Nebulization of sodium nitroprusside in lung-lavaged newborn piglets

Pharmacologic management of perioperative pulmonary hypertension

Perioperative pulmonary hypertension can originate from an established disease or acutely develop within the surgical setting. Patients with increased pulmonary vascular resistance are consequently at greater risk for complications. Despite the various specific therapies available, the ideal therapeutic approach in this patient population is not currently clear. This article describes the basic principles of perioperative pulmonary hypertension and reviews the different classes of agents used to promote pulmonary vasodilation in the surgical setting.

Smooth muscle myosin inhibition: a novel therapeutic approach for pulmonary hypertension

Objective

Pulmonary hypertension remains a major clinical problem despite current therapies. In this study, we examine for the first time a novel pharmacological target, smooth muscle myosin, and determine if the smooth muscle myosin inhibitor, CK-2019165 (CK-165) ameliorates pulmonary hypertension.

Materials and Methods

Six domestic female pigs were surgically instrumented to measure pulmonary blood flow and systemic and pulmonary vascular dynamics. Pulmonary hypertension was induced by hypoxia, or infusion of the thromboxane analog (U-46619, 0.1 µg/kg/min, i.v.). In rats, chronic pulmonary hypertension was induced by monocrotaline.

Results

CK-165 (4 mg/kg, i.v.) reduced pulmonary vascular resistance by 22±3 and 28±6% from baseline in hypoxia and thromboxane pig models, respectively (p<0.01 and 0.01), while mean arterial pressure also fell and heart rate rose slightly. When CK-165 was delivered via inhalation in the hypoxia model, pulmonary vascular resistance fell by 17±6% (p<0.05) while mean arterial pressure and heart rate were unchanged. In the monocrotaline model of chronic pulmonary hypertension, inhaled CK-165 resulted in a similar (18.0±3.8%) reduction in right ventricular systolic pressure as compared with sildenafil (20.3±4.5%).

Conclusion

Inhibition of smooth muscle myosin may be a novel therapeutic target for treatment of pulmonary hypertension.

Inhaled alternatives to nitric oxide

OBJECTIVE

Inhaled nitric oxide has gained an established place in the management of pulmonary hypertension. However, cost, potential toxicity, and the lack of positive outcome data with inhaled nitric oxide therapy has generated interest in alternative inhaled, selective pulmonary vasodilators. This article describes those alternatives that have been studied to date.

DESIGN

Literature review of inhaled, selective pulmonary vasodilators other than nitric oxide.

METHODS

A review of the molecular mechanisms, potential side effects, and the studies to date in both animal models and clinical studies describing the physiologic effects of alternative agents to inhaled nitric oxide.

CONCLUSION

There are a number of available agents that have comparable physiologic effects as inhaled nitric oxide. The best studied of these are the inhaled prostanoids (prostacyclin and iloprost), and there is growing interest in novel therapies such as phosphodiesterase inhibitors and neuropeptides.

Cardiopulmonary effects of nebulized sodium nitroprusside in term infants with hypoxic respiratory failure

OBJECTIVE

To study whether nebulized nitroprusside (neb-NP) improves oxygenation in term infants with hypoxic respiratory failure (HRF).

STUDY DESIGN

We studied 22 newborn term infants (gestational age, 39.7+/-0.4 weeks [mean+/-SEM]; birth weight, 3.6+/-0.1 kg) with hypoxia (Pao2<100 mm Hg) during mechanical ventilation (Fio2=1.0). Sodium nitroprusside (5 mg followed by 25 mg) was nebulized into the inspiratory arm of the ventilator circuit. Vital signs and arterial blood gas values were recorded after 20 minutes at each dose and before and after initiation of inhaled nitric oxide (iNO).

RESULTS

Pao2 increased significantly with 5 mg neb-NP (from 64.6+/-5.6 to 90.1+/-15.3 mm Hg, P=.04) and with 25 mg neb-NP (113.2+/-20.4 mm Hg, P=.009). Differences between mean Pao2 at 5 mg versus 25 mg neb-NP were also statistically significant (P=.03). When comparing the effect of neb-NP to iNO, the treatment-induced increases in Pao2 were similar (52.1+/-18.7 vs 62.2+/-18.2 mm Hg, respectively, P=not significant).

CONCLUSIONS

Neb-NP causes a dose-dependent increase in oxygenation in term infants with HRF, similar in magnitude to iNO* Neb-NP may be beneficial in infants with HRF when iNO is not readily available.

Nitric oxide- and nitric oxide donors-induced relaxation and its modulation by oxidative stress in piglet pulmonary arteries

Inhaled nitric oxide (iNO) is widely used in the treatment of pulmonary hypertension while inhaled NO donors have been suggested as an alternative therapy. The differential susceptibility to inactivation by oxidative stress and oxyhaemoglobin of NO and two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP) were analysed in isolated endothelium-denuded pulmonary arteries from 2-week-old piglets stimulated with U46619. NO, SNAP and SNP relaxed the arteries (pIC(30)=7.73+/-0.12, 7.26+/-0.17 and 6.43+/-0.13, respectively) but NO was not detected electrochemically in the bath after the addition of SNP and only at concentrations at which SNAP produced more than 50% relaxation. The sGC inhibitor ODQ (10(-6) M) or the sarcoplasmic Ca(2+)-ATPase thapsigargin (2x10(-6) M) markedly inhibited the relaxation induced by NO, SNAP and SNP. Addition of oxyhaemoglobin (3x10(-7) M) or diethyldithiocarbamate (1 mM) markedly inhibited NO- (pIC(30)=6.88+/-0.07 and 6.92+/-0.18, respectively), weakly inhibited SNAP- and had no effect on SNP-induced relaxation. Xanthine oxidase (5 mu ml(-1)) plus hypoxanthine (10(-4) M) markedly inhibited NO- (pIC(30)=6.96+/-0.12) but not SNAP- or SNP-induced relaxation. Superoxide dismutase (SOD), MnCl(2), diphenileneiodonium and exposing the luminal surface of the rings outwards (inversion) potentiated the relaxant responses of NO (pIC(30)=8.52+/-0.16, 8.23+/-0.11, 8.01+/-0.11 and 8.20+/-0.10, respectively). However, SOD did not modify the NO detected by the electrode and had no effect on SNAP- or SNP-induced relaxation. Therefore, the kinetics and local distribution of NO release of NO donors influence the susceptibility to the scavenging effects of oxyhaemoglobin and superoxide.

Mechanisms involved in SNP-induced relaxation and [Ca+]i reduction in piglet pulmonary and systemic arteries

1. We have compared the mechanisms involved in sodium nitroprusside (SNP)-induced relaxation and [Ca2+]i reduction in isolated piglet pulmonary (PA) and mesenteric (MA) arteries. 2. SNP (10(-8) M-3x10(-5) M) evoked a concentration-dependent relaxation of PA and MA (pD2=6.66+/-0.06 and 6.74+/-0.14, respectively) stimulated by noradrenaline, which was markedly reduced by the guanylate cyclase inhibitor ODQ. In fura 2-incubated PA and MA, SNP produced a parallel reduction in contractile force and in [Ca2+]i, expressed as the ratio of emitted fluorescence at 340 and 380 nm (F340/F380). 3. The inhibition of the Na+/K+-ATPase after the incubation in a K+-free medium or the exposure to ouabain (10(-6) M) inhibited SNP-induced relaxation in MA but not in PA. SNP-induced relaxation was not attenuated by 80 mM KCl plus nifedipine (10(-6) M) but was inhibited by thapsigargin (2x10(-6) M; pD2=5.69+/-0.19 and 5.89+/-0.19 for PA and MA, respectively). 4. Pretreatment of PA with thapsigargin and MA with thapsigargin plus ouabain induced a stronger inhibition on the reduction in [Ca2+]i than on the relaxation induced by SNP, indicating the existence of Ca2+-independent mechanisms. 5. The activation of the Na+/K+-ATPase by the addition of KCl after the incubation in a K+-free medium similarly reduced [Ca2+]i in PA and MA, whereas it relaxed with much less efficacy PA than MA. 6. We conclude that SNP reduces [Ca2+]i and causes relaxation through the activation of SERCA in PA and SERCA and Na+/K+-ATPase in MA. However, Ca2+-independent mechanisms also contribute to SNP-induced effects.