Comparison of mammalian prolactin-releasing peptide and Carassius RFamide for feeding behavior and prolactin secretion in chicks

doi:10.1016/j.ygcen.2005.06.012

General and Comparative Endocrinology

Volume 144, Issue 3, December 2005, Pages 264-269

https://doi.org/10.1016/j.ygcen.2005.06.012 Get rights and content

Abstract

Prolactin-releasing peptide (PrRP) was named for its originally reported effects as a prolactin (PRL) secretagogue in mammals. Carassius RFamide (C-RFa) is an orthologous PRL secretagogue in fishes and a gene encoding a 20-amino acid peptide of identical sequence is present in the chicken. These facts suggest that C-RFa is a putative chicken PrRP. However, no information is available for the physiological effects of C-RFa in chickens. Therefore, in the present study, we compared the effect of intracerebroventricular (ICV) injection of C-RFa and mammalian PrRP (mPrRP) on feeding behavior and plasma PRL, growth hormone (GH), and corticosterone (CORT) concentrations. ICV injection of C-RFa did not affect feeding behavior of chicks while mPrRP was stimulatory. The injection of C-RFa also did not significantly affect plasma PRL, GH, and CORT concentrations. In contrast, ICV injection of mPrRP exerted similar effects to those reported in mammals by increasing plasma CORT and decreasing GH concentrations. Additionally, the peptide induced an unexpected inhibitory effect on plasma PRL concentrations. Overall, these data suggest that an as yet unidentified peptide that shares some functional similarities with mPrRP is present in birds, but that the physiological role of the avian 20-amino acid C-RFa peptide remains to be determined.

Introduction

Prolactin-releasing peptide (PrRP, Fig. 1) was identified as a ligand for an orphan receptor and was originally proposed to be a stimulator of prolactin (PRL) release in mammals (Hinuma et al., 1998, Matsumoto et al., 1999). Physiological effects of the peptide on the neuroendocrine system are broader, including inhibition of growth hormone (GH) release (Iijima et al., 2001) and stimulation of luteinizing hormone, follicle-stimulating hormone, oxytocin, and adrenocorticotrophic hormone release (Maruyama et al., 1999a, Maruyama et al., 1999b, Matsumoto et al., 2000, Seal et al., 2000). Central administration of PrRP was also reported to decrease food intake in rats, suggesting that PrRP is involved in the regulation of behavior in mammals, in addition to its neuroendocrine effects (Lawrence et al., 2000).

We recently reported that intracerebroventricular (ICV) injection of mammalian PrRP (mPrRP) stimulated feeding behavior in chicks in contrast to the inhibitory effect observed in mammals (Tachibana et al., 2004). This suggested the existence of an endogenous chicken PrRP that is involved in the regulation of food intake. One possible candidate is Carassius RFamide (C-RFa, Fig. 1), a PRL secretagogue in teleost fish that is thought to be a piscine orthologue of mPrRP (Fujimoto et al., 1998, Moriyama et al., 2002, Satake et al., 1999, Seale et al., 2002). A C-RFa-like nucleotide sequence is present in the chickEST database (http://chick.umist.ac.uk/) and the translated 20-amino acid peptide sequence is identical to that of C-RFa. This suggests that C-RFa may be a chicken PrRP. However, no reports are available on the effect of C-RFa on feeding behavior and neuroendocrine secretion in chicks.

The purpose of the present study was therefore to investigate whether central administration of C-RFa influences food intake and plasma PRL, GH, and corticosterone (CORT) concentrations. Furthermore, the effects of C-RFa were compared with those of mPrRP.

Section snippets

Animals

Day-old male layer-type chicks (purchased from Murata Hatchery, Fukuoka, Japan) were maintained in a room at 30 °C under continuous lighting. The birds were freely given a commercial diet (Toyohashi Feeds and Mill, Aichi, Japan) and water except elsewhere noted. All experimental procedures were done according to the guidance for Animal Experiments in the Faculty of Agriculture and in the Graduate Course of Kyushu University and the Law (No.105) and Notification (No.6) of the Government.

ICV injection

Synthetic

Experiment 1: effects of ICV injection of C-RFa and mPrRP on food intake

Fig. 2 shows the effects of ICV injection of C-RFa and PrRP on food intake of chicks. A significant effect [F (4, 24) = 7.7, P < 0.01] was detected and the post hoc test revealed that ICV injection of both doses of C-RFa did not affect food intake compared to the control. On the other hand, 375 pmol PrRP significantly increased food intake when compared with other treatments.

Experiment 2: effects of ICV injection of C-RFa and mPrRP on plasma PRL, GH, and CORT concentrations

Plasma PRL, GH, and CORT concentrations after ICV injection of C-RFa are shown in Fig. 3. C-RFa treatment did not affect plasma

Discussion

In our previous report, ICV administration of 375 pmol mPrRP stimulated food intake of chicks (Tachibana et al., 2004). This effect was reproduced here. However, the putative chicken PrPR C-RFa did not affect food intake of chicks at a dose of 375 pmol (Fig. 2). Therefore, we also tested the effect of C-RFa up to a dose 1500 pmol, but no significant effects were observed (data not shown). Therefore, central C-RFa seems not to be involved in the regulation of feeding in the chick.

Although C-RFa is

Acknowledgments

This work was supported by a Grant-in-Aid for Young Scientists (No. 15780187) and a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science. We thank Nagoya University Radioisotope Center for use of facilities and Dr. A.F. Parlow and NIDDK National Hormone & Peptide Program for providing the chicken PRL and GH radioimmunoassay systems. We also thank Dr. K. Ukena, Hiroshima University, Japan, for his advices.

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Comparison of mammalian prolactin-releasing peptide and Carassius RFamide for feeding behavior and prolactin secretion in chicks

Abstract

Introduction

Section snippets

Animals

ICV injection

Experiment 1: effects of ICV injection of C-RFa and mPrRP on food intake

Experiment 2: effects of ICV injection of C-RFa and mPrRP on plasma PRL, GH, and CORT concentrations

Discussion

Acknowledgments

Horm. Behav.

Physiol. Behav.

Poult. Sci.

Biochem. Biophys. Res. Commun.

Gen. Comp. Endocrinol.

Neurosci. Lett.

Biochem. Biophys. Res. Commun.

Neurosci. Lett.

Regul. Pept.

FEBS Lett.

Gen. Comp. Endocrinol.

Neurosci. Lett.