Attempts to alter the heterogeneous response to ANP in sodium-retaining caval dogs.

Chronic caval dogs with ascites were identified as being natriuretic "responders" or "nonresponders" (delta UNaV less than 20 microequiv./min) following an infusion of atrial natriuretic peptide (ANP) (100 ng.kg-1.min-1). To learn more about the factors modulating tubular resistance to ANP, we attempted to convert responders into nonresponders and vice versa by manipulating the physiological environment. To responding dogs, we readministered ANP in the presence of noradrenaline (n = 5), angiotensin (n = 5), indomethacin (n = 4), and adenosine receptor blockage with theophylline (n = 4), and with purposeful reduction of blood pressure (n = 5). To nonresponding dogs, we readministered the ANP in the face of alpha-adrenergic blockade (n = 4), saralasin (n = 4), dipyridamole to block adenosine cellular uptake (n = 5), and elevation of blood pressure (n = 4). In no case were we able to alter the initial natriuretic response to ANP. Binding parameters of ANP receptors in suspensions of renal papillary cells were equivalent in responding caval dogs (n = 6), nonresponding dogs (n = 7), and normal controls (n = 7), as was cGMP generation. We conclude that the tubular resistance to ANP in caval dogs unresponsive to this natriuretic peptide is not due to antagonism from catecholamines or angiotensin but may be due to a post-cGMP problem in signal transduction, or a reduction in the delivery of ANP to the distal nephron.