Upregulated expression of rat heart intercellular adhesion molecule-1 in angiotensin II- but not phenylephrine-induced hypertension

Abstract

Intercellular adhesion molecule-1 (ICAM-1), part of an immunoglobulin-like superfamily of adhesion molecules, is involved in several cardiovascular diseases. We investigated whether in vivo angiotensin II (Ang II) increases ICAM-1 in rats. Sprague-Dawley rats were infused with vehicle or Ang II (750μg · kg-1 · d-1 SC) for 7 days. The contribution of Ang II receptors to ICAM-1 expression was investigated with a nonpeptide Ang II type 1 (AT1) receptor antagonist losartan (30 mg · kg-1 · d-1 in drinking water). Systolic blood pressure was elevated in Ang II-treated animals compared with sham-treated controls, and losartan blocked this increase. Tumor necrosis factor (TNF)-α (5 μg/kg IP bolus), a prototype inducer of ICAM-1, was administered as a positive control for ICAM-1 expression. After treatment, hearts were frozen in liquid nitrogen; homogenates were subjected to SDS-PAGE and immunoblotted with an anti-rat ICAM-1 monoclonal antibody. We detected a predominantly high-molecular-weight band in homogenates from non-TNF-α-treated rats, which was enhanced by 80±5% in TNF-α-treated rats. This band measured ≈200 kDa, which is the molecular weight of ICAM-1 in its native dimer form. The same band was detected in homogenates from sham and Ang II-treated rats, with the latter showing a 150±10% increase in ICAM-1 versus sham controls. Immunoprecipitation of rat heart homogenates with anti-rat ICAM-1 antibody resulted in a dominant band of the same molecular weight as samples not treated with antibody. Losartan prevented enhanced expression of ICAM-1 in the presence of Ang II but had no effect on basal ICAM-1 expression. Phenylephrine, an α-agonist (3 mg · kg-1 · d-1), was infused for 1 week but had no effect on ICAM-1 expression, even though systolic blood pressure was elevated to the same level as in rats treated with Ang II. Thus, heart ICAM-1 expression is enhanced via AT1 receptor activation independent of hypertension. Ang II-induced ICAM-1 expression was time and dose dependent, with maximal expression occurring within 5 to 7 days at 100 to 750 μg/kg Ang II. Immunohistochemical staining demonstrated markedly increased ICAM-1 levels in the perivascular area in Ang II-infused rats. Monocyte/macrophage accumulation was significantly greater in Ang II-treated rat hearts than in sham-treated hearts (10±1; P<0.001; n=5). Thus during inflammation, overexpression of ICAM-1 may contribute to cardiovascular damage in diseases characterized by increased activity of the renin-angiotensin system.