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Endocrinology Vol. 144, No. 12 5365-5371
Copyright © 2003 by The Endocrine Society

Alterations of Plasma Ghrelin Levels in Rats with Lipopolysaccharide-Induced Wasting Syndrome and Effects of Ghrelin Treatment on the Syndrome

Yuji Hataya, Takashi Akamizu, Hiroshi Hosoda, Naotetsu Kanamoto, Kenji Moriyama, Kenji Kangawa, Kazuhiko Takaya and Kazuwa Nakao

Department of Medicine and Clinical Science, Kyoto University Graduate School of Medicine (Y.H., N.K., K.M., K.N.), Kyoto 606-8507, Japan; Translational Research Center (T.A., H.H., K.K.), Kyoto University Hospital, Kyoto 606-8507, Japan; and Department of Biochemistry, National Cardiovascular Center Research Institute (H.H., K.K.), Osaka 565-8565, Japan

Address all correspondence and requests for reprints to: Dr. Takashi Akamizu, Translational Research Center, Kyoto University Hospital, 54 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan. E-mail: akataka{at}kuhp.kyoto-u.ac.jp.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Ghrelin not only strongly stimulates GH secretion, but is also involved in energy homeostasis by stimulating food intake and promoting adiposity through a GH-independent mechanism. These effects of ghrelin may play an important role in the pathophysiology of inflammatory wasting syndrome, in which both the somatotropic axis and energy balance are altered. In this study we investigated plasma ghrelin concentrations after lipopolysaccharide (LPS) administration to rats, a model of the wasting syndrome and critical illness. In addition, the therapeutic potential of the antiwasting effects of ghrelin was explored using LPS-injected rats. A single LPS injection suppressed plasma ghrelin levels 6 and 12 h later. Maximal reduction was observed 12 h after LPS injection, in a dose-dependent manner. In contrast, plasma ghrelin levels were elevated after repeated LPS injections on d 2 and 5. Peripheral administration of ghrelin twice daily (10 nmol/rat) for 5 d increased body weight gain in repeated LPS-injected rats. Furthermore, both adipose tissue weight and plasma leptin concentrations were increased after ghrelin administration in these rats. In conclusion, plasma ghrelin levels are altered in LPS-injected rats, and ghrelin treatment may provide a new therapeutic approach to the wasting syndrome and critical illness.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
WASTING SYNDROME may be defined as a severe state of malnutrition, weight loss, muscle atrophy, and anemia. This condition is characterized by continued protein loss from vital organs and tissues due to both activated degradation and suppressed synthesis, and it contributes to increased mortality, accelerated disease progression, and impaired strength and functional status (1, 2). GH is an anabolic hormone, sparing protein stores at the expense of fat in situations of caloric restriction. GH stimulates the synthesis and secretion of IGF-I from various tissues (3), and many GH effects are mediated by IGF-I (4). In addition to its use for treatment of short-statured children with impaired production or complete lack of GH and of GH deficiency in adults, GH has been used to improve protein metabolism in critical illness (5). However, recent large, multicenter-randomized, placebo-controlled clinical trials in critically ill adults have shown significant increases in morbidity and mortality with GH treatment (6). Therefore, the effects of GH treatment are controversial.

Ghrelin is the natural ligand of the GH secretagogue receptor and strongly stimulates GH secretion (7, 8, 9). In addition to this action, recent studies in rodents suggest that ghrelin is involved in energy homeostasis, acting as a peripheral signal stimulating food intake and promoting adiposity through a GH-independent mechanism (10, 11). GH-releasing peptide-2 was reported to be effective in improving alterations in the somatotropic axis and protein catabolism in patients with prolonged severe illness, and the nonpeptidyl GH-releasing peptide mimetic, MK-0677, reverses diet-induced catabolism (12, 13). Furthermore, peripheral administration of ghrelin attenuated body weight loss in a rat model of cachexia with chronic heart failure (14), in mice given IL-1ß (15) and in a rat model of cancer cachexia (16). These findings suggest that ghrelin may play an important role in the regulation of metabolic balance and improve the wasting syndrome through GH-dependent or independent effects.

Ghrelin is a unique 28-amino acid peptide hormone that contains an n-octanoyl modification on Ser3. This lipid modification is essential for ghrelin-mediated stimulation of GH release, and des-acyl ghrelin, the des-n-octanoyl form of ghrelin, has almost no biological activity (17). Two kinds of RIAs, namely C-RIA, for the carboxyl terminal, and N-RIA, for the amino terminal, of ghrelin, were previously reported to measure plasma ghrelin concentrations (17, 18, 19). However, little is known about the physiological conditions in which plasma levels of these two forms of ghrelin differ.

Bacterial lipopolysaccharide (LPS) is a component of the Gram-negative bacterial cell wall and is believed to mediate many of the sequelae of infection. LPS administration induces anorexia, body weight loss, and other catabolic responses and is commonly used to generate animal models of excessive inflammation, septic shock, and wasting syndrome (20, 21, 22). Concerning the somatotropic axis, acute endotoxin administration in rats decreased circulating GH and IGF-I (3, 23), and chronic LPS administration decreased pituitary GH content and circulating IGF-I (23). However, neither plasma ghrelin levels nor ghrelin treatment has been tested in this model.

The aim of this study was to analyze the effects of LPS administration on the relationship between plasma ghrelin and the somatotropic axis in rats. We investigated plasma ghrelin concentrations after a single LPS administration and after repeated LPS administration, using two kinds of RIAs. In addition, we examined the therapeutic potential of the antiwasting effect of ghrelin using rats repeatedly injected with LPS.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals
Seven-week-old male Wister rats (200–250 g) were purchased from Japan SLC (Hamamatsu, Japan). They were housed in a temperature-, humidity-, and light-controlled room (12-h light/12-h dark cycle, lights on at 0800 h) and allowed free access to water and standard rat food (CE-2, 352 kcal/100 g; Japan CLEA, Tokyo, Japan), unless otherwise indicated. Rats were individually housed in Experiments 2 and 3. Animals were weighed, and food intake was measured every morning. One-day food intake was measured by subtracting the amount of uneaten food on each day from that provided the previous day. Food spillage into the cage was assessed and found to be negligible. All experimental procedures were approved by the Kyoto University Graduate School of Medicine committee on animal research.

Experiment 1: single administration of LPS
Rats were injected ip with 0 or 10 mg/kg LPS (serotype O26:B6; Sigma-Aldrich Corp., St. Louis, MO) in 300 µl saline at 0800 h. The LPS dose used in the present study was sublethal; the 50% lethal dose was approximately 50 mg/kg body weight. For determination of plasma levels of ghrelin and serum concentrations of GH and IGF-I, animals were anesthetized with pentobarbital, and trunk blood was collected at 3, 6, 12, and 24 h post injection. Food was withdrawn after endotoxin injection because LPS-induced anorexia may change the plasma ghrelin concentration. To establish a dose dependency for LPS-induced changes in energy balance, animals were injected with 0, 0.1, 1, or 10 mg/kg LPS, and trunk blood was collected 12 h post injection.

Experiment 2: repeated administration of LPS
Rats were injected ip with 0 or 1 mg/kg LPS in 300 µl saline once daily at 0800 h for 2 or 5 d. Pair-fed (PF) rats were injected with saline and given the same amount of food as that consumed by LPS-treated rats on the previous day. Food was withdrawn after the final LPS injection. Twelve hours later, animals were anesthetized with pentobarbital, and trunk blood was collected and stored until hormone assays were carried out.

Experiment 3: ghrelin administration in rats with LPS-induced wasting syndrome
Rats were divided into four groups: control (n = 9), ghrelin (n = 8), LPS (n = 8), and LPS plus ghrelin (n = 8). Then 0 or 1 mg/kg LPS in 300 µl saline was injected ip once daily at 0800 h for 5 d. Fourteen hours after the first LPS injection, 0 or 10 nmol/rat ghrelin in 300 µl saline were injected sc twice daily at 1000 and 2200 h for 5 d. Ghrelin (10 nmol/rat) was chosen, as this dose was previously demonstrated to increase food intake 0–2 h after peripheral administration (24). Rat ghrelin was obtained from Peptide Institute, Inc. (Osaka, Japan). After the last weight measurement, animals were anesthetized with pentobarbital, trunk blood was collected, and the liver, spleen, adrenal gland, and testicular fat pad were dissected and weighed.

Blood sampling and assay for plasma ghrelin
Plasma samples were prepared as previously described (7). Blood samples were immediately transferred to chilled polypropylene tubes containing Na2EDTA and aprotinin and centrifuged at 4 C. Plasma was acidified with hydrogen chloride for a final concentration of 0.1 N immediately after separation and were stored at -80 C until use. The plasma ghrelin concentration was measured by an RIA specific for ghrelin as described previously: C-RIA for the carboxyl terminal and N-RIA for the amino terminal of ghrelin (17, 18). In brief, 1 ml of the prepared plasma sample was applied to a Sep-Pak C18 cartridge (Waters Corp., Milford, MA). After washing, the cartridge was eluted with 3.0 ml 60% CH3CN/0.1% trifluoroacetic acid. The eluate was subjected to RIA. The minimal detectable quantities by C-RIA and N-RIA were 5.0 and 0.5 fmol/tube, respectively.

Other biochemical measurements
Serum GH and leptin were measured with enzyme immunoassay kits (Biotrak EIA, Amersham Pharmacia Biotech, Arlington Heights, IL). Serum IGF-I was determined with an enzyme immunoassay kit (Active Rat IGF-I EIA, Diagnostic Systems Laboratories, Inc.,).

Statistical analysis
All values are presented as the mean ± SEM. Comparisons between groups were performed using the unpaired t test. For comparisons among several groups, statistical significance was determined using one-way ANOVA with the post hoc least significant difference test. P < 0.05 was considered significant.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Single LPS administration
As LPS administration induces anorexia, the experiment was performed under fasting conditions after LPS injection. Therefore, plasma ghrelin levels in saline-injected control rats gradually increased after fasting, whereas plasma ghrelin levels were suppressed 6 and 12 h after the administration of 10 mg/kg LPS (Fig. 1AGo). Plasma ghrelin levels measured by C-RIA remained at 70.0% (P < 0.05) and 63.8% (P < 0.01) of control levels, respectively, and those measured by N-RIA were 83.2% (P = NS) and 66.8% (P < 0.05) of control levels, respectively. Twenty-four hours after LPS administration, plasma ghrelin levels returned to control levels. Further, suppression of plasma ghrelin levels 12 h after LPS administration appeared to be dose dependent (Fig. 1BGo). The plasma ghrelin levels determined by C-RIA after 0.1, 1, and 10 mg/kg LPS administration were reduced to 87.5% (P = NS), 63.9% (P < 0.01), and 59.5% (P < 0.01) of control levels, respectively. Similarly, plasma ghrelin levels determined by N-RIA after 0.1, 1, and 10 mg/kg LPS administration were reduced to 86.1% (P = NS), 65.8% (P < 0.05), and 56.4% (P < 0.01) of control levels, respectively.



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  		FIG. 1. The effect of a single LPS injection on plasma ghrelin levels. At 0800 h, fasting was started, and rats were injected ip with saline ({square}) or LPS ({blacksquare}). A, Changes in plasma ghrelin levels measured by C-RIA (upper panel) and N-RIA (lower panel) after the administration of 10 mg/kg LPS. B, Changes in plasma ghrelin levels 12 h after the injection of various doses of LPS. Values are the mean ± SEM (n = 6 for each group). a, P < 0.05; b, P < 0.01 (vs. saline).

 
Serum GH levels were significantly reduced 3 h after LPS injection by 45.3% relative to levels in control rats, but thereafter GH concentrations recovered (Fig. 2AGo). IGF-I levels were significantly reduced to 72.4%, 85.9%, and 79.1% compared with control rats at 6, 12, and 24 h after LPS administration, respectively (Fig. 2BGo).



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  		FIG. 2. The effect of a single LPS (10 mg/kg) injection on serum GH (A) and IGF-I (B) concentrations. Values are the mean ± SEM (n = 6 for each group). {square}, Saline; {blacksquare}, LPS. a, P < 0.05 (vs. saline).

 
Repeated LPS administration
As chronic LPS treatments have been reported to change the activity levels of the somatotropic axis (23), we examined plasma ghrelin levels on d 2 and 5. Body weight gain was significantly reduced in LPS-treated and PF rats on d 2 (LPS-treated, -4.4 ± 1.6 g; PF, -3.2 ± 1.2 g; saline-treated, 17.2 ± 1.7 g; P < 0.01 vs. saline for both) and d 5 (LPS-treated, 21.3 ± 1.7 g; PF, 16.4 ± 2.3 g; saline-treated, 38.3 ± 1.8 g; P < 0.01 vs. saline for both). On d 2 plasma ghrelin levels measured by C-RIA in LPS-treated rats were 1.9-fold higher than those in control rats and 1.4-fold higher than those in PF rats. Plasma ghrelin levels determined by N-RIA in LPS-treated rats were 3.4-fold higher than those in control rats and 2.0-fold higher than those in PF rats (Fig. 3AGo). On d 5 plasma ghrelin levels measured by C-RIA in LPS-treated rats were higher than those in control or PF rats, although the levels were decreased compared with those on d 2 (d 2, 648.9 ± 50.7; d 5, 495.9 ± 31.6 fmol/ml; P < 0.05). Plasma ghrelin levels measured by N-RIA in LPS-treated rats were also higher than those in control rats on d 5, although levels were decreased relative to those on d 2 (d 2, 87.3 ± 10.5; d 5, 52.2 ± 5.1 fmol/ml; P < 0.01; Fig. 3AGo). Although plasma ghrelin levels in PF rats were significantly increased compared with controls, the levels were lower than those in LPS-treated rats (Fig. 3AGo). In contrast, administration of LPS for 2 and 5 d resulted in decreased serum GH concentrations relative to those in control and PF rats, although it did not significantly reduce serum IGF-I levels (Fig. 3BGo).



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  		FIG. 3. The effect of repeated LPS injection on plasma ghrelin levels (A), and serum GH and IGF-I concentrations (B). Twelve hours after the final injection, blood was taken, and plasma was separated for the assays indicated. A, Changes in plasma ghrelin levels measured by C-RIA (upper panel) and N-RIA (lower panel). B, Changes in serum GH (upper panel) and IGF-I (lower panel) concentrations. Values are the mean ± SEM (n = 9 for each group). a, P < 0.05; b, P < 0.01 (vs. saline). c, P < 0.05; d, P < 0.01 (vs. PF). {square}, Saline; {blacksquare}, LPS; {square} , PF.

 
Ghrelin administration in rats with LPS-induced wasting syndrome
Daily food intake was suppressed on d 1 (LPS, 12.0 ± 0.5 g; control, 20.7 ± 0.9 g; P < 0.01), d 2 (LPS, 18.6 ± 0.7 g; control, 22.4 ± 0.6 g; P < 0.01), and d 4 (LPS, 21.0 ± 1.1 g; control, 24.3 ± 0.9 g; P < 0.05) in rats treated with 1 mg/kg LPS (Fig. 4AGo). Furthermore, cumulative food intake over 5 d was significantly decreased relative to that in control groups (LPS, 95.5 ± 2.3; control, 112.4 ± 3.0 g/5 d; P < 0.01; Fig. 4BGo). Body weight was decreased on d 1 and began recovering on d 2, but was 51.8% lower than the control value on d 5 (LPS, 18.6 ± 2.1; control, 35.9 ± 2.2 g/5 d; P < 0.01; Fig. 4Go, C and D). To examine the effects of ghrelin on food intake and body weight, we administered saline (control) or 10 nmol/rat ghrelin sc twice daily. Treatment with ghrelin for 5 d significantly increased cumulative food intake relative to that of control groups (ghrelin, 121.3 ± 2.4; control, 112.4 ± 3.0 g/5 d; P < 0.05; Fig. 4BGo). The increased food intake induced by ghrelin was associated with a significant increase in body weight gain (ghrelin, 41.1 ± 1.6; control, 35.9 ± 2.2 g/5 d; P < 0.05; Fig. 4DGo). Although no significant difference was noted with ghrelin treatment in repeated LPS-injected rats in either daily or cumulative food intake, the LPS-induced reduction in body weight on d 5 was significantly attenuated by ghrelin treatment (ghrelin plus LPS, 24.9 ± 1.9; LPS, 18.6 ± 2.1 g/5 d; P < 0.05; Fig. 4DGo).



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  		FIG. 4. The effect of ghrelin treatment with repeated LPS injection (1 mg/kg) on daily food intake (A), cumulative food intake (B), body weight (C), and body weight gain 5 d after the first injection (D). Values are the mean ± SEM (n = 8–9 for each group). a, P < 0.05; b, P < 0.01 (vs. control). c, P < 0.05 (vs. LPS).

 
Spleen weights of LPS-injected rats were significantly increased relative to those of control rats (LPS, 0.81 ± 0.04; control, 0.65 ± 0.02 g; P < 0.01), but were not significantly modified by ghrelin treatment (Fig. 5AGo). White adipose tissue, as assessed by epididymal fat pad mass, was significantly increased in rats treated with ghrelin (ghrelin, 1.91 ± 0.06; control, 1.74 ± 0.05 g; P < 0.05) and increased still further in LPS-injected and ghrelin-treated rats (ghrelin plus LPS, 1.79 ± 0.04; LPS, 1.65 ± 0.04 g; P < 0.05; Fig. 5BGo). There was no significant difference in liver and adrenal weights among these groups (data not shown).



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  		FIG. 5. The effect of ghrelin treatment with repeated LPS injection on spleen (A) and testicular fat pad (B) mass weights. Values are the mean ± SEM (n = 8–9 for each group). a, P < 0.05; b, P < 0.01 (vs. control). c, P < 0.05 (vs. LPS).

 
Serum leptin concentrations were significantly increased by ghrelin treatment in LPS-injected rats (LPS plus ghrelin, 1.21 ± 0.24; LPS, 0.92 ± 0.32 ng/ml; P < 0.05), but were not significantly increased in normal control rats (Fig. 6Go). Repeated LPS injection decreased serum levels of albumin and hemoglobin and increased platelet counts (Table 1Go). Treatment with ghrelin caused a modest recovery in hemoglobin concentration from 11.9 ± 0.2 to 12.4 ± 0.2, but did not modify serum albumin levels or platelet counts. There were no significant differences in serum GH (control, 280.6 ± 49.5; ghrelin, 287.5 ± 41.8; LPS, 211.4 ± 18.7; LPS plus ghrelin, 176.6 ± 13.8 ng/ml) or IGF-I (control, 1223.1 ± 86.5; ghrelin, 1248.0 ± 99.7; LPS, 1152.1 ± 44.4; LPS plus ghrelin, 1210.1 ± 67.7 ng/ml) concentrations after ghrelin treatment.



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  		FIG. 6. The effect of ghrelin treatment with repeated LPS injections on serum leptin concentrations. Values are the mean ± SEM (n = 8–9 for each group). a, P < 0.05 (vs. LPS).

 

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  		TABLE 1. Effect of ghrelin on biological activities of LPS

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
This is the first report showing that a single LPS injection suppressed plasma ghrelin levels, wheras repeated LPS injection elevated plasma ghrelin levels. During revision of this manuscript, two independent groups reported that a single LPS injection shifted plasma ghrelin levels of male Sprague-Dawley rats: one group showed that plasma ghrelin levels were decreased 3 h after ip injection of 0.1 mg/kg LPS, and the other showed that levels were increased 24 h after iv injection of 5 mg/kg LPS (25, 26). In this study a single LPS injection suppressed plasma ghrelin levels 6 and 12 h after LPS injection. Maximal reduction was observed 12 h after LPS injection, and ghrelin was reduced in a dose-dependent manner. On the other hand, 3 h after LPS injection serum concentrations of GH were decreased, as were subsequent serum concentrations of IGF-I. Therefore, it is unlikely that the inhibitory effect of a single LPS injection on the somatotropic axis was mediated by the reduction of plasma ghrelin. This supports the recent idea that although ghrelin administration strongly increases GH secretion in animal models and humans, a role for ghrelin in endogenous GH secretion is not yet clear (27, 28). The effects of LPS on the neuroendocrine system were suggested to be mediated by cytokines released by LPS-stimulated macrophages and monocytes (29). Indeed, IL-1ß decreased gastric ghrelin mRNA expression (15). Alternatively, inhibition of plasma ghrelin levels by a single LPS injection may be mediated by somatostatin. Previous studies reported an increase in somatostatin release induced by acute LPS treatment both in vivo and in vitro (30, 31), and the suppression of GH secretion by acute endotoxin administration was reversed by antisomatostatin serum (32). In fact, plasma ghrelin levels have been reported to be suppressed by somatostatin (33). As plasma ghrelin levels have been shown to be suppressed by other factors, including increased body mass index and energy surplus (19, 34), insulin (35), glucose (19, 36), and hyperthyroidism (37), further studies are needed to elucidate the mechanism for this reduction.

Soto et al. (23) showed that chronic LPS administration (250 µg/kg daily for 8 d) decreased body weight, serum levels of IGF-I, and pituitary GH content and increased hypothalamic somatostatin content. We showed that repeated LPS injection caused body weight loss on d 2 and 5 in rats treated with 1 mg/kg LPS. Furthermore, serum GH concentrations were decreased on d 2 and 5. In contrast, plasma ghrelin levels were elevated after repeated LPS injection. Moreover, as plasma ghrelin levels in LPS-treated rats were even higher than those in PF rats, this increment was not purely induced by anorexia. Fasting (38), anorexia nervosa (38), cancer cachexia (16, 39), and chronic heart disease (14) have been previously reported to cause elevated plasma ghrelin levels. Similarly, elevation of ghrelin levels in rats after repeated LPS injection may reflect a physiological adaptation to negative energy balance.

Prolonged or repeated LPS administration leads to endotoxin tolerance, which is also observed with continuous endotoxin infusion (40, 41). Plasma ghrelin levels on d 5 after repeated LPS injection were lower than those on d 2. This difference in plasma ghrelin levels may be the result of tolerance. The reduced hemoglobin and albumin levels on d 5, however, indicated that the LPS-induced wasting state persisted. Most animal models of sepsis induce high mortality or early recovery and do not mimic the long-lasting catabolic state observed in patients (42). Chronic LPS administration appears to have several advantages as a wasting model. The dose of LPS can be accurately measured to adjust the severity of the condition, and furthermore, the activity of the somatotropic axis is altered after LPS administration (23).

In this study we used two kinds of RIAs, namely C-RIA for the carboxyl terminal and N-RIA for the amino terminal of ghrelin. The levels measured by N-RIA represent the active form of ghrelin with an n-octanoyl modification at Ser3, whereas the levels measured by C-RIA represent total ghrelin, including its inactive form (17). After both single and repeated LPS injections, we could not detect a marked discrepancy between ghrelin levels measured by C-RIA and N-RIA, in agreement with a previous study (19). The effect of glucose injection on plasma ghrelin levels in fasted Sprague Dawley rats was, however, observed more obviously in N-RIA than C-RIA (19). As there may be physiological or pathological conditions in which plasma levels of the total and active forms of ghrelin differ, it is necessary to measure the acylated form of this hormone in various conditions.

We showed that repeated LPS injection induced anorexia, weight loss, and hypoalbuminemia and reduced hemoglobin, characteristic of the wasting syndrome. In this study this model was used to examine the therapeutic potential of the antiwasting effects of ghrelin. We demonstrated that peripheral administration of ghrelin accelerated body weight gain in this model. However, we did not observe increased food intake in LPS-injected rats treated with ghrelin. This discrepancy may be explained by ghrelin-induced metabolic changes, which lead to a more efficient metabolic state, resulting in increased body weight and fat mass (10). Careful examination revealed that ghrelin treatment was effective at increasing adipose tissue weight in wasting rats. Furthermore, we confirmed that plasma leptin concentrations, which were thought to be positively correlated with the quantity of adipose tissue, were increased by ghrelin treatment in these rats. These findings suggest that chronic ghrelin treatment is likely to cause body weight gain and adipogenesis, even in the LPS-induced wasting state.

In the present study repeated LPS injection reduced serum hemoglobin and albumin levels. Ghrelin treatment modestly increased hemoglobin concentrations in LPS-injected rats, but had no effect on serum albumin concentrations. A few studies have reported that GH treatment resulted in increased hemoglobin concentrations in anemic patients with GH deficiency (43, 44). Thus, the increased hemoglobin concentrations induced by ghrelin treatment of LPS-injected rats could be explained by an anabolic effect of ghrelin mediated through GH/IGF-I. Furthermore, some studies showed that GH reduced net protein loss in the critically ill (5, 43, 44), whereas others demonstrated that GH treatment did not reduce protein catabolism (5, 45). This discrepancy suggests that the dose and timing of GH administration may be important. Further detailed studies are needed to fully establish the role of ghrelin treatment in the wasting syndrome.

The roles of GH and IGF-I in the regulation of immune function have been investigated (46). GH and IGF-I exert independent effects on lymphoid tissue, and the administration of these agents resulted in splenic enlargement. In the present study spleen weights of LPS-injected rats were increased compared with those of control rats, but they were not modified by ghrelin treatment. Furthermore, depending on the experimental conditions, GH can either reduce (47) or increase (4) susceptibility to endotoxin or bacterial challenge in animals. We observed that the biological activity of 10 mg/kg LPS was not enhanced by priming rats with 10 nmol/rat ghrelin twice daily for 5 d (data not shown). This suggests that ghrelin treatment can improve the endotoxin-induced wasting syndrome without changing the sensitivity to endotoxin.

In summary, the present study demonstrates that a single LPS injection suppressed plasma ghrelin levels in rats, whereas repeated LPS injection elevated ghrelin levels. Chronic sc administration of ghrelin increased body weight gain, adipose tissue weight, and plasma leptin levels in rats with LPS-induced wasting. Thus, ghrelin treatment may provide a new therapeutic approach to the wasting syndrome and critical illness.


   Footnotes
 
This work was supported in part by grants-in-aid from the Ministry of Education, Science, Culture, Sports, and Technology of Japan; the Ministry of Health, Labor, and Welfare of Japan; and the Foundation for Growth Science.

Abbreviations: LPS, Lipopolysaccharide; PF, pair-fed.

Received April 7, 2003.

Accepted for publication August 21, 2003.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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