Glomerular filtration rate and salt and water reabsorption during pregnancy in the conscious rat.

SUMMARY1. In rats receiving 200 gl. min-sodium chloride, glomerular filtration rate, single nephron glomerular filtration rate, and fractional reabsorption were measured at various points along the nephron, and ionic concentrations measured in early distal tubular fluid in virgin and 6, 12 and 19 day pregnant rats.2. Glomerular filtration increased progressively until the twelfth day ofpregnancy. At 19 days of pregnancy the glomerular filtration rate, while still above virgin levels, was reduced below 12 day pregnant levels.3. Single nephron glomerular filtration rates measured in proximal and distal tubules were different at both 12 and 19 days of pregnancy, indicating an alteration of tubuloglomerular feed-back. 4. A change in the ratio ofglomerular filtration rate: distal single nephron filtration rate indicated a redistribution of glomerular filtrate to juxtamedullary nephrons by the sixth day of pregnancy.5. Fluid reabsorption is similar up to the early distal tubule but it is not possible to say whether reabsorption is the same in proximal tubules. More fluid is reabsorbed by late distal tubules and collecting ducts in 12 and 19 day pregnant animals than in the virgin and 6 day pregnant animals.6. Changes in ion reabsorption by the loop of Henle occurred during pregnancy; sodium reabsorption was increased by the sixth day of pregnancy and potassium reabsorption by the twelfth day.

Section: Solute Handlingsupporting

confidence: 55%

Micropuncture study of changes in glomerular filtration and ion and water handling by the rat kidney during pregnancy

Garland

Green

1982

“…The detection of pregnancy-associated changes in whole-kidney fractional excretion might simply be the result of the infusion protocol. Thus, decreases in fractional salt and water excretion were reported for anaesthetized and conscious pregnant rats infused with 0-9 % saline at 200 ul min-1 (Atherton & Pirie, 1981;Garland & Green, 1982;Atherton, 1983;Arthur & Green, 1986), but was unchanged in the present study using 2-5 % dextrose infusion. It has to be concluded, therefore, that although differences in infusion protocols appear not to influence the detection of pregnancy-induced changes in total renal reabsorption they may prevent valid conclusions as to the relative contribution of altered fractional excretion to ECFV expansion.…”

Section: Discussionmentioning

confidence: 50%

“…Since pregnancy in both women and rats is accompanied by significant increases in both extracellular fluid volume (ECFV) and glomerular filtration rate (GFR; Davison & Hytten, 1974;Davison & Noble, 1981;Atherton & Pirie, 1981;Atherton, Dark, Garland, Morgan, Pidgeon & Soni, 1982;Garland & Green, 1982;Atherton 1983; Conrad, 1984) there must be considerable increases in renal salt and water reabsorption to avoid rapid volume depletion. It is perhaps surprising, therefore, that although there are many demonstrations of increased whole-kidney salt and water reabsorption (see Atherton & Green, 1983, for references) there is little information on the nephron site(s) involved.…”

Section: Introductionmentioning

confidence: 99%

Sodium and water reabsorption in the proximal and distal nephron in conscious pregnant rats and third trimester women.

Atherton

Bielińska

Davison

et al. 1988

Self Cite

SUMMARY1. Sodium and water reabsorption were determined in virgin controls and rats at 9 and 20 days of pregnancy during a water diuresis induced and maintained by infusion of 2f5% dextrose and in normally hydrated women during the third trimester and again 2-3 months after delivery.2. Reabsorption from the proximal tubules and distal nephron segments was assessed using the clearance of lithium as a marker of the sodium and water delivery from the proximal tubules to the loops of Henle.3. Glomerular filtration rate and whole-kidney reabsorption of sodium and water were significantly increased at both stages of pregnancy in rats and late in pregnancy in women when compared to the respective non-pregnant control. Fractional reabsorption was unaltered in pregnant rats but increased in pregnant women.4. Proximal tubule sodium and water reabsorption were increased in pregnant rats and women; fractional reabsorption was unaltered.5. Absolute reabsorption of sodium and water in distal nephron segments were increased during pregnancy in both rats and women. Although increases in fractional reabsorption were detected in pregnant women, this was not the case at either stage of gestation in rats.

“…and salt and water reabsorption at an early stage of pregnancy in the rat (Bishop & Green, 1980; Atherton, 1981;Atherton & Pirie, 1981;Garland & Green, 1982). Midterm changes in glomerular function appear to depend on an elevated renal plasma flow rate, resulting from plasma volume expansion (Baylis, 1980).…”

Section: Introductionmentioning

confidence: 99%

Changes in water and electrolyte balance, plasma volume and composition during pregnancy in the rat.

Atherton¹,

Dark²,

Garland³

et al. 1982

Self Cite

114

SUMMARY1. Daily changes in water and electrolyte balance during pregnancy were investigated in rats housed in metabolism cages.2. Fluid intake was significantly elevated above control values from day 13 of pregnancy, with urine output failing to be raised to the same extent. This would result in an extensive fluid retention if extrarenal fluid losses were not substantially altered.3. Electrolyte intake increased from as early as the third day after mating with an accompanying increase in renal ionic excretion. A net retention of Na, Cl and K did not occur until the final week of pregnancy when the urinary output of these ions was reduced.4. In a parallel study, changes in plasma volume and composition throughout pregnancy were investigated. 5. A significant increase in plasma volume occurred from day 6 of pregnancy at a time well before fluid intake or urine output were altered. This indicates either an altered extrarenal output or. a shift of fluid between body fluid compartments.6. Maternal plasma sodium and total osmolality were reduced during the last week of pregnancy despite the salt retention, suggesting an increased fetal usage.7. Such findings are related to the known renal and endocrine changes of rat pregnancy.