About ne of the most important factors in the regulation of secretion of vasopressin is the plasma osmolality. Osmoreceptors located in the hypothalamus are extremely sensitive to changes in plasma osmolarity. Increasing its level by only 1% is sufficient to stimulate the secretion of vasopressin. Normally, the osmotic threshold for osmoreceptors is the plasma osmolarity index from 280 to 290 washes / kg H2O. With increasing plasma osmolarity, there is a high positive correlation between its level and plasma vasopressin concentration. Osmoreceptors are most sensitive to sodium, mannitol, sucrose. Glucose and urea, which increases plasma osmolarity, have a weak effect on vasopressin secretion.
Normally, when serum osmolarity is less than 280 wash / kg, plasma vasopressin concentration is (1 pg / ml, which is the lower limit of sensitivity of radioimmune methods. With osmolarity values over 238 wash / kg, which is a normal threshold for vasopressin release, vasopressin concentration plasma increases in proportion to the osmolarity of the plasma, to a maximum concentration of about 20 pg / ml with an osmolarity of blood of about 320 wash / kg.
For vasopressin secretion, individual variations associated with hormonal status are characteristic. After 7 weeks of pregnancy, the osmotic threshold for both vasopressin release and thirst is reduced by 10 my / kg, so that the normal osmolarity of the blood during pregnancy is about 273 my / kg .
Significant effect on the secretion of vasopressin has a change in blood volume and pressure. The baroreceptor system includes the baroreceptors of the aortic arch and atria, associated with the brainstem and the supraoptic and paraventricular nuclei of the hypothalamus by p. Vagus and n.glossopharyn-geus. This regulation system determines the relationship between the level of blood pressure and the concentration of vasopressin in the blood plasma. Baroreceptors are less sensitive than osmoreceptors, since the secretion of vasopressin is stimulated by a change in blood volume of at least 5-10%. However, baro-receptor-stimulated hormone secretion can reach significantly higher levels than stimulated by osmoreceptors.