Aging and exercise training reduce testes microvascular PO2 and alter vasoconstrictor responsiveness in testicular arterioles

Dominguez JM 2nd, Davis RT 3rd, McCullough DJ, Stabley JN, Behnke BJ. Aging and exercise training reduce testes microvascular PO2 and alter vasoconstrictor responsiveness in testicular arterioles. Am J Physiol Regul Integr Comp Physiol 301: R801-R810, 2011. First published June 15, 2011; doi:10.1152/ajpregu.00203.2011.-Testicularfunction and associated testosterone concentration decline with advancing age, and an impaired O-2 supply may contribute, in part, to this reduction. We hypothesized that there would be a reduced microvascular PO2 (PO2m) in the testes from aged rats, and this reduced PO2m would be associated with impaired vasomotor control in isolated resistance arterioles. In addition, given the positive effect of exercise on microvascular PO2 and arteriolar function, we further hypothesized that there would be an enhanced PO2m in the testes from aged animals after aerobic exercise training. Testicular PO2m was measured in vivo via phosphorescence quenching in young and aged sedentary (SED) and exercise-trained (ET; 15 m/min treadmill walking, 15-degree incline, 5 days/wk for 10 wk) male Fischer-344 rats. Vasoconstriction to alpha-adrenergic [norepinephrine (NE) and phenylephrine (PE)] and myogenic stimuli in testicular arterioles was assessed in vitro. In the SED animals, testicular PO2m was reduced by similar to 50% with old age (aged SED 11.8 +/- 1.9 vs. young SED 22.1 +/- 1.1 mmHg; P = 0.0001). Contrary to our hypothesis, exercise training did not alter PO2m in the aged group and reduced testicular PO2m in the young animals, abolishing age-related differences (young ET, 10.0 +/- 0.8 vs. aged ET, 10.7 +/- 0.9 mmHg; P = 0.37). Vasoconstrictor responsiveness to NE and PE was diminished in aged compared with young (NE: young SED, 58 +/- 2 vs. aged SED, 47 +/- 2%; P = 0.001) (PE: young SED, 51 +/- 3 vs. aged SED, 36 +/- 5%; P = 0.008). Exercise training did not alter maximal vasoconstriction to NE in young or aged groups. In summary, advancing age is associated with a reduced testis PO2m and impaired adrenergic vasoconstriction. The diminished testicular microvascular driving pressure of O-2 and associated vascular dysfunction provides mechanistic insight into the old age-related decrease in testicular function, and a reduced PO2m may contribute, in part, to reduced fertility markers after exercise training.