Pulmonary vasodilation in the rat by insulin in vitro could indicate potential hazard for inhaled insulin.

AIMS/HYPOTHESIS: Hypoxic pulmonary vasoconstriction is an essential mechanism to prevent hypoxaemia in lung diseases. Insulin is known to be a systemic vasodilator but its effect on the pulmonary circulation is not known. Inhaled particulate insulin can generate locally high concentrations in the lung which could be physiologically important. METHODS: We therefore studied the effects of insulin in vitro on isolated rat pulmonary artery in a small vessel myograph. RESULTS: We have shown that pulmonary artery vasodilatation with insulin occurs in a dose-dependent manner. Pre-constriction with PGF2alpha can be abolished (105.7+/-2.9%, mean+/-SEM) and pre-constriction with hypoxia reduced (68.9+/-6.5%) by pharmacologically relevant concentrations of insulin. The characteristic phasic vasoconstriction by pulmonary vessel to hypoxia is substantially modified, resulting in sustained vasodilatation. CONCLUSIONS/INTERPRETATION: These effects could be clinically important for patients using inhaled insulins who have acute or occult chronic lung disease.

The effect of the ETA receptor antagonist (CI-1020) in rats with established hypoxic pulmonary hypertension.

ETA receptor antagonists have previously been shown to prevent the development of pulmonary hypertension induced by chronic hypoxia in the rat. Clinically, however, patients present with already established pulmonary hypertension. We have investigated the effects of the ETA receptor antagonist CI-1020 in rats previously adapted to chronic hypoxia. Two protocols were followed. Rats (n=32) were divided into two batches of four groups: normoxic controls in air for 10 days (NC10), chronic hypoxic controls in hypoxia for 10 days (CHC10), chronic hypoxic vehicle treated in hypoxia for 20 days (CHV20) and chronic hypoxic drug treated in hypoxia for 20 days (CHT20). Ten days after the onset of hypoxia, oral treatment with drug (40 mg/kg per day) or vehicle was started. Animal weight, ratio of right ventricular weight to left ventricular weight including septum (RV/LV+S) and percentage of double elastic lamina (DEL) were determined. In the second study, 12 rats were divided into three groups; normoxic controls in air for 20 days (NC20), (CHV20) and (CHT20). After 10 days hypoxia, oral treatment with drug (40 mg/kg per day) or vehicle was started. Isolated perfused lung preparations were then used to determine pulmonary artery pressure and pulmonary vascular resistance. Treatment with CI-1020 reduced the increase in RV/LV+S and the percentage DEL induced by chronic hypoxia and significantly lowered the increase in pulmonary resistance in isolated perfused lungs from chronically hypoxic animals. These results suggest that CI-1020 could have an important role in the treatment and reversal of established pulmonary vascular remodelling.

A comparison of pathophysiological changes during hypobaric and normobaric hypoxia in rats.

Littermate male Wistar specific pathogen-free rats were divided into three groups at 28 days of age. The pathophysiological effects seen in rats exposed to normobaric hypoxia (NB) at 10% O2 were compared with those seen in animals exposed to hypobaric hypoxia (HB) at 500 mbar, equivalent to an inspired O2 concentration of 10%, and controls after periods of 5, 10 and 14 days. 5 days' exposure to a low oxygen environment resulted in less weight gain, the development of right ventricular hypertrophy and double elastic laminae in the pulmonary arterioles and an increase in haematocrit and plasma levels of atrial natriuretic peptide (ANP) in both the HB and NB animals compared to controls. There was no significant difference in these values between the two hypoxic groups. After 10 days' exposure to a low oxygen environment, body weight, ventricular ratio, plasma ANP levels and double elastic laminae were higher than the levels seen after 5 days in both NB and HB groups of rats. At day 14 only body weight and haematocrit were greater when compared to day 10 values in NB and HB groups. In conclusion the stress of this hypobaric environment caused no additional changes in the pathophysiological variables studied, compared with the changes seen in NB.

Plasma levels of atrial natriuretic peptide and brain natriuretic peptide following intravenous saline infusion in oedematous chronic obstructive pulmonary disease and non-oedematous chronic obstructive pulmonary disease.

Some patients with chronic obstructive pulmonary disease (COPD) develop oedematous COPD (oCOPD) with peripheral oedema and have a poor prognosis. The cause of the fluid retention is poorly understood but could be due to defective release of a natriuretic factor. We investigated this hypothesis by measuring levels of brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) before and after a 0.1 ml/kg/min 2.7% saline infusion in 6 patients with hypoxemic COPD but no history of oedema and 7 COPD patients with oCOPD. Vasopressin, aldosterone, plasma and urinary urea and electrolytes and osmolality were measured. Arterial blood gases and spirometry were also recorded. The two groups were similar in terms of age, weight, PaO2, PaCO2 and FVC. FEV1 was significantly lower in the oCOPD group. The oCOPD group excreted less urine (202 +/- 23 vs. 364 +/- 48 ml; p < 0.05) and less sodium (32 +/- 3 vs. 68 +/- 9 mmol/l; p < 0.01) as a percentage of the saline load given (18 +/- 2 vs. 30 +/- 4%; p < 0.05). Pre-infusion BNP and ANP levels were similar in both groups. BNP and ANP had an exaggerated increase in the oCOPD group on saline loading. In the oCOPD group, ANP levels were significantly greater 1 h after the saline load compared to the pre-infusion values (30 +/- 7 vs. 11 +/- 2; p < 0.05). BNP did not reach significantly greater levels than baseline values until 3 h after the infusion had ended (45 +/- 6 vs. 27 +/- 2; p < 0.05). At 1 h after the saline load, BNP and ANP levels were significantly greater in the oCOPD group (BNP 32 +/- 2 vs. 24 +/- 1; p < 0.01 and ANP 30 +/- 7 vs. 7 +/- 2; p < 0.05) when compared to COPD controls. BNP levels remained significantly different from the COPD control group 3 h after the infusion ended (45 +/- 6 vs. 26 +/- 2; p < 0.05). Although aldosterone levels were greater in the oCOPD group before the saline infusion, the hormone level was suppressed appropriately by the infusion. In conclusion, the cause of oedema in oCOPD and the inability to excrete a saline load is not due to a failure of release of BNP or ANP.

Neutral endopeptidase (NEP) inhibition in rats with established pulmonary hypertension secondary to chronic hypoxia.

1. Atrial natriuretic peptide (ANP) causes vasorelaxation in the pulmonary vasculature. ANP levels are elevated in conditions characterized by pulmonary hypertension and it has been hypothesized that ANP may be autoregulatory in the pulmonary circulation. 2. One route of ANP metabolism in vivo is by the action of the enzyme neutral endopeptidase (NEP). We have studied the effects of the NEP inhibitor, SCH 42495, in rats with established pulmonary hypertension secondary to chronic hypoxia. 3. Rats (n = 32) were divided into 4 groups. Normoxic controls were kept in air for 10 days (NC10) and all other animals were placed in a normobaric hypoxic chamber (F1 O2 10%). Chronic hypoxic controls were studied at 10 days (CHC10). After 10 days hypoxia the two remaining groups received oral treatment for a further 10 days, consisting of either SCH 42495 (30 mg kg-1, twice daily CHT20) or methyl cellulose vehicle (0.4%, twice daily, CHV20). 4. Animals were anaesthetized and blood collected for measurement of plasma ANP. Hearts were dissected and ventricles weighed and the histology of the pulmonary vasculature examined. 5. CHC10 rats had significant right ventricular hypertrophy (0.53 +/- 0.08) and pulmonary vascular remodelling (29.0 +/- 0.01%) and had gained significantly less body weight (33.2 +/- 5.5 g) than NC10 rats (0.31 +/- 0.04, 10.9 +/- 0.01%, and 59.2 +/- 11.9 g respectively). CHC10 rats had significantly elevated plasma ANP levels (58.4 +/- 9.9 pM) compared with NC10 rats (23.9 +/- 32 pM). Treatment with SCH 42495 caused a significant reduction in pulmonary vascular remodelling (25.0 +/- 0.01%) and right ventricular hypertrophy (0.52 +/- 0.09) in CHT20 rats compared with CHV20 controls (33.0 +/- 0.02% and 0.61 +/- 0.09 respectively). Pulmonary vascular remodelling was also significantly lower in CHT20 rats than CHC1O animals.6. Thus, short term inhibition of NEP causes regression of established pulmonary vascular remodelling and may be a useful therapeutic strategy in pulmonary hypertension.

Effects of the neutral endopeptidase inhibitor, SCH 42495, on the cardiovascular remodelling secondary to chronic hypoxia in rats.

1. We have investigated the effects of inhibition of neutral endopeptidase on the cardiovascular remodelling secondary to chronic hypoxia in rats using a novel neutral endopeptidase inhibitor, SCH 42495. 2. Rats were divided into four groups, two of which were maintained in a normobaric, hypoxic chamber (10% O2) and two in room air. Animals received either neutral endopeptidase inhibitor, SCH 42495 (30 mg/kg), or aqueous methyl cellulose vehicle (0.4%) twice daily by oral gavage. 3. At 1, 3, 7, 10 and 14 days, animals (n = 4 per group for days 1, 3, 7 and 14, and n = 8 for day 10) were killed. Hearts were dissected and weighed for determination of ventricular ratios, lungs were perfused with formol saline for histological examination of the pulmonary vasculature, and blood was collected for measurement of plasma atrial natriuretic peptide level. 4. Treatment with SCH 42495 caused a significant reduction in the pulmonary vascular remodelling and ventricular hypertrophy in hypoxic rats after 10 days. Plasma atrial natriuretic peptide levels were significantly elevated in both SCH 42495-treated and control hypoxic animals (n = 8) after 10 days when compared with the normoxic groups. However, there was no difference in plasma ANP levels between SCH 42495-treated and control hypoxic groups at day 10. 5. Treatment with SCH 42495 leads to a decrease in cardiovascular remodelling secondary to chronic hypoxia in rats. A local action of atrial natriuretic peptide within the pulmonary vasculature may be responsible for this effect. Modulation of atrial natriuretic peptide may have therapeutic potential in the management of conditions characterized by pulmonary hypertension and pulmonary vascular remodelling.

Haemodynamic effects of atrial natriuretic peptide in hypoxic chronic obstructive pulmonary disease.

BACKGROUND: Pulmonary artery pressure is elevated in patients with advanced chronic obstructive pulmonary disease (COPD). Release of atrial natriuretic peptide (ANP) is increased in pulmonary hypertension and this hormone may both selectively vasodilate pulmonary vessels and inhibit pulmonary vascular remodelling. The hypothesis that ANP has a physiological role in protection of the pulmonary circulation from pressure overload, and that it may be beneficial in patients with COPD, has been examined. METHODS: Ten patients with hypoxic COPD were infused for 30 minute periods with saline followed by ANP at 0.4, 2, and 10 pmol/kg/min respectively via a pulmonary artery catheter whilst monitoring haemodynamics and oxygenation. RESULTS: Levels of immunoreactive ANP (irANP) increased from a mean (SD) of 23 (15) pmol/l to a maximum of 94 (41) pmol/l. Neither systemic blood pressure, cardiac output nor total systemic vascular resistance showed any correlation with irANP levels. There were negative correlations between levels of ANP and mean pulmonary artery pressure which fell from 28.7 to 25.9 mm Hg, pulmonary artery wedge pressure which fell from 6.5 to 4.6 mmHg, and total pulmonary vascular resistance which fell from 489 to 428 dynes s cm-5. There was a small fall in PaCO2 from 6.2 to 5.9 kPa, whilst venous admixture and oxygen delivery both increased non-significantly. CONCLUSIONS: At these pathophysiological concentrations there was evidence that ANP selectively reduced right ventricular afterload. These data support the hypotheses that increased plasma levels of ANP may be beneficial in hypoxic COPD, and that endogenous ANP may ameliorate pulmonary hypertension in humans.

Effects of SCH 34826, a neutral endopeptidase inhibitor, on hypoxic pulmonary vascular remodelling.

Atrial natriuretic peptide (ANP) is a potent vasodilator of hypoxia constricted pulmonary vessels. Chronic infusions of ANP have been shown to limit the anatomical pulmonary vascular remodelling associated with chronic exposure to a 10% oxygen environment. SCH 34826 elevates plasma ANP by inhibition of the enzyme neutral endopeptidase EC 3.4.24.11. We administered by subcutaneous injection 90 mg/kg SCH 34826 twice daily into six male Wistar rats. Six littermate controls received 1 ml of 0.4% aqueous methyl cellulose vehicle. All animals were exposed to a 10% oxygen environment for 2 weeks. Administration of SCH 34826 caused a significant reduction in the hypoxia-induced pulmonary vascular remodelling and right ventricle hypertrophy. Neutral endopeptidase inhibition by drugs such as SCH 34826 could prove useful in conditions characterized by pulmonary hypertension and pulmonary vascular remodelling.