Significance of serum inhibin B concentration for evaluating improvement in spermatogenesis after varicocelectomy

Masato Fujisawa1,, Masaki Dobashi, Takafumi Yamasaki, Masanori Kanzaki, Hiroshi Okada, Soich Arakawa and Sadao Kamidono

Department of Urology, Department of Organs Therapeutics, Faculty of Medicine, Kobe University Graduate School of Medicine, Kobe, Japan


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
BACKGROUND: The study aim was to clarify the relationship of serum inhibin B concentrations to recovery of spermatogenic function after varicocelectomy, both as a predictor of improvement in the seminogram and as a means of monitoring hormonal function after surgery. METHODS: Fifty-two varicocele patients, including five with normal sperm concentrations, were studied. Changes in the seminogram, serum hormone concentrations and serum inhibin B were evaluated in the 47 oligozoospermic patients after surgery. Preoperative inhibin B concentrations correlated significantly with serum concentrations of FSH (r = 0.598, P < 0.0001) and testosterone (r = 0.380, P < 0.02). Inhibin B concentrations also correlated significantly with sperm concentration (r = 0.351, P < 0.02) and total testicular volume (r = 0.578, P < 0.0001). No significant correlation was seen between inhibin B and the Johnsen score. Preoperative concentrations of inhibin B were higher in patients who increased their sperm concentration after surgery (responders) than in those without improved concentrations (non-responders). No significant difference was observed between pre- and postoperative inhibin B concentrations in responders or non-responders. However, 15 of 25 (60%) patients with increased inhibin B showed improvement of the seminogram, while only five of 22 (23%) patients with no change or a decrease in inhibin B had any improvement (P < 0.05). CONCLUSIONS: Preoperative serum inhibin B concentration could not reliably predict a response to varicocelectomy. However, a change in serum inhibin B concentration after varicocelectomy might be helpful to evaluate the improvement of testicular function after varicocelectomy.

Key words: inhibin B/spermatogenesis/sperm count/varicocele testis/varicocelectomy


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Varicocele is a common cause of male infertility, and improvement of the seminogram has been reported as an effect of varicocelectomy. However, the mechanism by which a varicocele can affect hormonal function within the testis remains controversial.

Inhibins, which are glycoprotein members of the transforming growth factor-ß family, participate in the control of spermatogenesis by a negative feedback influence on the secretion of FSH (De Kretser and McFarlane, 1966Go; de Jong, 1988Go; Maddocks et al., 1992Go; Spiteri-Grech and Nieschlag, 1993Go). Earlier immunoassays for inhibin were limited by cross-reaction with inactive monomeric precursor forms present in plasma, by lack of sensitivity, or by an inability to discriminate between inhibin A and B (Robertson et al., 1996Go). Recently assays able to distinguish bioactive dimeric inhibins from unprocessed higher molecular weight inhibin precursors and free subunits of inhibin have been developed, and hence the physiological role of inhibins in men can be investigated in greater detail. Biologically active forms include two dimers, each comprising a common {alpha} subunit linked by disulphide bonds to either a ßA subunit (inhibin A) or a ßB subunit (inhibin B). While men have measurable amounts of circulating inhibin B, circulating inhibin A concentrations are below the limits of detection of current assays (Illingworth et al., 1996Go). Several reports have documented a strong negative correlation between FSH and inhibin B in fertile and subfertile men (Su et al., 1995Go; Anwalt et al., 1996Go; Illingworth et al., 1996Go; Klingmuller and Haidl, 1997Go; Foresta et al., 1999Go). In addition, inhibin B concentrations are closely related to both sperm concentration (Jensen et al., 1998Go) and testicular volume (Klingmuller and Haidl, 1997Go; Pierik et al., 1998Go). Inhibin B has also been found to be slightly more sensitive than FSH as an index of spermatogenic status, showing a significant correlation (Von Eckardstein et al., 1999Go), and has also been proposed as a marker for spermatogenesis (Leifke et al., 1997Go; Pierik et al., 1998Go).

The correlation of serum concentrations of inhibin B with recovery of spermatogenesis induced by correction of a varicocele has not been investigated. In the current study, the relationship of inhibin B to serum concentrations of FSH, LH, prolactin, testosterone and oestradiol, as well as sperm concentration and testicular volumes, was examined in infertile men with varicocele. In addition, serum concentrations of inhibin B and FSH, LH, prolactin, testosterone and oestradiol were compared before and after varicocelectomy in order to determine whether inhibin B measurements might predict an improvement in the seminogram, as well as changes in reproductive hormonal function after surgery.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Patients
Eighty patients with varicocele who were referred to our outpatient clinic for assessment of fertility problems underwent varicocelectomy, and 52 of these participated in the study. The mean (± SD) patient age was 32.5 ± 4.3 (range 24–42) years, and the mean duration of infertility was 33.1 ± 25.5 months. An infertile couple was defined in terms of duration of infertility exceeding 1 year. Patients were evaluated clinically, according to the protocol of the World Health Organization (WHO, 1993Go). All patients in this study had a varicocele, these being graded from I to III based on physical findings (grade I, n = 13; grade II, n = 19; grade III, n = 20) according to published criteria (Suzuki, 1967Go). Testicular volume was measured using an orchidometer. Varicocelectomy was performed by microsurgical subinguinal technique when a varicocele was palpable. Bilateral testicular biopsies were performed after having obtained the patients' informed consent. Biopsy specimens were scored using Johnsen's score (Johnsen, 1970Go).

Semen samples were obtained by masturbation after at least 5 days of abstinence; semen analyses were performed according to published procedures (WHO, 1992Go). Only patients followed-up for more than 6 months were included in this study. Semen analysis was performed preoperatively and postoperatively at 3-month intervals. Preoperative and postoperative semen analysis after >=6 months were compared in order to identify any improvement according to published criteria (Fujisawa et al., 1994Go). Patients were regarded as responders when preoperative sperm counts of <1x106/ml, from 1–5x106/ml, from 5–10x106/ml, and from 10–20x106/ml were increased to >5x106/ml, 10x106/ml, 20x106/ml, and twice the preoperative value respectively.

Serum hormones and inhibin B assay
Measurements of serum hormones and inhibin B were performed preoperatively and 6 months postoperatively. Serum samples were obtained from all patients and stored at –20°C until the assays were performed. FSH, LH and prolactin were analysed using chemiluminescence assays (Bayer Corp., Germany). Testosterone and oestradiol were measured by radioimmunoassay (Yatoron, Japan). The detection limits were: FSH, 0.3 mIU/ml; LH, 0.1 mIU/ml; prolactin, 0.3 ng/ml; testosterone, 0.05 ng/ml; and oestradiol, 10 pg/ml. Inhibin B was measured using a commercially available, double-antibody, enzyme-linked immunoassay (Serotec, Oxford, UK). Intra- and inter-assay coefficients of variation (CV) for inhibin B were 6% and 15%, respectively. The lowest detectable inhibin B concentration was 15 pg/ml.

GnRH stimulation test
A gonadotrophin-releasing hormone (GnRH) stimulation test was performed in each subject using an i.v. injection of 200 µg GnRH. FSH and LH responses in serial blood samples, obtained at 0, 15, 30, 60, 90 and 120 min, were examined. This test was carried out before varicocelectomy, and repeated at 6 months after surgery.

Data analysis
All results were expressed as mean ± SD. Statistical analyses were performed using the Mann–Whitney test and {chi}2 test. Correlation was assessed using linear regression analysis. A P-value < 0.05 was considered significant.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Correlation of inhibin B, serum hormones and clinical parameters
Inhibin B concentrations showed a significant negative and positive correlation with serum FSH (r = 0.598, P < 0.0001) and testosterone (r = 0.380, P < 0.02) respectively. Correlation of inhibin B with LH was not significant, but showed a tendency towards negativity. No significant correlation was observed between inhibin B and prolactin or oestradiol. Inhibin B concentration correlated significantly with sperm concentration (r = 0.351, P < 0.02) and also with total bilateral testicular volume (r = 0.578, P < 0.0001). No significant correlation between inhibin B concentrations and Johnsen's score (mean 6.6 ± 1.1; range 3.3–8.4) was observed.

Effect of varicocelectomy on seminogram, clinical variables, and serum hormones
The seminograms of 47 oligozoospermic patients, excluding the five patients with a normal preoperative seminogram, were evaluated. On the basis of published criteria (Fujisawa et al., 1994Go), the sperm concentration was increased in 22 patients (responders, 46.8%). Neither responders nor non-responders showed any significant difference in age, duration of infertility, testicular volume, or preoperative sperm concentration (Table IGo). Furthermore, no significant difference was observed in concentrations of LH, testosterone or oestradiol between responders and non-responders (Table IIGo). In contrast, concentrations of FSH and prolactin were significantly higher in non-responders than in responders (P < 0.05). No apparent changes were observed in concentrations of FSH, LH, testosterone, prolactin or oestradiol before and after varicocelectomy (Table IIGo).


View this table:
[in this window]
[in a new window]
 
Table I. Clinical parameters of responders and non-responders
 

View this table:
[in this window]
[in a new window]
 
Table II. The changes of serum hormone and inhibin B concentrations
 
Changes in inhibin B and the improvement of seminogram after varicocelectomy
Preoperative inhibin B concentrations in responders appeared higher than those in non-responders, but this was not statistically significant (Table IIGo). Preoperative and postoperative inhibin B in responders were 123.1 ± 54.4 and 127.3 ± 48.9 pg/ml respectively. In non-responders, the pre- and postoperative inhibin B concentrations were 115.3 ± 58.2 and112.8 ± 64.3 pg/ml respectively. There was no significant difference between the pre- and postoperative mean concentrations of inhibin B in either responders or non-responders to varicocelectomy. Neither was any relationship observed between preoperative FSH and the changes in inhibin B concentration.

However, 15 out of 25 patients (60%) with increased inhibin B showed an improvement in the seminogram, while only five out of 22 patients (23%) with unchanged or decreased concentrations of inhibin B showed any such improvement. Those patients with an increased inhibin B concentration after varicocelectomy showed a significantly higher rate of the improvement in their seminogram than did those with no change or even reduced inhibin B (P < 0.05).

Inhibin B concentration and the GnRH test before and after varicocelectomy
Peak concentrations of FSH in response to GnRH correlated significantly with inhibin B concentrations (Figure 1Go; r = –0.577, P < 0.0001). The patients were classified into three groups on the basis of their pre- and postoperative peak FSH and LH concentrations. For FSH, group I included patients with normal pre- and postoperative peaks, while groups II and III included patients with a high preoperative peak that either decreased (group II) or did not decrease (group III) postoperatively. Both pre- and postoperative inhibin B concentrations in groups II and III were significantly lower than those in group I. No significant differences were observed between pre- and postoperative inhibin concentrations in any group. Even when high peak FSH concentrations before surgery were reduced after surgery (group II), inhibin B concentrations did not change significantly.



View larger version (14K):
[in this window]
[in a new window]
 
Figure 1. Serum inhibin B plotted against peak FSH response to gonadotrophin-releasing hormone. (r = –0.577, P < 0.0001).

 
Patients also were grouped by the LH peak in response to GnRH: group I included patients with normal pre- and postoperative normal peaks, while groups II and III included patients with preoperative peaks that decreased (group II) or did not decrease (group III) postoperatively. The inhibin B concentration in group III was significantly lower than that in group I (Table IIIGo).


View this table:
[in this window]
[in a new window]
 
Table III. Inhibin B and peak FSH and LH concentrations in response to gonadotrophin-releasing hormone
 

    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Recently, inhibin B has been shown to be an important factor related to testicular hormonal function, and several reports have been made indicating correlations between inhibin B and FSH, LH or testosterone (Illingworth et al., 1996Go; Andersson et al., 1997Go; Bohring and Krause, 1999Go). FSH concentrations reportedly correlate with inhibin B in healthy men (semen donors), and also in men with disturbances of spermatogenesis (Illingworth et al., 1996Go; Bohring and Krause, 1999Go). A significant correlation was also noted between testosterone and inhibin B (Bohring and Krause, 1999Go). Early in puberty, when serum inhibin B concentrations rise, a positive correlation can be seen between inhibin B and LH or testosterone (Andersson et al., 1997Go). These observations suggest that Leydig cell factors might be important in the maturation and stimulation of Sertoli cells during early pubertal development, and also in adulthood. However, no significant correlation was found between inhibin B and testosterone (Illingworth et al., 1996Go). Moreover, studies of immature and adult rat Sertoli cells in vitro have shown that LH (Bicsak et al., 1987Go; Simpson et al., 1992Go) and testosterone (Morris et al., 1988Go; Simpson et al., 1992Go) had either no effect, or a suppressive effect, on inhibin production. The current study demonstrated a significant negative correlation between inhibin B and FSH, and a significant positive correlation between inhibin B and testosterone in patients with varicocele, but only a weak correlation between inhibin B and LH, and therefore suggests that Leydig cell factors might participate in the regulation of Sertoli cell function. It is suspected that the mechanism of the LH effect on inhibin production might be indirect, through the action of testosterone or other Leydig cell factors which act either directly on Sertoli cells or influence them via peritubular cells.

Sperm concentration and testicular volume have been reported to correlate with the inhibin B concentration in serum (Bohring and Krause, 1999Go), and the current study confirmed these relationships. In addition, several studies have shown a correlation of inhibin B with the quality of spermatogenesis (Klaiji et al., 1994Go; Anwalt et al., 1996Go; Illingworth et al., 1996Go; Klingmuller and Haidl, 1997Go; Andersson et al., 1998Go; Jensen et al., 1998Go; Pierik et al., 1998Go; Von Eckardstein et al., 1999Go). One group (Andersson et al., 1998Go) reported that inhibin B concentrations correlated directly with testicular status based on concurrent biopsy specimens; serum inhibin B concentrations in adult men with normal spermatogenesis were higher than in subjects with maturation arrest (MA) or Sertoli cell only (SCO). Serum inhibin B concentrations in postpubertal men were closely related to the presence of germ cells from pachytene spermatocytes to early spermatids. It was reported (Von Eckardstein et al., 1999Go) that the percentages of SCO tubuli or tubules with elongated spermatids were closely related to serum inhibin B concentration, indicating the role of late-stage germ cells in the regulation of inhibin B. Circulating inhibin B concentrations may also reflect the extent of interaction between Sertoli cells and germ cells (Pineau et al., 1990Go; Von Eckardstein et al., 1999Go), and particularly elongated spermatids (Allenby et al., 1991Go). However, the current present study disclosed no significant correlation between the percentage of any stage of germ cell and inhibin B concentrations. In addition, no significant correlation was observed between the Johnsen score and inhibin B, probably because most of the patients in this small study had a Johnsen score of 5 to 6. Others (Bohring and Krause, 1999Go) found that there was no significant difference between inhibin B concentrations in normal spermatogenesis and hypospermatogenesis, and concluded that inhibin B cannot reliably predict spermatogenic failure. Thus, no specific type of germ cell appeared to be involved in the regulation of inhibin B secretion.

Although major cytotoxic damage to the testis reduces the overall circulating inhibin B concentration, the effect of minor damage to Sertoli cells or germ cells is unknown. However, inhibin B is considered a potentially useful marker of Sertoli cell and/or germ cell function, for the clinical assessment of individual patients as well as for future clinical and toxicological investigation of male infertility. In the current study, the pre- and postoperative serum inhibin B concentrations were examined in an effort to evaluate testicular function after varicocelectomy. Previously, a small but statistically insignificant difference was reported in mean inhibin B concentrations between patients with and without a varicocele and who had an identical sperm count (40x106/ml) (Bohring and Krause, 1999Go). However, others (Plymate et al., 1992Go), by considering all of their varicocele patients together, reported no abnormalities in either sperm concentration, inhibin B or FSH. Therefore, varicocele itself may not affect inhibin B concentrations. In contrast, it was reported that inhibin was more abundant in sera from a homogeneous group of sterile patients with varicocele and FSH abnormalities than in sera from normal fertile men (Baccetti et al., 1991Go, 1993Go). In observing that rat Sertoli cells in vitro produced more inhibin at 37°C than at 32°C, it was proposed that an increased temperature resulting from the varicocele directly stimulated Sertoli cells to increase secretion of inhibin, hence causing a reduction in FSH and a consequent alteration in spermatogenesis (Ultee-van Gessel et al., 1986Go). However, these studies were based on an assay that was unable to discriminate between the various inhibins, and so the results might have been different had current, highly specific assays been used. In the current study, inhibin B concentrations were lower in severe, than in mild, oligozoospermia. In addition, inhibin B concentrations in varicocele patients were much lower than the range reported for 356 normal Japanese men (Baba et al., 2000Go). Therefore, Sertoli cell function as reflected by inhibin B production was considered to be reduced in varicocele patients. Overall, no significant difference was found between pre- and postoperative inhibin B concentration, and the change in inhibin B related to surgery was not significant in either the responder or non-responder subgroups. However, patients with increased inhibin B showed significantly more improvement than those with no change or a decrease in inhibin B. Therefore, an increased concentration of inhibin B after surgery may be associated with an increase in sperm production. Although postoperative improvement in testosterone production in Leydig cells and in spermatogenesis may occur simultaneously, improvements in hormonal regulation may be independent of any improvement in spermatogenesis. The effect of varicocelectomy on spermatogenesis may be related to changes in venous pressure, temperature or intratesticular interstitial fluid volume, as opposed to purely hormonal changes. It is also possible that increased inhibin B secretion and improved spermatogenesis after varicocelectomy may not occur simultaneously in all patients.

With regard to the GnRH stimulation test, it has been reported previously that exaggerated gonadotrophin (LH and FSH) responses can normalize after surgical correction of the varicocele, supporting the view that varicocele can induce reversible testicular hormonal dysfunction (Fujisawa et al., 1994Go). Reduction of the LH peak after surgery is significantly related to an improvement in testicular function and fertility. In the current study, a postoperative decrease from the exaggerated preoperative FSH peak was not necessarily associated with a postoperative increase in inhibin B. Although it was not possible to demonstrate a change of testosterone concentration after varicocelectomy, a significant increase has been reported in mean serum testosterone following microsurgical inguinal varicocelectomy (Su et al., 1995Go). Therefore, normalization of the FSH peak may be related to small changes in testosterone and oestradiol concentrations.

In conclusion, it was found that mean concentrations of inhibin B and other hormones changed little between pre- and postvaricocelectomy sera. Sertoli cell function, as estimated by inhibin B concentrations, did not normalize during the early period after surgery, even if the sperm count increased. However, the increase in inhibin B concentration after varicocelectomy might suggest an improvement in testicular function.


    Notes
 
1 To whom correspondence should be addressed at: 7-5-2 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan. E-mail: masato{at}med.kobe-u.ac.jp Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Allenby, G., Foster, P.M.D. and Sharpe, R.M. (1991) Evidence that secretion of immunoactive inhibin by seminiferous tubules from the adult rat testis is regulated by specific germ cell types: correlation between in vivo and in vitro studies. Endocrinology, 128, 467–476.[Abstract]

Andersson, A.-M., Juul, A., Petersen, J.H. et al. (1997) Serum inhibin B in healthy pubertal and adolescent boys: relation to age, stage of puberty, and follicle-stimulating hormone, luteinizing hormone, testosterone, and estradiol levels. J. Clin. Endocrinol. Metab., 82, 3976–3982.[Abstract/Free Full Text]

Andersson, A.-M., Muller, J. and Skakkebaek, N.E. (1998) Different roles of prepubertal and postpubertal germ cells and Sertoli cells in the regulation of serum inhibin B levels. J. Clin. Endocrinol. Metab., 83, 4451–4458.[Abstract/Free Full Text]

Anwalt, B.D., Bebb, R.A., Matsumoto, A.M. et al. (1996) Serum inhibin B levels reflect Sertoli cell function in normal men and men with testicular dysfunction. J. Clin. Endocrinol. Metab., 81, 3341–3345.[Abstract]

Baba, K., Iwamoto, T., Nozawa, S. et al. (2000) Inhibin B as a serum biomarker of spermatogenesis: a study of 359 fertile Japanese men. J. Urol., 163, 305.

Baccetti, B., Burrini, A.G., Capitani, S. et al. (1991) Studies on varicocele. I. Submicroscopical and endocrinological features. J. Submicrosc. Cytol. Pathol., 23, 659–665.[ISI][Medline]

Baccetti, B., Burrini, A.G., Capitani, S. et al. (1993) Studies on varicocele. II. The inhibin secretion. J. Submicrosc. Cytol. Pathol., 25, 137–144.[ISI][Medline]

Bicsak, T.A., Vale, W., Vaughan, J. et al. (1987) Hormonal regulation of inhibin production by cultured Sertoli cells. Mol. Cell. Endocrinol., 49, 211–217.[ISI][Medline]

Bohring, C. and Krause, W. (1999) Serum levels of inhibin B in men with different causes of spermatogenic failure. Andrologia, 31, 137–141.[ISI][Medline]

de Jong, F.H. (1988) Inhibin. Physiol. Rev., 68, 555–596.[Abstract/Free Full Text]

De Kretser, D.M. and McFarlane, J.R. (1966) Inhibin in the male. J. Androl., 17, 179–182.

Foresta, C., Bettella, A., Petraglia, F. et al. (1999) Inhibin B levels in azoospermic subjects with cytologically characterized testicular pathology. Clin. Endocrinol., 50, 695–701.[ISI][Medline]

Fujisawa, M., Hayashi, A., Imanishi, O. et al. (1994) The significance of gonadotropin-releasing hormone test for predicting fertility after varicocelectomy. Fertil. Steril., 61, 779–782.[ISI][Medline]

Illingworth, P.J., Groome, N.P., Byrd, W. et al. (1996) Inhibin-B: a likely candidate for the physiologically important form of inhibin in men. J. Clin. Endocrinol. Metab., 81, 1321–1325.[Abstract]

Jensen, T.K., Andersson, A.M., Hjollund, N.H. et al. (1998) Inhibin B as a marker of spermatogenesis: correlation to differences in sperm concentration and follicle-stimulating hormone levels. A study of 349 Danish men. J. Clin. Endocrinol. Metab., 82, 4059–4063.[Abstract/Free Full Text]

Johnsen, S.G. (1970) Testicular biopsy score count-a method for registration of spermatogenesis in human testes: normal values and results in 335 hypogonadal males. Hormones, 1, 2–25.[Medline]

Klaiji, I.A., van Pelt, A.M., Timmerman, M.A. et al. (1994) Expression of inhibin subunit mRNAs and inhibin levels in the testes of rats with stage-synchronized spermatogenesis. J. Endocrinol., 141, 131–141.[Abstract]

Klingmuller, D. and Haidl, G. (1997) Inhibin B in men with normal and disturbed spermatogenesis. Hum. Reprod., 12, 2376–2378.[Abstract]

Leifke, E., Simoni, M., Kamischke, A. et al. (1997) Does the gonadotropic axis play a role in the pathogenesis of Sertoli-cell-only syndrome ? Int. J. Androl., 20, 29–36.[ISI][Medline]

Maddocks, S., Kerr, J.B., Allenby, G. et al. (1992) Evaluation of the role of germ cells in regulating the route of secretion of immunoreactive inhibin from the rat testis. J. Endocrinol., 132, 439–448.[Abstract]

Morris, P.L., Vale, W.W., Cappel, S. et al. (1988) Inhibin production by primary Sertoli cell-enriched cultures: regulation by follicle-stimulating hormone, androgens, and epidermal growth factor. Endocrinology, 122, 717–725.[Abstract]

Pierik, F.H., Vreeburg, J.T.M., Stijnen, T. et al. (1998) Serum inhibin B as a marker of spermatogenesis. J. Clin. Endocrinol. Metab., 83, 3110–3114.[Abstract/Free Full Text]

Pineau, C., Sharpe, R.M., Saunders, P.T.K. et al. (1990) Regulation of Sertoli cell inhibin production and of inhibin {alpha}-subunit mRNA levels by specific germ cell types. Mol. Cell. Endocrinol., 72, 13–22.[ISI][Medline]

Plymate, S.R., Paulsen, C.A. and McLachlan, R.I. (1992) Relationship of serum inhibin levels to serum follicle stimulating hormone and sperm production in normal men and men with varicocele. J. Clin. Endocrinol. Metab., 74, 859–863.[Abstract]

Robertson, D., Burger, H.G., Sullivan, J. et al. (1996) Biological and immunological characterization of inhibin forms in human plasma. J. Clin. Endocrinol Metab., 81, 3341–3345.[Abstract]

Simpson, B.J.B., Hedger, M.P. and De Kretser, D.M. (1992) Characterization of adult Sertoli cell cultures from cryptorchid rats: inhibin secretion in response to follicle-stimulating hormone stimulation. Mol. Cell. Endocrinol., 87, 167–177.[ISI][Medline]

Spiteri-Grech, J. and Nieschlag, E. (1993) Paracrine factors relevant to the regulation of spermatogenesis – a review. J. Reprod. Fertil., 98, 1–14.[Medline]

Su, L.M., Goldstein, M. and Schlegel, P.N. (1995) The effect of varicocelectomy on serum testosterone levels in infertile men with varicoceles. J. Urol., 154, 1752–1755.[ISI][Medline]

Suzuki, Y. (1967) A study on varicocele. Jpn. J. Urol., 58, 1105–1110.

Ultee-van Gessel, A.M., Leemborg, F.G., de Jong, F.H. et al. (1986) In vitro secretion of inhibin-like activity by Sertoli cells from normal and prenatally irradiated immature rats. J. Endocrinol., 109, 411–418.[Abstract]

Von Eckardstein, S., Simoni, M., Bergmann, M. et al. (1999) Serum inhibin B in combination with serum follicle stimulating hormone (FSH) is a more sensitive marker than serum FSH alone for impaired spermatogenesis in men, but cannot predict the presence of sperm in testicular tissue samples. J. Clin. Endocrinol. Metab., 84, 2496–2501.[Abstract/Free Full Text]

WHO (1992) WHO Laboratory Manual for the Examination of Human Semen and Sperm–Cervical Mucus Interaction. 3rd edition. Cambridge University Press, Cambridge.

WHO (1993) WHO Manual for the Standardized Investigation and Diagnosis of the Infertile Couple. 1st edition. Cambridge University Press, Cambridge.

Submitted on February 1, 2001; accepted on April 19, 2001.





This Article
Abstract
FREE Full Text (PDF )
Alert me when this article is cited
Alert me if a correction is posted
Services
Email this article to a friend
Similar articles in this journal
Similar articles in ISI Web of Science
Similar articles in PubMed
Alert me to new issues of the journal
Add to My Personal Archive
Download to citation manager
Search for citing articles in:
ISI Web of Science (5)
Request Permissions
Google Scholar
Articles by Fujisawa, M.
Articles by Kamidono, S.
PubMed
PubMed Citation
Articles by Fujisawa, M.
Articles by Kamidono, S.