Abstract
BACKGROUND: A mild increase in testicular and epididymal temperatures in men, bulls and rams (pendulous scrotum) inhibits spermatogenesis and increases the percentage of sperm with an abnormal morphology. However, the stages of spermatogenesis that are most sensitive to a mild increase in testicular temperature in men are unknown. The aim of the present study was to explore the effects of a mild induced increase in testicular and epididymal temperature (i.e., testicular temperature maintained below the core body temperature) on sperm morphology in humans depending on the physiological time of spermatogenesis and epididymal transit. METHODS: Five healthy volunteers were enrolled in an experimental study in which testicular and epididymal temperatures were increased by maintaining the testes in a supra-scrotal position with a specially designed underwear worn 15±1 h a day for 120 consecutive days. Semen collection was scheduled on specific days depending on spermatogenic stages and epididymal transit. RESULTS: Sperm morphology and the multiple anomalies index (MAI) were analysed before, during and after heating. This mild induced increase in testicular and epididymal temperatures resulted in a significant rise in the percentage of morphologically abnormal spermatozoa on day 34 of heating, which remained elevated throughout the heating period and persisted until 45 days after cessation of heating. The MAI was significantly increased on day 20 throughout the heating period and persisted 45 days after cessation of heating. An increase in the percentage of anomalies in the sperm head, acrosome or tail occurred on days 34 and/or 45 of heating. Abnormal sperm morphology and MAI reverted to control values 73 days after cessation of heating. CONCLUSIONS: A mild sustained increase in testicular and epididymal temperature in man leads morphological abnormalities in spermatozoa mainly due to an impairment of spermiogenesis and meiosis.