¹²⁵Iothalamate and ¹³¹I-hippuran clearances, sodium excretion and plasma renin activity (PRA) before and during indomethacin administration in an oral dose of 3 × 50 mg/day were studied in volunteers with a normal or reduced kidney function, as well on non-sodium-restricted as on sodium-restricted diet. Indomethacin induced a temporary sodium and water retention and a decrease in glomerular filtration rate. It also lowered PRA. The latter phenomenon did not depend on sodium retention and was present within 2 h after an oral dose of 50 mg. The results may be explained by indomethacin-induced inhibition of prostaglandin synthesis.

A radioimmunoassay (RIA) for arg8-vasopressin (AVP) in unextracted human plasma was based on a sensitive anti-AVP rabbit antiserum, inhibition of enzymatic damage to [125I]AVP and AVP, and the use of an individual plasma blank, to correct for interference of plasma factors with the RIA. Sensitivity was 0.4 pg of synthetic AVP detected, corresponding to 1.2 pg/ml of AVP in human plasma. Recovery of AVP added to pooled plasma was 94 +/- 9.3% (mean +/- S.D.) in the low range (AVP, 2.8 pg/ml added) and 106 +/- 11.7% in the high range (45.0 pg/ml added). In 26 healthy, ambulatory subjects on ad lib, water intake, plasma AVP concentration was 2.0 +/- 1.22 pg/ml in the supine position and in 28 healthy subjects, 6.2 +/- 4.3 pg/ml in the upright position. Water loading suppressed the plasma AVP concentration. Smoking caused increased plasma AVP in 3 subjects despite water loading.

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