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Biomedical subjects

V Dantzer

Publications and source records attributed to V Dantzer.

At least 73 records · Page 4Linked to original sources
PubMed1991

Aldosterone modulates electrogenic Cl secretion in the colon of the hen (Gallus domesticus).

The regulation of Na and Cl transport in hen colon by mineralocorticoids was investigated with isolated epithelia in vitro by histological and electrophysiological techniques. The electrogenic transport of Na and Cl was measured in Ussing chambers by the short-circuit current technique and was identified by the specific inhibitors amiloride and bumetanide or by the secretagogue theophylline. Hens were maintained either on low (LS)- or on high-NaCl diets (HS), and the plasma aldosterone (PA) levels of these groups were measured with radioimmunoassay. A group of HS hens received injections of aldosterone at a 6-h schedule before experiments. A group of LS hens was resalinated, and experiments were carried out at a 24-h interval for up to 3 days after resalination. The LS diet stimulated PA levels ninefold, compared with HS hens. Na transport was modulated by the hormonal stimulus in a way that the apical Na entry switched from an electrogenic Na-amino acid-hexose cotransport system completely to an amiloride-sensitive Na channel. Electrogenic Cl secretion was induced by theophylline and was inhibited by bumetanide. NaCl deprivation, resalination or aldosterone injection modulated electrogenic Cl secretion in parallel between 7 (HS) and 14.4 mu eq.cm-2.h-1 (LS), with pronounced alteration in tissue conductance. These findings reveal a new action of aldosterone that, besides stimulating Na absorption, also directly or indirectly modulates Cl secretion.

Aldosterone↗
PubMed1990

Gestational profile of the stimulatory effects of porcine amniotic and allantoic fluids on prostaglandin G/H synthase activity.

The effects of porcine fetal fluids (amniotic and allantoic) on microsomal prostaglandin G/H synthase (PGHS) activity were assessed. Both amniotic and allantoic fluids obtained from late-gestation sows stimulated PGHS activity (as indicated by increased formation of radiolabelled prostaglandin) in a dose-dependent manner. At the maximum dose tested, amniotic and allantoic fluids stimulated prostaglandin (PG) formation by 55.5 +/- 1.5 and 58.5 +/- 4.7%, respectively (n = 3, P less than 0.01). Based upon ED50 values, amniotic fluid was approximately threefold more effective than allantoic fluid in stimulating PG formation. The stimulatory effect of amniotic but not allantoic fluid increased significantly (P less than 0.01) during gestation (Days 47-112). The observed changes in the stimulatory effect of amniotic fluid on microsomal PG formation parallels the in vivo changes that occur in intra-uterine PG synthesis. Amniotic fluid stimulatory activity may contribute to this gestational increase in PG synthesis.

Allantois↗
PubMed1990

A sampling scheme intended for tandem measurements of sodium transport and microvillous surface area in the coprodaeal epithelium of hens on high- and low-salt diets.

A tissue sampling protocol for combined morphometric and physiological studies on the mucosa of the avian coprodaeum is presented. The morphometric goal is to estimate the surface area due to microvilli at the epithelial cell apex and the proposed scheme is illustrated using material from three White Plymouth Rock hens. The scheme is designed to satisfy sampling requirements for the unbiased estimation of surface areas by vertical sectioning coupled with cycloid test lines and it incorporates a number of useful internal checks. It relies on multi-level sampling with four levels of stereological estimation. At Level I, macroscopic estimates of coprodaeal volume are obtained. Light microscopy is employed at Level II to calculate epithelial volume density. Levels III and IV require low and high power electron microscopy to estimate the surface density of the epithelial apical border and the amplification factor due to microvilli. Worked examples of the calculation steps are provided.

Animals↗
PubMed1990

Comparative morphometry of the mammalian brain: estimates of cerebral volumes and cortical surface areas obtained from macroscopic slices.

Stereological methods for obtaining unbiased estimates of brain volumes and surface areas are illustrated on fixed brains (cerebrum only) from mammals varying in body weight between 2 kg (cat) and 550 kg (ox). Brain sampling was designed so that Cavalieri estimates of volumes (derived via point counting) could be combined with vertical sectioning estimates of surface areas (via intersection counting). Total volumes, cortical volumes and cortical surface areas were calculated. Each cerebral hemisphere was cut into 3 slabs. Each slab was cut further into macroscopic, parallel vertical slices having a uniform random start position. The term vertical as used here signifies orthogonal to the medial aspect of the hemisphere. The direction of vertical slices also had a random start but was varied systematically across the slabs. Test lattices bearing test points and cycloid test lines were superimposed on vertical slices. Fixed volumes and surfaces were corrected for shrinkage effects. A worked example of the calculation sequence is provided. The experimental design was flexible. Brains of different sizes could be analysed by simply altering the distance between slices and the size of the test lattice. Analyses took 30-45 minutes per hemisphere. Whilst volumes and surfaces increased with body weight, specific values declined. Thus, specific surfaces for the cortex fell from 25 cm2/kg (cat) to 2 cm2/kg or less (pig and ox).

Animals↗
PubMed1989

Ultrastructural differences between the two major components of chicken ceca.

The central parts of basis and corpus ceci from White Plymouth Rock hens on different salt regimen were investigated by light, scanning electron, and transmission electron microscopy. The mucosal surface varies from long broad, flat villi in basis to blunt rugae in corpus ceci. In the epithelium of basis ceci there are many goblet cells, whereas in corpus ceci they are few in number and predominantly located in the crypts and sides of rugae. The microvilli of basis ceci are longer than those of corpus ceci. The epithelium from corpus ceci contains apically located cytoplasmic inclusions of microtubular-like aggregations. The size and amount of these inclusions decrease towards the crypt openings, and none were observed in crypt epithelium. The mitochondria in the epithelium from basis ceci are seen close to the apical plasma membrane, but in corpus ceci they first appear deeper in the cytoplasm below the apical vesicles, microtubular-like aggregations, and lysosomes. The size and content of the apical vesicles varies between the two compartments, as do deposits of lipoglycoproteins in the intercellular space and vesicles of the lateral plasma membrane. Several differences were thus revealed between the epithelia from basis and corpus ceci, giving morphological evidence for different functions between the two compartments. There were no effects of the two salt diets on the development of microvilli, whereas some cytological differences, such as the degree of microtubular-like aggregations, were seen in corpus ceci.

Animals↗
PubMed1989

Gestational profile of prostaglandin E2 synthesis by porcine placenta and fetal membranes.

The capacity of the diffuse, epitheliochorial porcine placenta (chorioamnion plus endometrium: AMCE and chorioallantois plus endometrium: ALCE) and allantoamnion (ATA), obtained from sows at 47-112 days of gestation (n = 12), to release PGE2, during in vitro explant incubation, was determined. There was no significant difference between PGE2 release from AMCE and ALCE, and the data obtained from these two tissues were pooled. The release of PGE2 from ATA was, at all stages of gestation, significantly less (8-50 fold; p less than 0.01, n = 12) than that released from AMCE/ALCE. During gestation, the basal release of PGE2 from AMCE/ALCE increased from 13.7 +/- 2.8 pmol/100 mg per incubation (n = 8; mean +/- S.E.M.) at less than 80 days to a maximum of 176.5 +/- 30.9 pmol PGE2/100mg per incubation (n = 10) at greater than 109 days of gestation. Basal PGE2 release from ATA increased from 1.6 +/- 0.6 pmol PGE2/100 mg per incubation (n = 3) at less than 80 days to 3.5 +/- 0.5 pmol PGE2/100 mg per incubation at greater than 109 days gestation. At all stages of gestation and in all tissues, the addition of sodium arachidonate significantly stimulated PGE2 release, indicating that during gestation prostaglandin synthesis by porcine placenta and fetal membranes is, at least partly, substrate limited. The observed increase in the release of prostaglandin E2 from placenta and fetal membranes that occurred from 90 days of gestation and rapidly increased at term may reflect an increase in substrate availability, an increase in the activity of prostaglandin endoperoxide H synthase- E isomerase or a combination of these processes.

Animals↗
PubMed1988

Structural and functional aspects of porcine placental microvasculature.

The microvascular architecture of the pig placenta was studied by serial semithin histological sections for light microscopy, which were compared with scanning electron microscopy of artificially exposed materno-fetal contact surfaces as well as of vessel casts prepared from the maternal, fetal, and combined maternal and fetal sides. The superficial reliefs from the exposed surfaces as well as from the casts are almost identical with the complementary maternal and fetal sides. In order to meet the physiological needs of materno-fetal exchange for the rapidly growing fetuses, these reliefs develop from a simple to a more complex system during pregnancy and can be described as follows: (1) The degree of interlocking increases between the fetal ridges or bulbous protrusions and maternal ridges of different orders separated by maternal troughs of variable depth, most clearly seen on vessel casts. It creates a three-dimensional notch-arrangement, giving strength to the materno-fetal contact area. (2) The structure of precapillary vessels as well as of the meshwork, and the diameter of capillaries of the maternal and fetal sides, adapt during gestation giving a good distribution of oxygenated blood into the maternal capillaries; these, with the development of large prevenous connecting capillaries on the fetal side, favour a high arterio-venous difference of fetal blood O2 pressure. (3) The vascular architecture of endometrial and fetal ridges and troughs develop into a crosscurrent to countercurrent materno-fetal blood interrelationship. Our demonstration of the materno-fetal capillary inter-relationship in the porcine placenta thus shows that the latter is a much more efficient organ for exchange than hitherto assumed.

Animals↗
PubMed1988

A low-salt diet facilitates Cl secretion in hen lower intestine.

The regulation of sodium and chloride transport in hen coprodeum by mineralocorticoids was investigated with isolated epithelia under short-circuit conditions. Unidirectional fluxes of Na and Cl were measured by isotopes and modulated by amiloride, theophylline and bumetanide. Hens were maintained either on low-NaCl diet (LS) or on high-NaCl diet (HS). Plasma aldosterone (PA) levels of these groups were measured with radioimmunoassay. A group of HS hens received injections of aldosterone on a 6-hr schedule before experiments. Another group of LS hens was resalinated, and experiments carried out on a 24-hr interval. Salt deprivation stimulated PA levels ninefold, compared to HS hens. Na absorption was stimulated according to previous reports. Electrogenic Cl secretion was elicited by theophylline and partially inhibited by bumetanide. Modulation of PA levels by diet, resalination or aldosterone injection changed the magnitude of electrogenic Cl secretion in parallel between 0.5 mueq/cm2.hr (HS) and 4 mueq/cm2.hr (LS), with pronounced alteration in tissue resistance. The results demonstrate a new action of aldosterone which besides stimulating Na absorption also directly or indirectly elicits Cl secretion. Evidence is presented for a hormonal adaptation of chloride transport in this epithelium. There was a morphological change of the apical plasma membrane and further experiments will have to clarify the exact cellular nature of this process.

Aldosterone↗
PubMed1985

Electron microscopy of the initial stages of placentation in the pig.

To elucidate the morphology of the initial stages of epitheliochorial placentation in the pig, material from 10 sows of the Danish Landrace and from one Göttinger minipig gilt from day 13 to day 26 of gestation was processed for scanning and transmission electron microscopy. The observed foetomaternal interaction from day 19 1/2 minipig placenta corresponded well to the observations on the Danish Landrace placenta. From the results and the discussion it was concluded that the following structures were implicated in the initial phases of placentation in the pig: Protruding epithelial proliferations of the uterine epithelium enclosed by chorionic caps serving to immobilize the blastocyst (days 13 and 14). A thick glycocalyx on the maternal and a thin one on the foetal epithelium before contact. Close apposition between the apical plasma membranes from trophoblastic and uterine epithelium (day 14). Development of interdigitating microvilli (days 15-16). Formation of apical domes on the uterine epithelium closely related to the trophoblast provided with long cytoplasmic extensions into a luminal space between the apical domes, apparently representing a transition from histiotropic to haemotrophic nutrition (days 15-20). Placentation, development of interdigitating microvilli between foetal and maternal epithelium, was extended but not terminated in the peripheral zone at day 26.

Animals↗
PubMed1984

Scanning electron microscopy of exposed surfaces of the porcine placenta.

The three-dimensional development of the separated parts of the porcine placenta from 9 Danish Landrace sows at gestational stages from 20 to 100 days was studied. After cautious separation of the allantochorion and the endometrium in a 1 mM buffered ethylenediaminetetraacetic acid solution, the separated parts were processed for scanning electron microscopy by routine methods. The macroscopic enlargement resulted from primary and secondary circular folds or plicae, which were permanent on the maternal side, whereas they were mainly non-permanent on the fetal side. The areolar placenta and interareolar placenta with formation of permanent microscopic folding on both sides were described. The observations of the separated parts yielded new information on the development of surface enlargement during gestation and revealed a hitherto unknown regular architecture of the endometrium by the formation of parallel primary ridges or rugae with secondary ridges or rugae at their sides subdividing the maternal troughs or fossae. This configuration on the maternal side explains the transformation of the regular chorionic ridges from the 63-day stage into bulbous protrusions at the 100-day stage. Based on these observations the precise terminology used above was proposed.

Animals↗
PubMed1984

Intracellular pathways of native iron in the maternal part of the porcine placenta.

In the diffuse epitheliochorial porcine placenta iron is secreted as uteroferrin by the maternal epithelium of the areola-gland subunit of the placenta. To elucidate the intracellular pathways of physiological iron in uterine gland epithelium material from 10 sows at 15 to 111 days of gestation was processed for electron microscopy by different routine methods with or without postfixation in osmium tetroxide. Ferritin particles were identified by their size and shape and the content of iron was confirmed by X-ray energy dispersive microanalysis of accumulated ferritin particles. Distinct ferritin particles were not observed in the extracellular space either basal to or luminal to the epithelial cells. Intracellular ferritin was observed apparently free in the cytoplasm, but in variable amounts. Transfer tubules and dense bodies were located basally in the secretory cells. Both of these organelles contained ferritin particles, showed reaction sites for acid phosphatase and were stained by periodic acid-thiocarbohydrazide-silver proteinate. The ciliated cells differed by having apically located dense bodies containing numerous ferritin particles. Our finding of native ferritin in cells with hormonally regulated iron transport supports the concept that transfer tubules as part of the lysosomal complex are part of the endocytic pathway in secretory cells and indicate that ferritin here is an intracellular transport or storage intermediate.

Animals↗
PubMed1982

Gap junction pleiomorphism in the root system of the rhizocephalans (Arthropoda: Crustacea).

We have studied gap junctions in the root system of four different species of rhizocephalans (Arthropoda: Crustacea) using freeze-fracture. Numerous and often very extensive gap junctions are present between the root cells. They are of the characteristic E-type also found in other arthropods. Large junctional particles (ca. 13 nm) are located predominantly on the E-face, while complementary pits and a few dislocated particles are present on the P-face. The gap junctions show a remarkable pleiomorphism. Small macular gap junctions with rather densely packed particles, larger irregularly shaped gap junctions, often forming bands with intervening particle-free membrane domains, and gap junctions with widely dispersed particles are observed. These features are documented both in material after conventional preparation including glutaraldehyde fixation and glycerol cryoprotection and in material frozen directly in a nitrogen slush without any preceding preparation, and are discussed in relation to possible functional significance.

Animals↗
PubMedDate not supplied

Localisation of glycans in the placenta: a comparative study of epitheliochorial, endotheliochorial, and haemomonochorial placentation.

Specimens of mid-term (horse), near-term (pig, cow, sheep, mink) and term (human) placentae and associated tissues have been examined with a panel of 15 biotinylated lectins combined with an avidin-peroxidase revealing system. The aim of this study has been to analyse the expression of glycans at the materno-fetal interface in order to establish whether the morphological diversity exhibited by these six species is reflected by accompanying biochemical diversity, or whether similar types of glycan are expressed in tissues performing similar functions. Lectin staining intensity was scored in the following elements of the interhaemal placental barrier: maternal capillaries, maternal uterine epithelium, the materno-fetal interdigitating microvillous membrane (brush border in the human), trophoblast, and fetal capillaries. A high degree of biochemical diversity was found in the glycan expression of the various placental components within and among placental types. Each layer showed widely differing patterns of lectin binding between species, with only a few findings in common: 1) the relative lack of simple fucosyl termini, 2) the presence of non-bisected bi/tri-antennary N-glycan in most layers, 3) an abundance of terminal N-acetyl galactosamine, and 4) the restriction of high mannose glycans to intracellular granules. This diversity may be a mechanism to avoid hybridisation, although glycan patterns may change between conception and placental development, or it may have evolved as a consequence of morphological changes. It is possible that it may also be part of the cause, rather than the result, of the structural diversity that is so characteristic of mammalian placentation.

Animals↗
PubMedDate not supplied

Carbonic anhydrase activity in different placenta types: a comparative study of pig, horse, cow, mink, rat, and human.

The placenta has multiple functions, being the organ which provides oxygen and nutrients to the developing conceptus. In the placenta, the enzyme carbonic anhydrase (CA) may provide ions for exchange with Na+, K+, and Cl- in transepithelial movement of ions and fluid, as well as facilitating carbon dioxide diffusion. It can also be active in intermediary metabolism, such as gluconeogenesis, urea, and fatty acid synthesis. Placental material from pig, horse, cow, mink, rat, and human was therefore investigated, representing placenta types with variations in shape, internal architecture, and nature of the interhemal barrier. After glutaraldehyde fixation, sections were stained by a histochemical CA-method demonstrating all active isozymes. The most striking feature in common was a positive reaction in the maternal capillaries, when present, as in pig, horse, cow, and mink. In the maternal epithelium, the activation of CA was only observed in the pig, which also exhibited the strongest activity at the maternal interface, which reacted moderately in rat, weakly in horse, and was not visible in cow and human. The trophoblast was positive in pig and rat, whereas it was negative in horse, cow, human, and mink placentae except for few scattered trophoblast cells in pig, horse, and cow, which showed very intense activity. In the fetal capillaries, a positive reactivity was only observed in mink and human. The utilization of CA in placental transfer and metabolism is thus highest in the pig, rat, and mink, compared with horse, cow, and human. It can therefore be concluded that the activation and localization of CA in the placental interhemal barrier varies considerably among species.

Animals↗
PubMedDate not supplied

Vascular interrelationships of near-term mink placenta: light microscopy combined with scanning electron microscopy of corrosion casts.

The microvasculature of the near-term zonary placenta of the mink has been studied using light microscopy and scanning electron microscopy of corrosion casts, prepared from maternal and fetal vessel systems, respectively. The zonary area, most important for placental exchange, includes a characteristic labyrinth. The labyrinth is composed of lobules oriented in a maternal-fetal direction. One maternal stem artery serves as the central axis of a lobule, and about six pairs of fetal stem arteries and stem veins of the chorionic primary villi mark the periphery of the lobule. Viewed from the fetal side of the labyrinth, this lobular structure presents a roughly hexagonal pattern, with the central maternal stem artery and radially oriented arteriolar branches giving the lobule the shape of a star. These arterioles frequently form bridges to neighboring lobular systems; however, the majority continue into the feto-maternally oriented three-dimensional network of maternal capillary sinusoids, which converge on the outlets of the maternal stem veins on the maternal side of the labyrinth. Maternal main crypts are delimited by the rays of the star-shaped lobules containing chorionic primary villi. The latter penetrate into maternal crypts from the fetal side, and are characterized by their axial arterial and venous stem vessels. Fetal secondary villi are arranged at different levels from these stem vessels. The secondary villi are characterized by arterioles and venules branching in pairs from the stem vessels and supply the tributary capillary complexes of terminal villi. The lobular structure of the placental labyrinth provides a three-dimensional framework of vessels where maternal capillary sinusoids and fetal capillaries meet in a one-way cross-current arrangement. The blood flow conditions and the peculiarities of the mink placenta interhemal membrane are compared to those of other carnivores and discussed with respect to the efficiency of the endotheliochorial placenta.

Animals↗