Regional variation in radionuclide concentrations and radiation dose in caribou (Rangifer tarandus) in the Canadian Arctic; 1992-94.

Gamma-emitting radionuclides and 210Po, an alpha-emitting product of the 238U decay chain, were analysed in tissues from 16 caribou (Rangifer tarandus) collections in the Canadian North between 1992 and 1994. The study was conducted to determine the regional variability of anthropogenic and natural radionuclides in Canadian caribou, and to estimate the background radiation dose to caribou tissues. 137Cs, 40K, 210Pb and 210Po were consistently found in most herds. Mean muscle 137Cs varied from below detection limits on Banks Island to 231 Bq kg-1 wet weight (ww) in the Beverly herd in the central Arctic. Comparison of 1992-94 levels with published values from the 1960s and 1980s showed that 137Cs in caribou is declining with an effective half-life (Teff) of 9.9 years. The highest mean bone and liver 210Pb activities were observed on south Baffin Island, which included one bone sample with 3800 Bq kg-1 ww of 210Pb and 3070 Bq kg-1 ww of 210Po. The distribution of 137Cs and 210Pb between herds was attributed to higher atmospheric deposition rates between 60 and 65 degrees N, and changes in plant community structure and lichen species composition. The highest mean absorbed dose (30 mGy year-1) was observed in 1993 in the liver of caribou from Lake Harbour. This dose translated into a weighted absorbed dose of 300 mGy year-1, assuming a radiation weighting factor (wR) of 10 to account for the increased biological efficiency of alpha particles for deterministic effects. The Lake Harbour site also had the highest individual weighted absorbed dose in bone (810 mGy year-1) and liver (530 mGy year-1) in the study. There was no significant relationship between bone 210Pb activity and age for individual or pooled herds, indicating that the estimated doses are probably present throughout the lifetime of the caribou. Because some herds number several hundred thousand individuals, collective doses may also be very high. As yet, there have been no reports of observable effects due to these relatively high exposures and many of the herds continue to thrive and increase in size.

Testosterone autoregulation of its biosynthesis in the rat testis: inhibition of 17 alpha-hydroxylase activity.

Using the in vitro perfused rat testis, the effects of testosterone (T) on its own biosynthesis, and in particular on the inhibition of specific steroidogenic step(s) in the biosynthetic pathway from cholesterol to T, were examined. Rat testes perfused in vitro for 1 hour with medium containing 1.5 microM T secreted significantly less T than control testes in response to physiologic or maximal luteinizing hormone (LH) stimulation. To locate the site(s) of this rapid inhibition, the effects of arterial T infusion on steroidogenesis by testes also infused with pregnenolone (PREG), progesterone (PROG), 17 alpha-hydroxyprogesterone (17-PROG), or androstenedione (ADIONE) were measured by summing all the possible reaction products from each substrate. This approach allowed us to examine the effect of T in situ on the reactions: LH-stimulated PREG secretion; PREG to PROG; PROG to 17-PROG; 17-PROG to ADIONE; and ADIONE to T. Only PROG to 17-PROG (17 alpha-hydroxylase activity) was inhibited by arterial T infusion. A kinetic examination of the PROG to 17-PROG reaction demonstrated that the specific inhibition by T was competitive. The apparent km for PROG in this system was 16.0 microM, whereas the apparent ki of T was 1.6 microM, indicating a relatively high degree of sensitivity of the reaction to T. Taken together, these data confirm that T is able to regulate its own synthesis and indicate that this autoregulation is the result of rapid, specific inhibition by T of 17 alpha-hydroxylase activity.

The requirement of the testis in establishing the sensitivity of the canine prostate to develop benign prostatic hyperplasia.

A long-term study on the requirement of the testis in establishing the sensitivity of the canine prostate to develop benign prostatic hyperplasia (BPH) was conducted using 23 aging beagles both with and without their testes. The dogs had received long-term restoration of testosterone and estrogen through silicone implants. When young beagles (0.5 to 1 year of age) were castrated and normal serum testosterone and estrogen levels restored during aging to 5 years, only 50% of these dogs developed BPH in the absence of their testes as opposed to 100% BPH development in intact controls. In addition, two-thirds of the prostates in the treated groups were remarkably reduced in size, being smaller than any prostate observed in the intact controls. If, following castration, the steroid restoration was withheld for 4 years during aging and subsequently administered starting at 5 years of age and continuing for a 6-month period, none of the animals developed complex BPH. Moreover, two-thirds of the prostate glands were reduced in size by more than 60% and were atrophied in spite of the maintenance of normal prostatic tissue dihydrotestosterone levels. Regardless of the time of steroid restoration to a castrate beagle, the periurethral zone of the canine prostate exhibits various degrees of atrophy indicating functional regions within the canine prostate that are sensitive to the requirements of the testes during aging. This study implicates the importance of the testis in increasing the probability and/or sensitivity for the full development of canine BPH.

In vivo model for chronic direct intratesticular drug administration.

The efficacy and toxicity of a new method for chronic direct intratesticular drug infusion were assessed in a rat model. To this end, luteinizing hormone (LH) or buffer was infused via miniosmotic pumps for 14 days directly into the parenchyma of Copenhagen rat testes. The surgical manipulation and direct infusion of buffer did not have any apparent adverse effect upon either spermatogenesis or steroidogenesis as measured by testis weight, homogenization-resistant spermatid count, and in vitro response of the testes to a maximally stimulating concentration of LH. Histologic studies revealed only a localized inflammatory response in the testis around the Silastic tubing leading from the mini-osmotic pump to the testis. The biologic efficacy of direct infusion into the testis was assessed by determining the ability of mini-osmotic pump-infused LH to maintain steroidogenesis for 14 days in animals whose pituitary function was suppressed by simultaneous subcutaneous placement of testosterone/estradiol capsules. Steroidogenesis was found to be maintained quantitatively in testes infused with an appropriate dose of LH. At a given LH dose, the directly infused testes were found to produce fivefold more testosterone than contralateral testes and 10-fold more testosterone than testes from rats receiving systemic administration of the same dose of LH. We conclude that the miniosmotic pump system is a useful means to chronically administer a high concentration of LH, and presumably other agents, to the testis without any significant adverse effects.

Effects of ethane dimethanesulfonate (EDS) on adult and immature rabbit Leydig cells: comparison with EDS-treated rat Leydig cells.

Ethane-dimethanesulfonate (EDS) has been shown to selectively kill Leydig cells and depress testosterone production in adult rats. A recent study has shown that immature rat Leydig cells are less sensitive to EDS exposure. There is evidence that the rabbit metabolizes EDS to methane sulfonic acid more rapidly than does the rat, reducing exposure to the parent compound. In the study reported here, we examined the effects of EDS on the Leydig cells in both adult and immature rabbits and compared the effects found with those previously reported in the rat. In vivo, EDS exposure demonstrated that Leydig cells from adult rabbits were affected, with both serum and interstitial testosterone production depressed. EDS effects in adult rabbits and rats were compared by exposing explants of testicular parenchyma to EDS in vitro and evaluating testosterone production. With this procedure, the rabbit testis was less sensitive to EDS treatment than the rat, with a 50% reduction rate (EC50) achieved with 2026 microM EDS for the rabbit and with 336 microM EDS for the rat. Perfusion of adult and immature rabbit testis with 430 microM EDS demonstrated the insensitivity of the immature testis to EDS exposure: adult testosterone production was reduced 50% in 3.5 h, whereas no diminution was found in the immature rabbit. EDS exposure of interstitial cell preparations further demonstrated the insensitivity of immature rabbit Leydig cells, with an EC50 of 4397 microM compared to an EC50 of 1137 microM EDS in adult preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of [14C]ethane dimethanesulfonate in immature and adult male rats following an acute exposure.

In the adult rat, ethane dimethanesulfonate (EDS) reduces testosterone (T) production by killing Leydig cells. Studies have also shown that acute EDS administration produces transient infertility and epididymal effects. Although these later effects were believed to be indirect results of the reduced Leydig cell T production, it was recently found that the epididymal effects were partially a direct result of in vivo EDS treatment. In contrast to the Leydig cells of the adult rat, immature Leydig cells are affected by EDS only at doses four- to sixfold higher than those that affect mature Leydig cells. In fact, the Leydig cells of the adult rat seem to be uniquely susceptible to the cytotoxic effects of EDS. Steroidogenesis in other organs, like the adrenal and ovary, are unaffected in vivo at doses that eliminate T production in males. In addition, studies have shown that doses of EDS that kill Leydig cells in vitro, isolated from the testes of adult rats, have no effect on similarly exposed hepatocytes. Hence, it was the objective of this study to describe the distribution and temporal fate of EDS in target (testes and epididymides) and nontarget tissues in immature and adult male rats and to determine if this information would explain either the age- or tissue-related susceptibility to EDS. We have concluded from this study that tissue distribution, integrated in vivo EDS dose, and differences in EDS metabolism are not the only factors contributing to the difference in sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial tachycardia in infants and children: electrocardiographic classification and its significance.

An electrocardiographic classification of atrial tachycardia and its significance in children has not been reported. We reviewed the clinical histories and 12-lead surface electro-cardiograms (ECG) of 21 children with atrial tachycardia. Atrial rate and P-wave axis were determined for each patient. Some patients had features of typical atrial flutter (AF). Tachycardia was classified by atrial rate < 340/min or atrial rate > 340/min. Children with atrial tachycardia rate > 340/min consistently responded to conservative treatment (digoxin and/or cardioversion) without recurrences (p < 0.05 and p > 0.025); whereas in children with atrial rate < 340/min, only one case responded to conservative therapy. P-wave axis had no prognostic significance for either group. Additionally, high atrial rate (> 340/min) during tachycardia was noted in early infancy, compared to older children and adults, and probably represents the function of age. Classification of atrial tachycardia by rate is clinically useful for planning therapy and predicting response in children.

Echocardiographically guided balloon atrial septostomy during extracorporeal membrane oxygenation (ECMO).

Use of extracorporeal membrane oxygenation (ECMO) in infants with congenital heart disease is becoming more frequent. We present the first reported use of balloon atrial septostomy during ECMO support and describe possible complications of such procedures unique to ECMO therapy.

Testicular steroidogenesis in the aging brown Norway rat.

In seeking an animal model of age-associated changes in the male reproductive tract, we examined the effects of age on the health and testicular steroidogenic activity of the Brown Norway rat, with comparisons made to the Sprague-Dawley rat. When perfused in vitro under conditions of maximally stimulating luteinizing hormone significant age-associated reductions were seen in testosterone production by testes of Sprague-Dawley rats of 21-24 months of age and by testes of Brown Norway rats of 18-30 months of age. Decreases in the capacity of the testes to produce testosterone were reflected in age-associated decreases in both serum testosterone and in testosterone concentration within the seminiferous tubule fluid. In contrast to the Sprague-Dawley rat, changes in steroidogenic activity in the Brown Norway rat were not accompanied by the occurrence of pituitary adenomas, obesity, or testicular tumors. This along with its longevity, make the Brown Norway strain a highly promising model for testicular aging.

Soy of dietary source plays a preventive role against the pathogenesis of prostatitis in rats.

This study examined the effects of diet on the development of prostatitis in male rats. Adult male rats were placed on either of two specially formulated diets which differed from one another by the presence or absence of soy as the protein source. A third group of rats (control) was fed standard laboratory rat chow which also includes soy as a source of protein. After 11 weeks, it was found that rats maintained on soy-free diet developed prostatitis mainly in the lateral lobe of the prostate. Increased severity and incidence of prostatitis in rats maintained on the soy-free diet coincided with a significant decrease in urinary excretion of various phytoestrogens. There was no evidence of prostatitis in rats maintained on soy-containing diets. Urinary excretion of phytoestrogens in rats maintained on soy-containing diet was also not different from controls. These results suggest that soy as a dietary source plays a protective role against the development of prostatitis in rats, and indicate that the ventral, lateral and dorsal lobes of the rat prostate have different sensitivities to alterations in dietary factors.

Immature rat Leydig cells are intrinsically less sensitive than adult Leydig cells to ethane dimethanesulfonate.

Leydig cells from immature rat testes appear to be insensitive to doses of ethane-1,2-dimethanesulfonate (EDS) which eliminate Leydig cells from adult rat testes. We sought to determine whether this differential response to EDS is intrinsic to the Leydig cell or mediated by other intra- or extratesticular differences between adult and immature rats. To differentiate among these possibilities, Leydig cells were exposed to EDS (1) in vivo, (2) through in vitro testicular perfusion, or (3) in highly purified Leydig cell primary cultures. Four days after ip injections of 85 mg EDS/kg body wt Leydig cells were eliminated from testes of adult, but not immature rats. Total androgen production by testes perfused in vitro with 94 micrograms EDS/ml was dramatically reduced in adult, but not immature rats. Highly purified adult, but not immature, rat Leydig cells were far more sensitive to the effects of EDS on luteinizing hormone-stimulated androgen production (functional effects; apparent EC50 = 94 for adult and 407 micrograms/ml for immature rat Leydig cells) and on [35S]methionine incorporation (cytotoxic effects; apparent EC50 = 140 for adult and 1000 micrograms/ml for immature rat Leydig cells). Finally, the in vitro effects of EDS were both cell type and chemical specific. Since the differential response of adult and immature rat Leydig cells to EDS was manifest in vivo, during in vitro testicular perfusion, and in highly purified Leydig cell primary cultures, we conclude that immature rat Leydig cells are intrinsically less sensitive to the specific cytotoxic effects of EDS than adult rat Leydig cells.

Estradiol regulation of the rabbit corpus luteum: in vivo and in vitro studies.

The objective of this study was to determine whether estradiol has a direct effect on progesterone secretion by the rabbit corpus luteum. Empty or estradiol-filled Silastic capsules were implanted sc into pseudopregnant rabbits (day 0). Ten days later (day 10), peripheral blood was obtained via the marginal ear vein, and Silastic capsules were removed. Twenty-four hours after capsule removal (day 11), blood samples were obtained and ovaries removed for in vitro perfusion. The artery and vein of each ovary were individually cannulated, and ovaries were perfused in vitro for 6 h. Mean progesterone secretion rates were determined from perfusate samples taken every 30 min. On day 10, serum progesterone concentrations were similar in control and estradiol-treated animals. On day 11, 24 h after withdrawal of Silastic capsules, serum progesterone concentration in the estradiol-treated rabbits decreased significantly compared to controls. The withdrawal of estradiol also significantly reduced the secretion of progesterone by in vitro perfused ovaries in estradiol-withdrawn rabbits compared to empty capsule controls. Addition of estradiol or 25-hydroxycholesterol (25-OH) to the perfusion medium significantly increased progesterone secretion by ovaries from estradiol-withdrawn rabbits but not to control values. In contrast, a combination of estradiol plus 25-OH restored progesterone secretion to control levels. Although estradiol together with 25-OH stimulated progesterone secretion 24 h after estradiol withdrawal, progesterone secretion in vitro was unaffected 48 h after capsule removal, whereas pregnenolone stimulated secretion 5-fold. These results demonstrate that estradiol has a direct and acute stimulatory effect on progesterone secretion by the rabbit corpus luteum.

Male reproductive toxicology.

The objective of this paper is to discuss recent developments in the application of biological markers to animal models of male reproductive toxicology. We have divided this paper into three major sections: First, a discussion of the testing protocols currently under investigation by the National Toxicology Program (NTP) and the EPA's Health Effects Research Laboratory; second, an examination of what we consider to be important and practical biological markers available to investigators to assess the effects of toxicants on the male reproductive system; and third, a discussion of promising new technologies, such as molecular and immunological probes, and in vitro techniques using isolated and cultured cells, which in the future may be exploited for the development of additional biological markers of male reproductive toxicity. Where appropriate we have made specific recommendations for the use of these biological markers in animal protocols and have pointed out those noninvasive markers which have application to screening human males.

Hormonal control of Leydig cell differentiation.

Leydig cell progenitors contain significant concentrations of androgen receptors. When the metabolism of DHT to 3 alpha-DIOL is blocked, DHT stimulates testosterone production by Leydig cell progenitors, most probably via an androgen receptor dependent mechanism. Rapid metabolism by 3 alpha-HSD may limit the potency of exogenous DHT to stimulate differentiation of Leydig cell progenitors in vitro. Insulin-like growth factor-I enhances androgen production by purified immature Leydig cells. The elevated sensitivity of immature Leydig cells versus adult Leydig cells to IGF-I stimulation indicates that this peptide hormone has a role in their differentiation during puberty.

Luteinizing hormone causes rapid and transient changes in rat Leydig cell peroxisome volume and intraperoxisomal sterol carrier protein-2 content.

The aim of the present study was to investigate the effects of a single injection of LH on rat Leydig cell peroxisome volume and peroxisomal sterol carrier protein-2 (SCP2) content. Sexually mature Sprague-Dawley rats (n = 5) were injected sc with 500 micrograms LH and euthanized, and trunk blood was collected at 0, 0.5, 1, 2, and 3 h. Additionally, LH-treated rats were whole body perfused-fixed, and their testes were processed for qualitative and quantitative histochemical and immunocytochemical studies at 0, 0.5, 1, and 2 h. Peroxisomes were identified by cytochemical staining for catalase activity with the alkaline 3,3'-diaminobenzidine tetrahydrochloride method. Catalase and SCP2 were immunolocalized in Leydig cell organelles via 10-nm AuroProbe EM protein-A gold particles. Peak plasma testosterone concentrations were observed 1 and 2 h after the single sc LH injection. The average volume of a Leydig cell was unchanged by the LH treatment at all time points tested. Similarly, the absolute volumes of smooth endoplasmic reticulum and mitochondria per Leydig cell were unchanged at all time points tested. By contrast, the absolute volume of peroxisomes per Leydig cell increased 3-fold 0.5 h after LH injection (P less than 0.01) and then returned to control values by 2 h. The absolute volume of negative bodies (single membrane-bound cytoplasmic organelles lacking catalase) per Leydig cell was elevated above the control value 0.5 and 1 h after LH injection. Western blot analysis demonstrated a single protein at 14 and 60 kDa with anti-SCP2 and anticatalase, respectively, for both homogenates obtained from liver and purified Leydig cells. Quantitative immunocytochemical studies demonstrated that the gold particle density representing SCP2 over peroxisomes increased 5-fold 0.5 h after the LH injection (P less than 0.01) and then returned to control values by 2 h. In contrast, the gold particle density representing catalase over peroxisomes was not different in control and LH-injected groups. We conclude that a single sc injection of LH causes a rapid, specific, and transient increase in both the volume of peroxisomes and the peroxisomal content of SCP2 in Leydig cells.

Reversal of long-term LH deprivation on testosterone secretion and Leydig cell volume, number and proliferation in adult rats.

The purpose of this study was to determine whether Leydig cell volume and function could recover fully from long-term LH deprivation upon restoration of endogenous LH secretion, and whether the restoration of LH would elicit a mitogenic response, i.e. stimulate Leydig cell proliferation or affect Leydig cell number per testis. LH secretion was inhibited by treating adult rats with testosterone and oestradiol-filled (TO) silicone elastomer implants (16 weeks), and was restored by removing the implants. Changes in serum concentrations of LH and FSH, LH-stimulated testosterone secretion by testes perfused in vitro, Leydig cell volume and number per testis, average Leydig cell volume and Leydig cell [3H]thymidine incorporation were measured at weekly intervals following implant removal. The TO implants inhibited (P less than 0.01) LH secretion, but serum concentrations of FSH were not significantly different (P greater than 0.10) from control values. After implant removal, serum LH returned to control values within 1 week, whereas serum FSH increased twofold (P less than 0.01) and returned to control values at 4 weeks. LH-stimulated in-vitro testosterone secretion was inhibited by more than 99% in TO-implanted rats, but increased (P less than 0.01) to 80% of control values by 8 weeks after implant removal. The total volume of Leydig cells per testis and the volume of an average Leydig cell were 14 and 19% of control values respectively, after 16 weeks of TO implantation (P less than 0.01), but returned to 83 and 86% of controls (P greater than 0.10) respectively, by 6 weeks after implant removal. Leydig cell proliferation ([3H]thymidine labelling index) was low (less than 0.1%) in both control and TO-implanted rats, increased (P less than 0.01) fivefold from 1 to 4 weeks after implant removal and then declined to control values at 6 weeks. The increase in Leydig cell [3H]thymidine incorporation was mimicked by treating TO-implanted rats with exogenous LH, but not FSH. Leydig cells were identified in both the interstitium and the lamina propria of the seminiferous epithelium. The proportion of Leydig cell nuclei in the lamina propria was 30-fold greater (P less than 0.01) at 1 and 3 weeks after implant removal (3%) compared with that for control and TO-implanted rats (0.1%). Total Leydig cell number per testis was marginally but not significantly (P = 0.06) decreased in rats treated with TO implants for 16 weeks when compared with controls (18.4 +/- 2.2 vs 25.4 +/- 1.2 x 10(6)).(ABSTRACT TRUNCATED AT 400 WORDS)

Sources of error in the estimation of Leydig cell numbers in control and atrophied mammalian testes.

The effects of assuming (i) that testicular tissue shrinks equally regardless of species or treatment at fixing and processing, (ii) that all Leydig cells in a given testis have spherical nuclei of identical size, and (iii) that testicular volume (i.e. the reference volume) is constant regardless of species or treatment, on the estimation of Leydig cell numbers in mammalian testes were investigated. This was accomplished by comparing the results of stereological analyses of Leydig cell numerical density and Leydig cell number in control testes of hamster, guinea-pig, and rat and in atrophied testes of hamster, and rat, obtained via the disector method which is unbiased with respect to the particle shape under study, and the Floderus equation which assumes that the particles under study are identical spheres. In control hamster, and also in guinea-pig, the effects of the three assumptions on the estimates of Leydig cell number per testis were negligible, because in these two treatment groups, the total shrinkage of testis tissue at fixing and processing (ST%) was low, Leydig cell nuclear profiles were circular in section, and the average volume of a testis was close to unity (i.e. 1 cm3). By contrast, in hamsters, and rats with atrophied testes, these assumptions produced incorrect estimates in Leydig cell number per testis, because the ST% was high, the majority of Leydig cell nuclear profiles were pleomorphic, and the average volume of a testis was lower than control. In summary, this study documents that the assumptions of equal shrinkage in testis tissue at fixing and processing, a constant testicular reference volume, and spheroidal shape of Leydig cell nuclei may contribute significant errors in estimates of Leydig cell number in mammalian testes. The magnitude of the errors introduced by these assumptions depends upon the species and the experimental treatment.

Effects of hypophysectomy and alterations in spermatogenic function on Leydig cell volume, number, and proliferation in adult rats.

The two major objectives of this study were to determine (i) whether the pituitary is required to maintain Leydig cell number per testis, and (ii) whether alterations in spermatogenic function in the absence of LH can affect Leydig cell volume, number, and 3H-thymidine incorporation in vivo. Four experimental treatments tested the combinations of two factors: (i) the intact pituitary vs hypophysectomy (Hypox); and (ii) arrested vs active spermatogenesis. Subdermal Silastic capsules were used to deliver a low dosage of estradiol in addition to a low dosage of testosterone (TE), which arrested spermatogenesis, or a high dosage of testosterone (HTE) which maintained active spermatogenesis. All four treatments (TE, HTE, Hypox and Hypox-HTE) inhibited LH secretion for 16 weeks. Control rats were sham hypophysectomized. Leydig cell volume per testis and the volume of an average Leydig cell decreased 70-85% (P less than 0.01 vs controls) in all treated rats, whether deprived of LH (TE) or of all pituitary secretions (Hypox), and whether spermatogenesis was arrested (TE, Hypox) or maintained by exogenous testosterone (HTE, Hypox-HTE). This result suggested that LH was the only factor required to maintain Leydig cell volume, since the absence of other pituitary factors or alterations in spermatogenic function could not override or modify the effect of LH deprivation. No significant differences were found in Leydig cell number per testis or the proportion of Leydig cells labeled with 3H-thymidine among control and experimentally treated rats. In contrast to Leydig cell volume, which depended on LH, Leydig cell number and Leydig cell division were maintained at control values in the absence of pituitary factors and spermatogenic function for 16 weeks.

Differentiation of Leydig cell precursors in vitro: a role for androgen.

An enriched fraction of mesenchymal-like cells was isolated from the testes of 21 day old rats. Testosterone production (ng/10(6) cells.24 hours) by these cells when cultured in vitro was measured by radioimmunoassay of HPLC-purified extracts of culture medium. In the presence of LH + DHT there was a significant increase in testosterone secretion from 22 +/- 10 ng after day 1 of culture to 284 +/- 75 ng on day 3 (P less than 0.01). By contrast, LH or DHT alone were without significant effect. We conclude that LH alone is insufficient but that androgen and LH induce mesenchymal-like Leydig cell precursors from 21 day old rats to produce testosterone.

Does ethane 1,2-dimethanesulphonate (EDS) have a direct cytotoxic effect on the seminiferous epithelium of the rat testis?

The authors examined the possibility that ethane 1,2-dimethanesulphonate (EDS) has a cytotoxic effect on spermatogenesis that is not secondary to androgen withdrawal resulting from the well known cytotoxic effect of EDS on Leydig cells. Adult male rats were implanted with polydimethylsiloxane (PDS) capsules containing testosterone (T) and estradiol (E), and were simultaneously injected with EDS. The PDS-TE implants, by inhibiting luteinizing hormone (LH) production, prevented Leydig cells from repopulating the testis and clamped testosterone within the seminiferous tubules at increasing concentrations relative to implant size. In rats that received EDS alone, the number of advanced spermatids per testis was significantly reduced by 2 weeks, but within 8 weeks returned to the numbers maintained in vehicle-injected control rats or in vehicle-injected rats that received testosterone- and estradiol-filled capsules of 24 cm and 0.1 cm, respectively (PDS-24TE). Surprisingly, in rats that received an EDS injection plus PDS-24TE implants, the number of advanced spermatids per testis was significantly reduced at 8 weeks and severe seminiferous tubule atrophy occurred despite the fact that the testosterone concentration was sufficient to quantitatively maintain spermatogenesis in vehicle-injected rats. In rats injected with EDS and implanted with 24 cm testosterone but not estradiol-filled capsules (PDS-24T), the advanced spermatid number per testis was significantly higher than that in the EDS plus PDS-24TE rats, but significantly lower than that in control rats. These results suggest that EDS may have a cytotoxic effect on the seminiferous epithelium that is independent of the elimination of Leydig cells, and the EDS and estradiol act synergistically to exert a profound toxic effect on spermatogenesis.