Atrial natriuretic peptide and aldosterone secretions, and atrial natriuretic peptide-binding sites in kidneys and adrenal glands of pregnant and fetal rats in late gestation in response to a high-salt diet

Abstract

Objective: This study aimed at determining, in the term pregnant rat, whether maternal and fetal plasma atrial natriuretic peptide (ANP) concentrations were modified in response to an oral sodium load, and to investigate whether any changes in plasma concentrations were able to modify the density and affinity of the different ANP-binding site subtypes in maternal and fetal kidneys and adrenal glands. Methods: Pregnant rats kept in metabolic cages were divided into two groups. The normal sodium diet group had free access to rat chow and tap water whereas the high sodium diet group received 1% NaCl as drinking water for 10 consecutive days from day 11 to day 21 of gestation with free access to standard rat chow. Pregnant rats from both groups were killed by decapitation on day 21 of gestation. The plasma ANP and aldosterone concentrations were determined by RIA. The density and affinity of ANP receptors were determined in the maternal and fetal adrenal glands and kidneys. Results: In the pregnant rats on the high-salt diet, the sodium and water intakes, as well as the urine volume and sodium excretion, were significantly higher than in the control group. After 10 days of high-salt intake, water and sodium retentions were not significantly different in the two groups, indicating that the pregnant rats were able to excrete excess salt. The high sodium intake did not change the body weight of the pregnant rats but did increase the body weight of the fetal rats. Maternal and fetal hematocrits remained unchanged in both groups, the high sodium intake did not modify plasma sodium concentration in the maternal rats but increased that of the fetuses, indicating an accumulation of sodium in the fetal rats. The dietary sodium intake did not change the plasma ANP concentrations but significantly decreased the plasma aldosterone concentrations in both the maternal and fetal rats. In response to the high-salt diet, the density and affinity of total ANP, ANPb and ANPc receptors were not altered in the maternal isolated renal glomeruli or the adrenal zona glomerulosa membranes or the fetal adrenal gland and kidney membrane preparations. Conclusion: These results suggest that ANP is not involved in the regulation of water and electrolyte balance in maternal and fetal rats during salt-loaded intake.

High-sodium intake prevents pregnancy-induced decrease of blood pressure in the rat

“…On the opposite, high-sodium intake reduces the activity of this system (12). As expected, we observed that sodium supplements of 0.9 or 1.8% decreased the activity of RAAS, as measured by PRA and aldosterone levels.…”

“…However, this maneuver did not modify the decrease in blood pressure observed during rat pregnancy (31). On the opposing side, highsodium intake during pregnancy induces reduction in PRA and aldosterone (12). Such alteration of activity of RAAS can provide a valuable avenue to modify the reduction of blood pressure associated with the end of pregnancy in the rat.…”

“…However, although providing valuable information on cardiovascular regulatory mechanisms, these models are sometimes not specific to the pregnant condition and occasionally are associated with fetal mortality. Modifications of sodium intake have been shown to modulate RAAS activity (12,31). It is well known that reduction of sodium intake increased RAAS activity.…”

Feeding pregnant ewes a high-salt diet or saltbush suppresses their offspring’s postnatal renin activity

“…However, results from rat dams consuming large amounts salt have shown that although the plasma sodium of the mother may not change, the plasma sodium of the offspring may increase because of the immaturity of their kidney (Deloof et al, 2000). Hence, our third hypothesis is that a high-salt diet or saltbush will increase plasma concentrations of chloride and keep sodium the same in ewes but increase plasma concentrations of both chloride and sodium in lambs at birth.…”

Availability of a rich source of sodium during the perinatal period programs the fluid balance restoration pattern in adult offspring

“…On the other hand, it is well known that an increased sodium intake, like that of many other mineral and nutrient requirements, occurs during pregnancy, [23][24][25][26]. Barelare and Ritcher (1938) [27] for example, demonstrated for the first time that, when pregnant dams have access to a rich sodium source, the total sodium intake increases between 60-98% compared with pregnant rats who have access to water only.…”