Switchable reflection/transmission utilizing polarization on a plasmonic structure consisting of self-assembly polystyrene spheres with silver patches.

We report a plasmonic structure for switchable reflection and transmission by polarization. The structure is composed of a hexagonal-packed polystyrene sphere array with silver patches on them. Simulations and experiments demonstrated that the conversions between reflected beams and transmitted ones can be performed when the polarization directions of incident beams vary from 0° to 90°. A switchable reflection and transmission at a given wavelength can be obtained, as long as sizes of PS spheres and azimuthal angles are properly chosen. Such a patchy plasmonic structure serving as a switch between reflection and transmission have potential applications in photoelectric control devices.

Integrity of the blood-testis barrier in healthy men after suppression of spermatogenesis with testosterone and levonorgestrel.

STUDY QUESTION: Do exogenous male hormonal contraceptives that suppress intratesticular testosterone and spermatogenesis interfere with the blood-testis barrier integrity in men? SUMMARY ANSWER: When spermatogenesis was suppressed by testosterone alone or combined with levonorgestrel (LNG) treatment in men, the structural appearance of Sertoli cell tight junctions remained intact in the human testis. WHAT IS ALREADY KNOWN: Testosterone promotes the integrity of the blood-testis barrier. Intratesticular androgen deprivation induced by exogenous testosterone plus a progestin to suppress spermatogenesis in a contraceptive regimen may disturb the structural and functional integrity of the blood-testis barrier. STUDY DESIGN, SIZE AND DURATION: Testicular biopsies were obtained from a sub-study of a randomized clinical trial of 36 healthy Chinese men who were treated for 18 weeks and followed for at least a 12-week recovery period. PARTICIPANTS/MATERIAL, SETTING, METHODS: Healthy Chinese male volunteers (27-48 years) were randomized to two treatment groups (n = 18/group) for 18 weeks: (1) testosterone undecanoate (TU) 1000 mg i.m. injection followed by a 500 mg injection every 6 weeks and (2) TU + LNG 250 µg orally daily. Blood samples were obtained from all participants before and during treatment and at the end of the recovery phase. Open testicular biopsies for this study were obtained from four men before treatment and from four men in each of the TU and TU + LNG groups at 2 and 9 weeks of treatment. The presence of antisperm antibodies was checked in the archived serum samples of the subjects at baseline, during treatment and at the end of the recovery period. Stored testicular biopsy samples from cynomolgus monkeys treated with either sub-cutaneous testosterone or placebo for 12 weeks were used for additional protein expression studies. MAIN RESULTS AND ROLE OF THE CHANCE: Expression of blood-testis barrier associated proteins quantified by immunohistochemistry (claudin 3, claudin 11, junctional adhesion molecule-A, zonula occludens-1) remained unchanged despite a significant decrease in the numbers of pachytene spermatocytes and round spermatids in the seminiferous tubules at 9 weeks in the TU + LNG group. This was confirmed by immunoblots showing a lack of quantitative change in these tight junction proteins in monkeys after testosterone treatment. There were no increases in serum antisperm antibodies in the volunteers during the study. LIMITATIONS/REASONS FOR CAUTION: The duration of the study was short and the long-term effects of male hormonal contraceptive treatments on the integrity of the blood-testis barrier remain to be determined. WIDER IMPLICATIONS OF THE FINDINGS: This study supports the safety of male hormonal contraceptive treatment and does not corroborate the previous findings of disturbed immunological integrity of the blood-testis barrier from animal studies such as androgen receptor knockout mice and exogenous hormonal treatment in rats. STUDY FUNDING/COMPETING INTEREST: The study was supported by grants from the Contraceptive Research and Development Program and the Mellon Foundation (MFG-02-64, MFG-03-67), Endocrine, Metabolism and Nutrition Training Grant (T32 DK007571), the Clinical and Translational Science Institute at Los Angeles Biomedical and Harbor-UCLA Medical Center (UL1RR033176 and UL1TR000124) and the Los Angeles Biomedical Research Institute Summer High School Student Program.

Anatomy of the transversus nuchae muscle and its relationship with the superficial musculoaponeurotic system.

BACKGROUND: Previous studies have proved the existence of muscle fibers in the superficial musculoaponeurotic system (SMAS) of the parotid and masseter region; however, no studies have investigated the origination of the muscle fibers in the SMAS. Theoretically speaking, the muscle fibers within the SMAS in the parotid and masseter region might originate from a certain muscle with a definite origin and insertion. Based on this hypothesis, the authors' study investigated the origination of the muscle fibers in the SMAS of the parotid and masseter region to provide anatomical evidence that can improve our understanding of the SMAS. METHODS: An anatomical study was performed on 20 halves of seven fixed and three fresh adult cadavers (seven male and three female cadavers). A traditional bilateral face-lift incision was designed in each cadaver, and the muscle fibers within the SMAS in the parotid and masseter region, along with the origin and insertion, were investigated, dissected, analyzed, and photographed. RESULTS: The transversus nuchae muscle can be divided into two sections according to the origin of its tendons. The muscular fasciculi of the two sections run transversely across the sternocleidomastoid muscle, insert into the superficial fascia above the parotidomasseteric fascia, and terminate in the zygomatic region. The muscle fibers within the SMAS in the parotid and masseter region come from the transversus nuchae muscle. CONCLUSIONS: The authors' study first investigated the transversus nuchae muscle combined with the SMAS and clarified the issue that has been neglected by previous studies for more than 30 years. The authors hope this will unify their understanding of the SMAS and offer plastic surgeons and readers a brief insight into the SMAS.

[A study on population-based prenatal screening and diagnosis of Down's syndrome in Jiangsu province].

OBJECTIVE: To screen and diagnose Down's syndrome during mid-term pregnancy to reduce the number of babies with Down's syndrome. METHODS: With the multi-level of stratified cluster sampling, twenty thousand and eight hundred and three women at 15-20 weeks gestation were screened by maternal serum AFP and beta-hCG using the time resolved fluoroimmunoassay (TRFIA). Then the screened high-risk women were diagnosed by amniocentesis, cell culture and chromosome analyses. The born children were diagnosed by follow-up and peripheral blood chromosome analyses. RESULTS: Six fetuses were diagnosed by serum screening and amniotic fluid chromosome analyses, and 3 born children were diagnosed by follow-up and peripheral blood chromosome analyses. Nine cases of Down's syndrome were detected in total, with the positive prenatal screen rate being 67% (6/9). CONCLUSION: The prenatal screening and diagnosis can reduce the birth of Down's syndrome patients and improve the population quality. However, the diagnosis accuracy still needs to be improved to further reduce the false negative rate and prevent misdiagnosis.

(3S,4R)-3-Ethyl-4-hydr-oxy-3-(3-methoxy-phen-yl)-1-methyl-azepanium (2R,3R)-2,3-bis-(benzo-yloxy)-3-carboxy-propionate.

The crystal structure of the title compound, C(16)H(26)NO(2) (+)·C(18)H(13)O(8) (-), is stabilized by an extensive network of classical N-H⋯O and O-H⋯O hydrogen bonding. The crystal structure also shows an ammonium-driven diastereo-isomerism.

Highly selective and potent mu opioid ligands by unexpected substituent on morphine skeleton.

Unexpected substituent on the well-known morphine skeleton is described to be account for highly selective and potent mu opioid ligands, which is strongly connected to substituted aromatic groups on this omitted 8alpha-position.

[Long-term toxicity of Shen Yan Ling tablet and its effect on male reproductive function in rats].

OBJECTIVE: Shen Yan Ling Tablet is an innovative compound of traditional Chinese medicine, scientifically prepared with Tripterygium wilfordii, Radix Astragali, and others, with precise efficacy on renal diseases and reduced adverse effects of Tripterygium wilfordii. Based on the Guiding Principles for New Drug Toxicity Research Before Clinical Application, we investigated the long-term toxicity of Shen Yan Ling Tablet and its effect on the reproductive function in rats. METHODS: According to the clinical therapeutic dose and the results of the acute toxicity test of Shen Yan Ling Tablet, we equally divided 80 rats (males and females half-and-half) into a low-dose (1.25 g/kg body wt), a medium-dose (2.50 g/kg body wt), a high-dose (5.00 g/kg body wt) and a control group. After a 3-month medication, we conducted standardized long-term toxicity tests and observed the effects of Shen Yan Ling on the serum sexual hormones and epididymal sperm count. RESULTS: After 3 months of treatment with Shen Yan Ling, no death occurred, the general status remained unchanged, and the parameters of blood cytology and biochemistry fluctuated within the normal range, without any significant changes (P > 0.05). Some blood parameters, RBC, WBC, HGB, AST and TBIL, showed statistic changes (P < 0.05), but with no clinical significance. There were no significant differences in the mass coefficients of the main organs between the medication and control groups. The high-dose group exhibited slight hepatic and pulmonary pathological changes and significantly reduced sperm counts in the epididymis, but no significant changes in serum sexual hormones (P < 0.05). CONCLUSION: Three-month medication of Shen Yan Ling at 1.25 - 5.00 g/kg produced no significant accumulated toxicity on rats, but it had a negative effect on their reproductive function at a higher dose of > or = 5.00 g/kg.

[Changes of semen parameters in Chinese fertile men in the past 25 years].

OBJECTIVE: To analyze the changes of seminal parameters in Chinese fertile men during the past 25 years. METHODS: We collected semen samples from 5,834 fertile men in 14 different provinces (including Beijing) between 1980 and 2005 and retrospectively studied their seminal parameters, abstinence durations and total testis volumes by meta-analysis. RESULTS: Compared with the first 15 years, a significant decrease was observed in both sperm density and total number of sperm per ejaculate in the semen samples collected between 1996-2000 (P < 0.0001 and P < 0.05), but not obvious in those between 1996-2000 and after 2005 (P > 0.05). As for sperm motility, no time-related changes were noted (P > 0.05) except a reduction with the increase of age. CONCLUSION: There was a decline in sperm density and total number of sperm per ejaculate in Chinese fertile men over the past 25 years, although not significant in the latter 10 years since 1996, but with no time-related changes in sperm motility.

Determinants of the rate and extent of spermatogenic suppression during hormonal male contraception: an integrated analysis.

CONTEXT: Male hormonal contraceptive methods require effective suppression of sperm output. OBJECTIVE: The objective of the study was to define the covariables that influence the rate and extent of suppression of spermatogenesis to a level shown in previous World Health Organization-sponsored studies to be sufficient for contraceptive purposes (< or =1 million/ml). DESIGN: This was an integrated analysis of all published male hormonal contraceptive studies of at least 3 months' treatment duration. SETTING: Deidentified individual subject data were provided by investigators of 30 studies published between 1990 and 2006. PARTICIPANTS: A total of 1756 healthy men (by physical, blood, and semen exam) aged 18-51 yr of predominantly Caucasian (two thirds) or Asian (one third) descent were studied. This represents about 85% of all the published data. INTERVENTION(S): Men were treated with different preparations of testosterone, with or without various progestins. MAIN OUTCOME MEASURE: Semen analysis was the main measure. RESULTS: Progestin coadministration increased both the rate and extent of suppression. Caucasian men suppressed sperm output faster initially but ultimately to a less complete extent than did non-Caucasians. Younger age and lower initial blood testosterone or sperm concentration were also associated with faster suppression, but the independent effect sizes for age and baseline testicular function were relatively small. CONCLUSION: Male hormonal contraceptives can be practically applied to a wide range of men but require coadministration of an androgen with a second agent (i.e. progestin) for earlier and more complete suppression of sperm output. Whereas considerable progress has been made toward defining clinically effective combinations, further optimization of androgen-progestin treatment regimens is still required.

(3S,4S)-3-Ethyl-4-hydr-oxy-3-(3-methoxy-phen-yl)-1-methyl-azepan-1-ium d-tartrate dihydrate.

In the title compound, C(16)H(26)NO(2) (+)·C(4)H(5)O(6) (-)·2H(2)O, a meptaz-inol derivative, three C atoms of the azepane ring are disordered over two positions, with site-occupancy factors of 0.80 and 0.20; the major disorder component adopts a twist-chair conformation, while the minor component has a chair conformation. The benzene ring is axially substituted on the heterocyclic ring, resulting in a folded conformation of the cation. The absolute configuration was determined with reference to d-tartaric acid. The crystal structure is stabilized by an extensive network of intra- and inter-molecular O-H⋯O hydrogen bonds.

transient scrotal hyperthermia and levonorgestrel enhance testosterone-induced spermatogenesis suppression in men through increased germ cell apoptosis.

CONTEXT: In rodents and monkeys, a combination of hormonal and physical agents accelerates germ cell death. OBJECTIVE: A "proof of concept" study was performed to investigate whether addition of heat exposure or a progestin to an androgen induces germ cell death and more complete and rapid spermatogenesis suppression. DESIGN AND SETTINGS: A randomized clinical trial was performed at academic medical centers. PARTICIPANTS: We treated four groups of healthy male volunteers (18 per group) for 18 wk: 1) testosterone undecanoate (TU) 1000 mg im (first dose), followed by 500 mg im every 6 wk; 2) submersion of scrota at 43 C in water for 30 min/d for 6 consecutive days; 3) TU plus heat; and 4) TU plus oral levonorgestrel (LNG) 250 microg/d. MAIN OUTCOME MEASURES: Semen parameters, testicular histology, and germ cell apoptosis were the main outcome measures. RESULTS: Heat alone and TU plus heat suppressed sperm counts more than TU alone by wk 6. By wk 9, recovery began in the heat only group, whereas spermatogenesis remained suppressed in the TU plus heat group. Oral LNG plus TU suppressed spermatogenesis earlier and more severely than TU alone. At wk 2, significantly greater germ cell apoptosis occurred in heat and heat plus TU subjects, but not in subjects without heat treatment, compared with pretreatment subjects. By 9 wk, markedly smaller seminiferous tubule diameters and fewer spermatocytes and spermatids were noted in all 12 biopsies from men receiving TU, TU plus LNG, with most dramatic differences for the TU plus heat group, whereas no differences from pretreatment biopsies were observed in men who received heat treatment only. CONCLUSIONS: Heat causes a rapid and transient suppression of spermatogenesis. TU plus heat resulted in low-sperm output that was maintained by continuous treatment with TU. Addition of an oral progestin accelerated spermatogenesis suppression by TU alone. Increased germ cell apoptosis contributed to suppression of spermatogenesis.

Conformational re-analysis of (+)-meptazinol: an opioid with mixed analgesic pharmacophores.

AIM: To further investigate the analgesic pharmacophore of (+)-meptazinol. METHODS: Two different opioid pharmacophores, Pharm-I and Pharm-II, were established from structures of nine typical opiates and meperidine by using molecular modeling approaches according to their different structure activity relationship properties. They were further validated by a set of conformationally constrained arylpiperidines. Two conformers of (+)-meptazinol (Conformer-I and Conformer-II) detected in solution were then fitted into the pharmacophores, respectively, by Fit Atoms facilities available in SYBYL, a computational modeling tool kit for molecular design and analysis. RESULTS: Conformer-I fit Pharm-I from typical opiates well. However, Conformer-II fit none of these pharmacophores. Instead, it was found to be similar to another potent analgesic, benzofuro[2,3-c]pyridin-6-ol, whose pharmacophore was suggested to hold the transitional state between the two established pharmacophores. Unlike typical analgesics derived from 4-aryl piperidine (eg, meperidine) with one conformer absolutely overwhelming, the (+)-meptazinol exists in two conformers with similar amounts in solution. Furthermore, both conformers can not transform to each other freely in ordinary conditions based on our NMR results. CONCLUSION: (+)-meptazinol was suggested to be an opioid with mixed analgesic pharmacophores, which may account for the complicated pharmacological properties of meptazinol.

The frontal-temporal nerve triangle: a new concept of locating the motor and sensory nerves in upper third of the face rhytidectomy.

BACKGROUND: How to avoid damage to the temporal branch of the facial nerve has long been a central topic of discussion. Recently, damage to the supraorbital nerve, the auriculotemporal nerve, and other branches of the trigeminal nerve divisions has attracted much attention. Focusing on frontal and temporal rhytidectomy, the authors have investigated the course and distribution of the facial nerve branches, the supraorbital nerve, the auriculotemporal nerve, and other branches of trigeminal division. In this article, they present the concept of the frontal-temporal nerve triangle; its contents, vicinity, and clinical significances are discussed. METHODS: An anatomical study was performed using 30 temporal-parietal regions of 10 fixed adult cadavers and five fresh cadavers. A step-by-step dissection from the superficial layer to the deep layer was involved; all the measurement data were analyzed, and the mean and standard deviation were calculated and expressed in centimeters. RESULTS: The frontal-temporal nerve triangle is an approximately triangular area formed by the temporal branch of the facial nerve, the supraorbital nerve, and the auriculotemporal nerve. Together with its contents and vicinal structures, it forms a complicated three-dimensional rather than two-dimensional structure. Anatomical structures closely associated with rhytidectomy are located in or near this area. CONCLUSIONS: Acting as the anatomical body surface landmark for preoperatively locating the temporal branch, the supraorbital nerve, the auriculotemporal nerve, and its related structures, the concept of the frontal-temporal nerve triangle has practical significance in designing incisions and selecting planes of dissection in upper third of the face rhytidectomy.

QSAR study of 4-phenylpiperidine derivatives as mu opioid agonists by neural network method.

A nonlinear QSAR study was conducted on a series of 4-phenylpiperidine derivatives (4PPs) acting as mu opioid agonists by three-layer back-propagation neural network (NN) method. At first a variety of molecular descriptors were calculated and then selected with two-stage least squares combining partial least squares (PLS) method. The selected four molecular descriptors, out of 292 ones, were correlated with the known analgesic activities of 38 4PPs by NN method. The established QSAR model was further validated by five additional 4PPs, as an external testing set. Moreover, a pharmacophore model was hypothesized based on the results, which would be helpful for structural optimization of 4PPs.

Investigation of the binding mode of (-)-meptazinol and bis-meptazinol derivatives on acetylcholinesterase using a molecular docking method.

Molecular docking has been performed to investigate the binding mode of (-)-meptazinol (MEP) with acetylcholinesterase (AChE) and to screen bis-meptazinol (bis-MEP) derivatives for preferable synthetic candidates virtually. A reliable and practical docking method for investigation of AChE ligands was established by the comparison of two widely used docking programs, FlexX and GOLD. In our hands, we had more luck using GOLD than FlexX in reproducing the experimental poses of known ligands (RMSD<1.5 A). GOLD fitness values of known ligands were also in good agreement with their activities. In the present GOLD docking protocol, (-)-MEP seemed to bind with the enzyme catalytic site in an open-gate conformation through strong hydrophobic interactions and a hydrogen bond. Virtual screening of a potential candidate compound library suggested that the most promising 15 bis-MEP derivatives on the list were mainly derived from (-)-MEP with conformations of (S,S) and (SR,RS) and with a 2- to 7-carbon linkage. Although there are still no biological results to confirm the predictive power of this method, the current study could provide an alternate tool for structural optimization of (-)-MEP as new AChE inhibitors. [Figure: see text].

[Effect of large-dosage of 5alpha-reductase inhibitors on the spermatogenesis of male rats].

OBJECTIVE: To identify the role of 5alpha-reductase in the spermatogenesis of male rats by studying the effect of two 5alpha-reductase inhibitors, Epristeride and Finasteride, on the spermatogenesis in male Sprague-Dawley (SD) rats. METHODS: Changes in the weight of the testis, serum testosterone and dihydrotestosterone levels, epididymal sperm count, and reproductive function were observed and analyzed after the two 5alpha-reductase inhibitors were administered to male SD rats orally. RESULTS: The experiment showed that in comparison with control animals, both the two 5alpha-reductase inhibitors: 1. suppressed the development of the prostate and reduced the weight of the testis in the experimental groups (P < 0.05); 2. decreased the serum level of dihydrotestosterone and enhanced testosterone; 3. inhibited epididymal sperm count and productive function. CONCLUSION: High dosages of the 5alpha-reductase inhibitor, Epristeride, can suppress the development of the prostate and reduce the weight of the testis, decrease dihydrotestosterone, and inhibit spermatogenesis and productive function in male rats.

[Experiment on the sexual virility of immature mice immunized with LHRH fusion protein vaccine].

OBJECTIVE: To observe the sexual virility of immature immature male mice were divided into a pre-ablactation group (n 10). The first two groups were immunized with the LHRH fusion proportion of pregnant female mice, the morphological and histological examined to conform the emasculating effect of the vaccine. When ted with testosterone (1.0 ml each) , the post-ablactation ones were rameters. RESULTS: The sexual virility of the immature mice immunized in 3 -4 months. CONCLUSION: The LHRH fusion protein vaccine mice after ablactation, and the sexual virility can recover in the pre-ablactation decrease.

Using the frontal branch of the superficial temporal artery as a landmark for locating the course of the temporal branch of the facial nerve during rhytidectomy: an anatomical study.

BACKGROUND: Previous studies have proposed that the frontal branch of the superficial temporal artery could be used to determine the course of the temporal branch of the facial nerve; however, these studies have not documented this relationship. The objective of this study was to thoroughly examine the courses of the frontal branch and temporal branch in the temporal region and to describe their relationship in detail. The operating technique used to avoid damaging the temporal branch in the rhytidectomy also is discussed. METHODS: An anatomical study was performed on 30 temporoparietal regions from 10 fixed adult cadavers and five fresh cadavers. Twenty halves of head-vascular-cast specimens also were observed. RESULTS: Depending on whether the bifurcation point of the superficial temporal artery is superior or inferior to the horizontal line of the superior orbital rim, the frontal branch can be classified as having a high-location or low-location type. The temporal branch and its terminal twigs run deeper into the superficial temporal fascia and are inferior to the frontal branch in the high-location type. In the low-location type, one or more terminal twigs of the temporal branch interweave with the frontal branch above the horizontal plane of the upper orbital rim and terminate below the frontal eminence. The temporal branch locates within a triangular area formed by the lower aspect of the zygomatic arch, the frontal branch, and the vertical line where it crosses the highest point of the frontal eminence CONCLUSION: The frontal branch can be the anatomical landmark used to locate and protect the temporal branch during rhytidectomy.

[Effect of selective 5alpha-reductase inhibitor or/and testosterone undecanoate on the reproductive function of male rats].

OBJECTIVE: To investigate whether 5alpha-reductase inhibitor and dihydrotestosterone (DHT) play a role in spermatogenesis in male rats. METHODS: Thirty-two male rats were divided into 4 groups (Groups C, T, F and FT). Group C received plant oil injection and oral starch perfusion, Group T testosterone undecanoate (TU, 20 mg/kg) injection and oral starch perfusion, Group F plant oil injection and oral Finasteride perfusion, and Group FT TU (20 mg/kg) injection and oral Finasteride perfusion. Data on serum T and DHT, sperm count, sperm mobility and reproductive function were collected and analysed. RESULTS: (1) 5alpha-reductase inhibitor, Finasteride and TU reduced the weight of the testis and epididymis in the experiment groups compared with the negative control (Group C), but TU increased the weight of the prostate while Finasteride decreased it compared with the positive control (Group T). TU combined with Finasteride could counteract the effect of the weight increase of the prostate, but not that of the testis. (2) Finasteride, or Finasteride combined with TU, reduced the DHT but increased the testosterone level in comparison with the control group. (3) Both Finasteride and TU could inhibit epididymal sperm count and reproductive function compared with the control, but the effect was less significant in Group FT than in Group F. CONCLUSION: High dosages of 5alpha-reductase inhibitor, Finasteride, can suppress male reproductive function, but the inhibiting effect could be counteracted by administration of 5alpha-reductase inhibitor along with TU.

Quantitative (stereological) study of incomplete spermatogenic suppression induced by testosterone undecanoate injection in rats.

AIM: To evaluate the key lesions in spermatogenesis suppressed partially by testosterone undecanoate (TU) treatment. METHODS: Adult male SD rats were treated with vehicle or TU (19 mg/kg) injection (i.m.) every 15 days for 130 days. The numbers of all types of cells (nuclei) in the seminiferous tubules and the interstitial tissue were estimated using a contemporary stereological tool, the optical disector. RESULTS: In response to TU treatment, the numbers of non-type B spermatogonia, type B spermatogonia and late elongated spermatids per testis were reduced to 51 %, 66 % and 14 % of the controls, respectively. The conversion ratios from type B spermatogonia to early spermatocytes and pachytene spermatocytes were not significantly affected and the ratios to the later germ cell types fell to 51 % - 65 % of the controls. Less than 1.0 % of immature round spermatids were seen sloughing into the tubule lumen, 4.0 % of elongated spermatids retained in the seminiferous epithelium, and about half of the elongated spermatid nuclei appreciably malformed. Leydig cells were atrophied but their number and the peritubular myoid cell number per testis were unchanged. CONCLUSION: Double inhibition of spermatogenesis (i.e. inhibition at spermiation and spermatogonial conversion to type B spermatogonia), a scenario seen in the monkey and human following gonadotrophin withdrawal, was not sufficiently effective for a complete spermatogenic suppression in the rat after TU treatment, probably due to ineffective inhibition of the Leydig cell population and therefore the intra-testicular testosterone levels.