Reproductive toxicology of methyldopa in male F344/N rats

The impact of drugs on male fertility: a review

Beside cytotoxic drugs, other drugs can impact men's fertility through various mechanisms. Via the modification of the hypothalamic-pituitary-gonadal axis hormones or by non-hormonal mechanisms, drugs may directly and indirectly induce sexual dysfunction and spermatogenesis impairment and alteration of epididymal maturation. This systematic literature review summarizes existing data about the negative impact and associations of pharmacological treatments on male fertility (excluding cytotoxic drugs), with a view to making these data more readily available for medical staff. In most cases, these effects on spermatogenesis/sperm maturation/sexual function are reversible after the discontinuation of the drug. When a reprotoxic treatment cannot be stopped and/or when the impact on semen parameters/sperm DNA is potentially irreversible (Sulfasalazine Azathioprine, Mycophenolate mofetil and Methotrexate), the cryopreservation of spermatozoa before treatment must be proposed. Deleterious impacts on fertility of drugs with very good or good level of evidence (Testosterone, Sulfasalazine, Anabolic steroids, Cyproterone acetate, Opioids, Tramadol, GhRH analogues and Sartan) are developed.

Cardiovascular/Pulmonary Medications and Male Reproduction

Cardiovascular and respiratory medications are used by men of reproductive age although use of the former is most prevalent in advanced age. Many of these drugs have been associated with sexual dysfunction, including erectile and ejaculatory dysfunction, but for most there is insufficient evidence to link their use with testicular dysfunction, reduced semen quality or infertility. Some exceptions are the irreversible α₁-adrenergic antagonist phenoxybenzamine, which carries a high risk of retrograde ejaculation; the specific α_1A-adrenergic antagonists silodosin and tamsulosin, used primarily to treat BPH/lower urinary tract symptoms, which can cause retrograde ejaculation; and the peripheral β₁-adrenergic antagonist atenolol, used to treat hypertension, which may decrease testosterone/free-testosterone levels. In this chapter, we review the evidence available regarding adverse reactions on male reproduction of adrenergic receptor agonists/antagonists, calcium channel blockers, angiotensin converting enzyme (ACE) inhibitors, diuretics, digoxin, and hydralazine. For some of these medications, there is some evidence for male reproductive effects, along with some solid work in experimental and companion animal species suggesting negative effects. In contrast, and of special note, are calcium channel blockers, which have long been included on lists of medications with the potential to cause male infertility. This turns out to be a good example of a substance with profound effects on sperm function in vitro, but with limited evidence for in vivo effects on semen quality or fertility, even in experimental species. We hope that the evidence provided in this chapter will stimulate additional studies for these important classes of medications.

Detection of Effects on Male Reproduction—A Literature Survey

The 1CH (International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use) Guideline for Detection of Toxicity to Reproduction for Medicinal Products, adopted at the Second ICH Conference in Orlando, FL, U.S.A., emphasized the need for research into the suitability of various methods for the detection of effects on fertility in males. The current project was undertaken to compare the efficiency of methods by evaluating reports in the open literature. The results of the examination of 117 substances or substance classes support the view that histopathology and organ weight analysis provide the best general-purpose means of detecting substances with the potential to affect male fertility. Examinations at up to 4 weeks of treatment appear to be as effective as examinations conducted at later times. Mating with females for detection of effects unrelated to interference with sperm production appears to provide an optimal combination because adding other methodologies does not materially improve the detection rate. As to the timing of the mating trial, a 2-week premating period is as efficient as mating at 4 weeks and apparently more efficient than mating after prolonged premating treatment.

Increased sensitivity to testicular toxicity of transplacental benzo[a]pyrene exposure in male glutamate cysteine ligase modifier subunit knockout (Gclm-/-) mice

Polycyclic aromatic hydrocarbons (PAHs), like benzo[a]pyrene (BaP), are ubiquitous environmental pollutants formed by the incomplete combustion of organic materials. The tripeptide glutathione (GSH) is a major antioxidant and is important in detoxification of PAH metabolites. Mice null for the modifier subunit of glutamate cysteine ligase (Gclm), the rate-limiting enzyme in GSH synthesis, have decreased GSH concentrations. We investigated the effects of Gclm deletion alone on male fertility and spermatogenesis and its effect on the sensitivity of male embryos to the transplacental testicular toxicity of BaP. Gclm-/- males had dramatically decreased testicular and epididymal GCL enzymatic activity and total GSH concentrations compared with Gclm+/+ littermates. Ratios of reduced to oxidized GSH were significantly increased in Gclm-/- testes. GSH reductase enzymatic activity was increased in Gclm-/- epididymides. We observed no changes in fertility, testicular weights, testicular sperm head counts, or testicular histology and subtle changes in cauda epididymal sperm counts, motility, and morphology in Gclm-/- compared with Gclm+/+ males. Prenatal exposure to BaP from gestational day 7 to 16 was dose dependently associated with significantly decreased testicular and epididymal weights, testicular and epididymal sperm counts, and with vacuolated seminiferous tubules at 10 weeks of age. Gclm-/- males exposed prenatally to BaP had greater decreases in testicular weights, testicular sperm head counts, epididymal sperm counts, and epididymal sperm motility than Gclm+/+ littermates. These results show no effects of Gclm deletion alone on male fertility and testicular spermatogenesis and subtle epididymal effects but support increased sensitivity of Gclm-/- males to the transplacental testicular toxicity of BaP.

Knockout of the transcription factor NRF2 disrupts spermatogenesis in an age-dependent manner

Oxidative stress occurs when generation of reactive oxygen species (ROS) overwhelms antioxidant defenses. Oxidative stress has been associated with male infertility. The transcription factor nuclear factor-erythroid 2-related factor 2 (NRF2) regulates basal and inducible transcription of genes encoding enzymes important for protection against ROS. We hypothesized that deletion of the Nrf2 gene causes testicular and epididymal oxidative stress, which disrupts spermatogenesis. Our results show that male Nrf2(-/-) mice have decreased fertility compared to wild-type and heterozygous littermates, due to accumulating seminiferous tubule damage with increasing age. Testicular sperm head counts, epididymal sperm counts, and epididymal sperm motility in 2-month-old Nrf2(-/-) males did not differ from those of wild-type littermates; however, by age 6 months, Nrf2(-/-) males had 44% lower testicular sperm head counts, 65% lower epididymal sperm counts, and 66% lower epididymal sperm motility than wild-type males. Two- to 4-month-old Nrf2(-/-) males had elevated levels of testicular and epididymal lipid peroxidation and testicular germ cell apoptosis, and decreased levels of antioxidants, compared to wild-type males. These results provide evidence that oxidative stress has deleterious effects on the testis and epididymis and demonstrate a critical role for the transcription factor NRF2 in preventing oxidative disruption of spermatogenesis.

Pathogenesis of male reproductive toxicity

Toxicologic disturbance of male reproductive function can occur at many sites and produce a range of effects, some primary and some secondary to the initial insult. The challenge to the toxicological pathologist is to identify the primary site of damage and provide an insight into the pathogenesis of the morphologic lesion or functional deficit. Target sites include the testis, the epididymis, the mature sperm, and the hormonal regulatory system. Detection of effects at these varied sites requires the measurement of multiple endpoints only 1 of which is histopathology, but once identified, careful microscopic examination of the early changes in lesion development can provide essential information on the probable target cell and possible mechanisms of toxicity. Chemicals that affect different cell types or specific cellular functions generally elicit predictable patterns of pathological changes that can be readily recognized. Understanding the pathogenesis, the likely reversibility and the significance of reproductive tract lesions is aided by a sound knowledge of the physiology of the testis and epididymis and, in particular, an understanding of the timing of sperm production and transport.

Effect of hexavalent chromium on testicular maturation in the rat

Daily intraperitoneal administration of hexavalent chromium (Cr6+; 1, 2, and 3 mg/kg intraperitoneally as potassium dichromate) in weaned rats for an entire duration of 55 and 90 days of age produced dose- and duration-dependent enzymatic and pathologic alterations. At 55 days, the pathologic changes were not seen in testes of Cr6+ treated rats, but the activities of sorbitol dehydrogenase, lactic dehydrogenase, gamma-glutamyl transpeptidase, and glucose-6-phosphate dehydrogenase were significantly altered. When the treatment was prolonged to sexual maturity, that is, 90 days of age, the alterations in enzyme activities were greater, and there were dose-dependent pathologic changes in the testes of Cr(6+)-treated rats. These alterations suggest a risk to growing testes if rats are exposed to Cr6+ during the prepubertal stage of development, which, in turn, may disturb normal testicular physiology at adulthood.

Toxicity studies of amphetamine sulfate, ampicillin trihydrate, codeine, 8-methoxypsoralen, alpha-methyldopa, penicillin VK and propantheline bromide in rats and mice

Thirteen-week toxicity studies in F344/N rats and B6C3F1 mice were conducted to determine general toxicity and target organ toxicity with amphetamine sulfate, ampicillin trihydrate, codeine, 8-methoxypsoralen, alpha-methyldopa sesquihydrate, penicillin VK, and propantheline bromide. This paper discusses the toxicity observed; use of the toxicity data to set dose levels for subsequent 2-year studies; and comparison of dose levels administered to rodents with doses used in the treatment of human disease. Drugs were administered orally in the feed or by gavage. The lowest doses in the 13-week studies were comparable to therapeutic doses in man on a mg/m2 (body surface area) basis or 5-10 times doses used in man on a mg/kg body weight basis. Little toxicity was seen at the low dose level with ampicillin, penicillin VK, 8-methoxypsoralen or propantheline bromide. At higher doses, target organ toxicity seen included the urinary bladder in male rats after propantheline bromide; the glandular stomach in rats and mice after penicillin VK; the liver and adrenals in rats after 8-methoxypsoralen; and the kidney in mice and rats after alpha-methyldopa. After amphetamine, codeine, or ampicillin administration, no target organ toxicity was seen in rats or mice, even at doses which caused body weight gain depression. The high doses chosen for subsequent 2-year studies were within 10 times human dose levels when compared on a mg/m2 body surface area.

Mechanistic approaches in the study of testicular toxicity: toxicants that affect the endocrine regulation of the testis

This review will expand on the themes presented by Heindel and Treinen (1988). As a prelude to describing where selected compounds act on the endocrine regulation of the testis and the theories about their mechanisms, we will briefly review some of the central pathways that underlie this control. After reviewing some studies that define the site of action of lead on the reproductive system, we will discuss the "signature" lesion caused by androgen deficiency, and then move on to an evaluation of the effects of an antiandrogen (flutamide) on the male reproductive system. Finally, some consideration will be given to alterations in hepatic function which modify circulating levels of androgens.