Changes in testicular hCG binding and Leydig cell function in rats throughout life

Comparative Study of the Steroidogenic Effects of Human Chorionic Gonadotropin and Thieno[2,3-D]pyrimidine-Based Allosteric Agonist of Luteinizing Hormone Receptor in Young Adult, Aging and Diabetic Male Rats

Low-molecular-weight agonists of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptor (LHCGR), which interact with LHCGR transmembrane allosteric site and, in comparison with gonadotropins, more selectively activate intracellular effectors, are currently being developed. Meanwhile, their effects on testicular steroidogenesis have not been studied. The purpose of this work is to perform a comparative study of the effects of 5-amino-N-tert-butyl-4-(3-(1-methylpyrazole-4-carboxamido)phenyl)-2-(methylthio)thieno[2,3-d] pyrimidine-6-carboxamide (TP4/2), a LHCGR allosteric agonist developed by us, and hCG on adenylyl cyclase activity in rat testicular membranes, testosterone levels, testicular steroidogenesis and spermatogenesis in young (four-month-old), aging (18-month-old) and diabetic male Wistar rats. Type 1 diabetes was caused by a single streptozotocin (50 mg/kg) injection. TP4/2 (20 mg/kg/day) and hCG (20 IU/rat/day) were administered for 5 days. TP4/2 was less effective in adenylyl cyclase stimulation and ability to activate steroidogenesis when administered once into rats. On the 3rd–5th day, TP4/2 and hCG steroidogenic effects in young adult, aging and diabetic rats were comparable. Unlike hCG, TP4/2 did not inhibit LHCGR gene expression and did not hyperstimulate the testicular steroidogenesis system, moderately increasing steroidogenic proteins gene expression and testosterone production. In aging and diabetic testes, TP4/2 improved spermatogenesis. Thus, during five-day administration, TP4/2 steadily stimulates testicular steroidogenesis, and can be used to prevent androgen deficiency in aging and diabetes.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

Cell biology of Leydig cells in the testis

This article reviews results on differentiation, structure, and regulation of Leydig cells in the testes of rodents and men. Two different populations-fetal and adult Leydig cells-can be recognized in rodents. The cells in these two populations are different in ultrastructure, life span, capacity for androgen synthesis, and mechanisms of regulation. A brief survey on the origin, ontogenesis, characterization of precursors, ultrastructure, and functional markers of fetal and adult Leydig cells is presented, followed by an analysis of genes in Leydig cells and the role of luteinizing hormone and its receptor, steroidogenic acute regulatory protein, hydroxysteroid dehydrogenases, androgen and its receptor, anti-Müllerian hormone, estrogens, and thyroid hormones. Various growth factors modulate Leydig cell differentiation, regeneration, and steroidogenic capacity, for example, interleukin 1alpha, transforming growth factor beta, inhibin, insulin-like growth factors I and II, vascular endothelial growth factor, and relaxin-like growth factor. Retinol and retinoic acid increase basal testosterone secretion in adult Leydig cells, but decrease it in fetal Leydig cells. Resident macrophages in the interstitial tissue of the testis are important for differentiation and function of Leydig cells. Apoptosis of Leydig cells is involved in the regulation of Leydig cell number and can be induced by cytotoxins. Characteristics of aging Leydig cells in rodents seem to be species specific. 11beta-hydroxysteroid dehydrogenase protects testosterone synthesis in the Leydig cells of stressed rats. Last, the following aspects of human Leydig cells are briefly described: origin, differentiation, triphasic development, aging changes, pathological changes, and gene mutations leading to infertility.

Changes in lectin binding patterns of Leydig cells during fetal and postnatal development in mice

Changes in the lectin binding of mouse Leydig cells during fetal and postnatal development were examined by light- and electron-microscopy using eight different biotinylated lectins (ConA, WGA, RCA-I, UEA-I, GS-I, PNA, SBA and GS-II). At the light-microscopic level, ConA, WGA, RCA-I, UEA-I and GS-I showed the same binding pattern in which all five lectins bound to the plasma membrane and cytoplasm of Leydig cells from the 13th day post coitum (p.c.) to the 8th postnatal week. PNA, SBA and GS-II reactions were positive in the plasma membrane and cytoplasm of Leydig cells from the 13th day p.c. to 15th day post partum (p.p.) but disappeared completely by day 20. At the electron-microscopic level, gold particles representing the GS-I or GS-II binding sites were distributed primarily along the cell surface membrane, including that of microvilli, as well as in the cytoplasm. These results indicate that certain glycoconjugates bearing D-galactose, N-acetyl-D-galactosamine, and N-acetyl-D-glucosamine residues are expressed on the cell surface and in the cytoplasm of Leydig cells during the period from the 13th day p.c. to around the 20th day p.p. The results suggest that these glycoconjugates might play some role in modulating hormone-receptor interaction in the Leydig cells before the 20th day. Furthermore, these results may indicate that sugar residues expressed on the cell surface and in the cytoplasm of Leydig cells are different from those in the fetal-neonatal and adult phases.

Sertoli and Leydig cell numbers and gonadotropin receptors in rat testis from birth to puberty

In testes of rats from 2 to 60 days of age, we examined the number of Sertoli cells (SC) and Leydig cells (LC) as well as the binding of radioiodinated gonadotropins to frozen sections and homogenates. The number of SC per testis increased only during the first 2 postnatal weeks, whereas that of LC was stable up to days 7-10 and increased thereafter. The uptake of 125I-labelled human follicle-stimulating hormone (125I-FSH) to frozen sections was confined to sex cords or seminiferous tubules, while that of 125I-labelled human choriogonadotropin (125I-hCG) matched the distribution of LC in the interstitium. High affinity receptors for FSH and hCG were found in homogenates at all stages studied. The number of FSH receptors per testis increased steadily, whereas that of hCG receptors was low until days 7-10 and rose afterwards. Thus, SC in rat testis appear to proliferate in the presence of fetal LC during the first 2 postnatal weeks and to differentiate concomitantly with the emergence of the adult LC generation after day 10. The complement of FSH receptors in SC remains constant as they proliferate and increases after day 21 as they differentiate. The hCG receptor number is relatively fixed in each LC generation, being higher in adult compared to fetal LC.

Epididymal sperm profiles in young adult, middle-aged, and testosterone-supplemented old rats

Both ejaculated semen and epididymal contents from an individual male contain sperm that differ in various physicochemical characteristics. An experiment is reported in which epididymides from rats 5-24 months old were subjected to density gradient centrifugation to separate gametes of different stages of maturity. The research was designed to examine typical changes in "profiles" of sperm maturity during the reproductive lifetime of rats. Also, testosterone complexed with cyclodextrin that mimics the episodic release of the endogenous hormone was used to supplement the decreased circulating titers of some of the old males. Results revealed clear ontogenetic patterns of gradually decreasing reproductive competence as measured by absolute numbers of sperm, circulating levels of testosterone, and various other physiological markers of fertility. Sperm profiles also revealed age-specific changes with a shift toward progressively more mature, perhaps senile, gametes that begins at middle age. Testosterone supplementation (400 micrograms/kg b.w./day for 30 days) failed to restore sperm numbers or other measures of physiology in the old males, but the steroid modified sperm profiles to approximate more closely the profiles characteristic of young adult males than either untreated middle-aged or old males. The data were interpreted as suggesting that epididymal sperm profiles clearly identify males of different ages, and that the aging epididymis retains its capacity to respond to manipulations that modify the endocrine milieu.

Lighting conditions affect the levels of plasma gonadotropins differently in old and young castrated male rats

It has been suggested that the decreased plasma levels of FSH and LH, often found in old male rats, are due to a diminished adenohypophyseal capacity to secrete the hormones and/or by changes in the hypothalamic regulatory system. We studied the effect of varying lighting conditions (12/12 h LD, continuous light and continuous darkness) on the plasma levels of the gonadotropins in castrated young adult and old male rats. We expected the sensitivity of the regulatory system to light to decrease or disappear with aging. The results for FSH supported this hypothesis: the plasma levels of FSH were more stable to changes of lighting conditions in the old rats. In disagreement with our hypothesis, the levels of LH were more sensitive to light changes in old than in young rats. It was concluded that the regulatory systems of the two hormones vary differently with age.

Testicular LH receptors during aging in Fisher 344 rats

Levels of serum LH, prolactin, testosterone, progesterone and 17-OH progesterone and the testicular concentration and total content of LH receptors were measured in 4-, 11-, 18-, and 27-month-old Fisher 344 rats. All 27-month-old rats had Leydig cell tumors. At first, testicular LH receptor levels decreased with age, but with the appearance of the testicular tumors, these levels increased dramatically. Serum prolactin levels fluctuated with age, but were significantly decreased in 27-month-old rats, as were serum LH levels. Serum testosterone levels decreased steadily with age, while the testosterone-LH receptor ratio remained constant until the appearance of the testicular tumors, after which the ratio decreased precipitously. Serum progesterone levels remained constant throughout the life of Fisher 344 rats until the appearance of testicular tumors, when they increased dramatically. Serum 17-OH progesterone levels were increased significantly at 11 and 27 months as compared to four months of age, but levels at 18 months were similar to those seen in the 4-month-old animals. Therefore, in aged Fisher 344 rats with spontaneous Leydig cell tumors, there is an alteration in the testicular testosterone synthesizing pathway at a step after progesterone.

Testicular blood flow in young and old rats and influence of hCG

To evaluate the influence of age, testicular capillary blood flow (TCBF) was measured, using the microsphere technique, in rats 3 to 24 months old, under basal conditions and after hCG stimulation (10 IU/d for two days). Despite a decline in plasma T levels, testicular capillary blood flow did not decrease with age, and hCG stimulation resulted in similar increases of approximately 50% (P less than 0.01) in testicular capillary blood flow in all age groups. We concluded that the age-associated decrease in testosterone secretion in rats is not the consequence of a decreased testicular blood flow.

Changes in the mechanisms of hormone and neurotransmitter action during aging: current status of the role of receptor and post-receptor alterations. A review

Alterations in responsiveness to hormones and neurotransmitters during aging appear to be due to changes at both the receptor and post-receptor levels. Although many such observations have now been independently confirmed, disagreement over the extent and/or importance of receptor alterations exists in a number of cases. Receptors do not appear to change with age in certain systems, but only a few reports have actually been able to localize particular post-receptor alterations responsible for changes in response. This review attempts to catalogue studies in these areas which have been carried out to date, and discusses possible reasons for discrepancies as well as future research directions.