Studies on the mode of action of excess of vitamin A. 1. Effect of excess of vitamin A on the metabolism and composition of embryonic chick-limb cartilage grown in organ culture

Biochemical and Immunological Effects of Listeria monocytogenes Hemolysin

The biochemical and immunological effects of Listeria monocytogenes hemolysin in CD-1 mice were studied. Intraperitoneal injection of 256 complete hemolytic units (CHU) caused a twofold increase in plasma beta-glucuronidase levels but was not lethal. In contrast, 256 or more CHU caused 100% lethality in 4 to 5 min when administered intravenously. Intravenous administration of 50 CHU caused a 10- to 11-fold increase in plasma beta-glucuronidase levels and was lethal for a variable percentage of the animals. Carbon clearance experiments showed the phagocytic index to be depressed by relatively small amounts of intravenously administered hemolysin and suggested that hemolysin may function as a leucocidal agressin during listeric infection. Increased plasma levels of ornithine carbamyltransferase after intravenous injection of hemolysin indicated hepatocellular damage. Liver carbohydrate and blood glucose determinations on fasted mice showed a reduced gluconeogenic capability in hemolysin-treated animals. Mice immunized with purified hemolysin or live vaccine were more resistant to several of the toxic parameters studied. The data indicate that hemolysin is produced during listeric infection and is antigenic, but not necessarily a protective immunogen.

CHANGES IN CONNECTIVE TISSUE AND INTESTINE CAUSED BY VITAMIN A IN AMPHIBIA, AND THEIR ACCELERATION BY HYDROCORTISONE

In view of the theory that an excess of vitamin A causes release of cathepsins from intracellular lysosomes, hypervitaminosis A was induced orally in the larvae of Xenopus laevis. It was predicted that the tails of these amphibia would undergo resorption prior to metamorphosis, since the presence of abundant lysosomes, associated with measurable increases of catheptic activity, had previously been demonstrated in the resorbing tails of amphibia during metamorphosis. This prediction was confirmed; after 3 to 4 weeks of hypervitaminosis A, the tails of treated animals underwent partial resorption. Other transitory appendages, the rostral tentacles, collapsed after 2 weeks of treatment with an excess of vitamin A, an effect analogous to the collapse of rabbits' ears after intravenous papain. These effects were related to the loss of metachromatic extracellular material in these appendages. Excess of vitamin A caused kyphoscoliosis and prognathos in the larvae. The hypervitaminotic larvae always developed a mucinous diarrhea, which was associated with a remarkable overgrowth of metachromatic goblet cells of the intestine. The entire intestine of the treated animals was more advanced in development than that of control larvae at equivalent stages. All the effects of hypervitaminosis A were accelerated by the simultaneous administration of hydrocortisone. This was held to be due to liberation of vitamin A from hepatic stores by the steroid, and is in contrast to the retardation of hypervitaminosis A by hydrocortisone in vitro.

The classic : a morphogenetic matrix for differentiation of cartilage in tissue culture

This Classic Article is a reprint of the original work by Hiroshi Nogami and Marshall R. Urist, A Morphogenetic Matrix for Differentiation of Cartilage in Tissue Culture. An accompanying biographical sketch of Marshall R. Urist, MD is available at DOI 10.1007/s11999-009-1067-4; a second Classic Article is available at DOI10.1007/s11999-009-1068-3; and a third Classic Article is available at DOI 10.1007/s11999-009-1070-9. The Classic Article is copyright 1970 by the Society for Experimental Biology and Medicine and is reprinted with permission from Nogami H, Urist MR. A morphogenetic matrix for differentiation of cartilage in tissue culture. Proc Soc Exp Biol Med. 1970;134;530-535.

Tin mesoporphyrin in conjunction with retinoic acid reverses the retinoic acid induced enhancement of phospholipase A(2) activity in vivo in rats

Retinol (Vitamin A) is known to destabilize membranes. The effect of one of its natural derivatives, Retinoic Acid, was therefore studied on membrane stability, by inversely correlating this stability with Phospholipase A(2) activity. Lipid metalloporphyrin interactions have been the object of intense research in recent times. Our results revealed that the administration of Retinoic Acid (50,000 I.U.) caused a tremendous induction of hepatic Phospholipase A(2) activity in Wistar rats. However when Retinoic Acid and Tin-mesoporphyrin (50 micromol/kgbw) were co-administered, hepatic Phospholipase A(2) activity was inhibited. This result clearly reveals a possible therapeutic application of this metalloporphyrin in alleviating membrane destabilization, connected with Retinoic acid administration.

Effects of long-term exposure to glucosamine and mannosamine on aggrecan degradation in articular cartilage

OBJECTIVE

To investigate the effect of long-term exposure to glucosamine or mannosamine on the catabolism of aggrecan by explant cultures of bovine articular cartilage maintained in the presence of retinoic acid.

DESIGN

The kinetics of loss of 35S-labeled and total aggrecan from explant cultures of bovine articular cartilage maintained in the presence of 1 micro M retinoic acid and exposed to varying concentrations of glucosamine or mannosamine was investigated over a 9-day culture period. In other experiments, the reversibility of the inhibition of aggrecan catabolism by glucosamine or mannosamine was investigated in cultures exposed to these amino sugars for the first 5 days of a 15-day culture period. The metabolism of chondrocytes exposed to these amino sugars was evaluated by measurement of lactate production or 3H-serine and 35S-sulfate incorporation into protein and glycosaminoglycans, respectively. The direct effect of these amino sugars on soluble aggrecanase activity was determined from immunoblots of aggrecan digests.

RESULTS

Glucosamine at 5mM concentration and mannosamine at 2mM concentration inhibited degradation of radiolabeled and chemical levels of aggrecan. At concentrations of up to 10mM amino sugars, the metabolism of chondrocytes was not impaired, as determined by lactate production, protein synthesis and the incorporation of 35S-sulfate into proteoglycans. These amino sugars did not inhibit soluble aggrecanase activity. The exposure of articular cartilage explants to 5mM glucosamine or mannosamine for 5 days in culture in the presence or absence of retinoic acid did not provide long-term suppression of stimulated aggrecan loss.

CONCLUSIONS

This study indicates that continuous presence of amino sugars is required to protect cartilage from stimulated loss of aggrecan.

Lens regeneration in mice under the influence of vitamin A

The effect of vitamin A has been studied on lens regeneration in young (7 days old) as well as adult mice. A longitudinal slit was made under local anesthesia in the cornea over the lens. The lens was extracted intact through the incision. Intraperitonial injection of vitamin A (0.05 ml of 30 IU/ml in young and 0.05 ml of 50 IU/ml in adult) was given to the operated animals. Vitamin A was found to induce lens regeneration in not only young but also in adult mice. Regenerated lenses were similar in shape, size, transparency and histological features to normal intact lenses.

The effect of hydrocortisone on the response of fetal rat skin in culture to ultraviolet irradiation

1. The effect of hydrocortisone on the development of fetal rat skin in organ culture, and on its repair after exposure to a mixed beam from a mercury lamp, are described. 2. The addition of hydrocortisone (7.5 µg/ml) to the culture medium (HC medium) caused accelerated differentiation and keratinisation of the epidermis followed by atrophic changes as in vivo. 3. Explants were grown for 2 days in either normal or HC medium and then irradiated with light from an Hanovia lamp. 4. Irradiation of the control explants produced severe necrosis in both epidermis and dermis and much disorganisation of the dermal intercellular material; 2 days after exposure the s. corneum with adherent cellular debris had become either completely detached from the denuded dermis, or raised to form a fluid-filled blister. Epidermal regeneration had begun by the 4th day after irradiation and was usually complete by the 6th day. 5. Hydrocortisone modified the response to irradiation as follows: (1) reduced and retarded cellular breakdown, (2) prevented vesication, (3) preserved the organisation of the dermal intercellular material, (4) hastened epithelialisation, (5) accelerated the differentiation of the new epidermis. Effects (2), (3), and (4) were probably secondary to (1). 6. Experiments with various light filters showed that the effective wavelengths for producing lesions in the skin explants were those below 3000 A. 7. It is suggested that the beneficial effect of hydrocortisone on the repair of irradiated skin explants might be due, at least in part, to a reduced proteolytic activity in the damaged tissue through a stabilising action of the hormone on the lysosomes. 8. The relationship of these findings to clinical observations is discussed.

The influence of hydrocortisone on the action of excess vitamin A on limb bone rudiments in culture

The effect of hydrocortisone has been studied in organ cultures of the cartilaginous long bone rudiments from 7-day chick embryos and of the well ossified limb bones from late fetal mice. In the chick rudiments, which grow rapidly in culture, the growth rate was much reduced by hydrocortisone, less intercellular material was formed, and the hypertrophic cells of the shaft were much smaller than in the controls in normal medium. In the late fetal mouse bones, which grow very little in culture, hydrocortisone had no obvious effect on growth but arrested resorption of the cartilage. These effects resemble those described by others in the skeleton of animals treated with cortisone or hydrocortisone. The influence of hydrocortisone on the response of the chick and mouse explants to excess vitamin A was investigated. In the presence of excess vitamin A, cartilage (chick, mouse) and bone (mouse) rapidly disintegrated, but when hydrocortisone also was added to the medium, this dissolution of the intercellular material was much retarded, though not suppressed. The retardative action of hydrocortisone on the changes produced by excess vitamin A in skeletal tissue in culture, contrasts sharply with the strongly additive effect of the two agents on the skeleton in the intact animal (Selye, 1958). It is suggested that this discrepancy between the results obtained in vitro and in vivo is probably due to systemic factors that operate in the body but are eliminated in organ cultures.

A serine proteinase inactivator inhibits chondrocyte-mediated cartilage proteoglycan breakdown occurring in response to proinflammatory cytokines

The role played by serine proteinases with trypsin-like specificity in chondrocyte-mediated cartilage proteoglycan breakdown was investigated by use of a selective proteinase inactivator, 7-amino-4-chloro-3-(-3-isothiureidopropoxy)isocoumarin, in explant culture systems. This compound was a rapid inactivator of urokinase-type plasminogen activator. It potently inhibited interleukin 1- and tumor necrosis factor-stimulated proteoglycan release from both nasal and articular cartilage. Its less potent inhibition of basal and retinoic acid-stimulated release appeared to be due to cytotoxic effects. The functional half-life of the inactivator in culture medium was 95 min, and its concentration in cartilage was 2.5-fold higher than in the surrounding medium. Following spontaneous hydrolysis the breakdown products of the inactivator were unable to inhibit proteoglycan release. Trypsin-like activity was demonstrated by enzyme histochemistry to be chondrocyte-associated and inhibited by the serine proteinase inactivator. Cell-associated and secreted plasminogen activator activity was detected by zymography. These results suggest the involvement of a serine proteinase(s) with trypsin-like specificity, possibly urokinase-type plasminogen activator, in chondrocyte-mediated cartilage proteoglycan breakdown occurring as a result of stimulation with proinflammatory cytokines. Basal proteoglycan breakdown may occur via a different pathway. Our findings point to a pathological role for serine proteinase(s) in the development of cartilage diseases such as arthritis, possibly in a cascade which results in the activation of the enzyme(s) directly responsible for proteoglycan breakdown. It remains to be shown whether the target serine proteinase is urokinase-type plasminogen activator.

Proteoglycan breakdown from bovine nasal cartilage is increased, and from articular cartilage is decreased, by extracellular ATP

The addition of ATP, but not ADP or AMP, to the culture media of bovine nasal cartilage explants caused an acceleration in the rate of proteoglycan loss from the tissue. The ATP-stimulated loss of proteoglycan was not inhibited by the IL1-receptor antagonist protein, but was partially inhibited by the presence of ADP or AMP. The proteolytic events resulting from the presence of ATP were found to be similar to those following treatment with IL1, in that inhibitors of the cysteine-peptidase cathepsin B, serine-proteinases with trypsin-like specificity, and of some of the matrixins, could all prevent proteoglycan loss, which was mediated, at least in part, by the action of 'aggrecanase'. In contrast to its effects on nasal cartilage, ATP inhibited basal and stimulated proteoglycan release from articular cartilage. Both ADP and AMP had no effect on proteoglycan release in articular cartilage but enhanced the response to ATP when added concurrently. We conclude that extracellular ATP, probably acting via P2-purinoceptors, stimulates proteoglycan breakdown from bovine nasal cartilage and thus, may have a role in diseases which primarily involve destruction of non-articular cartilage. Extracellular ATP has, in contrast, a chondroprotective effect on bovine articular cartilage.

THE EFFECT OF ANTISERUM, ALONE AND WITH HYDROCORTISONE, ON FOETAL MOUSE BONES IN CULTURE

1. The effects of normal rabbit serum and of rabbit antiserum to whole foetal mouse tissues, on the isolated limb bones of late foetal mice were studied in organ culture, and the influence of hydrocortisone on these effects was investigated. 2. Unheated normal serum caused slight loss of metachromatic material from the cartilage matrix, and some resorption of both cartilage and bone. 3. In unheated antiserum to foetal mouse tissues, the terminal cartilage was smaller and less metachromatic than in paired controls in normal serum, while osteoclasis was so intense that in many explants the bone had almost disappeared. The amount of necrosis varied with different batches of antiserum. 4. The changes produced by normal serum and antiserum could be largely prevented by heating the sera to 57 degrees C for 45 minutes. 5. The effects could also be inhibited by the addition of hydrocortisone to the unheated sera; as little as 0.1 microg hydrocortisone per ml of medium had a well marked protective action. 6. It is suggested that (a) unheated antiserum causes a release of lysosomal enzymes with consequent breakdown of intercellular material, (b) this release is due to an indirect action on the lysosome via an increased permeability of the cell membrane, (c) hydrocortisone does not affect the antigen-antibody reaction, but inhibits the autolytic changes that normally follow this reaction, possibly by stabilising both the lysosomal and cell membranes.

ALTERATIONS IN THE LIPIDS OF BONE CAUSED BY HYPERVITAMINOSIS A AND D

1. The total lipid, phospholipid, total and free fatty acid, free and esterified cholesterol contents of the long bones of normal, hypervitaminotic A, D and A plus D rats were determined. 2. Toxic amounts of vitamin A decreased the total fatty content, whereas toxic amounts of vitamin D increased triglycerides, esterified cholesterol and in particular the phospholipids of bone. 3. An interaction occurred between toxic amounts of vitamins A and D, which prevented, to a large extent, the alterations in bone lipids that occur in hypervitaminosis D. 4. The studies suggest an involvement of vitamin D in lipid metabolism and tend to support the idea that lipids are involved in ossification.

STUDIES ON LYSOSOMES. III. THE EFFECTS OF STREPTOLYSINS O AND S ON THE RELEASE OF ACID HYDROLASES FROM A GRANULAR FRACTION OF RABBIT LIVER

Streptolysins O and S from hemolytic streptococci have been added to granular fractions of tissue homogenates in 0.25 M sucrose prepared from rabbit liver, heart, spleen and lymph nodes. At concentrations ranging from 0.65 microg/ml to 2.0 mg/ml of streptolysin S, and from 10 microg/ml to 1.0 mg/ml of streptolysin O, two lysosomal enzymes (beta glucuronidase and acid phosphatase) and, to a lesser degree, one mitochondrial enzyme (malic dehydrogenase) were released into the supernatants of the reaction mixture. Although the hemolytic action of each lysin paralleled the effect on lysosomes, at equivalent levels of hemolytic activity, SLS was approximately 10 times more active on lysosomes than SLO. SLO was inhibited by cholesterol, cortisol, and specific antibody in vitro; pretreatment of animals with cortisone decreased the susceptibility of their isolated lysosomes to SLO. These agents failed to prevent SLS action on lysosomes. SLO had a pH optimum of 6.5 against lysosomes while SLS was maximally active at 7.5. No other streptococcal extracellular products were as active on lysosomes as the streptolysins, although activated streptococcal proteinase precursor released some hydrolases from the granules. Similarities between the actions of SLO and SLS on red cells and lysosomes suggested that the membranes bounding lysosomes and erythrocytes have common properties.

Hypervitaminosis A as a complication of treatment for neuroblastoma

A case of hypervitaminosis A (HVA) as a complication of therapy for stage-IV neuroblastoma is presented. The patient was randomized to a trial of 13-cis -retinoic acid (a vitamin A-related compound) after completing routine chemotherapy. This acid was given as a means of maturing potential minimal residual disease. A routine follow-up bone scan revealed areas of increased activity, initially along the midshaft of the right ulna and subsequently bilaterally, which were ultimately found to be due to HVA. Hypervitaminosis A has not been previously reported in this setting, and awareness of the condition is important in centers where this treatment is contemplated.

Effect of retinoic acid in combination with platelet-derived growth factor-BB or transforming growth factor-beta on tissue inhibitor of metalloproteinases and collagenase secretion from human skin and synovial fibroblasts

This report shows for the first time that platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-beta (TGF-beta) can interact in a synergistic manner with retinoic acid to stimulate the production of tissue inhibitor of metalloproteinases (TIMP) from human skin and synovial fibroblasts. When cells are treated with 1, 10, and 100 ng/ml of either of these growth factors in combination with 10(-5) M retinoic acid, this results in a dose-dependent synergistic induction of TIMP protein secretion which is greater than the additive effect of the agents by up to fourfold. These responses can be inhibited by the presence of specific neutralising antibodies to the growth factors, demonstrating that they are not the result of an experimental artefact such as contamination with bacterial endotoxin. The mechanisms of these synergistic responses may involve the induction of receptors for retinoic acid, PDGF, or TGF-beta or may result from synergistic effects on TIMP gene transcription. We have also found that retinoic acid potently down-regulates PDGF-BB-stimulated collagenase in both types of fibroblast and that the effect of PDGF-BB alone on collagenase secretion from skin fibroblasts is biphasic. Finally, this study reports that retinoic acid and TGF-beta do not act in an additive fashion to inhibit the production of collagenase from skin fibroblasts.

Intracellular actions of vitamin A

Because the effects of vitamin A vary with tissue type and often with the form of vitamin A itself, a complete understanding of the mechanism(s) of action still has not been attained. The action of vitamin A may be at the level of genomic expression, at the membrane level, or both. Intercellular and intracellular transport of vitamin A are facilitated by specific binding proteins but probably not in the cellular uptake of vitamin A. Subcellularly, vitamin A may exert a direct effect on transit through the Golgi apparatus, as observed from both biochemical and morphological studies. In my laboratory, recent work using cell-free systems has shown that retinol stimulates transition vesicle formation from endoplasmic reticulum in a GTP-requiring step.

Transforming growth factor beta stimulates urokinase-type plasminogen activator and DNA synthesis, but not prostaglandin E2 production, in human synovial fibroblasts

Transforming growth factor beta (TGF-beta) is usually associated with matrix formation and tissue repair; in contrast, cellular expression of the serine proteinase, urokinase-type plasminogen activator (u-PA) is often correlated with tissue remodeling, as well as with cell migration and transformation. We report here that purified recombinant human TGF-beta (greater than or equal to 300 pg/ml) can stimulate rapidly (within 2 h) the u-PA activity of nonrheumatoid synovial fibroblast-like cells. As for interleukin 1 (IL-1), u-PA mRNA levels are raised in response to TGF-beta, but unlike IL-1, no increase in prostaglandin E2 levels occurs. In contrast to a number of other examples in the literature, in which these two cytokines have opposing actions, TGF-beta can potentiate the action of optimal concentrations of IL-1 in enhancing u-PA expression. These effects of TGF-beta are similar to those of all-trans-retinoic acid. In addition, synovial fibroblast DNA synthesis was stimulated by TGF-beta. Because TGF-beta has been detected in the synovia of patients with rheumatoid arthritis and has been shown to reduce the collagenase levels and proliferation of synovial fibroblast-like cells, it has been proposed by others to be involved beneficially in the reparative processes occurring in arthritic lesions. However, on the basis of our findings, we propose alternative functions for this cytokine--namely, roles in the destructive events as well as in the synovial hyperplasia observed in rheumatoid joints.

Matrix depletion of young and old human articular cartilage by cultured autologous synovium fragments: a chondrocyte-independent effect

Human articular cartilage of different ages was cultured for 8 days and proteoglycan (PG) release into the medium was measured. Retinol and synovial co-culture increased the PG release of cartilage of all ages. The effect of retinol was dose-dependent. Synovium increased also the PG release of dead cartilage, whereas retinol did not. The increased PG release by synovial co-culture is therefore mainly the result of synovial enzymes acting directly on the matrix rather than of a factor inducing chondrocyte-mediated breakdown.

Effects of products from macrophages, blood mononuclear cells and or retinol on collagenase secretion and collagen synthesis in chondrocyte culture

Collagenase secretion was studied on cultures of rabbit articular chondrocytes. Differentiation of the cells was assessed by characterizing the type of 3H-labelled collagen produced during treatment with (1) conditioned media from rabbit peritoneal macrophages and human blood mononuclear cells, and (2) with retinol, a potent cartilage resorbing agent in tissue culture. Conditioned media stimulated collagenase secretion. Total collagen synthesis was reduced due to a decrease of synthesis of alpha 1 chains; the amount of alpha 2 chains synthesized was unchanged. This is thought to be due to a reduction in type II synthesis. Retinol did not stimulate collagenase secretion. Total collagen synthesis was reduced by retinol. alpha 2 chain synthesis, however, was significantly increased, suggesting a switch of collagen synthesis in favor of type I collagen, and therefore, dedifferentiation. These results demonstrate that dedifferentiation of chondrocytes with respect to collagen synthesis is not necessarily associated with a stimulation of collagenase secretion.

Stimulation of the plasminogen activator activity of human synovial fibroblasts by retinoids

Nonrheumatoid human synovial fibroblasts in culture, while having low basal plasminogen activator levels, were stimulated to produce much more of this protease activity by low concentrations of a series of retinoids. The most potent retinoid tested, all-trans retinoic acid, was active over the range 10(-11)-10(-6)M. The increased plasminogen activator activity in the presence of 10(-6)M retinoic acid was first observed within 40 minutes under appropriate experimental conditions, required RNA and protein synthesis, and was reversible after short incubation periods. This stimulation was suppressed by low concentrations of antiinflammatory glucocorticoids such as dexamethasone.

Evidence that extracellular cathepsin D is not responsible for the resorption of cartilage matrix in culture

Cathepsin D, the major lysosomal aspartic proteinase, is responsible for the autolysis of cartilage at slightly acidic pH, and it has been suspected of making a significant contribution to the breakdown of the living tissue, such as in stimulated by retinol. Our finding, however, has been that neither inhibitory antibodies against cathepsin D, nor chemical inhibition with pepstatin, significantly decreases the rate of degradation of proteoglycan in the organ culture system. Most of the other proteinase inhibitors tested were similarly ineffective, although the EDTA and 1,10-phenanthroline inhibited the resorption by a cytotoxic effect. We conclude that although cartilage matrix degradation has clear characteristics of proteolytic process, the identity of the enzyme(s) responsible remains obscure.

Hypervitaminosis A and matrix alterations in maxillary explants from 16-day rat embryos

Hypervitaminosis A in treated pregnant rats has been shown to interfere with normal palatal closure and fusion, as demonstrated by the presence of cleft palates in offspring. The observation that palatal shelves of excess vitamin A exposed fetuses are stunted and delayed in rotation suggests that vitamin A may inhibit a biochemical event crucial to the successful contact of the palatal shelves. Maxillary explants from 16 day Wistar rat embryos cultured in the presence or absence of 30 IU/ml retinyl palmitate were analyzed for DNA, glycosaminoglycan, and collagen synthesis. Maxillary explants cultured in vitamin A-containing medium showed an inhibition in DNA, GAG, and collagen synthesis in comparison to control explants. Excess vitamin A in the culture medium of maxillary explants also resulted in a reduction of intermolecular cross-links in collagen. The possible significance of the results in terms of cleft palate and normal secondary palate formation is discussed.

Extracellular matrix metabolism by chondrocytes. 5. The proteoglycans and glycosaminoglycans synthesized by chondrocytes in high density cultures

Proteoglycans were extracted from the extracellular matrix of cultures of embryonic chick chondrocytes grown at high density and were purified by CsC1 density gradient centrifugation. The chemical, physical and hyaluronate binding properties of the proteoglycans were similar to those observed in proteoglycans from other hyaline cartilages. Proteoglycans in the media were also purified and on analysis showed three populations of proteoglycans to be present. One population had the physical characteristics of a typical proteoglycan subunit and bound hyaluronate, the other two populations were unable to complex with hyaluronate but one had the physical characteristics of the proteoglycan subunit and the other was of smaller molecular weight. The small molecular weight appears to be a product of the enzymatic degradation of the larger molecular weight species.

The effect of hypervitaminosis A on rat palatal development

Retinoic acid or retinyl acetate was administered to pregnant rats in doses sufficient to induce a 90% incidence of cleft palate. In another study, a delay in the reorientation of the palatal shelves was observed to be longer with the more potent teratogen, retinoic acid. On day 16 of gestation, 24 hours after final dosage with vitamin A, the synthesis of DNA and protein was studied in fetal carcass, mandible, and palate, and that of sulfated mucopolysaccharides (S-MPS) and glycoproteins (GP) in fetal head, mandible, and palate. Increases in DNA synthesis in fetal palate and in GP synthesis in fetal palate were found; thus, the mechanism of action of vitamin A in inducing cleft palates in rats may be caused by interference with the normal biochemical synthetic pattern of the palatal shelves.

A unifying concept for the role of matrix vesicles and lysosomes in the formal pathogenesis of diseases of connective tissues and blood vessels

The cells of the connective tissues contain lysosomes with enzymes capable of degrading intercellular substances (collagen, elastin, proteoglycans) and release their enzymes in membrane-bound or in free form into their intercellular substance. In this way extracellularly located lysosomes (= matrix lysosomes) can be detected by morphological and enzymatic means as well as by their metal concentrating property. This function of such matrix-lysosomes is in connection with the two step-degradation of the connective tissue and is thought to be the main part for the fibrocytic fibrolysis, chondrocytic chondrolysis, osteocytic osteolysis and myocytic mediolyses in the vessel wall. The cells of the mesenchymal tissues thus control the turnover and transformation of their own ground substance. Inflammatory and immunologic processes are suggested to be superimposed on this lysosomal action. If the lysosomal enzyme system in the connective tissues and the vessel wall gets out of control, the consequences can be dangerous as e.g. in case of relapsing polychondritis and arterial aneurysms. In this enzyme system proteolytic activators as well as proteolytic decomposable inhibitors are present. The corresponding proteolytic processes are of lysosomal nature and are subordinated to other regulatory mechanisms.

14C vitamin A in developing rat teeth and bone. A whole body-autoradiographic study

The distribution of vitamin A in developing young rats has been studied. Low doses of 14C-retinol were administered intraperiotoneally and the uptake analyzed autoradiographically. The vitamin was found to accumulate mainly in the intestines, liver, kidney, adrenal and brown fat. No uptake could be detected in hard tissue forming cells nor in any hard tissue, except in the secretory ameloblasts of the incisors.