Spironolactone improves structure and increases tone in the cerebral vasculature of male spontaneously hypertensive stroke-prone rats

Abstract

Background: Previous studies show that ischemic cerebral infarct size is related to cerebral vessel structure. Spironolactone, a mineralocorticoid receptor antagonist, decreases ischemic cerebral infarct size in male spontaneously hypertensive stroke-prone rats (SHRSP). Therefore, we hypothesized that chronic spironolactone treatment would improve cerebral artery structure in the SHRSP.

Methods: Six-week-old male SHRSP were treated with spironolactone (2.5 mg/day) for 6 weeks and were compared to untreated control SHRSP and normotensive Wistar Kyoto (WKY) rats. Using a pressurized arteriograph, structural measurements of the middle cerebral artery (MCA) were taken under passive (calcium-free), zero-flow conditions. Myogenic tone was calculated from active and passive measurements taken at 75 and 125 mmHg. Mean arterial pressure was measured using radiotelemetry.

Results: Myogenic tone was increased only at 75 mmHg in the spironolactone-treated SHRSP compared to control rats. The MCA lumen and outer diameters were increased in the spironolactone-treated SHRSP compared to control SHRSP, but were not different from WKY rats, indicating a decrease in vascular remodeling. There was no effect of spironolactone on blood pressure, suggesting that this is a blood pressure-independent effect.

Conclusion: Increased myogenic tone and lumen diameter in the spironolactone-treated SHRSP may be responsible for the protective role of spironolactone in ischemic stroke.

Figure 1

Telemetry Blood Pressure. Mean arterial pressure is presented as the average of the day and night measurements. Spironolactone treatment had no effect on mean arterial pressure in the SHRSP (n = 3 rats per group); mean arterial pressure was lower in control WKY rats (n = 4) compared to both groups of SHRSP. Abbreviations: SHRSP – spontaneously hypertensive stroke-prone rats, WKY – Wistar Kyoto

Figure 2

Cerebral Vessel Function. A) Percent tone is calculated as: 1 – (active diameter / passive diameter) × 100. Spironolactone treatment increased tone at 75 mmHg compared to control groups (*p<0.05 vs. control SHRSP and WKY rats). Percent tone was not different between groups at 125 mmHg. B) Reactivity to serotonin is presented as the change in lumen diameter in microns. Constriction to serotonin was blunted in the spironolactone-treated SHRSP at the highest doses (*p<0.05 vs. control SHRSP and WKY rats, †p<0.05 vs. WKY rats). n = 8 for spironolactone-treated SHRSP, n = 6 for control SHRSP, n = 4 for control WKY rats Abbreviations: MCA – middle cerebral artery, SHRSP – spontaneously hypertensive stroke-prone rats, WKY – Wistar Kyoto

Figure 3

Vessel structure was assessed under calcium-free conditions. A) Lumen Diameter. Over the range of pressures, the lumen diameter of the MCA was larger in the spironolactone-treated SHRSP compared to control SHRSP (*p<0.05). B) Outer Diameter. Over the range of pressures, the outer diameter of the MCA was smaller in the control SHRSP compared to spironolactone-treated SHRSP and control WKY rat groups (*p<0.05). C) Wall Thickness. Over the range of pressures, wall thickness was increased in the control and spironolactone-treated SHRSP groups compared to the control WKY rat group (*p<0.05). n = 8 for spironolactone-treated SHRSP, n = 6 for control SHRSP, n = 4 for control WKY rats Abbreviations: MCA – middle cerebral artery, SHRSP – spontaneously hypertensive stroke-prone rats, WKY – Wistar Kyoto

Figure 4

Vessel structure was assessed under calcium-free conditions. A) Cross-Sectional Wall Area. Over the range of pressures, there was no difference in cross-sectional wall area in the MCA between groups. B) Wall-to-Lumen Ratio. The wall-to-lumen ratio of the spironolactone-treated SHRSP was decreased compared to control SHRSP and increased compared to control WKY rats (*p<0.05). n = 8 for spironolactone-treated SHRSP, n = 6 for control SHRSP, n = 4 for control WKY rats Abbreviations: MCA – middle cerebral artery, SHRSP – spontaneously hypertensive stroke-prone rats, WKY – Wistar Kyoto

Figure 5

Remodeling and growth indices as calculated from structural measurements at 80 mmHg. Spironolactone treatment greatly reduced the remodeling index and only slightly increased the growth index in the MCA of SHRSP. n = 8 for spironolactone-treated SHRSP, n = 6 for control SHRSP, n = 4 for control WKY rats Abbreviations: MCA – middle cerebral artery, SHRSP – spontaneously hypertensive stroke-prone rats, WKY – Wistar Kyoto

Figure 6

Circumferential wall stress and strain were calculated from measurements made over a range of pressures in passive, calcium-free conditions. A) There was a rightward shift in the stress/strain curve of the spironolactone-treated SHRSP, indicating an increase in MCA compliance. B) Beta-coefficients, a measure of vessel stiffness, were calculated by performing exponential regression on individual stress/strain curves. Beta-coefficients were significantly decreased in the MCAs from spironolactone-treated SHRSP (*p<0.05). n = 5 for spironolactone-treated SHRSP, n = 5 for control SHRSP, n = 5 for control WKY rats Abbreviations: MCA – middle cerebral artery, SHRSP – spontaneously hypertensive stroke-prone rats, WKY – Wistar Kyoto