SUMMARY The acute effects of vasopressin (40 mU) were studied in the conscious sheep. Vasopressin caused consistent increases in K and C1 excretion and variable increases in Na and total solute output. These changes occurred within 10 min., reached a peak within 30 min. and subsided within 60 min. When the urine was initially dilute (< 800 μosmoles/ml.) vasopressin caused an antidiuresis. When the original concentration exceeded 1000 (μosmoles/ml. vasopressin caused small increases in urine flow. Vasopressin always increased water reabsorption relative to solute reabsorption.

Summary. 'I'he effect of dinretics on the distril)ntion of sodium (Na) and I^otassiuni (K) in the kidney was studied in alcohol anaesthetized rats during osniotie diuresis. As previously reported, these rats had a small yadient from eortex to papilla in the sodium concentration of renal tissue. Vasopressin increased this K^idient by inereasing the concentration of sodium in the niednlla and papilla.When either mcrcaptonieriu or hydroflilorotliia/idc was administered in therapeutic closes, the concentrations of sodium in the papilla were initially hijfh and were further increased by vasopressin. Tliese results were very similar to those obtained when infusions containing high levels of sodiimi chloride (NaGl) were adniinistered to normal rats.Prior administration of ctbaiTynic aeid caused very hijjli eoucentnitions