Vasopressin and Oxytocin in Regulation of Renal Cation and Water Excretion: Nephrone ‐ Kidney Interaction

Abstract

Hydrin, mesotocin, vasotocin are the neurohypophyseal nonapeptides of the vertebrates except the mammals, arginine‐vasopressin (AVP) and oxytocin (OT) are secreted into blood in man and rat. The activation of V‐ and OT‐receptors (OTR) provides different functions of the peptides, including osmoregulation. AVP effect on sodium transport in tubule cells was shown earlier: increased Na+ reabsorbtion was observed in TAL due to activation of V2R, and decreased Na+ reabsorbtion ‐ due to activation of V1aR. The aim of the study was an investigaion of the effect of the nonapeptides in vivo and evaluation of cumulative reaction of all the nephrone populations on renal ion and water excretion.Experiments were performed using Wistar rats in accordance with Russian and EU guidelines on the use of animals in research. Diuresis was recorded as spontaneous urination. Osmolality, concentration of Na+, K+, Mg++, Ca++ was measured in each sample. Concentration of the nonapeptides was measured using commercially available enzyme‐linked immunosorbent assay kits.An injection of 5 μmol/kg BW of AVP increased renal Na+ excretion from 6±1 to 137 ±19 μmol/100g BW; K+ excretion rised from 20±2 to 74±8 μmol/100g BW, Ca++ ‐ from 0.19±0.06 to 0.46±0.09 μmol/100g BW; Mg++ excretion decreased from 5.4±0.4 to 4.1±0.1 μmol/100g BW. Water load (WL, 50 ml/kg BW per os) that was used to suppress endogenous AVP secretion, induced enhancement of natriuresis: an injection of 0.5 μmol/kg BW of AVP following WL led to renal excretion of Na+, K+, Mg++ compared to a single administration of 1 μmol/kg BW of the peptide.An injection of 2.5 μmol/kg BW of OT led to increased urinary excretion of Na+ (133±14 μmol/100g BW), K+ (68±8 μmol/100g BW), Mg++ (6.59±1.35 μmol/100g BW), Ca++ (1.37±0.34 μmol/100g BW). But the co‐injection of maximal natriuretic doses of AVP and OT didn't lead to summation of natriuretic effect. In WL rats the peak of solute‐free water clearance was observed 15 min earlier following an injection of 0.1 μmol/kg BW of OT, but an injection of 2.5 μmol/kg BW of OT led to a short‐time water retention.Hyperosmia was induced using hypertonic sodium loading (2.5% NaCl 18 ml/kg BW i.p.) and stimulated endogenous AVP secretion consequently. An injection of antagonist of V1aR or OTR following sodium loading decreased Na+ excretion from 242±14 to 166±13 and 184±12 μmol/100g BW, Ca++ excretion from 1.88±0.16 to 0.87±0.09 and 0.78±0.11 μmol/100g BW, solute‐free water reabsorbtion from 2.42±0.07 to 2.05±0.11 and 2.18±0.06 ml/100g BW, accordingly; but didn't affect renal K+ excretion. An injection of OTR‐antagonist following sodium loading enhanced Mg++ excretion from 7.3±0.6 to 10.6±0.5 μmol/100g BW.OT and AVP increases Na+, K+, Ca++ renal excretion. An injection of OTR‐antagonist following sodium loading leads to increased Mg++ excretion. The cumulative effect of AVP is indicated in a shift of cation reabsorbtion to cation excretion following administration of different doses of AVP. The obtained data show particular actions of AVP and OT in vivo and help us to evaluate the reaction of the nonapeptides on renal ion and water excretion.Support or Funding InformationThe work was supported by the government budget funds for state assignment for 2013–2017 (N 01201351572).