As a prerequisite to studies of whether the plasma membrane of the rat thymocyte contains specific, saturable binding sites for the thyroid hormone 3,5,3′-triiodothyronine (T3), a method was developed for the isolation of a plasma membrane fraction from these cells. As judged from both electron microscopic and marker enzyme studies, the fraction was composed principally of plasma membrane vesicles, was free of nuclear contaminants, and was only slightly contaminated with other subcellular components. At 37°C and pH 7.4, binding of [125I]T3 by the fresh membrane preparation was rapid, reaching a maximum at 5 min and then declining with time, so that by 60 min binding was virtually nil. Decreased binding with time was due to a loss of functional binding sites, but did not reflect desensitization, since the decrease in binding activity with time was independent of the presence or absence of T3. Scatchard analysis of saturation studies revealed the presence of two binding sites, one with an apparent dissociation constant (Kd) of 0.95 nM and a maximum capacity of 5.3 × 1010 sites/100 μg protein, and the other with an apparent Kd of 25 nM and a binding capacity of 1.4 × 1012 sites/100 μg protein. Measurement of the ability of several thyronine analogues to inhibit the binding of [125I]T3 revealed the following rank order of potency: l-T3 > l-T4 > d-T3 = d-T4 > l-3,5-T2 > rT3 > d,l-thyronine. Binding of T3 was inhibited by the omission of calcium from the medium or by the addition of the beta adrenergic antagonist alprenolol. As judged from studies of the lower affinity binding site, these manipulations decreased the affinity, but not the number, of binding sites for T3. The relative potencies of thyronine analogues to inhibit the binding of [125I]T3 were generally parallel to their previously reported potencies in stimulating the uptake of the sugar analogue 2-deoxy-glucose (2-DG) in intact rat thymocytes in vitro. Further, the inhibition of T3-binding produced by l-alprenolol or by excluding calcium from the medium resembled the previously reported inhibition that these manipulations produce with respect to T3-induced enhancement of 2-DG uptake. These findings suggest that the binding sites for T3 present in the plasma membrane of rat thymocytes act as functional receptors linked to the stimulation of 2-DG uptake that T3 induces in these cells.
Joseph Segal, Sidney H. Ingbar
The bisphosphonates (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (APD) and disodium dichloromethylidene bisphosphonate (Cl2MDP) effectively inhibit the accelerated bone resorption associated with some skeletal disorders, e.g., Paget's disease. However, it has not been established whether these compounds exert their inhibitory effect by rendering the bone mineral more resistant to degradation, by diminishing the activity of resorbing cells, or through some combination of both activities. In this study, we have tested these possibilities using an in vitro resorption assay system consisting of elicited rat peritoneal macrophages co-cultured with particles of 45Ca-labeled, devitalized rat bone. This assay system permits the quantitative assessment of the action of APD and Cl2MDP on the two major phases of bone resorption (cell-substrate attachment and osteolysis) under circumstances where the drugs are present continuously or, most importantly for the issues in question, after the separate pretreatment of the particles or the resorbing cells.
Pieter H. Reitsma, Steven L. Teitelbaum, Olav L. M. Bijvoet, Arnold J. Kahn
Tangier disease is a rare familial disorder characterized by enlarged orange tonsils, transient peripheral neuropathy, hepatosplenomegaly, and lymphadenopathy, as well as striking reductions in plasma high density lipoproteins (HDL) and their major protein constituents, apolipoproteins (apo)A-I and A-II. In order to test the hypothesis that Tangier patients have abnormal apoA-I or apoA-II, the in vitro lipoprotein binding and in vivo metabolic characteristics of these proteins isolated from normal and Tangier plasma, were studied in normal subjects and patients with Tangier disease.
Ernst J. Schaefer, Linda L. Kay, Loren A. Zech, H. Bryan Brewer Jr.
The interaction of hemoglobin C (Hb C) with erythrocyte membranes was studied using changes in fluorescence intensity in a membrane-embedded probe. The affinity of Hb C for the membranes at pH 6.0 and pH 6.8 was compared to that of normal hemoglobin (Hb A). Steady-state and kinetic data were delivered. The affinity of Hb C for the erythrocyte membrane at pH 6.8 appeared to be about five times greater than that of Hb A. The associations of Hb C and Hb A with the membrane were reversible to about the same extent. The cytoplasmic portions of band 3 membrane proteins were suggested to be the binding sites for both hemoglobins. The membrane binding of Hb C at pH values of 6.8 to 7.0 indicates that this reaction may occur under physiological circumstances.
G H Reiss, H M Ranney, N Shaklai
Myeloid differentiation in vitro is characterized by the sequential appearance of morphological, functional, and biochemical markers of maturation. We examined the effect of agents that increased the intracellular concentration of adenosine 3′5′-cyclic monophosphate on the expression of these markers by human promyelocytic leukemia cells (HL60). Cells treated with 500 μM N6,O2-dibutyryl adenosine 3′5′-cyclic monophosphate expressed formyl peptide and complement receptors, reduced nitroblue tetrazolium, adhered to substrate, demonstrated chemotaxis and stimulated lysosomal enzyme release, rapidly ceased proliferation, and assumed the morphology of myelocytes and metamyelocytes. Prostaglandin E2 (100 nM) and theophyllin (500 μM) induced similar functional changes but the cells did not mature beyond the myelocyte stage. Cholera toxin (1 or 50 nM) induced formyl-peptide receptor expression and adherence, but the cells did not reduce nitroblue tetrazolium, continued to proliferate, and were unchanged morphologically. Formyl-peptide receptor expression was the earliest marker of these modified programs of maturation. The receptor appeared within 2 h after treatment and increased linearly for 72 h. Receptor expression was dependent on new protein synthesis. At 48 h, Scatchard analysis demonstrated 2.4 × 105 receptors/ cell with a KD of 1.3 nM.
Thomas J. Chaplinski, James E. Niedel
A 21-yr-old woman with Turner's syndrome presented with signs and symptoms of acromegaly. The serum growth hormone (GH) (95±9.4 ng/ml; mean±SEM) and somatomedin C (11 U/ml) levels were elevated, and an increase in GH levels after glucose instead of normal suppression, increase after thyrotropin-releasing hormone (TRH) administration instead of no change, and decrease after dopamine administration instead of stimulation were observed. The pituitary fossa volume was greater than normal (1,440 mm3) and the presence of a pituitary tumor was assumed. After tissue removal at transsphenoidal surgery, histological study revealed somatotroph hyperplasia rather than a discrete adenoma. Postoperatively, she remained clinically acromegalic and continued to show increased GH and somatomedin levels. A search was made for ectopic source of a growth hormone-releasing factor (GRF). Computer tomographic scan revealed a 5-cm Diam tumor in the tail of the pancreas. Following removal of this tumor, serum GH fell from 70 to 3 ng/ml over 2 h, and remained low for the subsequent 5 mo. Serum somatomedin C levels fell from 7.2 to normal by 6 wk postoperatively. There were no longer paradoxical GH responses to glucose, TRH, and dopamine. Both the medium that held the tumor cells at surgery and extracts of the tumor contained a peptide with GRF activity. The GRF contained in the tumor extract coeluted on Sephadex G-50 chromatography with rat hypothalamic GH-releasing activity. Stimulation of GH from rat somatotrophs in vitro was achieved at the nanomolar range, using the tumor extract.
M. O. Thorner, R. L. Perryman, M. J. Cronin, A. D. Rogol, M. Draznin, A. Johanson, W. Vale, E. Horvath, K. Kovacs
The effect of emphysema on the ability of the diaphragm to generate force was examined in costal diaphragm muscle strips from 10 Golden hamsters killed 18 mo after intratracheal injection of pancreatic elastase in a dose producing hyperinflation (mean total lung capacity [TLC] = 163% of control) and generalized panacinar emphysema. 13 saline-injected normal animals served as controls. The time course of isometric tension and the effect of alterations in muscle fiber and sarcomere length on the isometric tension (T) generated in response to tetanizing electrical stimuli (length-tension [L-T] relationship) were examined. Elastase administration caused an increase in diaphragm muscle thickness and reduction in the length of costal diaphragm muscle fibers measured in situ. Emphysema significantly increased the maximum tetanic tension as a result of hypertrophy. Maximal tension corrected for increases in muscle cross-sectional area (T/cm2), however, was the same in emphysematous (E) and control (C) animals. Emphysema also shifted the muscle fiber L-T curve of the diaphragm but not of a control muscle, the soleus, toward shorter lengths. In contrast to the effects of E on the diaphragm muscle fiber L-T curve, the sarcomere L-T curve was the same in E and C. Since the length at which tension was maximal correlated closely with sarcomere number (r = 0.94; P < 0.001) reduction in the number of sarcomeres in series in muscles from emphysematous animals appeared to explain the shift in the muscle fiber L-T curve. We conclude that in elastase-induced emphysema adaptive changes both in diaphragm cross-sectional area and sarcomere number augment the force-generating ability of the diaphragm. We speculate that changes in sarcomere number compensate for alterations in muscle fiber length resulting from chronic hyperinflation of the thorax, while diaphragmatic muscle hypertrophy represents a response to changes in respiratory load and/or diaphragm configuration (LaPlace relationship).
Gerald S. Supinski, Steven G. Kelsen
Binding of quinine- and quinidine-dependent antibodies to platelets was studied using an electroimmunoassay to measure platelet-bound IgG. Antibodies from four patients with drug-induced thrombocytopenia differed significantly in their interaction with platelets: association constants for binding to platelets at high drug concentrations ranged from 0.29 to 2.6 × 107 M−1, the maximum number of antibody molecules bound ranged from 36,000 to 161,000/platelet, the amount of drug necessary to achieve half-maximum binding of antibodies to platelets ranged from 2 to 60 μM, and only one of the antibodies cross-reacted with the stereoisomer of the drug to which the patient was sensitized. Binding of the antibodies to platelets was enhanced at the highest achievable molar ratio of drug:antibody, 10,000:1, rather than being inhibited, as would be expected in a conventional, hapten-dependent reaction. The drug-antibody-platelet reaction was unaffected by Factor VIII/von Willebrand protein, nonspecifically aggregated IgG, or heat-labile complement components. After pretreatment with tritiated quinine, platelets retained several hundred thousand molecules of drug each, but failed to bind detectable amounts of antibody. However, platelets treated simultaneously with quinine-dependent antibody and tritiated quinine retained significantly more drug after repeated washes than platelets treated with drug and normal serum.
Douglas J. Christie, Richard H. Aster
To determine whether the antidiarrheal action of opiate drugs in humans is due to enhanced intestinal absorption rates, as suggested by recent experiments in animals, or is due to altered intestinal motility, as traditionally thought, we studied the effect of therapeutic doses of codeine on experimental diarrhea and on the rate of intestinal absorption of water and electrolytes in normal human subjects. Our results show that codeine (30-60 mg i.m.) markedly reduced stool volume during experimental diarrhea induced by rapid intragastric infusion of a balanced electrolyte solution. There was, however, no evidence that codeine stimulated the rate of intestinal absorption in the gut as a whole or in any segment of the gastrointestinal tract, either in the basal state or when absorption rates were reduced by intravenous infusion of vasoactive intestinal polypeptide. We also measured segmental transit times to determine whether and where codeine delayed the passage of fluid through the intestine. Codeine caused a marked slowing of fluid movement through the jejunum, but had no effect on the movement of fluid through the ileum or colon. In other studies, we found that the opiate antagonist naloxone did not significantly affect water or electrolyte absorption rates in the jejunum or ileum. We conclude (a) that therapeutic doses of codeine increase net intestinal absorption (and thereby reduce stool volume) by increasing the contact time of luminal fluid with mucosal cells, not by increasing the rate of absorption by the mucosal cells; and (b) that endogenous opiates do not regulate intestinal absorption in humans.
Lawrence R. Schiller, Glenn R. Davis, Carol A. Santa Ana, Stephen G. Morawski, John S. Fordtran
Experimental diabetes consistently reduces the concentration of free myo-inositol in peripheral nerve, which usually exceeds that of plasma by 90-100-fold. This phenomenon has been explicitly linked to the impairment of nerve conduction in the acutely diabetic streptozocin-treated rat. However, the mechanism by which acute experimental diabetes lowers nerve myo-inositol content and presumably alters nerve myo-inositol content and presumably alters nerve myo-inositol metabolism is unknown. Therefore, the effects of insulin and elevated medium glucose concentration of 2-[3H]myo-inositol uptake were studied in a metabolically-defined in vitro peripheral nerve tissue preparation derived from rabbit sciatic nerve, whose free myo-inositol content is reduced by experimental diabetes. The results demonstrate that myo-inositol uptake occurs by at least two distinct transport systems in the normal endoneurial preparation. A sodium- and energy-dependent saturable transport system is responsible for at least 94% of the measured uptake at medium myo-inositol concentrations approximating that present in plasma. This carrier-mediated transport system has a high affinity for myo-inositol (Kt = 63 microM), and is not influenced acutely by physiological concentrations of insulin; it is, however, inhibited by hyperglycemic concentrations of glucose added to the incubation medium in a primarily competitive fashion. Thus, competitive inhibition of peripheral nerve myo-inositol uptake by glucose may constitute a mechanism by which diabetes produces physiologically significant alterations in peripheral nerve myo-inositol metabolism.
D A Greene, S A Lattimer
In hereditary pyropoikilocytosis (HPP) the erythrocyte membrane skeleton exhibits mechanical instability that can be correlated to defective self-association of spectrin heterodimers. To detect structural changes in the functional domains of HPP spectrin we have examined the peptide pattern produced by limited tryptic digestion of spectrin extracts from two families that contain three HPP patients. Limited tryptic digestion of all three HPP patients revealed a similar and reproducible decrease in the staining intensity of an 80,000-, and 22,000-, and an 88,000-dalton polypeptide with a concomitant increase in a 74,000- and a 90,000-dalton polypeptide as compared with controls. Only changes in the 80,000-, and 74,000-, and 22,000-dalton polypeptides could be correlated to defective spectrin self-association and the amount of spectrin dimers in 0°C extracts of the HPP patients and their affected kindred. Similar results were obtained when the tryptic digests were analyzed by two-dimensional isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the affected 74,000- and 80,000-dalton polypeptides focusing into multiple spots ranging in isoelectric point from 5.3-5.4. When HPP spectrin dimers and tetramers were separated and subjected to trypsin digestion, changes in the 80,000-, 74,000-, and 22,000-dalton polypeptides were found predominantly in the spectrin dimer pool. Similar results were obtained for spectrin from two of the probands' mother, whom we have identified as an HPP carrier. We conclude that these HPP patients contain a population of normal, (principally tetrameric) and mutant (principally dimeric) spectrin. The latter is characterized by a defective spectrin dimer self-association due to conformational changes that affect the 80,000-dalton domain.
Jack Lawler, Shih-Chun Liu, Jiri Palek
To study the effect of insulin on leucine kinetics, three groups of conscious dogs were studied after an overnight fast (16-18 h). One, saline-infused group (n = 5), served as control. The other two groups were infused with somatostatin and constant replacement amount of glucagon; one group (n = 6) received no insulin replacement, to produce acute insulin deficiency, and the other (n = 6) was constantly replaced with 600 μU/kg per min insulin, to produce twice basal hyperinsulinemia. Hepatic and extrahepatic splanchnic (gut) balance of leucine and α-ketoisocaproate (KIC) were calculated using the arteriovenous difference technique. l,4,5,[3H]Leucine was used to measure the rates (micromoles per kilogram per minute) of appearance (Ra) and disappearance (Rd), and clearance (Cl) of plasma leucine (milliliters per kilogram per minute).
Naji N. Abumrad, L. S. Jefferson, S. R. Rannels, P. E. Williams, A. D. Cherrington, W. W. Lacy
Supernatants from mitogen- or antigen-stimulated human blood mononuclear cells enhanced the capacity of human monocytes or monocyte-derived macrophages (MDM) to release H2O2 or O2̇̄ in response to phorbol myristate acetate or zymosan. The stimulatory effect of lymphokines (LK) lasted ∼5 d, regardless of the time of their addition. However, the magnitude of stimulation depended on whether LK were added to freshly explanted monocytes or to MDM. When LK were added on day 0 of culture, they enhanced MDM H2O2-releasing capacity ∼40% measured on day 3, when H2O2-releasing capacity in the controls was maximal. Addition of LK on day 2 retarded the decline in H2O2-releasing capacity normally seen by day 5, so that LK-treated cells released about twice as much H2O2 as the controls. Addition of LK to MDM that had already lost most of their H2O2-releasing capacity (e.g., on day 4-6) restored it to an average of 60% of the values seen with freshly explanted monocytes. In this case, LK-treated cells were about 12 times more active than cells incubated in medium alone. The effects of LK were dose- and time-dependent, with maximal effects requiring 3 d of exposure. The specific activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and myeloperoxidase, and the specific content of glutathione were not diminished in LK-treated MDM, suggesting that increased synthesis of H2O2 rather than decreased catabolism probably explained the greater release of H2O2 from LK-treated cells. In contrast, release of H2O2 was suppressed 93±4% by exposing monocytes for 4 d to hydrocortisone (50%-inhibitory concentration, 1.9±0.3 × 10−7 M). Thus, the oxidative metabolism of human mononuclear phagocytes can be markedly modulated in vitro: augmented by mediators released from lymphocytes during an immune response, and suppressed by antiinflammatory corticosteroids.
Akira Nakagawara, Nancy M. Desantis, Nadia Nogueira, Carl F. Nathan
Polymorphonuclear leukocytes (PMN) aggregate and avidly attach to endothelium in response to chemotactic agents. This response may be related in part to the release of the specific granule constituent lactoferrin (LF). We found by using immunohistology and biochemical and biophysical techniques that LF binds to the membrane and alters the surface properties of the PMN. Upon exposure of PMN treated with 5 micrograms/ml cytochalasin B to 2 x 10(-7) M formyl-methionine-leucine-phenylalanine for 5 min, the PMN mobilized LF to their surface as observed by immunoperoxidase staining for LF. At added LF levels ranging from 4 to 15 micrograms/10(7) PMN there was a dose-dependent reduction in PMN surface charge reaching 4 mV, when the partitioning into the membrane of a charged amphipathic nitroxide spin label was measured by electron spin resonance spectroscopy, whereas transferrin was without effect. When 125I-FeLF was added to human PMN in increasing amounts and the results corrected for the residual amount of free LF contaminating the cells, the PMN were saturated with LF at concentrations between 100 and 200 nM in the medium. Human PMN bound 1.35 x 10(6) molecules per cell and the calculated value for the association constant for these receptors was 5.2 x 10(6) M-1. Additionally, 6 micrograms/ml LF served as an opsonin for rabbit MN to promote PMN uptake by rabbit macrophages, when assessed by electron microscopy, but lysozyme did not. These studies indicate that LF can bind to the surface of the PMN and reduce its surface charge. This correlates with enhanced "stickiness" leading to a variety of cell-cell interactions.
L A Boxer, R A Haak, H H Yang, J B Wolach, J A Whitcomb, C J Butterick, R L Baehner
Acetyl glyceryl ether phosphorylcholine (AGEPC) and leukotriene B4 (LTB4) induce concentration-dependent neutrophil aggregation. On a molar basis, LTB4 is approximately 10 to 100 times more potent than AGEPC. AGEPC-induced aggregation is attenuated by two inhibitors of arachidonate lipoxygenation, eicosatetraynoic acid and nordihydroguaiaretic acid, and to a lesser extent by the cyclooxygenase inhibitor, indomethacin. LTB4-induced aggregation is not readily reduced by the above inhibitors of arachidonic acid metabolism. Reverse phase high performance liquid chromatography, coupled with selective ion gas chromatography/mass spectrometry, shows that AGEPC stimulates neutrophils to synthesize sufficient LTB4 to account for the AGEPC response. In addition, the rate of LTB4 biosynthesis in response to AGEPC correlates well with the rate of AGEPC- and/or LTB4-induced neutrophils aggregation, and desensitization experiments indicate that AGEPC and LTB4 cross-desensitize. These data suggest that AGEPC-induced neutrophil aggregation may be mediated by LTB4.
A H Lin, D R Morton, R R Gorman
Human skin fibroblasts synthesize and accumulate glycosaminoglycans (GAG). Recently, we reported that fibroblasts incubated in thyroid hormone-deficient media accumulate more GAG than do cultures incubated in the same media enriched with 0.1 μM triiodothyronine (T3) (1981. Endocrinology. 108: 2397). The current study characterizes that enhanced accumulation. Confluent cultures were maintained in thyroid hormone-deficient media without or with added T3, labeled with [3H]acetate and analyzed for total [3H]GAG and [3H]hyaluronic acid content.
Terry J. Smith, Yoshiharu Murata, Allen L. Horwitz, Louis Philipson, Samuel Refetoff
Mean cell hemoglobin concentration (MCHC) is thought to have an important influence in sickle cell disease, both through the strong dependence of sickling rates on hemoglobin S concentration, and through the profoundly limiting effect of high MCHC on the rheologic competence of oxygenated, irreversibly sickled cells (ISC). Recent studies have tested the ability of antidiuretic hormone to reduce sickle cell MCHC by reducing plasma sodium (Na) and osmolality. An alternative means of reducing MCHC is to elevate intracellular cation content, rather than to depress extracellular cation concentration. In an effort to do this, we have treated sickle cells with Monensin, an antibiotic that selectively enhances membrane Na permeability. At submicromolar concentrations, Monensin substantially reduced the MCHC of whole sickle blood and isolated ISC, causing an improvement in cell deformability. Monensin's effectiveness in producing a controlled increase in erythrocyte water content suggests that agents that selectively increase membrane Na permeability could be therapeutically useful.
M R Clark, N Mohandas, S B Shohet
These studies were carried out to investigate the mechanism of neutralization of purified Epstein-Barr virus (EBV) by fresh human serum from normal individuals lacking antibody to the EBV viral capsid (VCA) and nuclear antigens (EBNA). Such individuals thus lack serological evidence of immunity to EBV. Although an enzyme-linked immunosorbent assay (ELISA) with highly purified immobilized EBV detected low levels of IgG antibody reactive with EBV in these normal nonimmune sera, this antibody failed to neutralize EBV in the absence of complement. Studies with depleted sera and mixtures of purified complement proteins at physiologic concentrations showed that the IgG antibody and C1, C4, C2, and C3 of the classical pathway were able to fully neutralize EBV. Mixtures of the purified components of the alternative pathway at physiologic concentrations failed to neutralize purified EBV in the presence or absence of the antibody and the alternative pathway did not potentiate classical pathway-mediated neutralization. No evidence for a requirement for C8 was obtained, precluding lysis as the mechanism of neutralization. Since C3 deposition on the viral surface accompanied classical pathway activation, viral neutralization is most likely secondary to the accumulation of complement protein on the viral surface. A coating of protein on the virus could interfere with attachment to, or penetration of potentially susceptible cells.
Glen R. Nemerow, Fred C. Jensen, Neil R. Cooper
Factor V must be converted to Factor Va in order to bind to a high affinity platelet surface site and participate in prothrombin activation. Osterud et al. (10) presented data that suggested that human platelets contain an activated form of Factor V and a Factor V activator. We find that the Factor V released when platelets are disrupted by freezing and thawing or sonication is activated 3- to 10-fold by thrombin as determined by coagulation assay and is therefore stored as the relatively inactive procofactor rather than in the active form Factor Va.
William H. Kane, Jozef S. Mruk, Philip W. Majerus
The neuronal biosynthesis of somatostatin-like immunoreactivity (SLI) was investigated using mechanically dispersed neonatal rat hypothalamic cells kept in culture for up to 6 wk. Immunohistochemically, SLI was specifically localized to a small subpopulation of parvicellular neurons and their cell processes. By radioimmunoassay the cellular SLI content declined steadily during the first 2 wk in culture (nadir value of 60 fmol/dish at day 15) but then increased progressively to reach a maximum value of 381 fmol/dish at day 46. Gel chromatographic analysis showed this immunoreactivity to consist of forms corresponding to tetradecapeptide somatostatin (S-14), somatostatin-28 (S-28), and a 15,000-mol-wt molecule. After incubation of the cells with [3H]phenylalanine, the cellular extracts, purified by adsorption to C18 silica, contained material that bound specifically to an immobilized antisomatostatin antibody. Analysis by gel chromatography and high performance liquid chromatography of the specifically bound label provided evidence for the presence of labeled S-14, S-28, and the 15,000-mol-wt molecule. Pulse-chase experiments (20-min pulse, 20-min chase) demonstrated a transfer of radioactivity from the 15,000-mol-wt form to material corresponding to S-14 as well as to S-28. These studies demonstrate that cultured hypothalamic neurons are capable of synthesizing three somatostatin-like peptides (15,000-mol-wt SLI, S-28, S-14), one of which (15,000-mol-wt SLI) serve as a biosynthetic precursor for both S-28 and S-14. This in vitro system should provide a powerful tool for further investigation of the biosynthesis and regulation of biosynthesis of somatostatin in the hypothalamus.
H H Zingg, Y C Patel
Recent studies have shown that ∼75% of the nuclear 3,5,3′-triiodothyronine (T3) present in adult rat cerebral cortex (Cx) derives from 5′-deiodination of thyroxine (T4) within this tissue. The activity of iodothyronine 5′-deiodinase (I 5′D), the enzyme catalyzing T4 to T3 conversion, increases rapidly after thyroidectomy, suggesting that this could be a compensatory response to hypothyroxinemia. To evaluate this possibility during the period of central nervous system maturation, we studied several thyroid hormone-responsive enzymes (aspartic transaminase [AT], succinic dehydrogenase [S.D.], and Na/K ATPase) in the Cx of 2-, 3-, and 4-wk-old rats. The rats were made congenitally hypothyroid by placing 1, 2, 5, and 20 mg methimazole (MMI) in 100 ml of the mothers' drinking water from day 16 of gestation throughout the nursing period and to the litters after weaning. In addition, serum thyroid hormones, I 5′D, and, in some experiments, in vivo T4 to T3 conversion in Cx were measured in the same pups. Serum T4 concentrations varied from <1 to 40 ng/ml and were generally inversely related to maternal MMI dose. Serum T3 was less affected by MMI than was T4. At 2 wk, decreases in AT, S.D., and ATPase were present in the 20-mg-MMI group but not in the 5-mg-MMI pups despite low serum T4 (<10 ng/ml) in the latter. At 3 and 4 wk, both 5- and 20-mg-MMI groups had significant reductions in these cortical enzymes despite a normal serum T3 in the 5-mg-MMI rats. Cortical I 5′D activity was 10-fold the control value in 5- and 20-mg-MMI animals at 2 wk but increased only three- to fivefold at 3 and 4 wk. I 5′D correlated inversely with serum T4 (r ≥ 0.96) at all ages, but the less marked elevation of this enzyme in 3- and 4-wk-old pups was not accompanied by an increase in serum T4. Serum T3 increased or remained the same between 2 and 3 wk. These results suggested that the 10-fold increase in I 5′D at 2 wk protected the 5-mg-MMI group from tissue hypothyroidism, but that the three- to fivefold increase at 3 and 4 wk could not. Injection of ∼250 ng T4/100 g body weight to 2-wk-old, 20-mg-MMI pups (one-sixth the normal T4 production rate) led to both a 1.8-ng/g cortical tissue increment in cortical T3 and a significant increase in AT at 24 h, compared with a 0.38-ng/g cortical tissue T3 increment and no change in AT in euthyroid controls. The larger increment in T3 of the 20-mg-MMI pups was due in great part to increased fractional T4 to T3 conversion. Although the latter resulted in greater serum T3 concentrations, three-fourths of the newly formed T3 in the cortex was generated in situ, and it was blocked by iopanoic acid as was the increase in AT. We conclude that 70-80% of the T3 in the Cx of the neonatal rat is produced locally. Serum T4 appears to serve both as a precursor for T3 and as a critical signal for increases in cortical I 5′D. The increased I 5′D can result in normal or near-normal cerebrocortical T3 concentrations despite marked reductions in serum T4. This mechanism seems to be particularly effective around 2 wk of age when many thyroid-hormone-dependent maturational changes occur in the rat Cx.
J. Enrique Silva, P. Reed Larsen
A variant of von Willebrand's disease has been identified in which sodium dodecyl sulfate agarose electrophoresis provides evidence that the von Willebrand factor present is structurally abnormal. Rather than the repeating triplet seen in normal subjects and in patients with the IIA and IIB variants, a repeating doublet was present in the propositus. None of the bands had the same mobility as bands in normal subjects or previously described von Willebrand's disease patients. The larger multimers of von Willebrand factor were lacking both from plasma and platelets, and did not appear in the circulation after infusion of 1-deamino-[8-D-arginine]-vasopressin. There was a marked increase in the concentration of the smallest multimer in the propositus and his phenotypically normal children, indicating that this abnormality of von Willebrand factor is inherited in an autosomal-recessive manner.
Z M Ruggeri, I M Nilsson, R Lombardi, L Holmberg, T S Zimmerman
Bile acids in the spent medium for the cell culture were analyzed by gas-liquid chromatography and gas-liquid chromatography-mass spectrometry to determine whether human hepatoblastoma cell line could synthesize bile acids. Cholic, chenodeoxycholic, and lithocolic acids were found in the culture medium, and a portion of chenodeoxycholic acid and all of lithocholic acid were sulfated. Since the cells had been cultured in serum-free medium, it is clear that the bile acids were newly synthesized and sulfated by the cultured cells. Chenodeoxycholic acid was the main bile acid in the medium, suggesting that the cell line might predominantly synthesize chenodeoxycholic acid. On the other hand, the cells had fetal or hepatoma characters such as marked alpha-fetoprotein production. These results suggest that fetal or hepatoma type bile acid metabolism might occur in the cell line, and that the established cell line could be an useful in vitro model for the study of bile acid metabolism in hepatoma.
Y Amuro, M Tanaka, K Higashino, E Hayashi, T Endo, S Kishimoto, H Nakabayashi, J Sato
We have studied the influence of verapamil hydrochloride on the in vitro and in vivo effects of daunorubicin in Ehrlich ascites carcinoma. Daunorubicin-sensitive tumor was rendered resistant to daunorubicin by the continuous treatment of sequential generations of tumor-bearing BALB/c mice. The ability of daunorubicin to inhibit [3H]uridine and [3H]thymidine incorporation and the effect of daunorubicin on the mean survival time of host animals bearing daunorubicin-sensitive and daunorubicin-resistant Ehrlich ascites carcinoma were compared. The addition of verapamil to daunorubicin in vitro reduced the concentration of daunorubicin required to inhibit 50% of DNA and RNA synthesis in the daunorubicin-resistant tumor to that required in the daunorubicin-sensitive tumor, from 6 and 4.4 μg/ml to 1.5 and 1.3 μg/ml, respectively. Verapamil also restored drug sensitivity to daunorubicin-resistant Ehrlich ascites carcinoma in vivo. The 21.7±0.7 d mean survival time (MST) of BALB/c mice bearing daunorubicin-resistant tumor treated with daunorubicin alone rose to 44.0±0.7 d when the same tumor was treated with verapamil and daunorubicin, P < 0.001. This in vivo effect is specific for daunorubicin-resistant Ehrlich ascites carcinoma, since there is no alteration in MST of BALB/c mice bearing daunorubicin-sensitive or daunorubicin-resistant tumor when they are treated with verapamil alone or when BALB/c mice bearing daunorubicin-sensitive tumor are treated with daunorubicin and verapamil.
Lewis M. Slater, Sandra L. Murray, Martha W. Wetzel, Ronald M. Wisdom, Emily M. Duvall