465

Braz J Med Biol Res 30(4) 1997

ANP and feedingBrazilian Journal of Medical and Biological Research (1997) 30: 465-469ISSN 0100-879X

Atrial natriuretic peptide and feedingactivity patterns in rats

1Departamento de Medicina, Universidade Federal de Sergipe, 49060-100Aracaju, SE, Brasil2Centre de Recherche Hôtel-Dieu de Montreal, Pavilion Marie-de-la-Ferre,Montréal, Quèbec, H2W 1T8, CanadaDepartamentos de 3Fisiologia and 4Clínica Médica,Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo,14048-900 Ribeirão Preto, SP, Brasil

M.H.A. Oliveira1,J. Antunes-Rodrigues3,

J. Gutkowska2,A.M.O. Leal4,

L.L.K. Elias4 andA.C. Moreira4

Abstract

This review presents historical data about atrial natriuretic peptide(ANP) from its discovery as an atrial natriuretic factor (ANF) to its roleas an atrial natriuretic hormone (ANH). As a hormone, ANP caninteract with the hypothalamic-pituitary-adrenal axis (HPA-A) and isrelated to feeding activity patterns in the rat. Food restriction proved tobe an interesting model to investigate this relationship. The role ofANP must be understood within a context of peripheral and centralinteractions involving different peptides and pathways.

CorrespondenceA.C. MoreiraDepartamento de Clínica MédicaFaculdade de Medicina deRibeirão Preto, USP14048-900 Ribeirão Preto, SP

BrasilFax: 55 (016) 633-1144

Presented at the International

Symposium �NeuroendocrineControl of Body Fluid Homeostasis�,Ribeirão Preto, SP, Brasil,August 17-20, 1996.

Research supported by CNPq andHCFMRP-FAEPA. Publicationsupported by FAPESP.

Received November 29, 1996Accepted January 6, 1997

Key words• Atrial natriuretic peptide• Corticosterone• ACTH• Food restriction

A factor, at the beginning

The discovery of a natriuretic factor fromcardiac atria (1,2) led to further characteriza-tion of a complex natriuretic hormonal sys-tem, including a 126-amino acid prohormonesynthesized within myocytes of the heart andstored in granules for release into the circu-lation. This hormonal system includes sev-eral peptides such as the prohormone pro-atrial natriuretic factor (ANF) 1-30, a long-acting sodium stimulator, pro-ANF 31-67, avasodilator, pro-ANF 79-98, a kaliureticstimulator, and pro-ANF 99-126. Each ofthese peptides has blood pressure-lowering,diuretic, natriuretic, and/or kaliuretic prop-erties in both humans and animals. Whenreleased into the circulation, these peptidescirculate as a 28-amino acid C-terminus (i.e,ANF) of this prohormone and as a 98-aminoacid N-terminus which is proteolytically

cleaved into pro-atrial natriuretic peptide(ANP) 31-67 and pro-ANF 1-30. The pep-tides enhance the particulate form of theenzyme guanylate cyclase increasing the in-tracellular messenger cGMP that has beenshown to be the final mediator of the ob-served vasodilatation and natriuresis sec-ondary to atrial natriuretic peptides (3,4). Asingle ANF gene has been identified in allmammalian species examined to date. Inman this gene is located on chromosome 1,band p36, and is one of a syntenic group thatis present on chromosome 4 of the mouse.The gene consists of three exons separatedby two introns. More recently, brain natri-uretic peptide (BNP) and C-type natriureticpeptide (CNP) and at least three subtypes ofreceptors were identified (5). In this reviewwe will use the name ANP although the termatrial natriuretic hormone (ANH) would bemore appropriate.

466

Braz J Med Biol Res 30(4) 1997

M.H.A. Oliveira et al.

Atrial, but not only atrial

ANP has been identified in many differ-ent tissues and may have several importantphysiological functions other than natriure-sis and vasodilation. In brain it exists asamino-terminally truncated form. Two sys-tems are involved in the secretion of ANP:peripheral ANP (heart and plasma) and cen-tral ANP (paraventricular, periventricular,arcuate, and pre-optical-medial nuclei andother sites) (6). Despite the blood-brain bar-rier, these systems communicate through thecircumventricular organs, the organumvasculosum lamina terminalis and the or-ganum subfornicalis (7-9). They are con-nected by neuronal synapses (9-14), or bydischarge of peptides such as vasopressin(15), endothelin (11) and oxytocin (16) fromthe hypothalamus. Therefore, ANP may par-ticipate in the control of different functionssuch as the reduction of the activity of therenin-angiotensin-aldosterone system and in-hibition of salt and water intake in the rat(17,18). Nevertheless, ANP originating fromthe paraventricular nucleus (PVN) is respon-sible for 87 to 92% of the content of ANP inthe median eminence and is involved in theregulation of the function of the anteriorpituitary (19). Several experiments usingimmunoneutralization techniques have dem-onstrated that ANP, in addition to participat-ing in the control of LH and prolactin secre-tion (20,21), may be a factor inhibiting corti-cotropin release (21-24).

Natriuretic, but where?

ANP was discovered on the basis of itspharmacological properties of producing di-uresis and natriuresis, although at the pe-riphery its vasodilating action is probablymore important. Transgenic mice with ANPlevels 2- to 10-fold the normal values exhibitessentially normal fluid and electrolyte ho-meostasis, a fact that argues against a funda-mental role of peripheral ANP in water and

sodium metabolism. However, the mice withthe highest ANP levels were significantlyhypotensive indicating that these pharmaco-logic renal effects of the peptide are lessimportant than its hemodynamic actions (4).On the other hand, in rats or in humans, highANP concentrations are hypotensive evenwhen they are lower than natural concentra-tions in the pituitary portal system, and areable to inhibit ACTH secretion in vitro (25).Nevertheless, under appropriate conditions,the antagonism between the natriuretic pep-tide system and the renin-angiotensin systemcan promote natriuresis. For instance, ANPinhibition of stress-induced vasopressin re-lease may increase renal water loss and thediminished ACTH release induced by ANPmay lead to a reduction in aldosterone secre-tion, thereby diminishing the stress-inducedsodium retention (26), a mechanism demon-strating the central natriuretic action ofANP.

And what else? ANP and the HPA-A

Two lines of research have been exhaus-tively followed by our group since the earlyeighties. First, the investigation involved thebrain ANPergic neuron system and its role asantagonist of the renin-angiotensin system,its influence on ANP release including ANPrelease induced by volume expansion (9-14,17-18), and other hormonal effects of thebrain ANP system on LH, prolactin, GH,TSH, and ACTH secretion (20,24). In paral-lel, we investigated the circadian rhythmi-city of the hypothalamic-pituitary-adrenalaxis (HPA-A) in rats with continuous orrestricted access to food (27). It is well knownthat rats manifest a circadian peak of plasmacorticosterone and ACTH just before theonset of predominant food intake (28). Wedemonstrated for the first time circadian andparallel ANP and corticosterone variationsin rats with continuous (peak at 20:00 h) orrestricted access to food from 9:00 to 11:00h, with a peak at 8:00 h (29). Both lines of

467

Braz J Med Biol Res 30(4) 1997

ANP and feeding

investigation led to a better understanding ofthe relationship between brain and peripher-al ANP involving neuronal and peptidergicinteractions. The activation of the centralnoradrenergic pathway is involved in thevolume expansion-induced ANP release andthe circadian variation of corticosterone andANP in rats. High levels of noradrenalineand elevated numbers of alpha-2-adrenore-ceptors are found in PVN (30), producing alarge burst of food intake and activity at thebeginning of the dark period simultaneouslywith an increase of cardiac rate and pressure(31). In addition, the central noradrenergicpathway is activated before feeding time infood-restricted rats. Food restriction inducesa disruption of activity-rest and sleep-wakepatterns with changes in the hippocampalcontent of norepinephrine and serotonin, andin the cortical content of serotonin (32), andcorticotropin-releasing hormone (CRH)-re-lated neurotransmitters involved in feedingbehavior (33). Feeding patterns result from acomplex balance between anorectic (CRH,cholecystokinin (CCK), neurotensin) andorectic (neuropeptide Y (NPY), pancreaticpolypeptide, galanine) factors, constitutinga complex circuitry. CRH and NPY deserveadditional comments. Food restriction in-duces an increase of NPY mRNA level in thearcuate nucleus and reduces the CRH mRNAlevel in PVN in a physiological response torestore food intake (34). Dallman et al. (35)suggested that the NPYergic system, the ac-tivity of which is increased by fasting andreduced by feeding, by insulin and lack ofglucocorticoids, may mediate the fasting-induced override of diurnal rhythms in theHPA-A. We propose that the food-restrictedhigh corticosterone levels may contribute tothe observed reduction of CRH mRNAthrough an action of ANP. In addition, glu-cocorticoids areable to stimulate ANP secre-tion or genic activity (36-41). This effectmay be consistent with a possible hypotha-lamic-cardio-adrenal feedback control mech-anism (29).

Diurnal ANP variations andfood restriction

Because rats drink when they eat and eatwhen they drink, restriction of water or foodeffectively restricts consumption of both (35).To test the hypothesis of food restrictionbeing a paramount “zeitgeber” for the diur-nal variation of corticosterone, ACTH andANP and to determine the role of waterrestriction, we studied these rhythms in wa-ter-restricted rats (water from 9:00-11:00 h).Water-restricted rats showed a double corti-costerone peak at 8:00 and 20:00 h and anACTH peak at 8:00 h, and did not showdiurnal variation of ANP. We concluded thatfood intake is a more important synchronizerthan water intake for the activity and HPArhythmicity. We believe that the effects ofwater restriction on corticosterone and ACTHsecretion are mediated by changes in foodintake since there is a spontaneous burst offeeding in the presence of a water supply.Water-restricted rats are less active duringthe light period than food-restricted rats. Infact, food-restricted rats with exclusive 0.9%or 1.5% NaCl intake exhibit more hyperac-tivity and more intense drink-seeking behav-ior, thereby abolishing the diurnal circadianvariation in ANP due to a high ANP secre-tion during this period. Free fed adrenalecto-mized rats showed no diurnal ANP varia-tion. This may be attributed to a reduction ofthe spontaneous food intake and activity dur-ing the dark period in comparison to the lightperiod, due to a reduction in the alpha-2-adrenoreceptors in PVN, as shown byBhakthavatsalam and Leibowitz (42) andJhanwar-Uniyal et al. (30). We do not knowwhether a stimulating effect of glucocorti-coids on the genic transcription of ANP con-tributes to the evening ANP peak and iseventually suppressed by adrenalectomy(ADX). We demonstrated that dexametha-sone (50 µg/kg body weight) administeredintraperitoneally to ADX rats produced adrastic reduction of ACTH accompanied by

468

Braz J Med Biol Res 30(4) 1997

M.H.A. Oliveira et al.

a pronounced ANP increase within 90 min.This result suggests that a simultaneous in-crease in portal ANP content may mediatethe reduction of ACTH hypersecretion inADX rats. It is interesting that this feedbackmechanism uses the same type II receptorthat mediates the high food intake occurringat the onset of darkness, which is abolishedby ADX and restored by corticosterone (43).

ANP, a feeding-related peptide?Peripheral or central actions?

The interaction between insulin and cor-ticosteroid serves as a peripheral hormonalfeedback loop that regulates the well-knownNPYergic feeding and fasting system, but ifplasma insulin levels were elevated in anattempt to increase CNS insulin levels (inthe hope of observing a consequent decreasein food intake) the resulting hypoglycemiawould elicit an emergency increase in foodintake (44). Similarly, if plasma ANP levels

were increased to the high levels needed toinhibit the HPA-A, the resulting hypoten-sion could have a stimulatory effect. There-fore, central ANP sites (PVN, arcuatenucleus, perifornical lateral hypothalamus,AV3V, subfornical organ, supraopticnucleus) may act as integrating sites of acomplex system that couples feeding, HPA-A, physical activities and cardiovascular sta-tus. Corticosteroids and insulin may act asperipheral signals, and the locus ceruleus,nucleus tractus solitarius and dorsomedialnucleus as intermediate stations. The activa-tion of noradrenergic and serotonergic path-ways may be involved, but the nature ofother interactions and peptides deserves fur-ther study.

Acknowledgments

The authors thank Miss Ana Cristina C.Pereira and Mr. Alex A. da Silva for secre-tarial assistance.

References

1. De Bold AJ, Borenstein HB, Yerss AT &Sonnenberg H (1981). A rapid and potentnatriuretic response to the intravenous in-jection of atrial myocardial extract in rats.Life Sciences, 28: 89-94.

2. De Bold AJ (1985). Atrial natriuretic fac-tor. A hormone produced by the heart.Science, 230: 767-770.

3. Vesely DL, Douglass MA, Dietz JR,Giordano AT, McCormick MT, Rodrigues-Paz G & Schocken DD (1994). Negativefeedback of atrial natriuretic peptides.Journal of Clinical Endocrinology and Me-tabolism, 78: 1128-1134.

4. Rosenzweig A & Seidman CE (1991).Atrial natriuretic factor and related pep-tide hormones. Annual Review of Bio-chemistry, 60: 229-255.

5. Imura H, Nakao K & Itoh H (1992). Thenatriuretic peptide system in the brain:implications in the central control of car-diovascular and neuroendocrine func-tions. Frontiers in Neuroendocrinology,13: 217-249.

6. Ma LY, Zhang ML, Yang XD, Tian DR, QiJS & Zhang DM (1991). Neuroendocrinol-ogy of atrial natriuretic polypeptide in thebrain. Neuroendocrinology, 53: 12-17.

7. Phillips MI, Kimura B, Wang H & HoffmanWE (1989). Effect of vagotomy on brainand plasma atrial natriuretic peptide dur-ing hemorrhage. American Journal ofPhysiology, 257: 1393-1399.

8. Bahner U, Geiger H, Palkovits M, GantemD, Michel J & Heidland A (1990). Atrialnatriuretic peptides in brain nuclei of ratswith inherited diabetes insipidus (Brattle-boro rats). Neuroendocrinology, 51: 721-727.

9. Antunes-Rodrigues J, Ramalho MJ, ReisLC, Menani JV & Turrin MQA (1991). Le-sions of the hypothalamus and pituitaryinhibit volume-expansion-induced releaseof atrial natriuretic peptide. Proceedingsof the National Academy of Sciences,USA, 88: 2956-2960.

10. Antunes-Rodrigues J, Machado BH,Andrade HA, Mauad H, Ramalho MJ, ReisLC, Silva-Netto CR, Favaretto ALV,Gutkowska J & McCann SM (1992). Ca-rotid-aortic and renal baroreceptors medi-ate the atrial natriuretic peptide releaseinduced by blood volume expansion. Pro-ceedings of the National Academy of Sci-ences, USA, 89: 6828-6831.

11. Antunes-Rodrigues J, Marubayashi U,Favaretto ALV & Gutkowska J (1993). Es-sential role of hypothalamic muscarinicand alpha-adrenergic receptors in atrial na-triuretic peptide release induced by bloodvolume expansion. Proceedings of the Na-tional Academy of Sciences, USA, 90:10240-10244.

12. Antunes-Rodrigues J, Picanço-Diniz WL,Favaretto ALV, Gutkowska J & McCannSM (1993). Brain atrial natriuretic peptideneurons play an essential role in volumeexpansion-induced release of atrial natri-uretic peptide and natriuresis. Neuroen-docrinology, 58: 696-700.

13. Antunes-Rodrigues J, Ramalho MJ, ReisLC, Picanço-Diniz DWL, Favaretto ALV,Gutkowska J & McCann SM (1993). Thepossible role of endothelin acting withinthe hypothalamus to induce the releaseof atrial natriuretic peptide and natriure-sis. Neuroendocrinology, 58: 701-708.

14. Reis LC, Ramalho MJ, Favaretto AL,Gutkowska J, McCann SM & Antunes-Rodrigues J (1994). Participation of theascending serotonergic system in thestimulation of atrial natriuretic peptide re-lease. Proceedings of the National Acade-my of Sciences, USA, 91: 12022-12026.

469

Braz J Med Biol Res 30(4) 1997

ANP and feeding

15. Manning PT, Scwartz D, Katsube NC,Holmberg SW & Needleman P (1985). Va-sopressin-stimulated release of atriopep-tin: endocrine antagonists in fluid homeo-stasis. Science, 229: 395-397.

16. Haanwinckel MA, Elias LK, Favaretto ALV,Gutkowska J, McCann SM & Antunes-Rodrigues J (1995). Oxytocin mediatesatrial natriuretic peptide release and natri-uresis after volume expansion in the rat.Proceedings of the National Academy ofSciences, USA, 92: 7902-7906.

17. Antunes-Rodrigues J, McCann SM &Samson WK (1986). Central administra-tion of atrial natriuretic factor inhibits sa-line preference in the rat. Endocrinology,118: 1726-1728.

18. Baldissera S, Menani JV, Sotero S,Favaretto ALV, Gutkowska J, Turrin MQA,McCann SM & Antunes-Rodrigues J(1989). Role of the hypothalamus in thecontrol of atrial natriuretic peptide release.Proceedings of the National Academy ofSciences, USA, 86: 9621-9625.

19. Palkovits M, Eskay RL & Antoni FA (1987).Atrial natriuretic peptide in the medianeminence is of paraventricular nucleus ori-gin. Neuroendocrinology, 46: 542-544.

20. Franci CR, Anselmo-Franci JA & McCannSM (1990). Opposite effects of centralimmunoneutralization of angiotensin II oratrial natriuretic peptide on luteinizing hor-mone release in ovariectomized rats. Neu-roendocrinology, 51: 683-687.

21. Fink G, Dow RC, Casley D, Johnston CI,Lim AT, Copolov DL, Bennie J, Carroll S &Dick H (1991). Atrial natriuretic peptide isa physiological inhibitor of ACTH release:evidence from immunoneutralization invivo. Journal of Endocrinology, 131: 9-12.

22. Antoni FA, Hunter EFM, Lowry PJ, NobleJM & Seckl JR (1992). Atriopeptin: anendogenous corticotropin-release inhibit-ing hormone. Endocrinology, 130: 1753-1755.

23. Fink G, Dow RC, Casley D, Johnston CI,Bennie J, Carroll S & Dick H (1992). Atrialnatriuretic peptide is involved in the ACTHresponse to stress and glucocorticoidnegative feedback in the rat. Journal ofEndocrinology, 135: 37-43.

24. Franci CR, Anselmo-Franci JA & McCannSM (1992). The role of endogenous atrialnatriuretic peptide in resting and stress-induced release of corticotropin, prolac-tin, growth hormone, and thyroid-stimu-lating hormone. Proceedings of the Na-tional Academy of Sciences, USA, 89:11391-11395.

25. Lim AT, Shewardt WJ, Copolov D, Wind-mill D & Fink G (1990). Atrial natriureticfactor is released into hypophysial portalblood: direct evidence that atrial natriuret-ic factor may be a neurohormone involvedin hypothalamic pituitary control. Journalof Neuroendocrinology, 2: 15-17.

26. McCann SM, Gutkowska J, Franci CR,Favaretto ALV & Antunes-Rodrigues J(1994). Hypothalamic control of water andsalt intake and excretion. Brazilian Journalof Medical and Biological Research, 27:865-884.

27. Moreira AC & Krieger DT (1982). The ef-fects of subdiaphragmatic vagotomy oncircadian corticosterone rhythmicity in ratswith continuous or restricted food access.Physiology and Behavior, 28: 787-790.

28. Krieger DT (1979). Rhythms in CRF, ACTHand Corticosteroids. Raven Press, NewYork, 123-142.

29. Oliveira MHA, Antunes-Rodrigues J, LealAMO, Elias LLK & Moreira AC (1993).Circadian variations of plasma atrial natri-uretic peptide and corticosterone in ratswith continuous or restricted access tofood. Life Sciences, 53: 1795-1801.

30. Jhanwar-Uniyal M, Roland CR & LeibowitzSF (1986). Diurnal rhythm of alpha-2-nor-adrenergic receptors in the paraventricularnucleus and other brain areas: relation tocirculating corticosterone and feeding be-havior. Life Sciences, 38: 473-482.

31. Jansen BJA, Tyssen CM, Duindam H &Rietveld WJ (1994). Suprachiasmatic le-sions eliminate 24-h blood pressure vari-ability in rats. Physiology and Behavior,55: 302-311.

32. Krieger DT (1974). Food and water restric-tion shifts corticosterone, temperature,activity and brain amine periodicity. Endo-crinology, 95: 1195-1201.

33. Beck B (1992). Cholécystokinine,neurotensine et corticotropin-releasingfactor, trois importants peptidesanorexigènes. Annales d�Endocrinologie,53: 44-56.

34. Brady LS, Smith MA, Gold PW &Herkenham M (1990). Altered expressionof hypothalamic neuropeptide mRNAs infood-restricted and food-deprived rats.Neuroendocrinology, 52: 441-447.

35. Dallman MF, Strack AM, Akana SF,Bradbury MJ, Hanson ES, Scribner KA &Smith M (1993). Feast and famine: criticalrole of glucocorticoids with insulin in dailyenergy flow. Frontiers in Neuroendocri-nology, 5: 315-321.

36. Gardner DG, Hane S, Trachewsky D,Schenk D & Baxter JD (1986). Atrial natri-uretic peptide mRNA is regulated by glu-cocorticoids in vivo. Biochemical and Bio-physical Research Communications, 139:1047-1054.

37. Shields PP, Dixon JE & Glembotski CC(1988). The secretion of atrial natriureticfactor (99-126) by cultured cardiac myo-cytes is regulated by glucocorticoids.Journal of Biological Chemistry, 263:12619-12628.

38. Huang W, Choi GL, Yang Z, Copolov DL &Lim AT (1991). Plasticity of adrenoceptorresponsiveness on irANP secretion andpro-ANP mRNA expression in hypotha-lamic neuron cultures: modulation bydexamethasone. Endocrinology, 128:2591-2600.

39. Weidmann P, Matter DR, Matter EE,Gnadinger MP, Uehlinger DE, Shaw S &Hess C (1988). Glucocorticoid and miner-alocorticoid stimulation of atrial natriuret-ic peptide release in man. Journal of Clini-cal Endocrinology and Metabolism, 66:1233-1239.

40. Saxenhofer H, Angst M, Weidmann P,Shaw SG & Ferrier C (1988). Corticoste-roid-induced stimulation of atrial natriuret-ic peptide in man. Acta Endocrinologica,118: 179-186.

41. Garcia R, Debinski W, Gutkowska J,Kuchel O, Thibault G, Genest J & CantinM (1985). Gluco- and mineralocorticoidsmay regulate the natriuretic effect andthe synthesis and release of atrial natri-uretic factor by the rat atria in vivo. Bio-chemical and Biophysical Research Com-munications, 131: 806-814.

42. Bhakthavatsalam P & Leibowitz SF (1986).Alpha-2 noradrenergic feeding rhythm inparaventricular nucleus: relation to corti-costerone. American Journal of Physiolo-gy, 250: 83-88.

43. Tempel LD, Yamamoto M, Kim T &Leibowitz SF (1991). Effects of adrenalec-tomy on macronutrient selection patternsin the rat. Pharmacology, Biochemistryand Behavior, 40: 861-866.

44. Schwartz MW, Figlewicz DP, Baskin DG,Woods SC & Porte D (1992). Insulin in thebrain: a hormonal regulator of energy bal-ance. Endocrine Reviews, 13: 387-414.