N A Kokolis

Aristotle University of Thessaloniki, Thessaloníki, Kentriki Makedonia, Greece

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Publications (9)18.24 Total impact

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    ABSTRACT: Plasminogen activators (PA) are proteolytic enzymes present in the spermatozoa and seminal plasma of various species. They play a role in the binding of the spermatozoon and its penetration through the layers surrounding the oocyte. Plasminogen activator activity (PAA) is modulated by hormones that have a seasonal variation, such as testosterone and melatonin. The present study investigates the seasonal variation of PA activity in sperm extracts and seminal plasma of four farm animal species: boar, buck, bull and stallion. Semen samples were collected every second week during a 12-month period and PAA was determined. With respect to sperm enzyme activity, the boar showed a peak from late January until the beginning of April, whereas the activity in the bull was at the highest levels from April until October and gradually declined during autumn and winter period. Plasminogen activator activity of stallion spermatozoa peaked during March and April, and remained low throughout the rest of the year, whereas in the buck sperm, PAA increased from late October until the end of January. No biologically significant variation was detected regarding the seminal PAA activity in any of the species studied. While seasonality of reproduction is typically studied from the female perspective, the present data provide compelling information about a factor that may affect the reproductive ability of the male.
    Reproduction in Domestic Animals 04/2010; 45(6):e440-6. · 1.39 Impact Factor
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    ABSTRACT: The aim of the present study was to investigate the effect of melatonin on plasminogen activator activity (PAA), plasminogen activator inhibition (PAI) and plasmin inhibition (PI) in ram spermatozoa and seminal plasma, in correlation with changes in blood testosterone. Melatonin implants (18 mg) were placed subcutaneously in sixteen Chios rams in autumn and spring. Semen samples for spectrophotometrical assays were collected 36 h before the implantation of melatonin and thereafter once a week, for 17 weeks. Blood samples for testosterone assay (RIA) were collected 8h before implantation (one sample/30 min x 7.5 h) and thereafter every 15 days for 105 days after implantation. For each ram, six parameters of testosterone were estimated: mean value, basal level, number of peaks, peak amplitude, peak duration and mean testosterone concentration during peaks. Melatonin implantation during autumn induced an increase in PAA and t-PAI in spermatozoa; melatonin implantation in spring induced an additional increase in u-PAI and PI; no change in PAA, PAI or PI was found in seminal plasma, during autumn or spring. The melatonin-induced increase of PAA, PAI and PI in spermatozoa was in positive correlation with the increase of testosterone mean value, basal level and number of peaks; the increase of testosterone parameters was greater in autumn compared to spring. Changes of PAA, PAI and PI of spermatozoa, under the influence of melatonin, might indicate changes in the fertilizing ability of spermatozoa, since plasminogen activators and their inhibitors are present on the plasma and the outer acrosomal membrane of spermatozoa and are released during the acrosome reaction.
    Theriogenology 04/2008; 69(4):458-65. · 2.08 Impact Factor
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    ABSTRACT: The aim of this study was to determine the effect of norgestomet treatment, in the absence or the presence of a functional corpus luteum (CL), on plasminogen activators activity (PAA) in the cervical mucus and the endometrium in dairy cows. Eleven days after oestrus (Day 0 = oestrus), 38 cows were randomly assigned to one untreated control group (n = 9) and three treatment groups (S(1), S(2) and S(3)). Animals of S(1) group (n = 9) received an implantation of norgestomet on the outer surface of the ear for 8 days, simultaneous injection of oestradiol valerate 5 mg and norgestomet 3 mg, i.m., and on Day 19 an injection of ECG 500 IU, i.m. Animals of S(2) group (n = 11) received the treatment of S(1) group, plus an administration of PGF(2)alpha on Day 10 for the regression of CL. Animals of S(3) group received the treatment of S(2) group, plus two additional norgestomet implants inserted on Day 16 for 36 h. Both types of plasminogen activators [the tissue-type (t-PA) and the urokinase-type (u-PA)] were detected in the cervical mucus and the endometrium of the cows. Plasminogen activators activity in the cervical mucus was higher in control group than in S(1), S(2) and S(3) groups (P < 0.001). In contrast, endometrial PAA did not differ among groups (P > 0.05). Oestradiol-17beta concentrations on Day 21 were higher in S(2) group than in control group (P < 0.01) and S(3) group (P < 0.05). Progesterone concentrations did not differ among groups (P > 0.05). Oestradiol-17beta concentrations could positively affect cervical mucus PAA in control group (P < 0.1), but not in other groups (P > 0.05). These findings suggest that control of estrous cycle by norgestomet administration, in dairy cows, exerts a suppressive effect on plasminogen activators synthesis and/or secretion in the cervical mucus, regardless of the absence or the presence of the CL. On the contrary, endometrial PAA is not affected by norgestomet treatment.
    Journal of Veterinary Medicine Series A 10/2007; 54(8):393-7. · 0.93 Impact Factor
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    ABSTRACT: The mammalian oviduct is a dynamic tissue, which lies under the influence of ovarian steroids and produces proteins that affect various stages of fertilization and post-fertilization events. In this study, expression of urokinase-type plasminogen activator (u-PA mRNA) and plasminogen activator activity (PAA) were examined in porcine oviducts by reverse transcription and polymerase chain reaction (RT-PCR) and activity assays, respectively. For this purpose, oviducts were collected from Landrace cycling sows and divided into three segments (isthmus, ampulla, infundibulum). Different concentrations of u-PA mRNA were detected in the three segments following the pattern isthmus>ampulla>infundibulum and this pattern was maintained during the oestrous cycle. On the contrary, the highest PAA was measured in the ampulla compared to the isthmus and the infundibulum and the highest ampullary PAA was detected during the first 2 days of the oestrous cycle. The different regulation of u-PA mRNA expression and PAA is probably due to the existence of PA inhibitors. Recent observations suggest that PAI-1, the main inhibitor of PAs, shows greater expression in the isthmus compared to the ampulla and the local generation of plasmin is inhibited. The latter may be related to observations that spermatozoa are quiescent in the isthmus before fertilization. This study supports the suggestion that urokinase-type plasminogen activator has a biological role within the porcine oviduct, especially at or near the time of fertilization.
    Theriogenology 10/2005; 64(4):1007-15. · 2.08 Impact Factor
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    ABSTRACT: Acrosin and plasminogen activators are proteolytic enzymes of ram spermatozoa that play an essential role in the induction of the acrosome reaction, as well as the binding of spermatozoa to the oocyte and their penetration through the layers that surround the oocyte. Since vitamin A can alter gene expression in various tissues, testis included, this study was undertaken to evaluate the possible effect of vitamin A intake on acrosin- and plasminogen-activator activity. During a 20-week experiment, 15 rams of the Greek breed Karagouniki, divided to three groups, received different amounts of vitamin A per os in retinyl acetate capsules (group A, controls, 12,500 iu/animal per day; group B, 50,000 iu/animal per day; group C, 0 iu/animal per day up to the 13th week, then 150,000 iu/animal per day until the end of the experiment). Acrosin- and plasminogen-activator activity were determined by spectrophotometric methods. Vitamin A was determined in blood plasma by HPLC. No statistical differences were detected regarding the body weight of the rams or the qualitative and quantitative parameters of their ejaculate throughout the whole experiment. No statistically significant alterations of enzyme activity were detected in group B. In group C, both enzyme activities started declining in week 9. Compared with controls, maximum reduction for acrosin was 49% on week 11 and for plasminogen activators 51% in week 14. Activities returned to normal rates after vitamin A re-supplementation. To date, the main result of vitamin A deficiency was known to be arrest of spermatogenesis and testicular degeneration. A new role for vitamin A may be suggested, since it can influence factors related to male reproductive ability before spermatogenesis is affected.
    Reproduction (Cambridge, England) 07/2005; 129(6):707-15. · 3.56 Impact Factor
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    ABSTRACT: The aim of this study was to investigate the effect of dexamethasone on acrosin activity of spermatozoa in Chios rams during autumn (breeding season for sheep in Greece), in correlation with possible changes in blood testosterone. Dexamethasone was administered in four equal consecutive intramuscular injections, one every four hours (total dose: 3 mg kg(-1)). Total acrosin activity was determined in semen samples collected 48 h before and on the 4th and 7th day and thereafter once every week until the 77th day after dexamethasone administration. Blood samples for testosterone radioimmunoassays were collected 24 h before, during dexamethasone administration and on the 4th, 7th, 14th and 21st day after administration. Total acrosin activity in spermatozoa was reduced between days 7-28 after dexamethasone administration. Dexamethasone also induced a reduction in mean value and basal level of blood testosterone and inhibited its episodic secretion between 1 and 4 days after administration. As the reduction of acrosin activity appeared relatively soon after dexamethasone administration (7th day), it is likely that the increased amount of dexamethasone did not influence the synthesis of proacrosin in the late spermatids. As glucocorticoid receptors exist in the epididymis and accessory glands in various species, dexamethasone may have a direct influence on the synthesis and/or release of acrosin inhibitors in epididymal fluid or seminal plasma. These changes in acrosin activity in ovine spermatozoa mediated by dexamethasone may be of importance regarding the role of stress in the reduction of sperm fertilizing ability.
    Andrologia 07/2002; 34(3):188-93. · 1.75 Impact Factor
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    ABSTRACT: The effect of tannic acid, a common flavonoid, on the acrosin and plasminogen activator activity and plasmin activity of human and ram spermatozoa was evaluated. Acrosin and plasminogen activator activity were determined by spectrophotometry using the chromogenic substrates N-alpha-benzoyl-DL-arginine para-nitroanilide-HCl (BAPNA) and H-D-valyl-L-leucyl-L-lysine-p-nitroanilide-2HCl (S-2251), respectively. In extracts from both human and ovine acrosomes, the activities of acrosin and plasminogen activators were susceptible to tannic acid inhibition. The inhibitory effect of tannic acid was observed at concentrations > 50 micromol l(-1) in a dose-dependent manner. In additional experiments, low concentrations of tannic acid significantly inhibited tissue-type plasminogen activator, urokinase-type plasminogen activator and plasmin activity in a concentration-dependent manner over the range 0.25-200 micromol l(-1). Tannic acid reduced the motility of ram spermatozoa at a concentration of 1000 micromol l(-1) after 2 and 3 h co-incubation with spermatozoa. The motility of human spermatozoa remained unchanged over the range 0.1-1000 micromol tannic acid l(-1) during 3 h co-incubation. These results indicate that tannic acid inhibited the activity of both acrosin and plasminogen activator and indicates a possible mechanism by which flavonoids exert their antifertility effects.
    Reproduction (Cambridge, England) 02/2001; 121(1):131-7. · 3.56 Impact Factor
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    ABSTRACT: The effect of gossypol--a polycyclic compound isolated from cotton seeds--on the plasminogen activator activity of man and ram acrosomal extracts was explored in vitro. The action of gossypol on the plasminogen activator activity was investigated by a spectrophotometric method using the chromogenic substrate S-2251. Gossypol, a known antispermatogenic agent, was found to effectively inhibit human and ovine acrosomal plasminogen activator activity. The inhibition was dose-dependent. Plasminogen activator activity from man and ram extracts was completely inhibited by 350 mumol l-1 and 300 mumol l-1 of gossypol, respectively. In additional experiments, low, non-spermicidal concentrations of gossypol (2.5-40 mumol l-1) were found to significantly inhibit plasmin activity in a dose-dependent manner. The results suggest that inhibition of both acrosomal plasminogen activator and plasmin activity is a possible mechanism by which gossypol exerts its antifertility effect, since the plasminogen activator/plasmin system plays a role in the whole process of ovum fertilization.
    Andrologia 01/2000; 31(6):355-9. · 1.75 Impact Factor
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    ABSTRACT: This study was undertaken to investigate if low-dose dietary administration of tannic acid exerts its chemopreventive activity on hepatocarcinogenesis in male C3H mice through changes of plasminogen activator activity (PAA), plasminogen activator inhibition (PAI) or plasmin inhibition (Pl) in the liver of C3H hepatoma bearing male mice. Tannic acid was administered in the drinking water of hepatoma bearing C3H mice, in a concentration of 0.0075% (group B), 0.015% (group C) and 0.03% (group D) for 9 months. PAA, PAI and PI were measured by spectrophotometric methods in macroscopically healthy liver regions. Tannic acid induced a decrease of PAA (53%) and an increase of PAIs (50%) in the livers of group D while tannic acid received mice showed a dramatic decrease in liver carcinomas incidence (0% vs 33.3% in the control group). The decrease of PAA in the liver of C3H hepatoma bearing male mice, might be correlated with the chemopreventive activity of tannic acid in hepatoma development.
    In vivo (Athens, Greece) 01/2000; 14(6):767-71. · 1.15 Impact Factor

Publication Stats

47 Citations
18.24 Total Impact Points

Institutions

  • 2000–2005
    • Aristotle University of Thessaloniki
      • • Laboratory of Exercise Physiology and Biochemistry
      • • Faculty of Veterinary Medicine
      Thessaloníki, Kentriki Makedonia, Greece
  • 2000–2001
    • University of Thessaly
      • Laboratory of Physiology (Sector of Basic Science)
      Lárisa, Thessalia, Greece