Korean J Physiol Pharmacol.  2016 Nov;20(6):641-647. 10.4196/kjpp.2016.20.6.641.

Hypoxic pulmonary vasoconstriction and vascular contractility in monocrotaline-induced pulmonary arterial hypertensive rats

• Kim HJ
• Yoo HY

• KMID: 2364268
• DOI: http://doi.org/10.4196/kjpp.2016.20.6.641

Abstract

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by vascular remodeling of pulmonary arteries (PAs) and increased vascular resistance in the lung. Monocrotaline (MCT), a toxic alkaloid, is widely used for developing rat models of PAH caused by injury to pulmonary endothelial cells; however, characteristics of vascular functions in MCT-induced PAH vary and are not fully understood. Here, we investigated hypoxic pulmonary vasoconstriction (HPV) responses and effects of various vasoconstrictors with isolated/perfused lungs of MCT-induced PAH (PAH-MCT) rats. Using hematoxylin and eosin staining, we confirmed vascular remodeling (i.e., medial thickening of PA) and right ventricle hypertrophy in PAH-MCT rats. The basal pulmonary arterial pressure (PAP) and PAP increase by a raised flow rate (40 mL/min) were higher in the PAH-MCT than in the control rats. In addition, both high K⁺ (40 mM KCl)- and angiotensin II-induced PAP increases were higher in the PAH-MCT than in the control rats. Surprisingly, application of a nitric oxide synthase inhibitor, L-N(G)-Nitroarginine methyl ester (L-NAME), induced a marked PAP increase in the PAH-MCT rats, suggesting that endothelial functions were recovered in the three-week PAH-MCT rats. In addition, the medial thickening of the PA was similar to that in chronic hypoxia-induced PAH (PAH-CH) rats. However, the HPV response (i.e., PAP increased by acute hypoxia) was not affected in the MCT rats, whereas HPV disappeared in the PAH-CH rats. These results showed that vascular contractility and HPV remain robust in the MCT-induced PAH rat model with vascular remodeling.

Keyword

Hypoxia; Monocrotaline; Pulmonary arterial hypertension; Pulmonary artery; Vascular remodeling

MeSH Terms

Angiotensins
Animals
Anoxia
Arterial Pressure
Endothelial Cells
Eosine Yellowish-(YS)
Heart Ventricles
Hematoxylin
Hypertension
Hypertrophy
Lung
Models, Animal
Monocrotaline
Nitric Oxide Synthase
Pulmonary Artery
Rats*
Vascular Remodeling
Vascular Resistance
Vasoconstriction*
Vasoconstrictor Agents
Angiotensins
Eosine Yellowish-(YS)
Hematoxylin
Monocrotaline
Nitric Oxide Synthase
Vasoconstrictor Agents

Figure

• 

  Fig. 1 Medial thickening of PAs and right ventricular hypertrophy in PAH-MCT rats.(A~C) Representative histological images (H&E staining) of the lungs from the control (A), PAH-MCT (MCT, B), and PAH-CH (CH, C) rats. Compared to the control, the PAs from the MCT-injected and CH-exposed rats showed marked hypertrophic changes. (D, E) Representative images of the heart from the control (D) and PAH-MCT (E) rats. (F) The right ventricular hypertrophy index [RV/(LV+S)] is shown as bar graphs. ***p<0.001.

• 

  Fig. 2 Comparison of HPV, basal PAP, and Ang II-induced ΔPAP in V/P lungs of the control, PAH-MCT, and PAH-CH rats.(A~C) Representative traces of PAP recording in the control (A), PAH-MCT (B), and PAH-CH (C) rats. The basal PAP significantly increased in the PAH-MCT rats. The hypoxic ventilation (3% Po2)-induced PAP increase (ΔPAPHypoxia) was robust in the PAH-MCT rats, whereas HPV was abolished in the PAH-CH rats. The Ang II-induced contraction also improved in the PAH-MCT rats. (D~F) Summaries of Ang II-induced ΔPAP (D), basal PAP (E), and ΔPAPHypoxia (F) are shown as bar graphs comparing the results among the three groups. ***p<0.001.

• 

  Fig. 3 Effect of a high K+-induced membrane depolarization on PAP in the control and PAH-MCT rats.(A, B) Representative traces of PAP recording in the control (A) and PAH-MCT (B) rats. Application of a high potassium concentration (40 mM KCl, 40K) induced an increase of PAP in both groups. (C) The amplitude of PAP (ΔPAP) is shown as bar graphs. The ΔPAP in the presence of 40K was higher in the PAH-MCT group than in the control. *p<0.05.

• 

  Fig. 4 Effects of NOS inhibition on PAP and HPV in V/P lungs.(A~C) Representative traces of PAP recording in the control (A), PAH-MCT (B), and PAH-CH (C) rats. A marked increase of PAP was observed in the PAH-MCT rats with the non-specific NOS inhibitor, L-NAME (100 µM). (D) Summarized results for the three groups are shown as bar graphs. *p<0.05, **p<0.01, ***p<0.001.

• 

  Fig. 5 Effect of increased flow rate in V/P lungs of the control and PAH-MCT rats.(A, B) Representative traces of responses to the serially increased flow rate in the control and PAH-MCT rats (A). In accordance with the sequentially increased flow rate (from 5 to 45 mL/min, 5 mL/min increments), PAP in the PAH-MCT rats was significantly higher (B). Upon L-NAME (100 µM) pretreatment, the rate of the PAP increase in the PAH-MCT rats was much higher than that in saline (C). *p<0.05, **p<0.01, ***p<0.001.

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