LAUSR

Objective: Transient pressure overload (TPO) elicits stretch-induced myocyte injury in the absence of ischemia or infarction, but the extent to which this is associated with inflammation is unclear. The present study was designed to assess immune activation after TPO in swine and compare the inflammatory cytokine profile to that observed after myocardial infarction (MI). Methods: Swine received a brief infusion of phenylephrine (18 mg/hr iv; 30-60 min) to induce TPO and were studied for 1 hr (n=5), 3 hr (n=6), or 24 hr (n=6) before analysis of myocardial macrophage gene expression (CD68) via qPCR. Serial blood sampling was performed to assess neutrophil and monocyte counts as well as circulating cardiac troponin I (cTnI), IL-6, TNF-α, and CRP. Cytokine levels were compared to those from a separate group (n=5) subjected to a 60 min LAD occlusion to produce MI. Results: TPO increased circulating cTnI (from 20±5 ng/L to 340±58 ng/L at 3 hr and 1520±616 ng/L at 24 hr; p<0.01) without evidence of infarction. Compared with controls (n=6), swine subjected to TPO exhibited increased CD68 gene expression at 1, 3, and 24 hr ( A ). This was accompanied by a rise in peripheral blood neutrophils and monocytes ( B ) as well as an elevation in circulating IL-6, TNF-α, and CRP that was comparable to that observed after MI ( C ). Conclusion: Myocyte injury following TPO elicits mobilization of neutrophils and monocytes and a rise in circulating inflammatory cytokines comparable to that observed after MI. This is accompanied by an increase in cardiac macrophages and may be an important mechanism by which repetitive episodes of TPO lead to interstitial fibrosis and diastolic dysfunction without anatomic hypertrophy.