title: Role of melanocortin-4 receptors in mediating renal sympathoactivation to leptin and insulin.
abstract: Central melanocortin signaling plays an important role in regulation of energy homeostasis by leptin and insulin. We investigated the interaction between leptin, insulin, and melanocortin-4 receptors (MC-4Rs) in the control of renal sympathetic nerve activity (RSNA) in mice. We compared the effects of intracerebroventricular (ICV) administration of leptin, insulin, MC-3/4R agonist (MTII), and corticotrophin-releasing factor (CRF) on RSNA in leptin receptor-deficient (db/db) mice, MC-4R knock-out mice, and their wild-type controls. ICV administration of leptin and MTII caused a significant and dose-dependent increase in RSNA in control mice. As expected, leptin had no significant effect on RSNA in the db/db mice. Interestingly, db/db mice exhibited markedly attenuated RSNA responses to ICV administration of MTII. However, the increase in RSNA induced by insulin and CRF was comparable between db/db and control mice. In the heterozygous and homozygous MC-4R knock-out mice, the RSNA response to MTII was attenuated and abolished, respectively. The RSNA response to ICV leptin and insulin was also attenuated and abolished in the heterozygous and homozygous MC-4R knock-out mice, respectively. In contrast, CRF induced a similar increase in RSNA in the MC-4R knock-out and wild-type mice. Our data demonstrate that in the absence of leptin receptors, the sympathoexcitatory effects of melanocortin system stimulation are attenuated. In addition, the renal sympathoexcitatory responses to leptin and insulin are dependent on the MC-4R, demonstrating an important role for the MC-4R in the regulation of renal sympathetic nerve outflow by leptin and insulin.
authors.affiliation: Hypertension Genetics Specialized Center of Research, and Department of Internal Medicine, University of Iowa and the Veterans Administration Medical Center, Iowa City, Iowa 52242, USA. kamal-rahmouni@uiowa.edu
authors.forename: Kamal
authors.initials: K
authors.lastname: Rahmouni
authors.forename: William G
authors.initials: WG
authors.lastname: Haynes
authors.forename: Donald A
authors.initials: DA
authors.lastname: Morgan
authors.forename: Allyn L
authors.initials: AL
authors.lastname: Mark
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D003346:Corticotropin-Releasing Hormone / Q000008:administration & dosage / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D007276:Injections, Intraventricular; D007328:Insulin / Q000008:administration & dosage / Q000097:blood / Q000502:physiology*; D007668:Kidney / Q000294:innervation / Q000502:physiology*; D020738:Leptin / Q000008:administration & dosage / Q000097:blood / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D044105:Receptor, Melanocortin, Type 4; D011956:Receptors, Cell Surface / Q000172:deficiency / Q000235:genetics; D018043:Receptors, Corticotropin / Q000819:agonists / Q000235:genetics / Q000502:physiology*; D054411:Receptors, Leptin; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D000521:alpha-MSH / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D007328:Insulin; D020738:Leptin; D044105:Receptor, Melanocortin, Type 4; D011956:Receptors, Cell Surface; D018043:Receptors, Corticotropin; D054411:Receptors, Leptin; C081720:alpha-MSH (4-10)amide, Ac-Nle(4)-cyclo(Asp(5)-Phe(7)-Lys(10))-; C515447:leptin receptor, mouse; D000521:alpha-MSH; D003346:Corticotropin-Releasing Hormone