Testicular hyperthermia reduces testosterone concentrations and alters gene expression in testes of Nelore bulls

Increased testicular temperature reduces sperm motility, morphology and fertility. Our objectives were to characterize effects of testicular hyperthermia (scrotal insulation) on acute testosterone concentrations and gene expression in Bos indicus testes. Nelore bulls (n = 20), ∼27 mo of age, 375 kg, scrotal circumference >31 cm, with ≥30% motile sperm, were allocated into four groups (n = 5/group): non-insulated (Control) and insulation removed after 12, 24, or 48 h. Immediately after insulation, intratesticular temperatures (needle thermocouples) were coolest in Control bulls and warmest in 48-h bulls (mean ± SEM, 35.28 ± 0.31 vs 38.62 ± 0.57 °C, P < 0.05). Bulls were castrated and testes recovered. Testicular testosterone concentrations were higher in Control versus 48-h bulls (3119 ± 973.3 and 295.5 ± 122.8 ng/g of tissue, respectively, P < 0.05). Total RNA was extracted, reverse transcribed and RT-qPCR done. For STAR, mRNA abundance decreased from Control to 48 h (1.14 + 0.32 vs 0.32 + 0.5, P < 0.05). For BCL2, expression decreased from Control to 24 h (1.00 + 0.07 vs 0.70 + 0.12, P < 0.05), but then rebounded. In addition, GPX1 had a 70% increase (P < 0.05) at 48 h, whereas HSP70 had a 34-fold increase (P < 0.05) at 12 h and 2- and 14-fold increases (P < 0.05) at 24 and 48 h, respectively. HSF1, BAX, P53 and CASP 8 remained unchanged. Downregulation of STAR, critical in androgen production, was consistent with reduced testosterone concentrations, whereas increased GPX1 enhanced testicular antioxidative capability. Huge increases in HSP70 conferred protection again apoptosis and cell destruction, whereas reduced BCL2 promoted apoptosis. These findings provided novel insights into acute tissue responses (testosterone and gene activity) to testicular hyperthermia in B. indicus bulls.