Cerebral Cortical Microvascular Rarefaction in Metabolic Syndrome is Dependent on Insulin Resistance and Loss of Nitric Oxide Bioavailability

Abstract

Objective: Chronic presentation of the MS is associated with an increased likelihood for stroke and poor stroke outcomes following occlusive cerebrovascular events. However, the physiological mechanisms contributing to compromised outcomes remain unclear, and the degree of cerebral cortical MVD may represent a central determinant of stroke outcomes.

Methods: This study used the OZR model of MS and clinically relevant, chronic interventions to determine the impact on cerebral cortical microvascular rarefaction via immunohistochemistry with a parallel determination of cerebrovascular function to identify putative mechanistic contributors.

Results: OZR exhibited a progressive rarefaction (to ~80% control MVD) of the cortical microvascular networks vs. lean Zucker rats. Chronic treatment with antihypertensive agents (captopril/hydralazine) had limited effectiveness in blunting rarefaction, although treatments improving glycemic control (metformin/rosiglitazone) were superior, maintaining ~94% control MVD. Chronic treatment with the antioxidant TEMPOL severely blunted rarefaction in OZR, although this ameliorative effect was prevented by concurrent NOS inhibition.

Conclusions: Further analyses revealed that the maintenance of glycemic control and vascular NO bioavailability were stronger predictors of cerebral cortical MVD in OZR than was prevention of hypertension, and this may have implications for chronic treatment of CVD risk under stroke-prone conditions.

Keywords: capillary density; obesity; perfusion; rodent models of cardiovascular disease risk.

Figure 1

The change in skeletal muscle microvessel density in LZR and OZR between 7–8 and 16–17 weeks of age. Data are presented as mean±SE, n=6 animals in each age group for LZR; n=7 animals in each age group for OZR. *; p<0.05 vs. LZR at that age. Please see text for details.

Figure 2

The change in skeletal muscle microvessel density in LZR and OZR between 7–8 and 16–17 weeks of age. Data (mean±SE) are presented under control conditions (grey) and in response to chronic treatment with either captopril or hydralazine as an anti-hypertensive therapy. n=6 animals in each age group for LZR; n=5–6 animals in each age group for OZR. *; p<0.05 vs. LZR at that age. †; p<0.05 vs. OZR at that age. Please see text for details.

Figure 3

The change in skeletal muscle microvessel density in LZR and OZR between 7–8 and 16–17 weeks of age. Data (mean±SE) are presented under control conditions (grey) and in response to chronic treatment with either metformin or rosiglitazone as therapy for improving glycemic control. n=6 animals in each age group for LZR; n=5–6 animals in each age group for OZR.*; p<0.05 vs. LZR at that age. †; p<0.05 vs. OZR at that age. Please see text for details.

Figure 4

The change in skeletal muscle microvessel density in LZR and OZR between 7–8 and 16–17 weeks of age. Data (mean±SE) are presented under control conditions (grey) and in response to chronic treatment with TEMPOL, L-NAME or both agents together as means for separating oxidant stress from nitric oxide bioavailability. n=6 animals in each age group for LZR; n=5–6 animals in each age group for OZR. *; p<0.05 vs. LZR at that age. †; p<0.05 vs. OZR at that age. Please see text for details.

Figure 5

Data describing the bioavailability of vascular-produced nitric oxide from ex vivo segments of the abdominal aorta from LZR and OZR at 7–8 (Panel A), 12–13 (Panel B) and 16–17 (Panel C) weeks of age. Data are presented as the slope of the NO level with increasing concentrations of methacholine pooled arteries under control conditions and following the employed chronic interventions to the animal prior to use. Abbreviations: CAP (captopril), HDZ (hydralazine), MET (metformin), RGZ (rosiglitazone), TEM (TEMPOL), LNM (L-NAME), TLN (TEMPOL+L-NAME). Data are presented as mean±SE, n=6 animals in each age group for LZR; n=5–6 animals in each age group for OZR. *; p<0.05 versus responses in LZR under control conditions. †; p<0.05 versus responses in OZR under control conditions. Please see text for details.

Figure 6

Data describing the dilator reactivity of ex vivo middle cerebral arteries from LZR and OZR at 7–8 weeks (Panel A), 12–13 weeks (Panel B) and 16–17 weeks of age (Panel C). Data, presented for the dilator responses of MCA in response to increasing concentrations of acetylcholine, are shown as mean±SE, n=6 animals in each age group for LZR; n=5–6 animals in each age group for OZR. *; p<0.05 in the upper bound vs. LZR. †; p<0.05 in the upper bound) vs. OZR. Please see text for details.

Figure 7

The correlation between vascular nitric oxide bioavailability and cerebral cortical microvessel density for LZR and OZR at 7–10 (Panel A), 12–13 (Panel B), and 16–17 weeks of age (Panel C). Please see text for details.