The effect of endogenous pyrogen on the plasma zinc concentration of the rat

Separate mechanisms inside and outside the blood-brain barrier inducing metabolic changes in febrile rabbits

1. We investigated the acute phase response induced by either intravenous (I.V.) or intracerebroventricular injections of bacterial endotoxin or endogenous pyrogen. These caused either monophasic or biphasic fever, and the response includes changes in plasma concentration of iron, zinc, copper, fibrinogen and in circulating leucocyte count.2. The I.V. injection of a small dose of endotoxin or endogenous pyrogen produced a monophasic fever, while a large dose produced a biphasic fever. The ventricular injection of endogenous pyrogen produced a fever similar to the second phase of the biphasic fever.3. The I.V. injection of a small dose of endotoxin or endogenous pyrogen produced a low plasma zinc 8 h after injection, while the ventricular injection of endogenous pyrogen produced a low plasma zinc 24 h after injection. The I.V. injection of a large dose of endotoxin or endogenous pyrogen induced a low plasma zinc 8 and 24 h after injection, suggesting that the hypozincaemia induced by the large dose was mediated by both peripheral and central action of endogenous pyrogen with different time courses.4. The I.V. injection of the small dose did not affect the level of the plasma copper concentration but the I.V. injection of the large dose and the ventricular injection increased it 24 h after injection. It is considered that the plasma copper concentration is mainly controlled by the central action of endogenous pyrogen.5. The changes in the plasma iron and fibrinogen concentration and the circulating white blood cell count induced by the different doses and by the different routes showed very similar patterns, indicating that these are simultaneously controlled by both peripheral and central actions of endogenous pyrogen.6. The present results show that there are two separate mechanisms involved in the acute phase response, one inside and one outside the blood-brain barrier. From the consideration that endogenous pyrogen released from the phagocytic leucocytes induces fever and acute phase response by its action on both the peripheral target organs and the central nervous system, it is suggested that endogenous pyrogen acts both centrally and peripherally, in the same manner as other hormonal agents such as corticosteroids.

In vitro bone resorption is dependent on physiological concentrations of zinc

The addition of physiological concentrations of zinc (25-200 (microg/dL) to Dulbecco's Modified Eagle's Medium containing tibiae from 19-d chick embryos resulted in a concentration-dependent increase in tibial content of tartrate-resistant acid phosphatase (TRAP) and an increase in bone resorption, as measured by tibial calcium release. This increase in bone resorption was additive to the resorptive effect resulting from the addition of 10(-9)-10(-7) M parathyroid hormone (PTH), but was not additive to similar effects produced by the addition of 10(-9)-10(-7) M prostaglandin E2 (PGE2). An inhibitor of prostaglandin synthesis, flurbiprofen (10[-6] M), did not influence the effect of zinc on bone resorption. However, the addition of 2,6-pyridinedicarboxylic acid (10[-3] M, 2,6-PDCA), a chelator of zinc, did attenuate the effects of zinc, as did the addition of an inhibitor of DNA replication (hydroxyurea, 10[-3] M). Hydroxyurea also attenuated the bone resorptive response to PGE2, but had no influence on the effects of PTH. These results indicate that physiological concentrations of zinc alter bone resorptive rates in vitro by a mechanism that is dependent on DNA replication.

Effects of repetitive immunogen injections and fasting versus feeding on iron, zinc, and copper metabolism in chicks

Most investigations on the effect of immunogenic challenge on trace-mineral metabolism use a single immunogen injection in fasted animals. Because these investigations are not representative of realistic situations in which animals are constantly exposed to immunogens and still consume feed, the following studies were done. In Expt. 1, chicks were injected ip with sheep red blood cells (SRBC), Sephadex, SRBC+Sephadex, or saline. Chicks were then fasted or fed equal amounts of feed (equal fed) for 16 h. Immunogen injection decreased serum Fe and Zn and increased serum Cu within each feeding program. Differences in Cu, and to a lesser extent Zn, concentrations between immunogen- and saline-injected chicks were more pronounced in fasted than in equal-fed chicks. In Expt. 2, equalfed chicks were injected ip every 48 h for 6 d with SRBC+Sephadex or saline. Two days after each injection, tissues were taken. An additional group of chicks was injected once and subsequently fasted 16 h, whereupon tissues were taken. Changes in plasma Fe, Zn, Cu, and ceruloplasmin; hepatic Fe, Zn, Cu, and metallothionein; pancreatic Fe and Zn; and splenic Fe in repetitively injected chicks were different from changes observed in chicks injected once. The results indicate that the trace-mineral response to immunogenic challenge is dependent upon the number of immunogen injections and the nutritional state of the animal.

Serum zinc and copper levels in children with meningococcal disease

Mean serum zinc and copper levels were depressed in 94 children aged 1 month to 9 years who presented with meningococcal disease. The mean serum zinc level was 44 micrograms/dl (reference value 78 micrograms/dl, SD 18) and the mean serum copper level 157 micrograms/dl (reference value 159 micrograms/dl, SD 27). Nineteen patients had serum zinc levels less than 25 micrograms/dl and ten patients had serum copper levels less than 101 micrograms/dl. Serum zinc levels were significantly lower in patients who were septicaemic or in whom manifestations of severe disease such as shock, more than 20 petechiae, ecchymoses and evidence of disseminated intravascular coagulation occurred compared to those without these features. Serum copper concentrations were higher than reference levels in patients with meningitis and in less severely ill patients. Copper levels were significantly lower in patients with septicaemia, severe disease, shock, more than 20 petechiae, ecchymoses, disseminated intravascular coagulation, leucopenia and patients who died compared with patients without these features.

Inflammation triggers hypoferremia and de novo synthesis of serum transferrin and ceruloplasmin in mice

Oil of turpentine was used to induce an artificial inflammation so that we could study its effect on iron metabolism and on synthesis of serum transferrin and ceruloplasmin in mice. It was found that turpentine-induced inflammation triggered the establishment of a hypoferremic state characterized by low levels of serum iron, followed by recovery and a gradual return to normal plasma iron levels. This turpentine-induced hypoferremia and its subsequent recovery paralleled the hypoferremia obtained during meningococcal infection. Moreover, serum transferrin and ceruloplasmin activity levels increased drastically during the recovery from hypoferremia. [14C]leucine incorporation studies revealed a de novo synthesis of both transferrin and ceruloplasmin. Turpentine-induced hypoferremia was also found to provide a protective effect against meningococcal infection which could be partially reversed by exogenous iron. The results of this study suggest that transferrin and ceruloplasmin may be synthesized partly in response to the altered iron metabolism observed during hypoferremia.

Differential acute-phase responses in febrile and cold- and heat-exposed rabbits

Endotoxin (LPS) characteristically provokes both fever and the acute-phase reaction (APR). The present studies were undertaken to determine whether these two responses are mutually dependent or controlled separately. Rabbits were injected with LPS (2 micrograms/kg, IV) or exposed to heat (37 +/- 1 degree C) such that the patterns and magnitudes of the body temperature (Tco) rises (1.6 +/- 0.5 degrees C) were similar. While the plasma levels of Fe and Zn decreased, and those of Cu and N-acetylneuraminic acid (NANA) increased significantly after LPS-induced fever, no such changes occurred after heat-induced hyperthermia. In subsequent study, different rabbits were exposed to cold (3 +/- 1 degree C), first furred, then sheared. While furred, they thermoregulated by cutaneous vasoconstriction, whereas, while shaved, they additionally increased their metabolic rates. However, in neither case were the plasma levels of Fe, Zn, Cu, or NANA different in comparison to their pre-cooling values (Ta = 22 +/- 1 degree C). It would seem, therefore, that the acute-phase blood responses to LPS (and ultimately, to endogenous pyrogen [EP]) probably are not mediated merely by the rise in the Tco or by the concomitantly induced vascular and/or thermogenic effectors of fever; but rather, the APR appears to be a regulated, separate response to LPS/EP.

Mechanism of impaired iron release by the reticuloendothelial system during the hypoferremic phase of experimental Neisseria meningitidis infection in mice

Hypoferremia, the reduction of plasma transferrin iron levels during infection, has been shown to control Neisseria meningitidis infection in mice. The exact nature of the mechanism that regulates this response has been obscure. We have previously shown that hypoferremia does not result from an accelerated removal of iron from the plasma transferrin pool. In this study, we have examined the processing of iron by the reticuloendothelial system during infection. Normal and hypoferremic meningococcus-infected mice were injected with 59Fe-labeled erythrocytes. Kinetics of uptake and redistribution of the label indicated that during the hypoferremic phase of the infection, reticuloendothelial system-processed iron was not returned to the plasma transferrin pool. Fractionation of hepatic cellular compartments showed that this impaired release of iron resulted from a preferential incorporation of heme-derived iron into the intracellular ferritin pool during the hypoferremic phase of the infection. These findings indicate that this withholding of iron within the intracellular pool leads to hypoferremia and therefore denies the extracellular pathogen its essential iron.

In vitro leukocyte endogenous mediator production is not impaired following surgical stress in moderately malnourished patients

Leukocyte endogenous mediator (LEM), a protein produced by phagocytizing cells, plays a critical role in the metabolic response to injury and infection. There is an important interaction between protein-calorie malnutrition and the capacity of cells to produce LEM, since severely malnourished or severely stressed individuals, have a reduced capacity to produce LEM. The leukocytes of 10 mildly to moderately malnourished patients undergoing elective major surgery, a moderate stress, had an intact ability to produce LEM on preoperative assessment. This ability was not affected by a 5-day postoperative period of hypocaloric nutrient intake despite a significant loss of body protein in one-half of the patients and a significant fall in serum protein concentrations. These results suggest a high biologic priority for LEM production during the metabolic response to injury and for infection.

Plasma zinc in psoriasis: relation to surface area involvement

Plasma zinc, serum albumin and alkaline phosphatase (a zinc-dependent enzyme) were measured in thirty-five psoriatics and their age- and sex-matched controls. No significant difference was seen between these two groups as a whole, but psoriatics with less than 10% surface involvement had significantly higher mean plasma zinc levels than their respective control group. Psoriatic patients also showed a relationship between the extent of surface involvement and the plasma zinc level, those with more extensive involvement having lower levels than those with minimal involvement. The differences were not due to disturbances in serum albumin, and no abnormalities in serum alkaline phosphatase were observed.

Leukocytic pyrogen: a major mediator of the acute phase reaction

The acute phase reaction is initiated and regulated by leukocytic pyrogen which is released by activated host phagocytes at inflammatory sites during inflammatory reactions of any etiology. The physiological alterations which follow include, in addition to the characteristic acute phase protein changes, fever, granulocytosis, fall in serum iron and zinc, metabolic stimulation of blood granulocytes, activation of T-cell function and doubtless other effects as yet unrecognized. These responses are mediated by free or by protein-bound LP molecules and reflect both direct receptor coupled effects and more indirect mechanisms such as release of secondary mediators from cells or body fluids and involvement of neural or neurohumoral pathways. This unitarian hypothesis implies a functional interrelationship between the component parts, and allows a model for critical examination and new hypothesis testing. The wider availability of pure preparations of LP and of possible subtypes of LP and of a sensitive immunoassay would help us to prove or to expand this hypothesis and to advance our understanding of this important phase of acute inflammation. Earlier in this conference we heard that the mediator derepresses a message: I'd like to put forward the idea that in the acute phase reaction the mediator is the message.

An in vitro bioassay for leukocytic endogenous mediator(s) using cultured rat hepatocytes

Primary cultures of adult rat hepatocytes were used to assay for the presence of leukocytic mediator(s) (LEM), a neutrophil derived protein(s) capable of stimulating the synthesis of acute-phase plasma proteins when injected into rats. In the presence of physiological concentrations of dexamethasone (40 mM), the hepatocytes secreted a variety of plasma proteins as demonstrated by crossed immunoelectrophoresis. The addition of LEM to hepatocytes increased the secretion of several acute-phase related plasma proteins, including fibrinogen and hepatoglobin, and decreased albumin secretion. These results mimic the acute-phase response observed in the intact animal. Fibrinogen secretion was used as a quantitative marker for determining LEM activity. The rate of fibrinogen secretion depended upon both the concentration of dexamethasone and LEM present during a given 24-h assay period. One unit of LEM activity is defined as that concentration of LEM capable of producing a 50% maximal stimulation of fibrinogen secretion.

Role of the central nervous system in acute-phase responses to leukocytic pyrogen

Intracerebroventricular injection of rabbit leukocytic pyrogen (LP) into conscious, healthy cannulated rabbits produced markedly enhanced febrile and acute-phase responses as compared with equivalent-dose, single bolus intravenous injection. The increased effectiveness in inducing granulocytosis and hypoferremia on intracerebroventricular injection was matched by changing the method of administration of intravenous LP from a single initial bolus to multiple fractional doses over a 2-h period. This suggested that augmentation for these parameters may have reflected only a "reservoir" function of the cerebral ventricles which prevented rapid clearance of LP from the blood. The ability of LP to induce hepatic synthesis of haptoglobin and C-reactive protein was so markedly enhanced by intracerebroventricular injection, however, that a role of the central nervous system in mediating or in modifying in an important way a non-neural mechanism for this mediation must be postulated.

Further similarities of endogenous pyrogen and leukocytic endogenous mediator

The release of endogenous pyrogen (EP) from rabbit peritoneal granulocytes was measured with a three-point log dose-response curve. Release of EP was inhibited when the cells were incubated in media containing potassium or calcium. Measurements of leukocytic endogenous mediator (LEM) activity, i.e., lowering of plasma iron and zinc and increases in blood neutrophils, were made on the same supernatant media. When EP release was inhibited there was a similar inhibition of LEM activity. These results indicate a similarity between the release of pyrogenic and LEM activities. Together with previous purification studies, the results suggest that EP and LEM are similar and may be identical factors.

In vitro and in vivo actions of zinc ion affecting cellular substances which influence host metabolic responses to inflammation

Glycogen-stimulated rabbit peritoneal exudate cells (polymorphonuclear leukocytes, PMN) produce prostaglandins (PG) and substances which induce alterations (mediators) in experimental animals characteristic of host metabolic responses to infection and other acute inflammatory stresses. The effect of Zn2+ on mediator production and PG synthesis was examined because: Zn homeostasis is perturbed during infection, Zn is known to regulate some cellular functions, and there appears to be an interrelationship between PG synthesis and mediator production. Using exudate cells, 2 mM Zn2+ caused complete inhibition of in vitro PG synthesis as assessed by conversion of [1-14C] arachidonic acid into PG. This concentration of Zn2+ also inhibited production of substances mediating plasma Zn depression, hepatic amino acid "uptake", fever, and neutrophil release from bone marrow. Conversely, Zn2+ did not inhibit in vivo metabolic responses to these mediators. Zn-pretreatment of rabbits or simultaneous injection of Zn2+ and crude PMN-derived pyrogenic activity resulted in prolongation of fever. It is suggested that this action of Zn2+ may be attributed to either stabilization of cyclic AMP through inhibition of phosphodiesterase or a Zn-mediator interaction which stabilizes crude endogenous pyrogen. The potential physiological significance of these results includes: possible potentiation of the host's defense mechanisms by Zn2+ and its utilization for prolongation of fever to determine its effect on potentially temperature-dependent host defense mechanisms.

Biological function of metallothionein. V. Its induction in rats by various stresses

Induction of metallothionein (a Zn-binding protein) was investigated in liver and kidneys of rats under the following stresses: cold environment, hot environment, heat burn, strenuous exercise, and CCl4 intoxication. As markers of metallothionein (MT) synthesis, [14C]cystine and 65Zn were injected parenterally into rats, and MT in liver and kidney supernatants was separated on Sephadex G-75 columns. Among stresses tested, the greatest stimulations of MT synthesis in liver were observed under cold (315%), strenuous exercise (302%), and CCl4 intoxication (543%), as evidenced by increased amount of [14C]cystine and 65Zn incorporation into the MT fraction. In contrast to liver, only small responses were observed in MT synthesis in kidneys. There was a general decline in plasma Zn levels in rats under the stresses employed. However, no great differences were observed in Zn levels in whole liver and kidneys. The present study suggests that various unrelated physiological stresses, which are accompanied with a change in Zn distribution, increase the synthesis of MT in liver of rats.

Differentiation between endogenous pyrogen and leukocytic endogenous mediator

The crude material released from glycogen-stimulated rabbit peritoneal polymorphonuclear leukocytes when administered to experimental animals elicits a number of metabolic and physiologic alterations characteristic of those observed in the host inflammatory response. Classically, the mediator of febrile response observed in rabbits and other species has been termed endogenous pyrogen (EP), whereas leukocytic endogenous mediator (LEM) has been used as a general term to denote the substance(s) mediating multiple inflammatory responses observed in rats. The latter substance, however, has not been previously demonstrated to differ from EP. This report presents evidence indicating that EP and LEM are different molecular species. Evidence supporting the differentiation between these entities includes: physical separation of EP from one or more mediators that induce metabolic alterations attributed to LEM; production of LEM activities by stimulated polymorphonuclear leukocytes in the absence of detectable pyrogenic activity; and differences in the release of EP and LEM from stimulated rabbit granulocytes in the presence of potassium ion.

Possible relation of prostaglandins to PMN-derived mediators of host metabolic responses to inflammation

Stimulated rabbit peritoneal polymorphonuclear leukocyte (PMN) preparations simultaneously produce prostaglandin-like material and mediators that induce metabolic alterations in experimental animals characteristic of the host's responses to inflammation. The alterations observed in rats include responses by: proteins, carbohydrates, hormones, trace metals, and total blood neutrophils. This study demonstrates a possible relationship between prostaglandins and PMN-derived substances that mediate plasma zinc depression, hepatic amino acid uptake, and increased numbers of blood neutrophils. Production of these mediators by stimulated-PMN preparations was prevented by 23 muM indomethacin or 93 muM aspirin. Conversely, morphine (2 mM or less) had no detrimental effect on production of these mediators, although, it consistently stimulated production of a substance stimulating total blood neutrophia. In addition, 2 muM prostaglandin E and F stimulated production of substances mediating hepatic amino acid uptake plasma zinc depression, respectively. At this concentration, neither prostaglandin significantly altered production of substances mediating increased numbers of total blood neutrophils. A partial-nitrogen atmosphere, dibutyryl cyclic analogs of AMP and GMP, or homogenization of the PMN had no effect on mediator production. The inhibitory effect of indomethacin and aspirin also was observed with PMN-homogenastes. These experimental observations suggest that prostaglandin synthesis has a function in production of mediators by stimulated-PMN preparations.