title: Activation of protein kinase B/Akt and endothelial nitric oxide synthase mediates agmatine-induced endothelium-dependent relaxation.
abstract: The ability of agmatine, formed from L-arginine by the enzyme arginine decarboxylase (ADC), to modulate vasomotor function in rat aorta was investigated in the present study. Agmatine-mediated modulation of vasomotor tone was studied in organ chambers, protein expression quantified by Western blot analysis and cyclic guanosine 5'-monophosphate (cGMP) levels measured by radioimmunoassay. Agmatine (10(-10) to 10(-3) M) produced concentration-dependent relaxations (82+/-5%) in phenylephrine-contracted endothelium intact rat aorta. Relaxations to agmatine were diminished on denudation of endothelium and nitric oxide synthase (NOS) inhibition by L-Nomega-nitro arginine or soluble guanylate cyclase inhibition by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (P<0.001) abolished agmatine-mediated relaxations, while relaxations were insensitive to inducible NOS inhibition by 1400W. Agmatine-treated aorta demonstrated increased protein expression of phosphorylated S473-Akt and phosphorylated S1177-endothelial nitric oxide synthase (eNOS), and elevated the levels of cyclic GMP (P<0.01). Agmatine-mediated potentiation of relaxations and elevation of cGMP levels was sensitive to phosphatidylinositol 3'-kinase inhibitor, wortmannin. Relaxations to agmatine were also affected by pre-treatment with tetraethylammonium (P<0.01) or apamin (P<0.05), and were not affected by charybdotoxin. Relaxations to agmatine were partially affected by pre-treatment of aortic rings with barium chloride (P<0.05), and glybenclamide (P<0.05). Results obtained suggest that agmatine activates protein kinase B/Akt to phosphorylate eNOS and elevate cyclic GMP levels to produce vasodilatation of aorta. Agmatine-mediated relaxations in rat aorta seems to be mediated mainly by endothelial NO-mediated activation of small conductance Ca2+-activated K+ channels, and partly by ATP-sensitive and inward rectifying K+ channels.
authors.affiliation: Department of Anesthesiology, and Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA. santhanam.anantha@mayo.edu
authors.forename: Anantha Vijay R
authors.initials: AV
authors.lastname: Santhanam
authors.forename: Shivkumar
authors.initials: S
authors.lastname: Viswanathan
authors.forename: Madhu
authors.initials: M
authors.lastname: Dikshit
mesh_terms: D000376:Agmatine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology; D006152:Cyclic GMP / Q000378:metabolism; D004730:Endothelium, Vascular / Q000502:physiology*; D004789:Enzyme Activation; D066298:In Vitro Techniques; D054086:KATP Channels / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000502:physiology; D008297:Male; D009126:Muscle Relaxation; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000502:physiology
chemical_list: D054086:KATP Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D051640:Small-Conductance Calcium-Activated Potassium Channels; D000376:Agmatine; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; D006152:Cyclic GMP