HYPERTONIC NACL ENHANCES ADENOSINE RELEASE AND HORMONAL CAMP PRODUCTION IN MOUSE THICK ASCENDING LIMB

Adenosine 3',5'-cyclic monophosphate (cAMP), accumulated in the presence of adenosine, was measured in medullary portions of mouse thick ascending limbs of Henle's loop, suspended either in classic extracellular buffer or in the presence of added NaCl. Under control conditions (140 mmol/l Nacl), adenosine (< 10(-5) mol l/l) and N-6-cyclohexyladenosine, an A(1) adenosine receptor agonist, inhibit the cAMP accumulation induced by arginine vasopressin (AVP). On the other hand, high concentrations of adenosine and CGS-21680, an A(2) adenosine receptor agonist, stimulate cAMP formation. Addition of NaCl (+300 mmol/l) to extracellular buffer stimulates the release of endogenous adenosine. It also enhances A(2) receptor-induced cAMP accumulation but suppresses A(1) receptor-mediated inhibition of adenylyl cyclase. This hypertonic NaCl medium also potentiates the stimulatory action of AVP on adenylyl cyclase. The modifications of tubular responses to both AVP and A(1) and A(2) agonists, brought about by hypertonic NaCl, were all inhibited by adenosine deaminase, thereby demonstrating the involvement of endogenous adenosine. Adenosine, the release and the effects of which are modulated by hypertonic NaCl, thus appears to act as an endogenous physiological modulator of kidney medulla function.