Effect of neonatal or adult heat acclimation on testicular and epididymal morphometry and sperm production in rats

The accessory gland weight, testicular and epididymal morphometry and sperm production were analyzed in four groups of rats housed at 20 or 34 °C: (1) control rats (CR) kept at 20 °C from birth to day 90; (2) adult heat-acclimated rats (AHA) kept at 20 °C from birth to day 45 followed by 34 °C to day 90; (3) neonatal heat-acclimated rats (NHA) kept at 34 °C from birth to day 90 and (4) de-acclimated rats (DA) kept at 34 °C from birth to day 45 followed by 20 °C to day 90. In NHA and DA rats, accessory gland weight was higher than in controls. Despite the lack of differences in testicular and epididymal morphometry, curvilinear velocity of spermatozoa was lower in the NHA group compared to controls. Areas of seminiferous tubules were lower in the DA than in CR and NHA groups, however, sperm concentration and motility were not affected by the treatment in this group. In AHA rats, epithelium of approximately 20% of seminiferous tubules was degenerated and Sertoli cell number was lower in the remaining tubules. In contrast to sperm motility, epididymal duct area, area of the duct occupied by spermatozoa and cauda epididymis sperm concentration were lower in AHA rats than in the other groups. In conclusion, neonatal heat acclimation did not affect the testicular morphometry and epididymal sperm concentration, suggesting adjustment to high ambient temperature. On the contrary, adult heat acclimation of rats affected the examined parameters, leading to decreased sperm concentration.