Inhibition of adenosine-1 receptor-mediated preglomerular vasoconstrictionin AT(1A) receptor-deficient mice

The effect of the adenosine type 1 receptor agonist N-6-cyclohexyladenosine (CHA) on glomerular vascular reactivity was studied in male angiotensin II type 1A (AT(1A)) receptor knockout mice (9). Vascular reactivity was asses sed as the response of stop-flow pressure (P-SF) to infusion of CHA into lo ops of Henle using micropuncture techniques. In AT(1A) +/+ mice at ambient arterial blood pressure (96.7 +/- 2.8 mmHg), the presence of CHA (10(-5) M) in the perfusate increased P-SF responses from 6.8 +/- 0.6 to 14.3 +/- 0.9 mmHg when the loop of Henle of the index nephron was perfused and from 0.7 +/- 0.3 to 12.3 +/- 1.0 mmHg when the loop of an adjacent nephron was perf used. At reduced arterial blood pressure (82.8 +/- 1.3 mmHg), index nephron perfusion with CHA increased P-SF responses from 4.5 +/- 0.3 to 9.4 +/- 0. 4 mmHg. In AT(1A) -/- mice with a mean arterial blood pressure of 80 +/- 1. 9 mmHg, CHA increased P-SF responses only from 0.1 +/- 0.3 to 3.6 +/- 0.54 mmHg during index nephron perfusion and from 0.25 +/- 0.2 to 2.7 +/- 0.55 m mHg during adjacent nephron perfusion, significantly less than in wild-type animals (P < 0.001). Responses to CHA were intermediate in AT(1A) +/- mice . Thus AT(1A) receptor knockout mice show a markedly reduced constrictor re sponse to CHA both in the presence and absence of simultaneous activation o f the tubuloglomerular feedback system. These data support the notion of a functional interaction between adenosine and angiotensin II in the regulati on of afferent arteriolar tone.