Agmatine affects glomerular filtration via a nitric oxide synthase- dependent mechanism

Arginine decarboxylase is present in the kidney and metabolizes the amine acid, arginine, to agmatine. Agmatine increases filtration rate in single nephrons (J. J. Lortie, W. F. Novotny, O. W. Peterson, V. Vallon, K. Malvey, M. Mendonca, J. Satriano, P. Insel, S. C. Thomson, and R. C. Blantz. J. Clin. Invest. 97: 413-420, 1996). Experiments were conducted to determine whether exogenously administered agmatine exerts these effects via interaction with nitric oxide synthase (NOS) and whether this interaction depends upon α₂-adrenergic receptors. Agmatine microperfused (1 μM) into the urinary space of surface glomeruli of the rat increased nephron filtration rate from 33 ± 4 to 40 ± 5 nl/min with complete recovery within 10 min. When N(G)-monomethyl-L-arginine (L-NMMA), a nonselective NOS inhibitor, was systemically infused, agmatine no longer increased single- nephron glomerular filtration rate (SNGFR). BHT-933, an α₂-adrenergic agonist, did not increase SNGFR and was unaffected by concurrent L-NMMA. In vitro incubation of fleshly harvested glomeruli with agmatine resulted in significant increases in the generation of cGMP, effects similar to carbachol, and blocked by nitro-L-arginine methyl ester (L-NAME) but not yohimbine, an α₂-adrenergic antagonist. Agmatine exerts effects on glomerular ultrafiltration via a constitutive NOS-dependent mechanism, and this does not require the participation of α₂-adrenoreceptors.