Intrascrotal temperature, testicular histology and fertility of heart-acclimatized rats.

This study investigated intrascrotal and deep body temperatures, reproductive ability, and histological patterns in the testes of heat-acclimatized rats. Albino rats aged 100-110 days were acclimatized to 35 degrees C. and a relative humidity of 25-40% for at least 3 months. There was free access to food and water and 14 hours of light daily. A control group was kept at an ambient temperature of 22 degrees C. and relative humidity of 35-50%. Deep-body temperature was measured with a thermistor probe inserted 4 cm into the rectum. Intrascrotal temperatures were measured with a thermocouple contained in a 27-gauge hypodermic needle inserted into the scrotum after the testes had been displaced. Readings were taken on alternate days for 30 days. Deep-body and intrascrotal temperatures were higher in experminetal than in control animals. Both groups maintained differences between body and intrascrotal temperatures. The intrascrotal temperatures of heat-acclimatized rats resembled the deep-body temperatures of the controls and, therefore, were similar to the environmental temperatures of cryptorchid testes. The mating rate of heat-acclimated males was lower than that of controls and fewer females conceived when mated with experimental males. However, in females which did conceive the type of male had no effect on implantation, pregnancy loss, or number of young. In about 20% of the experimental animals seminiferous tubules showed necrobiosis of germinal epithelium. Slight hyperplasia of Leydig cells was noted. The epididymal epithelium was intact and normal spermatozoa were present in the lumen. It is suggested that the gradient between the internal body termperature and the termperature of the testes is essential for spermatogenesis. Similar temperatures without the gradient, as in cryptorchid testes or heated scrotum, have been shown to be detrimental to spermatogenesis.