| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Pharmacological and Physiological Sciences, St. Louis University School of Medicine, St. Louis, Missouri 63104
Address all correspondence and requests for reprints to: Willis K. Samson, Ph.D., Pharmacological and Physiological Science 1402 South Grand Boulevard, St. Louis University School of Medicine, St. Louis, Missouri 63104. E-mail: samsonwk{at}slu.edu.
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
The endogenous ligand for these orphan receptors remained unidentified until 2002, when the Takeda group of Shimomura et al. (4) isolated and sequenced neuropeptide W (NPW). In fact, they identified two endogenous ligands, NPW-30 and NPW-23, the shorter form being the N-terminal sequence of the larger peptide, both of which bound with similar affinity to GPR7 and GPR8 (4). They also, predicting that these peptides would alter hypothalamic function, administered 10 nmol NPW23 intracerebroventricularly (icv) and demonstrated significant increases in food intake and prolactin secretion. No dose-response experiments were reported and the magnitude of the increase in food intake (3- to 4-fold) and prolactin secretion (2- to 3-fold) was not trivial, but certainly at such a high dose [
26 µg intracerebroventricularly (icv)] and in the absence of dose-response data not convincing. However, their preliminary data motivated us to examine the possibility that NPW might act in hypothalamus, or in the adenohypophysis, to alter anterior pituitary hormone release. We report here the ability of exogenous NPW23, when administered icv in conscious male rats, to significantly elevate circulating levels of prolactin (PRL) and corticosterone and to significantly lower plasma GH levels.
| Materials and Methods |
|---|
|
|
|---|
In vitro experiments
Rats were killed by rapid decapitation. Anterior pituitary glands were collected into MEM (Life Technologies, Inc., Grand Island, NY) containing HEPES (20 mM, Fisher Scientific, Fair Lawn, NJ), 1% penicillin-streptomycin (Life Technologies, Inc.), 0.1% BSA (Sigma, St. Louis, MO), and 0.1% trypsin (Difco, Detroit, MI), and mechanically dispersed (5) until a single-cell suspension was obtained (37 C). Single-cell suspensions were aliquoted into polystyrene tubes (
200,000 cells/tube) and incubated for 34 d at 37 C in an atmosphere of 5% CO2/95% room air in DMEM (BioWhittaker, Inc., Walkersville, MD) containing 10% horse serum (Life Technologies, Inc.) and 1% penicillin-streptomycin. On the day of experimentation, cells were pelleted by centrifugation (600 x g, 10 min, room temperature), medium removed, and replaced with test medium [DMEM, 0.1% BSA, 1% penicillin-streptomycin, and 2.5 mM bacitracin (Sigma)] alone or medium containing log molar concentrations (1 pM to 100 nM) of NPW23, or 10 nM TRH, 10 nM CRH, or 10 nM GHRH alone or in combination with 100 nM NPW23 (all peptides purchased from Phoenix Pharmaceuticals, Inc., Belmont, CA). Incubations lasted 60 min and were terminated by centrifugation and collection of medium for subsequent determination of PRL, GH, and ACTH contents by RIA.
In vivo experiments
Under tribromoethanol anesthesia (2.5% in isotonic saline, 1 ml/100 g body weight ip injection; Sigma), rats were placed in a stereotaxic device and a 23-gauge stainless steel cannula (17 mm) implanted into the right lateral cerebroventricle as previously described (6). Minimally 5 d later, after the animals had returned to preimplantation body weights, an indwelling jugular vein cannula was implanted as previously described (7) again under tribromoethanol-induced anesthesia. The jugular cannula was exteriorized at the back of the neck and filled with heparinized saline (250 U/ml 0.9% NaCl) and tied shut. Rats remained in an isolated, quiet environment until the following day, when an extension tubing (PE-50) was attached to the jugular cannula to facilitate blood sampling and rats left undisturbed for 60 min. Then, an initial blood sample was withdrawn from the jugular vein without disturbing the animal. All blood samples (0.3 ml, into heparinized syringes) were removed from conscious, unrestrained rats and replaced with an equal volume of 0.9% NaCl (37 C). Blood samples were kept on ice before plasma was separated (3000 x g, 3 min) and stored at 20 C until hormone assays conducted. Immediately following the removal of the initial (0 time) blood sample, a 2-µl injection of isotonic saline vehicle alone or vehicle containing 0.3, 1.0, or 3.0 nmol NPW23 was conducted via the indwelling cerebroventricular cannula. Subsequent blood samples were removed 5, 10, 20, 30, and 60 min after icv injections. Each animal was employed only for one dose of test substance.
Feeding study.
The effect of icv administered NPW23 was examined in rats bearing a lateral cerebroventricular cannula, implanted minimally 1 wk earlier. Cannulated rats were placed in metabolic cages for a 4-d habituation period, during which time daily water and food consumptions and body weights were monitored. Food and water were available ad libitum at all times. On the day of experimentation, the animals were weighed before icv injection of 2 µl of saline vehicle or vehicle containing 3.0 nmol NPW23. Rats were returned to the metabolic cages and water bottles and food trays reintroduced 15 min later. Food and water intakes were monitored thereafter at 30-min intervals for 4 h and then again at 24 h.
RIAs.
PRL levels in incubation medium and plasma were determined using the kit materials provided by the National Hormone and Pituitary Program (rPRL-RP-3 standard). The minimum detectable hormone level in medium and plasma for PRL was 0.5 ng/ml (defined as <90% B/B0) and the interassay and intraassay coefficients of variability were less than 9%. GH levels were similarly measured using the material provided in the NIH kit (rGH-RP-2 standard, minimum detectable level: 0.5 ng/ml; interassay and intraassay coefficients of variability were less than 8%). ACTH content of incubation medium was determined using the commercial RIA kit (rat ACTH, Phoenix Pharmaceuticals, Inc.). All incubation samples were measured in the same ACTH assay (minimum detectable hormone level, 2 pg/tube; intraassay coefficient of variability less than 5%). Plasma corticosterone levels were determined according to the instructions of the commercial RIA kit (rat/mouse corticosterone, ICN Biomedicals, Inc., Costa Mesa, CA). The minimum detectable hormone level was 25 ng/ml, and the interassay and intraassay coefficients of variability were less than 10%.
Statistical analyses
Differences between treatment groups in the in vitro studies were analyzed by one-way ANOVA and Scheffés multiple comparison testing. Homogeneity of variance was established using the S test. Significance was assigned to results that occurred with less than 5% probability. For the in vivo experiments, data were similarly analyzed by ANOVA both within treatment groups across time and across treatment groups at any sampling time point.
| Results |
|---|
|
|
|---|
|
|
|
|
|
|
| Discussion |
|---|
|
|
|---|
We observed a general increase in the activity of the rats following central administration of NPW23, including increased locomotion and grooming. We also observed that, like the report of the Shimomura group (4), food intake was stimulated by NPW23, at a dose lower than that employed in their original study. Furthermore, we report that water consumption also was stimulated by icv administration of 3.0 nmol NPW23, something not reported by Shimomura et al. (4). We cannot conclude whether the effect of NPW23 on water consumption was unique or secondary to increased solute ingestion as a result of feeding; however, the time course of food and water consumption overlapped, suggesting that the water intake occurred before any absorption of solute from the digestive tract. It will be important in the future to study the effect of central administration of NPW23 in ad libitum-fed and -watered animals on water drinking when food is not provided during the testing period and in animals stimulated to drink by water restriction. Behavioral testing will be required as well to ensure that the increased water and food intakes were not merely a reflection of generalized increases in spontaneous locomotor activity. This is a distinct possibility because the magnitude of stimulation of feeding and drinking is certainly not remarkable compared with the effects of central administration of even lower doses of neuropeptide Y or angiotensin II, respectively. Finally, it is possible that the increased feeding is a reflection of the increased plasma corticosterone levels, which might inhibit central CRH release resulting in a loss of the anorexic effect of CRH; however, this is unlikely because it appears that the NPW injected acted to increase CRH release.
Our findings indicate that exogenous NPW23 can act in brain to alter the neuroendocrine regulation of PRL, GH, and ACTH release. These data differ from those of the Takeda group (4) with regards PRL secretion in that we were able to demonstrate an elevation of PRL levels in conscious rats that was dose related and more pronounced than they observed with an even higher dose of peptide. It is not clear from their report (4) whether or not their animals were anesthetized during their study. The presence of GPR7 in hypothalamic PVN (2) suggests that our observed action of NPW to stimulate PRL secretion may have been due to a stimulatory effect of the peptide on TRH release into the median eminence. Alternatively, GPR7 is present in the arcuate nucleus as well (2), and the ability of NPW to raise PRL levels may be explained by an action to inhibit the activity of tubero-infundibular dopamine neurons in these regions, thus removing physiologic inhibition of PRL secretion. We currently are examining that latter possibility using the experimental approach employed by us in the past to uncover a role for dopamine withdrawal in PRL secretion subsequent to central peptide administration (8).
The profound elevation in plasma corticosterone levels suggests that centrally administered NPW activates the hypothalamo-pituitary-adrenal axis. Because GPR7 is present in the PVN (2), it is possible that this action of NPW is mediated via an increase in the activity of CRH neurons that project to the median eminence. We are examining that possibility now using established in vivo models (9). Alternatively, the rapid increase in plasma corticosterone levels may reflect the ability of centrally administered NPW23 to activate sympathetic outflow and therefore exert neural control over adrenal function.
Both the elevation in plasma PRL and corticosterone levels suggest a role for NPW in the organization of the hypothalamic response to stress. Unlike in humans where stress elevates GH concentrations in circulation (3), the acute effect of stress in rats is inhibitory (10). Thus, all three neuroendocrine components of the stress response in rats (elevated PRL and corticosterone and lowered GH levels) were observed following central administration of NPW23. In addition, the behavioral responses observed mirror those reported in behavioral models of stress. In conclusion, we have identified novel, dose-related actions of the newly described, endogenous ligand for the orphan receptors GPR7 and GPR8. These pharmacologic effects are now being examined for physiological significance with the hypothesis that endogenous NPW is a necessary signaling molecule for the expression of the hypothalamic response to stress.
| Acknowledgments |
|---|
| Footnotes |
|---|
Abbreviations: icv, Intracerebroventricular(ly); NPW, neuropeptide W; PRL, prolactin; PVN, paraventricular nucleus.
Received December 17, 2002.
Accepted for publication March 17, 2003.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
M. Kawasaki, T. Onaka, M. Nakazato, J. Saito, T. Mera, H. Hashimoto, H. Fujihara, N. Okimoto, H. Ohnishi, T. Nakamura, et al. Centrally administered neuropeptide W-30 activates magnocellular neurosecretory cells in the supraoptic and paraventricular nuclei with neurosecretion in rats. J. Endocrinol., August 1, 2006; 190(2): 213 - 223. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. Spinazzi, P. G. Andreis, G. P. Rossi, and G. G. Nussdorfer Orexins in the regulation of the hypothalamic-pituitary-adrenal axis. Pharmacol. Rev., March 1, 2006; 58(1): 46 - 57. [Abstract] [Full Text] [PDF] |
||||
![]() |
M S Mondal, H Yamaguchi, Y Date, K Toshinai, T Kawagoe, T Tsuruta, H Kageyama, Y Kawamura, S Shioda, Y Shimomura, et al. Neuropeptide W is present in antral G cells of rat, mouse, and human stomach J. Endocrinol., January 1, 2006; 188(1): 49 - 57. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Lin Chang, J. Roh, J.-I. Park, C. Klein, N. Cushman, R. V. Haberberger, and S. Y. T. Hsu Intermedin Functions as a Pituitary Paracrine Factor Regulating Prolactin Release Mol. Endocrinol., November 1, 2005; 19(11): 2824 - 2838. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. A. Kelly, C. T. Beuckmann, S. C. Williams, C. M. Sinton, T. Motoike, J. A. Richardson, R. E. Hammer, M. G. Garry, and M. Yanagisawa From the Cover: Neuropeptide B-deficient mice demonstrate hyperalgesia in response to inflammatory pain PNAS, July 12, 2005; 102(28): 9942 - 9947. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. Mazzocchi, P. Rebuffat, A. Ziolkowska, G. P. Rossi, L. K. Malendowicz, and G. G. Nussdorfer G Protein Receptors 7 and 8 Are Expressed in Human Adrenocortical Cells, and Their Endogenous Ligands Neuropeptides B and W Enhance Cortisol Secretion by Activating Adenylate Cyclase- and Phospholipase C-Dependent Signaling Cascades J. Clin. Endocrinol. Metab., June 1, 2005; 90(6): 3466 - 3471. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. S. Levine, R. Winsky-Sommerer, S. Huitron-Resendiz, M. K. Grace, and L. de Lecea Injection of neuropeptide W into paraventricular nucleus of hypothalamus increases food intake Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2005; 288(6): R1727 - R1732. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. M. Taylor, E. A. Yuill, J. R. Baker, C. C. Ferri, A. V. Ferguson, and W. K. Samson Actions of neuropeptide W in paraventricular hypothalamus: implications for the control of stress hormone secretion Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2005; 288(1): R270 - R275. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. M. Taylor and W. K. Samson A Possible Mechanism for the Action of Adrenomedullin in Brain to Stimulate Stress Hormone Secretion Endocrinology, November 1, 2004; 145(11): 4890 - 4896. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. S. Mondal, H. Yamaguchi, Y. Date, T. Shimbara, K. Toshinai, Y. Shimomura, M. Mori, and M. Nakazato A Role for Neuropeptide W in the Regulation of Feeding Behavior Endocrinology, November 1, 2003; 144(11): 4729 - 4733. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |