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Role of endogenous testosterone in TNF-induced myocardial injury in males.

BACKGROUND
Gender-specific disparities have been observed in myocardium exposed to tumor necrosis factor-α (TNF). Male myocardium demonstrates greater loss in cardiac function in the presence of a given TNF level compared to female. In addition, we have previously demonstrated that estrogen has little influence on reducing TNF-caused myocardial dysfunction in female hearts, suggesting that male hormone - testosterone may be responsible for gender differences in TNF-mediated myocardial damage. Therefore, in this study, we hypothesize that endogenous testosterone plays a detrimental role in TNF-induced myocardial injury in male hearts.


METHODS
Isolated mouse hearts from age-matched adult males, females, castrated males and males treated with androgen receptor blocker-flutamide were subjected to 45 minutes of TNF infusion via a Langendorff model. Left ventricular developed pressure (LVDP) and heart rate were continuously recorded. After TNF infusion, heart tissue was analyzed for myocardial levels of caspase-8 and caspase-3 by Western blot assay.


RESULTS
TNF infusion significantly depressed LVDP, but not heart rate in males. Myocardial rate pressure product (RPP, LVDP*heart rate) was markedly decreased in male hearts compared to females in exposure to TNF, which was associated with higher levels of TNF-induced caspase-8 and caspase-3. Importantly, depletion of endogenous testosterone by castration or blockade of androgen receptor by flutamide treatment abolished TNF-decreased RPP in male hearts. However, castration or flutamide treatment did not affect TNF production and myocardial expression of TNFR1 and TNFR2.


CONCLUSION
Our study shows that testosterone is critical to the gender difference in TNF-induced detrimental effects on myocardium. Relative low threshold for TNF-caused myocardial damage in males is likely due to the interaction of testosterone with downstream signals of TNFR1 and/or TNFR2.