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

Abstract

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.

Fluid reabsorption by the proximal convoluted tubule of the kidney in lactating rats.

“…2 that this is indeed the case in lactating animals. In pregnancy fractional reabsorption by the proximal convoluted tubule is diminished as previously reported (Garland & Green, 1982). The reason why glomerulotubular balance does not occur in pregnancy is not known.…”

“…have previously been interpreted as indicating a redistribution of blood flow -a rise indicating a redistribution towards more superficially placed nephrons (Solomon, 1977;Garland & Green, 1982) which are the ones most amenable to micropuncture. The results in 19-day-pregnant 270 PROXIMAL TUBULAR REABSORPTION IN LACTATION animals are similar to those described by Garland & Green (1982) if one considers proximally measured S.N.G.F.R., but varies with what was deduced from distally measured values. In this study S.N.G.F.R.…”

“…It may be that there is some redistribution of blood flow and hence redistribution ofglomerular filtrate (Garland & Green, 1982;Garland & Walker, 1984) during pregnancy, but because of uncertainties over the use of proximal S.N.G.F.R. (see Garland & Green, 1982) too much reliance cannot be placed on this. In lactation, however, there is no evidence at all for a redistribution since S.N.G.F.R.…”

Glucose handling by distal portions of the nephron during pregnancy in the rat.

“…Distal tubules were identified and punctured as previously described (Garland & Green, 1982); pipettes with an outside diameter of 8-1G 0 ,m were used to collect samples for timed intervals, usually 8-10 min. Blood samples (50 Al) were collected from a tail vein hourly throughout the experiment.…”

“…Thus, there is an increase in glomerular filtration rate, an increased reabsorption of sodium and water (see Garland & Green, 1982 for references) and an increased glucose excretion. This increased glucose excretion is well documented in women (see Davison & Hytten, 1975 for references) and has recently also been shown to occur in rats (Bishop & Green, 1980).…”