Extrarenal Effects of Intravenous Pitressin in Nephrectomized Rats

Using inulin as indicator of the extracellular fluid volume, the effects of Pitressin on the movements of sodium and potassium were studied in the nephrectomized rat together with simultaneously determined direct blood pressure values. Pitressin caused a movement of sodium and water into cells coupled with the extrusion of some potassium during the phase of blood pressure elevation. The beginning of the phase of blood pressure decline coincided with a rapid shift of potassium into cells while the sodium and water acquired by cells in the early phase were gradually extruded. These shifts were demonstrable with as little as 10 mU. of Pitressin intravenously while the maximal effect occurred in the 30 to 50 mU. dose range. These effects may account for many of the changes observed with Pitressin in the intact animal and also may have some bearing on blood pressure homeostasis.