The Role of Testosterone Deprivation and Replacement on Stroke Outcome in Middle-Aged Rats

Background: Circulating levels of the steroid hormone testosterone fall in aging men, and in the last decade the number of men obtaining prescriptions for testosterone replacement therapy (TRT) has increased dramatically. However, other consequences of aging, such as increased oxidative stress, may result in detrimental effects when combined with TRT. This include increased risks of thromboembolism and stroke. In women, a delay in hormone therapy (estrogen/progesterone) after menopause results in a loss of benefit for the brain and an increase in risk for stroke and cognitive decline. Whether such a delay would alter the effects of TRT is not known. Hypothesis: In this study, we hypothesized that a delay in TRT following castration in middle-aged male rats would result in increased oxidative stress and a reduction in the neuroprotective effects of testosterone following stroke (transient cerebral ischemia). Methods: Twelve-month old male Fischer 344 rats were obtained from the National Institutes on Aging. Rats were divided into 5 groups as follows: 1) gonad Intact sham stroke (SHAM), 2) Intact stroke (INT), 3) short term castrate + TRT (STT), 4) long term castrate (LT), and 5) long term castrate + TRT (LTT). Rats were castrated 2 weeks (STT) or 10 weeks (LT, LTT) prior to TRT by subcutaneous silastic capsules containing T. L3T rats were treated with the antioxidant TEMPOL in drinking water starting 2 weeks before TRT. Middle cerebral artery occlusion (Stroke) was accomplished under gas anesthesia by stereotaxic injection of the vasoconstrictor endothelin 1 (ET1) adjacent to the left middle cerebral artery. One, 3, 7, and 14 days after stroke, rats were assessed for neurological deficits using a standardized scoring system. Forelimb bias to the ipsilateral left side was assessed using the cylinder test, and coordinated walking was assessed with an automated ladder walk. Following behavior assessments, rats were humanely euthanized and blood and brains were collected. The effects of stroke and treatments were compared to intact sham stroke (SHAM). Results: Peripheral oxidative stress measured by Advanced Oxidative Protein Products (AOPP) was significantly negatively correlated with T levels, similar to men. ST rats experienced the smallest neurological deficits following stroke, suggesting that