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The onset of spermatogenesis occurs during puberty, before adult blood levels of testosterone are achieved. It can be detected early by the presence of spermaturia.1 Sperm maturation is a temperature dependent process and most male mammals have externally sited gonads to maintain testicular hypothermy. In this issue ofADC, Partsch and colleagues (page 364) report the effect of reusable cotton versus plastic lined disposable nappies (diapers) on scrotal skin temperature during infancy and early childhood.2 Studies in adult men showed a strong correlation between intratesticular and scrotal skin temperatures.3 The use of plastic lined nappies resulted in significantly higher mean 24 hour scrotal skin temperatures in the 48 infants and children studied. The cooling effect of scrotal positioned testes can be quantified by measuring the rectoscrotal temperature difference. In one study of 36 normal adult men, examined in the supine position at room temperature, the mean temperature differential was 2.38°C (range 0.8–5.2°C).4
The intrascrotal cavity temperature in a study of boys treated surgically for cryptorchidism was as much as 4.8°C lower than body temperature.5 The highest rectoscrotal temperature difference in Partsch and colleague's study (2.63°C) was observed in toddlers when clothed in cotton nappies. The temperature differential was blunted in all boys after wearing plastic lined nappies, and abolished altogether in just over a quarter of the boys studied.
How is the testis cooled and what are the functional consequences if this does not happen? Thermoregulatory control mechanisms involve modulation of radiant heat loss through thin scrotal skin, which is devoid of fat, and via a countercurrent heat exchange system in the blood vessels of the spermatic cord.6-8 A higher environmental temperature leads to relaxation of the cremasteric and dartos muscles, increased blood flow to an enlarged scrotal skin surface area, and thus …
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