Cardiac fibroblast (CF) proliferation and differentiation into hypersecretory myofibroblasts can lead to excessive extracellular matrix (ECM) production and cardiac fibrosis. In turn, the ECM produced can potentially activate CFs via distinct feedback mechanisms. To assess how specific ECM components influence CF activation, isolated CFs were plated on specific collagen substrates (type I, III, and VI collagens) before functional assays were carried out. The type VI collagen substrate potently induced myofibroblast differentiation but had little effect on CF proliferation. Conversely, the type I and III collagen substrates did not affect differentiation but caused significant induction of proliferation (type I, 240.7 +/- 10.3%, and type III, 271.7 +/- 21.8% of basal). Type I collagen activated ERK1/2, whereas type III collagen did not. Treatment of CFs with angiotensin II, a potent mitogen of CFs, enhanced the growth observed on types I and III collagen but not on the type VI collagen substrate. Using an in vivo model of myocardial infarction (MI), we measured changes in type VI collagen expression and myofibroblast differentiation after post-MI remodeling. Concurrent elevations in type VI collagen and myofibroblast content were evident in the infarcted myocardium 20-wk post-MI. Overall, types I and III collagen stimulate CF proliferation, whereas type VI collagen plays a potentially novel role in cardiac remodeling through facilitation of myofibroblast differentiation.

Abstract-␤-Adrenergic agonists accelerate the clearance of alveolar fluid by increasing the expression and activity of epithelial solute transport proteins such as amiloride-sensitive epithelial Na ϩ channels (ENaC) and Na,K-ATPases. Here we report that adenoviral-mediated overexpression of a human ␤ 2 -adrenergic receptor (␤ 2 AR) cDNA increases ␤ 2 AR mRNA, membrane-bound receptor protein expression, and receptor function (procaterol-induced cAMP production) in human lung epithelial cells (A549). Receptor overexpression was associated with increased catecholamine (procaterol)-responsive active Na ϩ transport and increased abundance of Na,K-ATPases in the basolateral cell membrane. ␤ 2 AR gene transfer to the alveolar epithelium of normal rats improved membrane-bound ␤ 2 AR expression and function and increased levels of ENaC (␣ subunit) abundance and Na,K-ATPases activity in apical and basolateral cell membrane fractions isolated from the peripheral lung, respectively. Alveolar fluid clearance (AFC), an index of active Na ϩ transport, in ␤ 2 AR overexpressing rats was up to 100% greater than sham-infected controls and rats infected with an adenovirus that expresses no cDNA. The addition of the ␤ 2 AR-specific agonist procaterol to ␤ 2 AR overexpressing lungs did not increase AFC further. AFC in ␤ 2 AR overexpressing lungs from adrenalectomized or propranolol-treated rats revealed clearance rates that were the same or less than normal, untreated, sham-infected controls. These experiments indicate that alveolar ␤ 2 AR overexpression improves ␤ 2 AR function and maximally upregulates ␤-agonist-responsive active Na ϩ transport by improving responsiveness to endogenous catecholamines. These studies suggest that upregulation of ␤ 2 AR function may someday prove useful for the treatment of pulmonary edema.

Case reports of neurogenic pulmonary edema (NPE) often indicate that the edema resolves quickly. Because plasma epinephrine concentration may be elevated in NPE, and epinephrine has been shown to increase the rate of alveolar liquid clearance (ALC), we determined if ALC was increased in a canine model of NPE produced by the intracisternal administration of veratrine. ALC was determined by instilling autologous plasma into a lower lung lobe and using the increase in instillate protein concentration after 4 h to calculate the volume of fluid cleared from the airspaces by mass balance. To prevent pulmonary hypertension and edema, which would confound the mass balance analysis, carotid arterial blood was allowed to drain into a reservoir as pulmonary arterial pressure started to rise after veratrine administration. ALC in animals administered veratrine (n = 6) was 30.4 +/- 1.6 (SE)% of the instilled volume compared with 14.1 +/- 2.1% observed in control animals. The increase in ALC could be inhibited by adrenalectomy, beta2-adrenergic blockade using ICI 118,551, or sodium channel blockade using amiloride and could be duplicated by infusing epinephrine to increase plasma epinephrine concentration to levels observed in NPE. These data indicate that the increased ALC was mediated by adrenal epinephrine and suggest that edema resolution in patients with NPE might be accelerated by endogenous epinephrine.