Altered cyclic AMP responsiveness to vasopressin in rat renal medullary dispersed cells by acute elevation of endogenous vasopressin.

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Abstract
Medullary and cortical tubular cells were prepared from the rat kidneys with collagenase treatment. Arginine vasopressin (AVP) stimulated cAMP production both in medullary and cortical cells with a dose-response relationship at concentrations ranging from 10 .mu.U/ml to 10 mU/ml, while parathyroid hormone (PTH) and calcitonin did only in the latter. Using this medullary cell system, effects of acute changes in endogenous plasma AVP levels in vivo on its cAMP responsiveness to AVP (10 mU/ml) in vitro were examined. Acute elevation of plasma AVP levels induced by i.p. injection of 20% (wt/vol) polyethylene glycol-isotonic saline solution 3 h prior to sacrifice resulted in a 33% decrease in cAMP responsiveness to AVP (desensitization). More prolonged elevation of plasma AVP levels by water restriction for 48 h increased the responsiveness by 38 to 81%, which was restored to basal levels by ad libitum intake of water for another 48 h (positive feedback regulation). These maneuvers did not alter the cAMP responsiveness to PTH (10 .mu.g/ml) in cortical cells. Apparently AVP-stimulated adenyl cyclase in rat renal medulla may be regulated by changes in endogenous AVP levels even within the physiological range.