Testosterone application influences sympathetic activity of intracardiac nerves in non-trained and trained mice.

Application of testosterone and/or physical exercise causes degenerative and then regenerative patterns of intracardiac sympathetic neurons. Observations in 3 stages (1, 3 and 6 weeks) illustrate the adaptative changes of sympathetic neurons as a response to these stimuli and show that the effects following testosterone application or physical exercise are comparable. Ultrastructural investigations indicate that the sympathetic neurons are more sensitive to testosterone than to physical exercise. The combination of testosterone plus training indicates overlapping effects of these two stimuli. The system of adrenergic nerve fibers seems to be overstimulated. Its reaction pattern is found not only to depend on time but also on the intensity of the stimuli.