Degenerative changes, such as apoptosis, premature sloughing of cells, or formation of multinucleated giant cells, are readily apparent after exposure to such agents. Factors that negatively affect spermatogenesis include these:  Dietary defciencies. Reduced dietary intake is known to impair spermatogenesis. Vitamins, coenzymes, and microelements such as vitamin A, B12, C, E, -carotenes, zinc, and selenium have been shown to affect sperm formation.  Environmental/lifestyle factors. A recent study con-ducted in Denmark compared the sperm count in two groups of young men from rural and urban populations. A higher median sperm count (24%) was found in the men from the rural group compared with those from the urban group.  Developmental disorders. Cryptorchidism, hypospa-dias, and factors such as low birth weight have been found to be important risk factors for testicular cancer associated with reduced semen quality and reduced fertility.  Systemic diseases or local infections. Infections involving the testis (orchitis) may have an effect on sper-matogenesis. Systemic diseases that can impair sper-matogenesis include fever, kidney diseases, HIV and other viral infections, and metabolic disorders.  Elevated testicular temperature. A sedentary lifestyle may impair the ability to maintain the lower temperature of the testis in the scrotum. A higher than average scrotal temperature has been linked to failure of spermatogenesis. sure to synthetic estrogen (diethylstilbestrol) and other sex steroids can exert negative feedback on FSH secre-tion, resulting in decreased spermatogenesis. Prenatal exposure to estrogens can potentially inhibit fetal go-nadotropin secretion and inhibit Sertoli cell proliferation.  Toxic agents. Mutagenic agents, antimetabolites, and some pesticides, e.g., dibromochloropropane (DBCP), can drastically affect spermatogenesis and production of normal sperm. DBCP is a nematocide pesticide that is still used in some developing countries. It has been shown to cause a major decrease in sperm count and infertility after human exposure. Other agents that may affect fertility include chemicals in plastics (e.g., phtha-lates), pesticides (e.g., DDT), products of combustion (e.g., dioxins), polychlorinated biphenyls (PCBs), and others. Most of these chemicals possess very weak estrogen properties and may affect fertility. Direct toxic-ity to the spermatogonia is linked to changes in sperm quality.  Ionizing radiation and alkylating agents. Nitrogen mustard gas and procarbazine have been found to have toxic effects on spermatogonia. Electromagnetic and mi-crowave radiation also affect sperm count and motility. Proliferating cells are particularly sensitive to mutagenic agents and the absence of essential metabolites. There-fore, nondividing Sertoli cells, Leydig cells, and reserve stem cells, which demonstrate low mitotic activity, are much less vulnerable than actively dividing, differentiating spermatogenic cells.
 FOLDER 22.2 Clinical Correlation: Factors Affecting Spermatogenesis
Spermatogenic cells are very sensitive to noxious agents.  Steroid hormones and related medications. Expo-
Sertoli cells give structural organization to the tubules as they extend through the full thickness of the seminiferous epithelium.