Effects of Acute Volume Expansion and Altered Hemodynamics on Renal Tubular Function in Chronic Caval Dogs

A B S T R A C T Studies were designed to compare the segmental analysis of sodium reabsorption along the nephron during volume expansion with either 10% body weight Ringer's or 0.6% body weight hyperoncotic albumin. Total kidney and nephron glomerular filtration rate increased similarly with both, but urinary sodium excretion (12.7 vs. 4.0 Aeq/min, P <0.001) and fractional sodium excretion (5.0 vs. 1.6%, P < 0.001) increased to a greater extent with Ringer's. Fractional reabsorption of sodium in the proximal tubule was diminished in both groups but to a significantly greater extent during Ringer's (P < 0.005). Absolute reabsorption was inhibited only in the Ringer's group. Delivery of filtrate out of the proximal tubule was greater in the Ringer's studies, 45 vs. 37 nl/min (P < 0.001).However, both fractional and absolute sodium delivery to the early and late distal tubule were not significantly different in the two groups. Fractional reabsorption in the collecting duct decreased from 96% in hydropenia to 31% during Ringer's but fell only slightly to 80% in the albumin studies. Absolute collecting duct reabsorption was also greater in the albumin studies, 0.55 vs. 0.21 neq/min (P < 0.001), which could totally account for the difference in urinary sodium excretion between the two groups. 22Na recovery in the final urine after end distal microinjections was 71% during Ringer's infusion and 34% during albumin (P < 0.001). From these data we conclude that: (a) Ringer's solution has a greater inhibitory effect on proximal tubular sodium reabsorption, and (b) in spite of this effect, differences in mucosal to serosal collecting duct sodium transport are primarily responsible for the greater natriuresis during Ringer's infusion.

Section: Introductionmentioning

confidence: 99%

A Comparison of the Segmental Analysis of Sodium Reabsorption during Ringer's and Hyperoncotic Albumin Infusion in the Rat

Stein¹,

Osgood²,

Boonjarern³

et al. 1973

“…The causes of altered sodium excretion have been examined under a number of experimental conditions that lead to positive sodium balance (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). A great many possible causes of sodium retention have been identified, but a common unifying hypothesis has not yet been advanced.…”

Section: Introductionmentioning

confidence: 99%

“…The variability observed among differing experimental models may be due, at least in part, to fundamental mechanistic differences in the models themselves or to the differing stages of renal sodium retention at which experimental observations are made. Plasma volume, for example, is one factor which may change during the course of sodium retention; and the net impact of the changes in plasma volume upon renal function may vary at different stages (8)(9)(10)(11).…”

Section: Introductionmentioning

confidence: 99%

Intrarenal mechanisms of salt retention after bile duct ligation in rats.

Yarger¹,

Schrader²,

Boyd³

1976

A B S T R A C T In order to study renal salt-retaining mechanisms during the early stages of ascites formation, rats were subjected to bile duct ligation. After this procedure, plasma volumes were found to be reduced and hematocrits slightly increased. The whole-kidney glomerular filtration rate and plasma flows were reduced to 59 and 57% of control values, but the filtration fraction was unchanged. Absolute sodium excretion, as well as the fraction of the filtered sodium load excreted, was also significantly reduced.When micropuncture techniques were used to examine the function of single superficial nephrons, the glomerular filtration rate in these nephrons was found to be reduced to 70% of controlled values, and fractional reabsorption was found to be increased at all accessible sites along the nephron. Filtration by intermediate and juxtamedullary nephrons, determined by Hanssen's technique, was reduced to 55 and 48% of control values.By the use of radioactive microspheres, it was demonstrated that blood flow to superficial, intermediate, and juxtamedullary nephrons was reduced to 49, 59, and 73% of control values. Filtration by superficial nephrons decreased much more than plasma flow-a finding which suggests that the measured increase in fractional reabsorption was associated with an increase in the superficial nephron filtration fraction.From this study, it appears that two factors play an important part in the sodium retention observed in the initial stages of ascites formation following bile duct ligation in rats: (a) a decrease in the filtered sodium Several parts of this manuscript have previously appeared in abstract form (Clin. Res. 22: 52A and 551A) and were presented to the Southern Sectional Meeting of the Ameri-

“…Current micropuncture data have also failed to support the presence of redistribution of filtration in both acute and chronic volume expansion (13)(14)(15)(16)(17)(18)(19)(20)(21).…”

Section: Introductionmentioning

confidence: 99%

“…Utilizing cardiovascular manipulation (15,20,22,23 The dogs with arteriovenous fistulas were subjected to experimentation 14 days after their initial surgery. All animals were intubated with cuffed endotracheal tubes and ventilated witlh a Harvard Respirator.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Natriuresis after Closure of Chronic Arteriovenous Shunts

Mandin¹

1973

A B S T R A C T Animals subjected to certain cardiovascular manipulations, such as arteriovenous fistulas, diminish their urinary sodium excretion. It has been shown that closure of such fistulas results in a prompt increase in the rate of sodium excretion. However, the nature of the renal mechanisms increasing the excretion of sodium when the initial cardiovascular abnormality is corrected has remained unclear. Since the elucidation of such mechanisms might provide information pertinent to other sodium-retaining states, the effect of closure of chronic Teflon-Silastic arteriovenous shunts was studied in desoxycorticosterone acetate (DOCA) -treated dogs by utilizing micropuncture techniques.Nephron filtration rates were measured first during a control period vith open arteriovenous shunts and then again after closure of the shun.s in 12 dogs. Nephron filtration rate rose 32% while total glomerular filtration rate (GFR) decreased 8%. After closure of the arteriovenous shunt, fractional reabsorption increased 6%, while total kidney filtration fraction increased from 0.31 to 0.35. Renal plasma flow decreased from a mean of 111 ml/min to 90 ml/min. Closure of the arteriovenous shunts increased sodium excretion from a mean of 21Aeq/min to 45 Aeq/min. Concomitantlv, a redistribution of filtrate to superficial nephrons occurred. Since pharmacological doses of DOCA wvere being administered while total GFR was not increased and fractional reaisorption of sodium in the proximal tubule was not inhibited, it was concluded that filtrate distribution to superficial nephrons may have contributed to the observed natriuresis, although alternate explanations were also deemed possible.