Chronic hindlimb ischemia impairs functional vasodilation and vascular reactivity in mouse feed arteries

Abstract

Vasodilation of lower leg arterioles is impaired in animal models of chronic peripheral ischemia. In addition to arterioles, feed arteries are a critical component of the vascular resistance network, accounting for as much as 50% of the pressure drop across the arterial circulation. Despite the critical importance of feed arteries in blood flow control, the impact of ischemia on feed artery vascular reactivity is unknown. At 14 days following unilateral resection of the femoral-saphenous artery-vein pair, functional vasodilation of the profunda femoris artery was severely impaired, 11 ± 9 versus 152 ± 22%. Although endothelial and smooth muscle-dependent vasodilation were both impaired in ischemic arteries compared to control arteries (Ach: 40 ± 14 versus 81 ± 11%, SNP: 43 ± 12 versus and 85 ± 11%), the responses to acetylcholine and sodium nitroprusside were similar, implicating impaired smooth muscle-dependent vasodilation. Conversely, vasoconstriction responses to norepinephrine were not different between ischemic and control arteries, -68 ± 3 versus -66 ± 3%, indicating that smooth muscle cells were functional following the ischemic insult. Finally, maximal dilation responses to acetylcholine, ex vivo, were significantly impaired in the ischemic artery compared to control, 71 ± 9 versus 97 ± 2%, despite a similar generation of myogenic tone to the same intravascular pressure (80 mmHg). These data indicate that ischemia impairs feed artery vasodilation by impairing the responsiveness of the vascular wall to vasodilating stimuli. Future studies to examine the mechanistic basis for the impact of ischemia on vascular reactivity or treatment strategies to improve vascular reactivity following ischemia could provide the foundation for an alternative therapeutic paradigm for peripheral arterial occlusive disease.

Keywords: chronic ischemia; hindlimb; mouse; reactivity; vasodilation.

Figure 1

Intravital microscopy imaging field and functional vasodilation responses in the profunda femoris arteries, in vivo. (A) Representative photomicrographs of the distal profunda femoris artery–vein pair imaging site for functional vasodilation and vascular reactivity studies at rest and (B) immediately following the cessation of 8 Hz muscle contraction. (C) Resting diameter and 10 min following 90 s of 8 Hz muscle contraction in day-14 ischemic (gray circles) and contralateral control (black boxes) profunda femoris arteries. (D) Maximal functional vasodilation in day-14 ischemic (gray) and contralateral control (black) profunda femoris arteries following 90 s of 8 Hz muscle contraction. Data points are on a relative scale, with resting diameter represented by 0%. ^*p ≤ 0.05 versus day-14 ischemic.

Figure 2

Vasodilation responses to endothelial- and smooth muscle-dependent dilating agents in ischemic and non-ischemic profunda femoris arteries, in vivo. (A) Vasodilation responses to increasing doses of acetylcholine (Ach), applied in 10^−x M increments, and a maximal dose of sodium nitroprusside (SNP) in day-14 ischemic (gray) and non-ischemic (black) arteries. (B) Vasodilation responses to maximal doses of Ach (10⁻⁴ M) and SNP (10⁻⁴ M) in day-14 ischemic (gray) and contralateral control (black) profunda femoris arteries. Data points are on a relative scale, with resting diameter represented by 0%. ^*p ≤ 0.05 versus day-14 ischemic.

Figure 3

Vasoconstriction responses to norepinephrine in ischemic and non-ischemic profunda femoris arteries, in vivo. (A) Pilot study measuring the vasoconstriction responses to increasing doses of norepinephrine (NE), applied in 10^−x M increments, and (B) vasoconstriction responses to maximal doses of NE (10⁻⁴ M) in day-14 ischemic (gray) and contralateral control (black) profunda femoris arteries. Data points are on a relative scale, with resting diameter represented by 0%.

Figure 4

Dose response curve to acetylcholine in ischemic and non-ischemic distal profunda femoris arteries, ex vivo. Vessels were pressurized to 80 mmHg (baseline) and developed myogenic tone before exposure to the initial dose of Ach (10⁻⁸ M); increasing doses were applied at 3 × 10^−x M increments. Data points are on a relative scale, with myogenic tone represented as 0% and maximal passive vasodilation represented as 100% (Ca⁺²-free PSS + EGTA). ^*p ≤ 0.05 versus day-14 ischemic.