[Effect of hydrocortisone on the formation of osmotic concentration function in white rats].

The age-associated time course of renal concentration function was studied in Wistar rats after a single injection of hydrocortisone (100 micrograms/100 g bw) or physiological saline (the control group) on the 5th day after birth. In the experimental rats aged 20--30 and 60 days, the intrarenal gradients of urea and the osmotic concentration index of the urine (U over P) osm increased, after the test injection of pituitrin P (500 microunits/100 g bw, s. c.), to a less extent than in the control animals. Under dehydration, (U over P) osm in the experimental group was found to be lower than in the controls, whereas the gradients of urea to differ negligibly. It is suggested that hydrocortisone injection in the early postnatal period leads to the decrease in the efficacy of renal concentration function because of changes in ADH reception or in activity of enzymes involved in the reaction to the hormone.