Testosterone Production In Rats Research Articles

Mono-n-hexyl phthalate: exposure estimation and assessment of health risks based on levels found in human urine samples

Mono-n-hexyl phthalate (MnHexP) is a primary metabolite of di-n-hexyl phthalate (DnHexP) and other mixed side-chain phthalates that was recently detected in urine samples from adults and children in Germany. DnHexP is classified as toxic for reproduction category 1B in Annex VI of Regulation (EC) 1272/2008 and listed in Annex XIV of the European chemical legislation REACH; thereby, its use requires an authorisation. Health-based guidance values for DnHexP are lacking and a full-scale risk assessment has not been carried out under REACH. The detection of MnHexP in urine samples raises questions about the sources of exposure and concerns of consumer safety. Here, we propose the calculation of a provisional oral tolerable daily intake value (TDI) of 63 µg/kg body weight/day for DnHexP and compare it to intake levels corresponding to levels of MnHexP found in urine. The resulting mean intake levels correspond to less than 0.2% of the TDI, and maximum levels to less than 5%. The TDI was derived by means of an approximate probabilistic analysis using the credible interval from benchmark dose modelling of published ex vivo data on reduced foetal testosterone production in rats. Thus, for the dose associated to a 20% reduction in testosterone production, a lower and upper credible interval of 14.9 and 30.0 mg/kg bw/day, respectively, was used. This is considered a conservative approach, since apical developmental endpoints (e.g. changed anogenital distance) were only observed at higher doses. In addition, we modelled various scenarios of the exposure to the precursor substance DnHexP from different consumer products, taking measured contamination levels into account, and estimated systemic exposure doses. Of the modelled scenarios including the application of sunscreen (as a lotion or pump spray), the use of lip balm, and the wearing of plastic sandals, and considering conservative assumptions, the use of DnHexP-contaminated sunscreen was highlighted as a major contributing factor. A hypothetical calculation using conservative assumptions for the latter resulted in a margin of safety in relation to the lower credible interval of 3267 and 1007 for adults and young children, respectively. Most importantly, it was found that only a fraction of the TDI is reached in all studied exposure scenarios. Thus, with regard to the reported DnHexP exposure, a health risk can be considered very unlikely.

Efficient aqueous remote loading of peptides in poly(lactic-co-glycolic acid).

Poly(lactic-co-glycolic acid) (PLGA) long-acting release depots are effective for extending the duration of action of peptide drugs. We describe efficient organic-solvent-free remote encapsulation based on the capacity of common uncapped PLGA to bind and absorb into the polymer phase net positively charged peptides from aqueous solution after short exposure at modest temperature. Leuprolide encapsulated by this approach in low-molecular-weight PLGA 75/25 microspheres slowly and continuously released peptide for over 56 days in vitro and suppressed testosterone production in rats in an equivalent manner as the 1-month Lupron Depot®. The technique is generalizable to encapsulate a number of net cationic peptides of various size, including octreotide, with competitive loading and encapsulation efficiencies to traditional methods. In certain cases, in vitro and in vivo performance of remote-loaded PLGA microspheres exceeded that relative to marketed products. Remote absorption encapsulation further removes the need for a critical organic solvent removal step after encapsulation, allowing for simple and cost-effective sterilization of the drug-free microspheres before encapsulation of the peptide.

Chronic intermittent hypoxia stimulates testosterone production in rat Leydig cells

AimsThe hypoxia-stimulated response of the endocrine system depends on the kind and duration of hypoxia. Hypoxia has been reported to stimulate testosterone (T) production in rats, but the mechanisms remain to be investigated. Materials and methodsMale rats were divided into two groups. The rats exposed to chronic intermittent hypoxia (CIH) at 8 h/day were housed in a hypoxic chamber (12% O2) for 14 days. Normoxic rats were used as control animals. T was measured after challenging the rat Leydig cells (LCs) with different stimulators, including hCG (0.01 IU/ml), forskolin (10−5 M), 8-bromo-cAMP (10−4 M), A23187 (10−5 M), cyclopiazonic acid (10−4 M), and androstenedione (10−8 M). Meanwhile, the LCs were incubated with trilostane (10−5 M) and/or 25-OH-hydroxycholesterol (10−5 M); thereafter the media were collected for pregnenolone assay. Key findingsIn the CIH group, plasma T levels were increased, but the serum luteinizing hormone (LH) was decreased. Furthermore, at several time intervals after hCG injection, plasma T levels were higher in the CIH group. The evoked-release of T and pregnenolone were significantly increased in the CIH group. Compared with the normoxic group, the CIH group had higher mRNA and protein expression levels of the LH receptor and CYP11A1 but not StAR. The plasma and testicular microvasculature VEGF levels were increased in the CIH group. The testicular vessel distribution was more obvious in CIH rats. SignificanceCIH-induced T secretion might be partially mediated by mechanisms involving the induction of LH receptor expression, testicular angiogenesis, CYP11A1 activity, 17β-HSD activity, and calcium-related pathway.

Assessment of the analgesic dipyrone as a possible (anti)androgenic endocrine disruptor

Mild analgesics have been associated with antiandrogenic effects, but there are no such studies on dipyrone, despite its high prevalence of use in many countries. We examined the production of steroid hormones in human H295R cells after exposure to dipyrone and two metabolites, 4-Methylaminoantipyrine (MAA) and 4-Aminoantipyrine (AA), as well as fetal testicular testosterone production in rats following maternal dipyrone exposure. Androgen agonistic/antagonistic effects were examined in vitro for dipyrone and its metabolites in the Yeast Androgen Screen (YAS) assay and in vivo for dipyrone through the Hershberger assay. In vitro we tested dipyrone, MAA, and AA (0.1–1000 μM) while in vivo we used dipyrone (50, 100, 200 mg/kg/day). In the H295R assay, dipyrone, MAA and AA reduced the production of androgens and corticosteroids. Testosterone was reduced at concentrations 4–13 times higher than the maximum plasma concentrations reported in humans for MAA and AA. No effects were observed in the fetal testosterone production assay. In the YAS and Hershberger assays, no androgen agonistic/antagonistic activities were observed. These results indicate that dipyrone and its metabolites do not interact with the androgen receptor, but have the potential to inhibit steroidogenesis, however only at concentrations that are not relevant under normal medical use.

Androgenic and Anabolic Possibilities of Mucuna Pruriens

Mucuna pruriens is an Indian legume composed by high amounts of proteins and carbohydrates and small concentration of lipids. It has been used ethnopharmacologically as hipoglicemic, anti-inflammatory, diuretic, hypolipidemic and mainly to Parkinson Disease treatment. Since Mucuna pruriens improves spermatogenesis, testis weight and increased the production of testosterone in rats, it has been assumed that mucuna has anabolic potential for muscle hypertrophy, so it has been commercially exploited as an ergogenic aid. This mini-review shows, in addition to promoting increased testosterone, increase in epididymal protein, thus confirming that its extracts may have influence on androgenic aspect. Despite this, it is necessary to confirm these findings in humans, since the studies analyzed were made only in animal model.

High-fat diet aggravates 2,2′,4,4′-tetrabromodiphenyl ether-inhibited testosterone production via DAX-1 in Leydig cells in rats

Growing evidence has revealed that a high-fat diet (HFD) could lead to disorders of glycolipid metabolism and insulin-resistant states, and HFDs have been associated with the inhibition of testicular steroidogenesis. Our previous study demonstrated that 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) could increase the risk of diabetes in humans and reduce testosterone production in rats. However, whether the HFD affects BDE47-inhibited testosterone production by elevating insulin levels and inducing related pathways remains unknown. In male rats treated with BDE47 by gavage for 12 weeks, the HFD significantly increased the BDE47 content of the liver and testis and increased the weight of the adipose tissue; increased macrovesicular steatosis in the liver and the levels of triglycerides, fasting glucose and insulin; further aggravated the disruption of the seminiferous epithelium; and lowered the level of testosterone, resulting in fewer sperm in the epididymis. Of note, the HFD enhanced BDE47-induced DAX-1 expression and decreased the expression levels of StAR and 3β-HSD in the testicular interstitial compartments in rats. In isolated primary Leydig cells from rats, BDE47 or insulin increased DAX-1 expression, decreased the expression of StAR and 3β-HSD, and reduced testosterone production, which was nearly reversed by knocking down DAX-1. These results indicated that the HFD aggravates BDE47-inhibited testosterone production through hyperinsulinemia, and the accumulation of testicular BDE47 that induces the up-regulation of DAX-1 and the subsequent down-regulation of steroidogenic proteins, i.e., StAR and 3β-HSD, in Leydig cells.

Acteoside reduces testosterone by inhibiting cAMP, p450scc, and StAR in rat Leydig cells

The present study investigated the in vivo and in vitro effects of acteoside on testosterone production in Sprague-Dawley (SD) rats. The in vivo experiment revealed that acteoside reduced the testosterone level in serum significantly (P<0.05). The in vitro experiment also illustrated that acteoside significantly reduced testosterone production in SD rat Leydig cells in primary culture (P<0.05). Enzyme-linked immunosorbent assay results demonstrated that acteoside significantly reduced the cyclic adenosine 3', 5'-monophosphate (cAMP) level (P<0.05), and Western blot analysis showed that acteoside significantly reduced cholesterol side-chain cleavage enzyme (p450scc) and steroidogenic acute regulatory (StAR) expression (P< 0.05). Hoechst 33342 staining and Western blotting showed that acteoside did not induce apoptosis in Leydig cells. Together, these results suggest that the acteoside-induced reduction in testosterone production in rat may be at least partially due to down-regulation of cAMP, p450scc, and StAR, but not apoptosis.

Menaquinone-4 enhances testosterone production in rats and testis-derived tumor cells

BackgroundVitamin K is essential for the posttranslational modification of various Gla proteins. Although it is widespread in several organs, including the testis, the function of vitamin K in these organs is not well characterized. In this study, we investigated the function of vitamin K in the testis and analyzed its role in steroidogenesis.MethodsEight-week-old male Wistar rats were fed a diet supplemented with menaquinone-4 (MK-4, 75 mg/kg diet), one of the predominant K2 vitamins present in the testis, for 5 weeks. In vivo testosterone levels of the rats' plasma and testes were measured by enzyme-linked immunosorbent assay, and in vitro testosterone levels of testis-derived tumor cells (I-10 cells) maintained in Ham's F-10 medium with 10% fetal bovine serum were measured following treatment with MK-4 (0 to 100 μM) at several time points. Testosterone and cellular protein levels were analyzed with respect to their effects on steroidogenesis.ResultsTestosterone levels in the plasma and testes of MK-4-fed rats were significantly increased compared to those of control rats, with no obvious differences in plasma luteinizing hormone levels. Secreted testosterone levels from I-10 cells were elevated by MK-4, but not by vitamin K1, in a dose-dependent manner independent of cAMP treatment. Western blot analysis revealed that expression of CYP11A, the rate-limiting enzyme in steroidogenesis, and phosphorylation levels of protein kinase A (PKA) and the cAMP response element-binding protein were all stimulated by the presence of MK-4. Enhancement of testosterone production was inhibited by H89, a specific inhibitor of PKA, but not by warfarin, an inhibitor of γ-glutamylcarboxylation.ConclusionsMK-4 stimulates testosterone production in rats and testis-derived tumor cells via activation of PKA. MK-4 may be involved in steroidogenesis in the testis, and its supplementation could reverse the downregulation of testosterone production in elders.

Dietary vitamin K alleviates the reduction in testosterone production induced by lipopolysaccharide administration in rat testis

Vitamin K is essential for the posttranslational modifications of blood coagulation factors and proteins present in the bone matrix. Vitamin K is distributed not only in the liver and bones but is also abundant in the brain, kidney, and gonadal tissues. However, the function of extra-hepatic/bone vitamin K has not been fully elucidated. Previously, we observed that dietary supplementation with vitamin K suppresses inflammation, and vitamin K deficiency decreases testicular testosterone production in rats. Here, we examined whether the dietary vitamin K state affects testicular steroidogenesis in lipopolysaccharide (LPS)-treated rats because vitamin K has anti-inflammatory activity. Male Wistar rats were fed either vitamin K-free or control diets for 35 d, and then intraperitoneally administered LPS (0.5 mg kg(-1) body weight) to induce inflammation for 6 h. Vitamin K deficiency symptoms were not observed in the vitamin K-free diet group; however, the vitamin K levels in the testis were significantly lower in the vitamin K-free diet group than in the control diet group. After LPS treatment, plasma testosterone levels were significantly reduced in the vitamin K-free diet group compared with the control diet group. Testicular mRNA and protein levels of Cyp11a, a rate-limiting enzyme in steroidogenesis, corresponded to plasma testosterone levels. However, plasma luteinizing hormone levels were unaffected by diet and LPS. Phosphorylated nuclear factor κB p65 in the testis was significantly increased in the LPS-treated, vitamin K-free diet group compared with control. These results indicate that dietary vitamin K affects testicular vitamin K levels and ameliorates the LPS-induced reduction in testicular testosterone synthesis. Testicular vitamin K might facilitate the inhibition of inflammation signal transduction and maintain steady levels of testosterone.

Exposure to di(n-butyl)phthalate and benzo(a)pyrene alters IL-1β secretion and subset expression of testicular macrophages, resulting in decreased testosterone production in rats

Di(n-butyl)phthalate (DBP) and benzo(a)pyrene (BaP) are environmental endocrine disruptors that are potentially hazardous to humans. These chemicals affect testicular macrophage immuno-endocrine function and testosterone production. However, the underlying mechanisms for these effects are not fully understood. It is well known that interleukin-1 beta (IL-1β), which is secreted by testicular macrophages, plays a trigger role in regulating Leydig cell steroidogenesis. The purpose of this study was to reveal the effects of co-exposure to DBP and BaP on testicular macrophage subset expression, IL-1β secretion and testosterone production. Adult male Sprague–Dawley rats were randomly divided into seven groups; two groups received DBP plus BaP (DBP + BaP: 50 + 1 or 250 + 5 mg/kg/day) four groups received DBP or BaP alone (DBP: 50 or 250 mg/kg/day; BaP: 1 or 5 mg/kg/day), and one group received vehicle alone (control). After co-exposure for 90 days, the relative expression of macrophage subsets and their functions changed. ED2 + testicular macrophages (reactive with a differentiation-related antigen present on the resident macrophages) were activated and IL-1β secretion was enhanced. DBP and BaP acted additively, as demonstrated by greater IL-1β secretion relative to each compound alone. These observations suggest that exposure to DBP plus BaP exerted greater suppression on testosterone production compared with each compound alone. The altered balance in the subsets of testicular macrophages and the enhanced ability of resident testicular macrophages to secrete IL-1β, resulted in enhanced production of IL-1β as a potent steroidogenesis repressor. This may represent an important mechanism by which DBP and BaP repress steroidogenesis.

Effects of Type 2 Diabetes on Testosterone Production in Male Rats.

Diabetes mellitus (DM) is a grave metabolic disorder illness which gradually deteriorates most systems of the body, including reproductive system. Traditionally, this metabolic disorder is divided into two types: type 1 DM, which is lacking the ability of insulin production, and type 2 DM, which can produce insulin but do not fit the body requirement. The effects of type 2 DM on male reproduction including androgen production in Leydig cells are unclear. To investigate the effect of type 2 DM on testosterone levels in bloodstream and the production in Leydig cells, a type 2 DM model of neonatal streptozotocin injection (nSTZ) was established. In brief, streptozotocin (STZ, 90 mg/kg) was injected to 2-day-old newborn male rats intraperitoneally. The blood glucose levels were measured on day 4 and day 14 of birth to ensure the elevation and normalization of blood glucose, respectively. Thereafter, oral glucose tolerance test (OGTT), the major diagnostic character of type 2 DM, was performed and rats were sacrificed on 8-week of age. The enzymatically dispersed rat Leydig cells (1×105cells/0.5 ml) were prepared and challenged with or without human chorionic gonadotropin (hCG, 0.05 IU/ml), 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP, a membrane permeable analog of cAMP, 10-4M), forskolin (an adenylyl cyclase activator, 10-5M), A23187 (a calcium ionophore, 10-5M), and 25-hydroxy-cholesterol (a precursor of steroidogenesis, 10-5M) at 34°C under aeration of 95% O2 and 5% CO2 for 60 min. In nSTZ rats, the blood glucose of 4-day-old rats was over 300 mg/dl and returned to 120 mg/dl or less in 14-day-old animals. In 8-week-old rats, the basal plasma glucose levels were normal; however, the OGTT revealed poor glucose tolerance and the plasma glucose remained higher than 450 mg/dl at 120 min following OGTT. Rats were sacrificed 3 days after OGTT. Our results indicated that in type 2 DM rats, the plasma testosterone levels dropped to about 50% of that in the normal control group (n=6, p<0.05). Moreover, the testosterone secretion from Leydig cells (1×105cells/h) was tremendously reduced to one fifth of that in the normal control group (n=3, p<0.05) in basal condition. In chemical-evoked conditions, the stimulated testosterone secretion was lower (70% by hCG; 51% by 8-Br-cAMP. n=3, p<0.05) in neonatal STZ-injected rats as compared with control animals. These results suggested that in nSTZ type 2 DM rats, the metabolic abnormalities decreased the secretion of testosterone. Type 2 DM attenuated the basal release and chemical responsiveness of testosterone production in rat Leydig cells. It is a novel finding that type 2 DM inhibited the testosterone secretion and then caused sexual dysfunction.

Chronic Effects of Amphetamine and Methamphetamine on the Testosterone Production in Rats.

Chronic Effects of Amphetamine and Methamphetamine on the Testosterone Production in Rats.

Assessment of in vitro effects of metyrapone on Leydig cell steroidogenesis

Metyrapone, a specific inhibitor of 11β-hydroxylase inhibits glucocorticoid production and it is used in the diagnosis/treatment of hypercortisolism and also to test the functional integrity of hypothalamo-pituitary-adrenal axis. To assess the impact of glucocorticoid deficiency, this drug is preferred over adrenalectomy, which eliminates all the hormonal secretions of the adrenal cortex and medulla. However, whether metyrapone has any direct effect on the extra-adrenocortical cellular or tissue functions remains to be resolved. Our previous study showed a depressed testicular Leydig cell testosterone production in rats treated with metyrapone. Therefore, the present study was designed to examine the possible direct effect of metyrapone on testicular Leydig cell steroidogenesis in vitro. Leydig cell viability and the reactive oxygen species (ROS) concentration were not altered by any of the concentration of metyrapone tested. The efficacy of Leydig cell testosterone production under basal as well as LH-stimulated condition was not altered by metyrapone treatment. Further, Leydig cellular 14C-glucose oxidation, the activity and mRNA levels of cytochrome side chain cleavage (P 450scc), 3β- and 17β-hydroxysteroid dehydrogenase (3β-HSD and 17β-HSD) were not altered in metyrapone-treated cells. Therefore, it is concluded from the present study that metyrapone has no direct effect on Leydig cell testosterone production and, therefore, changes recorded in the in vivo studies are exclusively due to corticosterone deficiency.

The Testosterone Test: Phthalate Inhibits Leydig Cell Aggregation

Vol. 115, No. 3 EnvironewsOpen AccessThe Testosterone Test: Phthalate Inhibits Leydig Cell Aggregation Julia R. Barrett Julia R. Barrett Search for more papers by this author Published:1 March 2007https://doi.org/10.1289/ehp.115-a153aCited by:1AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Testicular cancer and low sperm count are adult disorders, but evidence increasingly suggests they have a fetal origin. Cryptorchidism and hypospadias, apparent at birth, also appear linked to prebirth events. According to the testicular dysgenesis syndrome (TDS) hypothesis, all four disorders, which by some reports have become more common in recent decades, partially stem from fetal abnormalities in testosterone-producing Leydig cells. An investigation now reveals that di(n-butyl) phthalate (DBP) and its metabolite monobutyl phthalate (MBP) suppress testosterone production in rats and primates [EHP 115:390–396; Hallmark et al.]. Attempts to establish in vitro models were unsuccessful, however.In rats, prenatal exposure to DBP can induce Leydig cell changes and TDS-like effects. Chronic, low-level exposure to DBP and other phthalates, widely used as plasticizers, is common among humans, but it is unknown if it causes the same effects. The primary goal of the current study was to determine whether effects seen in rats could be replicated in vitro with fetal rat and human testis explants (extracted tissue maintained in culture). The team also conducted experiments in male infant marmosets, whose neonatal testosterone production mirrors that of human males.Preliminary work revealed that rats with prenatal DBP exposure produced significantly less testosterone and had more medium or large Leydig cell clusters. This is notable because larger clusters are associated with defective testicular development. Rat fetal testis explants, however, showed only minor MBP-related effects, and results from comparable human explants were even less conclusive.Because known in vivo reactions could not be replicated in vitro—indicating either a problem with the method or misidentification of the active metabolite—the team tested MBP in marmosets. In five sets of marmoset twins, one twin was exposed to MBP for two weeks while the other served as a control. Blood testosterone levels did not differ significantly, but Leydig cell numbers and size were consistently increased in the MBP group.Because low testosterone triggers increased secretion of luteinizing hormone, which stimulates Leydig cell testosterone production, the researchers checked whether there was an initial MBP-associated suppression in testosterone production. They found that a single dose of MBP in newborn marmosets significantly reduced testosterone levels within hours. This finding led to the hypothesis that increased luteinizing hormone secretion compensates for an initial MBP-associated inhibition of testosterone production, which the researchers conclude should be considered in future animal studies. They also conclude that in vivo marmoset research represents the best current means for investigating the steroidogenic effects of DBP relevant to humans.Testicular effectThe numbers and size of Leydig cells (in brown, above) increased in MBP-treated marmosets.FiguresReferencesRelatedDetailsCited by Orsi A, Rees D, Andreini I, Venturella S, Cinelli S and Oberto G (2011) Overview of the marmoset as a model in nonclinical development of pharmaceutical products, Regulatory Toxicology and Pharmacology, 10.1016/j.yrtph.2010.12.003, 59:1, (19-27), Online publication date: 1-Feb-2011. Vol. 115, No. 3 March 2007Metrics About Article Metrics Publication History Originally published1 March 2007Published in print1 March 2007 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Sensitivity analysis for nonrandom dropout: a local influence approach.

Diggle and Kenward (1994, Applied Statistics 43, 49-93) proposed a selection model for continuous longitudinal data subject to nonrandom dropout. It has provoked a large debate about the role for such models. The original enthusiasm was followed by skepticism about the strong but untestable assumptions on which this type of model invariably rests. Since then, the view has emerged that these models should ideally be made part of a sensitivity analysis. This paper presents a formal and flexible approach to such a sensitivity assessment based on local influence (Cook, 1986, Journal of the Royal Statistical Society, Series B 48, 133-169). The influence of perturbing a missing-at-random dropout model in the direction of nonrandom dropout is explored. The method is applied to data from a randomized experiment on the inhibition of testosterone production in rats.

DROPOUTS IN LONGITUDINAL STUDIES: DEFINITIONS AND MODELS

The widely used distinction of Little and Rubin [1] about types of randomness for missing data presents difficulties in its application to dropouts in longitudinal repeated measurement studies. In its place, a new typology of randomness for dropouts is proposed that relies on using a survival model for the dropout process. In terms of a stochastic process, dropping out is a change of state. Then, the longitudinal measures and dropout processes can be modeled simultaneously, each conditional on the complete previous history of both repeated measures and states. In this context, Poisson regression is used to fit various proportional hazards models, some of which are new, to the dropout process using the longitudinal measurements responses as time-varying covariates. As examples of longitudinal measurement studies displaying nonrandom dropout processes, a dental study of testosterone production in rats and clinical trials for treatment of gallstones and of depression are analyzed.

Regulation of thyroid hormones on the production of testosterone in rats

Regulation of thyroid hormones on the production of testosterone in rats

Regulation of thyroid hormones on the production of testosterone in rats

The effects of a thyroidectomy and thyroxine (T4) replacement on the spontaneous and human chorionic gonadotropin (hCG)-stimulated secretion of testosterone and the production of adenosine 3',5'-cyclic monophosphate (cAMP) in rat testes were studied. Thyroidectomy decreased the basal levels of plasma luteinizing hormone (LH) and testosterone, which delayed the maximal response of testosterone to gonadotropin-releasing hormone (GnRH) and hCG in male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored the concentrations of plasma LH and testosterone to euthyroid levels. Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH, and testicular testosterone as well as the LH response to GnRH and testosterone response to hCG in vitro. T4 replacement in Tx rats restored the in vitro release of GnRH, GnRH-stimulated LH release as well as hCG-stimulated testosterone release. Administration of T4 in vitro restored the release of testosterone by rat testicular interstitial cells (TICs). The increase of testosterone release in response to forskolin and androstenedione was less in TICs from Tx rats than in that from sham Tx rats. Administration of nifedipine in vitro resulted in a decrease of testosterone release by TICs from sham Tx but not from Tx rats. The basal level of cAMP in TICs was decreased by thyroidectomy. The increased accumulation of cAMP in TICs following administration of forskolin was eliminated in Tx rats. T4 replacement in Tx restored the testosterone response to forskolin. But the testosterone response to androstenedione and the cAMP response to forskolin in TICs was not restored by T4 in Tx rats. These results suggest that the inhibitory effect of a thyroidectomy on the production of testosterone in rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH and its response to GnRH; 2) the decreased response of TICs to gonadotropin; and 3) the diminished production of cAMP, influx of calcium, and activity of 17beta-HSD. T4 may enhance testosterone production by acting directly at the testicular interstitial cells of Tx rats.

Quinalphos-induced suppression of spermatogenesis, plasma gonadotrophins, testicular testosterone production, and secretion in adult rats

Quinalphos (O,O-diethyl-O-[quinoxalinyl-(2)-thionophosphate]) is a well-known organophosphorus insecticide used extensively in agriculture that adversely interferes with the activity of testicular steroidogenic enzymes in rats. To investigate its effects on spermatogenesis, the other function of testes, quantitative evaluation of different varieties of germ cells at stage VII of the seminiferous epithelium cycle, namely, type A spermatogonia (ASg), preleptotene spermatocytes (pLSc), midpachytene spermatcytes (mPSc), and step 7 spermatids (7Sd), along with the radioimmunoassay of plasma FSH, LH, testosterone, and testicular testosterone, were performed in Wistar rats following treatment with quinalphos (250 micrograms/kg, ip) for approximately one (13 days) and two cycles (26 days) of the seminiferous epithilium. Massive degeneration of all varieties of germ cells at stage VII, remarkable reduction in the sperm count, and significant reductions in plasma concentrations of FSH and testosterone, along with testicular testosterone, were observed after quinalphos treatment. Significant reduction in the plasma concentration of LH was observed only after treatment for two cycles. Administration of human chorionic gonadotrophin for 26 days in rats injected with quinalphos partially prevented the degeneration of germ cells and increased testosterone production. It is suggested that quinalphos may have a suppressive influence on gonadotrophin release but its direct detrimental action at the level of the testes may also be responsible for the observed changes in spermatogenesis and in testicular testosterone production in rats.

The effect of guanethidine treatment of testicular blood flow and testosterone production in rats

Testicular blood flow was measured by means of Xenon-133 clearance in control rats and rats treated with guanethidine for 3 weeks. Plasma and testis testosterone concentrations were also measured, and the effect of hCG-treatment was examined. No difference in testicular blood flow between the control group and the guanethidine-treated group was found. However, in guanethidine-treated rats, plasma and testis testosterone concentrations after hCG-treatment were significantly decreased. The results may indicate that adrenergic nerves are involved in the regulation of Leydig cell function.