Adenosine modulates vasomotor tone in outer medullary descending vasa recta of the rat

Adenosine is generated within the renal medulla under hypoxic conditions and is known to induce net vasaconstriction within the renal cortex while increasing medullary blood flow and oxygenation, To test the hypothesis that vasoconstriction of outer medullary descending vasa recta (OMDVR) is modulated by adenosine, we examined the effects of adenosine and adenosine A(1) and A(2) receptor subtype agonists on in vitro perfused control and preconstricted rat OMDVR. Constriction with angiotensin II (ANG II, 10(-9) M) was attenuated by adenosine in a concentration-dependent manner (EC(50) = 2.0 x 10(-7) M, P < 0.05). Similarly, an adenosine A(2) agonist (CGS-21680, 10(-7) M), but not an adenosine A(1) agonist (cyclohexyladenosine, 10(-6) M), attenuated ANG II-induced vasoconstriction, Under control conditions, ablumenal application of adenosine (10(-12) to 10(-5) M) elicited a biphasic response. Additionally, cyclohexyladenosine (10(-6) M) caused vasoconstriction and CGS-21680 (10(-6) M) had no effect on untreated vessels, Finally, an influence of ANG II receptor stimulation on adenosine A(1) receptor-mediated vasoconstriction could not be shown. These data suggest that OMDVR possess both A(1) and A(2) adenosine receptors and that they mediate constriction and diiatation, respectively. We conclude that adenosine is a potent modulator of OMDVR vasomotor tone and that its net effect is dependent upon local concentrations.