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.