Influence of volume expansion on single-nephron filtration rate and plasma flow in the rat

Section: Introductionsupporting

confidence: 87%

Superficial and Juxtamedullary Nephron Function during Saline Loading in the Dog

Bruns¹,

Alexander²,

Riley³

et al. 1974

“…The specific operation of the servo-nulling device has been described in detail in a previous publication (9). The (18)(19)(20). Also in a recent study from this laboratory, snff was nearly identical to the total kidney filtration fraction in hydropenic rats (16).…”

Section: Methodsmentioning

confidence: 88%

Effect of Mannitol on Glomerular Ultrafiltration in the Hydropenic Rat

Blantz¹

1974

116

A B S T R A C T The effect of mannitol upon glomerular ultrafiltration was examined in hydropenic MunichWistar rats. Superficial nephron filtration rate (sngfr) rose from 32.0±:0.9 nl/min/g kidney wt to 42.0±1.6 (P < 0.001) in eight rats. Hydrostatic pressure gradients acting across the glomerular capillary (AP) were measured in glomerular capillaries and Bowman's space with a servo-nulling device, systemic (IrA) and efferent arteriolar oncotic pressures (7rE) were determined by microprotein analysis. These data were applied to a computer-based mathematical model of glomerular ultrafiltration to determine the profile of effective filtration pressure (EFP = AP -7r) and total glomerular permeability (LpA) in both states. Filtration equilibrium obtained in hydropenia (LpA ) 0.099± 0.006 nl/s/g kidney wt/mm Hg) and sngfr rose because EFP increased from a maximum value of 4.2±t1.1 to 12.8±0.5mm Hgaftermannitol (P <0.01). This increase was due to both increased nephron plasma flow and decreased 7rA. Computer analysis of these data revealed that more than half (> 58%) of this increase was due to decreased WA, consequent to dilution of protein. Since EFP was disequilibrated after mannitol, LpA could be calculated accurately (0.065 ± 0.003 nl/s/g kidney wt/mm Hg) and was significantly lower than the minimum estimate in hydropenia.Therefore, sngfr does increase with mannitol and this increase is not wholly dependent upon an increase in nephron plasma flow since the major factor increasing EFP was decreased 7rA INTRODUCTION There is evidence from both the reijal physiology laboratory (1-4) and the clinical experience (5,6)

“…In general, despite evidence to the contrary (1)(2)(3)(4)(5), recent studies in the rat and the dog have indicated that massive saline infusions cause a disproportionate increase in filtration rate in the SF nephrons (6)(7)(8)(9)(10) and in plasma flow to the J-M nephrons (10)(11)(12)(13); in the rat (9) and the dog (10) these changes are associated with a profound fall in deep nephron filtration fraction. These findings hcave given rise to the hypothesis that redistribution of filtrate, plasma flow, and filtration fraction may' be an important factor in the regulation of sodium excretion.…”

Section: Introductionmentioning

confidence: 98%

Characteristics of salt and water transport in superficial and juxtamedullary straight segments of proximal tubules.

Kawamura¹,

Imai²,

Seldin³

et al. 1975

A B S T R A C T The purpose of the lpresent studies was to characterize the nature of salt and water transport out of the superficial (SF) and juxtamnedullary (JIM) straight segments of rabbit proximal tubules as examined by in vitro microperfusion techniques. When the perfusate consisted of a solution simulating ultrafiltrate of plasma, there were no differences between SF and J.M straight tubules in either net reabsorption of fluid (SF = 0.47 nl/nmm per min; JAI = 0.56 nl/mm per min) or in transtubular potential difference (PD) (SF -2.1 mV; JM' -1.8 mV). Removal of glucose and alanine fronm the perfusate had no effect on the magnitude of the PD in either straight segment. Ouabain decreased both the net reabsorptive rates and the PD. Isosmolal replacement of NaCl by Na-cvclamate (a presumed imipermeant anion) in the perfusate and the bath caused an increase in luminal negativity in both segments whereas similar substitution of NaCl by choline-Cl (nontransported cation) changed the PD to near zero. These studies, therefore, suggest that sodium is transported out of the proximal straight tubules by an active noncoupled process that generates a PD (electrogenic process).When the perfusate consisted of a solution with a high chloride concentration (resulting from greater HCO3 than C1 reabsorption in the proximal convoluted tubule), different PDs in SF and JAI tubules were generated: SF = + 1.6±0.2 mV; J'M --1.3±0.3 mV. This difference in PD was attributed to relative differences in Na and C1 permeal)ilities in these two seg-