Testicular hyperthermia increases blood flow that maintains aerobic metabolism in rams

Abstract

There is a paradigm that testicular hyperthermia fails to increase testicular blood flow and that an ensuing hypoxia impairs spermatogenesis. However, in our previous studies, decreases in normal and motile spermatozoa after testicular warming were neither prevented by concurrent hyperoxia nor replicated by hypoxia. The objective of the present study was to determine the effects of increasing testicular temperature on testicular blood flow and O2 delivery and uptake and to detect evidence of anaerobic metabolism. Under general anaesthesia, the testicular temperature of nine crossbred rams was sequentially maintained at ~33°C, 37°C and 40°C (±0.5°C; 45min per temperature). As testicular temperature increased from 33°C to 40°C there were increases in testicular blood flow (13.2±2.7 vs 17.7±3.2mLmin−1 per 100g of testes, mean±s.e.m.; P<0.05), O2 extraction (31.2±5.0 vs 47.3±3.1%; P<0.0001) and O2 consumption (0.35±0.04 vs 0.64±0.06mLmin−1 per 100g of testes; P<0.0001). There was no evidence of anaerobic metabolism, based on a lack of change in lactate, pH, HCO3− and base excess. In conclusion, these data challenge the paradigm regarding scrotal–testicular thermoregulation, as acute testicular hyperthermia increased blood flow and tended to increase O2 delivery and uptake, with no indication of hypoxia or anaerobic metabolism.