Mechanisms regulating the renal excretion of sodium during pregnancy

Abstract

A B S T R A C T Observations were made on the relation of the renin-angiotensin-aldosterone system and renal hemodynamic function to sodium balance in 43 pregnant dogs. Daily balance studies revealed that about 30-40% of ingested sodium was retained during the last half of pregnancy; during the same period, potassium balance was also positive but to a lesser extent. For groups of pregnant dogs, plasma renin activity (n = 14) and aldosterone secretion (n = 19) were significantly higher than normal; however, in some animals one or both functions were normal even though sodium retention was present. In contrast, plasma renin substrate concentration was consistently elevated during pregnancy in seven dogs. In a group of nine dogs in which both aldosterone secretion and plasma renin activity were measured, aldosterone secretion was elevated in the three dogs with the highest values for plasma renin activity; in two of the remaining six animals aldosterone secretion was elevated but plasma renin activity was normal or only slightly increased. The sequestration of sodium and water into the uterine contents was defined quantitatively in this study but evidence was lacking to support the idea that such changes led to renin release. The glomerular filtration rate (GFR) was significantly elevated throughout pregnancy but a significant decrease from the high level of mid-pregnancy occurred during the last half of pregnancy; this decrease in GFR probably contributed to the sodium retention. Administration of a large dose of deoxycorticosterone acetate (DOCA) to dogs in late pregnancy produced marked sodium retention but "escape" from the sodium-retaining steroid occurred. The data demonstrate that although increased activity of the renin-angiotensin-aldosterone system was frequently present during pregnancy, a normal rate of aldosterone secretion occurred. This finding and the observed "es-

Uterine blood flow and uterine renin secretion

“…A similar wide variability in PRA has been described in pregnant dogs (17) and humans (18). Differences in substrate concentration known to be elevated with pregnancy might in part account for the variability.…”

Plasma Aldosterone Concentration at Delivery and during the Newborn Period

“…Whether estrogens are sufficiently elevated during pregnancy to contribute to the hyperaldosteronism is not known (46). Another hypothesis was that because of the increased glomerular filtration rate observed during pregnancy, increased sodium loss could occur causing secondary aldosterone elevation (49), but it has not been found to be a positive correlation (50). The plasma levels of aldosterone obtained after 10 hr of recumbency and cesarean section were significantly lower than those obtained during vaginal delivery.…”

Sodium and potassium in blood and milk and plasma aldosterone levels in high-yield dairy cows

“…Although the metabolic clearance rate of aldosterone in ewes increased after parturition, the changes observed in the plasma levels of this hormone during the perinatal period in those animals could not be directly related to modifications in its catabolism (Moncaup et al, 1980 (Weir et al, 1975). Similarly, normal aldosterone secretion rate has been measured in pregnant bitches which escape the sodium retention induced by deoxycorticosterone acetate, suggesting the existence of sodium-retaining mechanisms other than that provided by high plasma aldosterone levels (Robb et al, 1970). Similar conclusions have been reached recently in pregnant rats (Churchill, Bengele and Alexander, 1980).…”