Differences in brain edema and intracranial pressure following traumatic brain injury across the estrous cycle: involvement of female sex steroid hormones.

It has been shown that sex steroid hormones have profound neuroprotective effects in experimental traumatic brain injury (TBI). Because the endogenous hormone levels are proven to differ with estrous cycle stage, we evaluated whether estrous cycle stage affects various outcomes following diffuse TBI. TBI was induced by Marmarou's method in normal cycling and in ovariectomized rats with physiologically relevant restoration of hormonal levels by hormone capsule implantation. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) were measured before and different times after TBI and brain edema was assessed at 24h after trauma. Results indicated that after TBI, water content (WC) in traumatic proestrous (TP) rats was less than the one in traumatic non-proestrous (TNP) and ovariectomized (TOVX) and also in high estradiol (HE) and progesterone (HP) was statistically less than in TBI untreated groups.There was no significant difference in WC between high doses hormone treated and TP and also between TNP, TOVX, low estradiol (LE) and progesterone (LP) groups. At 4h and 24h after trauma, there was a significant difference in ICP between TP, HE and HP compared to TNP and other TBI nontreated groups. Also in these times, the CPP increased in TP and hormone treated groups compared with TOVX, but the difference between TNP and TOVX was not significant. The results indicate that the estrous cycle has a prominent role in TBI outcome's and the difference in female sex steroid levels might be the reason of the different neuroprotective effects in proestrous and non-proestrous groups.