Actions of vasotocin and some of its analogues on salt and water excretion by the frog

Abstract

The actions of small doses of arginine and lysine-vasotocin on urine flow (V), inulin (C_In), free water (CH_H2O), sodium (C_Na), and potassium (C_K) clearances were studied in Rana esculenta and compared with those of larger doses of oxytocin, lysine-vasopressin, Val³-oxytocin, Ileu⁸-oxytocin, Phe²-Phe³-Lys⁸-oxytocin, deamino-oxytocin, and oxypressin. Injections of either arginine or lysine-vasotocin (mean dose .030 µg) induce a small decrease in glomerular filtration rate (GFR) and two marked tubular effects: a) an increase in water reabsorption, CH_H2O being reduced even when related to C_In; b) an increase in tubular sodium reabsorption, C_Na/C_In being lowered, whereas C_K/C_In remains unchanged. Neither oxytocin nor lysine-vasopressin, even in doses 20–25 times higher, promotes the tubular effects typical of vasotocin. Oxytocin promotes a slight decrease in GFR and V. Lysine-vasopressin remains without any effect. All the other artificial analogues of oxytocin injected in large doses increase V, GFR, C_Na/C_In and C_K/C_In. It is concluded that the vasotocins specifically promote in the kidney tubules of the frog the same two actions described in the other target organs in the amphibians, namely an increase in osmotic permeability to water and a stimulation of active sodium transport.