Clinical studies on testicular growth and descent

Recent population-based cohort studies indicate that semen quality is declining and simultaneously the incidence of testicular germ-cell cancer is increasing globally. A failure of testicular descent i.e. cryptorchidism and reduced testicular volume are risk factors both for testicular germ-cell cancer and reduced semen quality. Epidemiological and experimental studies suggest that these disorders may originate from testicular dysgenesis and reduced intratesticular androgen action during fetal period, which may be caused by genetic factors or exposure to antiandrogen endocrine disrupters. In this study, we explored postnatal testicular descent and the physiological significance of the so-called ‘minipuberty’, the transient activation of the hypothalamic-pituitary-gonadal axis after birth for postnatal testicular position. In addition, we assessed whether the levels of persistent organic pollutants such as polychlorinated biphenyl (PCBs), polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs, or ‘dioxins’) and polybrominated diphenyl ethers (PBDEs) are associated with congenital cryptorchidism. Finally, we assessed the testicular development during puberty among boys with a history of congenital cryptorchidism. We observed that testicular descent continued until the age of three months, and was followed by a ‘physiological’ testicular ascent, which coincided with the decline in circulating reproductive hormones. We also discovered that the circulating concentration of insulin-like growth factor 1 and hormonal indices reflecting Sertoli and Leydig cell function correlated with testicular position. Our results also suggest that the exposure to dioxins may increase the risk of congenital cryptorchidism. Furthermore, we showed that boys who had a history of congenital cryptorchidism display poor testicular growth during puberty in comparison to controls, which may predispose them to reduced semen quality and subfertility.