Antidiuretic Activity in the Plasma of Human Infants After a Load of Sodium Chloride

Abstract

It is known that under comparable conditions of dehydration newborn and infant animals are unable to form urine of as high an osmotic concentration as adult animals [S, 171. The difference in concentration capacity in the young and in the adult is more pronounced the less mature the newborn. This low concentration capacity has also been described for human infants, and it has been stated that the mean maximum limits of osmolarity in children in the first weeks after birth are about 800 mOsm/L, which means that they only slightly exceed half the level of urine osmolarity in adults [9, 181. It is believed that functional and structural immaturity of the hypothalamo-neurohypophyseal system producing antidiuretic hormone (ADH), and insufficient sensitivity of the distal portions of the nephron to ADH are involved. The level of antidiuretic activity (ADA) in the neurohypophyses of newborn rats and puppies is very low [ 2 , 71. Even in newborn children the ADA content in the neurohypophysis does not reach the level of adults [lo]. In addition, thc findings of Rodeck [25, 261 ~~~ .. Technic.<:l ar,lstnnc~ V. 13dlmv& and H. Boui.kova. indicate undeveloped neurosecretion in the hypothalamus of newborn children. Under normal hydration ADA cannot bc identified in the plasma of infant rat before the 23rd day of life [3], and in puppies not before the eleventh day of life [2]. Under dehydration or after a NaCl load ADA can be detected in the plasma already in 10day-old rats and 5-day-old puppies [a, 41.Heller & Hradcovj [ l l ] have found ADA in the plasma of normally hydrated children only a t the beginning of the 5th month.In the present work it was enquired whether, after an osmolar stimulus, ADA can be detected in the plasma of even younger infants. Part of the findings has been published as a preliminary communication [14, 201. MethodsDisposal of an NaCl load NaCl (0.7 g/kg body weight dissolved in two thirds of the child's normal milk intake) was administered to 50 mat,ure children between thc ages of 1 6 clays and 6 months. The NaCl dosc was chosen in siich a ~v a y as not t o allow the relative wat.cr tieficit. rcsulting from administration of D hyp:rt.onic solution into the gastrointestirinl tract, t o excet:d 5 % of t,he body woight. Clost. be-

Renal Control of Sodium Homeostasis in Infancy

“…This may be regarded as a criterion of good reabsorption from the intestine even in the newborn infant. An increase in serum sodium 20 minutes after an oral NaCl administration has also been demonstrated by others (34).…”

“…The diluting some low values were observed, i.e. [25][26][27][28][29][30][31][32][33][34][35] capacity or free water cIearence which is also an index of distal tubular sodium re-:b (mean * 1 SD, ml/hour/1.73 m2.) absorption (5) was supernormal in preterm infants and in newborn full-term infants in the immediate neonatal period (I, 11).…”

Plasma aldosterone levels in the 1st week of life in infants of less than 30 weeks gestation

“…The physiological basis for this is incompletely understood but may include distal renal tubular unresponsiveness to aldosterone [22], reduced proximal renal tubular sodium absorption increasing the distal tubular sodium load [22], increased renal urinary sodium losses [22], counteracting the effect of elevated atrial naturetic peptide [10], increased sympatho-adrenergic activity [12] or reduced antidiuretic hormone levels [13].…”

Postnatal Development of Renal Concentration Capacity as Estimated by DDAVP-Test in Normal and Asphyxiated Neonates

“…Several factors might be responsible for these changes in renal concentrating performance. Thus it has been shown that there is a progressive lengthening of Henle's loops during the first weeks of life [5,8], According to some investigators, the availability of the antidiuretic hormone is decreased in the first weeks of extrauterine life, which might contribute to the lower renal concentration ability [10,12]. However, as just a little antidiuretic activity is needed to induce near maximal antidiuresis [9] the decreased availability is probably not the limiting factor.…”