This protocol describes a surgical procedure to create a model for flow-induced pulmonary arterial hypertension (PAH) in rats and the procedures to analyze the principle hemodynamic and histological end-points in this model.
In this protocol, PAH is induced by combining a 60 mg/kg monocrotalin (MCT) injection with increased pulmonary blood flow through an aorto-caval shunt (MCT+Flow). The shunt is created by inserting an 18-G needle from the abdominal aorta into the adjacent caval vein. Increased pulmonary flow has been demonstrated as an essential trigger for a severe form of PAH with distinct phases of disease progression, characterized by early medial hypertrophy followed by neointimal lesions and the progressive occlusion of the small pulmonary vessels. To measure the right heart and pulmonary hemodynamics in this model, right heart catheterization is performed by inserting a rigid cannula containing a flexible ball-tip catheter via the right jugular vein into the right ventricle. The catheter is then advanced into the main and the more distal pulmonary arteries. The histopathology of the pulmonary vasculature is assessed qualitatively, by scoring the pre- and intra-acinar vessels on the degree of muscularization and the presence of a neointima, and quantitatively, by measuring the wall thickness, the wall-lumen ratios, and the occlusion score.
The goal of this method is to create a reproducible model for severe, flow-induced pulmonary arterial hypertension in rats and to measure its principle hemodynamic and histopathological end points.
Pulmonary arterial hypertension (PAH) is a clinical syndrome that encompasses a progressive increase in pulmonary vascular resistance leading to right ventricular failure and death. Within the superordinate disease spectrum of pulmonary hypertensive diseases (PH), PAH is the most severe form and one that remains without a cure1. The underlying arteriopathy in PAH is characterized by a typical form of vascular remodeling that occludes the vessel lumen. Muscularization of normal non-muscularized vessels and hypertrophy of the medial vessel layer are regarded as early disease phenomena in PAH, are also seen in other forms of PH2, and are thought to be reversible3. As PAH advances, the intimal layer begins to remodel, eventually forming characteristic neointimal lesions2. Neointimal-type pulmonary vascular remodeling is exclusive to PAH and is currently regarded to be irreversible4.
As PAH is a rare disease, advances in its pathobiological comprehension and development of novel therapies have relied heavily on animal models. The monocrotalin (MCT) model in rats is a simple single hit model that has been, and still is, used frequently. MCT is a toxin that causes injury to the pulmonary arterioles and regional inflammation5. 60 mg/kg MCT leads to an increase in the mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), and right ventricular hypertrophy (RVH) after 3 – 4 weeks6. The histomorphology is characterized by isolated medial hypertrophy without neointimal lesions5. The MCT rat model thus represents a moderate form of PH, and not PAH, although it is commonly presented as the latter.
In children with PAH associated with a congenital left-to-right shunt (PAH-CHD), increased pulmonary blood flow is regarded as the essential trigger for the development of neointimal lesions7,8,9. In rats, increased pulmonary blood flow can be induced by the creation of a shunt between the abdominal aorta and the vena cava, a technique first described in 199010. Alternatives to create increased pulmonary flow are by unilateral pneumonectomy or by subclavian to pulmonary artery anastomosis11. Conceptual disadvantages of these models consist of potential compensatory growth of the remaining lung and adaptive pathway activation induced by the pneumonectomy, or of iatrogenic injury of the pulmonary vasculature due to pulmonary artery anastomosis, both confounding the effects of increased pulmonary blood flow.
When an aorto-caval shunt is created and increased pulmonary blood flow is induced as a second hit in MCT-treated rats, characteristic neointimal lesions occur, and a severe form of PAH and associated right ventricular failure (RVF) develop 3 weeks after the increased flow12. The hemodynamic progression of PAH in this model can be assessed in vivo by echocardiography and right heart catheterization. The vascular histomorphology, vessel wall thickness, degree of arteriolar occlusion, and parameters for right ventricular failure form the pillars of the ex vivo characterization of PAH.
This method describes detailed protocols for the aorto-caval shunt (AC-shunt) surgery, right heart catheterization, and qualitative and quantitative assessment of vascular histomorphology.
This method describes the surgical procedure of an aorto-caval shunt in rats pre-treated with MCT to create flow-induced PAH and the techniques to assess the principle hemodynamic and histopathological end points that characterize PAH and this model.
Critical Steps within the Protocol and Troubleshooting
Surgery and post-surgery. During the aorto-caval shunt surgery, the most critical step is the dissection of the aorta and vena cava. The membranes that enclose the aor…
The authors have nothing to disclose.
This study was supported by the Netherlands Cardiovascular Research Initiative, the Dutch Heart Foundation, the Dutch Federation of University Medical Centers, the Netherlands Organization for Health Research and Development, and the Royal Netherlands Academy of Sciences (CVON nr. 2012-08, PHAEDRA, The Sebald fund, Stichting Hartekind).
Shunt Surgery |
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Sterile surgical gloves | |||
Duratears Eye ointment | Alcon | 10380 | |
Chloride-Hexidine | |||
Cotton swabs | |||
Histoacryllic tissue glue | B. Braun Medical | 1050052 | |
Silkam 5-0 sutures black non-resorbable | B. Braun Medical | F1134027 | |
Safil 4-0 sutures violet resorbable | B. Braun Medical | ||
18 G needle | Luer | NN1838R BD | tip bent in 45 degrees orifice to the outside |
Gauzes 10×10 cm | Paul Hartmann | 407825 | |
Temgesic Buprenorphine | RB Pharmaceuticals | 5429 | subcutaneous injection |
Sodium Chloride 0.9 % | |||
Ventilation mask Rat | |||
Scalple blade | |||
Biemer clamp 18 mm, 5 mm opening | AgnTho | 64-562 | |
Heat mat | |||
Kocher Clamp | |||
Shaving machine | |||
Microscope | Leica | ||
Right Heart Catheterization |
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Name | Company | Catalog Number | Comments |
Sterile surgical gloves | |||
Eye ointment | Duratears | ||
Chloride-Hexidine | |||
Cotton swabs | |||
Gauzes 10×10 cm | Paul Hartmann | 407825 | |
Silkam 5-0 sutures black non-resorbable | B. Braun Medical | F1134027 | |
Needle 20 G | Luer | Tip slightly bent to the inside | |
Cannula 20 G | Luer | to introduce catheter, tip pre-formed in 20 degrees | |
Silastic Catheter 15 cm long | 0.5 mm ball 2 mm from tip | ||
Pressure transducer | Ailtech | ||
Bedside monitor Cardiocap/5 | Datex-Ohmeda | ||
Shaving machine | |||
10mL Syringe | |||
Sodium Chloride 0.9 % | for flushing | ||
Vascular Morphology |
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Name | Company | Catalog Number | Comments |
50ml Syringe | |||
4 % Formaldehyde | |||
18 G cannula with tube | |||
Verhoef staining kit | Sigma-Aldrich | HT254 | http://www.sigmaaldrich.com/catalog/product/sigma/ht254?lang=en®ion=US |
Digital slide scanner | Hamamatsu | C9600 | |
Image-J | |||
Elastic (Connective Tissue Stain) | Abcam | ab150667 | http://www.abcam.com/elastic-connective-tissue-stain-ab150667.html |
http://www.abcam.com/ps/products/150/ab150667/documents/ab150667-Elastic%20Stain%20Kit%20(website).pdf |