Different methods for administering 17β-estradiol to ovariectomized rats result in opposite effects on ischemic brain damage

Abstract

BackgroundNumerous stroke studies have controversially shown estrogens to be either neuroprotective or neurodamaging. The discordant results observed in rat brain ischemia models may be a consequence of discrepancies in estrogen administration modes resulting in plasma concentration profiles far from those intended. To test this hypothesis we reproduced in detail and extended an earlier study from our lab using a different mode of 17β-estradiol administration; home-made silastic capsules instead of commercial slow-release 17β-estradiol pellets. Four groups of female rats (n = 12) were ovariectomized and administered 17β-estradiol or placebo via silastic capsules. All animals underwent MCAo fourteen days after ovariectomy and were sacrificed three days later.ResultsIn contrast to our earlier results using the commercial pellets, the group receiving 17β-estradiol during the entire experiment had significantly smaller lesions than the group receiving placebo (mean ± SEM: 3.85 ± 0.70% versus 7.15 ± 0.27% of total slice area, respectively; p = 0.015). No significant neuroprotection was found when the 17β-estradiol was administered only during the two weeks before or the three days immediately after MCAo.ConclusionsThe results indicate that different estrogen treatment regimens result in diametrically different effects on cerebral ischemia. Thus the effects of estrogens on ischemic damage seem to be concentration-related, with a biphasic, or even more complex, dose-response relation. These findings have implications for the design of animal experiments and also have a bearing on the estrogen doses used for peri-menopausal hormone replacement therapy.

Challenges in experimental stroke research : The 17β-estradiol example

“…The principle is very straightforward but demands considerable skills and training for optimal results. Once the vessel is exposed, the blood fl ow is obstructed by electrocoagulation [29], suture ligation [30] or microclip application [31], with the latter two also allowing controlled reperfusion. An advantage of the craniotomy methods is the ability to visually confi rm occlusion and occlusion site, but the procedures are invasive and time-consuming.…”

“…Thus, the meta-analyses supported the hypothesis of dose-related neuroprotection vs neurodamage in response to 17β-estradiol administration. In addition, the 2005 experimental estrogen-stroke study had been repeated with 17β-estradiol administered in silastic capsules instead of pellets and interestingly, now a protective effect was found [31]. However, it remained to be proven that estrogens both exert neuroprotection and promote detrimental effects depending merely on dose and independent of the administration route.…”

“…When the administration method (slow-release pellets) used in that study was investigated, it was found that very high concentrations were produced [108][109][110]. In fact, when the estrogen-stroke study was repeated, only with a different administration method (silastic capsules), protection was seen [31]. These silastic capsules were in the abovementioned administration studies shown to produce lower and more stable hormone concentrations than the slow-release pellets.…”

“…The capsules used in Papers I and IV were assembled based on the description by Dubal et al [97], in the same way as those used in previous rat studies from our lab [31,109,110]. In paper IV, 30 mm segments of silastic tubing (inner/outer diameter: 1.575/3.175 mm, Dow Corning, VWR International, Buffalo Grove, IL, USA) were fi lled with 17β-estradiol (Sigma-Aldrich Sweden AB, CAS# 50-28-2, Stockholm, Sweden) dissolved in sesame oil (Sigma-Aldrich Sweden AB, CAS#8008-74-0, Stockholm, Sweden) and capped with 5 mm pieces of wooden applicator sticks (birch, length 15 cm, diameter 2 mm, SelefaTrade AB, Spånga, Sweden).…”

“…The vehicle group received two vehicle capsules (only sesame oil), the low-dose group received one vehicle capsule and one 180 μg/mL capsule, and the high-dose group received two 50 000 μg/mL capsules. The doses were chosen based on earlier results from our lab; the lower dose has previously been neuroprotective [31] whereas the high-dose regimen has been shown to produce levels of 17β-estradiol higher than or equivalent to the neurotoxic slowrelease pellets (unpublished pilot study and [1]). Since mice were used in Paper I, the size of the capsules was adjusted.…”