B RESEARCH Brain Research 738 (1996) 8-14 Research report Enhanced oxidative stress in female rat brain after gonadectomy June Kume-Kick, David C. Ferris, Iolanda Russo-Menna, Margaret E. Rice * Departments of Physiology and Neuroscience and Neurosurgery, New York Medical Center, 550 First Ave., New York, NY 10016, USA Accepted 11 June 1996 Abstract Oxidative stress, assessed by tissue ascorbate loss following ischemia, is greater in male than female rat brain. The factors mediating this gender difference are unclear. The goal of the present studies was to determine the influence of gonadal sex hormones on this difference. Three weeks prior to experiment, adult Long–Evans male and female rats were gonadectomized for comparison with controls. Ascorbate and glutathione levels were determined in brain and plasma under basal conditions and in brain after one-hour decapitation ischemia, using liquid chromatography with electrochemical detection. Basal ascorbate levels in brain were 6–9Y0 higher in males than in females, whereas plasma levels were 100% higher in males. After gonadectomy, the gender difference in plasma ascorbate levels was lost, while the effect on basal brain levels depended upon region. Ischemia-induced losses in brain ascorbate were three-fold greater in control males compared to control females. Significant losses occurredin frontalcortex,hippocampus,and cerebellumin males during ischemia,whereasloss in femaleswas significantin cerebellumonly.Aftergonadectomy,increasedascorbateloss was seenin all female brain regions, indicatingenhanced oxidative stress. This increase eliminatedthe gender differencein loss; male ascorbate loss was comparativelyunaffectedby gonadectomy.Glutathionelevels and loss were unaffectedby either gender or gonadectomy,indicating differencesin regulationfromthatof ascorbate.Thesefindingsprovideevidencefor thehypothesisthatprotectionagainstoxidativestress is affordedby ovariansex hormones,thus decreasingthe potentialfor oxidativecell darnagein femalescomparedto males. Keywords: Ascorbate; Glutathione; Free radicals; Decapitation ischemia; Gender; Hippomrnpus; Sex hormone 1. Introduction During normal cellular respiration at least 2% of oxy- gen metabolized by the electron transport chain results in the generation of reactive oxygen species [3,4]. Cellular damage from these pro-oxidants is prevented by anti- oxidant including low molecular weight ascorbate and glutathione (GSH), lipid-soluble a-tocopherol, and antioxi- dant enzymes like superoxide dismutase and glutathione peroxidase [5,45]. These systems act in concert to neutral- ize reactive oxygen species and prevent oxidative damage [5]. During normal aerobic metabolism, cytosolic ascorbate and GSH are recycled as they are utilized. Oxidized GSH is recycled by GSH reductase [33], while oxidized ascor- bate is recycled by GSH and possibly by a dehydroascor- bate reductase [43], although this is controversial [52]. Under conditions of oxidative stress, when pro-oxi- dant/antioxidant balance is disrupted [9,44], antioxidant * Corresponding author. Fax: +1 (212) 689-0334; E-mail: ricem@is2.nyu.edu cycling is also compromised, causing ascorbate and GSH levels to fall [10,13,52]. Ascorbate oxidation, especially, has been used as a marker of oxidative stress [6,13,15,17,37]. Loss of GSH, on the other hand, reflects degradation from enzymatic processes (e.g. GSH transpep- tidase activity), as well as oxidation [32,33], so that it is a less reliable marker of pro-oxidant/antioxidant imbalance. Cellular damage in cerebral ischernia has been linked to oxidative stress [8,23,24]. Cerebral antioxidants, including ascorbate, GSH, and superoxide dismutase are depleted during ischemia [1,8,10,15,30,38]. When oxidative metabolism resumes during reperfusion, the levels of oxy- gen radicals are measurably increased [7] which can result in cell damage. To assess the effect of ischemia on brain antioxidants, this laboratory and others [1,8,13] have used a global model, decapitation ischemia [16] which permits ischemic events to be investigated without the additional influence of residual blood flow or reperfusion. We recently reported that loss of ascorbate during 1 h decapitation ischernia is significantly lower in female com- pared to male rat brain [13]. Because ascorbate loss is a reflection of oxidative stress [6,15,37], this suggested that 0006-8993/96/$15.00 Copyright @ 1996 Elsevier Science B.V. All rights reserved PIZ S0006- 8993 (96)00744-5