Abstract
A number of well-controlled experiments have indicated the existence of a nonadrenal humoral natriuretic substance which is released in response to expansion of the extracellular fluid volume (1-4). Several laboratories, including our own, have demonstrated biologic activities which are compatible with such a humoral natriuretic substance (5-8).
In our own studies, we showed that plasma of dogs with acute expansion of the extracellular fluid volume contains an ultrafilter-able inhibitor of anuran membrane sodium transport, which is also natriuretic (7, 8). However, there has been a report that studies utilizing techniques similar to ours have failed to confirm our results (9). Since our original studies were not performed in a blind manner, and because of the question raised concerning the reproducibility of our results, we felt that a totally blind study was advisable. Accordingly, plasma samples collected in two separate, independent laboratories were studied by us for effect on toad bladder short-circuit current in a blind manner. The results obtained in this study were similar to those previously reported (7, 8).
Materials and Methods. Samples of jugular venous plasma were obtained from mongrel dogs of both sexes. Twenty-six samples were collected in laboratory 1 (Mayo Clinic) 1 and eight samples in laboratory 2 (National Institutes of Health) 2 . Plasma was frozen at —4°, coded, and shipped in dry ice to laboratory 3 (VMB) for ultrafiltration and toad bladder assay.
Hydropenic samples were obtained from 12 dogs in laboratory 1. The dogs ingested a diet containing 3 meq per day of sodium for 10 days and were given 15 mg/day of deoxy-corticosterone (DOC) intramuscularly. After overnight dehydration, they were anesthetized with pentobarbital sodium, and jugular venous blood was drawn 1-3 hr later.
Fourteen samples from acutely volume-expanded dogs were obtained in laboratory 1. The dogs were deprived of water for 12-14 hr prior to the experiment, anesthetized with pentobarbital, and given 0.9% NaCl equal to 6-10% of body weight in 60 min.
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