RE System Research Articles

Comparison of three RE agents—99mTc-phytate, 99mTc-sulfur colloid and 99mTc-Sb2S3 colloid in the rodent species

99mTc-phytate, 99mTc-sulfur colloid and 99mTc-antimony sulfide colloid are recognised as RE agents in clinical nuclear medicine. Since these three agents exist in vitro in different forms of particulate aggregation it was of interest to compare their properties and to evaluate the merits and limitations of each of these agents. A comparison was carried out in rats and rabbits as a prelude to a systematic study in human subjects. Quality tested radiopharmaceuticals were prepared and their pharmacokinetics studied in rats. The blood clearance, tissue distribution and scinti-imaging patterns of the RE system were also compared in rabbits. All the agents have excellent localizing properties in the liver but differ in varying extents in their disposition in other tissues. 99mTc-sulfur colloid has some predisposition for the lungs while 99mTc-phytate has a little propensity for the kidney and gut at late time periods. 99mTc-Sb2S3 colloid shows a more pronounced concentration in the bone-marrow, and displays intermediate properties between 99mTc-phytate and 99mTc-sulfur colloid, besides being the most stable (in vitro) radiopharmaceutical in this series of RE agents.

Improvement of iron removal from the reticuloendothelial system by liposome encapsulation of N,N′-bis[2-hydroxybenzyl]-ethylenediamine-N,N′-diacetic acid (HBED)

Abstract An iron chelator of low water solubility, HBED, has been encapsulated in the lipid bilayers of unilamellar and multilamellar liposomes. The effectiveness of liposome-encapsulated HBED for removing excess iron burden from the RE system of the mouse liver (i.e., Kupffer cells) has been compared to that of the most commonly used iron chelator, DF, a water-soluble drug. We report the following: (1) At a single dose of 25 mg/kg, HBED in liposomes is more effective in removing excess iron than free nonencapsulated HBED. (2) HBED is a more potent iron chelator than DF; after a single dose of 25 mg/kg, about 25% of the originally injected iron is excreted within 7 days from mice given HBED either in small unilamellar or in large multilamellar liposomes, whereas about 18% is excreted from mice given the same dose of liposome-encapsulated DF. (3) Although the iron burden is introduced into the Kupffer cells, liposome-encapsulated HBED promotes iron excretion mainly via the bile and feces, whereas liposome-encapsulated DF promotes iron excretion through the kidney. (4) Cell fractionation studies show that encapsulation of HBED in the lipid bilayers of liposomes does not alter the uptake pattern of liposomes by the Kupffer and parenchymal cells of the liver; in other words, Kupffer cells are more effective in taking up large-sized multilamellar liposomes while parenchymal cells take up small-sized unilamellar liposomes more effectively. (5) Electron microscopic studies demonstrate that the liver biliary canaliculi are enlarged and filled with vesicular materials in mice given liposome-encapsulated HBED and that this condition does not occur in control mice or mice given liposome-encapsulated DF. Our results have thus demonstrated that liposomes could be very useful as injection vehicles for metal chelators that are not readily soluble in water. HBED is also demonstrated to be far superior to DF, the iron chelator of choice for therapy of transfusional iron overload.

Mechanism of desferrioxamine-induced iron excretion in thalassaemia.

The mechanism of desferrioxamine (DF)‐induced iron excretion was investigated in 16 thalassaemic patients. Transferrin‐59Fe has been injected intravenously and the fraction of radioiron located to iron stores was determined as the difference between total injected 59Fe and % RBC utilization. Following the intravenous infusion of 4 g DF, the specific acitivity of excreted urinary iron has been measured in 11 patients and the total chelatable pool was calculated as (100–% RBC utilization)/specific activity of urinary iron. Despite the wide variation in DF induced urinary iron excretion, ranging from 3 to 86 mg/d, an unexpected uniformity in the specific activity of chelated urinary iron was found in all patients, and the calculated chelatable pool was 4.5±1.2 (mean±SD) g of iron. These findings suggested that iron chelated by DF was probably not obtained directly from the total storage iron pool but rather from a smaller high specific activity iron compartment derived from the catabolism of labelled non‐viable erythrocytes. This postulate was tested by the direct measurement of specific activities in the liver and spleen in five patients undergoing surgery. In all patients, the specific activity of splenic non‐haem iron representing RE iron stores (31±8%59Fe/gFe), was much higher than that of hepatic iron (2±1%), and the specific activity of iron excreted in the urine (30p8%) was identical with the specific activity of splenic iron. These findings indicate that DF‐induced urinary iron excretion is derived from a chelatable pool located in the RE system.

New kinetic role for serum ferritin in iron metabolism.

Summary. The role of the iron in serum ferritin was investigated with regard to iron kinetics. Serum (or plasma) was fractionated on a sucrose gradient by ultra‐centrifugation to separate iron in ferritin from other iron‐containing components in serum. After injection of heat‐treated [59Fe]RBC in rats, detectable labelling of the serum ferritin fraction was brief, between 20 and 40 min. The labelling of other iron components in the serum was maximal between 1 and 2 hr. No labelling of the serum ferritin fraction was detected after intravenous administration of [59Fe]‐transferrin in man and in the rat, or after [59Fe]haemoglobin‐haptoglobin or oral [59Fe2+]citrate in the rat. These results indicate that iron in serum ferritin originates in part from the degradation of haemoglobin in senescent red cells and that this labelled ferritin is cleared from the serum rapidly.In normal rats, [59Fe]ferritin, purified from rat liver and injected intravenously, disappeared from the serum at an exponential rate with a half‐disappearance time (HDT) of 4 min. After 1 hr 97% of the label had accumulated in the liver. After a delay of 24 hr, increasing amounts of label appeared in the RBC to an estimated maximum of 70–80% at 5 days. Conditions which increased or decreased rates of synthesis of haemoglobin altered the percentage of [59Fe]ferritin incorporated into haemoglobin, but these conditions did not change the rate of removal of [59Fe]ferritin from the serum by the liver. These results indicate that the iron in serum ferritin is cleared from the serum much more rapidly than transferrin‐bound iron. The data are consistent with the passage through serum ferritin of a major portion of the iron that is released from the degradation of red cell haemoglobin in the RE system.

Response of the opsonic and phagocytic system to trauma in adrenalectomized animals.

SummaryAdrenalectomy and sham-adren-alectomy resulted in a significant stimulation of the reticuloendothelial system (RES) at the 24 hr postoperative period. This response was primarily reflected in an enhanced vascular clearance of test colloids and an associated hepatic hyperphagocytosis. The physiological factor apparently mediating this response was the presence of a “hyperopsonemia” with an associated alteration of Kupffer cell function mediated at the cellular level in the adrenalectomized animals. Evaluation of the physiologic response of both the opsonic system and RE system to surgical trauma in the bilaterally adrenalectomized rats revealed that the “hypoopsonemia” and RE failure response during the early posttrauma interval (60 min) was not dependent on the presence of the adrenal glands. However, the data does support the concept that the opsonic or humoral deficit is related to the posttrauma RE depression. It is suggested that the hyperfunctional state of the hepatic RE system resulting from...

Experimental infection with Plasmodium falciparum in Aotus monkeys. II. Observations on host pathology.

Organs from more than 43 Aotus monkeys inoculated with 1 × 104 or 1 × 108 erythrocytes infected with chimpanzee-derived Plasmodium falciparum (Camp strain) and from 9 control monkeys injected with saline were studied by histologic and histochemical methods. Parasitemia at the time of death varied from 5% to 74%. Pathologic changes observed in various organs of the infected monkeys were generally mild and nonspecific. Most conspicuous were RBC's parasitized with late stages of Plasmodia which tended to marginate on the walls of blood vessels or to form aggregates packing, at times, the capillaries of deep organs. No intravascular thrombi were demonstrable and no tissue lesions accompanied capillary packing. Characteristic of the malaria-infected Aotus was the generally moderate response of the RE system; specifically, stimulated Kupffer's cells and swollen pulmonary endothelial cells were not very numerous. Likewise, the spleen, while enlarged, still maintained the normal structure of the red pulp. However, malpighian follicles showed marked hyperplasia and marked proliferation of immunoblasts. Otherwise, organ involvement, such as cerebral hemorrhages or glial scars, ruptured spleen, hemoglobinuric nephrosis, etc., was not observed. It is suspected that death was due to hypovolemia and shock.

Utilization of in vivo liver perfusion to prevent pulmonary damage following regional ischemia

A 4-hour period of extremity ischemia in dogs produces intravascular coagulation and results in 50 per cent mortality at 24 hours. Hemorrhagic atelectasis of the lungs is produced, and microemboli can be identified within the pulmonary arterioles. Portacaval transposition followed by the regional ischemia preparation results in no gross or microscopic abnormality in the lungs or liver, although there is a significant elevation of SGOT values. The mortality of the combined procedure is 7 per cent. The importance of the RE system to recovery from shock is emphasized.

The hepatic response to endotoxin shock; Hemodynamic and enzymatic observations

In order to evaluate the role of the liver in endotoxin shock, purified endotoxin was injected into the portal vein or into the systemic circulation in dogs. Systemic administration of endotoxin produces a more severe hypotension than does injection into the portal vein, which suggests that endotoxin may be removed from the circulation and detoxified by the hepatic RE system. When the liver was excluded from the circulation, profound hypoglycemia followed administration of endotoxin and death soon occurred. Circulating SGOT, SGPT, and alkaline phosphatase levels increased greatly after administration of endotoxin in dogs with normal hepatic circulation, but the blood LDH levels were higher in dogs in which the hepatic inflow was excluded, which suggests an extrahepatic origin of the LDH isoenzymes. Although the present studies suggest that the liver exerts a protective effect during the initial phase of endotoxin shock, it is believed that with progression of shock the liver deteriorates and hepatic intracellular metabolites may be released into the circulation to accelerate the irreversibility of shock.

Calculated Beam-Loading Effects in the NAL Main-Ring RF System

The synchronous transfer of beam from the booster into the NAL main ring results in a partial turn of beam circulating in the main ring. This situation presents large step changes in beam-loading to the main-ring RF system which must be handled by the cavity-regulation loops. The behavior of the main-ring RF system under these conditions has been studied with the aid of the IBM S/360 Continuous System Modeling Program (CSMP). The CSMP provides an analysis of system behavior starting from a system block diagram and a description of the driving functions. This paper describes the RE system under study and the response predicted by the program to a variety of beam-loading conditions.

Differential recognition of Brucella organisms by Kupffer cells: studies with isolated perfused liver.

SummaryStriking differences in capacity of the Kupffer cells of the isolated perfused rat liver to recognize and clear B. abortus on the one hand and B. melitensis and S. typhosa on the other have been demonstrated. B. abortus organisms not removed from the perfusate in absence of antibody are promptly engulfed in the presence of antibodies. It is suggested from in vivo experiments involving clearance and distribution of tagged bacteria that striking compartmentalization exists in the RE system.

A further note on the mechanism of action of endotoxin.

Death from endotoxin is the result of injury to vascular muscle, which leads to a progressive decline in venous return, and consequently to a fall in cardiac output that is incompatible with survival (1). In a previous communication evidence was given that the injury to vascular muscle by endotoxin is inflicted indirectly, i.e., by virture of its neurotoxic action, and not because of any direct action upon this muscle(2). The experimental data in support of this view are: (a) the severity and lethality of peripheral vascular collapse produced by 2000 gamma of an endotoxin given intravenously is equalled by that following 100 gamma injected subdurally(3), and by that following one or two gamma of endotoxin placed in direct contact with the coeliac ganglion (4,5); (b) in an animal dead from endotoxic shock the tissues of a denervated area including vascular muscle are free of the injuries that are present in a corresponding area that is not denervated. Thus, prophylactic denervation of the splanchnic viscera by coeliac blockade prevents hemorrhagic necrosis of the intestinal mucosa except in the distal half of the colon(6). Coeliac blockade also prevents death from a lethal dose of endotoxin. This is because the elimination of vasoconstriction in this area not only preserves the integrity of the liver and spleen, but allows better access for the clearance and detoxification of circulating endotoxin by the RE system in these tissues. The foregoing evidence for the neurotoxic hypothesis notwithstanding, one can expect considerable hesitation in accepting it because of other potentially lethal effects on the vascular system that might be the result of direct action of the endotoxin (e.g., myo-cardial necrosis, degeneration of intima, capillary rupture, changes in platelets, leukocytes, titer of circulating plasminogen and fibrino-gen) and that might also be prevented by preserving liver function.

The Emily Cooley Lecture. Etiology and Pathogenesis of Acquired Hemolytic Anemia

The demonstration of recurrent lymphadenitis attributable to CMV during periods of hemolysis in a patient with chronic acquired hemolytic anemia of autoimmune type, led to the investigation of the possible etiologic relationship between this virus and acquired hemolytic anemia. In children a frequent association was demonstrated. Previously unrecognized clinical manifestations attributable to CMV were frequently observed. In this age group lymphadenopathy was a prominent finding in the majority of the cases and appeared to correspond to periods of rapid virus multiplication. It was noted that the predominant cellular lesion was not the well known pathognomonic large inclusion‐bearing cell which is a comparatively rare end state in the cellular response to the virus but less fully developed cellular lesions representing early and intermediate states. Recognition of these lesions permitted a rough appraisal of the extent of viral activity and showed that the latter generally correlated well with the hemolytic process.A basis for active infection by an ordinarily occult virus was sought and frequently found in an apparent impairment of the normal immune mechanism expressed clinically by extreme susceptibility to intercurrent infections and frequently associated with organic defects conducive to such a state. In young infants age‐determined susceptibility alone seemed to explain the lack of resistance to the occult viral agent.The findings led to the following interrelated hypotheses:1. The presence of CMV in AHA is not fortuitous or coincidental but reflects a (not necessarily exclusive) etiologic relationship.2. Acute, intermittent, or chronic hemolysis in AHA is related to primary or reactivated latent infection with CMV or other occult viruses in individuals susceptible by virtue of physiologically or pathologically impaired immunity, the cause of which is apparent in symptomatic forms but not as yet in the idiopathic type.3. The pathogenesis of AHA involves viremia or the presence of noninfective viral particles or products in the circulation. Infection within the RE system as opposed to sites less accessible to the circulation, such as epithelium, permits their discharge into the blood stream and determines hemolysis.4. The demonstration of the same agent in autoimmune and non‐autoantibody AHA suggests a unified concept of pathogenesis in which erythrocyte autoantibodies represent a variable secondary response to heterogenetic stimuli of viral origin.5. In the light of this theory the role of autoantibodies in autoimmune AHA is likely to be at most contributory, as also indicated by the frequent dissociation of hemolysis and antiglobulin reaction, and earlier data bearing on this question need to be reevaluated.

Evidence for a lethal endotoxemia as the fundamental feature of irreversibility in three types of traumatic shock.

The data here reported (Table I) show that a toxin is present in the blood of animals with two types of irreversible hypovolemic shock. These data also show that although blood volume therapy does not correct the hypovolemia because of continuing loss of plasma at the site of injury, the major factor in the progressive decline and death is the endotoxemia rather than the hypovolemia. This is also true of severe and prolonged hemorrhagic shock that is irreversible to transfusion. The data also show that even when there is bacterial activity at the site of injury, the pool of endotoxin in the intestine is the chief source of the circulating endotoxin. In all three types of shock, the endotoxemia develops because persisting hypovolemic shock renders the RE system unable to destroy the endotoxin. The demonstration of an endotoxemia as the cause of irreversibility and death in three types of traumatic shock caused by three different agents suggests that a single pathophysiological mechanism accounts for the phenomenon of irreversibility in all types of traumatic shock.

A Study of Skin Homografting in Patients with Lymphomas

Abstract Skin homografts were performed on seven patients with lymphomas, three patients with miscellaneous conditions affecting their RE system and four control patients. The ability to reject skin homograft was impaired in most of the patients with lymphomas, in a patient with bronchogenic carcinoma who had received extensive treatment, and in a patient with multiple myeloma. The presence of normal amounts of gamma globulin and normal response to typhoid antigen did not necessarily indicate a normal response to skin homografts. If marrow homotransplants or other organ homotransplants become a form of therapy in patients with lymphomas, the result of skin grafts from the same donor may be of interest. Our study supports the previous impressions of the immunologic handicaps in patients with lymphomas.

Reticulo-endothelial blockade and capillary resistance response to cortisone and STH.

SummaryIt is shown that blocking the RE system with India ink diminishes or abolishes capillary resistance response to cortisone and STH. That large doses of cortisone can overcome the block suggests that the RE system functions by increasing sensitivity of tissues to cortisone.