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Basic Chemical Hazards to Human Health and Safety — II
Published in Jack Daugherty, Assessment of Chemical Exposures, 2020
For males, the time required to restore the sperm count is a significant reproductive effect. Any toxic substance that interferes with the control mechanism for the male pituitary hormones, Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH), can lead to male infertility. LH and FSH are regulated by hypothalamic releasing factors, which are controlled by the pituitary and hypothalamus. LH stimulates Leydig cells, which synthesize steroid hormones, particularly testosterone, which controls the activity of accessory sex organs and the development of secondary sexual characteristics. FSH stimulates the Sertoli cells to initiate spermatogenesis and maintain optimal testicular function. Male germ cells are susceptible to toxic insult during the stages of spermatogenesis, in particular, by either being killed or undergoing heritable alterations or suffering non-heritable alterations that affect morphology, motility, and viability. Reduction of sperm count leads to male infertility, while mutated sperm may lead to adverse effects in a fertilized egg. Abnormal sperm raises the probability of spontaneous abortion, still birth, or any number of birth defects.
Reproduction
Published in Alan G. Heath, Water Pollution and Fish Physiology, 2018
In the males, the germ cells in the testes may be in synchronous or variable stages of development, depending on the species. These spermatogonia are surrounded by Sertoli and Leydig cells which provide support and regulation of spermatogenesis (Callard, 1991). The Leydig cells produce the androgens, primarily testosterone, ketotestosterone, and androstenodione. In male brook trout, testosterone and 11-ketostetosterone levels rise at spermiation and then fall rapidly thereafter (Sangalang and Freeman, 1974). “Female” sex steroids are also present in the males, as is testosterone in the female. Sperm production is a synchronous event in some teleosts whereas in others it is cyclic or continuous.
Reprotoxic and Endocrine Substances
Published in Małgorzata Pośniak, Emerging Chemical Risks in the Work Environment, 2020
Katarzyna Miranowicz-Dzierżawska
In males, LH stimulates testosterone secretion by interstitial cells of Leydig (the Leydig cells) and FSH stimulates growth processes of the testicles and induces the production of androgen-binding proteins in Sertoli cells, which are a part of seminiferous tubules, required to maintain sperm maturation processes. The androgen-binding protein ensures a high local testosterone concentration in the testicles, constituting an important factor in the development of proper spermatogenesis (sperm production and maturation). Therefore, sperm cell maturation requires the presence of both LH and FSH.
A male germ cell assay and supporting somatic cells: its application for the detection of phase specificity of genotoxins in vitro
Published in Journal of Toxicology and Environmental Health, Part B, 2020
Khaled Habas, Martin H. Brinkworth, Diana Anderson
Spermatogenesis is a complex process involving division and differentiation of spermatogonial stem cells into mature spermatozoa. The spermatogenesis process comprises several phases, namely the mitosis proliferation of spermatogonial stem cells to differentiate into spermatocytes, which then undergo meiotic divisions. The division of spermatocyte meiosis to produce haploid round spermatids undergoes spermiogenesis, a differentiation process that comprises the shedding of cytoplasm and compaction of the nucleus of spermatids production of a flagellum and undergoes elongation and condensation of the nucleus, creating elongating and condensing spermatids and untimely mature spermatozoa (Wistuba, Stukenborg, and Marc Luetjens 2007).
Mixture analysis of associations between exposure to low levels of multiple metals and semen quality and sperm DNA integrity
Published in Journal of Environmental Science and Health, Part A, 2022
Hueiwang Anna Jeng, Sinjini Sikdar, Yeou-Lih Huang, Chih-Hon Pan
Several limitations of the present study should be considered. A limitation was lack of measurement of metals in seminal plasma. A high percentage of seminal plasma samples had Pb and Cd levels < LOD. To achieve the objective of the study including mixture analysis on metal joint effects, we only used urinary metal levels to ensure a suitable sample size to maintain a certain power. The second limitation was the collection of a single urine and semen sample from each subject for measurement of metals and semen quality, respectively. Some metals have long half-lives, such as Pb; a single biological sample may be sufficient. However, some metals are rapidly excreted. Repeated measurements may be required to reflect exposure status in the period of spermatogenesis, which lasts 65–75 days. The reliability of a single semen sample to represent semen quality continues to be debated. Currently, there is limited evidence to confirm whether one semen sample may be adequately representative of semen quality over several weeks in epidemiologic studies. The third limitation was a lack of detailed dietary intake information. The study included basic dietary intake information. Considering high consumption of seafood and rice of the Asian population, more detailed dietary intake data, such as frequency and quantity of seafood and rice consumption, is recommended to be included in future studies and to be treated as a covariate in mixture analysis. The fourth limitation was the small sample size. However, the sample size still sufficed for yielding a statistical power to detect a 1.5-fold difference between the mean concentrations of the outcomes of semen quality and sperm DNA integrity. We recommended a follow up study with a large sample size to confirm the findings of the study.
Maternal bisphenol A exposure disrupts spermatogenesis in adult rat offspring
Published in Journal of Toxicology and Environmental Health, Part A, 2019
Patricia De Campos, Isabela M. Oliveira, Janaina Sena de Souza, Rodrigo Rodrigues Da Conceição, Gisele Giannocco, Maria I Chiamolera, Magnus R.Dias-Da Silva, Marco A. Romano, Renata Marino Romano
The expression of genes is an important step to cellular function. All types of information are necessary in order for each cell type to develop its function which is stored in DNA in the form of genes. To be functional, DNA is converted into RNA during transcription, which is regulated by stimulation and repression factors, according to cellular function status. In the cytoplasm, the mRNA is recruited by polysomes to be translated into proteins. The proteins develop their functions including binding receptors, acting as enzymes, or constituents of the cell structure. In this manner, the cell regulates its biological function stimulating or repressing genes through transcription and translation processes (Alberts et al. 2002). As mRNA is critical for protein production, the up- or down-regulation of genes by chemicals may markedly affect cellular function. The results of the present study also demonstrated that perinatal exposure to BPA led to a significant reduction in Ar mRNA expression. Androgen receptor is highly expressed in the testes, especially in Sertoli cells; and plays a key role in the maintenance of spermatogenesis, as evidenced by diminished spermatogenesis and lowered response of Leydig cells to testosterone that occurs as a result of a reduction in expression of Ar (Qiu et al. 2013). The action of androgens in spermatogenesis occurs via Sertoli cells, as germinative cells do not possess receptors for androgens and are required for maintenance of blood-testis barrier, adhesion, and release of sperm from Sertoli cells (Smith and Walker 2014). In ArKO mice, a reduction in the number of spermatids was observed, possibly due to a severe disruption of germ cell development and decreased adhesion of spermatids by Sertoli cells (De Gendt et al. 2004; Wang et al. 2006). Interestingly, it is well-established that testosterone stimulates synthesis of AR and stabilizes mRNA (Mora, Prins, and Mahesh 1996), which accumulates in the polysomes (Mora and Mahesh 1999). However, in the present study, the elevation in testosterone levels was accompanied by inhibition in Ar expression, indicating possible multiple effects of BPA on endocrine regulation. The reduction in Ar expression might also be involved in the decreased caput and corpus epididymis weight. In contrast, the seminal vesicle fluid was increased in the higher BPA-treated group, indicating that androgen-sensitivity of this tissue is maintained.