Permeability of the endothelium and partitioning of the pulmonary blood flow resistance in isolated perfused pig lungs: effects of breed and age

Using multidimensional scaling in model choice for congenital oesophageal atresia: similarity analysis of human autopsy organ weights with those from a comparative assessment of Aachen Minipig and Pietrain piglets

Swine models had been popular in paediatric oesophageal surgery in the past. Although being largely replaced by rodent models, swine experienced a revival with the establishment of minipig models. However, none of them has ever been investigated for similarity to humans. We conducted a pilot study to determine whether three-week old Pietrain piglets and three-month old Aachen Minipigs are suitable for experimental paediatric oesophageal atresia surgery. We tested the operation's feasibility, performed a necropsy, weighed organs, measured organ length and calculated relative weights and lengths, and measured laboratory parameters. We used multidimensional scaling to assess the similarity of the swine breeds with previously published human data. Pietrain piglets had a higher a priori bodyweight than Aachen Minipigs (Δ = 1.31 kg, 95% confidence interval (CI): 0.37-2.23, p = 0.015), while snout-to-tail length was similar. Pietrain piglets had higher absolute and relative oesophageal lengths (Δ = 5.43 cm, 95% CI: 2.2-8.6; p = 0.0062, q1* = 0.0083 and Δ = 11.4%, 95% CI: 5.1-17.6; p = 0.0025, q3* = 0.0053). Likewise, absolute and relative small intestinal lengths were higher in Pietrains, but all other parameters did not differ, with the exception of minor differences in laboratory parameters. Multidimensional scaling revealed three-week old Pietrain piglets to be similar to two-month old humans based on their thoracoabdominal organ weights. This result indicates three-week old Pietrain piglets are a suitable model of paediatric oesophageal atresia surgery, because clinically many procedures are performed at around eight weeks age. Three-month old Aachen Minipigs were more dissimilar to eight-week old humans than three-week old Pietrain piglets.

Possible role of substance P in the ischemia-reperfusion injury in the isolated rabbit lung

The origin of the endothelial damage leading to the ischemia-reperfusion injury after lung transplantation has not been elucidated. We postulated that neurotransmitters released during the preservation of the donor lung might explain this vascular derangement. Thus, in isolated rabbit lungs preserved over 24 hours, we evaluated the release of acetylcholine (ACh) and substance P (SP), the activity of their major degrading enzymes, acetylcholinesterase (AChE) and neutral endopeptidase (NEP), and changes in the capillary permeability. Both neurotransmitters showed the highest release rate in the first 15 minutes, followed by a sharp exponential decrement at 1, 6, 12 and 24 hours. AChE and NEP activities showed no variation at these time intervals. Basal capillary permeability significantly increased (P<0.01) after 24 hours preservation with saline. This increased permeability was avoided (P<0.01) by the SP fragment 4-11 (an SP receptors antagonist), but not by atropine. These results suggest for the first time a pathogenic role of SP in the ischemia-reperfusion injury, and thus the potential usefulness of SP antagonists as additives in the lung preservation solutions should be explored.

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.

Disruptive effects of anion secretion inhibitors on airway mucus morphology in isolated perfused pig lung

Since anion secretion inhibitors reproduce important aspects of cystic fibrosis (CF) lung disease, the effects of these antagonists on airway mucus morphology were assessed in isolated perfused pig lungs. Maximal inhibitory concentrations of bumetanide and dimethylamiloride, which respectively block Cl- and HCO3- secretion in porcine airways, induced the formation of dense 'plastered' mucus on the airway surface, depletion of periciliary fluid and collapse of cilia. This effect was more pronounced when lungs were also exposed to bethanechol to stimulate submucosal gland secretion, when plastered mucus covered > 98 % of the airway surface. Bethanechol also reduced gland duct mucin content in the absence, but not presence, of the anion secretion inhibitors. Anion secretion inhibitors did not induce measurable increases in goblet cell degranulation. We conclude that inhibition of anion and liquid secretion in porcine lungs disrupts the normal morphology of airway surface mucus, providing further evidence that impaired anion secretion alone could account for critical aspects of CF lung disease.

Effects of age and indomethacin on response and sensitivity of pulmonary artery to phenylephrine and to histamine in pigs

The vasoconstrictor effects of phenylephrine and histamine were investigated in isolated strips of pulmonary arteries in pigs during ageing. Interactions between phenylephrine-induced responses and arachidonic acid derivatives were also studied by incubating the blood-vessels with indomethacin. Potency (pD2 values) and maximal effects (EmaxX) recorded in 5-week-old piglets (group I, n = 5) with phenylephrine [5.71 +/- 0.17 and 0.76 +/- 0.22 g/mg of dry tissue respectively (mean +/- SEM)] were similar to values found in 12-week-old animals (group 2, n = 5) (5.49 +/- 0.30 and 1.06 +/- 0.27 g/mg of dry tissue respectively). The sensitivity and responsiveness of tissues to this agonist were significantly reduced in 26-week-old mature pigs (group 3, n = 6) as indicated by the decrease in pD2 (3.91 +/- 0.23; P < 0.01) and Emax (0.27 +/- 0.13 g/mg of dry tissue; P < 0.05) values observed in this group. Histamine (10(-3) M)-induced maximal responses (Emax) were significantly higher in group 2 (2.23 +/- 0.49 g/mg) than in group 1 (0.85 +/- 0.11 g/mg; P < 0.05) and in group 3 (0.48 +/- 0.10 g/mg; P < 0.01). In 5-week-old animals, indomethacin (3 x 10(-5) M) significantly (P < 0.05) shifted the concentration-response curve to phenylephrine to the right (0.28 log. units) and depressed contractions to this drug as shown by the significant decrease of 39.5% (P < 0.05) in Emax. This cyclo-oxygenase inhibitor had no effect in other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of capsaicin on the endothelial permeability in isolated and perfused rabbit lungs

Changes in pulmonary endothelial permeability and in microvascular hemodynamics in response to capsaicin (10(-4) M) were investigated in isolated, perfused rabbit lungs. Blood-free perfusate was recirculated through ventilated lungs in an isogravimetric state, under zone III conditions with a constant flow. Using the occlusions method, the total pressure gradient between the arterial and the venous levels (delta Pt) was partitioned into four components: arterial (delta Pa), pre-(delta Pa') and post-(delta Pv') capillary, and venous (delta Pv). The capillary filtration coefficient (Kf,c) was evaluated by measuring the amount of fluid filtering through the endothelium when arterial and venous pressures were suddenly increased. Capsaicin caused no changes in the vascular pressures at any level of the pulmonary circulation but induced a significant 3-fold increase in the Kf,c (P < 0.05). This reaction was accompanied by pulmonary oedema. The mechanisms involved in the permeability changes were investigated by testing the capacity of different drugs to block the response to capsaicin. Clonidine (10(-7) M to 10(-5) M), morphine (10(-6) M), aspirin (10(-3) M), ketanserin (10(-8) M) and (+/)- CP 96,345 (10(-6) M), an antagonist of neurokinin NK1 receptor, completely prevented the effects of capsaicin on the Kf,c. In contrast, terfenadine (10(-7)) together with cimetidine (10(-5) M) had no protective effect against capsaicin. It was concluded that capsaicin-induced pulmonary oedema was due to an increase in the capillary filtration coefficient and not to hemodynamic changes. This alteration in the endothelium permeability is mediated by the release of endogenous peptides from C-fibers upon the action of capsaicin and subsequent activation of NK1 receptors, probably by substance P. Moreover, 5-hydroxytryptamine receptors and arachidonic acid derivates are also involved in this reaction.

Endotoxin-induced microvascular injury in isolated and perfused pig lungs

The lungs of 13 healthy Landrace piglets were isolated, perfused and maintained in an isogravimetric state under zone III conditions. By applying vascular occlusion methods, the total blood flow resistance (Rt) was partitioned into four components: arterial (Ra), pre- (Ra') and post-capillary (Rv'), and venous (Rv). The capillary filtration coefficient (Kfc) was evaluated using a gravimetric technique. A bolus of 55 micrograms of Escherichia coli endotoxins (LPS) per 100 g of lung was injected into the arterial reservoir of eight lungs, followed by an infusion of LPS at a rate of 55 micrograms per 100 g of lung per hour for 180 min. A bolus of theophylline (85 mg per 100 g of lung weight) was injected into the arterial reservoir after the last determination of the Kfc value. All the parameters were evaluated again when the lungs reached a new steady state. Endotoxin induced a significant increase in Rt from 54.7 +/- 7.0 at zero time to 184.7 +/- 44.2 cmH2O min L-1 (100 g)-1 180 minutes later, which can be ascribed to the increase in Ra' and Rv'. These haemodynamic modifications were related to the increases in the arterial pressure and in the pressure at the distal end of the arterial segment and to the decreases in the pressure at the proximal end of the venous segment and in the blood flow. The capillary pressure and the lung weight remained unchanged. Endotoxin infusion induced an increase in the Kfc value from 0.208 +/- 0.011 (at t = 0) to 0.391 +/- 0.034 ml min-1 (cmH2O)-1 (100 g)-1 (at t = 180). Administration of theophylline significantly reduced Rt,Ra,Ra' and Rv' towards or under the baseline values and also induced a significant increase in the lung weight and in the Kfc value. It was concluded that the endotoxin-induced increase in the total blood flow resistance can be ascribed to a vasospasm occurring at the level of the pre- and post-capillary small vessels and that changes in the permeability of the endothelium greatly contribute to the development of the pulmonary oedema observed in endotoxaemic pigs.

Altered capillary filtration coefficient in parathion- and paraoxon-induced edema in isolated and perfused rabbit lungs

Changes in pulmonary endothelium permeability and in microvascular hemodynamics induced by parathion (Pth) and paraoxon (Pox), its active metabolite, were investigated in isolated, perfused rabbit lungs. Blood-free perfusate was recirculated through isolated and ventilated lungs in an isogravimetric state and in zone III conditions. The arterial/venous/double occlusion technique was used to divide the total vascular resistance (Rt) into four components: arterial, precapillary, postcapillary, and venous. The capillary filtration coefficient (Kfc) was evaluated by measuring the amount of fluid filtering through the endothelium when the arterial and venous pressures were suddenly increased. Pth and Pox induced pulmonary edema by increasing endothelium permeability without changing the hemodynamic parameters at any level of the vascular bed. The Kfc value increased progressively, reaching a maximum (Emax) 60 min after administration of organophosphate (558 +/- 65% (n = 5) and 707 +/- 109% (n = 5) of baseline values, for Pth and Pox, respectively). During the next 60 min, it decreased. The time course of Pox-induced changes in Kfc was similar to that obtained with Pth. The concentration-response curve (Emax) expressed as a percentage of the baseline value versus the logarithm of the molar Pth concentration, ranging from 2 x 10(-5) to 4 x 10(-4) M) was linear (y = 1661.1 + 327.3x, r = 0.89, p < 0.001, n = 14). Piperonyl butoxide (4 x 10(-4) M), an inhibitor of cytochrome P450, had a strong protective effect against Pth (4 x 10(-4) M)-induced alterations of endothelium permeability (n = 5, p < 0.001). The effects of Pox (4 x 10(-4) M) on Kfc were completely abolished by pretreatment with 10(-5) M atropine, as shown by the significantly lower Emax value recorded in atropine-pretreated lungs (129 +/- 33%, n = 4) than in Pox-treated lungs (707 +/- 109%, n = 5, p < 0.001). The effects of Pth, on the other hand, were only partially inhibited, since the Emax value recorded in atropine-pretreated lungs (196 +/- 20%, n = 4) remained significantly higher than that recorded for control lungs (129 +/- 15%; n = 5; p < 0.05). These results show that isolated and perfused rabbit lungs constitute an appropriate model for studying the direct pulmonary effects of organophosphates. The edema-inducing action of Pth depends on its activation by conversion to Pox in the lung tissue.(ABSTRACT TRUNCATED AT 400 WORDS)