Analysis of the oligosaccharides on rat androgen-binding protein using serial lectin chromatography

The microheterogeneity seen when rat androgen-binding protein (rABP) is analyzed by two-dimensional polyacrylamide gel electrophoresis is attributable, at least in part, to the differential glycosylation of a single promoter. Further insight into the chemical nature of the oligosaccharide units on rABP was obtained by serial lectin chromatography. When rABP was chromatographed on immobilized Concanavalin A (Con-A), it was fractionated into three classes: (1) one that did not bind to the lectin (about 44% of the rABP), (2) one that was bound and could be eluted with 10 mM 1-O-methyl alpha-D-glucopyranoside (glucoside), about 34%, and (3) one that could be eluted with 0.5 M methyl alpha-D-mannopyranoside (mannoside), about 23%. Binding to Con-A indicates the presence of asparagine-linked oligosaccharides. Chromatography of the glucoside-eluted peak on lentil lectin (LcH) indicated that the rABP in that fraction contained a fucose residue on the chitobiose core. Chromatography of the mannoside-eluted peak on wheat germ agglutinin (WGA) indicated the presence of rABP with high mannose- (44%) and hybrid-type (56%) glycans attached. Chromatography on Ricinus communis I (RCA-I) lectin indicated a species containing galactosylated complex-type oligosaccharide chains. Treatment of rABP forms with exoglycosidases confirmed the presence of externally disposed fucose, sialic acid, mannose, and galactose residues. LcH chromatography indicated that about 30% of the rABP that did not bind to Con-A possessed triantennary oligosaccharides with fucose on the chitobiose core. About 28% of the rABP was retarded when it was chromatographed on Phaseolus vulgaris E lectin, suggesting the presence of bisected biantennary chains with terminal galactose residues. We were unable to detect rABP species with serine- or threonine-linked oligosaccharide chains in this fraction. Other forms of rABP in the nonretained fraction of Con-A were not resolved. Western blotting did not reveal major differences in relative molecular weight (Mr) among the rABP species; some differences in the ratio of the heavy to the light subunit of the molecule were detectable.

Sertoli cells, proximal convoluted tubules in the kidney, and neurons in the brain contain cyclic protein-2

We analyze by immunocytochemistry the in vivo distribution in rat Sertoli cells of Cyclic Protein-2 (CP-2), which is maximally synthesized and secreted in vitro at stages VI and VII of the cycle of the seminiferous epithelium. This analysis demonstrates that CP-2 staining is strongest in Sertoli cells in stage VI and VII tubules. Additionally, we demonstrate that the staining for CP-2 within a stage VII tubule differs from the staining of another Sertoli cell secretory product, androgen-binding protein. CP-2 is not detected by immunocytochemistry in any other tissues of the reproductive tract, though immunoblot analysis demonstrates the presence of CP-2 in rete testis and epididymal fluids. CP-2 was immunocytochemically detected in only three other organs: the kidney, the brain (with greatest concentration in the supraoptic and paraventricular nuclei), and the posterior pituitary. The presence of CP-2 in the kidney was confirmed by metabolic radiolabeling, immunoprecipitation, and peptide analysis. The presence of CP-2 in the brain was confirmed by immunoblot analysis of radioinert protein immunoprecipitated from the anterior hypothalamus.

Partial purification of androgen binding protein from bull epididymis

An androgen binding protein (ABP), with an equilibrium dissociation constant of 4.2 nM and a molecular weight of about 100 kDa, has been purified from bull epididymal extracts using a four-step procedure. These preliminary results underline the main difficulties encountered in the purification of this protein present at a very low concentration (i.e. 50-fold less than in rat or rabbit epididymides). Ammonium sulfate precipitation is not a suitable step due to the formation, in presence of salt, of insoluble material leading to a loss of ABP. Lipids, particularly phospholipids, might be implicated in this phenomenon. Several steps, including anion exchange in batch followed by concentration, affinity chromatography and HPLC gel filtration allowed us to obtain a 7667-fold purified protein with a 9% yield.

Histochemical examination of expression of ras p21 protein and R 1881-binding protein in human prostatic cancers

Expression of ras p21 was examined with monoclonal antibody RASK-3 in normal, benign hyperplasic, and cancerous prostates. In patients with stage D2 disease who received endocrine therapy, the relation between ras p21 expression, response to therapy, and prognosis was studied. In these patients, R 1881-binding protein (androgen receptor and progestin-binding protein) was also examined. Non-cancerous cells and most cancer cells from stage A patients did not express ras p21, while expression increased with both higher staging and grading. Staging pelvic lymphadenectomy was done in some stage A2-C cases, and presence of nodal metastasis was correlated with ras p21 expressions in the primary tumours. In stage D2, there was no correlation between ras p21 expression and R 1881-binding protein. Response to therapy and survival did not correlate with expression of ras p21, but was influenced by presence of R 1881-binding protein.

Hormonal regulation of a rat seminiferous tubule factor which inhibits LH action on interstitial cells

The cytosol from rat testes or seminiferous tubules contains a factor that markedly reduces the responsiveness of interstitial cells to stimulation by LH. It was noted previously that the inhibitor cannot be found until 35 days of age, suggesting that gonadotrophic stimulation of the testes is of importance for its formation. In the present studies, treatment of intact 20-day-old rats with FSH or with a combination of FSH and LH caused a premature appearance of the inhibitory activity. LH alone had a weak effect. However, hypophysectomy at 20 or 35 days of age did not influence the inhibitor content of the testes. Moreover, when the Leydig cells of adult rats were destroyed selectively by treatment with ethylene dimethane sulphonate, inhibitor levels were unchanged. It is suggested that induction of the Leydig cell inhibitor is under the control of FSH. However, once induced, its regulation seems to be independent of the pituitary gland. In separate experiments, ligation of the efferent ducts of the testes in adult animals did not cause any accumulation of inhibitory activity in the ligated testes, nor could the inhibitor be traced in the caput epididymis. Thus, it does not seem to be secreted into the epididymis, but rather may act as a paracrine factor in the testis.

Prolonged suppression of rat testis function by a depot formulation of Zoladex, a GnRH agonist

A sustained-release formulation of a potent gonadotropin-releasing hormone (GnRH) agonist, Zoladex (D-Ser(But),6 Aza Gly10-GnRH; ICI 118,630; goserelin), was administered subcutaneously (3.6 mg/depot) to male rats once every 28 days for 2-24 wk to determine the extent to which pituitary-testis function could be suppressed and whether suppression was maintained throughout the period of treatment. Administration of Zoladex resulted in sustained decreases in weight of the testis, epididymis, seminal vesicles and prostate gland. The decreases were apparent within 2 wk of initiating treatment. Patchy degeneration of the seminiferous tubules and atrophy of the Leydig cells were observed, but did not progress beyond the degree observed after 1 month of treatment. Serum and testis testosterone were markedly depressed after 2 wk of treatment, as was testis [125I]hCG binding. Serum gonadotropins were also reduced by treatment. Serum androgen binding protein (ABP) was elevated, testis ABP content remained unchanged, and epididymal ABP content was reduced. The changes are consistent with the hypothesis that this compound affects both the anterior pituitary gland and the testis. These findings indicate that depot delivery systems are a convenient way to administer GnRH analogs for sustained treatment schedules.

Clinical evidence of the minimal androgenic activity of norgestimate

The goal in improving the progestational component of oral contraceptives (OCs) is to enhance the selectivity of the progestin by achieving a high degree of contraceptive efficacy while decreasing undesirable side effects associated with existing progestational agents. The androgenic activity of current progestins results in changes in lipid metabolism, particularly decreased levels of high-density lipoprotein cholesterol (HDL), which have been associated with an increased risk of coronary heart disease (CHD). A progestin with high antiovulatory activity and minimal androgenicity would offer a clear therapeutic advantage in oral contraception. Norgestimate (NGM) is a new progestin with a unique profile of biological activity that has demonstrated a high level of selectivity in preclinical assays. The present studies were conducted to confirm clinically the low androgenic activity of NGM. Norgestimate (0.25 mg) in combination with 0.035 mg ethinyl estradiol (NGM 0.25/35) was compared with 0.30 mg norgestrel combined with 0.030 mg ethinyl estradiol (Lo/Ovral) in two multicenter clinical studies. In the first study (1,261 women), HDL levels were significantly increased from baseline levels in NGM 0.25/35 subjects but were significantly decreased in Lo/Ovral subjects. Increases in low-density lipoprotein cholesterol (LDL) levels were moderate in the NGM 0.25/35 group and pronounced in the Lo/Ovral group. A favorable lipid profile in NGM 0.25/35 subjects was also reflected in the LDL/HDL ratios, which were significantly lower in the NGM 0.25/35 subjects than in the Lo/Ovral subjects. Sex hormone binding globulin (SHBG) binds androgens, preventing clinical expression of androgenic activity. As a result, elevations in SHBG levels reduce bioactive (unbound) androgen levels and decrease the potential for androgenic side effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of androgen binding-protein (ABP) from testis and epididymis of the seasonal rodent, Octodon degus (Molina, 1872)

ABP, a Sertoli cell secretory product, was identified in the seasonal rodent Octodon degus (Molina, 1872). It was shown to be present in cytosols from the testis and epididymis. It migrated with an Rf of 0.37 on nondenaturing polyacrylamide gels. Ligation of the vas efferens caused the disappearance of ABP from the epididymis and its accumulation in the testis, indicating its testicular origin. Binding to [3H]5 alpha-DHT was specific and completely reversible, with an apparent Kd of 3.5 +/- 0.4 X 10(-9) M. Half-times of association and dissociation were at 15 and 120 minutes, respectively. Binding equilibrium was achieved at 120 minutes. Steroid affinity relative to the best competitor, 5 alpha-DHT, was 0.27 for testosterone, 0.06 for 17 beta-estradiol, and 0.01 for cyproterone acetate. The presence and similar characteristics of ABP in a wide variety of mammals, including those with special reproductive strategies such as seasonal breeding, suggests that this protein may play a general role in the mechanisms regulating spermatogenesis, probably affecting the transport and concentration of androgens in the testis and epididymis.

The androgen-binding protein gene is expressed in CD1 mouse testis

Androgen-binding protein (ABP) is a testicular Sertoli cell secretory protein that acts as a carrier of androgen in the male reproductive tract. ABP has been characterized from a wide range of animal species, including man, rabbit and rat. However, it has been widely accepted that mice do not produce testicular ABP. We have used immunological and molecular biological techniques to demonstrate that the ABP gene is expressed in the CD1 mouse. Steroid-binding, radioimmunoassay and immunocytochemical studies demonstrated that ABP is present in mouse testis and epididymis, but at 1/50 to 1/25 the level of rat epididymis. A 1.7 kilobase mRNA, homologous with rat ABP cDNA, was identified in mouse testis and Sertoli cells by Northern blot hybridization, but at a much lower level than in the rat. An ABP cDNA was isolated from a mouse testis cDNA library and encoded a protein (403 residues) with 89% of the amino acid residues identical to rat ABP, including a signal peptide. Our results indicate that ABP is expressed in the mouse and past failures to detect androgen-binding activity were due to the low level of ABP protein.

Characterization of cis-platinum-induced Sertoli cell dysfunction in rodents

The present study examined the effects of dosage and frequency of cis-platinum administration on various aspects of Sertoli cell function and its correlation with the status of spermatogenesis in rats 1 and 9 weeks after the initial drug administration. Adult male Sprague-Dawley rats were administered cis-platinum (10 mg/kg) intraperitoneally as a single dose or as five daily doses of 2 mg/kg. Electron microscopic observation of testicular tissues fixed in the presence of lanthanum revealed that cis-platinum administration resulted in leakage of the Sertoli cell tight junctions. This occurred as early as 24 hr after the five daily injections, and persisted at least 40 days. Testicular androgen-binding protein (ABP) content was not significantly affected by either treatment regimen after 1 or 9 weeks of recovery. On the other hand, serum ABP values were significantly elevated after 9 weeks of recovery. In addition, the increased sodium and decreased potassium concentrations in seminiferous tubular fluid noted in cis-platinum-treated animals were also indicative of abnormal Sertoli cell secretory function. Degeneration of spermatogenic cells was noted as early as 5 days after the last drug administration; and partial restoration of spermatogenesis was noted after 40 days of recovery. We conclude that in rats both morphological and biochemical properties of Sertoli cells are affected by cis-platinum administration. These changes in Sertoli cell function may be responsible for the cis-platinum-induced impairment of spermatogenesis in these animals.

A specific androgen-binding protein (ABP) in Necturus testis and its zonal distribution

The urodele amphibian Necturus maculosus has a zoned testis, which is advantageous for separating Leydig cells from germinal elements and for studying stage-dependent biochemical changes. Using [3H]testosterone (T) in a standard binding assay and dextran-coated charcoal (DCC) or Sephadex LH-20 to separate free and bound steroids, we identified an androgen-binding protein (ABP) in Necturus testis cytosols. This protein was of high affinity (Kd = 10(-9) M) and was saturable (Bmax = 10(-9) M) and specific for androgen (T; 5 alpha-dihydrotestosterone, DHT) but could be distinguished from the androgen receptor of Necturus testis by its relative abundance (300-550 fmol/mg protein), short half-time of dissociation (3 min at 22 degrees C), inability to adhere to DNA-cellulose, and absence from nuclear extracts. Additionally, when analyzed on sucrose gradients, the ABP of Necturus testis sedimented at 6-7 S in both low or high ionic strength buffers. In that estradiol (E2) is a poor competitor for T-binding, this protein resembles a sex steroid-binding protein previously identified in urodele serum but differs from the ABP and testosterone-estradiol-binding globulin (TEBG) of rodents, humans, goldfish, and sharks. It is differentially distributed within the testis, with the highest levels in immature lobular regions composed of Sertoli cells and germ cells in premeiotic stages and lower levels in regions composed primarily of Leydig cells. The cellular source and function of this protein in Necturus testis remain to be determined.

Sertoli cell proteins in the human seminiferous tubule

It is well known that rat Sertoli cells in culture secrete both testis-specific proteins, such as inhibin and androgen binding protein (ABP), and proteins which are very similar, if not identical, to serum proteins, such as transferrin (TF), ceruloplasmin, and IGF-I. It is also well known that very few data have been reported about the secretory activity and the hormonal regulation of the Sertoli cell in man, mainly because of the difficulties associated with the isolation of pure cell populations from human tissue. Using histoimmunochemical techniques we tried to localize, with specific antisera, Sertoli cell proteins and, when possible, their receptors in the human testis. The results obtained with our Light Microscopy studies suggest that: (1) human Sertoli cells produce and/or store transferrin (TF), IGF-I, an albumin-like protein and ABP; (2) TF receptors are localized in spermatocytes and early spermatids and are absent in spermatogonia, in the cytoplasm of Sertoli cells and in differentiated spermatids; (3) IGF-I type I receptors are localized in the same germ cells and in the cytoplasm of Sertoli cells. The results obtained with our Electron Microscopy studies suggest that TF and IGF-I are internalized through a receptor mediated endocytosis mechanism both in Sertoli cells (basal compartment) and in germ cells (spermatocytes and early spermatids).

Reproductive toxicity of 2,4-toluenediamine in the rat. 3. Effects on androgen-binding protein levels, selected seminiferous tubule characteristics, and spermatogenesis

In previous studies we demonstrated reduced fertility, arrested spermatogenesis, and diminished circulating testosterone levels in rats fed 0.03% 2,4-toluenediamine (TDA) for 10 wk. These studies were extended in three experiments by determining TDA effects on androgen-binding protein (rABP) production and on seminiferous tubule structure, and on early changes in testes morphology and spermatogenesis. In the first experiment, rats fed 0.03% TDA for 10 wk showed a 7- to 9-fold increase in rABP content in testicular cytosol or in media of cultured seminiferous tubules, a 4-fold increase in serum rABP, but a two-thirds decrease in epididymal rABP levels. Testes examination by transmission electron microscopy revealed degenerative changes in Sertoli cells with, where present, normal spermatocytes and spermatids. In the second experiment, 0.03% TDA fed for 4, 6, or 8 wk resulted in a doubling of testes/body weight ratios and a highly correlated 2.5- to 2.9-fold increase in seminiferous tubule fluid volume. An approximately 50% decrease in epididymal sperm reserves was found after 6 or 8 wk of TDA exposure. After 10 wk of exposure to 0.03% TDA, testicular weight was the same as in control-fed rats but seminiferous tubule fluid volume was still elevated. These changes in testicular characteristics indicate TDA effects on Sertoli cell function, on RABP release from the testes (and epididymides), and possibly on tubular fluid transport. In the third experiment, rats fed 0.06% TDA for 1 wk showed a 25% decrease in epididymal sperm content, reduced epididymal weight, and minor structural changes in Sertoli cells. After 3 wk of 0.06% TDA feeding, sperm counts were further reduced, and were accompanied by a dramatic increase in testes weight, intense fluid accumulation, and ultrastructural changes in Sertoli cells. No significant changes in serum testosterone levels were noted in the TDA-treated rats. The results of this third experiment demonstrate TDA toxicity on testicular spermatogenesis within 3 wk of TDA feeding. The within 3 wk of TDA feeding. The findings in this study suggest that the early inhibition of spermatogenesis by TDA is mediated through Sertoli cell damage.

Factors affecting the secretion of immunoactive inhibin into testicular interstitial fluid in rats

Immunoreactive inhibin was measured in testicular interstitial fluid (IF) from rats during sexual maturation or after impairment of spermatogenesis induced by ethane dimethanesulphonate (EDS), unilateral cryptorchidism or local heating (43 degrees C, 30 min) of the testes, to ascertain its usefulness as a marker of changing Sertoli cell function. Cultures of isolated seminiferous tubules were also studied. Inhibin was measured by a radioimmunoassay directed towards the first 26 amino acids of the N-terminus of the alpha-subunit, and the results confirmed for selected pools of IF by in-vitro bioassay using dispersed ovine pituitary cells. During puberty, IF levels of immunoactive inhibin fell by more than 90% (P less than 0.001) between 30 and 60 days of age, a decrease paralleled by the levels of androgen-binding protein (ABP), another Sertoli cell product secreted into IF. These changes also paralleled, but preceded, the fall (60%; P less than 0.001) in serum levels of FSH between 40 and 70 days, while the serum and IF levels of testosterone increased more than two-fold over this period. When adult rats were injected with EDS to destroy the Leydig cells, testosterone levels in IF and serum were undetectable at 3 and 7 days after treatment, were just detectable at 14 days and thereafter returned slowly towards normal by 42 days. The initial androgen withdrawal following EDS treatment caused a progressive reduction in testicular weight up to 21 days and this was accompanied by a significant increase in the serum levels of FSH and a two- to threefold increase in the IF levels of immunoactive inhibin (and also of ABP). Serum FSH and IF levels of immunoactive inhibin returned to within the normal range by 42 days when testosterone levels had normalized. In contrast, in two other experimental situations in which a marked decrease in testicular weight coupled with an increase in IF levels of ABP occurs, different results for the IF levels of immunoactive inhibin were obtained. Thus, in rats exposed to local heating of the testes, IF levels of immunoactive inhibin remained unchanged from control values at 21-40 days after treatment, a finding confirmed by bioassay results. In rats made unilaterally cryptorchid for 10 months, levels of immunoactive inhibin in IF were reduced by 60% (P less than 0.01) in the abdominal compared with the contralateral scrotal testis.(ABSTRACT TRUNCATED AT 400 WORDS)

Validation of a new system for androgen binding protein measurement

A new technique that permits measurement of Androgen-Binding Protein (ABP) is validated by reproducibility, linearity and correlation studies. Using this apparatus allowing Scatchard plot analysis, it is also possible to measure association and dissociation rate constants. In addition, it is a very useful tool for a rapid screening of ABP binding capacity during a chromatographic stepwise purification.

Partial prevention of procarbazine induced germinal cell aplasia in rats by sequential GnRH antagonist and testosterone administration

The present study examined the feasibility of using a combination of gonadotropin releasing hormone antagonist (GnRH-A) and testosterone in the prevention of procarbazine induced germinal aplasia. Daily injections of GnRH-A or vehicle were given to adult male rats for 21 days prior to procarbazine (PCB) administration and continued until 2 days after the second of two doses of procarbazine (200 mg/kg i.p.) given 1 week apart. One group of rats receiving GnRH-A and PCB was given s.c. two 5-cm testosterone capsule (TC) implants (inside diameter, 3.5 mm) immediately following the second dose of PCB. Eight weeks after the last PCB treatment, more than 99% of the seminiferous tubular cross-sections of rats receiving PCB alone were devoid of spermatogenic activity. Spermatogenesis in PCB injected animals receiving GnRH-A pretreatment alone was abortive but was partially preserved when exogenous testosterone was given following PCB administration. At 16 weeks, spermatogenesis was absent in all PCB treated animals and was only observed in less than 1% of the tubular cross-sections of the PCB treated rats receiving GnRH-A pretreatment alone. On the other hand, active spermatogenesis was noted in 68% of the tubular cross-sections, and complete spermatogenesis was noted in four of the five PCB treated rats receiving both GnRH-A pretreatment and subsequent TC implantation. At the time of sacrifice, testicular testosterone concentrations in animals receiving TC implants were below 10% of normal levels, while both serum and testicular testosterone content were increased in PCB treated animals with or without GnRH-A pretreatment. Concomitantly, testicular androgen binding protein content remained suppressed and serum androgen binding protein was elevated, indicating a prolonged defect in Sertoli cell function. These lesions were prevented by GnRH-A pretreatment. The present study demonstrates that GnRH-A pretreatment and subsequent TC implantation resulted in restoration of complete spermatogenesis in adult male rats given a 400-mg/kg cumulative dose of PCB. It is postulated that GnRH-A may ameliorate PCB induced Sertoli cell dysfunction and/or stimulate the number of spermatogonia to provide more proliferating cells ready for repopulation of the germinal epithelium following PCB injury. The differentiation of these spermatogonia was further supported by exogenous testosterone through certain unknown local mechanisms, resulting in the completion of spermatogenesis.

Influence of germ cells upon Sertoli cells during continuous low-dose rate gamma-irradiation of adult rats

The effects of continuous gamma-irradiation of adult rats at two low-dose rates (7 cGy and 12 cGy/day; up to a total dose of 9.1 Gy and 10.69 Gy 60Co gamma-ray, respectively) were investigated. Over a period of 3-131 days of irradiation, groups of experimental and control animals were killed. Body weight, testis, epididymis, prostate and seminal vesicle weights, the number of germ cells and Sertoli cells, tubular ultrastructure, epididymal and testicular levels of biologically active androgen-binding protein (ABP), and the plasma concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were monitored. Irradiation had no effect on body weight, whereas testicular and epididymal weight began to decrease following 35 and 50 days of irradiation at 7 and 12 cGy, respectively. At 7 cGy the target cells of the gamma-rays were essentially A spermatogonia, whereas at 12 cGy A spermatogonia and preleptotene spermatocytes were primarily affected. This resulted in a progressive and sequential dose-related reduction in the number of pachytene spermatocytes, round spermatids and late spermatids (LS). Under both irradiation procedures the Sertoli cell number remained unchanged whereas partial (7 cGy) or no change (12 cGy) was seen at the Leydig cell level. Whatever the irradiation protocol, from the time LS numbers decreased, vacuolisation of the Sertoli cell cytoplasm progressively occurred, followed by thickening and folding of the peritubular tissue. Moreover, in parallel to the drop in the number of these germ cell types, ABP production fell whereas FSH levels rose. A highly significant positive correlation was found between LS numbers and these Sertoli cell parameters. This study supports our previous concept of a control of certain important aspects of Sertoli cell function by late spermatids in the adult rat.

Paracrine control of immature Sertoli cells by adult germ cells, in the rat (an in vitro study). Cell-cell interactions within the testis

Enriched populations of germ cells prepared from adult rats were found to influence 20-day-old rat Sertoli cell secretory activity by stimulating androgen-binding protein (ABP) and inhibiting oestradiol-17 beta production in the presence of follicle-stimulating hormone (FSH) as well as of dibutyryl cyclic AMP (dbcAMP). Among the different populations tested in coculture, pachytene spermatocytes were the most effective at stimulating ABP and inhibiting oestradiol production, whereas early spermatids had relatively less effects. Cytoplasts from elongated spermatids only slightly stimulated ABP secretion. The influence of germ cells upon Sertoli cells may be mediated via paracrine component(s) detected in nonconcentrated conditioned culture media. The stimulatory (ABP) and inhibitory (oestradiol) effects of pachytene spermatocyte and early spermatid-spent media were reversible (change of media), dose related, specific (no effect of cytoplast, peritubular cell, rat liver epithelial cell or 3T3 cell-conditioned media) and strictly proportional to the cell viability estimated at the end of the incubation periods. Furthermore, the nature of the germ cell factor(s) influencing Sertoli cell secretory function is likely to be proteinaceous since both germ cell-spent media effects were trypsin and heat (100 degrees C; 3 min) sensitive and retained by molecular weight (MW) greater than 10,000 cut-off dialysis membranes. It is hypothesized that germ cells, in particular pachytene spermatocytes and early spermatids, may influence Sertoli cell function during sexual development in the rat.

The microheterogeneity of androgen-binding protein in rat serum and epididymis is due to differences in glycosylation of their subunits

The microheterogeneity of androgen-binding protein (ABP) from rat serum and epididymis was examined by subjecting purified native or deglycosylated preparations to analysis by one- or two-dimensional polyacrylamide gel electrophoresis (PAGE) followed by electrophoretic transfer to nitrocellulose and immunochemical localization. Analysis of native ABP by one-dimensional sodium dodecyl sulfate-PAGE confirmed earlier observations that it is composed of subunits and that the subunits of serum ABP had higher apparent molecular weights than those of epididymal ABP. Treatment with neuraminidase, N-glycanase, or O-glycanase, alone or in combination, resulted in decreases in the apparent molecular weight of the subunits. These analyses indicated that terminal sialic acid residues and Asn-linked oligosaccharides were present on both subunits of ABP from the two sources. The fact that the greatest reduction in the Mr of the heavy subunit occurred following treatment with all three enzymes provides evidence that O-linked sugars are present on it. While enzyme treatment did not result in the appearance of a single subunit, chemical deglycosylation did (Mr 39,600). The carbohydrate composition of the heavy and light subunits of intact serum and epididymal ABP was 22 and 9% and 19 and 8%, respectively. Analysis by two-dimensional PAGE indicated that both subunits of the ABPs were composed of isoelectric variants. Although ABP from the two sources had several variants in common, differences were also observed. Treatment of the ABPs with the enzymes resulted in a shift of the pI values to a more basic pH range, indicating that carbohydrate removal also removed charged moieties. The most dramatic shift in the pI values of the isoforms occurred when O-glycanase was present in the enzyme mixture, providing further evidence for the presence of O-linked oligosaccharides on ABP. Isoelectric variants were present even after chemical deglycosylation of ABP.

Effect of continuous low-dose gamma-irradiation on rat Sertoli cell function

Continuous low-dose gamma-irradiation of mature rats induced a progressive degeneration of the germ cells. Blood FSH increased by 127, 176 and 214%, respectively, after 55, 70 and 85 days of treatment when compared to FSH levels in control rats (8.50 +/- 0.60 ng/ml); conversely, serum LH and testosterone levels were unchanged. The Sertoli cell function was affected by the treatment from 70 days on, as attested by androgen binding protein (ABP) and transferrin secretions which diminished 35-40%. Serum ABP levels were not altered, whatever the duration of irradiation, even though epididymal ABP contents (as well as concentrations) diminished 34-60% when compared to those of the controls. Moreover, in purified Leydig cells, LH-stimulated intracellular cAMP levels, which were decreased by seminiferous tubule medium (STM) from control rats, were enhanced in presence of STM from treated animals. Testosterone output was stimulated 9-fold in presence of oLH and further increased (46-76%) from stages XIV-V by STM prepared from control and irradiated rats, respectively. After 85 days the STM effects on both cAMP and testosterone syntheses were zero. These results demonstrate a probable alteration of Sertoli cell function after irradiation, but also a role of the germ cells in the regulation of the synthesis of ABP, transferrin and Sertoli cell paracrine factors.

A minicolumn apparatus for androgen-binding protein measurement

An easy, rapid, and sensitive assay that permits measurements of androgen-binding protein (ABP) in tissue as well as in spent media from Sertoli cells is described; this method involves the specific binding of labeled dihydrotestosterone (DHT) to ABP. The apparatus holds 36 minicolumns loaded with a DEAE Bio-Gel matrix. A peristaltic pump is used for the free fraction elution, taking into account the extremely rapid rate of dissociation of the ABP-DHT complexes. This technique, which allows Scatchard plot analysis, has been used to measure the rates of association (5.15 X 10(5)M-1 S-1 and dissociation (21.32 X 10(-4) S-1; t 1/2 = 5.5 min): the ratio of these rate constants is in perfect agreement with equilibrium dissociation constants determined by Scatchard plot analysis (KD = 4-4.5 nM). The intraassay and interassay coefficients of variation are 5 and 8%, respectively. A good correlation (r = 0.98) is obtained with the standard method of steady-state polyacrylamide gel electrophoresis below a value of 250 micrograms cytosolic proteins/gel. This apparatus, which allows either the measurement of ABP in 12 samples (in triplicates) at a saturating concentration or the analysis of two Scatchard plots (each of 6 points), is also very useful for a rapid localization of ABP during chromatographic purification.

The distribution of rat testibumin in the male reproductive tract

A glycoprotein, designated CMB-1, has been identified in media from Sertoli cell-enriched cultures that increases in concentration in response to follicle-stimulating hormone (FSH) and testosterone. Subsequent studies indicated that CMB-1 is immunologically related to albumin and alpha-fetoprotein and is concentrated in the luminal compartment of the testis in adult rats. Thus, CMB-1 was termed testibumin. The goal of the present study was to determine the concentrations of this protein in testes, epididymides, and serum of normal rats between 10 and 180 days of age and to compare them to rat androgen-binding protein (rABP). Testibumin concentration in rat testes increased with age and peaked at Day 60; thereafter, unlike rABP, its concentration declined, reaching a plateau by 150 days of age. Testibumin concentration in the epididymal compartment also increased with age and peaked at Day 90; thereafter, its concentration remained relatively unchanged. Unlike rABP, which accumulates in the caput epididymis, testibumin did not accumulate preferentially in any particular region of the epididymis. In spite of the marked changes of testibumin concentration in the male reproductive tract, the levels in blood remained relatively constant between 10 and 180 days of age. In adult male and female rats, the serum concentrations of testibumin were similar. Following orchiectomy, serum testibumin concentration decreased by 50% with an apparent t1/2 of approximately 8 h. The presence of immunoreactive macromolecules in other species that share epitopes with rat testibumin was also investigated. Material in human sera and extracts of human and monkey testes cross-reacts with rat testibumin. After [35S]methionine was added to the primary Sertoli cell-enriched cultures, anti-testibumin antiserum selectively immunoprecipitated a radiolabeled protein with the same electrophoretic mobility as purified testibumin on sodium dodecyl sulfate (SDS)-polyacrylamide gels. We conclude that 1) rat testibumin is synthesized and secreted by Sertoli cell-enriched cultures; 2) the relative concentrations and distribution of testibumin in testis, epididymis, and serum of the rat as a function of age are strikingly different from those of rABP; 3) rat testibumin shares epitopes with proteins in human serum and testicular extracts of monkey and man.