Renal Function in the Term Pregnant Rat: A Micropuncture Study

Abstract

The purpose of this study was to define individual nephron function and salt and fluid reabsorption in the term pregnant rat utilizing standard micropuncture techniques. The studies were performed at the time of maximal sodium retention and when extracellular fluid volume was significantly increased. During micropuncture in 7 pregnant and 9 non-pregnant rats, we found no difference, respectively, in GFR 1.04 + 0.06 vs. 1.13 ± 0.06 ml/min/kidney or nephron GFR 35 ± 0.9 vs. 33 ± 1 ml/min. Fractional and absolute Na reabsorption was also not significantly different in the proximal tubule or the loop of Henle. Along the distal tubule, fractional reabsorption was higher in pregnancy, 71 + 3 vs. 62 + 4 but not statistically different, 0.05 < p < 0.10. Beyond the late distal tubule absolute delivery and reabsorption were greater in the nonpregnant rats. Distal nephron potassium secretion was similar in both groups. In anesthetized rats during clearance studies but without surgery for micropuncture, GFR in the pregnant group was significantly higher than the nonpregnant rats, 1.65 + 0.06 vs. 1.28 + 1.10ml/min/kidneys as was tubular reabsorption of sodium. We conclude that pregnant rats exhibit glomerular tubular balance and that potassium handling along the superficial nephron is unaffected by pregnancy. The sodium retention of pregnancy appears to occur because of the failure of inhibition of tubular sodium reabsorption, a response which is normally expected when extracellular volume is expanded.

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

“…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.…”

Compensatory Growth and Other Growth Responses of the Kidney

“…GFR is increased by 50-80% through most of pregnancy in women [108,239,503]. Although changes in kidney weight, if any, during pregnancy are unknown [293], glucose Tm is not increased [92,502], In the rat GFR and ERPF are increased by 20-30% during the last half of pregnancy [26,27,41,93,100,109,175,292], Similar changes were also seen in the pseudopregnant rat [42]. Although wet weight is increased early in rat [109] and mouse [337], no changes in dry weight have been found [109].…”

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

“…Thus, factors such as the method and degree of body fluid volume expansion employed, measurements being made during non-steady-state conditions, and the extent of the anaesthesia/surgery employed may be important. In this respect, Churchill, Bengele & Alexander (1982) demonstrated that g.f.r. in term-pregnant rats prepared for micropuncture was similar to that in virgin controls, whereas in anaesthetized non-micropunctured term-pregnant animals g.f.r.…”