[The effects of enkephalins on the water-salt metabolism of rats in ontogeny].

The experiments were carried out in white Wistar rats of three ages: 25-30 days (Group 1, n = 102), 45-50 days (group 2, n = 62), over 180 days (group 3, n = 115). The water loading was given through a gastric tube in an amount of 5% of the body weight. A synthetic analogue of leu-enkephalin (SAE) was injected intraperitoneally in a dose of 100 mg/kg. The control animals received physiological saline. In the baby rats of group 1, administration of SAE slowed down the polyuric and ionouretic reactions in response to the water loading. In older rats of group 2 administration of SAE enhanced water elimination but with this the osmolarity of the blood plasma increased together with the content of potassium and sodium ions in it. In adult rats (group 3) injections of SAE produced a smooth diuretic reaction which retained constant ion levels in the blood plasma.