Abstract-The aim of the present study was to determine the relationship between the hypotensive effect of the atrial natriuretic peptide (ANP) and the nitric oxide (NO) pathway. N G -nitro-L-arginine methyl ester bolus (L-NAME, 1 mg/kg) reverted the decrease in mean arterial pressure induced by ANP administration (5 g/kg bolus and 0.2 g ⅐ kg Ϫ1 ⅐ min Ϫ1 infusion), and the injection of L-NAME before peptide administration suppressed the ANP hypotensive response. To confirm these findings, a histochemical reaction was used to determine NADPH-diaphorase activity (a NO synthase marker) in the endothelium and smooth muscle of aorta and arterioles of the small and large intestine. ANP increased aorta and arteriole endothelium staining after both in vivo administration and in vitro tissue incubation. In both cases, L-NAME prevented the ANP effect on NADPH-diaphorase activity. Tissues incubated with 8-bromoguanosine 3Ј, 5Ј-cyclic monophosphate mimicked ANP action. In addition, ANP administration increased urinary excretion of NO x end products. These findings indicate that ANP increases NO synthesis capability and NO production and suggest that the cGMP pathway may be involved. In conclusion, the NO pathway could be an intercellular messenger in the ANP endothelium-dependent vasorelaxation mechanism. (Hypertension. 2000;35:1119-1123.) Key Words: natriuretic peptides Ⅲ nitric oxide Ⅲ arterial pressure Ⅲ NADPH diaphorase Ⅲ cyclic GMP Ⅲ vasodilation A trial natriuretic peptide (ANP) and nitric oxide (NO), a free radical in the form of a highly diffusible gas, are vasoactive substances that induce hypotension through their vasorelaxant effects. 1 -3 Several factors, such as an increase in intracellular cGMP levels, a decrease in cytosolic Ca 2ϩ levels, and the activation of calcium-gated potassium channels, are involved in the cellular vasorelaxation mechanism. 4,5 An increase in cGMP results in the activation of cGMPdependent protein kinases and the phosphorylation of proteins involved in the dephosphorylation of myosin light chains, which is a precondition for smooth muscle relaxation. 6 Both ANP and NO induce an increase in intracellular cGMP levels, but they do so through different pathways. The cellular effects of ANP are mainly mediated by the guanylyl cyclase-coupled natriuretic receptors, natriuretic peptide receptor (NPR)-A and NPR-B. 7,8 These receptors are expressed on the surface of different types of cells, including renal endothelial cells, both arterial and venous smooth muscle and endothelial cells, etc. 6 These receptors present an intracellular protein kinaselike domain (KLD), a domain with an autoinhibitory function that mediates adenine nucleotide effects on the guanylyl cyclase domain. On binding of ANP to the extracellular domain of the receptor, a conformational change would ensue, allowing binding of ATP to the KLD. This, in turn, would lead to a further conformational change, freeing the guanylyl cyclase domain from the inhibitory constraint of the KLD and enabling cGMP production. 9 NO is produced ...

Background/Aims: Diabetes mellitus may impact on the regulation of renal Na⁺-glucose cotransporter type 2 (SGLT2), however, previous studies have yielded conflicting results on the effects of streptozotocin (STZ)-induced diabetes on SGLT-mediated glucose transport. Methods: Diabetes was induced in male Wistar rats. The studies were performed at 3 (D3), 7 (D7) and 14 (D14) days after a single i.p. injection of STZ. SGLT2 activity was measured using α-¹⁴C-methyl glucose uptake in brush-border vesicles (BBV) from renal cortex, and SGLT2 expression was assessed by immunoblotting. Phospholipids were quantified by a modification of Fiske-Subarow‘s method after being separated by thin-layer chromatography. Results: Glucose uptake was reduced in all groups of diabetic rats. SGLT2 expression decreased in D3 and D7. There was a decrease in sphingomyelin (SM) content and an increase in phosphatidylcholine (PC) content in BBV from D14 versus control, without differences in phosphatidylinositol (PI), phosphatidylserine (PS) and phosphatidylethanolamine (PE). Conclusion: The downregulation of SGLT2 activity during STZ-induced diabetes may be a protective mechanism to control the excess of circulating glucose and could be a consequence of a decrease in SGLT2 expression in D3 and D7, whereas altered activity of SGLT2 in D14 could be a consequence of changes in membrane lipid composition. However, we cannot discard the possibility that the decrease in SGLT2 activity could be due to a covalent modification of the active site of the protein.

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