Studies on the structure and function of the mammalian testis. II. Cytological and histochemical observations on the testis of the rat after a single exposure to heat applied for different lengths of time

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Abstract
The scrotal regions of five groups of rats were exposed to a temperature of 43 degrees C for progressively longer periods, ranging from 10 to 30 min in steps of 5 min. The animals were then killed at 3 days, 7 days, 3 weeks and 6 weeks after heat-treatment, and their testes examined by various cytological and histochemical procedures. Appropriate control animals were killed alongside the experimental groups. There was essentially no change seen in the 10 min group. In the 15 min group two critical periods were established where further development of the germ cells failed; the first occurred as cells in the early transitional condition attempted to develop into late transitional forms, while the second operated from late pachytene to the end of the maturation division. This led to what has been termed the pattern of mild heat damage. As the exposure time was increased the pattern of mild heat damage was extended, and after 20 min the two critical periods merged. A third also began to appear, such that while cells in the Golgi phase were able to form cap-phase cells they could not develop into acrosome-phase spermatids. Twenty-five minutes exposure produced a similar result but the third critical period was then firmly established, since neither the Golgi or cap-phase spermatids developed into acrosome-phase spermatids. After 30 min all the previous critical periods were extended and merged and their extreme boundaries marked two new critical periods, one operating at the spermatogonial level and the other at the acrosome-phase. In animals treated for 15, 20 and 25 min there was a variable degree of recovery which occurred between 7 and 21 days after heating, during which time the critical periods disappeared. The damage to the germinal epithelium was accompanied by an increase in the lipid content of the Sertoli cells which progressively gave a red colour with Nile blue (non-acidic) and a positive reaction to Schultz's test for unsaturated sterols. This effect is interpreted as an indirect one resulting from the damage to the germinal epithelium and the cessation of spermatogenic activity. The high lipid/sterol content of the Sertoli cells was reduced to normal levels with the recovery of the germinal epithelium, notably during the maturation division of the primary and secondary spermatocytes corresponding to stages IX-XIV of the cycle of the seminiferous epithelium. Injections of follicle-stimulating hormone (FSH) into rats exposed to the heat for 30 min did not reduce the lipid/sterol content of the Sertoli cells to normal levels as found previously when the same gonadotrophin was administered to oestrogen-treated rats. This is attributed to the extensive damage caused to the germ cells in the 30 min group. The work on the heat-treated animals provides further evidence in support of the view that the lipids/sterols of the Sertoli cells represent material normally utilized by the germ cells in the course of their development; it emphasizes that the cells which primarily use this material are the spermatocytes and finally suggests that the last-mentioned cells govern or regulate sterol metabolism by the Sertoli cells. The Leydig cells in all groups appeared to be unaffected by the heat-treatment.