437. Whole body heat stress induces selective germ cell apoptosis in mice

Abstract

Introduction: In scrotal mammals, heat stress (43°C/ 20 min) to the scrotum results in germ cell death in the testes1, abnormal spermatozoa, and infertility2 whereas two days of whole body heating (36°C, 12 h/ day) reduces testes weight, sperm numbers and fertility3. The aim of the present study was to determine the intratesticular effects of whole body heating on germ cell maturation and apoptosis. Methods: C57BL/6 mice (n = 16) were housed at 37–38°C for 8 h/ day for 3 days while controls (n = 4) were kept at 23–24°C. Animals from heat treated (n = 4), and control groups (n = 1) were sacrificed at 16 h, 7, 14 and 21 days post exposure to heat. Testes were weighed and analysed by t-test. In testes from each animal, two sections 70µm apart were end labelled for TdT-mediated-dUTP nick (TUNEL). Apoptosis was determined in 200 seminiferous tubules by a colour threshold set in the particle analysis program (Olympus).The tubules were staged as I-VI (early), VII-VIII, IX-X and XI-XII (late) and results analysed using Wilcoxon test. Results: The weights of testes were significantly reduced in heat-treated animals (P < 0.05) at 16 h, 7 and 14 days with no significant difference at 21 days. Apoptosis was significantly higher in the heat-treated group in stages I-VI and XI-XII at 16 h, 7 and 14 days (P < 0.05). In addition, in stages VII-VIII and IX-X apoptosis was significantly higher at 16 h (P < 0.05) with no statistical difference between other time intervals. By day 21, the levels of apoptosis did not differ significantly from the controls in any of the stages (P > 0.05).Conclusion: Whole body heat stress can induce stage and cell specific degeneration of the germ cells in the seminiferous epithelium. The germ cells undergoing apoptosis are spermatogonia, primary spermatocytes and early spermatids. In addition, heat stress produces significant apoptosis of germ cells in the hormone dependent stages VII-VIII immediately after heat stress. (1) Rockett, J.C. et al. (2001) Biol. Reprod. 65:229–239. (2) Banks, S. et al. (2005) Reproduction 129:505–514. (3) Yaeram, J. et al. (2006) Reprod. Fert. Dev. 18:647–653.