Growth and differentiation of stage 24 limb mesenchyme cells in a serum-free chemically defined medium

A serum-free defined medium which supports the differentiation of chick limb mesenchymal cells has been developed. In this medium, stage 24 embryonic limb mesenchymal cells which are plated at high density (5 x 10(6) cells/35-mm culture dish) differentiate into chondrocytes. Morphologically, these cultures appear only slightly different from those in which the cells are maintained in serum-containing medium. DNA levels and proline incorporation in cultures grown in defined medium are indistinguishable from control cultures. The rate of radiolabeled sulfate incorporation, a monitor of the rate of proteoglycan synthesis, in Day 8 high-density cultures maintained in defined medium is approximately 70-80% of control values. Additionally, growth and differentiation of intermediate-density (2 x 10(6) cells/35-mm culture dish) and low-density (1 x 10(6) cells/35-mm dish) cultures are also supported by this defined medium. The availability of this medium allows exploration of bioactive factors which affect or modulate mesenchymal cell differentiation and subsequent development.

Altered cartilage proteoglycans synthesized by chick limb bud chondrocytes cultured in serum-free defined medium

Chick high-density culture chondrocytes synthesize cartilage-specific proteoglycans with much structural similarity to the proteoglycans made by cartilage in vivo. Such cultures can be maintained in a defined medium formulated in this laboratory in which chondrogenesis occurs without the addition of serum. The proteoglycans synthesized by the chondrocytes in the presence of defined medium are of a cartilage-specific structure but differ in some aspects from the proteoglycans made in serum-containing medium. While their buoyant density, ability to aggregate with hyaluronic acid, and keratan sulfate chain size are unchanged, the proteoglycans synthesized in defined medium have altered chondroitin sulfate chains. This chondroitin sulfate is of significantly larger size and has a different sulfation pattern relative to that produced in serum-containing medium. The larger size of the chondroitin sulfate results in a larger monomer size of the defined medium proteoglycans. These differences have implications about the regulation of the structure of chondroitin sulfate proteoglycans.

Elevations in the endogenous levels of the putative morphogen retinoic acid in embryonic mouse limb-buds associated with limb dysmorphogenesis

Retinoic acid, an endogenous metabolite of vitamin A (retinol), possesses striking biological activity akin to a morphogen in developing and regenerating vertebrate limbs. Systemic administration of retinoic acid (RA) to pregnant mammals during the period of limb organogenesis invariably results in dose-dependent dysmorphogenesis. In an attempt to uncover the mode of action of RA in the developing limb bud we analyzed, by HPLC methods, the levels of RA and its metabolic precursor, retinol, in embryonic mouse tissues prior to and following maternal exposure to a teratogenic dose of RA. Detectable levels of both RA and its isomer 13-cis-retinoic acid were found in the limb buds of Day 11 mouse embryos (40 +/- 2 somites). Although retinol was the major retinoid found in ethanolic extracts of either whole embryo or the limb buds, the latter is enriched in RA compared to the whole embryo. This indicated either a higher degree of retinol metabolism or a sequestration of RA in the limb bud compared to the rest of the embryo at this stage of development. A study of the time course of retinoid levels in treated embryos showed that changes occur rapidly, are stable for several hours, and then begin to return to pretreatment levels. After a maternal dose of 10 mg/kg RA, which resulted in a mild degree of limb anomalies, peak RA levels in the limb bud increased 50-fold over the endogenous level; a full 300-fold increase was found after a 100 mg/kg dose which results in 100% incidence of phocomelia. Interestingly, a dose-dependent depression in retinol levels was observed after RA treatment both in maternal plasma as well as the embryo. Studies are in progress to trace the intracellular disposition of both retinol and RA as well as any further active metabolite of RA in the limb buds and other embryonic tissues.

Two gene members of the murine HOX-5 complex show regional and cell-type specific expression in developing limbs and gonads

This study reports the expression domains of two murine HOX gene members of the HOX-5 complex (Hox-5.2, Hox-5.3). These two genes have very similar homeodomain sequences, as well as temporal and spatial specificities of expression. They are both expressed at very posterior levels in the central nervous system, in sclerotome derivatives and in a few internal organs. In addition to these expression domains which are shared with other HOX genes, transcripts from both Hox-5.2 and Hox-5.3 are present at high levels in developing limbs. After an early homogeneous expression in mesodermal limb bud cells, transcription becomes restricted to cartilage-differentiating cells. In addition, Hox-5.2 is a marker for gonadal development. The possible involvement of such genes during inductive processes or organogenesis is discussed.

Insulin gene expression in chicken ontogeny: pancreatic, extrapancreatic, and prepancreatic

Insulin has metabolic, growth, and differentiation effects in chicken embryos in vivo and it is required for normal development. Whether the pancreas is the sole source of insulin in embryogenesis is controversial. In the present study we investigated (1) the developmental pattern of expression of the chicken insulin gene in the pancreas; (2) the expression of the insulin gene in three nonpancreatic tissues, liver, brain, and lower limb, during chicken development; and (3) the expression of the insulin gene at prepancreatic stages and during chicken embryo organogenesis. Hybridization of synthetic species-specific insulin oligonucleotides to pancreatic frozen section in situ and to Northern blots revealed a major increase in insulin messenger RNA (mRNA) levels during the third week of embryonic development. The hybridization histochemistry showed both an increase in the levels of insulin mRNA per pancreatic islet and, in addition, an increase in the number of insulin mRNA containing islets with development. By Northern analysis there was a major polyadenylated transcript of 0.6 kb, which increased in abundance approximately 30-fold during this interval. Under the same stringency conditions used for pancreatic RNA an insulin transcript was detected in liver RNA blots. The abundance of this hepatic insulin mRNA was about 100-fold less than the pancreatic insulin mRNA and, in contrast to the latter, did not increase in late development. Primer extension experiments demonstrated that the insulin transcripts of pancreas and liver had similar 5' ends. No insulin mRNA was detected by Northern analysis or primer extension either in whole brain or lower limb total RNA from several developmental stages. A very low abundance insulin mRNA was detected in whole embryo at Day 8 and body regions at Day 4 and Day 5 when organogenesis of the pancreas takes place. Interestingly, a polyadenylated insulin transcript was detected, as well, in whole Day 2 and Day 3 embryos (stages 10 to 20, with 20 to 40 somites) before differentiation of beta cells occurs. Thus, there is differential developmental regulation of the insulin gene in several chicken embryo tissues and the expression of insulin precedes pancreatic maturation. These findings support the proposed role of insulin in differentiation and development in vivo and suggest a paracrine type of action of the hormone in early embryos before blood circulation begins.

Hyaluronate accumulation and nerve-dependent growth during regeneration of larval Ambystoma limbs

Hyaluronate-mediated expansion of the extracellular matrix has been suggested as an important element of growth and morphogenesis in several developing systems. In vitro, various growth factors have been shown to stimulate hyaluronate synthesis as well as cell proliferation. A similar link between proliferation and hyaluronate production during in vivo growth is difficult to demonstrate, because in most systems the source of growth-promoting factors is either not known or not amenable to experimental manipulation. During amphibian limb regeneration, cell proliferation depends upon paracrine release of factors from axons in the limb stump, and the nerve supply can be eliminated or augmented experimentally for study of growth in this system. Denervated and amputated limbs of larval salamanders do not begin to regenerate until distal areas of the limb stumps are reinnervated. We have used such limbs to examine the effect exerted by the reappearance of nerves on the amount of hyaluronate in the tissue undergoing the growth response. Hyaluronate was demonstrated by the metachromatic dye Ethyl Stains-all, which stains hyaluronate blue while sulfated glycosaminoglycans (GAGs) and proteins in the extracellular matrix stain various shades of violet, and by microspectrophotometry of alcian-blue-stained GAGs in serial sections pretreated with buffer or with Streptomyces hyaluronidase (SH) to remove hyaluronate specifically. Both methods showed little hyaluronate in the distal region of limb stumps prior to reinnervation, while reinnervated stumps had amounts of hyaluronate similar to those of control blastemas. Autoradiography of 3H-glucosamine-labeled limbs indicated that hyaluronate in the blastemas of reinnervated limb stumps included material newly synthesized by cells throughout the growing tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid hormone induces synthesis and accumulation of tropomyosin and myosin heavy chain in limb buds of premetamorphic tadpoles

Myosin heavy chain (MHC) and tropomyosin (Tm) have been isolated from limb muscles of the North American bullfrog, Rana catesbeiana, and injected into rabbits to raise monospecific antibodies. These antibodies were used to study the localization and synthesis of myosin heavy chain and tropomyosin in the limb buds of premetamorphic (stage VI-VII) tadpoles treated with triiodothyronine (T3) to induce metamorphosis. Indirect immunofluorescence localization detects the accumulation of both MHC and Tm in the developing thigh region within 24 h of T3 treatment. During the subsequent 48 h, the accumulation of these proteins is enhanced in the thigh and progresses from thigh to the distal regions of the limb. Quantitative immunochemical determinations indicate that within 24 h of T3 treatment, synthesis of Tm and MHC are increased 23-fold and 6-fold, respectively. Following 5 days of T3 treatment, the synthetic rates of Tm and MHC are 266 and 70 times the control values, respectively. Both methods suggest that Tm is synthesized and accumulated at a greater rate than myosin heavy chain. These observations suggest that T3 promotes the differentiation of muscle in the limb buds of premetamorphic tadpoles and that limb development promoted by T3 in tadpoles is similar to that described during the embryonic development of higher vertebrates.

Spatial and temporal changes in the pattern of glycosylation of the developing chick limb tissue components as revealed by fluorescent conjugated lectin probes

The changing pattern of expression of glycoconjugates during the differentiation of the chick leg bud between stages 17 to 34 (days 3 to 8 of incubation) was studied using fluorochrome-labelled plant lectins. Limb buds were fixed in cold acetic-alcohol and wax-embedded. Agglutinins of peanut (PNA), soybean (SBA) and succinylated wheat germ (WGAs) revealed a specific binding pattern in the apical ectodermal ridge (AER) between Hamburger and Hamilton stages 19-32. These stages coincide with the period of elevation of the AER. This specific binding pattern was absent from the adjacent dorsal and ventral ectoderm. Prechondrogenic cells were positive for WGA and for PNA, and the PNA-binding capacity was intensified after neuraminidase treatment. Premyogenic cells at stage 23 can be identified as negative to PNA after neuraminidase, while the blood vessels became positive. PNA, SBA, WGA, WGAs and, in addition, Ricinus communis (RCA-I) lectins stained the basal membrane. Strands of extracellular matrix which connect with the basal membrane and cross the limb transversely between dorsal and ventral ectoderm were stained by RCA-I, SBA and PNA after neuraminidase.

Fibroblast growth factor levels in the whole embryo and limb bud during chick development

A growth factor with properties very similar to fibroblast growth factor (FGF) was detected in the yolk and white of unfertilized chick eggs, and in the limb bud and bodies of Day 2.5 (stage 18)-13 chick embryos using two complementary and highly sensitive biological assays-competition of 125I-a-FGF binding to the FGF receptors of 3T3 cells and stimulation of DNA synthesis in MM14 cells, a permanent mouse skeletal muscle cell line that is dependent upon FGF for proliferation. Further evidence of the similarity of this growth factor to FGF is provided by the finding that biological activity is lost when the material is bound to a heparin-Sepharose column and restored upon elution with 2.5 M NaCl; the 2.5 M NaCl fraction from Day 12 embryos contains several polypeptides of apparent molecular weights 12,500-17,500. The level of FGF in the embryonic chick body is fairly constant between Days 2.5 and 6 (stages 18-29), ranging between 1 and 2 ng FGF/mg protein; but thereafter the level increases so that by Day 13 the body contains about 15 ng FGF/mg protein. In contrast, the level of FGF in the limb but is higher than that in the rest of the body until Day 5 (stage 27); it then undergoes a transient decrease between Days 6 and 7, after which it increases but remains below the level observed in the remainder of the body.

Direct demonstration of production of transforming growth factor activity by embryonic chick tissue

The presence of transforming growth factor activity in early chick embryos was directly demonstrated by the ability of limb and tail buds to induce anchorage independent division in NRK 49 f cells. Colony number increased with limb bud number and developmental stage. Medium conditioned by tail buds contained some stimulating effect, and strongly promoted the action of other transforming growth factors.

Effects of molecular oxygen on chick limb bud chondrogenesis

Chondrogenesis is an important process in the development of the embryonic chick limb. If limb buds are dispersed just prior to the initiation of chondrogenic differentiation and their cells seeded densely in culture as three-dimensional "micromasses," some of the cells differentiate to form chondrogenic nodules. These nodules characteristically produce sulfated proteoglycans and type II collagen. Two conditions within the early avian limb core have been linked causatively to the initiation of chondrogenesis: a limitation in the availability of molecular oxygen and a low NAD content of the tissue. The O2 limitation is thought to be responsible for the low NAD level. We examined the effects of molecular oxygen on the NAD content of chick limb-bud cells in micromass culture, the formation of chondrocytic nodules, and the production of type II collagen and sulfated proteoglycans. The NAD content of the cells in the micromasses and the production of type II collagen did not vary greatly as a function of oxygen availability. The development of the nodules was modified, but not eliminated, by high oxygen partial pressure (0.95). It was eliminated by anoxia. Proteoglycan synthesis was decreased significantly by high oxygen tension and its sulfation was also decreased, more so in the wing-bud than the leg-bud cells. The results suggest that in culture, high oxygen tension is compatible with some, but not all, aspects of chondrogenic differentiation of cells from embryonic chick limbs.

Proteoglycan biosynthesis is stimulated by D-penicillamine in chondrifying high density cell cultures

Chondrifying high density cell cultures of stage 22-24 chick embryo limb bud mesenchyme were treated with 5, 10 and 15 mmol/l D-penicillamine (DPA) for 4 and 6 days. The cultures were analyzed with morphological and biochemical techniques to learn more about the effect of DPA on the metabolism of cartilage glycosaminoglycans (GAGs). Using light and electron microscopic histochemical reactions for GAG, a considerable increase in the intensity of staining of the cartilage matrix could be detected in cultures treated with DPA as compared to the untreated controls. The uronic acid content of the treated cultures was higher than that of the controls. Liquid scintillation measurements and autoradiography revealed that DPA treatment increased the 35S-sulfate into the cultures. These data suggest that DPA - besides its well known inhibitory effect on collagen crosslink formation - alters the metabolism of sulfated GAGs in differentiating cartilage. It is supposed that DPA stimulates the biosynthesis of these macromolecules.

Evidence for sequential appearance of cartilage matrix proteins in developing mouse limbs and in cultures of mouse mesenchymal cells

The initiation of synthesis and the accumulation of four cartilage matrix proteins (type II collagen and three noncollagenous proteins, one of Mr 148, one of Mr 59, and an oligometric protein of Mr above 500 with 100-kDa subunits, respectively) were studied in developing mouse limbs and in cultures of limb bud mesenchyme by means of immunolocalization. On day 13 of gestation, type II collagen was observed throughout the entire humerus, whereas the 148-kDa protein was localized only in the central portion. Neither the 100-kDa-subunit protein nor the 59-kDa protein could be demonstrated in the humerus at that stage. On day 14 1/2, type II collagen and the 148-kDa protein were codistributed throughout the humerus. The 100-kDa-subunit protein was detectable in the periphery of the humerus, whereas little 59-kDa protein could yet be demonstrated. On day 18, all four proteins being studied could be detected immunologically in the developing mouse humerus. They differed in immunolocalization. Type Ii collagen, the 148-kDa protein, and the 100-kDa-subunit protein were codistributed throughout the distal and proximal parts of the cartilage. However, the 148-kDa protein could no longer be detected immunochemically in the outermost part of the cartilage in the proximal shoulder joint. The 148-kDa protein codistributed with type II collagen and the 100-kDa-subunit protein in the distal cartilaginous region, where joint development was less advanced. On the other hand, the 59-kDa protein was not demonstrated directly within the hyaline cartilaginous structures, but surrounded the entire structure. This protein was also present in the same part of the proximal joint region as that in which the 148-kDa protein was not detected. To develop an in vitro model for studies of skeletogenesis, mesenchymal cells prepared from mouse limb buds were cultured as micromass cultures at high initial cell density to favor chondrogenesis. On day 3 of culture, type II collagen was the only protein that could be detected immunochemically in the cultures, whereas on day 6 the 148-kDa protein was demonstrated, and a few chondrocytes in the central portion of each cartilaginous nodule were associated with the 100-kDa-subunit protein. The 59-kDa protein could not yet be immunochemically detected.(ABSTRACT TRUNCATED AT 400 WORDS)

[Relationship of fetal hind limb and fetal liver on amino acid metabolism in pregnant rats]

A tracer technique for injections into rat fetal abdomen in utero was employed to obtain a better knowledge of amino acid metabolism in fetal hind limb and fetal liver. Calculation of tissue fluid distribution via 3H-inulin space made possible an estimation of the fetal hind limb and fetal liver intracellular amino acid concentration based upon the fetal plasma and fetal tissue amino acid concentration. A significant concentration gradient between fetal plasma and fetal hind limb was found for glutamate (37.3) but not for alanine (9.7) or leucine (3.0). The radioactivity of fetal hind limb and fetal liver after the injection of 1 microCi of radioactive 14C-glutamate 14C-alanine or 14C-leucine into fetal abdomen was measured. In fetal hind limb, significant radioactivity was recognized after 14C-alanine administration, but not after 14C-glutamate administration as against the significant concentration gradient. However, in fetal liver, significant radioactivity was recognized after 14C-glutamate administration, but not after 14C-alanine administration. We concluded that in fetus, glutamate was released from the hind limbs and a large amount taken up by fetal liver.

Early changes in parathyroid hormone response and proteoglycan synthesis of chick embryonic femur produced by exposure to 6-aminonicotinamide in ovo

The mechanism of induction of micromelia in 6-day-old chick embryo by 6-aminonicotinamide (6-AN) was investigated. Six-day-old chick embryo exposed to 6-AN did not show micromelia when tenfold excess of nicotinamide over 6-AN was co-administered. The ability of nicotinamide to prevent the induction of micromelia was partially offset after 4 hr of exposure to 6-AN and completely disappeared after 6 hr. The length of time necessary for the induction of micromelia was not affected by the concentration of 6-AN. These results indicate that exposure to 6-AN for only a short period of 6 hr is sufficient to commit the limb to micromelia and that cellular components involved in the induction of micromelia alter during this period. During this period, newly synthesized proteoglycan monomers typical of cartilage decreased in average molecular size, and isolated femora did not respond to parathyroid hormone (PTH) but to dibutyryl cyclic AMP to stimulate growth of cartilage in organ culture.

Receptors for insulin-like growth factors I and II in developing embryonic mouse limb bud

Insulin-like growth factors (IGF) or somatomedins (SM) have been classically defined as promoting the actions of growth hormone in skeletal growth. IGF is divided into two groups, IGF-I and II, and are presumed to act via IGF type I (higher affinity for IGF-I and II and very low affinity for insulin) and II (higher affinity for IGF-II than I and no affinity for insulin) receptors, respectively. Recently, a switchover role of IGF-II to I during fetal to adult growth has been suggested. We have investigated the possible transitional role of IGF-II to I in a developing mouse embryonic limb bud organ culture model. In this in vitro system, limb bud develops from the blastoma stage to a well-differentiated cartilage tissue. Both IGF type I and II receptors were found to be present in limb buds at all stages of differentiation. Type I receptor decreased with differentiation while Type II receptor increased. The effect of IGF-I on [3H]thymidine and [35S]sulfate uptake by the tissue increased with differentiation while the effect of IGF-II on [3H]thymidine uptake of the undifferentiated tissue was abolished with differentiation of the tissue. The increase of the IGF-I response with decreased type I receptor may reflect an altered receptor sensitivity (occupancy) during differentiation. The decrease of the IGF-II response with increased type II receptor with differentiation may on the other hand suggest that IGF-II in differentiated tissue no longer acts as a classical growth factor. These results tend to support the hypothesis of the switchover role of IGF-I and II during fetal and adult growth, however, confirmation of the precise role of IGF-I and II in biological growth may have to wait until further studies clarifying the significance of the increased IGF type II receptor in differentiated tissue are made.

Molecular cloning of the chicken nerve growth factor gene: mRNA distribution in developing and adult tissues

The gene for chicken nerve growth factor was cloned by screening a chicken genomic library with a mouse nerve growth factor cDNA clone. Northern blot analysis indicated the presence of nerve growth factor mRNA throughout the central nervous system of the chick, with the highest levels in retina, midbrain/hindbrain and spinal cord. In embryonic brain, nerve growth factor mRNA was expressed at low levels at day 8, with a progressive increase up to postnatal day 2. Substantial amounts of nerve growth factor mRNA were expressed in embryonic leg tissues at a time when the dorsal root ganglia that project to the limb are maximally responsive to nerve growth factor.

Retinoic acid-binding protein in the chick limb bud: identification at developmental stages and binding affinities of various retinoids

The application of retinoic acid (RA) to the developing chick limb bud causes 6-digit double posterior limbs to form instead of the normal 3-digit limb. As an attempt to begin a molecular analysis of this phenomenon we have identified and characterized a soluble cytoplasmic receptor for RA, namely cytoplasmic retinoic acid-binding protein (CRABP), from the cells of the chick limb bud. It is present from stages 20-35 at similar levels and has an apparent Kd of 140-280 nM. In competition experiments with other retinoids Ro 13-7410 was found to be the most effective at competing for sites on CRABP followed by all-trans-RA, 13-cis-RA, Ro 10-1670 and retinal. Retinol, retinyl palmitate, retinyl acetate, etretinate and arotinoid showed low or no affinity for CRABP. Specificity for binding was thus demonstrated since analogues with an acid end group competed effectively, the aldehyde competed less effectively and the ester or alcohol groups did not compete. At the concentration of RA that needs to be administered to cause duplications in the pattern of the limb bud, we estimate that 4% of the CRABP present in the limb bud has RA bound. The similarities between steroid receptors in the mediation of steroid hormone action and CRABP in the mediation of RA action is discussed. In this regard we note that while there are 10(4) steroid receptors per cell in other cell types we estimate that there are about 10(5) RA receptors per cell in the chick limb bud.

The clearance of 125I-labelled fibrin from the subcutaneous tissue of limbs with lipodermatosclerosis

The clearance of radioactive fibrin from the subcutaneous tissues has been measured in the rat and in the limbs of normal subjects, patients with varicose veins, and patients with lipodermatosclerosis. The animal experiments showed that the most effective way of producing a subcutaneous deposit of fibrin was by the simultaneous injection of labelled fibrinogen and thrombin. The clearance of these clots was delayed when fibrinolysis was depressed with epsilon-aminocaproic acid. Clearance of subcutaneous fibrin in man was significantly slower in the arms of patients with varicose veins and lipodermatosclerosis. Similarly clearance in the legs of patients with lipodermatosclerosis was significantly slower than that of the normal subjects and those with uncomplicated varicose veins. The clearance of fibrin from the legs of patients with lipodermatosclerosis was significantly slower than the clearance from their arms but there was no difference between arm and leg clearance in the normal subjects and those with uncomplicated varicose veins. The patients with lipodermatosclerosis had a significantly longer dilute blood clot lysis time. The inability to clear subcutaneous fibrin may be an aetological factor of lipodermatosclerosis.

In vivo degradation of bacterial cell wall by the muralytic enzyme mutanolysin

The muralytic enzyme mutanolysin can act in vivo to eliminate chronic erosive arthritis induced in rats by polymers of peptidoglycan-polysaccharide isolated from group A streptococci (PG-APS). The amounts of PG-APS in the livers and spleens of rats treated with mutanolysin were significantly reduced compared with the amounts in control rats treated with phosphate-buffered saline. However, the amounts of PG-APS in the limbs of mutanolysin- and phosphate-buffered saline-treated rats were comparable. PG-APS polymers extracted from the livers, spleens, and limbs of mutanolysin-treated rats were extensively degraded, whereas PG-APS extracted from phosphate-buffered saline-treated rats had a high molecular weight. We propose that mutanolysin abrogates arthritis in rats by degrading PG-APS polymers to a size which is no longer able to induce chronic erosive arthritis, even though the polymers are still present in the limbs.

Quantitative analysis of the contribution of pulmonary and hind limb circulation to the clearance of exogenous catecholamines

The contribution of pulmonary and hind limb circulation to the clearance of exogenous catecholamines was analyzed quantitatively. During infusion of clinical doses of norepinephrine, epinephrine and dopamine in dogs, the plasma level of catecholamine and the plasma flow were measured simultaneously. Percentage of contribution was calculated from the following equation; transorgan difference of plasma catecholamine (nanograms per milliliter) X plasma flow (milliliters per minute) X 100/dose (nanograms per minute). This value means the percentage of the amount of catecholamine cleared by an organ to the amount of catecholamine administered into the body. Small but significant transpulmonary gradients of plasma levels of norepinephrine, epinephrine and dopamine and large translimb gradients of plasma levels of these catecholamines were observed. The plasma flow of pulmonary circulation was increased by infusion of epinephrine and dopamine, whereas it remained unchanged by infusion of norepinephrine. The plasma flow of hind limb circulation showed no significant change by infusion of catecholamines. The calculated contribution values indicate that pulmonary circulation clears 35.7% of norepinephrine (at 0.2 ng X kg-1 X min-1), 27.1% of epinephrine (0.2 ng X kg-1 X min-1) and 21.5% of dopamine (10 micrograms X kg-1 X min-1) administered exogenously, and that the corresponding figures for hind limb circulation are 8.2, 7.8 and 4.5%.

Glucocorticoid receptor-mediated teratogenesis and cell proliferation in the limbs and face of the chick embryo

The susceptibility of the face region of the chick embryo to the teratogenic action of intraamniotically injected hydrocortisone contrasts with the resistance of the limbs to its action while at the same time their dysmorphogenesis may be induced by other agents. Since glucocorticoid receptors were shown to mediate face teratogenesis, their development was investigated in freshly dissected limb buds of 3-, 3.5-, and 4-day-old chick embryos in comparison with the face region. The specific binding of 3H-dexamethasone to molybdate-stabilized glucocorticoid receptors was estimated by the dextran-coated charcoal method and complemented by cytologic analysis of mitotic activity in control and hydrocortisone-treated embryos. The glucocorticoid receptors were found in both organ anlagen already on day 3 when their concentration in femtomoles per microgram DNA was significantly higher in the face region. Accordingly, on day 3 intraamniotic hydrocortisone inhibited the mitotic activity in the face without affecting the developing limbs. On days 3.5 and 4 the concentration of glucocorticoid receptors was similar in both organ anlagen. Administration of hydrocortisone on day 4 induced mitotic depression in the face as well as in the limbs. However, the degree of inhibition appeared to be dependent upon the actual mitotic rate. In the face region where the mitotic activity culminated at that time, the inhibition was much deeper and longer-lasting than in the developing limbs characterized by continuous decrease of proliferation rate in controls. These findings are consistent with a view that glucocorticoid receptors are a prerequisite, but not the only factor in receptor-mediated teratogenesis.

Ontogeny of receptors for insulin-like peptides in chick embryo tissues: early dominance of insulin-like growth factor over insulin receptors in brain

Recently, we confirmed early data showing deleterious effects of exogenous insulin on chick embryos at 2 days of development, although insulin receptors were not clearly demonstrable until days 3-4. Now we report that insulin-like growth factor (IGF) receptors are present in whole embryos on day 2. The developmental patterns of [125I]IGF-I and [125I]IGF-II binding to brain were similar, and IGF-I showed approximately a 2-fold higher binding than IGF-II; there was a sharp increase from days 3 to 6, and a subsequent gradual fall during the second and third weeks of ontogeny. Competitive binding experiments with unlabeled analogs suggested that both labeled IGFs were binding to type I IGF receptors, and insulin interacted with them. The temperature and pH dependence were relatively higher than those for some other known IGF receptors. We have previously reported that [125I]insulin binding to brain is barely detectable on day 3 and shows a progressive rise throughout the rest of embryonic life. The pattern of IGF and insulin receptors appears to be organ specific, since nonneural tissues such as heart, liver, and limb buds showed different binding profiles in ontogeny. We conclude from these data that IGF receptors develop in chick embryo brain before insulin receptors and probably can mediate effects of IGF and insulin at early stages of embryogenesis.

The in vivo biosynthesis of embryonic proteins after maternal administration of phenytoin in the mouse

Pregnant A/J mice received 60 mg phenytoin/kg body weight on Day 10 of gestation. Eighteen hours after phenytoin injection, animals were injected (ip) with 20 microCi/g of [35S]methionine. After 6 hr of incorporation animals were sacrificed and the embryos were removed. Protein synthesis in the embryo, as measured by [35S]methionine incorporation into trichloroacetic-precipitable protein, was analyzed by SDS-PAGE and quantitation of autoradiograms. The results of gel electrophoresis indicate that in embryonic primary palates and limb buds from phenytoin-treated mothers there is an increase in synthesis of 66-, 50-, 44-, and 13-kDa proteins and a decrease in synthesis of an 18-kDa protein compared with values for the control counterpart. No role has been assigned to the 66-, 44-, or 13-kDa proteins but the 50-kDa band comigrates with tubulin and the 18-kDa band comigrates with calmodulin. Palatal cells in vitro stained positively with specific antibody to both these proteins. An adverse effect of the anticonvulsant drug phenytoin, when administered to pregnant A/J mice is an increase in the incidence of cleft lip with or without cleft palate [CL(P)] in their offspring. These alterations in protein synthesis may be a direct or secondary result of maternal phenytoin treatment and may play a role in CL(P) formation in vivo.

Bone matrix-directed chondrogenesis of muscle in vitro

Bone matrix is the largely collagenous residue of demineralized bone. Experimental data demonstrate that a substance, which is acid-stable during demineralization, occurs as a part of bone matrix, and that it is capable of stimulating the redifferentiation of skeletal muscle into cartilage. Reproducibility of redifferentiation is high and all cells derived from embryonic mesoderm appear competent to yield cartilage. This effect is highly significant to the developmental biology of musculoskeletal tissues, as muscle and cartilage arise from a similar embryonic origin. With regard to the embryonic limb as a model system, it appears that both muscle and cartilage progenitor cells do not have rigidly-defined developmental programs, and that this is a result of their origin from a common pool of embryonic mesoderm. This pool originates as embryonic mesenchyme long before any evidence of limb development can be detected. It is proposed that the active component of bone matrix, termed "bone morphogenetic protein (BMP)," acts upon a tissue whose developmental program is not stabilized, or has been experimentally destabilized (by injury), to augment and sustain syntheses of cartilage extracellular matrix. The use of bone matrix, and active substances derived from it, suggests that differentiation is not irreversible. Hard tissue growth and repair may occur via recruitment of competent responding cells from a variety of nonchondrogenic sources, provided that the extracellular milieu (i.e., presence of BMP) is supportive.

In vivo inhibition of adenosine triphosphate (ATP) synthesis associated with thiabendazole-induced teratogenesis in mice and rats

Ogata et al. (1984) reported that thiabendazole (TBZ) was teratogenic in mice when olive oil was used as a vehicle, but not teratogenic when administered in gum arabic. Results of investigations into the possible association between TBZ-induced teratogenicity and adenosine triphosphate (ATP) are reported here. ATP levels in the limb buds were measured at day 10 of gestation in controls and mice treated with 1300 mg/kg TBZ 24 h previously. The results showed that there was a correlation between the dosage of TBZ and the ATP levels of fore and hind limb buds (r = -0.827 and r = -0.799, respectively). ATP levels in mouse limbs were reduced to 22-31% of control values when TBZ was given in olive oil, but the ATP reduction was only 6-9% when TBZ was given in gum arabic. This suggests that there may be a relationship between the teratogenic and ATP-depressing action of TBZ on the limb buds of mouse embryos. Pregnant rats were also treated with TBZ. TBZ at a dose level of 1000 mg/kg was given orally on day 11 of gestation. After 24 h, ATP levels in fetal rat limbs were still 82% of control values. These results confirm the observations of Ogata et al. on the vehicle effect and the difference in response between mice and rats.

Biosynthesis of type IX collagen during chick limb development

We analyzed the collagens synthesized by developing chick limbs (stages 22 to 34). Type IX collagen synthesis started at stage 26, concurrently with the chondrogenic differentiation of limb mesenchyme, and gradually increased during subsequent stages. By stage 34, the central cartilaginous region of the limbs substantially synthesized type IX collagen, in addition to cartilage-specific type II collagen, while the outer non-cartilaginous region of the limbs synthesized predominantly type I collagen. The present study indicates that type IX collagen is cartilage-specific and can be used as a marker for the chondrogenic phenotype.

Pharmacokinetics of melphalan in clinical isolation perfusion of the extremities

The pharmacokinetics of melphalan in clinical hyperthermic isolation perfusion was studied in 16 patients with malignant melanoma. Analysis by computer-generated lines of best fit showed that the loss of melphalan from perfusate conforms best to a biexponential equation. The initial loss with a half-life (t1/2) of approximately 5 to 10 min is interpreted as rapid uptake of melphalan by the tissue of the perfused extremity. The terminal portion of the curve with a half-life of approximately 35 to 50 min is interpreted as due predominantly to the hydrolysis of melphalan, with a lesser component of loss due to absorption of melphalan to the filters and tubing of the perfusion apparatus. Determination of the area under the curve suggests that there is no appreciable uptake of melphalan by the tissue of the perfused extremity after 30 min.

Limb development in chick embryos: cyclic AMP-dependent protein kinase activity, cyclic AMP, and prostaglandin concentrations during cytodifferentiation and morphogenesis

The effects of prostaglandin E2 (PGE2) on cyclic AMP (cAMP) concentrations of chick limb bud cells obtained from limbs at various stages of development were investigated. In addition, endogenous concentrations of PGE2 were examined in whole limbs from comparable stages. Prior to either chondrogenesis or myogenesis (stages 20-23), cells were more responsive to PGE2, in terms of cAMP levels, than those of differentiated phenotypes, obtained at stages 25-28. This greater responsiveness to PGE2 of undifferentiated cells was correlated with endogenous concentrations of PGE2 which were significantly higher in undifferentiated limbs than in limbs containing differentiated cartilage and muscle. Cyclic AMP-dependent protein kinase (PKA) activity was detectable in cell homogenates at each stage examined and did not appear to change in cAMP dependency at any stage. The majority (80-85%) of total enzyme activity was localized in soluble fractions of cell homogenates while the residual activity was localized to membrane-enriched, particulate fractions. The results demonstrate that both responsiveness of limb mesenchyme to PGE2 and endogenous concentrations of PGE2 are maximal prior to cytodifferentiation of limb tissues. The presence of cAMP-dependent protein kinase in these undifferentiated cells supports a regulatory role for both PGE2 and a cAMP-protein phosphorylation system in the differentiation of limb tissues.

The effects of hyperoxia on oxygen uptake during acute anemia

The effects of normobaric hyperoxia on the oxygen uptake (VO2) and cardiovascular responses of the whole body and hindlimb during anemia were investigated. Anesthetized, paralyzed dogs were ventilated for 20-min periods with room air (normoxia), 100% O2 (hyperoxia), and returned to room air. Anemia (hematocrit = 15%) was then induced by isovolemic dextran-for-blood exchange and the normoxia, hyperoxia, normoxia sequence was repeated. Whole body VO2 and cardiac output rose following anemia, and then fell (p less than 0.05) with hyperoxia during anemia. These responses were not abolished by beta-blockade with propranolol (1 mg/kg, iv) or bilateral vagotomy. The hindlimb data for blood flow and VO2 were similar in direction to those of the whole body but were more variable. Section of the sciatic and femoral nerves did not appear to have significant effect on the limb responses to hyperoxia. The decrease in whole body and hindlimb VO2 with hyperoxia during anemia may have resulted from a redistribution of capillary blood flow away from exchange vessels in response to the elevated PO2.

Alterations of lectin binding during chondrogenesis of mouse limb buds

The binding of six different FITC-labelled lectins to mesenchyme, blastemal cells and cartilage was investigated in limb buds of mouse embryos during their development from day 10 to day 13. Concanavalin A, wheat germ agglutinin and phaseolus vulgaris agglutinin labelled mesenchymal cells of earlier stages, day 10 or 11, distinctly more than those of later stages. Chondrogenic blastema, basement membrane and muscle were always strongly stained. The galactosamine-specific ricinus communis agglutinin (RCA) bound preferentially to the blastema, whereas the mesenchyme was only weakly labelled. The galactose-specific peanut agglutinin (PNA), however, stained solely the blastema. In the mesenchyme, no binding was detectable light microscopically with this lectin. In cartilage, RCA- and PNA-staining was found to a lesser extent. With the fucose-specific lectin Lotus A, no staining was detectable. Due to the apparent differences in the binding of PNA in mesenchyme and blastema, peroxidase-labelled PNA was used to study the binding behaviour electron microscopically. It is shown that peroxidase-PNA very strongly labelled the intercellular matrix and the plasma membrane of cells in the late blastemal stages, whereas in young blastema no reaction product was detectable. In contrast to light microscopic findings, some label could be demonstrated also in the mesenchyme. The results show a general reduction of lectin receptors in more developed mesenchyme of later stages and the occurrence of galactose and galactose derivatives during early chondrogenesis in the matrix and at the cell membrane. The significance of these changes for chondrogenesis, however, remains to be elucidated.

Gene coding for a lens-specific protein, delta-crystallin, is transcribed in nonlens tissues of chicken embryos

The question of whether or not delta-crystallin gene (delta-gene) is transcribed in tissues of chicken embryos other than lens was examined by Northern blot analysis, using cloned delta-crystallin cDNA as a probe. delta-Crystallin mRNA was detected in neural retinas, brains, and limb buds of 3.5-day-old embryos. However, the distribution of delta-gene transcripts is limited to lens only in posthatched chickens. It was indicated that the ratio of large delta-crystallin RNA, probably precursor RNA, to mature delta-crystallin mRNA is always much higher in nonlens tissues.

O2 transport during two forms of stagnant hypoxia following acid and base infusions

Cardiac output and mean arterial pressure were decreased in two groups of 16 anesthetized paralyzed dogs ventilated by pump. Pericardial tamponade was used in one group, and hemorrhagic hypotension was used in the other. After a 30-min control period and 30 min of circulatory shock by either method, 0.3N HCl was infused into half the dogs in each group and 1.0N NaHCO3 into the other half so that pH was separated by 0.3-0.4 units. The slope of the line relating O2 uptake to total O2 transport (blood flow X arterial O2 concentration) was used to evaluate how well the tissues extracted O2 relative to O2 supply. During the initial shock period before infusion, the slope of the line relating O2 uptake of left hindlimb skeletal muscle to total O2 transport in the limb was almost twice as great as that for the whole body. Acid infusion increased the slope of the whole-body line but did not alter that for the hindlimb. Base infusion, on the other hand, decreased the slope of the line for the limb during hemorrhagic shock but had no other effect. We concluded that acid either improved the distribution of a limiting blood supply to nonmuscle organ systems, or increased tissue capillary PO2 and O2 diffusion by decreasing hemoglobin O2 affinity (HOA), or both. The effect of an increased HOA with base infusion was noticeable in hindlimb skeletal muscle only when volume depletion by hemorrhage presumably greatly increased the normally short intercapillary diffusion distance in muscle.

The patterns of protein synthesis during foetal and neonatal organ development in the mouse are remarkably similar

The extent to which differential gene expressions can be correlated with organ development was examined at the level of protein synthesis during pre- and postnatal development in the mouse. High resolution, equilibrium, two-dimensional polyacrylamide gel electrophoresis detected, for each of five to ten successive stages for each of seven organ systems, between 850 and 1000 separate newly synthesized proteins. The possibility that the 1000 detectable proteins synthesized at any one time during organ development represent a sampling bias was contra-indicated (a) because a different and larger population of [14C]amino acid-incorporating protein syntheses gave similar results and (b) because nonequilibrium isoelectric focusing, electrophoresis, isoelectric points between pH 5.5 and 8.7 confirmed the results from yet a different population of protein syntheses. Within limits of the sampling of protein syntheses, the entire period of organ development examined proceeds with altered expression of small proportion of the total proteins being synthesized. While all protein changes were stage specific, approximately three organ-specific protein syntheses were detected per organ system. One family of five protein syntheses seen in 16-day foetuses had homologous primary structures and presumably are keratins derived from a single genomic expression. These selected stage-specific protein syntheses examined by electrophoresis of partial proteolytic digests disclosed a programme for post-translational changes in protein syntheses. The current observations indicate that the examined pre- and postnatal organ development of the seven organs occurs in the presence of greater than 99% similarity among proteins synthesized in the same and different organ systems. Functional differentiation during organogenesis, therefore, occurs in the presence of less than 1% change in qualitative or quantitative switch in protein syntheses. Evidence is presented to indicate that even this remarkably small number of changes in protein syntheses during functional organ differentiation may be derived from an even smaller subset of gene expressions. Collectively, the data suggest that explanatory mechanisms for molecular organogenesis must encompass both selective gene expressions along with post-translational programmed events.

Incorporation of 5-bromo-2'-deoxyuridine into mesenchymal limb-bud cells destined to die: relationship to polydactyly induction in rats

The thymidine analogue, 5-bromo-2'-deoxyuridine (BUdR), given at the proper dose and time to pregnant rats produces preaxial hindlimb polydactyly in a high proportion of near term foetuses. The lack of physiological cell death in an area of preaxial mesenchyme known as the foyer primaire preaxial (fpp) is thought to be important in the pathogenesis of this defect. This study addresses the question of whether BUdR's well-known antidifferentiative effects, which are due in some way to drug incorporation into DNA, are operative in this in vivo system. The dose and temporal response of BUdR for the induction of preaxial polydactyly inversely parallels the frequency of embryonic hindlimbs with an fpp. Incorporation of BUdR into degenerative fragments within the fpp of these treated limbs is demonstrated with indirect immunofluorescence using an antibody to bromouridine. Hindlimbs exposed to a threshold dose of BUdR at the optimal time for producing polydactyly have incorporated the drug into degenerative fragments within the fpp. This suggests that a higher, teratogenic dose of BUdR might likewise be incorporated. The resulting higher level of incorporation presumably alters the normal course of terminal differentiation for these cells originally destined to die. Teratogenic doses of BUdR injected at later than the optimal time are also incorporated into dead cell fragments within the fpp, suggesting that presumptive dead cells have additional rounds of DNA synthesis which are BUdR-insensitive. Approximately 12 h prior to overt death presumptive fpp cells no longer incorporate the drug. Results reported support the hypothesis that incorporation of teratogenic levels of BUdR prevent cell death in the fpp. The extra cells are thought to contribute directly or indirectly to the added digit. Contrary to other views, it is suggested that BUdR-induced teratogenesis can be a result of the drug's antidifferentiative effects on specific, 'sensitive', populations of cells.

In vitro effects of the teratogen and folic acid antagonist, 9-methyl pteroylglutamic acid, on glycosaminoglycan accumulation in fetal rat limbs

Fetal rat limbs were obtained from pregnant females on the 14th day of gestation. Forelimbs and hindlimbs were pooled separately and preincubated for 22 hours at 37 degrees C in Eagle's MEM containing the teratogen and folic acid antagonist, 9-methyl pteroylglutamic acid (9-mePGA). Following removal of old medium, fresh medium together with the teratogen were added at the same concentration as before. Tritiated glucosamine (10 micro Ci) was added to each vial and the incubation continued for 4 hours at 37 degrees C. Tissues were homogenized, digested with pronase, and glycosaminoglycans (GAG) selectively precipitated with cetylpyridinium chloride. In vitro exposure of fetal limbs to various doses of 9-mePGA resulted in a significant increase in the accumulation of labeled GAG by fetal forelimbs at the high and intermediate dosage levels. No effect was observed at the lowest dose. Accumulation of labeled GAG by fetal hindlimbs although similar to fetal forelimbs in control incubations, was unaffected by in vitro exposure to 9-mePGA at any of the dosage levels studied.

Absence of response of chick embryonic limb to the growth stimulatory effect of parathyroid hormone in vitro after exposure to 6-aminonicotinamide in ovo

The biochemical effect of a nicotinamide analogue, 6-aminonicotinamide (6-AN), on developing chick embryonic femur was studied. Growth of femur from 9-day-old embryos that had been exposed to 6-AN for 5 days in ovo was not stimulated by PTH in an in vitro culture system. PTH caused a much smaller increase in the cyclic-AMP content in 6-AN-treated femur than in control femur. However, dibutyryl cyclic-AMP stimulated growth of 6-AN-treated femur. A defect in response of 6-AN-treated femur to the growth stimulating action of PTH may explain the production of micromelia by 6-AN.

Immunohistochemical localization of cyclic AMP during normal and abnormal chick and mouse limb development

This paper describes the immunohistochemical localization of cAMP during limb chondrogenesis in talpid3 chick, brachypod mouse, and normal embryos. Comparisons were made between chick wing buds at Stages 22, 25, and 30, and mouse hind limb buds at Days 11, 12.5 and 14. At Stage 22, the normal mesenchyme in the chick displayed areas of bright fluorescence compared to a lesser intense and more evenly distributed fluorescence in talpid3. Sections of the central region from normal Stage 25 limb buds exhibited an intense fluorescence that was uniformly distributed, whereas, in talpid3 staining was more mosaic with some areas fluorescing brightly and others showing little fluorescence. At Stage 30 the staining pattern was similar between normal and talpid3, with the fluorescence being brighter in the cartilage tissue than in the surrounding soft tissue. Difference in the staining patterns of normal and brachypod limb tissue were not detectable. At Days 11 and 12.5, tissue from both genotypes displayed a very bright, uniform fluorescence. In the 14-day hind limb buds, the staining patterns were comparable to those observed in Stage 30 chick wing buds. However, under in vitro conditions conducive for the expression of the chondrogenic phenotype, differences in the intensity and extensiveness of fluorescent staining were detectable in cultures derived from 12-day normal and brachypod hind limb mesenchyme. Compared to the control, the uneven distribution of immunofluorescence in the talpid3 limb buds and the differences in intensity and extensiveness of fluorescence in the brachypod cultures support the hypothesis that cAMP is involved in limb cartilage differentiation.

Effects of biochemical inhibitors on positional signalling in the chick limb bud

In 3- to 4-day embryonic chick limb buds, a region at the posterior margin of the limb, the zone of polarizing activity, appears to be responsible for signalling positional information along the anteroposterior axis. Our experiments were designed to test which biosynthetic processes are required for polarizing activity. We have treated polarizing regions with biochemical inhibitors, and then assayed their abilities to induce limb reduplications when grafted into anterior sites on host limb buds and also measured their capacities for protein, RNA, and DNA synthesis. DNA synthesis, and possibly oxidative phosphorylation, do not seem to be required for polarizing activity. But, glycolysis and protein and RNA synthesis are necessary, although not sufficient, for polarizing region activity. Activity seems particularly sensitive to inhibitors (actinomycin D and alpha-amanitin) of RNA synthesis.

Muscarinic acetylcholine receptor in chick limb bud during morphogeneis

In the chick embryo a cholinesterase activity appears in various organ anlagen which has been correlated with morphogenetic movements (Drews 1975). The cholinesterase activity is present in the mesenchyme of the limb bud during aggregation of the central chondrogenic core. In the present study binding of tritium labelled quinuclidinyl benzilate ((3H)QNB), a muscarinic antagonist, to homogenates of chicken limb buds was investigated by a filtration assay. In the homogenate of limb buds at Stage 24 specific binding of (3H)QNB was demonstrated. Determination of binding constants and inhibition of binding by agonists and antagonists was studied at Stage 25/26. Specific binding was defined by the difference in binding in the absence and presence of atropine (1 microM). Specific binding of (3H)QNB reflected a muscarinic receptor. The Kd in two experiments was 0.11 nM and 0.16 nM, the binding capacity was 15.7 fmol (3H)QNB/mg protein and 12.0 fmol (3H)QNB/mg protein, respectively. Data on displacement of specific bound (3H)QNB by various nicotinic and muscarinic ligands confirmed the muscarinic nature of the receptor. Muscarinic ligands inhibited the (3H) QNB binding, whereas nicotinic ligands caused no inhibition at pharmacological concentrations. I conclude that a specific muscarinic acetylcholine receptor is part of the cholinergic system whose presence is indicated by cholinesterase activity in the chondrogenic core of the limb bud during morphogenesis.

Estimation of creatine phosphokinase and hydroxyproline in the developing limb: its use in evaluating the effect of teratogens on myogenesis and chondrogenesis

Forelimbs of mouse fetuses were examined for tissue-specific, drug-induced alterations in their biochemical composition. The activity of the enzyme creatine phospholinase (CPK; to estimate myogenesis) and the content of hydroxyproline (HP; to estimate chondrogenesis) were compared in homogenates of control and treated mouse-fetus forelimbs on day 14 of gestation. In addition, the content of DNA, RNA, and protein was also measured. Injection of 6-aminonicotinamide (6-AN) (15 mg/kg) on day 10 resulted in an overall growth retardation in day 14 fetuses and all biochemical parameters tested were reduced. The ratio of PH:CPK was unaffected by 6-AN treatment. Retinoic acid (vitamin A acid; 100 mg/kg), administered to pregnant female mice on day 10, produced severe forelimb defects and resulted in a signific 10 resulted in an overall growth retardation in day 14 fetuses and all biochemical parameters tested were reduced. The ratio of PH:CPK was unaffected by 6-AN treatment. Retinoic acid (vitamin A acid; 100 mg/kg), administered to pregnant female mice on day 10, produced severe forelimb defects and resulted in a signific 10 resulted in an overall growth retardation in day 14 fetuses and all biochemical parameters tested were reduced. The ratio of PH:CPK was unaffected by 6-AN treatment. Retinoic acid (vitamin A acid; 100 mg/kg), administered to pregnant female mice on day 10, produced severe forelimb defects and resulted in a significant reduction in day 14 forelimb HP and RNA content, without altering CPK, DNA, or protein; thus, the HP:CPK ratio was decreased. These results indicated that 1) 6-AN nonspecifically retards growth and cyto-differentiation in limbs; 2) retinoic acid inhibits synthesis of collagen and RNA; 3) retinoic acid has a differential effect upon chondrogenic and myogenic tissues of the limb, and 4) the comparison of HP content and CPK activity in tissue homogenates is an acceptable method of evaluating teratogenic compounds for selective effects.

Extracellular matrix synthesis in the chick embryo lateral plate prior to and during limb outgrowth

Little is known at the present time about the molecular basis and mechanisms of morphogenesis. The present study is an attempt to determine what influence the extracellular matrix has on the initial outgrowth of the limb bud. Stage -12 to -18 chick embryo lateral plates were examined in relation to proline and sulfate incorporation into collagen and proteoglycan. The flank and limbs incorporated the same amount of labeled proline and sulfate before stage 16. At stage 16 the flank began to incorporate more of both isotopes until at stage 18 there was twice as much incorporation into the flank as into the limbs. The flank and limbs contained the same type of collagen during the period examined. The limbs contained both large and small proteoglycans but the flank contained only small proteoglycans. These data suggest that the extracellular matrix in the flank and limb regions may play a role in limb outgrowth and that the limb buds at these stages may be more inclined toward cartilage development.

Calcium regulation in clam foot muscle. Calcium sensitivity of clam foot myosin

1. The ATPase activity of clam foot myosin alone in the presence of 10 mM MgCl2 was activated approximately ten-fold by 10 muM free calcium ions. The calcium activation was observed in various concentrations of KCl (35-600 mM) and ATO (1 muM-1 mM), and at various pHs (pH 6-9.4). 2. The superprecipitation and ATPase activities of clam foot myosin B were studied by conducting experiments in two different ways. In one of these, the ATP concentration was varied at a fixed concentration of MgCl2, and in the other, the MgCl2 concentration was varied at a fixed concentration of ATP. The following was found: (a) The activities responded in a biphasic manner to change in either the ATP or MgCl2 concentration, giving a peak activity around 10 muM ATP or MgCl2. It is thus suggested that Mg-ATP complex is responsible for both activation and inhibition in the biphasic response. (b) When the ATP or MgCl2 concentration was higher than 100-300 muM, practically no superprecipitation occurred in either the presence or absence of calcium, whereas the ATPase activity was still strongly activated by calcium. 3. Similar results to those described above (a, b) were obtained by using rabbit skeletal actoclam foot myosin in place of clam foot myosin B. Moreover, it was found that as the ATP concentration increased from 1 muM to 1 mM, Mg-ATPase activity of clam foot myosin in the presence of calcium increased in a monophasic manner and that it was as active as actomyosin in the presence of calcium when the ATP concentration was higher than approximately 200 muM. In other words, actin-activation of myosin-ATPase was absent in the ATP concentration where no superprecipitation of actomyosin was observed. 4. Clam foot myosin contained two types of light chain subunits: LCl (17,000 daltons) and LC2 (16,000 daltons). Only LC1 was removed upon washing clam myosin with 10 mM EDTA, and removal of LC1 resulted in loss of the calcium sensitivity of actomyosin-ATPase. 5. In our previous report (J. Biochem. 85, 1543-1546, 1979), it was shown that removal of LC1 from clam foot myosin also resulted in loss of the superprecipitation activity of actomyosin reconstituted from "EDTA-washed" myosin. We now provide further evidence that removal of the regulatory light chain (LC1) results in a reversible uncoupling of ATPase reaction from superprecipitation reaction.

Effect of corticosterone and protein malnutrition on muscle protein breakdown in vivo in rats as measured by the urinary excretion of 3-methylhistidine

The role of corticosterone in regulating the rate of muscle protein breakdown was evaluated by measuring the urinary excretion of 3-methylhistidine (3-Mehis) during the administration of 0.0 (vehicle), 0.8 (physiological dose) and 10 (pharmacological dose) mg of the glucocorticoid/100 g body weight/day to adrenalectomized rats (AdX, AdX 0.8 and AdX 10 respectively). A fourth group of intact rats receiving only vehicle (In) was included as control. Rats were fed on either adequate protein and energy (Co) or low-protein (1-P) diets, for eight consecutive days. No differences were found between AdX and AdX 0.8 groups as compared to the In group in regard to body and liver weights. The AdX 10 group exhibited a significant reduction in body weight and a considerable increase in liver weight; these results were found in rats fed on the Co and 1-P diets, although rats on the 1-P diet showed a proportional decrease in those parameters as compared to the rats fed on the Co diet. Gastrocnemius, tibialis and E.D.L. muscle weights were significantly reduced in AdX 10 group, approximatley at the same extent in the two dietary groups. Soleus muscle weight increased in the AdX 10 group, at the same extent in the two dietary groups, as compared to the In group. Plasma corticosterone levels were significantly greater in the AdX 10 group in both dietary treatments, though restriction of protein in the diet induced a higher plasma hormone level than that of the Co group. Urea-N and creatinine outputs were significantly higher in the AdX 10 group. 3-Mehis excretion underwent an immediate and significant rise in the AdX 10 group, although rats fed on 1-P diet showed a more persistent rise than those fed on the Co diet. No differences were found among the other groups. It is concluded that high plasma corticosterone levels can accelerate muscle protein breakdown and that this action is not seriously affected by the protein content of the diet.

Changing patterns of proteoglycan synthesis during chondrogenic differentiation

The pattern of proteoglycan synthesis was examined in the cartilages of the anterior and the posterior limbs, the vertebra and the sterna of the developing chick embryo, during chondrogenic differentiation. At stage 18, the limb primordia synthesize small monomeric proteoglycans. In all nine cartilages examined, there was a shift during differentiation from small to larger intermediate forms followed by a transition toward the aggregate forms. As development proceeds, the proportion of aggregates increases and the small proteoglycans almost disappear. Chondrogenic differentiation is thus marked by a increase in the size of the proteoglycan molecules, and an increase in the proportion of the large proteoglycan aggregates.

The human tumor-bearing limb: an ex vivo model

The present report describes a viable, isolated, perfused, human, tumor-bearing limb model suitable for the study of human host-tumor metabolism. The model is hemodynamically stable with high flow rates (50 cc/kg/min) and low perfusion pressures (mean, 77.2 mm Hg) which are stable over time. Metabolically, the preparation is viable with initial oxygen and glucose uptake 0.88 cc/kg/min and 0.029 mmole/kg/min, respectively. These parameters and lactate concentrations do not change significantly with time.

Alterations in insulin absorption and in blood glucose control associated with varying insulin injection sites in diabetic patients

In seven insulin-dependent diabetic subjects the disappearance rate of 125I-labelled short-acting insulin from injection sites in the abdominal wall was 86% greater than from the leg (P less than 0.005) and 30% greater than from the arm (P less than 0.05). Absorption from the arm was 40% greater than from the leg (P less than 0.05). The postprandial rise in plasma glucose concentration varied inversely with the rate of insulin absorption and was 30 to 50 mg/dL less after abdominal than after leg injection; the glycemic response after arm injection was intermediate between that after leg and abdominal injection. These results indicate that changing the insulin injection site from the leg to the abdomen or arm accelerates the absorption of insulin and diminishes the postprandial rise in plasma glucose. Varying insulin injection sites within the same anatomic region rather than between different regions may diminish daily variations in insulin absorption and in metabolic control in insulin-dependent diabetic subjects.