The effects of standard and soy-free chow on cerebral artery function in ovariectomized female mice

Abstract

As females age, they transition through menopause, experiencing a decrease in estrogen and an increase in cardiovascular and neurodegenerative disease risk. When studying the effects of menopause in mice, modeled by ovariectomy, it is important to consider the effects of diet. Most standard rodent chows contain phytoestrogen-rich soybean meal, which can mimic the effects of estrogen. Understanding the impact of this soybean meal on outcomes is crucial to proper experimental design. Thus, the aim of this study was to compare the effects of standard and soy-free chows on cerebral artery endothelial function and cognitive function. We studied young female C57Bl/6J mice (n=43; ~6 months) divided into three groups: sham-controls on a soy-free diet (sham-SF), ovariectomized on a soy-free diet (OVX-SF), or OVX on a standard chow diet (OVX-SC). We assessed endothelium-dependent and -independent vasodilation in isolated pressurized posterior cerebral arteries (PCAs). We measured gene expression in cerebral arteries by real-time PCR. To assess behavioral function, we measured instinctual behavior via nest building. Data are presented as mean±SD. Compared with sham-SF, OVX-SF mice had impaired PCA endothelium-dependent vasodilation as evidenced by a maximal response that was 21% lower to acetylcholine (ACh, 60±14% vs. 47±14%, p=0.002) and 27% lower to insulin (52±17% vs. 38±8%, p=0.005). OVX-SC mice had a 27% greater PCA maximal vasodilation to insulin compared with OVX-SF mice (52±11% vs. 38±8%, p=0.001). The PCA responses to ACh and insulin did not differ between sham-SF and OVX-SC (p>0.05). Additionally, the PCA response to ACh and insulin in the presence of nitric oxide synthase inhibitor L-NAME did not differ between groups (p>0.05). Endothelium-independent vasodilation, measured as the PCA response to sodium nitroprusside, also did not differ between groups (p>0.05). There was a trend for lower gene expression of superoxide dismutase 2 ( Sod2) in cerebral arteries from OVX-SF mice (0.7±0.2 AU) compared with OVX-SC (1.0±0.4 AU, p=0.14) but this difference did not reach statistical significance. Cerebral artery gene expression was not different between groups for Esr1 (estrogen receptor α), Insr (insulin receptor), Slca2 (GLUT1), Sod1, or Sod3 (all p>0.05). Lastly, nest building scores were higher in the OVX-SC (4.3±0.5 AU) compared with sham-SF (3.2±1.2 AU, p=0.02) and OVX-SF (3.2±1.0 AU, p=0.04) mice. In summary, we found that ovariectomy impairs endothelial function in cerebral arteries by reducing nitric oxide bioavailability, but a diet containing soy mitigates these effects of ovariectomy. In addition, a diet containing soy leads to better instinctual nest-building behavior in mice. These findings highlight the importance of considering dietary soy when performing vascular and behavior tests in mice, particularly when interested in the effects of sex hormones. Luvaas Family Fund This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.