Stretch-induced Myocardial Injury, Inflammation, and Pro-Fibrotic Transcriptional Activity After Transient Left Ventricular Pressure Overload in Swine

Tyler J. Rolland, Emily R. Hudson, Ronzon R. Shihab, Dorcas Nsumbu, Arezou Tajlil, John M. Canty, Jr., and Brian R. Weil

Departments of Physiology & Biophysics and Medicine at the University at Buffalo and the VA WNY Healthcare System, Buffalo, NY

Objective: Using the α1-adrenergic agonist phenylephrine (PE), we previously demonstrated that an acute
episode of transient left ventricular (LV) pressure overload (TPO) elicits stretch-induced myocardial injury and
reversible LV-systolic dysfunction without ischemia or infarction. However, transcriptional changes associated
with TPO-induced injury and the role of direct α1-adrenergic receptor activation has yet to be studied.
Accordingly, this study was designed to assess the cardiac response to TPO resulting from administration of
vasopressin (VP), a vasoconstrictor lacking α1-adrenergic agonist properties.

Methods: Hemodynamic and echocardiographic parameters were assessed in propofol-anesthetized swine
before, during, and after a 30-minute infusion of VP (VP-TPO; 0.04 U/kg/min, n=7) to increase LV end-diastolic
pressure (EDP) to ~30mmHg. Serial jugular venous blood sampling was performed to quantify circulating
cardiac troponin I (cTnI), leukocytes, and inflammatory cytokines. Post-mortem heart tissue samples were
collected 3-hours after TPO to evaluate leukocyte infiltration (immunohistochemistry) and quantify proinflammatory and pro-fibrotic gene expression (qPCR) vs. normal controls (n=8).

Results: VP elicited a significant rise in mean arterial pressure (91±5 to 165±11 mmHg) and LV EDP (10±1
to 29±2 mmHg; both p<0.05 vs. baseline). After cessation of VP-TPO, circulating cTnI levels were ~10-fold
higher than baseline concentrations 3-hour post-TPO (18±5 to 118±21 ng/L; p<0.05). This was accompanied
by increased circulating neutrophils, monocytes, TNF-α, and IL-6, as well as heightened cardiac macrophage
infiltration (4.1-fold higher than controls, p<0.001). VP-TPO also elicited a ~2-fold increase in cardiac
expression of inflammatory and pro-fibrotic genes, including Loxl2, Galectin-3, Fibronectin, and Collagen-1
(all p<0.05 vs. controls).

Conclusions: VP-TPO elicits myocardial injury, leukocyte mobilization and infiltration, and elevations in
circulating pro-inflammatory cytokines, recapitulating several features of PE-induced TPO in the absence α1-
adrenergic stimulation. These findings demonstrate that stretch-induced myocardial injury induces an acute
inflammatory response and cardiac transcriptional changes that may promote LV fibrosis and diastolic
stiffening after repetitive episodes of TPO.