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Changes in the seminiferous epithelium of the rat testis occurring within 24 hr after exposure to 43\ s=deg\ C for 15 min were investigated using a quantitative technique. The earliest cytochemical or morphological changes were detected in the pachytene spermatocytes in stages IX to XII, the diakinetic and dividing spermatocytes in stages XIII and XIV and the young spermatids at stage I of spermatogenesis within 1 hr after exposure. The spermatocytes showed changes in the cytoplasm and the spermatids, in the nucleus.The number of abnormal spermatocytes increased progressively with time after the exposure and the damage was detectable in more stages at later time intervals. Within 4 hr after exposure, the damage could also be detected in pachytene spermatocytes at stages VII and VIII, as well as through all the stages up to XIV. The pachytene, diakinetic and dividing spermatocytes from stages IX to XIV were essentially absent 24 hr after the exposure, and those at stages VII and VIII showed a drastic reduction in count. Similarly, a progressive increase in the number of abnormal spermatids was noted, associated with an intensification of the morphological changes in the nucleus characterized by typical ring formation pyknosis and chromatolysis. The sequence of degenerative changes varied considerably between spermatids and spermatocytes\p=m-\the former showing the earliest changes in the nucleus, and the latter in the cytoplasm.These findings extend and confirm earlier observations on the specific susceptibility of testicular germinal cells to heat. The pachytene, di a\ x=req-\ kinetic and dividing spermatocytes at stages IX to XIV and the young step-1 spermatids are most susceptible to heat under the described experimental conditions.

A quantitative study of changes in the germinal epithelium of rat testes exposed to 43°C for 15 minutes was performed. Testicular tissue was studied at intervals of 2, 4, 6,s and 26 days after exposure to heat. The frequency distribution of the various stages of spermatogenesis, the resting spermatocytes, spermatogonia and Sertoli cells were not affected by the exposure to heat. On the other hand, primary spermatocytes in stage IX (leptotene), to and including dividing spermatocytes in stage XIV, were injured, excepting for pachytene spermatocytes in stages V and VI of spermatogenesis. The spermatids were affected by heat only in step 1 and the early part of step 2 of spermiogenesis. Those beyond step 2 continued to mature and form adult spermatozoa. The data indicate that heat produces selective damage to the germinal epithelium affecting only specific types of germinal epithelium cells.

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