Biomedical subjects

R E Poelmann

Publications and source records attributed to R E Poelmann.

At least 73 records · Page 4Linked to original sources

PubMed1992

The development of the myocardium and endocardium in mouse embryos. Fusion of two heart tubes?

The formation of the single heart tube by hypothetical fusion of two separately developed heart tubes is re-investigated, because this intricate process is ambiguously and often incompletely described. To gain a better insight into this problem ten mouse embryos ranging from 7.5 to 8.5 days of development (presomite to 6 somites) were serially sectioned (1 micron) and reconstructed graphically. Twenty mouse embryos of comparative ages, were studied by scanning electron microscopy. Two large embryonic mesodermal compartments, derived from the primitive streak, extend rostrally on either side of the embryonic axis, and meet in front of the buccopharyngeal membrane. In each compartment a coelomic cavity develops, splitting the mesoderm into a splanchnic and somatic layer. The splanchnic mesoderm differentiates into a layer of cuboidal splanchnic mesothelial cells (promyocardium) and a subjacent plexus of elongated endothelial cells (proendocardium). Before the 1-somite stage the left and right splanchnic mesoderm are separated in front of the buccopharyngeal membrane by a thickening of the yolk sac endoderm. The splanchnic mesoderm then fuses, forming a single horseshoe-shaped heart primordium consisting of a promyocardial layer and a subjacent vascular plexus. Until the 2-somite stage both coelomic cavities remain separated by a bilayer of squamous somatic mesothelial cells ('mesocardium'). The plexus of endothelial cells that forms the proendocardium, also seems to be the source of the lining of the vitelline veins, the pharyngeal arch arteries and the dorsal aortae. The relatively close adherence of endoderm to the medial part of the horseshoe-shaped heart primordium, combined with a bilateral accumulation of cardiac jelly, is suggestive of a double heart tube. However, promyocardium and proendocardium are both translocated as one horseshoe-shaped layer, thus fusion of the left and right parts of the heart primordium does not occur.

Animals↗

PubMed1992

Formation of intimal cushions in the ductus arteriosus as a model for vascular intimal thickening. An immunohistochemical study of changes in extracellular matrix components.

There is a great resemblance in the sequence of events that take place in the pathological development of intimal thickening, so called arteriosclerosis and the formation of intimal cushions in both the normal ductus arteriosus (DA) and the persistent ductus arteriosus (PDA). The human DA was used as a model to study the changes in the extracellular matrix during this process with immunohistochemistry. The formation of intimal cushions was studied in 4 normal fetal DA, 4 normal mature DA and 3 persistent DA. The process of intimal thickening in the fetus starts in the second trimester of pregnancy with an accumulation of glycosaminoglycans in the subendothelial region (SER), accompanied by separation of endothelial cells from the internal elastic lamina and followed by migration of smooth muscle cells into the subendothelial region. This phenomenon was also observed in the mature DA in the neonate, indicating that cushion formation is a continuous process. Intimal cushions had also developed in the persistent DA, although they were morphologically different from the cushions found in the normal mature DA. It was remarkable that two elastic lamellae could be distinguished: one at the original site on the borderline of intimal cushion and media and the other in a subendothelial position. The endothelial cells were firmly attached to this subendothelial lamina, which was wrapped in the basal lamina components laminin and type IV collagen. The main morphological difference between the normal mature DA and the persistent DA is the close relation between endothelial cells and the subendothelial elastic lamina, suggesting an altered elastin metabolism in the PDA. PGI2 synthase was increased in the wall of both the normal and persistent DA as compared with the aorta. It may be related to a role of PGI2 in the formation of intimal cushions.

Aorta↗

PubMed1991

The role of fibronectin and laminin in development and migration of the avian Wolffian duct with reference to somitogenesis.

It has been suggested that matrix molecules like fibronectin and laminin influence the differentiation and migration of embryonic cells. We investigated the role of these two glycoproteins in somitogenesis as well as in the differentiation and migration of the avian Wolffian (pronephric and mesonephric) duct. At first, we described essential steps in the development of these two organ anlagen by light microscopy, SEM and TEM. To localize fibronectin and laminin more exactly in the actual stages, we used the indirect immunoperoxidase reaction at the light microscopic level and the peroxidase-antiperoxidase technique at the ultrastructural level. Fibronectin was found at the surface of the unsegmented paraxial mesoderm, increasing in the cranial direction, and in the basal laminae of somites and Wolffian duct. The mesenchymal tip of the duct contains a moderate amount of fibronectin. In the two investigated organ anlagen, laminin was found mainly in the basal laminae. The role of fibronectin and laminin was investigated further by using synthetic peptides that mimic the main cell binding domain of either fibronectin or laminin, and that competitively inhibit their cell surface receptors. Thus, the pentapeptides GRGDS, YIGSR, and for control, SHLVE were micro-injected under the ectoderm of 2-day-old embryos. After treatment with GRDS, the Wolffian duct and the segmental plate are more compact. The rounded cells exhibit only short processes and narrow intercellular spaces. At the side of injection the duct shows a delay in migration. After treatment with YIGSR the Wolffian duct migrated laterally over the somatopleure. The basal laminae seem to be incomplete. SHLVE had no effect. Our results suggest that fibronectin is a prerequisite for the migration of the Wolffian duct, and that laminin probably plays a role in guiding the duct. The epithelialization during somitogenesis and differentiation of the duct is a more complex process involving also fibronectin and laminin.

Animals↗

PubMed1991

The development of the vascular system in quail embryos: a combination of microvascular corrosion casts and immunohistochemical identification.

Although vascular casts, obtained by injection with methacrylates, are frequently used to investigate the adult vascular system, little data are available for embryonic stages. In this paper we use Mercox in quail embryos in the period of 2 to 7 days after incubation. The microvascular corrosion casts were evaluated in the scanning electron microscope (SEM) with special attention to the development and remodelling of the large arteries and veins. Our results show that the remodelling of the large arteries and veins together with their developing tributary vessels can be visualized from very early embryonic stages onwards. However, complete replication of a developing vascular system depends on diameter and regularity of the lumen. In the stages investigated, the vascular lumen, even of the largest vessels, is still very irregular. Detailed cellular characteristics like nuclear impressions of endothelial cells, as often seen in adult material, were seldom found in the embryos. To examine whether blind-ending sprouts are completely or incompletely replicated in a developing vascular system, additional series of quail embryos were stained immunohistochemically with a monoclonal antibody (MB1) specific for endothelial and hemopoietic cells. It seems that a plexus consisting of endothelial precursors (endothelial cells lacking a lumen) is present in the developing organ before the formation of a lumen and assembly into vessels, which are connected to an adjacent artery or vein. Expansion of the vascular system may in part be due to incorporation of these endothelial precursors in the wall of existing vessels.

Animals↗

PubMed1991

The neural crest as a possible pathogenetic factor in coarctation of the aorta and bicuspid aortic valve.

Patients (n = 109) operated on for coarctation of the aorta were analyzed for occurrence of associated cardiac and noncardiac anomalies. Attention was also paid to the prevalence of cardiac anomalies in the relatives of these patients. Of the patients with coarctation of the aorta, 57 (52%) had a bicuspid aortic valve. Forty-three (39%) of the 109 patients had one or more noncardiac anomalies. In 29 (27%) patients the noncardiac anomaly involved the head/neck structures. Noncardiac anomalies were much more prevalent in patients with coarctation and bicuspid aortic valve, especially anomalies involving the head/neck structures: 44% compared to 8% of patients with a normal aortic valve. Congenital cardiac malformations were present in relatives in the first or second degree of 18% of the patients. Bicuspid aortic valve was more prevalent in patients with an affected relative (75%) than in patients with unaffected relatives (47%). Recent studies showed that the neural crest plays an important role in the development of cardiac and a variety of noncardiac structures. The cardiac structures derived from the neural crest involve the outflow tract of the heart and the aortic arch system. Maldevelopment of neural crest cells could therefore be responsible for the combined occurrence of outflow tract (e.g., bicuspid aortic valve), aortic arch (e.g., coarctation), and noncardiac anomalies. This study supports the concept that some anomalies of the aortic arch system, including aortic coarctation, are cardiovascular manifestations of a spectrum of anomalies involving the head and neck region that may be due to a genetic-environmental disorder of the neural crest.

Aortic Coarctation↗

PubMed1991

Teratogenic effects of transplacental transfusion of heterologous antisera simulated in an experimental model using in vitro whole rat embryo culture.

The effects of the transplacental transfusion of heterologous rabbit-anti-rat antiserum (RAR antiserum) and subsequent immunological interaction on the development of 9-10 days old rat embryos (stages 8-10 somites) were studied using an in vitro whole rat embryo culture. Transplacental transfusion was simulated by the embryonic intracardiac microinjection of approximately 0.5 microliter RAR antiserum, followed by an incubation period of 24 and 48 hours. All the tested embryos survived the incubation period. Embryos taken from the incubator after 24 hours showed signs of growth retardation and axial non-rotation, a delayed closure of the neural tube and ear vesicle, and a delayed formation of the foregut. They also had a moderate number of areas with local pathogenetic cell degeneration. Embryos taken from the incubator after 48 hours demonstrated signs of growth retardation and incomplete axial rotation. The formation of the foregut and closure of the neural tube was complete, with the exception of one embryo with a persisting open neuroporus posterior. All embryos displayed a considerable number of areas with local pathogenetic cell degeneration. The intracardiac injection technique is an elegant method to test the effects of teratogens administered directly into the embryonic circulation. The results demonstrate that heterologous antisera have teratogenic potential, believed to be due to an immunological reaction, with a particular sensitivity of the neurectoderm in 9-10 day old embryos.

Abnormalities, Drug-Induced↗

PubMed1990

Changes in distribution of elastin and elastin receptor during intimal cushion formation in the ductus arteriosus.

Changes in distribution of elastin and elastin receptor were studied during maturation of the ductus arteriosus. In this vessel intimal thickening is a normal process. It starts with separation of endothelial cells from the internal elastic lamina by the formation of a wide subendothelial region, followed by an increase in number of radially orientated cells in the inner media and subendothelial region. For the first time the nature of these originally inner media cells could be definitely determined as being derived from smooth muscle cells. Areas rich in these modified smooth muscle cells contained less elastin as compared with regions rich in circularly orientated smooth muscle cells. The internal elastic lamina had disappeared underneath intimal cushions of the canine ductus arteriosus, whereas in the fetal human ductus arteriosus, splitting of the internal elastic lamina was observed. Elastin was not present underneath separated endothelial cells, which suggests that these cells do not synthesize elastin, at least not after separation. Both smooth muscle cells and endothelial cells demonstrated the presence of the elastin receptor. Changes in its distribution were not observed. The temporal and spatial association between the altering distribution of elastin and the absence of normal cushion formation in the persistent ductus arteriosus suggests a role of the elastin receptor in the process of intimal thickening.

Animals↗

PubMed1990

Vascular endothelial cells migrate centripetally within embryonic arteries.

Migration of vascular endothelial cells was traced in quail-chick chimeras. After heterospecific transplantations of quail limb bud pieces, or other tissues containing blood vessels, into the limbs or the coelomic cavity, the immunohistochemically stained endothelial cells of the quail were found to invade the chick host vessels, favouring the arteries. Within these vessels the endothelial cells regularly reach the host aorta, where they contribute to the endothelium on the ipsilateral side. It is concluded that the endothelial cells activity migrate, because microinjections of a synthetic peptide which contains the RGD-sequence and mimics fibronectin, stop the invasion of endothelial cells.

Animals↗

PubMed1990

The early development of the tunica media in the vascular system of rat embryos.

The use of a monoclonal antibody (HHF-35) against muscle-cell-specific actin has led to new insights into the early development and differentiation of the tunica media of blood vessels. The localization of this substance was studied by light and electron microscopy, in 22 rat embryos ranging between 10 and 15 days post coitum. Actin expression was already seen in the mesoderm around the dorsal aortae at 10 days post coitum, i.e. 1.5 day before circular mesenchymal condensations were detectable by light microscopy. These condensations are usually regarded as the first indication of arterial tunica media formation. The actin expression starts in the dorso-medial mesoderm surrounding the dorsal aortae at the level of the developing pharyngeal arch system, followed at 11.5 days by positive cells in the lateral mesoderm. In 12-day-old embryos most of the mesenchymal cells around the dorsal aortae contain actin, except for those aspects of the dorsal aortae which participate in outgrowing and connecting vessels to specific organs, such as the pharyngeal arch arteries, dorsal intersegmental arteries and aorto-pulmonary plexus, which themselves are still negative. At this stage the vitelline and umbilical arteries, which belong to the early developing ventral segmental arteries, are already surrounded by actin-containing mesenchymal cells. From 13 days onwards the tributary arteries, such as the subclavian and vertebral arteries, start to present the first differentiation of a tunica media in a proximo-distal development. In general the actin-negative areas are involved in vascular remodelling, implying the formation of new vessels, as as well as the disappearance of those previously developed.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗

PubMed1990

The extracellular matrix during neural crest formation and migration in rat embryos.

Changes in the distribution of extracellular matrix components have been investigated immunohistochemically during neural crest development in the rat. Inside the ectodermal epithelium basal lamina components are formed resulting in a separation of neurectoderm and epidermal ectoderm. Within the presumptive neural crest area fibronectin, hyaluronan and chondroitin sulphate become apparent. Upon subsequent neural crest migration the basal lamina becomes disrupted. As the neural crest cells take part in mesectoderm formation, fragments of the basal lamina remain attached to their surface, as is demonstrated with antibodies against laminin and collagen type IV. The extracellular matrix is therefore active both in the separation of neuroectoderm from epidermal ectoderm and in mesectoderm formation.

Animals↗

PubMed1989

The special status of the pulmonary arch artery in the branchial arch system of the rat.

A renewed study of the development of the branchial arch system was essential in view of the special morphologic characteristics of the ductus arteriosus, which derives from the pulmonary arch artery or sixth branchial arch artery. In congenital heart disease certain aorto-pulmonary collateral arteries have a marked histological similarity to the ductus arteriosus. To gain a better insight into the development of these vessels, 27 rat embryos, with the number of somites ranging between 19 and 41, were studied. Most embryos were collected after shortterm in vitro-culture, allowing precise staging of age and development. The vascular system of these embryos was injected with Indian ink, to enable easy recognition of even the smallest endothelium-lined vessels. The embryos were serially sectioned (3-5 microns) and reconstructed using a graphic method. The results show that the pulmonary arch artery differs from the other arch arteries in that it is the most cranial vessel of a system of ventral splanchnic arteries, which connects the pulmonary plexus with the dorsal aortae at an early stage. With the exception of the pulmonary arch artery, these connections are transient. The pulmonary arteries develop from the remaining parts of the plexus. It is argued that these connections can persist in the human as aorto-pulmonary collaterals, in certain cases with abnormalities in the pulmonary part of the cardiac outflow tract.

Animals↗

PubMed1989

Development of the origin of the coronary arteries, a matter of ingrowth or outgrowth?

Inconsistencies still exist with regard to the exact mode of development of proximal coronary arteries and coronary orifices. In this regard 15 quail embryos were investigated using a monoclonal anti-endothelium antibody, enabling a detailed study of the development of endothelium-lined vasculature. Coronary orifices emerged at 7-9 days of incubation (Zacchei stages 24-26) and were invariably present at 10 days of incubation (Zacchei stage 27). We never observed more than 2 coronary orifices; these were always single in either of the facing sinuses of the aorta. A coronary orifice was always observed being connected to an already developed proximal coronary artery, which belonged to a peritruncal ring of coronary arterial vasculature. We did not find any coronary orifice without a connection to a proximal coronary artery. Moreover, at 7-9 days of incubation (Zacchei stages 24-26) we observed coronary arteries from the peritruncal ring penetrating the aortic media. In 2 specimen this coronary artery, with a lumen, was in contact with the still intact endothelial lining of the aorta. We conclude that coronary arteries do not grow out of the aorta, but grow into the aorta from the peritruncal ring of coronary arterial vasculature. This throws new light on normal and abnormal development of proximal coronary arteries and coronary orifices.

Animals↗

PubMed1989

Ultrastructural and immunohistochemical changes of the extracellular matrix during intimal cushion formation in the ductus arteriosus of the dog.

The changes of the intima during subendothelial edema formation were studied by ultrastructural and immunohistochemical methods in the ductus arteriosus (DA) of the dog. Subendothelial edema formation is the first stage in the development of intimal cushions in the DA. Development of intimal cushions is a physiological process preceding normal spontaneous closure after birth. The material consisted of normal canine DA and DA from a strain of dogs with hereditary persistence of the DA (PDA). In the normal DA intimal thickening starts with separation of the endothelial cells from the internal elastic lamina by a widened subendothelial region (SR). Initially this SR is, at the ultrastructural level, composed of granular and amorphous material. Collagen fibrils and elastin are not detected. During the formation of the SR a shedding of the basal lamina underneath the endothelial cells is observed. In the PDA the endothelial cells remain attached to the internal elastic lamina. The topography of the extracellular matrix components collagen type I, III, IV, fibronectin and laminin were studied immunohistochemically. These are important factors in the adherence of the endothelial cells to the underlying intimal layers. Laminin and collagen type I are diffusely present before but absent after detachment of the endothelial cells. Collagen type III, barely detectable before detachment, becomes visible underneath the detached cells. No changes are observed in the distribution of collagen type IV and fibronectin. Comparison of the normal DA with the various types of the PDA strain and controls allowed the conclusion that the observed changes in the extracellular matrix components were confined to those parts of the vessel wall that showed development of intimal thickening. The observed alterations both at the ultrastructural and immunohistochemical level do not explain the initiation of the process of endothelial cell detachment, which have been shown in a previous study to be related to an increase in hyaluronic acid.

Animals↗

PubMed1989

Distribution of prostacyclin synthase, 6-keto-prostaglandin F1 alpha, and 15-hydroxy-prostaglandin dehydrogenase in the normal and persistent ductus arteriosus of the dog.

The presence of prostacyclin synthase (PGI2 synthase), 6-keto-prostaglandin F1 alpha (6k-PGF1 alpha), and the stable hydrolysis product of prostacyclin (PGI2), prostaglandin E2 (PGE2), as well as the activity of 15-hydroxy-prostaglandin dehydrogenase (PGDH) were studied in the aorta, pulmonary artery, the normal ductus arteriosus (DA), and persistent DA (PDA) of the dog using histochemical and immunohistochemical techniques. The normal DA is characterized by the development of intimal thickening, a process that does not occur in the persistent DA. Distribution of PGI2 synthase was identical in the aorta, pulmonary artery, and persistent DA. In these vessels endothelial cells contained higher levels of PGI2 synthase as compared with medial smooth muscle cells. In the normal DA, levels of PGI2 synthase were clearly higher in smooth muscle cells at the sites of intimal thickening than at other sites. Distribution of 6-keto-PGF1 alpha resembled the localization of PGI2 synthase. Presence of PGE2 and activity of PGDH could not be demonstrated. The results demonstrated existence of a clear relationship between ductal morphology and the presence of PGI2 synthase. This finding suggests a more important role for PGI2 in regulating ductal patency than has heretofore been appreciated. It was assumed that the role of PGI2 in regulating ductal patency is, at birth, at least overruled by the constrictive effect of the cytochrome P450 mono-oxygenase mechanism. It is still possible to attribute a role to PGI2 in the regulation of cushion formation. Once smooth muscle cell activity has been enhanced by the presence of a glycosaminoglycan rich environment, increase in PGI2 may produce a concurrent inhibition of smooth muscle cell growth.

6-Ketoprostaglandin F1 alpha↗

PubMed1988

The onset of myotome formation in the chick.

The onset of myotome formation in somites of chick embryos was studied by use of a polyclonal antidesmin antibody and by histochemical demonstration of acetylcholine esterase activity. The myotome cells originate from the dermatome only; sclerotome cells do not contribute to the myotome. The formation of the myotome starts in the craniomedial corner of the dermatome. From there the myotome formation continues simultaneously along the medial and the cranial edge of the dermatome. It was found that only the already longitudinally oriented cells of the cranial dermatome edge give rise to the myotome; the cells of the dorsomedial dermatome edge do not contribute to the myotome. Myotome cells do not originate directly from the surface of the overlying dermatome by delamination.

Acetylcholinesterase↗

PubMed1988

The formation of mesoderm and mesectoderm in 5- to 41-somite rat embryos cultured in vitro, using WGA-Au as a marker.

The formation of mesectodermal cells by the neural crest in 5- to 41-somite stage embryos was investigated experimentally in rat embryos cultured in vitro, using lectin-coated colloidal gold as a probe. This method labelled all ectodermal cells, among them neural crest, surface ectodermal placodal and epiblastic (primitive streak) cells. The neural crest provides the mesodermal compartment of the entire head region with cells, including the primitive cranial ganglia and the branchial arches. In the head region migration of neural crest cells over a great distance (long-distance migration) was not observed. In the trunk region neural crest derived cells were mainly found to form the primitive spinal ganglia and the sympathetic trunk, once again without long-distance cell migration. Structures and tissues that supposedly were derived from the primitive streak were hardly labelled with colloidal gold. Surface ectodermal placodes were not only found at the expected sites (e.g. epibranchial placodes) but also in the ectoderm covering the transverse septum and lateral abdominal walls.

Animals↗

PubMed1988

Maternoembryonic transfusion and congenital malformations: an experimental study using rat embryos.

In an experimental study, using an in vitro whole rat embryo culture, the effects of a maternoembryonic transfusion and immunologic interaction on the development of ten-day-old rat embryos (stages 8 to 10 somites) has been studied. Transplacental transfusion has been simulated by embryonic intracardiac microinjection of 0.1 to 0.5 microL immunologically active rat serum. After an incubation of 24 and 48 hours, respectively, the embryos were killed. All tested embryos have survived the incubation period. On microscopic examination of the tested embryos those that were taken from the incubator after 24 hours showed no signs of pathogenic cell degeneration, while the embryos that were taken from the incubator after 48 hours all had localized lesions with pathogenic cell degeneration in one or multiple major structures. The neurectoderm and endoderm seem to be the most sensitive tissues in this period of organogenesis. The results suggest that immunologic reaction to transplacental transfusion of maternal serum may lead to congenital malformations.

Animals↗

PubMed1988

Hyaluronic acid accumulation and endothelial cell detachment in intimal thickening of the vessel wall. The normal and genetically defective ductus arteriosus.

The closing ductus arteriosus (DA) was studied as a model for the development of intimal thickening of vessel walls using ultrastructural and immunohistochemical techniques. The material consisted of DA from neonatal dogs of three types: normal beagles, DA-defective pups from a line of mixed poodles with a genetic defect in the closure of the DA leading to persistent ductus arteriosus (PDA line), and normal litter-mates of DA-defective pups in the PDA line. The DA of the normal litter-mates of DA-defective pups did not differ from those of normal beagles. In the DA of normal beagles and normal PDA-line pups, closure is preceded by intimal thickening characterized by formation of a widened subendothelial region (SR), detachment of endothelial cells, invagination of endothelial cells, and migration of smooth muscle cells into the SR. It was observed that immediately before and after endothelial cell detachment, there was an increase in hyaluronic acid (HA) in the SR and inner media. In the DA-defective pups, the increase in hyaluronic acid failed to occur and there was no intimal thickening. The SR failed to expand, endothelium remained attached to the internal elastic membrane, and there was no invagination of endothelium or migration of smooth muscle cells. It is hypothesized that the increased synthesis of HA is an important early event leading to intimal thickening in the normal DA and perhaps to abnormal intimal thickening of other vessels. By its hygroscopic properties, HA may be directly involved in the formation of a wide SR, inducing endothelial cell detachment and favoring smooth muscle cell migration. In affected pups of the PDA line, there is a genetically-determined "block" in the normal process of intimal thickening at or before the initiation of increased HA synthesis.

Animals↗