Pulmonary vasoreactivity in spontaneously hypertensive rats--effects of endothelin-1 and leptin

Abstract

Background: Systemic hypertension may be associated with an increased pulmonary vascular resistance, which we hypothesized could be, at least in part, mediated by increased leptin.

Methods: Vascular reactivity to phenylephrine (1 μmol/L), endothelin-1 (10 nmol/L) and leptin (0.001-100 nmol/L) was evaluated in endothelium-intact and -denuded isolated thoracic aorta and pulmonary arteries from spontaneously hypertensive versus control Wistar rats. Arteries were sampled for pathobiological evaluation and lung tissue for morphometric evaluation.

Results: In control rats, endothelin-1 induced a higher level of contraction in the pulmonary artery than in the aorta. After phenylephrine or endothelin-1 precontraction, leptin relaxed intact pulmonary artery and aortic rings, while no response was observed in denuded arteries. Spontaneously hypertensive rats presented with increased reactivity to phenylephrine and endothelin-1 in endothelium-intact pulmonary arteries. After endothelin-1 precontraction, endothelium-dependent relaxation to leptin was impaired in pulmonary arteries from hypertensive rats. In both strains of rats, aortic segments were more responsive to leptin than pulmonary artery. In hypertensive rats, pulmonary arteries exhibited increased pulmonary artery medial thickness, associated with increased expressions of preproendothelin-1, endothelin-1 receptors type A and B, inducible nitric oxide synthase and decreased endothelial nitric oxide synthase, together with decreased leptin receptor and increased suppressor of cytokine signaling 3 expressions.

Conclusions: Altered pulmonary vascular reactivity in hypertension may be related to a loss of endothelial buffering of vasoconstriction and decreased leptin-induced vasodilation in conditions of increased endothelin-1.

Figure 1

Maximal contractile responses to phenylephrine and endothelin-1 in control Wistar and spontaneously hypertensive rats. Comparison of contractile responses of endothelium-denuded (−) and –intact (+) thoracic aortic and pulmonary artery rings to phenylephrine (1 μmol/L) (A) and endothelin-1 (10 nmol/L) (B). Thoracic aortic and pulmonary artery segments are collected in control Wistar rats (white bars; n = 7-13) and in spontaneously hypertensive rats (black bars; n = 10-15). Contractile responses are expressed as the percentage of the maximal contractile response to 80 mmol/L KCl. Results are expressed as means ± SEM. ** 0.001 < p < 0.01, *** p < 0.001 compared to the corresponding endothelium-intact (+) artery; $ 0.01 < p < 0.05, $$$ p < 0.001 compared to the corresponding artery from the control group; ♯ 0.01 < p < 0.05, ♯♯♯ p < 0.001 compared to the thoracic artery in the same strain of rats.

Figure 2

Concentration-response curves to leptin after phenylephrine precontraction in pulmonary artery compared to thoracic aortic segments. The endothelium-denuded (−) and –intact (+) thoracic aortic and pulmonary artery rings collected from control Wistar (A) and spontaneously hypertensive rats (B) were precontracted with phenylephrine (1 μmol/L) before cumulative addition of leptin (0.001 to 100 nmol/L). Relaxation responses are expressed as the percentages of the maximal tension response obtained with 1 μmol/L phenylephrine. Response curves to leptin after endothelin-1 precontraction in pulmonary artery compared to thoracic aortic segments. The endothelium-denuded (−) and –intact (+) thoracic aortic and pulmonary artery rings from control Wistar rats (C) and spontaneously hypertensive rats (D) were precontracted with endothelin-1 (10 nmol/L) before the addition of leptin (100 nmol/L). Relaxation responses are expressed as the percentages of the maximal tension response obtained with 10 nmol/L endothelin-1. Thoracic aortic and pulmonary artery segments are collected in control Wistar rats (n = 7-13) and in spontaneously hypertensive rats (n = 10-15). Results are expressed as means ± SEM. *** p < 0.001 compared to the corresponding endothelium-intact (+) artery; ♯ 0.01 < p < 0.05, ♯♯ 0.001 < p < 0.01, ♯♯♯ p < 0.001 compared to the thoracic artery in the same strain of rats.

Figure 3

Concentration-response curves to leptin after phenylephrine precontraction in spontaneously hypertensive compared to control Wistar rats. The endothelium-denuded (−) and –intact (+) thoracic aortic (A) and pulmonary artery (B) rings were precontracted with 1 μmol/L phenylephrine before cumulative addition of leptin (0.001 to 100 nmol/L). Relaxation responses are expressed as the percentages of the maximal tension response obtained with 1 μmol/L phenylephrine. Response curves to leptin after endothelin-1 precontraction in spontaneously hypertensive rats compared to control Wistar rats. The endothelium-denuded (−) and –intact (+) thoracic aortic (C) and pulmonary artery (D) rings were precontracted with endothelin-1 (10 nmol/L) before addition of leptin (100 nmol/L). Relaxation responses are expressed as the percentages of the maximal tension response obtained with 10 nmol/L endothelin-1. Thoracic aortic and pulmonary artery segments are collected in control Wistar rats (n = 7-13) and in spontaneously hypertensive rats (n = 10-15). Results are expressed as means ± SEM. * 0.01 < p < 0.05, *** p < 0.001 compared to the corresponding endothelium-intact (+) artery; $$$ p < 0.001 compared to the corresponding artery from the control group.

Figure 4

Representative slides of pulmonary arterioles obtained from control Wistar and from spontaneously hypertensive rats. Hematoxyllin-Eosin method staining (A; scale bars: 50 μm). Morphometry on pulmonary arterioles expressed as the medial thickness percentage versus the pulmonary artery external diameter in control Wistar rats (n = 6; white bars) and in spontaneously hypertensive rats (n = 6; black bars) pigs (B). Values are expressed as mean ± SEM. $ 0.01 < p < 0.05 compared to the control pulmonary artery.

Figure 5

Expression of genes implicated in the endothelin-1 and nitric oxide signaling pathways. Relative gene expressions of the preproendothelin-1 (PPET-1, A), the endothelin converting enzyme-1 (ECE-1; B), the endothelin receptor type A (ET_A; C), the endothelin receptor type B (ET_B; D) and the endothelial (eNOS; E) and the inducible (iNOS; F) nitric oxide synthase in thoracic aorta and pulmonary artery from control Wistar rats and from spontaneously hypertensive rats (SHR). Results are expressed as means ± SEM. $ 0.01 < p < 0.05 compared to the corresponding artery from the control group; ♯ 0.01 < p < 0.05, ♯♯ 0.001 < p < 0.01 compared to the thoracic artery in the same strain of rats.

Figure 6

Expression of genes implicated in the leptin signaling. Relative gene expressions of the leptin (A), the leptin receptor (B) and the suppressor of cytokine signaling 3 (SOCS3; C) in thoracic aorta and pulmonary artery from control Witar rats and spontaneously hypertensive rats (SHR). Results are expressed as means ± SEM. $ 0.01 < p < 0.05 compared to the corresponding artery from the control group; ♯ 0.01 < p < 0.05, ♯♯ 0.001 < p < 0.01, ♯♯♯ p < 0.001 compared to the thoracic artery in the same strain of rats.