Effects of altered platelet number on pulmonary hypertension and platelet sequestration in monocrotaline pyrrole-treated rats

doi:10.1016/0041-008X(89)90012-4

Toxicology and Applied Pharmacology

Volume 99, Issue 2, 15 June 1989, Pages 302-313

https://doi.org/10.1016/0041-008X(89)90012-4 Get rights and content

Abstract

To study the role of platelets in monocrotaline pyrrole (MCTP)-induced pulmonary hypertension, pulmonary sequestration of ¹¹¹In-labeled platelets in rats treated with MCTP and anti-rat platelet serum (PAS) was examined. Lung injury from a single, intravenous injection of MCTP (3.5 mg/kg) at Day 8 was evident as elevated lung weight and lavage fluid protein and lactate dehydrogenase activity. Additionally, right ventricular hypertrophy and elevated pulmonary arterial pressures (PAP) occurred. Treatment with PAS on Days 6–8 did not affect the lung injury but resulted in an attenuation of the pulmonary hypertensive response. Pulmonary platelet sequestration was also decreased in PAS-treated rats, yet the sequestration in the lungs of MCTP-treated rats that received PAS was significantly higher than that in the lungs of N,N-dimethylformamide (DMF) controls. MCTP-treated rats receiving control serum (CS) tended to sequester more ¹¹¹In-labeled platelets than respective DMF controls, but this was not statistically significant. Blood platelet half-life was unaltered in rats receiving CS. When rats were treated similarly with MCTP and PAS and were killed at 18 days, the attenuation of the pulmonary hypertensive response previously described was not observed, and lung injury was more extensive than when CS was given. Apparently, platelet depletion delayed the development of the pulmonary hypertensive response. Supranormal platelet numbers produced by splenectomy did not affect MCTP-induced lung injury or the elevation in PAP. These results support the hypothesis that the development of MCTP-induced pulmonary hypertension is mediated in part by platelets.

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2001, Chest
Citation Excerpt :
Most reports describe patients who had elevated platelet counts, and there are reports of patients whose symptoms mirrored the changes in platelet counts.2 Platelet-derived growth factor released from activated platelets is a strong stimulus for smooth muscle hyperplasia,17 and in an animal model of PH the control of the platelet count retards the development of PH.18 Twelve of our patients were receiving aspirin before PH was diagnosed, and this suggests that aspirin may not be effective in preventing the onset of PH in these patients. Often, patients with CMDs have evidence of chronic disseminated intravascular coagulation19 and this can result in microthrombosis in the pulmonary circulation with PH as a consequence.
To investigate the potential association between the chronic myeloid disorders (CMDs), including the chronic myeloproliferative disorders, and pulmonary hypertension (PH).
Retrospective chart review of patients who had received diagnoses of both CMD and PH. Patients with a known cause of PH were excluded. The diagnosis of a CMD was based on established criteria. The diagnosis of PH was based on echocardiographic data or right heart catheterization data.
Twenty-six patients satisfied the criteria for both a CMD and PH. Twelve patients had myeloid metaplasia with myelofibrosis (MMM), 5 patients had essential thrombocythemia (ET), 6 patients had polycythemia vera, 2 patients had a myelodysplastic syndrome, and 1 patient had chronic myeloid leukemia. Twenty-two patients (92%) received treatment for their CMDs, which included therapy with hydroxyurea (18 patients), anagrelide (7 patients), and busulfan (3 patients). PH was diagnosed a median of 8 years after recognition of the CMD (range, 0 to 26 years). The median right ventricular systolic pressure (RVsys) was 71 mm Hg (range, 32 to 105 mm Hg). RVsys correlated with the platelet count in patients with MMM (r = 0.30) and ET (r = 0.6) and with the hemoglobin levels in patients with PV (r = 0.77). Treatment of CMD did not seem to affect the severity of the pulmonary artery pressures as measured by serial echocardiography. With a median survival time of 18 months after the diagnosis of PH, the cause of death in the majority of the patients was cardiopulmonary.
The current study suggests a higher than expected incidence of PH in patients with MMM, PV, and ET. Prognosis in such a setting is poor and may not be influenced by aggressive treatment of the underlying hematologic disorder.
Role of complement in rats injected with liposome-encapsulated hemoglobin
1997, Journal of Surgical Research
Previous studies have documented that liposome-encapsulated hemoglobin (LEH) can cause a rapid and transient thrombocytopenia following intravenous injection into small animals. The present study evaluated the role of complement during the LEH-induced thrombocytopenia in rats. We have compared changes in platelet levels in the blood, platelet organ distribution, and total hemolytic complement levels following intravenous administration of LEH in control and complement-depleted rats. Changes in platelet organ distribution at various times after LEH administration were monitored by labeling autologous platelets with indium-111 (¹¹¹In)-oxine and imaging the¹¹¹In-platelets with a gamma camera after reinjection. Platelet counts were determined by light-scattering methods and by following¹¹¹In radioactivity at various times after LEH administration. Platelet levels did not significantly change for the complement-depleted rats during the 60 min following an injection of LEH, whereas thrombocytopenia (40% decrease) was noted within 4 min post-LEH-injection for control rats with a gradual return to baseline circulating platelet levels within 60 min. This drop in circulating platelets was correlated with a rapid redistribution of¹¹¹In-platelets from the circulation to the lungs and liver, whereas complement-depleted rats showed no transient movement of the¹¹¹In-platelets from the circulation. Baseline complement levels of 21.6 ± 2.2 CH₅₀/ml for control rats and 0.2 ± 0.1 CH₅₀/ml for complement-depleted rats did not significantly change during the 60 min following LEH administration. This study suggests that complement must be present during LEH-induced transient thrombocytopenia, as complement-depleted rats underwent no thrombocytopenia, and that the transient LEH-induced thrombocytopenia may be associated with complement activation.
Cellular fibronectin and von Willebrand factor concentrations in plasma of rats treated with monocrotaline pyrrole
1996, Biochemical Pharmacology
The monocrotaline pyrrole (MCTP)-treated rat is a useful model for the study of certain chronic pulmonary vascular diseases. A single, i.v. administration of a low dose of MCTP causes pneumotoxicity, pulmonary vascular remodeling, sustained increases in pulmonary arterial pressure, and right ventricular hypertrophy in rats. The pulmonary vascular lesions are characterized by endothelial cell alterations, platelet and fibrin microvascular thrombosis, pulmonary edema, and thickening of the intimal and medial layers of the vessel wall. These lesions suggest that some dysfunction of the hemostatic system occurs in the lungs of rats treated with MCTP. We evaluated the concentrations of two adhesion proteins, cellular fibronectin (cFn) and von Willebrand factor (vWF), in the plasma of rats treated with MCTP. We hypothesized that changes in these factors occur along with markers of pneumotoxicity and ventricular hypertrophy and that such changes might contribute to the genesis of the vascular lesions. Enzyme-linked immunosorbent assays were used to measure cFn and vWF concentrations in the plasma of rats after MCTP treatment. Rats treated with a single, i.v. injection of 3.5 mg MCTP/kg body weight had delayed and progressive lung injury characterized at 5 days post-treatment by increases in the lung-to-body weight ratio and in lactate dehydrogenase activity and protein concentration in cell-free bronchoalveolar lavage fluid (BALF). Values for these markers were further increased at 8 days and reached a plateau thereafter. The number of nucleated cells within the BALF was increased at 8 and 14 days. Right ventricular hypertrophy, an indirect marker of pulmonary hypertension, was evident at 14 days. The cFn concentration was increased in plasma of rats at 8 and 14 days after treatment with MCTP. There was no difference between the vWF concentration in plasma of rats treated with MCTP and those treated with vehicle at any time. We conclude that an increase in plasma cFn concentration occurs prior to the onset of right ventricular hypertrophy and that this change is consistent with a role for cFn in the genesis of vascular remodeling and pulmonary hypertension in the MCTP-treated rat. The lung vascular injury and pulmonary hypertension in this model were not reflected in altered vWF concentration in the plasma. BIOCHEM PHARMACOL 51;2:187–191. 1996.
Chemical-induced vasculature injury. Summary of the symposium presented at the 32nd annual-meeting of the society of toxicology, new-orleans, louisiana, march 1993
1995, Toxicology and Applied Pharmacology
The cross-sectional structure of the vasculature is comparatively simple, comprising three layers-the intima, adjacent to the lumen, the media, and the adventitia. Notwithstanding this simplicity, the vessels are host to a variety of reactions to injury. Two cell types, endothelial cells of the intima and smooth muscle cells of the media, are principal targets of damage and repair. The endothelial cells of the intimal layer of the vessel wall present a macromolecular barrier and are important in maintaining vessel integrity. When the integrity is compromised by physical or chemical injury, endothelial cells play a key role in the repair processes. The use of single-cell wound models allows the mechanisms of damage and subsequent repair to be studied in depth. Repair processes can be observed using time-lapse photography and differences between cytoskeleton changes during repair and reendothelialization of small and large wounds can be discriminated. In rats treated with the plant toxin monocrotaline, pulmonary vascular injury occurs which manifests as thrombosis and remodeling with consequent progressive pulmonary hypertension. In vivo and in vitro studies of the mechanism of monocrotaline toxicity suggest that the endothelial cells are an important target. In vitro studies show monocrotaline to be directly cytotoxic; in cells that survive, there are functional changes to the endothelial cells, resulting in a decreased repair capability which may lead to the complex, progressive lung lesions that develop. The other target cells of the vasculature are the smooth muscle cells of the media. Ingestion of primary amines allylamine and β-aminopropionitrile (β-APN) results in chronic vasculotoxicity to the aorta and medium-sized arteries. For allylamine, subtle changes in smooth muscle result in medial hypertrophy and subintimal proliferation. The changes are slow to occur, taking weeks or months of repeated treatment. For β-APN, which is the active ingredient of the toxic sweet pea Lathyrus odoratous, vascular toxicity is manifested by fatal rupture of aortic aneurysms. When these agents are administered concomitantly, a synergistic acute smooth muscle necrosis occurs in large elastic arteries and degenerative changes are seen in muscular arteries. A change in the target for toxicity of allylamine toward the vasculature may be responsible for this synergistic toxic insult. Medial smooth muscle necrosis is also noteworthy after administration of certain pharmaceutical agents of diverse structure and pharmacological activity. These agents induce arteriopathies in dogs and rats, although at different sites. In dogs, the coronary arteries are susceptible, whereas in rats the mesenteric arteries are the principal sites of injury. Since these agents are diverse in structure and biochemical activity, the mechanism of toxicity of these agents appears to be related to their pharmacodynamic activity rather than to a direct effect. Studies on the relationship between vasodilatory and hypotensive properties of these agents and toxic response suggest the mechanism may be related to profound and exaggerated hemodynamic properties.
Toxicity of mitomycin C toward cultured pulmonary artery endothelium
1995, Toxicology and Applied Pharmacology
Mitomycin C (MMC) is a bifunctional alkylating agent used in cancer chemotherapy. MMC therapy occasionally results in pulmonary vascular injury, including alterations in endothelial cells. Reactive metabolites of MMC can cross-link DNA, and its cytotoxicity has been attributed in part to this capacity, but effects in vascular cells have not been explored extensively. Accordingly, the direct effects of MMC on cultured porcine pulmonary artery endothelial cells (PECs) were examined. A single administration of MMC (0-10 μM) to PEC monolayers resulted in concentration-dependent cytolytic injury that was delayed in onset and progressive in nature. Cells treated at subconfluent densities were inhibited in their ability to proliferate. MMC treatment resulted in DNA cross-linking at concentrations (0.01-1 μM) that inhibited cell proliferation but caused only limited overt cytotoxicity, supporting an association between DNA cross-linking and impairment of cell division. This pattern of PEC injury is reminiscent of that seen after treatment with another pneumotoxic, bifunctional alkylating agent, monocrotaline pyrrole. The similarity of the endothelial cell response to different bifunctional alkylating agents suggests that DNA cross-linking may inhibit cell proliferation and thereby limit the repair capacity of endothelial monolayers. This might contribute to the progressive pulmonary vascular injury that occurs after administration of certain DNA cross-linking agents in vivo.
Platelets and α-naphthylisothiocyanate-induced liver injury
1994, Toxicology and Applied Pharmacology
Administration of alpha-naphthylisothiocyanate (ANIT) to rats results in periportal cholangiolitic hepatopathy. Inflammation is a hallmark of the liver injury, and expression of toxicity is dependent on blood neutrophils. The role of other cellular mediators of inflammation in ANIT-induced hepatic insult is unknown. We hypothesized that platelets participate in the expression of ANIT hepatotoxicity. To test this, circulating platelets were decreased by administration of anti-rat platelet serum (PAb) prior to treatment of rats with ANIT. The PAb treatment regimen effectively reduced circulating thrombocytes over the course of the experiment. Twenty-four hours after oral ANIT administration, rats were euthanized and liver injury was estimated by increases in serum alanine aminotransferase (ALT) and γ-glutamyltransferase (GGT) activities. Cholestasis was assessed by measurement of serum total bilirubin concentration and bile flow. Reduction in platelet numbers was associated with attenuation of the increases in plasma ALT activity and bilirubin concentration seen after ANIT administration. However, PAb treatment did not attenuate the increase in plasma GGT, a marker of biliary epithelial cell injury. ANIT-induced changes in platelet function were assessed by evaluating platelet aggregation responses in platelet-rich plasma from rats treated with ANIT in vivo. ANIT treatment modestly decreased ex vivo platelet aggregation in response to ADP and collagen stimuli. To address further the role of platelet-derived cyclooxygenase products in ANIT hepatotoxicity, rats were treated with aspirin or ibuprofen. Neither pretreatment ameliorated ANIT-induced hepatic insult. These results suggest that platelets contribute to the expression of ANIT-induced liver injury, but they do not appear to act through the production of cyclooxygenase metabolites.

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Effects of altered platelet number on pulmonary hypertension and platelet sequestration in monocrotaline pyrrole-treated rats

Abstract

Exp. Mol. Pathol.

Clin. Chim. Acta

J. Biol. Chem.

J. Biol. Chem.

Toxicol. Appl. Pharmacol.

Blood

Toxicol. Appl. Pharmacol.

Pulmonary hypertension and ECG changes from monocrotaline pyrrole in the rat

Amer. J. Physiol.

Ventricular weight in cardiac hypertrophy

Brit. Heart J.