Male Reproductive Functions Disrupted by Pharmacological Agents

In this chapter, we review the male reproductive functions disrupted by medications. Medications can affect the hypothalamic-pituitary-gonad axis, acting as endocrine disrupting chemicals (EDCs). Disturbances may be directly at androgen receptors, modifying the activity of endogenous androgens at the target tissue, or may disrupt feedback loops at the hypothalamus or pituitary resulting in modification of gonadotropin release. Impaired testosterone production and/or spermatogenesis result. Other EDC activities can be indirect via effects on levels of prolactin (PRL), estrogen, cortisol, thyroid hormone, or sex hormone binding globulin (SHBG). Appropriate regulation of these hormones and SHBG are essential for normal reproductive function. An increase in circulating PRL levels is a common adverse medication effect. The consequence is lower gonadotropin and testosterone secretion. Drugs can also have direct toxicity on the seminiferous tubule epithelium, including effects on Leydig cells, Sertoli cells, or germ cells. In some cases, spermatogenesis is severely impaired. After leaving the testis, sperm spend a week or more in the epididymis. It is clear from the timing of some drug effects that sperm are damaged during epididymal transit. There can also be impairment of the ejaculatory reflex, resulting in alterations of emission or expulsion of semen. Even after ejaculation, exposure to seminal plasma can alter sperm function, and some drugs may affect sperm at this stage. The most critical effects on male reproduction are decreased fertility and/or health effects on offspring. These endpoints have received little research attention. Another consideration is the metabolism of drugs. Medications may become more toxic if metabolic systems are suboptimal due to comorbid conditions.