The Renin Angiotensin System in Newborn Dogs: Developmental Patterns and Response to Acute Saline Loading

Abstract

SummaryPlasma renin (PRC) and aldosterone concentrations are known to be high during early postnatal life. Whether this is related to the low rates of renal blood flow or to sodium homeostasis remains unknown. Measurements of PRC, renal Mood flow, and its intrarenal distribution were performed in 1-to Iwk-dd puppies subjected to maneuvers known to stimulate or inhibit renin release. In the awake state, PRC was observed to be higher in t w k d puppies than in older or younger dogs, (P < 0.0001). Signincant differences in PRC were also found between Utters (P < 0.0001), but they did w t account for the age-related changes. Anesthesia resulted in a 3-to 5-fold rise in PRC, whereas saline expansion suppressed PRC at all ages, the fall tending to become progressively greater with age (P < 0.09). There was no significant correlation between the age-related changes in PRC and those in renal blood flow or its intrarenal distribution. The results of these experiments demonstrate that in the newborn from a aualitative poht of view, PRC changes appropriately in response io various stimuli. However, quantitative age-related differences exist in this regard, reflecting an initial immaturity of the feedback system. SpeculationThe lack of correlation between plasma renin concentration and the intrarenal distribution of blood flow, corroborated with the existence of a relationship between plasma renin and the state of the extracellular fluid volume, suggest that during development the renin-Pogiotensin-aldosteme system is geared toward the maintenance of the positive sodium balance intrinsic to the process of growth.The renin-angiotensin-aldosterone system is known to play an important role in the regulation of blood pressure and in sodium homeostasis in the adult animal and human (4,13,19,20,23,31). It also has been implicated in the phenomenon of autoregulation of renal blood flow, single nephron glomerular filtration rate, and intrarenal distribution of blood flow (1,21,22,28). In the newborn period, plasma renin levels are higher by about one order of magnitude than they are later in life (5,9, 11,18). This may relate to the low rates of total renal blood flow (2, 14) and outer cortical blood flow (2) observed at this age. It is known that the rcninangiotensin system can be stimulated in the newborn by peritoneal dialysis or by administration of diuretics (9, 11,29), but there is a relative paucity of information regarding its responsiveness to agents known to suppress it in adults (1 1, 15, 27), and the results of these studies conflict with each other. Another asDect that needs to be investigated is the relationship between the ienin-angiotensin-aldosterone system and sodium homeostasis. The limited natriuretic response of the newborn following volume expansion might be related to the high plasma concentration of aldosterone. In the present study, normal values of immunoassayable plasma renin concentrations (PRC) were established, the developmental pattern was assessed, and the effect of acute volume expansion on PRC was...

Nimesulide, a Cyclooxygenase-2 Preferential Inhibitor, Impairs Renal Function in the Newborn Rabbit

“…The kidneys of fetal and newborn experimental animals are known to synthesize and secrete renin in abundance (48). In the newborn rabbit, total renin concentration increases with postnatal age and relatively more than kidney weight between 1 and 2 wk of age (49).…”

Intrarenal Distribution of Renin in the Developing Rabbit

“…The data on PRC in the developing rabbit differ from those observed in other species, including the rat, dog, piglet, lamb and human (2,8,14,18,21,24,25,27,28,30,33). Plasma renin concentration in the newborn rabbit was not high and was comparable to adult values.…”

“…Abbreviations AI, angiotensin I GRC, glomerular renin concentration PAI, plasma angiotensio I PRC, plasma renin concentration RAS, renin-aqbteasia system RRC, renal renin content responds quali&tively though not quantitatively, to stimuli in a manner similar to that observed at a later age (8,12,13,17,21,24,30). Relatively few data are available regarding the physiologic role of the R A S in infanw and childhood.…”

The Effects of Salt Loading on the Renin-Angiotensin Control of Blood Pressure in the Newborn Lamb

“…The renin-angiotensin system levels are high in the newborn human (6,13,16), lamb (20), and canine puppy (5). These high renin-angiotensin levels contribute to basal control of blood pressure (19)and possibly decreased pressor responsiveness to angiotensin 11 (18) in the newborn lamb.…”