Adenosine A2A receptor activation attenuates tubuloglomerular feedback responses by stimulation of endothelial nitric oxide synthase

Abstract

Adenosine A(2) receptors have been suggested to modulate tubuloglomerular feedback (TGF) responses by counteracting adenosine A(1) receptor-mediated vasoconstriction, but the mechanisms are unclear. We tested the hypothesis that A(2A) receptor activation blunts TGF by release of nitric oxide in the juxtaglomerular apparatus (JGA). Maximal TGF responses were measured in male Sprague-Dawley rats as changes in proximal stop-flow pressure (ΔP(SF)) in response to increased perfusion of the loop of Henle (0 to 40 nl/min) with artificial tubular fluid (ATF). The maximal TGF response was studied after 5 min intratubular perfusion (10 nl/min) with ATF or ATF + A(2A) receptor agonist (CGS-21680; 10(-7) mol/l). The interaction with nitric oxide synthase (NOS) isoforms was tested by perfusion with a nonselective NOS inhibitor [N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME); 10(-3) mol/l] or a selective neuronal NOS (nNOS) inhibitor [N(ω)-propyl-L-arginine (L-NPA); 10(-6) mol/l] alone, and with the A(2A) agonist. Blood pressure, urine flow, and P(SF) at 0 nl/min were similar among the groups. The maximal TGF response (ΔP(SF)) with ATF alone (12.3 ± 0.6 mmHg) was attenuated by selective A(2A) stimulation (9.5 ± 0.4 mmHg). L-NAME enhanced maximal TGF responses (18.9 ± 0.4 mmHg) significantly more than L-NPA (15.2 ± 0.7 mmHg). Stimulation of A(2A) receptors did not influence maximal TGF response during nonselective NOS inhibition (19.0 ± 0.4) but attenuated responses during nNOS inhibition (10.3 ± 0.4 mmHg). In conclusion, adenosine A(2A) receptor activation attenuated TGF responses by stimulation of endothelial NOS (eNOS), presumably in the afferent arteriole. Moreover, NO derived from both eNOS and nNOS in the JGA may blunt TGF responses.

Fig. 1.

Top: change in proximal stop-flow pressure (ΔP_SF) in response to increased perfusion of loop of Henle from 0 to 40 nl/min. Broken lines represent individual nephrons. The maximal tubuloglomerular feedback (TGF) response was studied after 5 min intratubular perfusion (10 nl/min) with artificial tubular fluid (ATF) alone (control; m/n = 6/12) (A) or in combination with A_2A receptor agonist [4-(2-{[6-amino-9-(N-ethyl-β-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino}ethyl)benzenepropanoic acid hydrochloride (CGS-21680); m/n = 4/10] at 10⁻⁷ mol/l (B). m/n, No. of animals and nephrons, respectively. *P < 0.05 compared with proximal stop-flow pressure (P_SF), at 0 nl/min, within each group (paired t-test). Bottom: sample recordings of mean arterial pressure (MAP) and P_SF during loop of Henle perfusion with ATF alone (control) (A) or with A_2A receptor agonist (CGS-21680) at 10⁻⁷ mol/l (B). Gray boxes represent a loop of Henle perfusion flow of 40 nl/min for 2 min.

Fig. 2.

Top: ΔP_SF in response to increased perfusion of loop of Henle from 0 to 40 nl/min. Broken lines represent individual nephrons. The maximal TGF response was studied after 5 min intratubular perfusion (10 nl/min) with the nonselective nitric oxide synthase (NOS) inhibitor [N^ω-nitro-l-arginine methyl ester hydrochloride (l-NAME); m/n = 3/9] at 10⁻³ mol/l alone (A), or in combination with A_2A receptor agonist (CGS-21680; m/n = 3/9) at 10⁻⁷ mol/l (B). m/n, No. of animals and nephrons, respectively. *P < 0.05 compared with P_SF, at 0 nl/min, within each group (paired t-test). Bottom: sample recordings of MAP and P_SF during loop of Henle perfusion with nonselective NOS inhibitor (l-NAME) at 10⁻³ mol/l alone (A) or in combination with A_2A receptor agonist (CGS-21680) at 10⁻⁷ mol/l (B). Gray boxes represent a loop of Henle perfusion flow of 40 nl/min for 2 min.

Fig. 3.

Top: ΔP_SF in response to increased perfusion of loop of Henle from 0 to 40 nl/min. Broken lines represent individual nephrons. The maximal TGF response was studied after 5 min intratubular perfusion (10 nl/min) with selective nNOS inhibitor [N^ω-propyl-l-arginine (l-NPA); m/n = 4/6] at 10⁻⁶ mol/l alone (A) or in combination with A_2A receptor agonist (CGS-21680; m/n = 4/10) at 10⁻⁷ mol/l (B). m/n, No. of animals and nephrons, respectively. *P < 0.05 compared with P_SF, at 0 nl/min, within each group (paired t-test). Bottom: sample recordings of MAP and P_SF during loop of Henle perfusion with selective nNOS inhibitor (l-NPA) at 10⁻⁶ mol/l alone (A) or in combination with A_2A receptor agonist (CGS-21680) at 10⁻⁷ mol/l (B). Gray boxes represent a loop of Henle perfusion flow of 40 nl/min for 2 min.

Fig. 4.

Summary of maximal TGF responses (ΔP_SF) during ATF perfusion (control) (A), nonselective NOS inhibition (l-NAME; 10⁻³ mol/l) (B), selective nNOS inhibition (l-NPA; 10⁻⁶ mol/l) (C) alone (black bars), or together with adenosine A_2A receptor agonist (CGS-21680; 10⁻⁷ mol/l) (gray bars). Values are means ± SE. *P < 0.05 compared with control. #P < 0.05 compared with l-NPA alone.