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K R Stenmark

Publications and source records attributed to K R Stenmark.

At least 19 recordsLinked to original sources
PubMed1997

Right ventricular angiotensin converting enzyme activity and expression is increased during hypoxic pulmonary hypertension.

OBJECTIVE: To determine whether local cardiac angiotensin converting enzyme (ACE) expression is upregulated during the development of hypoxia-induced right ventricular hypertrophy. METHODS: ACE activity was measured in membrane preparations from the right ventricle and left ventricle plus septum in normoxic rats and animals exposed to chronic hypoxia for 8 and 14 days. Local cardiac ACE expression was studied by immunohistochemistry using a monoclonal antibody to ACE (9B9). RESULTS: In the normal rat heart, ACE expression was confined to vascular endothelium, the valvular endocardium, and localized regions of parietal endocardium. We found that the development of pulmonary hypertension and right ventricular hypertrophy were associated with 2.6- and 3.4-fold increases in membrane-bound right ventricular ACE activity by 8 and 14 days of hypoxia, respectively. Right ventricular ACE activity was positively correlated with the degree of right ventricular hypertrophy (r = 0.83, P < 0.001). In contrast, left ventricular plus septal ACE activity was significantly reduced by approximately 40 and 60% by 8 and 14 days of hypoxia, respectively, compared to controls. In the right ventricle of chronically hypoxic rats, immunohistochemistry demonstrated increased ACE expression in areas of myocardial fibrosis. Interestingly, increased ACE expression was noted in the right ventricular epicardium in chronically hypoxic rats. In the free wall of the left ventricle there was a significant reduction in the number of myocardial capillaries which expressed ACE in chronically hypoxic rats. CONCLUSION: Chronic hypoxia has a differential effect on left and right ventricular ACE activity and that the sites of altered ACE expression are highly localized. We speculate that locally increased right ventricular ACE activity and expression may play a role in the pathogenesis of right ventricular hypertrophy secondary to hypoxic pulmonary hypertension.

Animals↗
PubMed1997

Cellular and molecular mechanisms of pulmonary vascular remodeling.

In many organs and tissues, the cellular response to injury is associated with a reiteration of specific developmental processes. Studies have shown that, in response to injury, vascular wall cells in adult organisms express genes or gene products characteristic of earlier developmental states. Other genes, expressed preferentially in adult cells in vivo, are down-regulated following injurious stimuli. Complicating matters, however, are recent observations demonstrating that the vascular wall is comprised of phenotypically heterogeneous subpopulations of endothelial cells, smooth muscle cells, and fibroblasts. It is unclear how specific subsets of cells respond to injury and thus contribute to the vascular remodeling that characterizes chronic pulmonary hypertension. This review discusses vascular development in the lung and the cellular responses occurring in pulmonary hypertension; special attention is given to heterogeneity of responses within cell populations and reiteration of developmental processes.

Animals↗
PubMed1997

Pulmonary artery smooth muscle cells from chronically hypoxic neonatal calves retain fetal-like and acquire new growth properties.

Growth properties retained and acquired by immature pulmonary artery (PA) smooth muscle cells (SMC) in vivo after chronic exposure to hypoxia and the mechanisms that regulate hypoxia-induced change in proliferative phenotype are not known. We tested the hypothesis that PA SMC from neonatal calves exposed to hypoxia after birth would both retain fetal-like and acquire new growth characteristics and that these changes would be at least partially dependent on protein kinase C (PKC), a key proproliferative signal transduction pathway. Like fetal cells, PA SMC from hypoxic calves grew faster in the presence and absence of serum and were more responsive to insulin-like growth factor I and platelet-derived growth factor-BB than control neonatal and adult cells. PA SMC from hypoxic calves also acquired other growth properties (i.e., including increased hypoxic growth after PKC activation) that were new compared with those observed for fetal cells. The proliferative response to hypoxia was first detectable in the neonatal period and was further increased in cells from hypoxic calves. SMC from fetuses and hypoxic calves were more susceptible to the growth-inhibiting effects of PKC antagonists (dihydrosphingosine and calphostin C) than control neonatal and adult cells. To test if the Ca(2+)-dependent isozymes of PKC were uniquely important in the developmental and acquired growth changes observed, the antagonistic effect of the specific, but isozyme nonselective, PKC inhibitor Ro-81-8220 was then compared with GF-109203X, a structural analog with relative specificity for the Ca(2+)-dependent isozymes of PKC (alpha and beta in PA SMC). The faster growing PA SMC from bovine fetuses and hypoxia-exposed calves again demonstrated greater growth inhibition in response to both inhibitors. GF-109203X was equipotent to Ro-31-8220, and its antiproliferative effects were shown to not be due to an increase in apoptosis. Phorbol ester-induced PKC downregulation, another inhibitor strategy that selectively depletes bovine PA SMC of PKC-alpha, but not -beta, mimicked the antiproliferative effects of GF-109203X. Whole cellular PKC catalytic activity paralleled the pattern of peptide-induced growth and susceptibility to PKC inhibition. These results suggest that PA SMC from hypoxia-exposed neonatal calves retain enhanced fetal-like proliferative capacity and acquire new growth properties that are at least partially dependent on the Ca(2+)-regulated isozymes of PKC and in particular PKC-alpha.

Aging↗
PubMed1997

Smooth muscle cell heterogeneity in pulmonary and systemic vessels. Importance in vascular disease.

Experimental evidence is rapidly accumulating which demonstrates that the arterial media in both pulmonary and systemic vessels is not composed of a phenotypically homogeneous population of smooth muscle cells (SMCs) but rather of heterogeneous subpopulations of cells with unique developmental lineages. In vivo and in vitro observations strongly suggest that marked differences in the phenotype, growth, and matrix-producing capabilities of phenotypically distinct SMC subpopulations exist and that these differences are intrinsic to the cell type. These data also suggest that differential proliferative and matrix-producing capabilities of distinct SMC subpopulations govern, at least in part, the pattern of abnormal cell proliferation and matrix protein synthesis observed in the pathogenesis of vascular disease. Within the pulmonary circulation, the observation that the isolated medial SMC subpopulations exhibit differential proliferative responses to hypoxic exposure is important, since this in vitro cell-model system can now be used to better understand the mechanisms that regulate increased responsiveness of specific medial cell subpopulations to low oxygen concentrations. Our data also support the idea that protein kinase C is likely to be one important determinant of differential cell growth responses to hypoxia. The data also suggest differential involvement of specific arterial SMC subpopulations in the elastogenic responses of the vessel wall to injury. We believe that a better understanding of the mechanisms contributing to the unique behavior of specific arterial cell subpopulations will provide important future directions for therapies aimed at preventing abnormal cell replication and matrix protein synthesis in vascular disease.

Actins↗
PubMed1997

Hypoxia increases bromodeoxyuridine labeling indices in bovine neonatal pulmonary arteries.

Thickening of peripheral pulmonary arteries (PA) in the pulmonary hypertensive neonate has been well described morphologically, but less is known regarding the role of cell proliferation in either the normal or hypertensive neonatal PA. Thus we studied DNA synthetic indices in the tunica media and tunica adventitia of four different sizes/generations of PA in normoxic calves (n = 15) and calves exposed to hypobaric hypoxia (n = 15) during the first 14 days of life. DNA synthetic indices were determined by incorporation of the thymidine analogue bromodeoxyuridine (BrdU). Hemodynamic studies confirmed a steady decline in PA pressure in normal neonatal calves during the first 2 wk of life and progressive pulmonary hypertension in the hypoxic group. Lungs were perfusion-fixed and pulmonary arteries were evaluated for BrdU incorporation by immunohistochemistry. DNA synthetic indices (BrdU-labeled cells/1,000 cells) in the tunica media from normoxic calves were highest between 4 and 7 days postpartum and decreased to their lowest levels by day 14. The highest indices were observed in smaller generations of PA in the normoxic newborn. Adventitial cells exhibited the same general pattern of BrdU incorporation except that the postpartum peak occurred earlier, at 1 to 4 days. Exposure to hypoxia significantly increased (P = 0.001) DNA synthetic indices in both the tunica media and adventitia. The highest DNA synthetic indices were observed in smaller-generation vessels. These findings indicate that the fraction of cells traversing the S phase (i.e., actively replicating in the cell cycle) in the normal neonatal pulmonary vasculature during transition are initially high compared to reported rates in hilar PA from adult rats, but then decrease by 14 days after birth. Further, exposure to hypoxia during transition dramatically increases and prolongs pulmonary vascular cell proliferation. We conclude that structural remodeling in the hypertensive neonatal PA is due partly to increased cell proliferation in the tunica media and adventitia.

Animals↗
PubMed1997

High-dose epinephrine is not superior to standard-dose epinephrine in pediatric in-hospital cardiopulmonary arrest.

OBJECTIVE: To compare the efficacy of high-dose epinephrine (HDE) with that of standard-dose epinephrine (SDE) for resuscitation from in-hospital pediatric cardiopulmonary arrest (CPA). DESIGN: Fifty-four-month retrospective study of all pediatric patients who had a CPA while hospitalized at a tertiary care children's hospital. Standard pediatric advanced life support techniques were used for all patients. Patients received HDE or SDE in accordance with physician orders and standard protocols at the time of CPA. Primary outcome measures were the return of spontaneous circulation (ROSC), the duration of survival after resuscitation, survival to hospital discharge, and Pediatric Overall Performance Category scores at the time of discharge. RESULTS: During the study period, 51 patients met entry criteria and had a total of 58 CPAs. Twenty-one patients received HDE during resuscitation from 24 arrests, at a dose of 0.12 +/- 0.05 mg/kg (mean +/- SD); 30 patients received SDE during resuscitation from 34 arrests, at a dose of 0.01 +/- 0.01 mg/kg (mean +/- SD). The HDE and SDE groups were not significantly different in terms of gender, initial cardiac rhythm, location of CPA, primary diagnoses at the time of CPA, initial pH, or additional resuscitation medications received; the SDE group had a significantly higher mean age, although the median ages were not different. Fourteen of 24 resuscitations using HDE resulted in ROSC (58%) with a mean time to ROSC of 19 minutes; 7 (29%) of 24 led to survival for 24 hours, and 6 (26%) of 23 patients survived to hospital discharge, all with moderate to severe neurologic and functional impairment. Twenty-four of 34 resuscitations using SDE resulted in ROSC (71%) with a mean time to ROSC of 12 minutes; 17 (50%) of 34 led to survival for 24 hours; and 7 (23%) of 30 patients survived to hospital discharge, 4 with mild to moderate neurologic impairment. No significant differences in rates of ROSC, survival rates, or Pediatric Overall Performance Category scores of survivors were found between the two groups. The mean time to ROSC was significantly longer in the HDE group. CONCLUSIONS: In this study, the use of HDE did not improve the rates of ROSC, short-term survival, or long-term survival after pediatric in-hospital CPA, nor did it improve overall outcome scores. Given the conflicting evidence surrounding possible detrimental effects of HDE use, a large, blinded, prospective trial of HDE use in this setting is necessary to clarify the appropriate role for HDE in pediatric resuscitation.

Child, Preschool↗
PubMed1996

Developmental regulation of angiotensin converting enzyme and angiotensin type 1 receptor in the rat pulmonary circulation.

Factors that influence the development of the normal pulmonary vasculature are poorly understood. Since increased local production of angiotensin II (AII) by angiotensin converting enzyme (ACE) has been implicated in the medial hypertrophy of systemic and pulmonary hypertension, we questioned whether ACE and angiotensin receptor expression may influence the muscularization of the normal pulmonary vasculature during development. The approach employed measurement of lung ACE activity, assessment of local ACE expression by immunohistochemistry, and angiotensin type 1 receptor (AT1) expression by in situ hybridization in rat lungs ranging from 15 days of intrauterine life (term = 21 d) to adulthood. The temporal and spatial pattern of ACE expression was compared with that of the endothelial marker, von Willebrand factor (vWF), and the smooth muscle cell markers, alpha smooth muscle actin and smooth muscle myosin. ACE activity was first detected in lung homogenates on day 17 of gestation (1 +/- 0.2 mU/mg) and increased progressively to term (27.7 +/- 3.2 mU/mg). However, the greatest increase in lung ACE activity to adult levels (379 +/- 25.2 mU/mg) occurred between 2 and 4 wk of postnatal life. Immunohistochemistry demonstrated vWF expression by vascular endothelium throughout the lung as early as day 15 of gestation. In contrast, ACE expression was observed in the endothelium of only hilar pulmonary arteries on day 15 of gestation, and thereafter was noted to be expressed in endothelial cells of progressively more distal arteries, such that by term, endothelial cells of all muscularized arteries expressed ACE. Alveolar capillary ACE expression was not detected until day 20 of gestation, and increased dramatically after birth. Smooth muscle actin expression in lung arteries closely paralleled the expression of endothelial ACE. AT1 receptor mRNA was first expressed in the peripheral lung on day 17 of gestation by non-epithelial undifferentiated mesenchyme. In contrast, AT1 mRNA signal was much reduced in differentiated smooth muscle. We speculate that ACE expression in the fetal lung circulation may influence the muscularization of fetal pulmonary arteries by the interaction of locally produced angiotensin II with the AT1 receptor.

Animals↗
PubMed1996

Expression and localization of tropoelastin mRNA in the developing bovine pulmonary artery is dependent on vascular cell phenotype.

During vascular development, the expression of tropoelastin (TE) messenger ribonucleic acid (mRNA) has been shown to be time dependent and to form complex patterns along the longitudinal and radial arterial axes. The factors contributing to these patterns of TE expression are not known, but it has been suggested that they reflect phenotypic changes in developing smooth muscle cells (SMC). In order to examine a possible correlation between the developmental state of the SMC and TE expression during lung vascular development, we localized and assessed relative TE mRNA expression in the developing bovine main pulmonary artery (PA), and correlated the observed patterns of TE expression to changes in SMC phenotype as determined by the expression of various developmentally related SMC proteins. Further, because TE expression can be modulated by physical forces such as pressure, fetal PA TE expression was evaluated with regard to changes in fetal arterial pressure. We found that expression of TE mRNA exhibited a biphasic pattern during fetal development. In early gestation, expression was noted throughout the entire PA wall; at midgestation, expression was markedly decreased in the outer wall but maintained in the inner vascular media; at late gestation, reexpression was observed throughout the entire PA wall, albeit in a heterogeneous pattern. Immunohistochemical studies showed that the decrease in SMC TE expression during midgestation coincided with the acquisition of SMC-specific proteins such as smooth muscle myosin heavy chains and desmin. The reexpression of TE late in gestation occurred in these "differentiated" SMC and was temporally associated with a large increase in arterial pressure shown to occur in late gestation. In addition, we identified an SMC population defined by its immunoreactivity to the muscle-specific cytoskeletal protein meta-vinculin that did not express TE mRNA either during fetal PA development or postnatally when PA hypertension was induced. We conclude that both the developmental state of the SMC and hemodynamic forces correlate with the pattern of PA TE mRNA expression during pulmonary vascular development. Further, a subpopulation of SMC defined by meta-vinculin expression exists in the fetal and neonatal bovine vascular wall and does not express detectable levels of TE mRNA regardless of vascular pressure.

Animals↗
PubMed1995

The mitogenic effects of the B beta chain of fibrinogen are mediated through cell surface calreticulin.

We have previously shown that soluble partially degraded fibrin(ogen) remains in solution after fibrin clot formation and is a potent fibroblast mitogen (Gray, A.J., Bishop, J.E., Reeves J.T., Mecham, R.P., and Laurent, G.J. (1995) Am. J. Cell Mol. Biol. 12, 684-690). Mitogenic sites within the fibrin(ogen) molecule are located on the A alpha and B beta chains of the protein (Gray, A.J., Bishop, J. E., Reeves, J.T., and Laurent, G.J. (1993) J. Cell Sci. 104, 409-413). However, receptor pathways through which mitogenic effects are mediated are unknown. The present study sought to determine the nature of fibrin(ogen) receptors expressed on human fibroblasts which interact with the fibrinogen B beta chain. Receptor complexes were isolated from 125I-surface-labeled fibroblasts and purified on a fibrinogen B beta chain affinity column. Subsequent high performance liquid chromatography and SDS-polyacrylamide gel electrophoresis analysis indicated fibrinogen B beta chain bound specifically to a 60-kDa surface protein. Sequence analysis of the amino terminus of this protein indicated 100% homology to human calreticulin. Immunoprecipitation experiments employing a polyclonal anti-calreticulin antibody provided further evidence that the 60-kDa protein isolated in this study was calreticulin. Further, polyclonal antibodies to human calreticulin significantly inhibited the mitogenic activity of fibrinogen B beta chain on human fibroblasts. The present study has shown that cell surface calreticulin binds to the B beta chain of fibrinogen mediating its mitogenic activity.

Amino Acid Sequence↗
PubMed1995

Role of angiotensin-converting enzyme and angiotensin II in development of hypoxic pulmonary hypertension.

Although angiotensin converting enzyme (ACE) inhibitors are known to attenuate the development of hypoxic pulmonary hypertension in rats, the precise mechanism of this protective effect remains unknown. Thus we utilized specific angiotensin II (ANG II)-receptor antagonists to investigate whether ANG II is involved directly in the hemodynamic and structural changes of pulmonary hypertension, and we tested whether the protective effects of ACE inhibition can be attributed partly to potentiation of bradykinin. During 14 days of hypobaric hypoxia, rats received, via intraperitoneal osmotic minipumps, either 1) the ACE inhibitor captopril, 2) captopril plus the bradykinin B2-receptor antagonist CP-0597, 3) the ANG II type 1 receptor antagonist losartan, 4) the ANG II type 2 receptor antagonist PD-123319, or 5) saline. At 14 days, mean pulmonary arterial pressure (MPAP) was reduced (P < 0.05) in hypoxic rats treated with captopril (26.6 +/- 0.8 mmHg) or losartan (24.4 +/- 1.0 mmHg) compared with saline (32.0 +/- 1.4 mmHg) but was unaffected by PD-123319 (29.5 +/- 1.7 mmHg). Right ventricular hypertrophy was reduced in hypoxic rats treated with captopril or losartan compared with saline-treated rats. Morphometry showed less medial thickening and peripheral muscularization of small pulmonary arteries in hypoxic animals treated with captopril or losartan. Coadministration of CP-0597 did not reverse the protective effects of captopril on pulmonary vascular remodeling. These results suggest a novel role for endogenous ANG II, acting through the type 1 receptor, in the vascular remodeling associated with hypoxic pulmonary hypertension. The beneficial effects of ACE inhibition in this model can be attributed to reduced ANG II production rather than potentiation of bradykinin.

Angiotensin II↗
PubMed1995

Enhanced growth of fetal and neonatal pulmonary artery adventitial fibroblasts is dependent on protein kinase C.

The earliest and most striking proliferative changes in the neonatal pulmonary arterial wall occur in the adventitia where the fibroblast resides. The protein kinase C (PKC) pathway is developmentally regulated and important in vascular cell growth. We tested the hypothesis that developmental differences in growth of pulmonary artery adventitial fibroblasts would be detectable in vitro and dependent on PKC. Fibroblasts were isolated from bovine fetal, neonatal, and adult pulmonary arteries. Growth was measured by [3H]thymidine incorporation and cell counts. Under serum-stimulated conditions, fetal and neonatal pulmonary artery fibroblasts grew faster and reached higher plateau densities than adult cells. Increased growth of fetal cells in vitro was dependent on time of harvest during fetal life (early > late). Under quiescent conditions, fetal and neonatal fibroblasts had increased DNA synthesis compared with adult cells in response to the PKC agonist phorbol 12-myristate 13-acetate. To test whether the developmental differences in fibroblast growth were dependent on PKC, three different inhibitor strategies were used (dihydrosphingosine, phorbol-ester-induced downregulation, and heparin). Fetal and neonatal fibroblasts were more susceptible than adult cells to each antagonist strategy. Finally, we measured whole cellular PKC catalytic activity and found it correlated with growth and susceptibility to PKC inhibition (i.e., fetal PKC activity > neonatal > adult). We conclude that PKC-dependent developmental differences in growth of pulmonary artery fibroblasts are detectable in vitro and that the enhanced growth capacity of fetal and neonatal cells may contribute to the dramatic adventitial thickening seen in vivo after hypoxic exposure in the neonatal calf.

Animals↗
PubMed1995

Hypoxia selectively induces proliferation in a specific subpopulation of smooth muscle cells in the bovine neonatal pulmonary arterial media.

Medial thickening of the pulmonary arterial wall, secondary to smooth muscle cell (SMC) hyperplasia, is commonly observed in neonatal hypoxic pulmonary hypertension. Because recent studies have demonstrated the existence of multiple phenotypically distinct SMC populations within the arterial media, we hypothesized that these SMC subpopulations would differ in their proliferative responses to hypoxic pulmonary hypertension and thus contribute in selective ways to the vascular remodeling process. Expression of meta-vinculin, a muscle-specific cytoskeletal protein, has been shown to reliably distinguish two unique SMC subpopulations within the bovine pulmonary arterial media. Therefore, to assess the proliferative responses of phenotypically distinct SMC subpopulations in the setting of neonatal pulmonary hypertension, we performed double immunofluorescence staining on pulmonary artery cryosections from control and hypertensive calves with antibodies against meta-vinculin and the proliferation-associated nuclear antigen, Ki-67. We found that, although neonatal pulmonary hypertension caused significant increases in overall cell replication, proliferation occurred almost exclusively in one, the meta-vinculin-negative SMC population, but not the other SMC population expressing meta-vinculin. We also examined fetal pulmonary arteries, where proliferative rates were high and meta-vinculin expression again reliably distinguished two SMC subpopulations. In contrast to the hypertensive neonate, we found in the fetus that the relative proliferative rates of both SMC subpopulations were equal, thus suggesting the existence of different mechanisms controlling proliferation and expression of cytoskeletal proteins in the fetus and neonate. We conclude that phenotypically distinct SMC populations in the bovine arterial media exhibit specific and selective proliferative responses to neonatal pulmonary hypertension. Distinct SMC subpopulations may, thus, contribute in unique ways to vascular homeostasis under both normal and pathologic conditions.

Animals↗
PubMed1995

Angiotensin converting enzyme expression is increased in small pulmonary arteries of rats with hypoxia-induced pulmonary hypertension.

Previous studies suggest that while lung angiotensin converting enzyme (ACE) activity is reduced during chronic hypoxia, inhibitors of ACE attenuate hypoxic pulmonary hypertension. In an attempt to explain this paradox we investigated the possibility that whole lung ACE activity may not reflect local pulmonary vascular ACE expression. The experimental approach combined in vivo hemodynamic studies in control and chronically hypoxic rats, measurement of whole lung ACE activity, and evaluation of local pulmonary vascular ACE expression by in situ hybridization and immunohistochemistry. Total lung ACE activity was reduced to 50% of control activity by 5 d of hypoxia and remained low for the duration of the study. Immunohistochemistry showed a marked reduction of ACE staining in alveolar capillary endothelium. However, an increase in ACE staining was observed in the walls of small newly muscularized pulmonary arteries at the level of alveolar ducts and walls. In situ hybridization studies showed increased signal for ACE mRNA in the same vessels. Inhibition of ACE by captopril during chronic hypoxia attenuated pulmonary hypertension and markedly reduced distal muscularization of small pulmonary arteries. In addition, we demonstrated marked longitudinal variation in ACE expression along the normal pulmonary vasculature with the highest levels found in small muscular arteries associated with terminal and respiratory bronchioles. We conclude that local ACE expression is increased in the walls of small pulmonary arteries during the development of hypoxic pulmonary hypertension, despite a generalized reduction in alveolar capillary ACE expression, and we speculate that local arteriolar ACE may play a role in the vascular remodeling associated with pulmonary hypertension.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1994

Enhanced growth capacity of neonatal pulmonary artery smooth muscle cells in vitro: dependence on cell size, time from birth, insulin-like growth factor I, and auto-activation of protein kinase C.

Based on the unique susceptibility of the neonatal pulmonary circulation to hypoxia-induced structural alteration in vivo, we hypothesized that pulmonary artery (PA) smooth muscle cells (SMC) from the neonate would demonstrate enhanced growth capacity in vitro compared to adult cells. To test this hypothesis, matched neonatal and adult bovine SMC were tested for differences in size, serum-stimulated proliferation, susceptibility to senescence, resistance to serum withdrawal, autocrine growth capacity, and responsiveness to a locally important growth factor (insulin-like growth factor I; IGF-I) and an activator of protein kinase C (PKC) (phorbol 12-myristate 13-acetate; PMA). Neonatal PA SMC were smaller, grew faster, reached a higher plateau density, and were less susceptible to senescence. They were more resistant to serum withdrawal, had spontaneous autocrine growth capacity, and were more responsive to IGF-I, PMA, and the combination. Acquisition of increased growth factor responsiveness occurred between d5 and d14 after birth. Increased neonatal growth to IGF-I was associated with reduced IGF-I binding activity, implicating a post-receptor mechanism in enhanced responsiveness. Increased membrane-bound PKC catalytic activity was found in serum-deprived neonatal SMC. This basal increase was equal to that stimulated by 1 nM PMA in adult SMC, a pretreatment that caused these cells to become as responsive to IGF-I as untreated neonatal ones. We conclude that neonatal bovine PA SMC have marked enhancement of growth capacity in vitro, the acquisition of which is dependent on time from birth and is associated with auto-activation of PKC, These increased growth properties detected in vitro may contribute to the striking hyperplasia of neonatal PA SMC found in vivo following hypoxic exposure.

Aging↗
PubMed1994

Multiple phenotypically distinct smooth muscle cell populations exist in the adult and developing bovine pulmonary arterial media in vivo.

Different smooth muscle cell (SMC) functions may require different cell phenotypes. Because the main pulmonary artery performs diverse functions, we hypothesized that it would contain heterogeneous SMC populations. If the hypothesis were confirmed, we wished to determine the developmental origin of the different populations. Using specific antibodies, we analyzed the expression of smooth muscle (SM) contractile and cytoskeletal proteins (alpha-SM-actin, SM myosin, calponin, desmin, and meta-vinculin) in the main pulmonary artery of fetal (60 to 270 days of gestation), neonatal, and adult animals. We demonstrated the existence of a complex, site-specific heterogeneity in the structure and cellular composition of the pulmonary arterial wall. We found that at least four cell/SMC phenotypes, based on immunobiochemical characteristics, cell morphology, and elastic lamellae arrangement pattern, were simultaneously expressed within the mature arterial media. Further, we were able to assess phenotypic alterations in each of the four identified cell populations during development. We found that each cell population within the arterial media expressed alpha-SM-actin at least at certain stages of development, thus demonstrating its smooth muscle identity. However, each cell population progressed along different developmental pathways, suggesting the existence of multiple and distinct cell lineages. A novel anti-metavinculin antibody described in this study reliably distinguished one SMC population from the others during all the developmental stages analyzed. We conclude that the pulmonary arterial media is indeed composed of multiple phenotypically distinct cell/SMC populations with unique lineages. We speculate that these distinct cell populations may serve different functions within the arterial media and may also respond in unique ways to pathophysiological stimuli.

Age Factors↗
PubMed1994

Eicosanoids decrease with successful extracorporeal membrane oxygenation therapy in neonatal pulmonary hypertension.

Elevated concentrations of eicosanoids have been reported in bronchoalveolar lavage fluid (BALF) and blood of infants with persistent pulmonary hypertension (PPHN), thereby indicating their potential role in its pathophysiology. Extracorporeal membrane oxygenation (ECMO) has improved the outcome in selected infants with PPHN. We hypothesized that ECMO, by alleviating lung injury, would be associated with decreased eicosanoid production and clinical improvement. Twenty-two newborns with PPHN treated with either ECMO or conventional means were studied. Concentrations of TxB2, 6-keto-PGF1 alpha, PGD2, PGE2, LTB4, and LTE4 were serially measured in BALF. Elevated concentrations of all eicosanoids measured were observed in all infants with PPHN at the initiation of ECMO. Eicosanoid concentrations decreased in all infants with a good clinical outcome after ECMO, but they remained elevated in those with a poor outcome. In patients with less severe PPHN, not requiring ECMO, lower concentrations of eicosanoids were observed at initiation of therapy. Eicosanoid levels increased or did not change over the course of conventional treatment. We conclude that eicosanoids are present in high concentrations in infants with PPHN. Iatrogenic factors, including oxygen and barotrauma, appear to correlate with their concentrations. Removal of these factors is associated with decreased production of mediators and clinical improvement.

Acute Disease↗
PubMed1994

Persistence of the fetal pattern of tropoelastin gene expression in severe neonatal bovine pulmonary hypertension.

Neonatal hypoxic pulmonary hypertension causes increases and spatial changes in tropoelastin expression in pulmonary arteries. However, it is not clear if this is due to recruitment of quiescent smooth muscle cells (SMC) into an elastin-producing phenotype or persistence of the fetal pattern of tropoelastin gene expression. We evaluated the distribution and relative concentration of tropoelastin mRNA in intralobar pulmonary arteries from late gestation fetuses and in animals exposed to hypobaric hypoxia (430 mmHg) from birth for 1, 3, 7, or 14 d, as well as in age-matched and adult room air-breathing controls. In situ hybridization demonstrated that tropoelastin mRNA was distributed throughout the entire radius of the pulmonary vessel wall in the fetus and newborn calf. By 15 d of age, only cells in the inner third of the media expressed tropoelastin mRNA, and by adulthood no tropoelastin mRNA was detected in the vessel wall. These findings demonstrated that tropoelastin expression shuts off in a spatially specific pattern, moving from the abluminal to the luminal side of the medial in the neonatal pulmonary artery when pressures and resistance are falling. In the aorta of 15-d-old calves, tropoelastin mRNA expression was seen equally throughout the media, indicating tissue-specific regulation of elastin in the neonatal period. In contrast, intralobar pulmonary arteries from calves exposed to hypoxia, which prevented the normal postnatal decline in pulmonary artery pressure, maintained the fetal pattern and levels of tropoelastin mRNA expression at all time points. Thus, rather than causing a recruitment of SMC into an elastin-producing phenotype, neonatal pulmonary hypertension caused a persistence of the fetal pattern of tropoelastin expression in medial SMC. Cell-free translation showed that the same tropoelastin isoforms were made by mRNA from control and hypertensive calves and, unlike the ligamentum nuchae, did not change during the transition from fetal to neonatal life. We conclude that pulmonary hypertension in the neonate perturbs the normal postpartum repression of tropoelastin expression resulting in a persistence of the fetal spacial and isoform patterns of tropoelastin gene expression.

Animals↗