophilic factor B). Biochemistry. 1985; 24:3736-3750.[Medline]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
