Direct measurement of pulmonary capillary transit times.

Direct measurements of capillary transit times in dog lungs were made by using in vivo television microscopy. Mean transit times were unexpectedly long. As pulmonary artery pressures were raised, transit times decreased, suggesting that the normally existing hydrostatic pressure gradient in the lung causes a vertical distribution of transit times. The more rapid transit times approached the minimum time required for complete oxygenation.

Polyamine synthesis blockade in monocrotaline-induced pneumotoxicity.

Based on the documented regulatory role of polyamines in cell growth and differentiation, we have proposed that these organic cations are involved with the development of monocrotaline (MCT)-induced hypertensive pulmonary vascular disease. Two lines of evidence support this hypothesis: (1) MCT causes progressive increases in lung polyamine contents which are temporarily related to the development of cardiopulmonary abnormalities, and (2) blockade of polyamine synthesis with the site-selective enzyme-activated inhibitor, alpha-difluoromethylornithine (DFMO), attenuates development of medial arterial thickening, increased pulmonary arterial pressure, and right ventricular hypertrophy. To evaluate the mechanism of DFMO protection, the present study assessed when, during the course of MCT-induced pneumotoxicity, DFMO exerts its salutary effects, and determined if the protection afforded by DFMO could be reversed through supplementation with exogenous polyamines. To address the first issue, rats were treated with 30 mg/kg MCT and, 10 days after administration when lung polyamine contents were augmented and when pulmonary edema was evident, DFMO treatment was initiated as a 2% solution in the drinking water. In animals receiving MCT only, lung polyamine contents were elevated and right ventricular hypertrophy was evident at both 20 and 35 days after treatment. DFMO treatment initiated at day 10 attenuated the increases in putrescine and spermidine but not spermine and reduced the degree of right ventricular hypertrophy at both the 20- and 35-day time points. To determine if the blockade by DFMO could be reversed by supplementation with exogenous polyamines, animals were treated simultaneously with MCT and DFMO as described above and the immediate precursor to the polyamines, ornithine, was added to the drinking water as a 2% solution. Relative to animals receiving MCT and DFMO, ornithine supplementation increased lung polyamine contents to levels normally associated with MCT treatment only. Ornithine also reversed the protection against right ventricular hypertrophy normally afforded by DFMO. These observations indicate that the salutary effects of DFMO in MCT-induced pulmonary hypertension cannot be ascribed solely to interference in the early events after MCT treatment and that restoration of lung polyamine contents to high levels by supplementation with exogenous ornithine reverses DFMO protection against sustained pulmonary hypertension. It is concluded, therefore, that polyamines play a central role in delayed responses of lung cells underlying the development of MCT-induced sustained pulmonary hypertension.

Prolonged activation of rat lung ornithine decarboxylase in monocrotaline-induced pulmonary hypertension.

Polyamines are believed to have an essential role in cellular growth and differentiation. Activation of ornithine decarboxylase, the initial rate-limiting enzyme in polyamine biosynthesis, is an early event characteristic of cell growth processes. Monocrotaline-induced pneumotoxicity is associated with cellular hypertrophy and proliferation, most notably pronounced medial thickening of pulmonary arterioles and hypertrophy of right ventricular myocardial cells. We reasoned that polyamines may be causally related to these events and, therefore, elevations in lung and right ventricular ornithine decarboxylase activities might precede development of pulmonary hypertension and right ventricular hypertrophy. To test this hypothesis adult male rats were given monocrotaline (105 mg/kg, s.c.); lung and right and left ventricular ornithine decarboxylase activities, pulmonary artery pressure, and right ventricular hypertrophy were assessed at 1, 4, 7, 10, 14, 16 and 21 days post treatment. Lung ornithine decarboxylase activity was increased approximately 8-fold on day 1 and remained elevated through day 7. Right ventricular ornithine decarboxylase activity was not elevated above control values at any time. Elevated pulmonary artery pressure and right ventricular hypertrophy were not apparent until day 16 and day 14 respectively. Thus, sustained activation of lung ornithine decarboxylase occurred at least 1 week prior to the development of pulmonary hypertension, suggesting that polyamines may play an important role in the pulmonary vascular remodeling that accompanies monocrotaline-induced pneumotoxicity.

Autacoid binding to serum proteins. Interaction of platelet activating factor (PAF) with human serum alpha-1-acid glycoprotein (AAG).

Platelet activating factor (PAF; 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent bioactive phospholipid released from platelets, neutrophils, basophils and macrophages that has been proposed as a mediator of anaphylaxis, acute lung injury and other disorders. Specific factors which stabilize PAF and/or regulate PAF activity in body fluids are largely unknown. As part of a general autacoid-serum protein binding screen, the platelet activating factor-alpha-1-acid glycoprotein (PAF-AAG) interaction was indirectly characterized by examining the ability of PAF to displace propranolol from AAG. Both PAF and its deacetylated metabolite (lyso-PAF), at 20 microM, doubled the fraction unbound of propranolol (0.4 microM) from purified human AAG (20 microM). None of the other autacoids that were studied (epinephrine, serotonin, spermidine, putrescine, leu-enkephalin or phenethylamine) exhibited any propranolol displacement activity. Scatchard analysis indicated that PAF competitively displaced propranolol from AAG, causing the apparent affinity constant for propranolol-AAG to decrease from 1.8 X 10(5) M to 6.9 X 10(4) M. PAF behaved qualitatively like chlorpromazine (a documented inhibitor of propranolol binding to AAG), but PAF was less effective at displacing propranolol. The apparent binding to AAG may help stabilize and transport extracellular PAF. Furthermore, the interaction of PAF and AAG suggests that serum AAG, which fluctuates in a number of diseases, may function to regulate PAF activity during acute and chronic disease states.

Alterations of growth factor transcripts in rat lungs during development of monocrotaline-induced pulmonary hypertension.

Although pathologic and hemodynamic changes in monocrotaline (MCT)-induced pulmonary hypertension have been studied extensively, relatively little is known about the inter- and intracellular signaling mechanisms underlying such alterations. As a first step to delineating signaling mechanisms governing adverse structural alterations in the hypertensive lungs, we examined changes in the steady-state levels of mRNAs encoding several growth factors including transforming growth factors (TGF), platelet-derived growth factors (PDGF), vascular endothelial cell growth factor (VEGF) and endothelin (ET) as a function of time in MCT-induced pulmonary hypertension in rats. These studies demonstrated a very diverse pattern of growth factor gene expression in response to MCT administration. In general, alterations in the steady-state levels of mRNAs encoding the growth factors preceded the onset of MCT-induced pulmonary hypertension. TGF-beta 1, -beta 2 and -beta 3 transcripts were seen to be elevated, whereas that of TGF-alpha and PDGF-A remained unchanged. Transcripts for PDGF-B and ET were increased in the early stages but declined to less than controls in the latter stages of MCT-induced hypertension. In contrast, levels of VEGF mRNA decreased to less than controls as the disease progressed. Viewed collectively, the diverse pattern of expression suggests that alterations in the levels of the growth factor transcripts may have a significant role in the development of pulmonary hypertensive disease and may be relevant to the pathological and structural changes in MCT-induced pulmonary hypertension.

Role of ATP and sodium in polyamine transport in bovine pulmonary artery smooth cells.

Increased polyamine transport may be a key mechanism driving elevations in lung cell polyamine content necessary for the development of chronic hypoxic pulmonary hypertension. Bovine pulmonary artery smooth muscle cells (PASMCs) in culture exhibit two carriers for polyamines, a non-selective one shared by the three polyamines, putrescine (PUT), spermidine (SPD), and spermine (SPM), and another that is selective for SPD and SPM. Hypoxia appears to up-regulate both carriers. In this study, we examined the role of ATP and the Na+ gradient in regulating polyamine transport in control PASMCs and in PASMCs with polyamine transport augmented by culture under hypoxic conditions (Po2: 15-30 torr). Inhibition of ATP synthesis with dinitrophenol+iodoacetate profoundly reduced polyamine uptake in both control and hypoxic PASMCs. Putrescine uptake was somewhat more sensitive to iso-osmotic replacement of extracellular Na+ with choline chloride or sucrose than were SPD or SPM in both hypoxic and standard cells, but under no conditions did Na+ replacement substantially alter polyamine uptake. Treatment of PASMCs with ouabain, a Na(+)-K+ ATPase inhibitor, or with gramicidin, a Na+ ionophore, minimally attenuated polyamine transport, whereas the Na+/K+ ionophore monensin increased polyamine uptake in standard, but not in hypoxic, cells. In general, the reduction in the extracellular Na+ content or ionophore-induced increases in Na+ permeability had a greater suppressive effect on polyamine transport in hypoxic cells than in standard cells, suggestive of the induction of Na(+)-dependent polyamine carriers by hypoxia. These observations indicate that the activities of the two putative polyamine transport pathways in standard PASMCs, as well as their up-regulation by hypoxia, require ATP synthesis. In addition, it appears that polyamine transport in PASMCs is composed of two components: one a prominent sodium-independent transporter and the other a relatively minor component that is sodium dependent. The latter may be activated by hypoxic exposure in combination with the induction of new polyamine carriers.

Ventilatory dysfunction precedes pulmonary vascular changes in monocrotaline-treated rats.

Rats with established monocrotaline (MCT)-induced pulmonary hypertension also exhibit a profound increase in lung resistance (RL) and a decrease in lung compliance. Because airway/lung dysfunction could precede and influence the evolution of MCT-induced pulmonary vascular disease, it is important to establish the temporal relationship between development of pulmonary hypertension and altered ventilatory function in MCT-treated rats. To resolve this issue, we segregated 47 young Sprague-Dawley rats into four groups: control (n = 13), MCT1 (n = 9), MCT2 (n = 11), and MCT3 (n = 14). Each MCT rat received a single subcutaneous injection of MCT (60 mg/kg) 1 MCT1), 2 (MCT2), or 3 (MCT3) wk before the functional study. At 1 wk after MCT, significant increases in RL and alveolar wall thickness were observed, as was a significant decrease in carbon monoxide diffusing capacity (DLCO). Medial thickness of pulmonary arteries (50-100 microns OD) and right ventricular hypertrophy were not observed until 2 and 3 wk post-MCT, respectively. Coincident with the right ventricular hypertrophy at 3 wk post-MCT were decreased DLCO and increased alveolar wall thickness and lung dry weight. Pressure-volume curves of air-filled and saline-filled lungs showed marked rightward shifts during the 1st and 2nd wk after MCT administration and then decreased at the 3rd wk. These data suggest that MCT-induced alterations in airway/lung function preceded those of pulmonary vasculature and, therefore, implicate airway/lung dysfunctions as potentially contributing to the later development of pulmonary vascular abnormalities.

Monokine-induced acute lung injury in rabbits.

Interleukin-1 (IL-1) mediates components of the acute phase response, stimulates granulocyte metabolism, and induces endothelial cell surface changes. We studied in unanesthetized rabbits the effects of intravenous divided dose infusions of a murine monokine preparation containing IL-1 activity, on circulating granulocytes, their sequestration within the pulmonary microvasculature, pulmonary edema formation, and changes in pulmonary vascular permeability. Monokine administration induced significant (P less than 0.01) granulocytopenia as well as a significant (P less than 0.001) increase in mean alveolar septal wall granulocytes per high power field (HPF) compared with saline-injected controls. Infusions of the monokine preparation significantly (P less than 0.005) increased lung wet-to-dry weight ratios as well as significantly (P less than 0.025) increased pulmonary extravasation of radiolabeled albumin. Electron microscopic analysis of lung sections obtained from monokine-infused animals demonstrated endothelial injury, perivascular edema, and extravasation of an ultrastructural tracer. We conclude that a monokine preparation containing IL-1 activity can induce profound granulocytopenia, pulmonary leukostasis, and acute pulmonary vascular endothelial injury.

Evidence that hypoxic pulmonary vascular remodeling in rats is polyamine dependent.

This study tested the hypothesis that the polyamines, a family of low-molecular-weight organic cations with documented regulatory roles in cell growth and differentiation, are mediators of chronic hypoxia-induced pulmonary vascular remodeling. Relative to room air controls, chronically hypoxic animals (inspired O2 fraction = 0.1; 21 days) exhibited higher pulmonary arterial pressures (measured in room air), thicker medial layers in pulmonary arteries of 50-100 microns diam, increased hematocrits, and right ventricular hypertrophy. In addition, lung contents of the polyamines, putrescine, spermidine, and spermine were greater in hypoxic animals than in controls. alpha-Difluoromethylornithine (DFMO), an inhibitor of polyamine synthesis, attenuated the hypoxia-induced elevations in lung putrescine and spermidine content and blunted the increases in pulmonary arterial pressure and medial thickness. Neither the increased hematocrit nor right ventricular hypertrophy associated with chronic hypoxia were abrogated by DFMO. In addition, DFMO failed to influence vasoconstrictor responses provoked by acute hypoxic ventilation in isolated, buffer-perfused rat lungs. These observations suggest that depression of polyamine biosynthesis with DFMO blunts the sustained increase in pulmonary arterial pressure by attenuating hypoxia-induced medial thickening.

Interleukin-1-induced granulocytopenia and pulmonary leukostasis in rabbits.

Pulmonary leukostasis is a postulated prerequisite lesion for acute lung injury. Interleukin-1 (IL-1) mediates components of the acute-phase response, stimulates granulocyte metabolism and secretion, and augments endothelial adhesiveness. We studied the effects of murine IL-1 infusion on circulating granulocytes, their sequestration within the pulmonary microvasculature, lung water, and bronchoalveolar lavage fluid (BALF) protein concentration in rabbits at 3 and 24 h after infusion. IL-1 administration induced significant (P less than 0.01) granulocytopenia compared with saline-injected controls and at 3 h induced significant increases in both mean alveolar septal wall granulocytes per high power field (HPF) (P less than 0.001) and mean myeloperoxidase (MPO) activity per gram lung tissue (P less than 0.001). At 24 h, IL-1 induced a marked granulocytosis and again significantly increased both mean alveolar septal wall granulocytes per HPF (P less than 0.001) and lung MPO (P less than 0.01). Increased lung water or BALF protein concentration could not be demonstrated in animals killed at either 3 or 24 h after IL-1 administration. Therefore, IL-1 can induce an early profound granulocytopenia followed by later granulocytosis, as well as sustained pulmonary leukostasis in the absence of detectable pulmonary edema formation or an alveolar-capillary leak.

Capillary filtration coefficient, vascular resistance, and compliance in isolated mouse lungs.

Although many recently produced transgenic mice possess gene alterations affecting pulmonary vascular function, there are few baseline measurements of vascular resistance and permeability. Therefore, we excised the lungs of C57/BL6 mice and perfused them with 5% bovine serum albumin in RPMI-1640 culture medium at a nominal flow of 0.5 ml/min and ventilated them with 20% O(2)-5% CO(2)-75% N(2). The capillary filtration coefficient, a sensitive measurement of hydraulic conductivity, was unchanged over 2 h (0.33 +/- 0.03 ml. min(-1). cmH(2)O(-1). 100 g(-1)) in a control group ventilated with low peak inflation pressures (PIP) but increased 4. 3-fold after high PIP injury. Baseline pulmonary vascular resistance was 6.1 +/- 0.4 cmH(2)O. ml(-1). min. 100 g(-1) and was distributed 34% in large arteries, 18% in small arteries, 14% in small veins, and 34% in large veins on the basis of vascular occlusion pressures. Baseline vascular compliance was 5.4 +/- 0.3 ml. cmH(2)O(-1). 100 g(-1) and decreased significantly with increased vascular pressures. Baseline pulmonary vascular resistance was inversely related to both perfusate flow and microvascular pressure and increased to 202% of baseline after infusion of 10(-4) M phenylephrine due to constriction of large arterial and venous segments. Thus isolated mouse lung vascular permeability, vascular resistance, and the longitudinal distribution of vascular resistance are similar to those in other species and respond in a predictable manner to microvascular injury and a vasoconstrictor agent.

Substance P fails to mimic vagally mediated nonadrenergic bronchodilation.

The ability of substance P to mimic vagally mediated nonadrenergic bronchodilation was assessed in vivo in anesthetized, paralyzed, artificially ventilated cats. Infusion of the peptide at a rate of 10 micrograms kg-1 min-1 for 10 minutes did not attenuate the increase in pulmonary resistance evoked by efferent vagal stimulation. Similarly, when administered as an aerosol (1-15 breaths of a 100 micrograms ml-1 aqueous solution) or by bolus intravenous injection, substance P failed to reverse the increase in pulmonary resistance maintained by a continuous intravenous infusion of 5-hydroxytryptamine. These results indicate that substance P is unlikely to be the neurotransmitter responsible for mediating nonadrenergic inhibitory responses in feline airways.

Pulmonary vasoactivity of lung endocrine cell-related peptides.

Lung endocrine-like cells are believed to contain three immunohistochemically distinct peptides: bombesin, calcitonin, and Leu-enkephalin. Because these peptides exhibit smooth muscle stimulatory or inhibitory activity in some tissues, it has been suggested that their release from endocrine-like cells may influence airway or pulmonary vascular smooth muscle tone. To determine whether lung endocrine cell-related peptides could exert a regulatory influence in the pulmonary circulation, we evaluated their ability to constrict or dilate the vasculature of isolated perfused rat lungs. Neither bombesin nor calcitonin exhibited any pulmonary vascular effects. However, Leu-enkephalin provoked dose-dependent pulmonary vasoconstriction. These results suggest that Leu-enkephalin released from lung endocrine-like cells could be involved with regulation of pulmonary vascular tone.

Reversal of doxorubicin, etoposide, vinblastine, and taxol resistance in multidrug resistant human sarcoma cells by a polymer of spermine.

We have previously described the synthesis of a cytotoxic polymeric conjugate of spermine (Poly-SPM) which is able to inhibit the transport of polyamines (spermine, spermidine, and putrescine) into normal and malignant cells. Recent studies examining the toxicity of Poly-SPM in parental and multidrug resistant (MDR) cancer cells have revealed a cross-resistance in the MDR variant Dx5 to the toxic effects of the conjugate in the MDR-positive cells. There were also differences in spermine and putrescine uptake rates between parental and MDR-positive with the MDR-positive cells having a lower Vmax and a higher Km. The ability of this Poly-SPM to reverse MDR was examined in MDR variants (Dx5 cells) of the human sarcoma cell line MES-SA. The cells express high levels of the mdr1 gene product, P-glycoprotein, and are 25-to 60-fold resistant to doxorubicin (DOX), etoposide (VP-16), vinblastine (VBL), and taxol (TAX). Cytotoxicity was measured by the MTT [3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. Poly-SPM (50 microM) lowered the drug concentration IC50 values in the Dx5 cells by 37-fold with VBL, 42-fold with DOX, 29-fold with VP-16, and 25-fold with TAX when compared to the control IC50 values without Poly-SPM. This reversal of resistance was concentration dependent, decreasing 17-fold with DOX, 6.1-fold with VBL, 19-fold with VP-16, and 5-fold with TAX when 25 microM Poly-SPM was used. No modulation was observed in the parental cell line MES-SA, which does not express the mdr1 gene. Poly-SPM had no influence on the IC50 of non-MDR chemotherapeutic agents such as cisplatin. The modulation studies correlated with the ability of Poly-SPM to reverse the cellular accumulation defect of [3H]-VBL and [3H]-TAX in the Dx5 but not MES-SA cells. Pretreatment of the Dx5 cell with alpha-difluoromethylornithine (DFMO at 2 and 5 microM) for 24 h increased the function of the MDR transporter to further decrease the cellular accumulation of VBL and TAX when compared to untreated cells. DFMO pretreatment is known to upregulate the polyamine transporter(s). These findings show that, in addition to inhibiting polyamine transport, Poly-SPM reverses MDR in Dx5 cells, suggesting a potential relationship between the polyamine influx transporter and the MDR efflux pump. This potential functional link between the polyamine influx transporter(s) and the MDR efflux transporter (P-glycoprotein) offers a novel approach to inhibiting this form of drug resistance.

Attenuation of vagal noradrenergic tachycardia by naloxone.

Electrical stimulation of the transected right vagus nerve in anesthetized and atropinized dogs produced tachycardia that was not attenuated by beta-adrenoceptor blockade. Naloxone in intravenous doses of 1 and 4 mg/kg antagonized the tachycardia evoked by nerve stimulation in a dose-dependent manner. However, the attenuation was maximal at approximately 55% of the control response. These results suggest that an endogenous opiate peptide(s) may have a mediator or modulator role in nonadrenergic tachycardia evoked by vagal nerve stimulation in anesthetized and atropinized dogs.

Chronic administration of water soluble tobacco smoke extract or nicotine fails to influence porcine coronary artery reactivity.

To determine if tobacco smoke components directly influence coronary vascular reactivity, we evaluated the contractile effects of prostaglandin (PG)F2 alpha and hypertonic KCl in porcine isolated left anterior descending coronary arteries derived from animals chronically treated (18 weeks) with either water soluble tobacco smoke extract, nicotine alkaloid, or saline. Dosing protocols for the extract and for nicotine were designed to achieve blood levels of nicotine approximating those attained by consumption of 2 packs/day of University of Kentucky 2Rl reference cigarettes. Histochemical evaluation of the arteries indicated that both the extract and nicotine caused expected increases in the collagen content of the tunica media. Neither the water soluble extract nor pure nicotine significantly altered coronary vascular sensitivity (as expressed by the ED50) to KCl or PGF2 alpha. Similarly, neither treatment altered the maximum contractile responses (determined as the tension developed normalized to mg wet wt) evoked by KCl and PGF2 alpha. These results indicate that prolonged exposure to water soluble components of tobacco smoke, in doses sufficient to elevate the collagen content of the coronary vascular wall, do not have direct effects on coronary reactivity to selected vasoconstrictor stimuli.

Polyamine synthesis in rat lungs injured with alpha-naphthylthiourea.

The diamine, putrescine, and polyamines, spermidine and spermine, are low molecular weight organic cations with documented regulatory roles in cell growth and differentiation. Multiple lines of direct and indirect evidence suggest that these organic cations also may function in stimulus-response coupling processes regulating cellular injury and repair. For example, recent studies in monocrotaline-treated rats, hyperoxic rats, and in cultured pulmonary endothelial cells suggest that polyamines regulate pulmonary endothelial integrity and may thus participate in development and/or regression of acute edematous lung injury. To determine if the polyamines are involved in a well-characterized animal model of acute lung injury, the present experiments assessed the relation between changes in polyamine synthesis and development of edema in lungs from rats treated with alpha-naphthylthiourea (ANTU). ANTU caused dose- and time-dependent increases in the lung activity of the initial and rate-limiting enzyme in polyamine biosynthesis, ornithine decarboxylase (ODC) and in the lung contents of the polyamines putrescine, spermidine, and spermine. ANTU also caused dose- and time-dependent increases in the lung wet-to-dry weight ratio indicative of pulmonary edema formation. Changes in lung polyamine biosyntheic activity after ANTU did not relate temporally to changes in the lung wet-to-dry weight ratio: ODC activity was depressed during the 3-h period immediately following ANTU administration, a period when the wet-to-dry weight ratio was increasing, and markedly elevated at 18 h after ANTU administration when the wet-to-dry weight ratio had returned to control levels. Pretreatment of the animals with alpha-difluoromethylornithine, a highly specific inhibitor of ODC, failed to attenuate ANTU-induced increases in lung wet-to-dry weight ratio. These observations indicate polyamine synthesis is enhanced in rat lungs with ANTU-induced pulmonary edema but, unlike certain other models of lung injury and pulmonary edema, accumulation of polyamines probably is not essential for development of edematous lung injury. It is conceivable that in this animal model polyamines play a role in lung repair processes or some longer-term consequence of lung injury.

Enhanced chemotaxis and superoxide anion production by polymorphonuclear leukocytes from nicotine-treated and smoke-exposed rats.

Although previous studies have shown that polymorphonuclear leukocytes (PMNs) exposed to nicotine in vitro exhibit enhanced superoxide anion generation and chemotactic responses, it is not known whether in vivo exposure to the alkaloid causes the same alterations in PMN function. Accordingly, this study evaluated superoxide anion generation evoked by phorbol myristate acetate (PMA) and chemotactic responses to formylmethionylleucylphenylalanine (fMLP) in PMNs isolated from rats treated acutely or subchronically with nicotine and from rats chronically exposed to cigarette smoke. Acute or subchronic (twice daily for 7 days) i.p. injection of 0.2 or 0.02 mg/kg nicotine potentiated PMA-induced superoxide anion generation by PMNs. Similarly, acute i.p. injection of 0.2 mg/kg nicotine or subchronic treatment with 0.02 mg/kg nicotine potentiated fMLP-induced chemotaxis. Subchronic treatment with 0.2 mg/kg of the alkaloid blunted fMLP-induced chemotaxis, in contrast to the potentiating actions of the lower dose. Treatment with nicotine mimicked the effects of tobacco smoke exposure. A 15-week exposure regimen to either sidestream and mainstream smoke from University of Kentucky 2R1 reference cigarettes potentiated PMA-induced superoxide anion generation. Mainstream but not sidestream smoke also enhanced chemotactic responses to fMLP. Viewed collectively, these observations indicate that in vivo exposure to nicotine or to tobacco smoke augment PMN superoxide anion generation and chemotactic responses to selected stimuli and thus implicate such adverse actions of smoking on PMN function in certain pathologies associated with excessive tobacco smoke exposure.

Exaggerated nicotine-induced norepinephrine release from atherosclerotic rabbit hearts.

Excessive cigarette smoking acts synergistically with atheromatous coronary artery disease to greatly enhance the risk of acute myocardial infarction. To explore a possible mechanism of this relation, the present study tested the hypotheses that diet-induced atherosclerosis in rabbits is associated with an increase in myocardial (-)-norepinephrine content and that the increased (-)-norepinephrine can be released by nicotine. Adult male rabbits were rendered atherosclerotic by feeding them a standard laboratory diet enriched with 2% cholesterol. After 12-13 weeks on the diet, hearts were excised and retroperfused according to the Langendorff technique. There were no differences between control and atherosclerotic animals in terms of baseline (-)-norepinephrine concentration in the coronary effluent. However, increases in effluent (-)-norepinephrine concentration provoked by 10 micrograms and 30 micrograms nicotine were significantly greater in atherosclerotic hearts than in controls. Similarly, myocardial tissue from atherosclerotic animals contained significantly more (-)-norepinephrine than controls. These observations suggest that diet-induced atherosclerosis in rabbits is associated with an increase in myocardial (-)-norepinephrine content and that the augmented (-)-norepinephrine pool can be mobilized by nicotine.

Surfactant disposition in rats with monocrotaline-induced pneumotoxicity.

Monocrotaline (MCT)-treated rats exhibit airways and gas exchange abnormalities which precede development of sustained pulmonary hypertension (Lai et al., 1991). Because the density of type II pneumocytes is reduced in MCT-treated rat lungs (Wilson and Segall, 1990), decreased abundance or activity of type II pneumocyte-derived surfactant may contribute to pulmonary dysfunction. On the other hand, since the remaining type II pneumocytes undergo an apparent hypertrophic response, it is possible that they compensate for the reduction in population density by elaborating more surfactant or surfactant with enhanced surface activity. As an initial means of discriminating between these possibilities, the amount, surface activity, and synthesis rate of surfactant was examined in rats at 1, 2, and 3 weeks after MCT administration. The amounts of surfactant phospholipid and protein recovered in bronchoalveolar lavage fluid did not differ substantially between control and MCT-treated rats at any time post MCT administration. Similarly, neither the initial rate of surface tension reduction nor the maximum reduction in surface tension differed between surfactant preparations recovered from control and MCT-treated rats. The rate of surfactant synthesis in lung explants, as determined by incorporation of [3H]glycerol into phospholipid, also was not different between MCT-treated and control rats at any time after MCT administration. MCT treatment failed to alter the distribution of [3H]glycerol into surfactant phospholipid. Collectively, these data indicate that airways abnormalities in MCT-treated rats cannot be ascribed to a reduction in the abundance or the activity of surfactant. Furthermore, in light of previous studies indicating that the density of type II pneumocytes is reduced in MCT pneumotoxicity, the present findings suggest that surfactant regulatory pathways must undergo a compensatory response that preserves normal functional status.