Early experimental hypertension preserves the myocardial microvasculature but aggravates cardiac injury distal to chronic coronary artery obstruction

Abstract

Coronary artery disease is a leading cause of death. Hypertension (HT) increases the incidence of cardiac events, but its effect on cardiac adaptation to coexisting coronary artery stenosis (CAS) is unclear. We hypothesized that concurrent HT modulates microvascular function in chronic CAS and aggravates microvascular remodeling and myocardial injury. Four groups of pigs (n=6 each) were studied: normal, CAS, HT, and CAS+HT. CAS and HT were induced by placing local irritant coils in the left circumflex coronary artery and renal artery, respectively. Six weeks later multidetector computerized tomography (CT) was used to assess systolic and diastolic function, microvascular permeability, myocardial perfusion, and responses to adenosine in the "area at risk." Microvascular architecture, inflammation, and fibrosis were then explored in cardiac tissue. Basal myocardial perfusion was similarly decreased in CAS and CAS+HT, but its response to adenosine was significantly more attenuated in CAS. Microvascular permeability in CAS+HT was greater than in CAS and was accompanied by amplified myocardial inflammation, fibrosis, and microvascular remodeling, as well as cardiac systolic and diastolic dysfunction. On the other hand, compared with normal, micro-CT-derived microvascular (20-200 μm) transmural density decreased in CAS but not in HT or CAS+HT. We conclude that the coexistence of early renovascular HT exacerbated myocardial fibrosis and vascular remodeling distal to CAS. These changes were not mediated by loss of myocardial microvessels, which were relatively preserved, but possibly by exacerbated myocardial inflammation and fibrosis. HT modulates cardiac adaptive responses to CAS and bears cardiac functional consequences.

Fig. 1.

A: 3-dimensional fast computerized tomography (CT) image illustrating coronary artery stenosis (CAS) in the swine left circumflex artery (LCX). LAD, left anterior descending coronary artery. B: myocardial perfusion obtained before (open bars) and after (filled bars) adenosine infusion by fast CT in the lateral wall “area at risk” in normal, CAS, renovascular hypertension (HT), and CAS+HT pigs. Basal myocardial perfusion decreased in CAS and CAS+HT. C: subendocardial-to-subepicardial myocardial perfusion ratio. D: myocardial perfusion response to adenosine. Adenosine disclosed impaired responses in CAS, which were relatively preserved in HT and CAS+HT. E: myocardial microvascular permeability [MP, arbitrary units (AU)]. Basal MP increased in CAS+HT, while adenosine increased MP in CAS and HT. *P < 0.05 vs. normal; ^#P < 0.05 vs. baseline; †P < 0.05 vs. CAS, ^$P < 0.05 vs. CAS+HT.

Fig. 2.

Myocardial microvascular density assessed by micro-CT in normal, CAS, HT, and CAS+HT. A: representative micro-CT images of myocardial microvessels. B and C: quantitation of microvascular density. The transmural density of small microvessels (20–200 μm in diameter) in normal decreased in CAS and was preserved in HT and CAS+HT. D: capillary density expressed as ratio of capillaries to cardiac muscle fibers. *P < 0.05 vs. normal; †P < 0.05 vs. HT; ^#P < 0.05 vs. CAS+HT.

Fig. 3.

Myocardial macrophage (CD163+, left) and T lymphocyte (CD8+, right) infiltration in normal, CAS, HT, and CAS+HT pigs detected by immunohistochemistry (top, ×40) and quantified (bottom). Inflammatory infiltration increased in CAS, HT, and CAS+HT compared with normal, but CD8+ cells significantly increased in CAS+HT compared with normal, HT, and CAS. *P < 0.05 vs. normal; †P < 0.05 vs. HT, ^#P < 0.05 vs. CAS.

Fig. 4.

A: expression of myocardial collagen I, matrix metalloproteinase (MMP)-9, zonula occludens-1 (ZO-1), vascular endothelial growth factor (VEGF), basic fibroblastic growth factor (bFGF), VEGF receptor FLK-1, Notch-1, and its receptor Delta-like receptor 4 (DLL-4). B: respective quantitation showing increased fibrosis and angiogenic factors in CAS and in CAS+HT compared with normal and increased bFGF and Notch-1 only in CAS+HT. *P < 0.05 vs. normal; †P < 0.05 vs. HT.

Fig. 5.

Myocardial vessel wall-to-lumen ratio quantified in α-smooth muscle actin (SMA)-stained slides (right, ×40) and myocardial fibrosis in trichrome-stained slides (left, ×40). Myocardial fibrosis and microvascular media-to-lumen ratio increased in HT and CAS+HT compared with normal. CAS increased fibrosis compared with HT. *P < 0.05 vs. normal; †P < 0.05 vs. HT; ^#P < 0.05 vs. CAS.