Body Fluid Variations and Endogenous Digitalis-Like Compounds During Chronic NaCl Loading in Wistar Rats

Circulating digitalis-like compounds have been proposed to be raised in volume expanded hypertension and to participate in Na⁺ homeostasis. We have investigated the temporal relationships between the activity of these circulating digitalis-like compounds, blood pressure and body fluid volume variations during a chronic NaCl load in the Wistar rat.

Characteristics of salt-loaded rats were compared to those of weight-matched controls. At one week, when extracellular fluid volume (ECFV) was elevated, the capacity of plasma extracts to inhibit the Na⁺K⁺ATPase activity begun to rise. At two weeks, ECFV remained elevated, and plasma volume, blood pressure and the activity of plasma digitalis-like compounds increased. After 13 weeks, the continuous rise in plasma digitalis-like activity and in blood pressure was accompanied by the return of body fluid volumes towards control values. These changes in plasma digitalis-like activity, body fluid volumes, and systolic blood pressure during a high NaCl diet are compatible with the proposed role of circulating digitalis-like compounds as natriuretic and hypertensive factors.