Identification of Leydig cell-specific mRNA transcripts in the adult rat testis.

The adult population of Leydig cells acts to secrete testosterone which is essential for reproductive health and fertility in the adult male. However, other physiological functions of these cells are uncertain, and to address this issue a cell ablation model has been used to identify Leydig cell-specific mRNA transcripts. Ethane dimethane sulphonate (EDS) was synthesised by a novel process and was used to ablate Leydig cells in adult male rats previously treated with butane dimethane sulphonate (busulphan) to delete the germ cell population. Levels of mRNA transcripts were measured in the testis using microarrays 1, 3, 5, 8 and 12 days after EDS injection. During this period, there was a significant change in the levels of 2200 different transcripts with a marked decline in the levels of canonical Leydig cell transcripts, such as Cyp11a1, Cyp17a1 and Insl3. A total of 95 transcripts showed a similar decline in expression after EDS treatment, suggesting that they have a Leydig cell-specific origin. Analysis of selected transcripts confirmed that they were expressed specifically in Leydig cells and showed that most had a late onset of expression during adult Leydig cell development. Apart from transcripts encoding components of the steroidogenic apparatus, the most common predicted function of translated proteins was endogenous and xenotoxicant metabolism. In addition, a number of transcripts encode acute-phase proteins involved in reduction of oxidative stress. Results show that, in addition to androgen secretion, Leydig cells may have a critical role to play in protecting the testis from damage caused by toxicants or stress.

Leydig cell re-generation and expression of cell signaling molecules in the germ cell-free testis.

Leydig cells in the rat testis can be specifically ablated with ethane dimethane sulfonate (EDS) and will subsequently re-generate. In this study, we have characterized Leydig cell re-generation and expression of selected cell-signaling molecules in a germ cell-free model of EDS action. This model offers the advantage that re-generation occurs on a stable background without confounding changes from the regressing and repopulating germ cell population. Adult rats were treated with busulfan to remove the germ cell population and Leydig cells were then ablated with EDS. Testicular testosterone levels declined markedly within 24 h of EDS treatment and started to recover after 8 days. After EDS treatment there were marked declines in levels of Leydig cell-specific mRNA transcripts coding for steroidogenic enzymes cytochrome P450 11a1 (Cyp11a1), cytochrome P450 17a1 (Cyp17a1), 3beta-hydroxysteroid dehydrogenase type 1 (Hsd3b1), 17beta-hydroxysteroid dehydrogenase type 3 (Hsd17b3) and the LH receptor. Levels of all transcripts recovered within 20 days of EDS treatment apart from Hsd17b3, which remained undetectable up to 20 days. Immunohistochemical localization of CYP11A1 during the phase of early Leydig cell re-generation showed that the Leydig cell precursors are spindle-shaped peritubular cells. Studies on factors which may be involved in Leydig cell re-generation showed there were significant but transient increases in platelet-derived growth factor A (Pdgfa), leukemia inhibitory factor (Lif), and neurofilament heavy polypeptide (Nefh) after EDS, while desert hedgehog (Dhh) levels declined sharply but recovered by 3 days. This study shows that the Leydig cell precursors are peritubular cells and that expression of Pdgfa and Lif is increased at the start of the re-generation process when precursor proliferation is likely to be taking place.

Protection of spermatogenesis in rats from the cytotoxic procarbazine by the depot formulation of Zoladex, a gonadotropin-releasing hormone agonist.

The hypothesis that adjuvant treatment designed to produce testicular atrophy would preserve fertility in males receiving cancer chemotherapy was examined in the rat. Testicular atrophy was induced by a depot formulation of Zoladex [D-Ser(Bu(t))6-Aza-Gly10-GnRH], a gonadotropin-releasing hormone (GnRH) analogue. The experiments were conducted in albino Wistar as well as in the piebald variegated rat. Rats received the depot Zoladex formulation 2 weeks before and immediately prior to being treated with four weekly doses of procarbazine (200 mg/kg). Testicular function was evaluated 50 and 90 days after the last procarbazine dose. Procarbazine induced testicular atrophy concomitant with marked germinal cell aplasia in both strains of rat. In the Wistar rat adjuvant treatment with Zoladex caused slight but not significant alleviation of the testicular toxicity of procarbazine. The testicular toxicity of procarbazine was more extensive in the piebald variegated rat, and 50 days after the last procarbazine treatment the testes were small, sperm were absent, and the stem cell index was close to zero. Serum luteinizing hormone (LH) concentrations were raised and testicular LH receptor binding was low in the presence of normal serum and testicular testosterone concentrations, indicating compensated Leydig cell failure. Testicular weight and sperm content, as well as LH receptor binding, were still decreased in rats which received both Zoladex and procarbazine, suggesting that the analogue offered no protection. However, the stem cell index of the seminiferous tubules in the procarbazine-Zoladex-treated rats was not significantly different from vehicle-treated rats, which suggested that recovery from the effects of procarbazine was in progress. Ninety days after the end of procarbazine treatment alone the testes of rats were still atrophied and there was little evidence of active spermatogenesis. Leydig cell failure appeared to have progressed as, in addition to the low testicular LH receptor content and raised serum LH concentration, the prostate and seminal vehicle weights were decreased. The combination of Zoladex treatment with procarbazine was successful in preserving testicular function in the piebald variegated rats as virtually all the functional and morphological parameters of both the seminiferous tubule and the Leydig cell were not significantly different from those of vehicle-treated rats. This study demonstrates for the first time that effective gonadal protection from the toxic effects of procarbazine chemotherapy can be achieved by administration of the depot formulation of the gonadotropin-releasing hormone analogue Zoladex. The results show clearly that complete suppression of spermatogenesis is not a prerequisite for the successful outcome of treatments designed to protect the gonad from cytotoxic chemotherapy.

Regulation of testicular infiltration in acute lymphoblastic leukaemia of the rat.

The testis is a common site of relapse in childhood acute lymphoblastic leukaemia (ALL). In adults, testicular relapses of ALL are very rare. A similar age-difference in the frequency of the testicular infiltration exists also in the rat T-cell leukaemia. In the present investigation, the effect of various hormonal treatments and unilateral cryptorchidism on the form of testicular infiltrates by the rat T-cell leukaemia was studied. Inhibition of testicular activity by estradiol treatment (E2) of early pubertal rats injected i.p. with rat T-leukaemic lymphoblasts significantly decreased the proportion of the testis occupied by leukaemic infiltrates. The proportion of the testis occupied by leukaemic infiltrates was significantly higher in the abdominal testes of both early and late pubertal unilaterally cryptorchid rats, than in the scrotal testes of leukaemic control rats. Daily treatment of early pubertal rats with human chorionic gonadotrophin (hCG), or human menopausal gonadotrophin (hMG), did not have an effect on testicular leukaemic infiltration. These studies demonstrate that the leukaemic infiltration of the testis is influenced by the changes in the physiological activity of the testes.

Ethylene dimethanesulfonate destroys Leydig cells in the rat testis.

Ultrastructural changes in the interstitial cells of the adult rat testis were studied up to 45 days after administration of a single dose (100 mg/kg) of the antifertility compound ethylene dimethanesulfonate (EDS). Most Leydig cells showed degenerative changes 12 h after treatment. Twenty-four and 48 h after injection, all Leydig cells observed showed gross degenerative changes. At 4 and 14 days, intact Leydig cells could not be identified in the interstitial spaces. Twenty-one days after treatment with EDS, small Leydig cells were visible, and at 45 days, Leydig cells appeared normal. The seminiferous epithelium appeared morphologically normal until 4 days after injection of EDS, when slight abnormalities were observed. At 14 and 21 days, the seminiferous epithelium was grossly abnormal, but at 48 days, spermatogenesis appeared normal. Twelve, 24, and 48 h after treatment, large quantities of material, presumably from dead Leydig cells, were observed within the macrophage cytoplasm. The predominant cell in the interstitial space 4 and 14 days after EDS was the macrophage. Inclusions from the dead Leydig cells within the cytoplasm of the macrophages had almost disappeared. LH receptors (hCG binding) in testicular homogenates were consistent with the cytological changes in Leydig cells. Receptor concentration was low at 24 h and was almost zero at 4 days. This change was accompanied by a decrease in serum testosterone to castrate levels by 2 days. The responses of the endocrine system to destruction of the Leydig cell by EDS, as monitored by serum FSH, LH, and testosterone, were slower than those after castration, indicating that the response to EDS reflects the time required to kill the Leydig cell rather than direct impairment of the steroidogenic pathway. These experiments demonstrate that Leydig cells can be specifically destroyed by a cytotoxic drug. The availability of a specific cytotoxic agent for Leydig cells offers further opportunities to study the interrelationships between the Leydig cell and the seminiferous tubule.

Leydig cell apoptosis after the administration of ethane dimethanesulfonate to the adult male rat is a Fas-mediated process.

Leydig cells undergo apoptosis in response to the cytotoxin ethane dimethanesulfonate (EDS), with numbers declining at 12-18 h and maximal apoptosis at 24 h postinjection. The Bcl-2 family members, Bcl-2, Bcl-xl, and Bax, appear not to be involved in this process. To further investigate this phenomena, a single dose of EDS was administered to adult rats to induce the killing of Leydig cells. The interstitial cells were examined up to 3 days after EDS administration by Western blot analysis for the Bcl-2 family members (Bak and Bcl-w). Western blotting showed that Bak expression in the interstitial cell preparations was unchanged after EDS, and immunohistochemistry showed that it was not up-regulated in Leydig cells in response to EDS. Bcl-w expression in the Leydig cells and interstitial cell preparations was unchanged until 48 h when it became undetectable, suggesting that Leydig cell-associated Bcl-w is not involved in initiating apoptosis. We also investigated the role of the Fas system in Leydig cell apoptosis. Both Fas receptor and Fas ligand protein levels increased after EDS, peaking at 12-18 h and declining thereafter. Fas receptor and ligand were shown by immunohistochemistry to be present in Leydig cells, and after EDS all Leydig cells became strongly positive for both proteins. The intensity of staining increased in the early stages of apoptosis and decreased as the nuclear morphology became more fragmented. These data suggest that Bcl-2 family members are not involved in Leydig cell apoptosis after EDS administration. However, up-regulation of the Fas system does occur, implicating activation of Fas receptor in the induction of Leydig cell apoptosis.

Leptin acts on metabolism in a photoperiod-dependent manner, but has no effect on reproductive function in the seasonally breeding Siberian hamster (Phodopus sungorus).

Leptin may play a role in appetite regulation and metabolism, but its reproductive role is less clear. In photoperiodic Siberian hamsters, seasonal changes in fatness, leptin gene expression, and metabolism occur synchronously with activation or suppression of reproduction, analogous to puberty. Here, we test the hypothesis that seasonal changes in leptin secretion mediate the photoperiodic regulation of reproduction. Mature male and ovariectomized estrogen-treated female Siberian hamsters were kept in long (LD; 16 h of light, 8 h of darkness) or short days (SD; 8 h of light, 16 h of darkness) for 8 weeks, and recombinant murine leptin (15 microg/day) was infused for 2 weeks via osmotic minipumps. SD hamsters exhibited significant weight and fat losses, reduced serum leptin and food intake, and suppressed pituitary LH concentration. Leptin did not suppress food intake over the 2-week treatment on either photoperiod, but significantly reduced fat reserves in SD hamsters. Leptin had no significant effect on pituitary LH concentrations in either sex or photoperiod or on testicular size and testosterone concentrations in males. These results suggest hamsters are more responsive to leptin on SD than on LD and that effects on food intake and fat loss can be dissociated in this species. Our data suggest that leptin does not mediate photoperiodic reproductive changes.

Adenovirus-mediated herpes simplex virus type-1 thymidine kinase gene therapy suppresses oestrogen-induced pituitary prolactinomas.

We tested the hypothesis that gene transfer using recombinant adenovirus vectors (RAds) expressing herpes simplex virus type 1 thymidine kinase (HSV1-TK) might offer an alternative therapeutic approach for the treatment of pituitary prolactinomas that do not respond to classical treatment strategies. HSV1-TK converts the prodrug ganciclovir (GCV) to GCV monophosphate, which is in turn further phosphorylated by cellular kinases to GCV triphosphate, which is toxic to proliferating cells. One attractive feature of this system is the bystander effect, whereby untransduced cells are also killed. Our results show that RAd/HSV1-TK in the presence of GCV is nontoxic for the normal anterior pituitary (AP) gland in vitro, but causes cell death in the pituitary tumor cell lines GH3, a PRL/GH-secreting cell line, and AtT20, a corticotrophic cell line. We have used sulpiride- and oestrogen-induced lactotroph hyperplasia within the rat AP gland as an in vivo animal model. Intrapituitary infection of rats bearing oestrogen-induced lactotroph hyperplasia, with RAd/ HSV1-TK and subsequent treatment with GCV, decreases plasma PRL levels and reduces the mass of the pituitary gland. More so, there were no deleterious effects on circulating levels of other AP hormones, suggesting that the treatment was nontoxic to the AP gland in situ. In summary, our results show that suicide gene therapy using the HSV1-TK transgene could be further developed as a useful treatment to complement current therapies for prolactinomas.

Inhibitory effects of alkane sulphonates on the function of immature rat Leydig, Sertoli and peritubular cells cultured in vitro.

Ethane 1,2-dimethane sulphonate (EDS) selectively destroys Leydig cells in the interstitium of the testis of adult rats. The toxic activity of this compound is much less obvious in the immature rat testis. We examined the effects of EDS, its monomethyl derivative and busulphan on cultured interstitial cells, percoll-purified Leydig cells, Sertoli cells and peritubular cells derived from immature rats. The studies with interstitial cells and Leydig cells showed that EDS (40-160 micrograms/ml) blocked the conversion of C21 and androgen precursors into testosterone and androstenedione. Higher concentrations of this compound also inhibited the production of C21 steroids and the LH-induced production of cyclic AMP (cAMP). The observed effects required a latent period of at least 8 h and were slowly reversible. Isolated cells were more sensitive to EDS than monolayer cultures. Reaggregation cultures were even less sensitive. EDS was markedly more effective on immature Leydig cells than its monomethyl derivative and busulphan. In cultured Sertoli cells FSH-inducible aromatase activity, cAMP production, androgen-binding protein (ABP) production and the secretion of a paracrine factor with Leydig cell-stimulatory activity were markedly reduced by busulphan. In these cells, busulphan was clearly more active than EDS and its monomethyl derivative. The production of paracrine factors which increase ABP production and decrease FSH-inducible aromatase activity in Sertoli cells was studied as a parameter of the effects of alkane sulphonates on peritubular cells. Only busulphan markedly decreased the production of these paracrine factors. It is concluded that EDS displays a selective toxicity to Leydig cells derived from immature animals and that, apart from its effects on germ cells, busulphan may also directly impair the function of Sertoli cells and peritubular cells.

Insulin-like growth factor-I mRNA expression in the interstitial cells of the rat testis.

IGF-I mRNA has been demonstrated in testicular tissue and, more recently, localized specifically to Leydig cells. This study investigated the expression of IGF-I and side-chain cleavage enzyme (SCC) mRNA in two preparations of rat interstitial testicular cells which were separated by buoyant density into Leydig cell-enriched and -depleted fractions. RNA was prepared from interstitial cells obtained from the testes of untreated adult and immature rats and adult rats treated with human chorionic gonadotrophin (hCG) or ethane dimethanesulphonate (EDS; to destroy Leydig cells). IGF-I mRNA was detected in all samples, with five major transcripts ranging from 7.5 to 0.6 kb. Leydig cells (3 beta-hydroxysteroid dehydrogenase-positive and sensitive to EDS) expressed abundant IGF-I and SCC mRNAs, and levels of both were increased following hCG treatment. However, in addition, IGF-I mRNA which was derived from non-Leydig interstitial cells was detected, in the complete absence of SCC message, either in the more buoyant interstitial cells or in both interstitial cell fractions following the destruction of Leydig cells by EDS treatment. IGF-I expression in the Leydig cell-depleted cell fraction was also increased by hCG treatment, and it is therefore suggested that at least part of this non-Leydig interstitial cell IGF-I mRNA originates in Leydig cell precursors. In conclusion, Leydig cells are not the sole origin of IGF-I mRNA in the testis, and the non-Leydig cell expression may be an important component of testicular IGF-I production.

Insulin-like growth factor-I gene expression in human granulosa-lutein cells.

IGF-I is an important local regulator of ovarian function, stimulating follicular growth and steroidogenesis in human granulosa cells. However, it is not known whether ovarian IGF-I is derived from the circulating serum pool or from local production. IGF-I peptide has only been detected in human thecal cells and not in granulosa cells. This study has used the sensitive technique of reverse transcription of mRNA followed by PCR amplification (RT/PCR) to examine IGF-I gene expression in human preovulatory granulosa cells. Granulosa-lutein cell (GLC) samples were obtained by follicular puncture of seven women enrolled in an ovulation induction programme. Treatment had included buserelin acetate, human menopausal gonadotrophin to stimulate follicular growth and human chorionic gonadotrophin to induce ovulation. Total RNA (TRNA), extracted from the GLCs, was amplified by RT/PCR, using combinations of leader and 3' IGF-I exon-specific primers, to yield four IGF-I gene products: IGF-IA (exons 1, 3, 4, 6), IGF-IB (exons 1, 3, 4, 5), IGF-IA' (exons 2, 3, 4, 6) and IGF-IB' (exons 2, 3, 4, 5). As controls from other tissues, an identical procedure was undertaken on TRNA from peripheral blood monocytes and liver. All four mRNAs were expressed in GLCs, monocytes and liver. However the pattern of IGF-I mRNA expression differed between the tissues; in liver and GLCs, the IGF-IA transcript was dominant, but in monocytes the IGF-IA' species was the most prominent. Quantitative RT/PCR using standardization to the house-keeping gene for glyceraldehyde-3'-phosphate dehydrogenase revealed that IGF-IA mRNA was 300-fold more abundant in liver than GLCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell proliferation and death in the irradiated pituitary gland and its modification by growth stimulants.

PURPOSE: This study was undertaken to show whether the rate of expression of radiation injury in the rat pituitary gland could be accelerated by the use of growth stimulants. METHODS AND MATERIALS: Rat pituitary glands were irradiated in situ with a range of single doses up to 20 Gy. The rats were then given subcutaneous slow-release implants containing 17beta-estradiol (E2) and sulpiride (S) to stimulate lactotroph proliferation. Two sequential cycles were used, each consisting of stimulation (3 weeks) and withdrawal (2 weeks). Measurements were made of gland weight; BrdU-labeled, giant, and apoptotic cells; lactotrophs; as well as pituitary prolactin content, in response to exogenous thyroid-releasing hormone (TRH). RESULTS: The two cycles of stimulation/withdrawal resulted in marked changes in gland weight, BrdU-labeling index, and serum prolactin (PRL) levels in unirradiated rats. The proportion of immunopositive growth-hormone-producing (GH) cells increased after irradiation. Radiation inhibited the hypertrophic response to E2 + S and also inhibited increases in BrdU-labeling index and serum PRL levels. Also, giant lactotrophs were observed in the irradiated pituitaries. However, they were not seen in the unirradiated rats or in the irradiated rats treated with E2 + S. TRH promoted PRL secretion in the unirradiated rat. In contrast, TRH inhibited PRL secretion in the irradiated rat and in all treatment groups receiving E2 + S. Apoptosis was induced by irradiation and was substantially increased in lactotrophs and in other cell types by withdrawal of the E2 and S stimulus, although the highest observed incidence was only 7 per 10,000 cells. CONCLUSION: Both irradiation and E2 + S treatment removed the hypothalamic control of PRL secretion, which reveals this important inhibitory action of TRH upon PRL secretion. This suggests that it is not suitable as a dynamic test of pituitary PRL reserves in such abnormal situations, where there may also be damage to the hypothalamic-pituitary vasculature. The increasing proportion of GH cells after irradiation indicates that lactotrophs respond more rapidly to irradiation. The stimulation by E2 + S somehow prevented the radiation-damaged lactotrophs from becoming giant cells. Also, the ratio of apoptotic cells to BrdU-labeled cells was increased by the E2 + S treatment, indicating that the E2 + S did enhance radiation-induced cell death relative to cell renewal. However, overall, the E2 + S stimulus protocol did not promote a dramatic increase in cell death (apoptosis) nor a marked decrease in residual gland weight after irradiation. Hence, its use would probably not be beneficial in the treatment of slow-responding prolactinomas, if malignant lactotrophs respond similarly to the normal pituitary lactotrophs. However, the observation of induced apoptosis after hormone and drug withdrawal suggests that agents which promote tumor shrinkage may be effective by causing rapid apoptosis of tumor cells in vivo.

The effect of naloxone on some neuroendocrine responses to limb ischaemia.

The finding that naloxone reverses the arterial hypotension produced by bacterial endotoxin in the rat was confirmed and the effect of naloxone on the responses to another form of injury, limb ischaemia was studied. Naloxone had no effect on the fall in blood pressure and colon temperature or on behaviour and survival after bilateral hind-limb ischaemia. The ambient temperature threshold for the onset of shivering was depressed by limb ischaemia as in untreated rats. The increases in the plasma concentrations of glucose and corticosterone and the decrease in that of prolactin after limb ischaemia were unaltered by naloxone. In control rats naloxone reduced the ambient temperature threshold for the onset of shivering and the plasma prolactin concentration. It is concluded that the endogenous opioids do not play a very significant part in the responses to ischaemic limb trauma.

Transferrin-dependent uptake and dosimetry of Auger-emitting diagnostic radionuclides in human spermatozoa.

UNLABELLED: Localization of Auger-emitting radionuclides within spermatozoa could lead to the induction of transmissible genetic damage. We have quantified in vitro uptake of the widely used diagnostic Auger-emitters, (111)In and 99mTc, by ejaculated human spermatozoa and investigated the role of transferrin in their cellular localization. The resultant dose to sperm heads, including cellular dosimetry for Auger emissions, has been calculated for each radionuclide and compared with that achieved using conventional macrodosimetry. METHODS: Freshly isolated human spermatozoa were incubated in a physiological salt solution containing (111)In-chloride, 99mTc-pertechnetate or the transferrin-binding isotope 59Fe-citrate as a positive control. Cellular uptake mechanisms were investigated with transferrin competition and temperature dependence studies. The percentage uptake of each radionuclide was determined, and the dose to individual sperm heads was calculated using both conventional macrodosimetric methods and by consideration of radionuclide localization and energy deposition at the cellular level, including Auger electron emissions from (111)In and 99mTc. RESULTS: On in vitro incubation, human spermatozoa were found to accumulate (111)In and 59Fe but not 99mTc. Cell uptake of (111)In and 59Fe was transferrin-mediated; however, an alternative transferrin-independent uptake pathway was also present for (111)In. The dose to sperm heads from (111)In, calculated using measured uptake and cellular dosimetry, was found to be larger than that calculated using conventional dosimetry by a factor of more than 100. In contrast, conventional dosimetry was adequate for 99mTc and 59Fe. CONCLUSION: Isolated human spermatozoa appear to accumulate transferrin-binding isotopes, such as the Auger-emitter (111)In. If this uptake mechanism operates in the male reproductive tract, the resultant high dose to the sperm head could indicate that contraception may be advisable after large diagnostic doses of (111)In and, possibly, other transferrin-binding radionuclides. Such precautions could prevent transmission of any genetic damage from irradiated spermatozoa.

Transferrin-mediated uptake of radionuclides by the testis.

UNLABELLED: In an attempt to explain the deleterious effects of gonadal radionuclide localization, we examined the role of transferrin in testicular radionuclide uptake. METHODS: In vivo testicular uptake and retention of the transferrin binding radionuclides 114mIn-citrate and 59Fe-citrate were compared with that of the nontransferrin binding isotopes 137Cs-citrate and Na125I for 63 days postinjection. Isotope uptake mechanisms were investigated in vitro using isolated seminiferous tubules and Sertoli cell monolayers grown in bicameral culture chambers. RESULTS: Indium-114m, 59Fe and 137Cs were localized in the testis by 24 hr postinjection, but accumulation of 125I was minimal. Although testicular 114mIn remained constant, 59Fe declined slowly over the following 63 days and 137Cs fell very rapidly. When 114mIn- or 59Fe-loaded testes were fractionated, and markedly more 114mIn was associated with the seminiferous tubules than 59Fe, suggesting that 114mIn may be retained. In vitro uptake of 59Fe, 67Ga and 114mIn by isolated seminiferous tubules was inhibited by transferrin, but uptake of 137Cs and 125I was unaffected. Iron-59, 67Ga and 114mIn were retained by isolated tubules in contrast to 137Cs and 125I. Whereas 137Cs, 59Fe and 114mIn all crossed Sertoli cell monolayers, the rate of transcellular transport of 137Cs was faster than that of 59Fe or 114mIn, suggesting differences in the intracellular processing of transferrin binding and nontransferrin binding radionuclides. CONCLUSION: These data suggest that some radionuclides may access the seminiferous epithelium through receptor-mediated endocytosis of transferrin. Such radionuclide localization could lead to continuous irradiation of the testes, resulting in mutagenic damage to spermatogenic cells.

Differential depletion of cytoplasmic high affinity oestrogen receptors after the in vivo administration of the antioestrogens, clomiphene, MER-25 and tamoxifen.

1 The in vivo actions of the oestrogen antagonists, MER-25 and tamoxifen upon the cytosol oestrogen receptors prepared from amygdala, hypothalamus, pituitary and uterus of rats were studied 24 h after drug administration. 2 There was a dose-related depletion of cytosol oestrogen receptors. However, the uterine and pituitary receptors were consistently affected at a lower dose than were those from the brain. 3 The ratios of the combined central ED50 to the combined peripheral ED50 were clomiphene 169 greater than MER-25 19.2 greater than tamoxifen 2.13. 4 The receptor changes were not related to biological activity monitored by serum luteinizing hormone levels and uterotrophic response. 5 The possible role of these drug effects in the induction of ovulation and future developments are discussed.

The biological activity of a single dose of tamoxifen in the adult ovariectomized rat.

1 The peripheral and central activities of tamoxifen were studied in the ovariectomized adult rat, up to 16 d after a single dose of 7.0 or 0.7 mg/kg. 2 Food consumption and body weight were decreased; only food consumption returned to control values after 16 d. 3 The weights of the uterus and of the uterine luminal fluid were increased for up to 8 d. 4 Serum follicle-stimulating hormone (FSH) concentrations decreased, but only significantly 1 and 8 d after 7.0 mg tamoxifen/kg. Serum luteinizing hormone (LH) and prolactin concentrations were elevated for up to 4 d. 5 Lordosis behaviour was absent throughout the period studied. 6 Within 3 d of administration, tamoxifen partially antagonized the oestrogen-induced changes in uterine luminal fluid, prolactin and LH secretion and lordosis behaviour. 7 Tamoxifen did not alter oestrogen-induced changes in uterine weight, food consumption and body weight. 8 The experiments demonstrate that tamoxifen is active for up to 16 d after a single intraperitoneal dose; oestrogen agonist, partial agonist and antagonist activities were demonstrated. The duration and type of activity depends upon the dose of tamoxifen and the target tissue response examined.

The specificity of oestrogen receptor in brain, pituitary and uterus.

1 The specificity of oestrogen receptor in rat brain regions (hypothalamus, amygdala and cortex), pituitary and uterus was studied by measurement of the inhibition of 17beta-oestradiol high affinity binding in cytosol, in the presence of unlabelled putative inhibitors of binding. 2 Binding was inhibited only by those of the compounds tested that possessed oestrogen agonist or antagonist activity. The affinities were estimated and the ranking order of the compounds was the same in all tissue sources of cytosol and corresponded to the ranking order of agonist or antagonist potency. 3 There were some significant differences between some of the estimated affinities in different tissues, these being seen most commonly between pituitary and hypothalamus on one hand and uterus on the other. 4 The possibility of heterogeneity of oestrogen receptor is discussed.

Leydig cell resistance to the cytotoxic effect of ethylene dimethanesulphonate in the adult rat testis.

Weekly doses of the Leydig cell cytotoxic ethylene dimethanesulphonate (EDS) were administered to adult male rats in an attempt to study the endocrine activity of the testis in the absence of Leydig cells. One week after the first dose serum testosterone and LH concentrations and seminal vesicle weights were close to levels in castrated rats and testicular human chorionic gonadotrophin (hCG) binding was severely depressed. These changes were maintained for a further week but subsequently began to return to, but did not achieve, control levels. After six weekly doses seminal vesicle weight and serum testosterone concentrations were significantly higher than in the castrated rats. Serum LH concentrations were declining towards control values at 4 weeks but had risen again at 6 weeks. Serum FSH concentrations were raised to about 50% of the value in castrated rats throughout the period studied. Testis weight and hCG binding, which initially fell, were partially restored at 6 weeks and spermatogenesis was recovering. The data show that responses of the testis to multiple doses of EDS are similar to those after a single dose. This apparent resistance indicates that the regenerating Leydig cells are functionally different from the mature Leydig cell. The similarities between the maturing Leydig cell seen after EDS destruction and those in the immature rat suggest that EDS will provide a valuable model for the investigation of Leydig cell physiology.

Changes in brain, pituitary and uterine cytoplasmic oestrogen receptors induced by oestradiol-17beta in the ovariectomized rat.

The oestrogen specific, high-affinity cytosol receptor receptor (HAR) from amygdala, anterior, middle and posterior hypothalamus, pituitary and uterus was studied in the ovariectomized rat. A single in-vivo injection of oestradiol-17beta produced significant changes in both the tissue HAR concentrations and the apparent dissociation constants (Kd) determined in vitro. Four hours after oestradiol-17beta treatment (20 mug/kg), the HAR concentration was depleted in all tissues except the posterior hypothalamus. A lower dose of oestradiol-17beta (4 mug/kg) produced similar changes in HAR concentration with the exception of those in the amygdala and posterior hypothalamus. Twenty-four hours after oestradiol-17beta, HAR concentrations had returned to pre-injection levels in all tissues except the uterus. The uterine HAR concentrations were raised after both doses of oestradiol-17beta. The apparent tissue cytosol Kd values were decreased by both doses of oestradiol-17beta. The results suggest that brain, pituitary and uterine oestrogen cytosol HARs react to plasma oestrogen in a manner predictable by the steroid receptor hypothesis. The oestradiol-17beta-induced differential effects upon the tissue cytosol concentration may contribute to the overall spectrum of action of oestrogen in the central and peripheral reproductive processes.

PIP: Changes in brain, pituitary, and uterine cytoplasmic estrogen receptors induced by estradiol-17beta were studied in the ovariectomized rat. A single in vivo injection of estradiol-17beta produced marked changes in both the tissue high-affinity cytosol receptor (HAR) concentrations and the apparent dissociation constants determined in vitro. 4 hours after estradiol-17beta treatment (20 mcg/kg), the HAR concentration was depleted in all tissues except the posterior hypothalamus. 4 mcg/kg of estradiol-17beta produced similar changesin HAR concentration with the exception of those in the amygdala and posterior hypothalamus. 24 hours after estradiol-17beta HAR concentrations had returned to preinjection levels in all tissues except the uterus. the uterine HAR concentrations were raised after both doses and the apparent tissue cytosol dissociation constant values were decreased by both doses. These data suggest that brain, pituitary and uterine estrogen cytosol HARs react to plasma estrogen in a manner predictable by the steroid receptor hypothesis. The induced differential effects upon the tissue cytosol concentration may contribute to the overall spectrum of action of estrogen in the central and peripheral reproductive process.