The Mechanism of the Solute-Free Water Reabsorption Increase in the Rat Kidney by Oxytocin Saluresis.

We found an experimental solution to the paradox when the reabsorption of solute-free water increases with a simultaneous increase in diuresis and saluresis in the rat kidney under the oxytocin action. Injection of oxytocin to rats (0.25 nmol/100 g of body weight) increases diuresis from 0.

Subtypes of Neurohypophyseal Nonapeptide Receptors and Their Functions in Rat Kidneys.

The nonapeptides of neurohypophysis, vasotocin and mesotocin, detected in most vertebrates, are replaced by vasopressin and oxytocin in mammals. Using bioinformatics methods, we determined the spectrum of receptor subtypes for these hormones in mammals and their physiological effects in the kidneys of rats. A search for sequences similar to the vertebrate vasotocin receptor by proteomes and transcriptomas of nine mammalian species and the rat genome revealed three subtypes of vasopressin receptors (V1a, V1b, and V2) and one type of oxytocin receptors.

The Cascade System of Osmotic Homeostasis Regulation.

The human and animal osmoregulation system is aimed at stabilizing serum osmolality in order to maintain cell volume. It has been shown that the introduction of 5 mL water per 100 g of body weight into the stomach of rats decreases serum osmolality and the concentration of Na and Ca, but not K and Mg. The cascade system of osmotic homeostasis increases secretion of glucagon-like peptide-1 (GLP-1) and oxytocin, and decreases secretion of vasopressin, which reduces the osmotic permeability of collecting duct.

Mechanism of Natriuretic Effect of Oxytocin.

In rats, intramuscular injection of oxytocin (0.25 nmol/100 g body weight) increased sodium excretion from 19±5 to 120±11 μmol/min. A significant correlation (p<0.

Vasopressin receptor subtypes and renal sodium transport.

In mammals, three subtypes of V-receptors have been identified in the kidney. The effects of vasopressin, a hormone synthesized in the hypothalamus, are triggered by three distinct receptor isoforms: V2, V1a, and V1b. Stimulation of V2-receptors regulates urine osmotic concentration by increasing sodium reabsorption in the thick ascending limb of the loop of Henle and enhancing osmotic permeability of the epithelium cells in the collecting duct.