Endogenous estrogen attenuates pulmonary artery vasoreactivity and acute hypoxic pulmonary vasoconstriction: the effects of sex and menstrual cycle

Sex differences exist in a variety of cardiovascular disorders. Sex hormones have been shown to mediate pulmonary artery (PA) vasodilation. However, the effects of fluctuations in physiological sex hormone levels due to sex and menstrual cycle on PA vasoreactivity have not been clearly established yet. We hypothesized that sex and menstrual cycle affect PA vasoconstriction under both normoxic and hypoxic conditions. Isometric force displacement was measured in isolated PA rings from proestrus females (PF), estrus and diestrus females (E/DF), and male (M) Sprague-Dawley rats. The vasoconstrictor response under normoxic conditions (organ bath bubbled with 95% O(2)-5% CO(2)) was measured after stimulation with 80 mmol/l KCl and 1 mumol/l phenylephrine. Hypoxia was generated by changing the gas to 95% N(2)-5% CO(2). PA rings from PF demonstrated an attenuated vasoconstrictor response to KCl compared with rings from E/DF (75.58 +/- 3.2% vs. 92.43 +/- 4.24%, P < 0.01). Rings from M also exhibited attenuated KCl-induced vasoconstriction compared with E/DF (79.34 +/- 3.2% vs. 92.43 +/- 4.24%, P < 0.05). PA rings from PF exhibited an attenuated vasoconstrictor response to phenylephrine compared with E/DF (59.61 +/- 2.98% vs. 70.03 +/- 4.61%, P < 0.05). While the maximum PA vasodilation during hypoxia did not differ between PF, E/DF, and M, phase II of hypoxic pulmonary vasoconstriction was markedly diminished in the PA from PF (64.10 +/- 7.10% vs. 83.91 +/- 5.97% in M, P < 0.05). We conclude that sex and menstrual cycle affect PA vasoconstriction in isolated PA rings. Even physiological increases in circulating estrogen levels attenuate PA vasoconstriction under both normoxic and hypoxic conditions.     

Inhalation of the ETA receptor antagonist LU-135252 selectively attenuates hypoxic pulmonary vasoconstriction

Endogenous endothelin (ET)-1 modulates hypoxic pulmonary vasoconstriction (HPV). Accordingly, intravenously applied ET(A) receptor antagonists reduce HPV, but this is accompanied by systemic vasodilation. We hypothesized that inhalation of an ET(A) receptor antagonist might act selectively on the pulmonary vasculature and investigated the effects of aerosolized LU-135252 in an experimental model of HPV. Sixteen piglets (weight: 25 +/- 1 kg) were anesthetized and mechanically ventilated at an inspiratory oxygen fraction (Fi(O(2))) of 0.3. After 1 h of hypoxia at Fi(O(2)) 0.15, animals were randomly assigned either to receive aerosolized LU-135252 as bolus (0.3 mg/kg for 20 min; n = 8, LU group), or to receive aerosolized saline (n = 8, controls). In all animals, hypoxia significantly increased mean pulmonary arterial pressure (32 +/- 1 vs. 23 +/- 1 mmHg; P < 0.01; means +/- SE) and increased arterial plasma ET-1 (0.52 +/- 0.04 vs. 0.37 +/- 0.05 fmol/ml; P < 0.01) compared with mild hyperoxia at Fi(O(2)) 0.3. Inhalation of LU-135252 induced a significant and sustained decrease in mean pulmonary arterial pressure compared with controls (LU group: 27 +/- 1 mmHg; controls: 32 +/- 1 mmHg; values at 4 h of hypoxia; P < 0.01). In parallel, mean systemic arterial pressure and cardiac output remained stable and were not significantly different from control values. Consequently, in our experimental model of HPV, the inhaled ET(A) receptor antagonist LU-135252 induced selective pulmonary vasodilation without adverse systemic hemodynamic effects.     

Diacylglycerol regulates acute hypoxic pulmonary vasoconstriction via TRPC6

Background

Hypoxic pulmonary vasoconstriction (HPV) is an essential mechanism of the lung that matches blood perfusion to alveolar ventilation to optimize gas exchange. Recently we have demonstrated that acute but not sustained HPV is critically dependent on the classical transient receptor potential 6 (TRPC6) channel. However, the mechanism of TRPC6 activation during acute HPV remains elusive. We hypothesize that a diacylglycerol (DAG)-dependent activation of TRPC6 regulates acute HPV.

Methods

We investigated the effect of the DAG analog 1-oleoyl-2-acetyl-sn-glycerol (OAG) on normoxic vascular tone in isolated perfused and ventilated mouse lungs from TRPC6-deficient and wild-type mice. Moreover, the effects of OAG, the DAG kinase inhibitor {"type":"entrez-nucleotide","attrs":{"text":"R59949","term_id":"830644","term_text":"R59949"}}R59949 and the phospholipase C inhibitor {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075"}}U73122 on the strength of HPV were investigated compared to those on non-hypoxia-induced vasoconstriction elicited by the thromboxane mimeticum U46619.

Results

OAG increased normoxic vascular tone in lungs from wild-type mice, but not in lungs from TRPC6-deficient mice. Under conditions of repetitive hypoxic ventilation, OAG as well as {"type":"entrez-nucleotide","attrs":{"text":"R59949","term_id":"830644","term_text":"R59949"}}R59949 dose-dependently attenuated the strength of acute HPV whereas U46619-induced vasoconstrictions were not reduced. Like OAG, {"type":"entrez-nucleotide","attrs":{"text":"R59949","term_id":"830644","term_text":"R59949"}}R59949 mimicked HPV, since it induced a dose-dependent vasoconstriction during normoxic ventilation. In contrast, {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075"}}U73122, a blocker of DAG synthesis, inhibited acute HPV whereas {"type":"entrez-nucleotide","attrs":{"text":"U73343","term_id":"1688125"}}U73343, the inactive form of {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075"}}U73122, had no effect on HPV.

Conclusion

These findings support the conclusion that the TRPC6-dependency of acute HPV is induced via DAG.     

Attenuation of acute hypoxic pulmonary vasoconstriction and hypoxic pulmonary hypertension in mice by inhibition of Rho-kinase

RhoA GTPase mediates a variety of cellular responses, including activation of the contractile apparatus, growth, and gene expression. Acute hypoxia activates RhoA and, in turn, its downstream effector, Rho-kinase, and previous studies in rats have suggested a role for Rho/Rho-kinase signaling in both acute and chronically hypoxic pulmonary vasoconstriction. We therefore hypothesized that activation of Rho/Rho-kinase in the pulmonary circulation of mice contributes to acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension and vascular remodeling. In isolated, salt solution-perfused mouse lungs, acute administration of the Rho-kinase inhibitor Y-27632 (1 x 10(-5) M) attenuated hypoxic vasoconstriction as well as that due to angiotensin II and KCl. Chronic treatment with Y-27632 (30 mg x kg(-1) x day(-1)) via subcutaneous osmotic pump decreased right ventricular systolic pressure, right ventricular hypertrophy, and neomuscularization of the distal pulmonary vasculature in mice exposed to hypobaric hypoxia for 14 days. Analysis of a small number of proximal pulmonary arteries suggested that Y-27632 treatment reduced the level of phospho-CPI-17, a Rho-kinase target, in hypoxic lungs. We also found that endothelial nitric oxide synthase protein in hypoxic lungs was augmented by Y-27632, suggesting that enhanced nitric oxide production might have played a role in the Y-27632-induced attenuation of chronically hypoxic pulmonary hypertension. In conclusion, Rho/Rho-kinase activation is important in the effects of both acute and chronic hypoxia on the pulmonary circulation of mice, possibly by contributing to both vasoconstriction and vascular remodeling.     

缺氧性肺血管收缩的细胞机制

缺氧直接作用于肺血管平滑肌细胞而使肺血管收缩。缺氧使细胞膜Ca~(2 )通透性增加,K~ 电导降低、膜电位下降,产生Ca~(2 )依赖性动作电位,导致肺血管张力增加和肺血管收缩。缺氧还能使平滑肌细胞内能量代谢发生改变,抑制氧化磷酸化和三羧酸循环作用,降低磷酸势能,引起肺血管收缩。缺氧减少细胞内氧自由基的产生而使细胞内氧化还原状态发生改变,GSH/GSSG和NADPH/NADP~ 比值增高,导致肺血管阻力增高。     

Effects of hypoxic pulmonary vasoconstriction on pulmonary gas exchange

Brimioulle, Serge, Philippe Lejeune, and Robert Naeije.Effects of hypoxic pulmonary vasoconstriction on pulmonary gasexchange. J. Appl. Physiol. 81(4):1535-1543, 1996.Several reports have suggested that hypoxicpulmonary vasoconstriction (HPV) might result in deterioration ofpulmonary gas exchange in severe hypoxia. We therefore investigated theeffects of HPV on gas exchange in normal and diseased lungs. Weincorporated a biphasic HPV stimulus-response curve observed in intactdogs (S. Brimioulle, P. Lejeune, J. L. Vachièry, M. Delcroix, R. Hallemans, and R. Naeije, J. Appl.Physiol. 77: 476-480, 1994) into a 50-compartment lung model (J. B. West, Respir.Physiol. 7: 88-110, 1969) to control the amount ofblood flow directed to each lung compartment according to the localhypoxic stimulus. The resulting model accurately reproduced the bloodgas modifications caused by HPV changes in dogs with acute lung injury.In single lung units, HPV had a moderate protective effect on alveolaroxygenation, which was maximal at near-normal alveolarPO₂ (75-80 Torr), mixed venousPO₂ (35 Torr), andPO₂ at which hemoglobin is 50%saturated (24 Torr). In simulated diseased lungs associated with40-60 Torr arterial PO₂,however, HPV increased arterial PO₂ by 15-20 Torr. We conclude that HPV can improve arterialoxygenation substantially in respiratory failure.

     

PEEP inhibits hypoxic pulmonary vasoconstriction in dogs

The effects of an increase in alveolar pressure on hypoxic pulmonary vasoconstriction (HPV) have been reported variably. We therefore studied the effects of positive end-expiratory pressure (PEEP) on pulmonary hemodynamics in 13 pentobarbital-anesthetized dogs ventilated alternately in hyperoxia [inspired O2 fraction (FIO2) 0.4] and in hypoxia (FIO2 0.1). In this intact animal model, HPV was defined as the gradient between hypoxic and hyperoxic transmural (tm) mean pulmonary arterial pressure [Ppa(tm)] at any level of cardiac index (Q). Ppa(tm)/Q plots were constructed with mean transmural left atrial pressure [Pla(tm)] kept constant at approximately 6 mmHg (n = 5 dogs), and Ppa(tm)/PEEP plots were constructed with Q kept constant approximately 2.8 l.min-1.m-2 and Pla(tm) kept constant approximately 8 mmHg (n = 8 dogs). Q was manipulated using a femoral arteriovenous bypass and a balloon catheter in the inferior vena cava. Pla(tm) was held constant by a balloon catheter placed by left thoracotomy in the left atrium. Increasing PEEP, from 0 to 12 Torr by 2-Torr increments, at constant Q and Pla(tm), increased Ppa(tm) from 14 +/- 1 (SE) to 19 +/- 1 mmHg in hyperoxia but did not affect Ppa(tm) (from 22 +/- 2 to 23 +/- 1 mmHg) in hypoxia. Both hypoxia and PEEP, at constant Pla(tm), increased Ppa(tm) over the whole range of Q studied, from 1 to 5 l/min, but more at the highest than at the lowest Q and without change in extrapolated pressure intercepts. Adding PEEP to hypoxia did not affect Ppa(tm) at all levels of Q.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of acid-base status on acute hypoxic pulmonary vasoconstriction and gas exchange.

To investigate the relationship between hypoxic pulmonary vasoconstriction and respiratory and metabolic acidosis and respiratory alkalosis, the pulmonary gas exchange and pulmonary hemodynamic responses were measured in anesthetized, paralyzed, and mechanically ventilated dogs in two sets of experiments (series A, n = 6; series B, n = 10). The animals were treated with acute hypoxia, CO2 inhalation, hyperventilation, and dinitrophenol in various combinations. Multiple regression analysis indicated that mean pulmonary arterial pressure (Ppa) was significantly correlated with end-tidal PO2, mixed venous PO2, and the mean pulmonary capillary pH (average of arterial and mixed venous pH) as independent variables [series A: r = +0.999, standard error of estimate (SEE) = 0.4 mmHg; series B: r = +0.98, SEE = 1.4 mmHg]. Similar analyses of mean values published by other authors from an acute study on humans with exercise at sea level and simulated altitudes of 10,000 and 15,000 ft also indicated a good relationship (n = 14, r = +0.98, SEE = 2.1 mmHg). The mean data (n = 19) obtained in Operation Everest II at various exercise loads and simulated altitudes gave a correlation of r = +0.87, SEE = 6.1 mmHg. These empirical analyses suggest that variations in the rise of Ppa with hypoxia can be accounted for in vivo by the superimposed acid-base status. Furthermore, ventilation-perfusion inhomogeneity, as estimated in the dogs from end-tidal and arterial O2 and CO2 differences and assuming no true shunt or diffusion impairment, was highly correlated with Ppa and mean pulmonary capillary pH (r = +0.999 in series A, r = +0.77 in series B). The human data from the above studies also showed significant correlations between Ppa and directly measured ventilation-perfusion (standard deviation of perfusion obtained from inert gas measurements). These observations indicate that the beneficial effects of hyperventilation during hypoxia may be related to the marked alkalosis that serves to reduce Ppa and improve pulmonary gas exchange efficiency.     

Red blood cells prevent inhibition of hypoxic pulmonary vasoconstriction by nitrite in isolated, perfused rat lungs

Nitrite reduction to nitric oxide (NO) may be potentiated by a nitrite reductase activity of deoxyHb and contribute to systemic hypoxic vasodilation. The effect of nitrite on the pulmonary circulation has not been well characterized. We explored the effect of nitrite on hypoxic pulmonary vasoconstriction (HPV) and the role of the red blood cell (RBC) in nitrite reduction and nitrite-mediated vasodilation. As to method, isolated rat lungs were perfused with buffer, or buffer with RBCs, and subjected to repeated hypoxic challenges, with or without nitrite. As a result, in buffer-perfused lungs, HPV was reduced at nitrite concentrations of 7 muM and above. Nitrite inhibition of HPV was prevented by excess free Hb and RBCs, suggesting that vasodilation was mediated by free NO. Nitrite-inhibition of HPV was not potentiated by mild acidosis (pH = 7.2) or xanthine oxidase activity. RBCs at 15% but not 1% hematocrit prevented inhibition of HPV by nitrite (maximum nitrite concentration of approximately 35 muM) independent of perfusate Po(2). Degradation of nitrite was accelerated by hypoxia in the presence of RBCs but not during buffer perfusion. In conclusion, low micromolar concentrations of nitrite inhibit HPV in buffer-perfused lungs and when RBC concentration is subphysiological. This effect is lost when RBC concentration approaches physiological levels, despite enhanced nitrite degradation in the presence of RBCs. These data suggest that, although deoxyHb may generate NO from nitrite, insufficient NO escapes the RBC to cause vasodilation in the pulmonary circulation under the dynamic conditions of blood flow through the lungs and that RBCs are net scavengers of NO.     

Regional hypoxic pulmonary vasoconstriction in prone pigs.

Hypoxic pulmonary vasoconstriction (HPV) is known to affect regional pulmonary blood flow distribution. It is unknown whether lungs with well-matched ventilation (V)/perfusion (Q) have regional differences in the HPV response. Five prone pigs were anesthetized and mechanically ventilated (positive end-expiratory pressure = 2 cmH2O). Two hypoxic preconditions [inspired oxygen fraction (FI(O2)) = 0.13] were completed to stabilize the animal's hypoxic response. Regional pulmonary blood Q and V distribution was determined at various FI(O2) (0.21, 0.15, 0.13, 0.11, 0.09) using the fluorescent microsphere technique. Q and V in the lungs were quantified within 2-cm3 lung pieces. Pieces were grouped, or clustered, based on the changes in blood flow when subjected to increasing hypoxia. Unique patterns of Q response to hypoxia were seen within and across animals. The three main patterns (clusters) showed little initial difference in V/Q matching at room air where the mean V/Q range was 0.92-1.06. The clusters were spatially located in cranial, central, and caudal portions of the lung. With decreasing FI(O2), blood flow shifted from the cranial to caudal regions. We determined that pulmonary blood flow changes, caused by HPV, produced distinct response patterns that were seen in similar regions across our prone porcine model.     

Precursors and inhibitors of hydrogen sulfide synthesis affect acute hypoxic pulmonary vasoconstriction in the intact lung

The effects of hydrogen sulfide (H(2)S) and acute hypoxia are similar in isolated pulmonary arteries from various species. However, the involvement of H(2)S in hypoxic pulmonary vasoconstriction (HPV) has not been studied in the intact lung. The present study used an intact, isolated, perfused rat lung preparation to examine whether adding compounds essential to H(2)S synthesis or to its inhibition would result in a corresponding increase or decrease in the magnitude of HPV. Western blots performed in lung tissue identified the presence of the H(2)S-synthesizing enzymes, cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfur transferase (3-MST), but not cystathionine β-synthase (CBS). Adding three H(2)S synthesis precursors, cysteine and oxidized or reduced glutathione, to the perfusate significantly increased peak arterial pressure during hypoxia compared with control (P < 0.05). Adding α-ketoglutarate to enhance the 3-MST enzyme pathway also resulted in an increase (P < 0.05). Both aspartate, which inhibits the 3-MST synthesis pathway, and propargylglycine (PPG), which inhibits the CSE pathway, significantly reduced the increases in arterial pressure during hypoxia. Diethylmaleate (DEM), which conjugates sulfhydryls, also reduced the peak hypoxic arterial pressure at concentrations >2 mM. Finally, H(2)S concentrations as measured with a specially designed polarographic electrode decreased markedly in lung tissue homogenate and in small pulmonary arteries when air was added to the hypoxic environment of the measurement chamber. The results of this study provide evidence that the rate of H(2)S synthesis plays a role in the magnitude of acute HPV in the isolated perfused rat lung.     

Reduction of hypoxic pulmonary vasoconstriction during trichloroethylene anesthesia.

A double-lumen tube was inserted into the trachea of dogs anesthetized with intravenous pentobarbital (30-40 mg/kg). Blood flow/unit lung volume in each lung was measured with 133Xe. Both lungs were initially ventilated with oxygen and measurements of pulmonary blood flow, CO2 output, cardiac output, and blood gases were made. When nitrogen was administered to one lung blood flow was diverted to the opposite lung. The diversion of flow was reduced by the inhalation of 1% trichloroethylene but returned after withdrawal of the anesthetic. There were no significant changes in cardiac output. Changes in CO2 output and arterial Po2 were compatible with the xenon results. It is concluded that trichloroethylene may increase arterial hypoxemia by reducing vasoconstriction in hypoxic areas of lung.