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

Abstract

SUMMARY1. Using free-flow micropuncture techniques, the rate of reabsorption from the proximal convoluted tubules was measured in virgin, 19-day-pregnant and 6-to 7-day-lactating Sprague-Dawley rats.2. In separate groups of animals proximal convoluted tubules were filled with silicone rubber, dissected out and their lengths measured.3. Single nephron glomerular rate was increased in pregnant and lactating animals. 4. The rate of reabsorption per unit length of the proximal convoluted tubule was decreased in pregnant animals but similar in virgins and lactating rats.5. The proximal convoluted tubule was increased in length in pregnant and lactating animals. As a result the total reabsorption by the proximal convoluted tubule was similar in virgin and pregnant animals but increased in lactating animals.6. The amount reabsorbed by the loop of Henle and distal parts of the nephron is greater in pregnant and lactating animals than in virgins.

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

“…More recent experiments in our laboratory (Hutchinson, 1987) have confirmed these observations in conscious normotensive and spontaneously hypertensive rats infused with 0-9 % saline at either 40 or 200 ,u min-1. Such data, while confirming those from micropuncture experiments in rats at mid-gestation (Garland & Green, 1982), are at variance with those obtained close to term; absolute fluid reabsorption in the proximal tubule had returned to values seen in virgin controls and fractional reabsorption was lower (Garland & Green, 1982;Arthur & Green, 1986). To ascribe the reduced fractional reabsorption to the concommitant increase in ECFV (Arthur & Green, 1986) may not be appropriate since, although acute volume expansion decreases fractional reabsorption in proximal tubules (Landwehr, Klose & Grebisch, 1967) this may not occur during chronic expansion (e.g.…”

“…Increased distal nephron water (CLi -V) and sodium ([CLi -CNa]PNa) reabsorption in 9-and 20-day-pregnant rats and in third trimester women must also contribute to the increases in whole-kidney reabsorption; observations consistent with micropuncture and microperfusion experiments (Garland & Green, 1982;Arthur & Green, 1986;Green & Hatton, 1987) and recent work using CLi in saline-infused, conscious rats (Hutchinson, 1987). Furthermore in pregnant women, water and sodium excretion, expressed as a fraction of the amount delivered from the proximal tubules (V/CLi; CNa/CLU), were reduced.…”

“…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.…”

“…However, just prior to delivery (19-20 days), when ECFV is maximal (Atherton & Pirie, 1981), absolute reabsorption had returned towards values observed in virgin controls and fractional reabsorption was reduced (Garland & Green, 1982;Arthur & Green, 1986). In midand late-gestation increased sodium and water reabsorption were observed in loops of Henle (Garland & Green, 1982;Green & Hatton, 1987) and in nephron sites distal to early distal convoluted tubules (Garland & Green, 1982;Arthur & Green, 1986). In contrast, Churchill, Bengele & Alexander (1982) were unable to demonstrate altered proximal and loop of Henle sodium reabsorption in late-pregnant rats.…”

Impairment of renal sodium excretion in tropical residents - phenomenological analysis

“…Also, proximal tubular fluid reabsorption determines the amount of fluid entering the distal nephron. Among other factors that determine renal sodium excretion, the amount of sodium finally excreted by the kidney is also dependent on the amount of fluid delivered from the proximal tubule into the loop of Henle (Arthur and Green 1986;Knox and Granger 1987). Moe et al (1993) have described a renin/angiotensin system in the proximal tubule that is potentially autocrine and paracrine in nature and is involved in essential hypertension in humans.…”