Measurement Human Testicular Temperature and Its Interpretation

Scrotal structure is well adapted to serve a local thermoregulatory function. Scrotal skin is thin and is supplied with a large number of sweat glands. There is also little or no subcutaneous fat or connective tissue. The tunica dartos and cremasteric muscles vary in degree of contraction in response to changes in environmental temperature, altering the characteristics of the scrotum itself. In addition, the temperature within the testis is regulated by a countercurrent heat-exchange system between the pampiniform plexus and the testicular artery.

Scrotal temperature measured at the skin surface [23, 165, 166] can change with posture or clothing. Normal scrotal surface temperature (the external surface of the scrotum) is approximately 34°C in a normally clothed man walking about or maintaining a loose stance. Scrotal surface temperature differs from testicular temperature, and testicular temperature within the scrotum is estimated to be between 0.1 and 0.6°C higher than the scrotal surface temperature [24, 167]. Controversies exist regarding the absolute value of the scrotal temperature, because of the different modalities of its measurement. Contact thermometers measure the temperature at a depth of 5-10 mm from the skin [168, 169]. Measurement of deep-body temperature

(CoreTemp CTM204®, Terumo, Tokyo) reflects testicular temperature, but not scrotal surface temperature [169]. Yamaguchi et al. reported the usefulness of deep-body temperature to evaluate patients with varicocele and have shown that deep-body temperature increased in a standing position in patients with varicocele, but decreased in a standing position in men without varicocele [168]. In addition, mean testicular temperature of men without varicocele is reported to be 35.7°C, which is 1-2°C higher than the scrotal surface temperature, but still lower than the core abdominal temperature. Involvement of heat stress in the pathophysiology of vari-cocele, cryptorchidism, or environmental heat exposure is determined by this narrow 2-3°C difference. This means that completely different mechanisms will be observed in animal studies in which transient heat exposure is applied. Furthermore, the impact of other factors such as the pattern of heat exposure (cryptorchidism is continuous and varicocele is intermittent) may also be significant.

Actually, 43°C for 15 min is a good experimental condition to assess the effect of heat on spermatogenesis: heat-induced molecular events occur from minutes to hours after heat exposure, deterioration of spermatogenesis continues for several days to weeks, and then spermatogenesis recovers after 1-2 months. Experimental animals are bred under strict temperature control, which is supposed to minimize the effects of heat stress. On the other hand, humans are usually exposed to environmental stress, including changes in scrotal temperature, all day and all night, and these heat stresses are quite different in each man. Scrotal temperature was measured using a continuous recording system [166, 170, 171] and has since been applied in several studies. Lerch et al. found no difference in mean scrotal temperature between the right and left scrotum in six normal, fertile men, irrespective of whether the temperature was measured during the day or night. In contrast, for scrotal temperature measured over 24 h in 10 fertile men, Jung et al. reported a median value of 34.99°C on the right and 35.29°C on the left side [24]. In a recent study, the same authors found that mean scrotal temperature was significantly higher on the left (35.56°C) than on the right (35.37°C) in 50 clothed, male volunteers, who did not have a history of infertility and had normal results on clinical examination [166],

In humans, testicular temperature may increase as a result of occupational exposure, lifestyle, or a clinical disorder [4] . For example, occupational exposure can occur in men who work in high-temperature environments, such as bakers and welders [172], and also occupations that involve long periods in a sedentary position, such as professional drivers. Recent studies have also reported that posture and clothing can increase the scrotal temperature [172]. Clinical disorders, including cryptorchidism, where one or both testes fail to descend into the scrotum and remain in the abdominal cavity, can also result in exposure of the testes to higher than normal temperatures. Oxidative stress, which is caused by numerous factors, including elevated temperature, is shown to be widely involved in the pathophysiologies of male infertility [8] . Increased oxidative stress in human testes with varicocele has been reported, as shown by elevations of MDA [152], 8-OHdG [173], and 4-HNE-modified proteins [54, 75, 91]. One of the enigmatic issues in human studies is that elevation of testicular temperature does not necessarily result in harmful effects on spermatogenesis. Actually, when elevation of testicular temperature is observed in fertile men with varicocele, testicular oxidative stress is low [105], suggesting that the generation of oxidative stress and expression of antioxidants differ among men. In humans, a more comprehensive understanding is needed to evaluate heat stress, which includes the degree of temperature, its duration, its interval, and basal body temperature.

Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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