Role of Renal Interstitial Hydrostatic Pressure in the Blunted Natriuretic Response to Saline Loading in the Piglet

Abstract

ABSTRACT. Acute saline volume expansion (VE) in the developing animal is associated with a blunted natriuretic response when compared with that in adults. Recent studies have suggested that renal interstitial hydrostatic pressure (RIHP) plays an important role in mediating VE-induced natriuresis in the adult. The purpose of our study was to determine whether abnormalities in the RIHP response to VE could be involved in the blunted natriuretic response in the developing animal. The effect of an acute saline load (5 % body wt) on RIHP and sodium excretion was examined in adult pigs (>70 d) and piglets (26-43 d). In response to an acute saline load , the piglets excreted significantly less sodium than the adults (1.7 ± 0.5 versus 3.8 ± 0.7 /-tmol/ min/g kidney wt). The incre ase in fractional excretion of sodium in response to VE was also significantly less in the piglets. There was no significant change in GFR in either group. Associated with the blunted natriuretic response in the piglet was an absence of an increase in RIHP (6.1 ± 1.1 versus 6.1 ± 1.6 mm Hg) in response to VE. In contrast, the adult pig, which exhibited a normal natriuretic response, showed a significant increase in RIHP (8.8 ± 1.3 to 12.3 ± 1.5 mm Hg) during VE. When RIHP was prevented from increasing during VE in the adult pigs, the natriuretic response was significantly attenuated, as it was in the piglets. The results of our study indicate that the piglet does not exhibit a normal adult RIHP response to VE. The absence of any discernible increase in RIHP durin g VE may explain, in part, why piglets have a limited ability to excrete a saline load. (Pediatr Res 28: 460-463, 1990) such as the renin-an giotensin system (5). However, the exact mechanism respon sible for th e blunted natriuresis in the dev eloping a ni mal has not yet been elu cidated.R ecent st udies have suggested th at RIHP may play an important role in mediating the inc reas e in sodiu m excretion during VE in the ad ult. Acute saline VE in th e ad ult results in signi ficant increases in RIHP and sodium excretion (6). When th e rise in RIHP is prevented from in creasing during VE in the adult, the increase in sodium excretion is signific antly attenuated (7,8). Furthermore , direct increa ses in RIHP comparable to the RIHP measured during VE result in significa nt increases in sod iu m excretion (9). Altho ugh th ese studies suppo rt a ro le for RIHP in mediating saline expa nsion-ind uced natriuresis in th e adult animal, th e importan ce of RIHP in th e blunted sodi um excret ory respon se to VE in the de velop ing animal is not known . Indeed, RIHP has never been measured in the developing ani m al under any ph ysiologic or pathophysiologic co ndition.An important factor that influences RIHP is ren al perfusio n pressure (10). Renal perfu sion pre ssure is significa ntly lower in th e developing an im al than in the adult ani m al (2). Co nversely, renal vascular resistan ce in th e developing animal is signi fica ntly high er th an in th e ad ult ( 11). The co mbina ...

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