Adenosine A1-receptor knockout mice have a decreased blood pressure response to low-dose ANG II infusion

Abstract

Adenosine, acting on A(1)-receptors (A(1)-AR) in the nephron, increases sodium reabsorption, and also increases renal vascular resistance (RVR), via A(1)-ARs in the afferent arteriole. ANG II increases blood pressure and RVR, and it stimulates adenosine release in the kidney. We tested the hypothesis that ANG II-infused hypertension is potentiated by A(1)-ARs' influence on Na(+) reabsorption. Mean arterial pressure (MAP) was measured by radiotelemetry in A(1)-AR knockout mice (KO) and their wild-type (WT) controls, before and during ANG II (400 ng·kg(-1)·min(-1)) infusion. Baseline MAP was not different between groups. ANG II increased MAP in both groups, but on day 12, MAP was lower in A(1)-AR KO mice (KO: 128 ± 3 vs. 139 ± 3 mmHg, P < 0.01). Heart rates were significantly different during days 11-14 of ANG II. Basal sodium excretion was not different (KO: 0.15 ± 0.03 vs. WT: 0.13 ± 0.04 mmol/day, not significant) but was higher in KO mice 12 days after ANG II despite a lower MAP (KO: 0.22 ± 0.03 vs. WT: 0.11 ± 0.02 mmol/day, P < 0.05). Phosphate excretion was also higher in A(1)-AR KO mice on day 12. Renal expression of the sodium-dependent phosphate transporter and the Na(+)/glucose cotransporter were lower in the KO mice during ANG II treatment, but the expression of the sodium hydrogen exchanger isoform 3 was not different. These results indicate that the increase in blood pressure seen in A(1)-AR KO mice is lower than that seen in WT mice but was increased by ANG II nonetheless. The presence of A(1)-ARs during a low dose of ANG II-infusion limits Na(+) and phosphate excretion. This study suggests that A(1)-AR antagonists might be an effective antihypertensive agent during ANG II and volume-dependent hypertension.

Fig. 1.

Mean arterial pressure during control and 14 days of ANG II (400 ng·kg⁻¹·min⁻¹) treatment in WT and KO mice. Data are expressed as mean ± SE. ‡P < 0.05, comparison between baseline period and ANG II treatment. *P < 0.05, comparison between WT + ANG II and KO + ANG II.

Fig. 2.

A: urinary Na⁺ excretion on day 3 of the control period and day 12 of ANG II treatment in WT and KO mice. B: urinary phosphate excretion on day 3 of the control period and day 12 of ANG II treatment in WT and KO mice. C: 24-h food intake in WT and KO mice during the control period and day 12 of ANG II treatment. (‡P < 0.05, comparison between control and ANG II treatment; *P < 0.05, comparison between WT + ANG II and KO + ANG II).

Fig. 3.

Densitometry summary (means ± SE) expressed as % change for Na⁺/Pi cotransporter isoform 2 (NaPi2) (A), SGLT (B), and Na⁺/H⁺ exchanger isoform 3 (NHE3; C) in the renal cortex from WT and KO mice treated with ANG II (400 ng·kg⁻¹·min⁻¹) (*P < 0.05).