Variations In Salt Intake Research Articles

Glomerular adaptations to chronic dietary salt restriction or excess.

Micropuncture studies were performed in 33 Munich-Wistar rats maintained chronically either on dietary NaCl restriction (group 1) or excess (group 2). Values for single nephron (SN) and total kidney glomerular filtration rate (GFR) were identical in both groups. Nevertheless, because of preferential efferent vasoconstriction, glomerular capillary hydraulic pressure (PGC) was higher in group 1, offsetting the lower initial glomerular plasma flow rate (QA) also found in group 1. The pressor response to infusion of exogenous angiotensin II (AII) was less in group 1 than in group 2, suggesting that vascular receptors for AII may have been occupied by endogenous hormone, the latter leading to the efferent arteriolar vasoconstriction. In addition to AII, prostaglandins also appear to be involved in the adaptations of the glomerular microcirculation to chronic variations in salt intake. In group 1, indomethacin or meclofenamate infusion mimicked exogenous AII, causing declines in QA and SNGFR. These changes were lacking in group 2. Because of relative contraction of plasma volume, the vasodilatory effects of prostaglandins appear to be needed in low salt animals to sustain SNGFR and QA. In the high salt group, however, since plasma volume is not contracted, maintenance of SNGFR and QA appears to be less critically dependent on endogenous prostaglandins.

Desoxycorticosterone in normal pregnancy: I. Sequential studies of the secretory patterns of desoxycorticosterone, aldosterone, and cortisol

Plasma concentrations of desoxycorticosterone (DOC) and aldosterone are markedly elevated in pregnancy. Although DOC secretion in nongravid women has been assumed to be dependent mainly on adrenocorticotropic hormone (ACTH), in a previous study of women in the third trimester of pregnancy it was found to be unresponsive to ACTH, dexamethasone, and variations in salt intake. In this study plasma DOC, aldosterone, and cortisol levels, as well as their responses to ACTH stimulation and overnight dexamethasone suppression, were observed sequentially in seven normal women during the course of pregnancy and at three months post partum. Plasma DOC, aldosterone, and cortisol levels rose substantially during gestation, but increments in DOC did not necessarily coincide with those of the other two. Responses of all three corticosteroids to ACTH were enhanced during the first two trimesters compared to the nongravid state; DOC became unresponsive in the third trimester, while aldosterone and cortisol rose to an even greater extent. Elevated maternal DOC was not decreased significantly by dexamethasone at any stage of pregnancy, while plasma cortisol was suppressed. Nonsuppressibility of DOC with dexamethasone and also the lack of correlation of the rise in DOC with the increase in cortisol during the course of pregnancy suggest that increased DOC secretion in pregnancy does not arise from ACTH-dependent pathways of the maternal adrenal. The loss of responsiveness of DOC to ACTH in the third trimester suggests that the maternal adrenals have undergone an alteration in their steroidogenic response to ACTH, but also may indicate that their output of DOC has reached a maximal rate.

The effect of a different glomerular filtration rate on the regulation of body water in rabbits during hypotonic expansion of the extracellular space (author's transl)

The regulation of body water during hypotonic expansion (0.6% NaCl; 0.32 ml/kg/min i.v.) of the extracellular space was investigated in 16 male rabbits with different creatinine clearances due to variations in salt intake. In group A (n = 6) sodium intake was 43 mEq/kg/day, in group B (n = 10) 0.6 mEq/kg/day. After 2 weeks the exogenous creatinine clearance in group A averaged 3.85 ± SD 0.62 ml/min/kg, in group B 2.52 ± SD 0.58 ml/min/kg (p < 0.01). Comparable urine flows (group A: 0.40 ± SD 0.064 ml/min/kg, group B: 0.42 ± SD 0.094 ml/min/kg, p > 0.90) were not caused by differences in the free water clearance (group A: ± 0.13 ± SD 0.07 ml/min/kg, group B: ± 0.11 ± SD 0.05 ml/min/kg, p > 0.60), but by a different tubular reabsorption of sodium: group A: 95.1 ± SD 2.11%, group B: 89.4 ± SD 1.53% (p < 0.001). Our results suggest that a physiological mechanism controls the decreased tubular reabsorption of sodium in kidneys with reduced glomerular filtration rates during a rapid hypotonic expansion of the extracellular space.

Effect of age and salt intake on renal function of rats.

The effect of variations in salt intake on plasma composition in renal function has been studied in three populations of animals of different weights. Animals on a low salt diet were found to have lower hematocrits than control animals or animals on a high salt diet. Small animals had lower hematocrits than large ones. No changes in plasma cation concentrations were found under conditions of these experiments.Changes in urinary excretion of sodium was similar to that found by others, being related to salt intake. Potassium excretion was not meaningfully affected by changing salt intake. As animals became larger, they excreted less potassium when expressed per unit body weight. No dependence of total kidney GFR on salt intake was found. Superficial nephron GFR was no different than controls on animals on high or low salt diets for intermediate sized and the largest animals. In the smallest animals, high salt intake led to an increase in superficial single nephron GFR, while in those on a low salt diet, there was no difference from controls.