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Effects of long-term cardiac hypertrophy on coronary vasodilator reserve in SHR rats
Insights
Long-term left ventricular hypertrophy (LVH) impairs coronary vascular reserve in rats, especially during active development. However, this impairment resolves once LVH stabilizes, suggesting duration matters.
Area of Science:
- Cardiovascular Physiology
- Animal Models of Hypertension
- Coronary Circulation Research
Background:
- Left ventricular hypertrophy (LVH) effects on coronary vascular reserve are not fully understood.
- Investigating the impact of LVH duration on coronary blood flow regulation is crucial.
Purpose of the Study:
- To test if the duration of LVH modulates coronary vascular reserve.
- To compare coronary reactive hyperemia in Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats.
Main Methods:
- Utilized a novel pulsed Doppler flowmeter for coronary blood flow velocity measurements.
- Compared coronary reactive hyperemia characteristics in WKY and SHR rats at different ages (3, 7, and 12 months).
- Measured mean arterial pressures in all rat groups.
Main Results:
- Rat coronary reactive hyperemia differs significantly from larger animals, with lower peak/rest flow velocity and repayment/debt ratios.
- SHR rats showed decreased coronary reactive hyperemia during developing and peak LVH (3 and 7 months) compared to WKY controls.
- Coronary reactive hyperemia in 12-month-old SHR rats with stable LVH was similar to age-matched WKY rats.
- Elevated mean arterial pressures were observed in all SHR groups.
Conclusions:
- Coronary vascular reserve is significantly reduced during active LVH development and peak hypertrophy.
- This reduction in coronary vascular reserve is reversible upon stabilization of LVH.
- LVH duration plays a key role in modulating the relationship between cardiac mass and coronary vasculature growth.
Abstract:
The effects of long-term left ventricular (LV) hypertrophy on coronary vascular reserve have not been extensively investigated. To test the hypothesis that the duration of LV hypertrophy may modulate coronary vascular reserve, a newly developed pulsed Doppler flowmeter was used to compare the characteristics of coronary reactive hyperemia in Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. The data suggest that coronary reactive hyperemic responses in the rat are markedly different from those in larger animals and humans, e.g., peak/rest blood flow velocity ratio and the repayment/debt area ratio were 30 to 50% of those observed in larger laboratory animals. Because minimal coronary vascular resistance is similar in the rat and larger animals, the relatively high myocardial oxygen consumption at rest and consequent high myocardial blood flow at rest probably account for the alteration of coronary reactive hyperemia in the rat. In SHR rats, the characteristics of coronary reactive hyperemia decreased during developing (3-month-old) and peak (7-month-old) LV hypertrophy compared with those in their age-matched WKY controls. However, in 12-month-old SHR rats with stable LV hypertrophy, the coronary reactive hyperemic response was similar to that of 12-month-old WKY rats. Mean arterial pressures were significantly elevated in each of the 3 SHR groups. These data suggest a significant decrement in coronary vascular reserve during actively developing and peak LV hypertrophy, but the decrement disappears during stabilized hypertrophy. These studies suggest that the duration of LV hypertrophy may modulate the interaction between pathologic increases in cardiac mass and growth of the coronary vasculature.