Modulatory effect of neuropeptide Y on acetylcholine-induced oedema and vasoconstriction in isolated perfused lungs of rabbit

Non-neuronal neuropeptide Y and its receptors during acute rejection of rat pulmonary allografts

This study tested the hypothesis that neuropeptide Y (NPY) and NPY receptors 1 (Y1) and 2 (Y2) participate in lung allograft rejection. Inflammation in grafts may include interaction between blood leukocytes and graft endothelial cells and marked accumulation of intravascular blood leukocytes. Fewer leukocytes accumulate in lung than in kidney allografts. Lung transplantion was performed in the Dark Agouti to Lewis rat strain combination. Intravascular and intraalveolar leukocytes were isolated from the grafts, and we evaluated the mRNA expression of NPY, Y1, and Y2 by real-time RT-PCR as well as the peptide expression of NPY by radioimmunoassay and immunohistochemistry. NPY and Y1 were expressed by pulmonary intravascular and intraalveolar leukocytes. Y1 was up-regulated by pulmonary intravascular and intraalveolar leukocytes during allograft rejection while Y2 could not be detected. Higher NPY expression levels in intravascular leukocytes were observed in lung compared to kidney allografts, which were investigated previously. Our findings suggest that an increased leukocytic expression of NPY in lung compared to kidney allografts results in a reduced accumulation of leukocytes in allograft vessels.

Evaluation of particle translocation across the alveolo-capillary barrier in isolated perfused rabbit lung model

Particulate air pollution is associated with respiratory and cardiovascular morbidity and mortality. It has been suggested that ultrafine particles are able to translocate from the airways into the bloodstream in vivo. We have investigated this in an isolated perfused and ventilated rabbit lung preparation lacking pulmonary lymphatic flow. Fluorescent polystyrene particles of different diameters (24, 110 or 190 nm) and surface chemistry (carboxylate or amine modified) were injected either intratracheally (i.t.) or intravascularly (i.v.) and, after a period of 2 h, their presence in the perfusion liquid or in the bronchoalveolar lavage (BAL) fluid, was assessed by spectrofluorimetry. Vascular pressures and lung weights were monitored. Following the i.t. administration, no particle translocation was observed from the alveoli into the vascular compartment. Similarly, no particle translocation was found after i.v. administration of particles. However, when microvascular permeability was pharmacologically increased by administering histamine (10(-4) M) in the vascular compartment, inducing a positive driving force provided by fluid filtration, a fluorescent signal in BAL was recorded (2.5 +/- 1% of the dose of particles administered), suggesting a translocation of particles through the alveolo-capillary barrier. We conclude that ultrafine polystyrene particles cannot significantly diffuse from lung into the vascular compartment in our model, but they are able to translocate in the opposite direction when the microvascular permeability is increased by histamine. The relevance of these ex vivo findings for the in vivo translocation of inhaled ultrafine particles remains to be established.

Effect of polystyrene particles on lung microvascular permeability in isolated perfused rabbit lungs: role of size and surface properties

The aim of this study was to investigate the role of particle number, total surface area, mass and surface chemical groups in (K(f,c)) changes. The lung effects of four different fine (110 nm) and ultrafine (24 nm) polystyrene particles have been tested in an isolated perfused rabbit lung model. Pulmonary microvascular permeability (K(f,c)) modifications were measured in response to intratracheal particle challenge. Polystyrene particles, mainly located in alveolar spaces and macrophages, induced a K(f,c) increase that was related to the total surface area and number of particles rather than to the instilled mass. Moreover, the positively charged amine-modified polystyrene particles were more effective in the K(f,c) response than the negatively charged carboxylate-modified polystyrene particles. We concluded that particle number and diameter that mathematically equally determined total surface area do not have the same importance in explaining the biological effects observed and that particle number could be an alternative to total surface area to describe the particle exposure. Furthermore, surface properties of polystyrene particles need to be considered to investigate the microvascular permeability changes measured in our model.

Interactions between cytochrome P-450 activities and ozone-induced modulatory effects on endothelial permeability in rabbit lungs: influence of gender

The effects of rabbit exposure to ozone (O(3)) (0.4 ppm for 4 h) on two different cytochrome P-450 (CYP450)-dependent activities were investigated. In turn, the role of CYP450 in the inhibitory effect of O(3) on acetylcholine (ACh)-evoked increase in endothelial permeability was also assessed. Immediately after the period of exposure, rabbits of both sexes were sacrificed and their lungs were extracted. Some lungs were used for preparation of microsomes and measurement of 7-ethoxyresorufin O-deethylase (EROD) and parathion oxidase activities. Other rabbit lungs were isolated and recirculatingly blood-free perfused. Arterial, venous pressures, and lung weight were continuously recorded. Capillary pressure was measured by applying the double occlusion method. Capillary filtration coefficient (K(f,c)) was evaluated by measuring the amount of fluid filtering through the endothelium when vascular pressures were suddenly increased. Dose-response curves to ACh were constructed in air- or O(3)-exposed rabbits. Some animals were pretreated with piperonyl butoxide (PBO), a well-known inhibitor of CYP450. O(3) significantly reduced both EROD and parathion oxidase lung microsomal activities in females, while it had no effect in males. Exposure to O(3) strongly inhibited the ACh-induced increase in K(f,c). Pretreatment with PBO reversed the modulatory effect of O(3) on endothelial permeability in male rabbits, but not in females. It was concluded (1) that inhibition of 2 different CYP450-dependent activities after exposure to 0.4 ppm O(3) for 4 h appears to be a gender-dependent phenomenon, and (2) that CYP450 is probably involved in the O(3)-evoked inhibitory mechanism against ACh-induced increase in endothelial permeability, but only in males.

Comparison of ozone-induced effects on lung mechanics and hemodynamics in the rabbit

The effects of rabbit exposure to ozone (O3)(0.4 ppm for 4 h) on pulmonary mechanical properties and hemodynamics have been investigated on the isolated perfused lung model. Tracheal pressure, airflow, and tidal volume were measured in order to calculate lung resistance (RL) and dynamic compliance (Cdyn). Using the arterial/venous/double occlusion method, the total pressure gradient (deltaPT) was partitioned into four components (arterial, pre-, postcapillary and venous). Dose-response curves to acetylcholine (ACh), substance P (SP), and histamine were constructed in lungs isolated from rabbits immediately or 48 h after air or O3 exposure O3 induced a significant increase in the baseline value of deltaPt, more markedly 48 h after the exposure. Immediately after the exposure, O3 partly inhibited the ACh-, SP-, and histamine-induced decreases in Cdyn and increases in RL. This inhibitory effect was still in part present 48 h after O3 treatment. In the groups studied immediately after exposure, O3 did not significantly modify the ACh-, SP-, and histamine-induced vasoconstriction. Forty-eight hours after exposure, O3 induced a contractile response to ACh and SP in the arterial segment but decreased the response to histamine. We conclude that O3 can induce direct vascular constriction. Directly, but also 48 h after exposure, O3 can inhibit the ACh-, SP-, and histamine-induced changes in lung mechanical properties. Ozone can also induce some changes in the intensity and in the location of the vascular responses to ACh, SP, and histamine.

Effect of neuropeptide Y on hemodynamics of the rabbit lung

We evaluated the effect of neuropeptide Y (NPY) on the hemodynamics of the isolated rabbit lung perfused at constant flow and outflow pressure. Doses of 10(-8) and 10(-7) M NPY increased pulmonary arterial pressure (Ppa) from 11.5 +/- 1.0 (SE) mmHg to, respectively, 16.4 +/- 1.5 and 26.0 +/- 3.8 mmHg (P < 0.05, n = 5 mmHg lungs), with 78 +/- 4% of the increase at 10(-7) M resulting from an increased arterial resistance. At the latter dose, pulmonary capillary pressure increased from 5.8 +/- 0.9 to 9.4 +/- 1.0 mmHg (P < 0.05). When administered in the presence of norepinephrine, 10(-8) and 10(-7) M NPY (n = 6) produced extreme increases in Ppa to 66.1 +/- 20.5 and 114.7 +/- 25.5 mmHg, respectively, that were due primarily to an increased arterial resistance. To determine the significance of circulating NPY as a pulmonary vasoactive agent, we measured plasma NPY-like immunoreactivity in anesthetized rabbits after massively activating the sympathetic nervous system with veratrine. NPY-like immunoreactivity increased from 74 +/- 10 to 111 +/- 10 (SE) pM (P < 0.05). Thus, although NPY is a potent vasoconstrictor in the rabbit lung, it is not likely that plasma NPY concentrations rise sufficiently, even after massive sympathetic nervous system activation, to produce pulmonary vasoconstriction in the intact rabbit.

Ozone-induced stimulation of pulmonary sympathetic fibers: a protective mechanism against edema

Tropospheric ozone exerts well-described toxic effects on the respiratory tract. Less documented, by contrast, is the ability of ozone to induce protective mechanisms against agents that are toxic to the lungs. In particular, interactions between ozone and the sympathetic nervous system have never been considered. Using a model of permeability edema in isolated perfused rabbit lungs, we report here that, immediately after exposure of rabbits to 0.4 ppm ozone for 4 hr, the pulmonary microvascular responses to acetylcholine and substance P are completely blocked. Several lines of evidence, including partial inhibition of the ozone-induced protective effect by several drugs (alpha2- and beta-adrenergic antagonists, neuropeptide Y antagonist, guanethidine), measured levels of released catecholamines in blood and urine and the in vitro response of isolated lungs exposed to 0.4 ppm ozone all seem to suggest that ozone can stimulate pulmonary adrenergic fibers and induce the local release of catecholamines and neuropeptide Y, this resulting in transient protection against pulmonary edema. We also showed that, 48 hr after the exposure, ozone increased the baseline microvascular permeability and the response to low concentrations of acetylcholine.

Interactions between acetylcholine and substance P effects on lung mechanics in the rabbit

The pharmacological mechanisms involved in the acetylcholine (ACh)- and substance P (SP)-induced changes in pulmonary mechanics were studied in isolated perfused rabbit lungs. Tracheal pressure (Ptr) and airflow were measured by a Fleisch pneumotachograph and pressure transducers. Air volume, lung resistance (RL) and dynamic compliance (Cdyn) were calculated. ACh induced a dose-dependent increase in Ptr and RL, and a decrease in Cdyn. These effects were strongly prevented by atropine, and partly by SR140333, a neurokinin NK1 receptor antagonist; SR48968, a neurokinin NK2 receptor antagonist; indomethacin and antihistaminics. Ketanserin had no significant protective effect against ACh. SP also induced concentration-dependent increases in RL and decreases in Cdyn. SR140333 and atropine strongly inhibited the effects of SP, while ketanserin, SR48968, antihistaminics and indomethacin did not protect the lungs against this drug. 5-hydroxytryptamine induced no significant change in lung mechanic parameters. Cumulative concentrations of histamine increased RL and decreased Cdyn. We conclude that ACh-induced changes in lung resistance and compliance are in part mediated by a direct effect on airway smooth muscle and in part by the stimulation of C fibers, by the release of histamine from mast cells and by the synthesis of arachidonic acid metabolites. In turn, the effects of SP on lung mechanics are partly due to cholinergic activation.

Modulation of acetylcholine, capsaicin and substance P effects by histamine H3 receptors in isolated perfused rabbit lungs

The modulatory role of histamine H3 receptors in pulmonary oedema induced by acetylcholine, capsaicin and by exogenous substance P was investigated in isolated, ventilated rabbit lungs. Endothelial permeability was evaluated by measuring the capillary filtration coefficient (Kf,c). Acetylcholine (10(-8) to 10(-4) M), substance P (10(-10) to 10(-6) M), capsaicin (10(-4) M) and 5-hydroxytryptamine (5-HT) (10(-4) M) induced an increase in the Kf,c. Carboperamide, a novel histamine H3 receptor antagonist, induced a significant leftward shift of the concentration-response curve to acetylcholine and also enhanced the effect of capsaicin on the Kf,c, while it had no significant effect on the response to substance P and 5-HT. Imetit, a new histamine H3 receptor agonist, strongly inhibited the effects of acetylcholine and capsaicin. Imetit also strongly protected the lung against substance P effects but did not prevent the 5-HT-induced increase in the Kf,c. Carboperamide completely blocked the inhibitory effect of Imetit on the acetylcholine response. (R)-alpha-Methylhistamine, an other histamine H3 receptor agonist, had the same protective effect against acetylcholine response as Imetit. We conclude that histamine H3 receptors could protect the lung against acetylcholine- and capsaicin-induced oedema via a prejunctional modulatory effect on the C-fibres. However, since the response to exogenous substance P was also inhibited by histamine H3 receptor stimulation, the presence of such receptors at a postsynaptic level, probably on mast cells, was also suggested.