Trends of SHBG and ABP levels in male farmers: Influences of environmental fluoride exposure and ESR alpha gene polymorphisms.

A number of epidemiological studies have reported that chronic exposure to high concentrations of fluoride not only causes dental and skeletal fluorosis but additionally affects serum levels of reproductive hormones. However, possible interaction between fluoride exposure and estrogen receptor alpha (ESRα) gene polymorphisms on sex hormone-binding globulin (SHBG) and androgen binding protein (ABP) of male farmers has not been detailed. Here, we conducted a cross-sectional study including 348 male farmers with different fluoride exposure levels from drinking water in Henan province of China to explore effects of fluoride exposure and ESRα genetic variation on serum SHBG and ABP levels. We found serum SHBG levels in male farmers from the high exposure group to be lower than those of the low exposure group. We also found that concentrations of SHBG affected ABP levels. Furthermore, fluoride exposure and single nucleotide polymorphisms at the XbaI and rs3798577 loci of the ESRα gene affected serum ABP levels. Our findings suggest that chronic fluoride exposure from drinking water is associated with alterations of serum SHBG and ABP concentrations in local male farmers and that the effect of fluoride exposure on ABP levels vary depending on ESRα gene polymorphisms.

[Influence of water fluoride exposure on sex hormone binding globulin and testosterone in adult male].

OBJECTIVE: To explore the influence of water fluoride exposure on sex hormone binding globulin (SHBG) and testosterone in adult male. METHODS: Cross-sectional study was conducted in three villages of Tongxu county including high fluoride group (HFG), defluoridation project group (DFPG) and control group (CG) based on the fluoride concentration in drinking water. Adult male who were born and raised in the village and aged 18 - 50 years old were recruited using cluster sampling. Fasting blood and morning urine samples were collected. The fluoride levels in drinking water and urine were detected by fluoride-ion selective electrode method. Serum SHBG level was determined using enzyme-linked immunosorbent assay (ELISA). The chemical luminescence immune analysis method was used to detect serum testosterone content. RESULTS: Serum SHBG level was 47.85 nmol/L in CG, 31.37 nmol/L in DFPG and 24.52 nmol/L in HFG respectively. There were significant difference among of three groups (P < 0.05). Serum testosterone level was 3.69 ng/ml in CG, 4.61 ng/ml in DFPG and 4.83 ng/ml in HFG respectively. Serum testosterone level in HFG was significantly higher than that in CG (P < 0.05). Serum SHBG level in HFG has positive correlation with serum testosterone (r = 0.230, P = 0.049), which has not been observed in DFPG and CG. CONCLUSIONS: Long-time fluorine exposure may affect serum SHBG and testosterone level in adult male.

Comparison of free testosterone results by analog radioimmunoassay and calculated free testosterone in an ambulatory clinical population.

INTRODUCTION: The most widely used method for measuring free testosterone (FT) is by analog immunoassay (aFT); however, this assay has been criticized as unreliable based on laboratory studies in small groups of men. Calculated FT (cFT), derived from total testosterone (TT) and sex-hormone binding globulin (SHBG) values has been recommended in its place. There are limited data comparing aFT and cFT in clinical populations. AIM: The purpose of this study was to compare aFT with cFT in a population of ambulatory men in a clinical setting. METHODS: Medical records were reviewed for 100 randomly selected men in a urology practice, yielding 140 test results complete for TT, aFT, and SHBG. Calculated FT was determined via an online calculator. Comparisons were made with Pearson rank coefficients. MAIN OUTCOME MEASURES: Pearson rank correlation between aFT and cFT. RESULTS: Mean patient age was 52.3 +/- 14.3 years (range 24-80). Mean TT was 443.0 +/- 208.3 ng/dL (range 110-1276). Mean aFT was 1.22 +/- 0.54 ng/dL (range 0.24-3.8) and mean cFT 9.4 +/- 4.5 ng/dL (range 1.8-27.8). Mean SHBG was 34.2 +/- 19.5 nmol/L (range 9-127). A strong correlation was observed for aFT and cFT (r = 0.88, P < 0.0001), particularly at low concentrations. Significant correlations were also noted between aFT and TT (r = 0.73, P < 0.0001), and between cFT and TT (r = 0.82, P < 0.0001). Numerical values for aFT were approximately one-eighth of the values obtained for cFT. Neither aFT nor cFT correlated with SHBG. CONCLUSIONS: A strong correlation was observed between aFT and cFT in this clinical population of ambulatory men. Different sets of reference values must be applied for each of these tests.

Associations of serum sex hormone binding globulin (SHBG) levels with SHBG gene polymorphisms in the CARDIA Male Hormone Study.

In the sex hormone binding globulin (SHBG) gene, a pentanucleotide-repeat polymorphism [(TAAAA)(n)] and a single nucleotide polymorphism (D327N) have been associated with circulating SHBG concentrations in women. Only one study, limited to Scandinavians, has examined these associations in men. Using data from the Coronary Artery Risk Development in Young Adults (CARDIA) Male Hormone Study, the authors assessed associations of SHBG polymorphisms with serum SHBG levels in 511 Black men and 698 White men who had SHBG measured in multiple serum samples collected over an 8-year period from 1987 to 1996 and were aged 20-34 years at the time of the first SHBG measurement. Multivariable repeated-measures analyses were used to assess associations of (TAAAA)(n) and D327N polymorphisms with SHBG concentrations. Results showed statistically significant differences in mean SHBG concentrations for White men with genotypes of (TAAAA) 6/6 (35.1 nmol/liter), 6/x (30.8 nmol/liter), and x/x (29.6 nmol/liter), where x represents a repeat length greater than 6 (p = 0.001). For Black men, the pattern of association was similar, albeit not statistically significant (p = 0.35). There was no relation between D327N genotype and SHBG levels. These results suggest that the (TAAAA)(n) repeat length in the SHBG gene, but not the D327N variant, might contribute to the interindividual variability in serum SHBG levels.

The effects of methyl tert-butyl ether (MTBE) on the male rat reproductive system.

Methyl tert-butyl ether (MTBE) is an oxygenated compound, which has been widely used in Asia, Europe and North America. Although numerous in vitro and in vivo studies have demonstrated the carcinogenicity and the toxicity of MTBE, there is still a lack of data on reproductive system exposure of MTBE in male rodent animals. We studied subacute exposure of MTBE on the reproductive systems of male Sprague-Dawley rats. MTBE was administered to rats at dose levels of 0, 400, 800 and 1600 mg/kg/day. After 2 or 4 weeks of treatments, the rats were euthanized, and their serum, epididymis and testes were collected. Significant adverse effects in their reproductive system were observed including: a significant increase in the percentage of abnormal sperm; an irregular and disordered arrangement of the seminiferous epithelium indicated by a histopathological examination; changed serum levels of testosterone (T), luteinizing hormone (LH) and follicle stimulating hormone (FSH); and decreased levels of mRNA and of androgen binding protein (ABP). In the oxidative stress study, results indicated an increased maleic dialdehyde (MDA) content, implying a raised peroxide level, and that the total antioxidant ability in serum was significantly increased. This finding was especially strong at 1600 mg/kg/day MTBE. In the 2-week treatment, at 1600 mg/kg/day, the mRNA level of 8-oxoguanine DNA glycosidase (OGG1) was significantly decreased, and the mRNA level of the extra-cellular form of superoxide dismutase (SOD(EX)) was significantly increased. Our experiments suggest that relatively high doses of MTBE can exert reproductive system toxicity of male rats and disturb the secretions of T, LH and FSH, possibly due to oxidative stress induced by MTBE.

Effects of vitamins C and E on steroidogenic enzymes mRNA expression in polychlorinated biphenyl (Aroclor 1254) exposed adult rat Leydig cells.

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent environmental contaminants that disturb normal endocrine functions including gonadal functions in humans and mammals. The present study was conducted to elucidate the protective role of vitamins C and E against Aroclor 1254-induced changes in Leydig cell steroidogenic acute regulatory (StAR) protein and steroidogenic enzymes mRNA expression. Adult male rats were dosed for 30 days with daily intraperitoneal (i.p.) injection of 2 mg/kg Aroclor 1254 or vehicle (corn oil). One group of rats was treated with vitamin C (100 mg/kg bw day) while the other group was treated with vitamin E (50 mg/kg bw day) orally, simultaneously with Aroclor 1254 for 30 days. One day after the last treatment, animals were euthanized and blood was collected for the assay of serum hormones such as luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone and estradiol. The serum androgen binding protein was also estimated. Testes were quickly removed and Leydig cells were isolated in aseptic condition. Purity of Leydig cells was determined by 3beta-hydroxysteroid dehydrogenase (3beta-HSD) staining methods. Purified Leydig cells were used for quantification of androgen and estrogen receptors. In addition, total RNA was isolated from control and treated Leydig cells to monitor the steady-state mRNA levels by RT-PCR for StAR protein, cytochrome P(450)scc, 3beta-HSD and 17beta-HSD. Aroclor 1254 treatment significantly reduced the serum LH, FSH, testosterone, estradiol and androgen binding protein. In addition to this, Leydig cell androgen and estrogen receptors were markedly decreased. RT-PCR analysis of StAR mRNA level did not alter Aroclor 1254 treatment while steroidogenic enzymes such as cytochrome P(450)scc, 3beta-HSD and 17beta-HSD mRNAs were drastically decreased in Aroclor 1254 treatment. However, the simultaneous administration of vitamins C or E in Aroclor 1254-exposed rats resulted a significant restoration of all the above-mentioned parameters to the control level. These observations suggest that vitamins C and E have ameliorative role against PCBs-induced testicular Leydig cells dysfunction.

Does Fluoride Affect Serum Testosterone and Androgen Binding Protein with Age-Specificity? A Population-Based Cross-Sectional Study in Chinese Male Farmers.

Many studies have demonstrated that exposure to excess fluoride was associated with a variety of diseases. Little is known about the variation of testosterone (T) levels caused by fluoride exposure. The aim of this study is to explore the association of fluoride exposure and age with serum T and androgen-binding protein (ABP) levels in male farmers. A cross-sectional study was conducted in a county of Henan Province, China, including high fluoride exposure from drinking water villages and control villages. Male farmers aged 18-55 years old who lived in these villages were recruited by cluster sampling and divided into a higher fluoride exposure group (HFG) and a lower fluoride exposure group (LFG) according to the level of urinary fluoride. Levels of T and ABP in serum were measured using chemiluminescence immunoassay (CLIA) and enzyme-linked immunosorbent assay (ELISA) respectively. Markedly lower T levels were observed in male farmers from the HFG than in those from the LFG (t = 2.496, P < 0.05). Furthermore, younger farmers, 18-29 and 30-39 years old, may be the most likely to have lower T levels when exposed to fluoride (P < 0.05). No significant differences were observed in serum ABP levels in all male farmers between the two groups with different fluoride exposure. These results supported that excess fluoride exposure decreased serum T levels of male farmers with age-specificity.

The epididymis contributes minimally to serum androgen-binding protein in the rat: a whole body kinetic study.

The half-times, MCRs, and secretion rates of androgen-binding protein (rABP) were determined in male rats under a variety of conditions. After orchiectomy, the disappearance of endogenous immunoassayable rABP from serum was described by a single exponential term with half-lives of 21 +/- 0.2 and 20 +/- 0.8 h at 25 and 90 days, respectively. The MCR (milliliters per g/day) was not affected by age or hormonal status of the animals. The secretion rate of rABP into the blood was higher in the immature animals than in adults. The decrease in serum rABP concentrations after 20-25 days of age was due to a decrease in the rate of secretion into blood rather than an increase in MCR, a finding consistent with the observation that after formation of the blood-testis barrier, most of the rABP is secreted into the seminiferous tubular lumen. The disappearance curve after injection of purified epididymal rABP was best described by two exponential terms. The first component disappeared very rapidly and the second more slowly, with a half-time corresponding to that of endogenous rABP. The MCR calculated from the latter component was the same as that for endogenous rABP. Having established the kinetic parameters for rABP in serum, a series of experiments was conducted to determine whether it was possible for the epididymis to release this protein into the blood. The apparent half-time of rABP measured in rats in which the testes had been removed and the epididymides left intact was found to be 65 +/- 3 to 70 +/- 5 h in three separate experiments. This increase over the actual half-life of rABP (20 h) was due to the release of rABP from the epididymis into the blood. A similar experiment was performed in an identical group of animals (testes removed, epididymides intact) that had been treated with testosterone via Silastic implants. In these animals the apparent half-time (24 +/- 4 to 28 +/- 2 h; three experiments) closely approximated the actual half-life (20 h). These findings indicate that androgens retarded degeneration of the epididymides, thus minimizing their release of rABP into blood. Our experimental findings suggest the following conclusions. The dramatic rise and subsequent decline of serum rABP concentrations that occur before puberty are due to changes in the secretion rate rather than in the MCR, which is unaffected by age or hormonal states.(ABSTRACT TRUNCATED AT 400 WORDS)

The heterogeneity of rat androgen-binding protein in serum differs from that in testis and epididymis.

Fractionation of testicular, epididymal, and serum extracts containing rat androgen-binding protein (rABP) on a Concanavalin A-Sepharose (Con A) column resolved two peaks of immunoreactive protein. The first peak was present in the void volume, and the other was bound by the column and specifically eluted by alpha-methyl-D-glucoside. These two peaks of immunoreactive rABP have been designated form I and form II for the portions of rABP that do not and do bind, respectively, to Concanavalin A. In the course of studying this heterogeneity, we observed that the distribution of the two forms of rABP was the same in the blood and cytosols prepared from testis and epididymis of young rats before the formation of the blood-testis barrier; that is, the ratio of form I to form II ranged from 1:1 to 1:2. Similar heterogeneity was observed in extracts of the reproductive tract from mature animals. However, the blood of adult rats contained reduced amounts of form I relative to form II, so that their ratio was about 1:5. Subsequent studies of infertile rats heterozygous for the Hre gene (Hre/ +), in which total rABP secretion was decreased, and of their normal littermates, indicated that the reduced amount of form I ABP in the sera of mature rats is typical of adult animals regardless of strain or genetic abnormality. The reduced amount of form I relative to form II observed in the blood of adult rats could result from either reduced secretion or increased metabolic clearance of form I in the blood compartment. To distinguish between these possibilities, the blood clearance of the two forms was estimated after orchiectomy. The disappearance rate of form I was not significantly different from that of either form II or unfractionated serum. These results are consistent with reduced release into blood of form I relative to form II rABP rather than increased clearance of form I in adult animals.

Synergistic effects of follicle-stimulating hormone and testosterone on the maintenance of spermiogenesis in hypophysectomized rats: relationship with the androgen-binding protein status.

The present study examined the relationship between the functional status of Sertoli cells and the maintenance and restoration of spermatogenesis in immature hypophysectomized (HPX) rats given various doses of exogenous testosterone with or without daily injections of FSH for 90 days. Subcutaneous implantation of a 2- to 10-cm testosterone capsule (TC) increased serum testosterone levels of HPX rats 2-10 times above the normal control levels, but did not significantly increase the testicular testosterone level. Daily injections of FSH significantly increased the accumulation of testosterone in testes of TC-implanted HPX rats. Maintenance of early spermiogenesis was observed in all TC-implanted animals. Although elongated spermatids were present, step 18-19 spermatids at the luminal edge of stages VII-VIII epithelium were only observed in rats bearing 10-cm TC implants. Daily injection of FSH resulted in the completion of spermiogenesis in all TC-implanted animals, and the number of step 18-19 spermatids was dependent on the length of TC implants used. These results demonstrate the importance of the synergism of FSH and testosterone in the final steps of spermiogenesis. The androgen-binding protein (ABP) content per testis of the HPX rats was stimulated by TC implants. However, a significant increase in epididymal ABP was only noted in rats bearing 10-cm TC implants. Injection of FSH resulted in a significant increase in the testicular ABP content in rats bearing 2- or 5-cm TC, but not in those with 10-cm TC implants. In addition, the epididymal ABP content was significantly stimulated by FSH in all TC-implanted animals. The ABP status in the testis and its transport toward the epididymis are closely related to the extent of maintenance of spermiogenesis. It is speculated that the production of ABP by Sertoli cells and the biochemical properties of ABP molecules may have some role in the control of the final steps of spermiogenesis.

Sertoli cell-only syndrome produced by cold testicular ischemia.

This report describes a new method for producing Sertoli cell-only testes in the Lewis rat using 90 min of hypothermic testicular ischemia. The method employs selective occlusion of the testicular blood supply using atraumatic microclips applied with the aid of an operating microscope. The testis is packed in ice-cold saline throughout the ischemic interval, and the deferential artery and vein are ligated. Twelve weeks after the ischemic insult, the testes weigh half that of control testes while there were no differences in prostate or seminal vesicle weights. Microscopic examination of the ischemic damaged testes revealed normal-appearing Leydig and Sertoli cells, but complete absence of germ cells. Assays of testicular enzyme activities indicated that lactic dehydrogenase and sorbitol dehydrogenase were reduced, while alpha-glutamyl transpeptidase activity was normal, consistent with the marked reduction of germ cells. Serum androgen binding protein (rABP) levels were elevated relative to nonischemic controls. By contrast, serum concentrations of testosterone, LH, and FSH were normal. In addition, LHRH elicited identical LH and testosterone responses in control and experimental animals. Testicular blood flow measured with 133Xenon was slightly decreased in Sertoli-cell-only testes. Intratesticular temperatures was normal in all groups. These observations in rats with ischemia-induced Sertoli-cell-only testes are strikingly different from those induced by radiation or genetic defects. Animals with these latter disorders have elevated FSH levels, evidence of altered Leydig cell function as evidenced by elevated LH or abnormal response to LHRH; and normal or low serum rABP levels. We conclude that 1) ischemia produces no abnormalities of the pituitary testicular axis in spite of marked germ cell depletion and 2) Sertoli-cell-only testes of different etiologies can have varied patterns of hormone and rABP secretion.

Do testicular opiates regulate Leydig cell function?

beta-Endorphin is believed to be synthesized in testicular Leydig cells. To gain more information about the role of this and other endogenous opioid peptides in the testis, opiate antagonists (naloxone and nalmefene, 100 micrograms/testis) were administered intratesticularly to hemicastrated adult rats. Leydig cell function was evaluated by measurement of serum testosterone and testosterone production in vitro. Estimation of androgen binding protein (rABP) was used as an index of Sertoli cell function. Serum testosterone was reduced significantly by intratesticular administration of naloxone and nalmefene in treated animals. Systemic administration of these antagonists had no effect at the doses used. Testes from treated animals incubated in vitro with or without hCG produced significantly less testosterone than vehicle-treated control testes. Hemicastration reduced rABP synthesis and secretion; however, treatment with opiate antagonists did not alter the amount of this protein in the serum or epididymides of these rats. These observations suggest that endogenous testicular opiates modulate testosterone secretion by Leydig cells.

The effects of opioid receptor antagonists suggest that testicular opiates regulate Sertoli and Leydig cell function in the neonatal rat.

beta-Endorphin and other peptides derived from proopiomelanocortin are synthesized in testicular Leydig cells. To better understand the possible function of these and other endogenous opioid peptides in the testis, the opioid antagonists naloxone and nalmefene were administered intratesticularly to hemicastrated 5-day-old rats. Both naloxone and nalmefene potentiated testicular hypertrophy induced by unilateral orchidectomy at 11 days of age. Unexpectedly, at least a 100-fold lower dose of nalmefene was required to produce maximal hypertrophy than that previously reported for naloxone. Leydig and Sertoli cell functions were evaluated, respectively, by measurement of basal testosterone production in vitro and rat androgen-binding protein (rABP) in serum. The optimal dose of naloxone for hypertrophy (1 microgram/testis) suppressed testosterone production and had a nonuniform effect on rABP secretion (either had no effect or produced a slight increase). By contrast, the optimal dose of nalmefene for hypertrophy (0.01 microgram/testis) not only suppressed basal testosterone secretion, but also uniformly increased rABP levels in serum. Larger doses of this opioid antagonist, up to 1 microgram/testis, were not as effective on the three parameters measured (hypertrophy, testosterone secretion, and rABP levels). These results suggest that this agent has both antagonistic and agonistic activities in the testis. At the doses that produced optimal effects on hypertrophy, systemic administration of these antagonists produced no effects. The results of these studies suggest that intratesticular opiates exert a suppressive effect on Sertoli cell growth and rABP secretion. In addition, these peptides may modulate testosterone secretion by Leydig cells.

Evidence from Sertoli cell-depleted rats indicates that spermatid number in adults depends on numbers of Sertoli cells produced during perinatal development.

To probe the relationship between the size of the Sertoli cell population, established during perinatal development, and production of germ cells in the adult testis, a Sertoli cell-depleted rat model was developed. This was accomplished by delivering an antimitotic drug, cytosine arabinoside (araC), directly to the testis of newborn pups. Initial studies of these araC-treated neonates indicated that 1) the drug is cleared rapidly from the testis; 2) it substantially reduces the level of Sertoli cell proliferation; 3) Sertoli cell division ceases at a normal time in spite of the previous drug treatment; and 4) araC itself has no residual effect on germ cell proliferation, which begins several days after the injection. Pups given araC were allowed to reach maturity, and their testes were perfuse-fixed for light microscopic morphometry. When the numbers of Sertoli cells in adult rats given araC as were compared with those in normal littermates, a 54% decrease in the size of the Sertoli cell population was detected in treated rats, now referred to as Sertoli cell-depleted. Moreover, when round spermatids were quantified and compared in normal and Sertoli cell-depleted adults, testes of the latter were found to contain 55% fewer round spermatids. Since, in the araC-treated group, the decrease in Sertoli cell population size was paralleled by a reduction in spermatid production of equal magnitude, the number of round spermatids per Sertoli cell was essentially identical in normal and Sertoli cell-depleted animals. Measurements of serum androgen-binding protein (ABP) and FSH in both groups indicated that the circulating level of ABP in Sertoli cell-depleted rats was approximately half, and the concentration of FSH approximately twice, that in normal animals. Thus, even though FSH is elevated in Sertoli cell-depleted rats, the production of ABP per Sertoli cell is unchanged. In addition, collective volume of Leydig cells and ventral prostate weights were normal in the Sertoli cell-depleted group, suggesting that Leydig cell function in these rats is normal. In summary, a Sertoli cell-depleted rat model has been produced by interfering specifically with Sertoli cell proliferation early in postnatal life, before onset of germ cell division. Moreover, our findings with this model indicate that production of normal numbers of germ cells in adults depends, at least in part, on the size of the Sertoli cell population. Thus, our observations identify the perinatal period, when the Sertoli cell population is established, as critical for development of quantitatively normal spermatogenesis in the adult.

The effects of a gonadotropin-releasing hormone antagonist on androgen-binding protein distribution and other parameters in the adult male rat.

The effects of gonadotropins and gonadal steroids on androgen-binding protein (ABP) production and its distribution among the epididymis, seminiferous tubule fluid (STF), testicular interstitial fluid (TIF), and blood were studied in 300-g adult male Sprague-Dawley rats. The rats either received no treatment or their pituitary function was suppressed by administration of the GnRH antagonist [AcD2Nal,D4ClDPhe2,D3Pal3,Arg5,DGlu6 (AA),D-Ala10]LHRH (antagonist). Other groups of rats were treated with hCG, FSH, FSH plus hCG, testosterone, or estradiol, alone or together with antagonist. Treatment was conducted for 30 days, after which time, ABP was detected by its ability to bind [3H]5 alpha-dihydrotestosterone. Transport of ABP from the testis to the epididymis was inhibited by antagonist administration. Simultaneous treatment with antagonist and hCG, or antagonist and hCG plus FSH prevented antagonist-induced inhibition of ABP transport. Neither FSH, testosterone, nor estradiol alone was effective in this process. Inhibition of ABP transport to the epididymis was accompanied by its accumulation within the testis. Treatment with antagonist and FSH resulted in a 4.5-fold increase in the concentration of ABP in TIF, but had little effect on the amount of ABP in STF, indicating selective secretion of ABP from the basal surface of the Sertoli cells. Treatment with antagonist alone, antagonist together with testosterone or estradiol, or estradiol alone resulted in increased concentrations of ABP in both TIF and STF, but the increase in TIF was proportionately greater. Treatment with hCG or FSH plus hCG alone or with antagonist not only facilitated ABP transport to the epididymis, but also increased TIF levels of ABP above control values. The former treatment resulted in increased concentrations of testosterone in TIF, but not in STF. Both treatments resulted in testosterone levels in both compartments that were higher than those in animals treated with antagonist alone. No treatment had a statistically significant effect on blood levels of ABP. About 50% of ABP synthesis appears to be constitutive, i.e. is not regulated by hormones. Although ABP production continues in the presence of antagonist, its transport to the epididymis is halted, indicating that epididymal transport of ABP is a hormone-dependent process. It is likely that elevated intratesticular levels of testosterone or FSH and testosterone acting in concert regulate epididymal transport of ABP.

Seminiferous epithelial function in the pubertal rat following local testicular irradiation.

The dose- and time-related responses of the irradiated seminiferous epithelium in the pubertal rat have been investigated. The threshold dose for Sertoli cell dysfunction, as assessed by serum androgen binding protein (ABP) concentrations, was estimated to be 5 Gy. A significant reduction (to less than 50% of control levels) in serum ABP was observed at 8 weeks post-irradiation, with further reductions at later times (24 and 36 weeks). Serum follicle-stimulating hormone (FSH) was elevated to between 130 and 175% of control at only 2 weeks post-irradiation, but recovered with time. Normal FSH levels seemed to be related to recovery of spermatogenesis, as assessed by counts of regenerating tubule cross-sections. The results indicate that the clonogenic spermatogonia and Sertoli cells of the pubertal rat testis are less sensitive to radiation than those of the adult.

Hepatic expression of sex hormone-binding globulin associated with the postnatal surge of serum androgen-binding activity in the Djungarian hamster.

Serum androgen-binding capacity in Djungarian hamsters, as in many other mammals, increases within days after birth and remains elevated until puberty. This increased activity has been attributed to a hepatic glycoprotein, sex hormone-binding globulin (SHBG), but expression of SHBG by the postnatal liver has not been demonstrated. Therefore, a full-length SHBG cDNA was cloned from the liver of neonatal hamsters and the expression of SHBG during development was examined. Hepatic SHBG RNA levels, as measured by both competitive RT-PCR and Northern analysis, were very low in fetal animals but increased significantly within 24 h of birth. Maximal values were maintained for 1 week after parturition, and then declined to basal adult levels. The developmental pattern in hepatic SHBG immunoactivity, as determined by Western analysis, mirrored that of hepatic SHBG mRNA. However, changes in serum SHBG immunoactivity and steroid-binding activity occurred approximately 1 week later. There were no sex differences in the levels of hepatic SHBG mRNA or protein during development, but serum immunoactivity tended to be higher in females at puberty. Sex- and age-related differences in the relative abundance of SHBG isoforms were also noted. Results of these studies demonstrate that Djungarian hamsters express an authentic SHBG and indicate that the postnatal surge in serum androgen-binding activity is due to perinatal up-regulation of SHBG expression.

Zinc acetate pretreatment ameliorates cisplatin-induced Sertoli cell dysfunction in Sprague-Dawley rats.

The present study was undertaken to determine if prior administration of zinc acetate (ZnAc) or copper sulfate (CuSO4) could prevent pituitary, Leydig, or Sertoli cell dysfunction subsequent to cisplatin administration in adult Sprague-Dawley rats. Animals were given cisplatin at a dose of 2 mg/kg daily for 5 days, with or without the i.p. administration of ZnAc (6 mg/kg per day) or CuSO4 (5 mg/kg per day), beginning 5 days prior to and continuing through the administration of cisplatin. Control animals were given vehicle, ZnAc1, or CuSO4. Animals were sacrificed 1 week after the initial cisplatin injection. Cisplatin administration resulted in suppressed serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels as well as a 77% reduction in serum testosterone and an 82% reduction in testicular testosterone. The concomitant administration of either ZnAc or CuSO4 did not result in a significant difference relative to animals receiving cisplatin alone, although administration of both cations alone significantly reduced testicular testosterone content. Serum androgen-binding protein (ABP) was not significantly lowered in any treatment group. There was a marked reduction of 57% in testicular ABP content relative to control values subsequent to cisplatin administration. This reduction was partially prevented by ZnAc treatment: the testicular ABP concentration was only 15% lower than that in controls (not significant). Since the cisplatin-induced reduction in serum FSH was not altered by ZnAc pretreatment, we conclude that the near normalization of testicular ABP content may be evidence of improved Sertoli cell function. In contrast, cisplatin-induced decreases in the serum gonadotropins and testicular androgens were not lessened by pretreatment with either cation. Further studies may be warranted to determine whether ZnAc pretreatment has a beneficial effect on spermatogenesis during cisplatin treatment.

The heterogeneity of rat androgen binding protein (rABP) in the vascular compartment differs from that in the testicular tubular lumen. Further evidence for bidirectional secretion of rABP.

Fractionation of testicular extracts and serum on a Concanavalin A-Sepharose column resolved two peaks of immunoreactive rat androgen binding protein. The rat androgen binding protein in the first peak, designated Form I, was present in the void volume; the other, designated Form II rat androgen binding protein, was bound by the column and specifically eluted by alpha-methylmannoside. In the course of studying the heterogeneity of rat androgen binding protein on Concanavalin A-Sepharose, it was observed that the distribution of the two forms of this protein was similar in the fluid obtained by micropuncture from the seminiferous tubule and the rete testis, that is, the ratios of Form I to Form II were 1:1 and 1:1.8, respectively. By contrast, Form I rat androgen binding protein in blood, interstitial fluid, and thoracic duct lymph of adult rats was reduced relative to Form II; the ratios of Form I:Form II in these fluids were 1:4.4, 1:3.1, and 1:4.6, respectively. since previous studies indicated that the reduced amount of Form I relative to Form II observed in the blood of adult rats was not the result of more rapid clearance of Form I, these results suggest that Form I rat androgen binding protein is preferentially secreted into the lumen of the seminiferous tubule rather than into the interstitial fluid and blood. We conclude that Sertoli cells in adult rats may partition rat androgen binding protein between the interstitial and luminal compartments of the testis based on the carbohydrate composition of this protein.

Concentrations of free testosterone, total testosterone, and androgen binding protein in the peripheral serum of male rats during sexual maturation.

To investigate the relationship between free testosterone and sexual maturation in the male rat, animals were decapitated every 5 days from 25 through 75 days of life. Serum was assayed for androgen binding protein and total testosterone by radioimmunoassay. Free testosterone concentrations were calculated from the total testosterone concentration and the free testosterone fraction. The free testosterone fraction was determined by ultrafiltration. The pubertal increase in relative prostate and relative seminal vesicle weights began between 45 and 50 days and 40 and 45 days, respectively. Although the over-all trend in the free testosterone fraction was to increase with increasing age (r = 0.46, P less than 0.0001), there was a significant secondary peak at 50 days. The serum concentration of androgen binding protein was highest on day 25, fell rapidly until day 40, and declined slowly thereafter. Despite these variations in both androgen binding protein and the free testosterone fraction during sexual maturation, the calculated serum concentration of free testosterone was remarkably similar in pattern to that of total testosterone (r = 0.99, P less than 0.0001). These data indicate that the serum concentration of total testosterone is an accurate reflection of the serum concentration of free testosterone during the sexual maturation of the male rat.