Adenosine regulates renal nitric oxide production in hypothyroid rats

Abstract

In the hypothyroid kidney, exogenous adenosine (ADO) produces vasodilation and restores renal function to near-normal values. This study evaluates whether this response is mediated by nitric oxide synthesis stimulated by adenosine. GFR and urinary excretion of NO2/-/NO3/- (UNO2/-/UNO3/-) were measured in normal (NL) and hypothyroid (HTX) rats under basal conditions and during infusion of: intra-aortic ADO, intravenously, 1,3-dipropyl-8p-sulfophenylxanthine (DPSPX), 8-cyclopentyl- 1,3-dipropyl xanthine (DPCPX), N(ω)-nitro-L-arginine methylester (L-NAME) + ADO, L-NAME + PSPX, L-NAME + DPCPX, and intrarenal (IR) ADO or DPCPX + IR ADO. Intra-aortic ADO induced a fall in GFR and increased UNO2/-/NO3/- slightly in NL rats; in HTX rats, both GFR and UNO2/-/NO3/- increased significantly. DPSPX and DPCPX increased UNO2/-/NO3/- excretion in NL animals with minor changes in GFR; the blockers increased both GFR and UNO2/-/NO3/- in HTX rats. L-NAME completely blocked the increase in NO2/-/NO3/- induced by ADO, DPSPX, and DPCPX. The intrarenal infusion of ADO at 1, 10, and 35 nmol/kg per min progressively decreased GFR with a slight increase in UNO2/-/NO3/- in NL rats; in the HTX, GFR increased with the highest dose and UNO2/-/UNO3/- progressively increased. DPCPX prevented the fall in GFR induced by intrarenal ADO in NL rats, with no further changes in UNO2/-/NO3/-; in HTX rats, intrarenal ADO under A1 blockade further increased GFR and UNO2/-/UNO3/-. Arterial and venous ADO concentrations were lower in the HTX rats. In the HTX kidney, NO production was stimulated by ADO, most likely through activation of A2 or A3 receptors, whereas A1 receptors had an inhibitory effect. Thus, ADO receptors are involved in the regulation of kidney function in pathophysiologic conditions.