JOE
HOME HELP CONTACT US SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Journal of Endocrinology (2006) 191, 459-463    DOI: 10.1677/joe.1.06784
© 2006 Society for Endocrinology
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Oliveira, K J
Right arrow Articles by Pazos-Moura, C C
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Oliveira, K J
Right arrow Articles by Pazos-Moura, C C

Peptide YY (PYY)3–36 modulates thyrotropin secretion in rats

K J Oliveira, G S M Paula, R H Costa-e-Sousa, L L Souza, D C Moraes, F H Curty and C C Pazos-Moura

Laboratório de Endocrinologia Molecular, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21949-900, Brazil

(Requests for offprints should be addressed to C C Pazos-Moura; Email: cpazosm{at}biof.ufrj.br)


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Peptide YY (PYY)3-36 is a gut-derived hormone, with a proposed role in central mediation of postprandial satiety signals, as well as in long-term energy balance. In addition, recently, the ability of the hormone to regulate gonadotropin secretion, acting at pituitary and at hypothalamus has been reported. Here, we examined PYY3-36 effects on thyrotropin (TSH) secretion, both in vitro and in vivo. PYY3-36-incubated rat pituitary glands showed a dose-dependent decrease in TSH release, with 44 and 62% reduction at 10–8 and 10–6 M (P < 0.05 and P < 0.001 respectively), and no alteration in TSH response to thyrotropin-releasing hormone. In vivo, PYY3-36 i.p. single injection in the doses of 3 or 30 cg/kg body weight, administered to rats fed ad libitum, was not able to change serum TSH after 15 or 30 min. However, in fasted rats, PYY3-36 at both doses elicited a significant rise (approximately twofold increase, P < 0.05) in serum TSH observed 15 min after the hormone injection. PYY3-36 treatment did not modify significantly serum T4, T3, or leptin. Therefore, in the present paper, we have demonstrated that the gut hormone PYY3-36 acts directly on the pituitary gland to inhibit TSH release, and in the fasting situation, in vivo, when serum PYY3-36 is reduced, the activity of thyroid axis is reduced as well. In such a situation, systemically injected PYY3-36 was able to acutely activate the thyrotrope axis, suggesting a new role for PYY3-36 as a regulator of the hypothalamic–pituitary–thyroid axis.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Peptide YY (PYY)3-36 is a gut-derived hormone, produced by endocrine L cells lining the distal small bowel and colon, released postprandially in proportion to the calories ingested (Adrian et al. 1985). Peripheral administration of PYY3-36 in rodents or humans has been reported to induce a marked inhibition of food intake (Batterham et al. 2002, 2003). PYY3-36 inhibits food intake at plasma concentrations that are within the normal physiological range seen in man after meals (Batterham et al. 2002, 2003) and therefore, a role for the hormone in central mediation of postprandial satiety signals has been proposed. Moreover, long-term administration has been demonstrated to induce a reduction in body weight (Batterham et al. 2002, 2003) although this is still a matter of controversy (Tschöp et al. 2004).

In addition, recent studies suggested that PYY3-36 may act as a neuroendocrine regulator. It has been demonstrated in prepubertal rats that PYY3-36 stimulated prolactin, luteinizing hormone (LH), and FSH secretion acting directly at pituitary gland, although it seems to have an inhibitory action at the hypothalamic level (Aguilar et al. 2004, Fernandez-Fernandez et al. 2005). Therefore, similar to other hormones involved in energy homeostasis, PYY3-36 is also able to influence the reproductive axis. However, there is no information concerning the thyrotrope axis.

PYY3-36 is a member of the neuropeptide Y (NPY) family and it is an agonist of receptor subtypes NPY-Y2 and NPY-Y5 (Keire et al. 2000). Experimental evidence suggests that circulating PYY3-36 inhibits appetite by acting directly on the arcuate nucleus via the Y2 receptor, a presynaptic inhibitory autoreceptor (Batterham et al. 2002, Talsania et al. 2005). NPY is a potent stimulator of food intake and PYY3-36 was able to inhibit the electrical activity of arcuate NPY neurons as well as to reduce the expression of the NPY mRNA (Batterham et al. 2002, Challisa et al. 2003). In addition, NPY originating in the hypothalamic arcuate nucleus exerts a profound inhibitory effect on the thyroid axis via effects on hypophysiotropic thyrotropin-releasing hormone (TRH) neurons. Chronic intracerebroventricular administration of NPY to normally fed rats resulted in reduction of circulating levels of thyroid hormones with inappropriately normal or low thyrotropin (TSH), and suppression of proTRH mRNA in the hypothalamic paraventricular nucleus (PVN; Fekete et al. 2001). NPYeffects were reproduced by NPY-Y1 and NPY-Y5 analogs injected into the third cerebral ventricle, suggesting that both the receptors mediate NPY suppression of the hypothalamic–pituitary–thyroid axis (Fekete et al. 2002).

During fasting, as a means of conserving energy, the hypothalamic–pituitary–thyroid axis is suppressed and the activation of arcuate NPY neurons is a major component of the regulatory mechanism that causes a decline in proTRH mRNA in PVN, reducing circulating levels of TSH and thyroid hormones. Fasting is associated with reduced serum concentrations of PYY3-36 (Tovar et al. 2004, Chan et al. 2005), and peripherally injected PYY3-36 partly reversed the fasting-induced c-Fos expression in arcuate nucleus neurons of mice (Riediger et al. 2004), suggesting a role for the peptide in fasting adaptation.

Therefore, considering NPYeffects on thyroid axis, and the presence of Y5 receptors, and the mRNA encoding Y2 and Y5 receptors in pituitary gland (Parker et al. 2000, Fernandez-Fernandez et al. 2005), we tested the hypothesis that PYY3-36 may act directly at the pituitary to modulate TSH secretion. In addition, we also investigated whether PYY3-36, injected systemically, may modify the thyrotrope axis in fed and fasting rats.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals

Adult male Wistar rats, weighing 250–300 g, were kept under controlled lighting (12 h light:12 h darkness cycle, lights on at 0700 h) and controlled temperature (23 ± 1 °C). All experimental protocols were approved by our institutional animal care committee.

In vitro experiments

Ad libitum fed rats were killed by decapitation, and their anterior pituitaries were quickly dissected out for in vitro testing as described before (Rettori et al. 1989, Ortiga-Carvalho et al. 2002) Each hemi-pituitary was immediately transferred to a flask containing 1 ml Krebs–Ringer bicarbonate medium (pH 7.4) at 37 °C in an atmosphere of 95% O2/5% CO2 in a Dubnoff metabolic shaker. After a 30-min preincubation period, medium was changed to 1 ml medium alone (control) or medium containing PYY3-36 (Bachem California, Inc., Torrance, CA, USA) to a final concentration of 10–10, 10–8, or 10–6 M. At the end of a 2 h incubation period, an aliquot was removed for TSH measurement. In another set of experiments, after 2 h incubation, a small aliquot was removed for TSH measurement and TRH (Bachem California, Inc.) was added to a final concentration of 50 nM in all tubes. The incubation was continued for 30 min to determine the TRH-stimulated TSH release in the absence or presence of the different concentrations of PYY3-36.

In vivo experiments

Ad libitum fed rats were divided into three groups that received a single i.p. injection of 3 or 30 µg/kg body weight (BW) PYY3-36 or 0.2 ml saline vehicle (control group). Another set of rats was fasted for 3 days before they received a single i.p. injection of 3 or 30 µg/kg BW PYY3-36 or 0.2 ml saline vehicle (control group). In both experiments, rats were killed by decapitation, 15 or 30 min after the injection. Experiments were performed in the morning between 1000 and 1100 h. Serum was obtained from trunk blood for hormone measurements.

Quantification of TSH

TSH concentration in the serum and in the incubation medium was measured by specific RIA, employing reagents supplied by the National Institute of Diabetes, Digestive and Kidney Diseases, National Hormone & Peptide Program (NIDDK–NHPP) (Torrance, CA, USA), as previously described (Chard 1987, Ortiga-Carvalho et al. 1996), and was expressed in terms of the reference preparation 3 (RP3). Within-assay variation was 5.7%. Samples of the same experiment were measured within the same assay. Minimum assay detection was 0.52 ng/ml.

Quantification of serum concentrations of T4, T3, and leptin

Serum T4 and T3 were detected by RIA (MP Biomedicals Inc, Irvine, CA, USA). Detection limits were: 1 µg/dl for T4 and 25 ng/dl for T3. Serum leptin was measured using a specific rat RIA by LINCO Research (St Charles, MO, USA). Minimum detectable level was 0.5 ng/ml. Intraassay variation was less than 7% for all hormone measurements and all the samples were run within the same assay.

Statistical analysis

Data are reported as means ± S.E.M. One-way ANOVA followed by a Student–Newman–Keuls multiple comparisons test was employed for the assessment of significance of data. Serum TSH was analyzed after logarithmic transformation (Zar 1996). Differences were considered to be significant at P < 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
In vitro experiments

PYY3-36-incubated hemi-pituitary glands showed, after 2 h incubation, a dose-dependent decrease in TSH release, statistically significant at 10–8 M (P < 0.05) and 10–6 M (P < 0.001), with a reduction of 44 and 62% respectively (Fig. 1Go). However, the TSH response to TRH was not significantly different among groups, presenting an increment around four times above the basal levels (TSH before TRH) in all groups.


Figure 1
View larger version (14K):
[in this window]
[in a new window]
  		Figure 1 TSH release from isolated rat hemi-anterior pituitary glands incubated in absence (C, control) or presence of PYY3-36 at different concentrations (10–10, 10–8, 10–6 M) for 2 h. n= 10 hemi-pituitaries per group. *P < 0.05, {dagger}P< 0.001 vs control group. Data represent means ± S.E.M. Figure representative of two independent experiments.

 
In vivo experiments

The i.p. administration of 3 or 30 µg/kg BW of PYY3-36 to ad libitum fed rats induced no changes in serum TSH either after 15 or 30 min (Fig. 2Go). Also, serum leptin and serum T4 (Table 1Go) and T3 concentrations (data not shown) were not significantly modified by the treatment with PYY3-36. However, in fasted rats (Fig. 3Go), a significant rise in serum TSH was detected 15 min after PYY3-36 administration at both doses (approximately twofold increase, P< 0.05). This effect was transitory, since no statistically significant effect was observed 30 min after PYY3-36 injection of both doses in fasted rats. Serum concentrations of T4 and leptin were not changed by PYY3-36 treatment at any time point or doses (Table 1Go). Fasted rats presented approximately 11% reduction in body weight and in most of them serum T3 was below 25 ng/ml.


Figure 2
View larger version (17K):
[in this window]
[in a new window]
  		Figure 2 Serum TSH concentration in fed rats after intraperitoneal administration of PYY3-36 3 (A) and 30 (B) µg/kg BW or saline (C). Determinations were performed at 15 and 30 min after injection of the peptide.n= 9–10 animals per group. Data are presented as means ± S.E.M.

 

View this table:
[in this window]
[in a new window]
  		Table 1 Serum concentration of T4 and leptin in fed and fasting rats after intraperitoneal administration of peptide YY (PYY)3-36. Data are presented as means ± S.E.M. of two separated experiments (fed and fasting rats). n = 7–10 per group.
 

Figure 3
View larger version (14K):
[in this window]
[in a new window]
  		Figure 3 Serum TSH concentrations in fasted rats after intraperitoneal administration of PYY3-36 3 (A) and 30 (B) µg/kg BW or saline (C). Determinations were performed at 15 and 30 min after injection of the peptide. n= 8–10 animals per group. *P < 0.05, {dagger}P < 0.001 vs C (control vehicle-injected). Data are presented as means ± S.E.M.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Here, we first demonstrated that PYY3-36 acts directly at the pituitary to inhibit TSH secretion. Y2 and Y5 mRNA receptors had been detected at low levels in pituitary gland (Parker et al. 2000, Fernandez-Fernandez et al. 2005), however, binding studies indicated the presence of Y5 (Parker et al. 2000) and the absence of Y2 receptors (Sheikh et al. 1998). Therefore, it is probable that PYY3-36 elicited the inhibitory effect on TSH secretion acting through activation of pituitary Y5 receptors. This would be consistent with the fact that an Y5 analog, injected centrally in rats, was able to suppress the hypothalamus–pituitary–thyroid axis. In addition, the present data are in agreement with a previous study showing that NPY, also a Y5 ligand, acts directly at rat pituitary to reduce ß-TSH mRNA levels, as demonstrated by the incubation of pituitary cell cultures with NPY (Chowdhury et al. 2004). However, TRH action at the thyrotropes seems to be preserved, since the fold increment on TSH release induced by TRH was not significantly modified by the presence of PYY3-36 in the incubation medium.

Contrary to what could be expected in view of the inhibitory pituitary action of PYY3-36 on TSH release, systemic i.p. administration of the hormone in normally fed rats (3 and 30 µg/kg) failed to significantly modify serum TSH levels. Previous work of Fernandez-Fernandez et al.(2005), using a similar PYY3-36 administration protocol, was also unable to demonstrate in vivo effects of PYY3-36 on LH secretion, although the peptide had stimulated LH release from incubated rat pituitaries. Similar findings were reported concerning PYY3-36 effects on PRL secretion (Aguilar et al. 2004). The doses of PYY3-36 that we employed can be considered low and moderate, and it is possible that a higher dose would be necessary to modify TSH secretion. However, as demonstrated in previous studies (Batterham et al. 2002, Challisa et al. 2003, Talsania et al. 2005), similar PYY3-36 doses were sufficient to inhibit food intake in rats, suggesting that these doses were enough to activate arcuate nucleus Y2 receptors. An alternative explanation could be that the final effect of injected PYY3-36 may be the result of its action at different targets. In this sense, it must be considered that systemic PYY3-36 rapidly reaches the arcuate nucleus, an area partially outside the blood–brain barrier, where it binds with high affinity to autoinhibitory Y2 receptors in NPY neurons, which is the main postulated mechanism for its anorexigenic effect (Batterham et al. 2002). Therefore, by reducing NPY neuron activity, PYY3-36 potentially may decrease NPY inhibitory input into TRH neurons. Thereby, it is possible that PYY3-36 systemic administration had induced a higher TRH secretion that was counteracted by the direct pituitary inhibitory action, resulting in no alteration in serum TSH.

However, in fasted rats, it is likely that inhibition of NPY neurons via arcuate Y2 receptors is the predominant mechanism leading to the increase in serum TSH. In fasting conditions, there is a higher NPY inhibitory tonus on TRH neurons (Fekete et al. 2001) and, in addition, fasting was associated with reduced PYY3-36 serum levels, as reported by others (Tovar et al. 2004, Chan et al. 2005), which may render the tissues more sensitive to PYY3-36 action. Other reports support the concept that fasting enhances PYY3-36 effects, such as those concerning the peptide action on gonadotropin secretion (Pinilla et al. 2006) and on food intake (Challisa et al. 2003, Riediger et al. 2004).

PYY3-36 effect on TSH release was observed 15 min after the hormone administration, coincidently with previous reported time for peak PYY3-36 serum levels after a single i.p. injection in the dose of 3 µg/kg BW (Batterham et al. 2002). This fast action is consistent with a central action of PYY3-36 through activation of Y2 receptors in arcuate nucleus, since these receptors have high affinity for PYY3-36. However, the effect was transitory, which may reflect the short-life of the peptide, and the fact that a single dose would not be enough to normalize the reduced levels of PYY3-36 in fasting rats. However, it cannot be excluded that the activation of inhibitory Y5 receptors pathways in the pituitary may counteract the arcuate nucleus Y2-mediated stimulus in thyrotrope axis.

As expected, fasted rats exhibited lower serum thyroid hormone levels and leptin; however, the effect of PYY3-36 on TSH release could not be attributed to changes in these hormone levels, since they remained similar among groups.

Reduction in serum leptin during fasting is believed to have a major role as a peripheral signal of energy insufficiency, resulting in an integrated response at the central nervous system which includes the activation of NPY-producing neurons in the hypothalamic arcuate nucleus. Considering that peripherally injected PYY3-36 partly reversed the fasting-induced c-Fos expression in arcuate nucleus neurons of mice (Riediger et al. 2004), it is possible that reduction in serum PYY3-36 also plays a role in neuroendocrine adaptation to fasting, which is an important component in the suppression of thyrotrope axis, a hypothesis that remains to be fully explored.

In conclusion, in the present paper we have demonstrated that the gut hormone PYY3-36 acts directly at the pituitary gland to inhibit TSH release and that in vivo, systemically injected PYY3-36 is able to acutely activate the thyrotrope axis during fasting. Therefore, we propose a new role for PYY3-36 as a regulator of the hypothalamic–pituitary–thyroid axis.


   Funding
 
This work was supported by Conselho Nacional de Pesquisa e Desenvolvimento and Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro. There is no conflict of interest that would prejudice its impartiality.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Adrian TE, Ferri GL, Bacarese-Hamilton AJ, Fuessl HS, Polak JM & Bloom SR 1985 Human distribution and release of a putative new gut hormone, peptide YY. Gastroenterology 89 1070–1077.[ISI][Medline]

Aguilar E, Fernandez-Fernandez R, Tena-Sempere M & Panilla L 2004 Effects of Peptide YY(3-36) on PRL secretion: pituitary and extra-pituitary actions in the rat. Peptides 25 1147–1152.[CrossRef][ISI][Medline]

Batterham RL, Cowley MA, Small CJ, Herzog H, Cohen MA, Dakin CL, Wren AM, Brynes AE, Low MJ, Ghatei MA et al. 2002 Gut hormone PYY(3-36) physiologically inhibits food intake. Nature 418 650–654.[CrossRef][Medline]

Batterham RL, Cohen MA, Ellis SM, Le Roux CW, Withers DJ, Frost GS, Ghatei MA & Bloom SR 2003 Inhibition of food intake in obese subjects by peptide YY3-36. New England Journal of Medicine 349 941–948.[Abstract/Free Full Text]

Challisa BG, Pinnock SB, Colla AP, Carter RN, Dickson SL & O’Rahilly S 2003 Acute effects of PYY3-36 on food intake and hypothalamic neuropeptide expression in the mouse. Biochemical and Biophysical Research Communications 311 915–919.[CrossRef][ISI][Medline]

Chan JL, Stoyneva V, Kelesidis T, Raciti P & Mantzoros CS 2005 Peptide YY levels are decreased by fasting and elevated following caloric intake but are not regulated by leptin. Diabetologia 49 169–173.

Chard T 1987 An introduction to radioimmunoassay and related techniques. In Laboratory Techniques in Biochemistry and Molecular Biology, pp 1–74. Eds RH Burdon & PH van Kiniooenberg. Amsterdam: Elsevier Science.

Chowdhury I, Chien JT, Chatterjee A & Yu JYL 2004 Effects of leptin and neuropeptide-Yon transcript levels of thyrotropin beta and common alpha subunits of rat pituitary cells in vitro. Life Science 75 2897–2909.[CrossRef][ISI][Medline]

Fekete C, Kelly J, Mihály E, Sarkar S, Rand WM, Légrádi G, Emerson CH & Lechan RM 2001 Neuropeptide Y has a central inhibitory action on the hypothalamic–pituitary–thyroid axis. Endocrinology 142 2606–2613.[Abstract/Free Full Text]

Fekete C, Sarkar S, Rand WM, Harney JW, Emerson CH, Bianco AC, Beck-Sickinger A & Lechan RM 2002 Neuropeptide Y1 and Y5 receptors mediate the effects of neuropeptide Y on the hypothalamic–pituitary–thyroid axis. Endocrinology 143 4513–4519.[Abstract/Free Full Text]

Fernandez-Fernandez R, Aguilar E, Tena-Sempere M & Pinilla L 2005 Effects of polypeptide YY3–36 upon luteinizing hormone-releasing hormone and gonadotropin secretion in prepubertal rats: in vivo and in vitro studies. Endocrinology 146 1403–1410.[Abstract/Free Full Text]

Keire DA, Mannon P, Kobayashi1 M, Walsh JH, Solomon TE & Reeve JR 2000 Primary structures of PYY, [Pro34]PYY, and PYY-(3-36) confer different conformations and receptor selectivity. American Journal of Physiology. Gastrointestinal and Liver Physiology 279 G126–G131.[Abstract/Free Full Text]

Ortiga-Carvalho TM, Polak J, McCann S & Pazos-Moura CC 1996 Effect of thyroid hormones on pituitary neuromedin B and possible interaction between thyroid hormones and neuromedin B on thyrotropin secretion. Regulatory Peptides 67 47–53.[CrossRef][ISI][Medline]

Ortiga-Carvalho TM, Oliveira KJ, Soares BA & Pazos-Moura CC 2002 The role of leptin in the regulation of TSH secretion in the fed state: in vivo and in vitro studies. Journal of Endocrinology 174 121–125.[Abstract]

Parker MS, Wang JJ, Fournier A & Parker SL 2000 Upregulation of Pancreaticpolypeptide - sensitive neuropeptide Y (NPY) receptors in estrogen-induced hypertrophy of the anterior pituitary gland in the Fischer-344 rat. Molecular and Cellular Endocrinology 164 239–249.[CrossRef][ISI][Medline]

Pinilla L, Fernandez-Fernandez R, Vigo E, Navarro VM, Roa J, Castellano JM, Pineda R, Tena-Sempere M & Aguilar E 2006 The stimulatoryeffect of PYY3-36 on gonadotropin secretion is potentiated in fasted rats. American Journal of Physiology. Endocrinology and Metabolism 290 1162–1171.

Rettori V, Milenkovic L, Fahim AM, Polak J, Bloom SR & McCann SM 1989 Role of neuromedin B in the control of the release of thyrotropin in the rat. PNAS 86 4789–4792.[Abstract/Free Full Text]

Riediger T, Bothe C, Becskei C & Lutz TA 2004 Peptide YY directly inhibits ghrelin-activated neurons of the arcuate nucleus and reverses fasting-induced c-Fos expression. Neuroendocrinology 79 317–326.[CrossRef][ISI][Medline]

Sheikh SP, Feldthus N, Orkild H, Goke R, McGregor GP, Turner D, Moller M & Stuenkel EL 1998 Neuropeptide Y2 receptors on nerve endings from the rat neurohypophysis regulate vasopressin and oxytocin release. Neuroscience 82 107–115.[ISI][Medline]

Talsania T, Anini Y, Siu S, Drucker DJ & Brubaker PL 2005 Peripheral exendin-4 and peptide YY3-36 synergistically reduce food intake through different mechanisms in mice. Endocrinology 146 3748–3756.[Abstract/Free Full Text]

Tovar SA, Seoane LM, Caminos JE, Nogueiras R, Casanueva FF & Diéguez C 2004 Regulation of peptide YY levels by age, hormonal, and nutritional status. Obesity Research 12 1944–1950.[ISI][Medline]

Tschöp M, Castañeda TR, Joost HG, Thöne-Reineke C, Ortmann S, Klaus S, Hagan MM, Chandler PC, Oswald KD, Benoit SC et al. 2004 Physiology: does gut hormone PYY3–36 decrease food intake in rodents? Nature 430 165.[CrossRef][Medline]

Zar JH 1996 Data Transformations – Biostatistical Analysis, edn 3 pp 277–279.London: Prentice Hall International.

Received in final form 17 August 2006
Accepted 22 August 2006
Made available online as an Accepted Preprint 15 September 2006





This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Oliveira, K J
Right arrow Articles by Pazos-Moura, C C
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Oliveira, K J
Right arrow Articles by Pazos-Moura, C C

HOME HELP CONTACT US SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS