An increase in renal dopamine does not stimulate natriuresis after fava bean ingestion

Abstract

Background: Fava beans (Vicia faba) contain dihydroxyphenylalanine (dopa), and their ingestion may increase dopamine stores. Renal dopamine regulates blood pressure and blood volume via a natriuretic effect.

Objective: The objective was to determine the relation between dietary fava beans, plasma and urinary catechols, and urinary sodium excretion in 13 healthy volunteers.

Design: Catechol and sodium data were compared by using a longitudinal design in which all participants consumed a fixed-sodium study diet on day 1 and the fixed-sodium diet plus fava beans on day 2. Blood was sampled at 1, 2, 4, and 6 h after a meal, and 3 consecutive 4-h urine samples were collected.

Results: Mean (±SD) plasma dopa was significantly greater 1 h after fava bean consumption (11,670 ± 5440 compared with 1705 ± 530 pg/mL; P = 0.001) and remained elevated at 6 h. Plasma dopamine increased nearly 15-fold during this period. Fava bean consumption also increased urinary dopamine excretion to 306 ± 116, 360 ± 235, and 159 ± 111 μg/4-h urine sample compared with 45 ± 21, 54 ± 29, and 44 ± 17 μg in the 3 consecutive 4-h samples after the control diet (P ≤ 0.005). These substantial increases in plasma and urinary dopa and dopamine were unexpectedly associated with decreased urinary sodium.

Conclusion: The failure of fava bean consumption to provoke natriuresis may indicate that dopa concentrations in commercially available beans do not raise renal dopamine sufficiently to stimulate sodium excretion, at least when beans are added to a moderate-sodium diet in healthy volunteers. This trial was registered at clinicaltrials.gov as NCT01064739.

Figures

FIGURE 1.

Proposed effect of fava bean ingestion on urinary sodium excretion. We proposed that dietary dopa ingested as fava beans would increase plasma dopa, urinary DA, and urinary sodium. DA, dopamine; dopa, dihydroxyphenylalanine.

FIGURE 2.

Relation between dietary dopa concentrations in FB and plasma dopa concentrations. Plasma dopa increased as the dietary dopa content increased. R2 values from linear regression are shown. P = 0.011 at 1 h (solid line), P = 0.016 at 2 h (dashed line), and P = 0.068 at 4 h (dotted line); n = 13 at all times. dopa, dihydroxyphenylalanine; FB, fava bean.

FIGURE 3.

Mean (±SEM) plasma concentrations of dopa, DA, and NE after the fixed-sodium study diet (solid line) and the diet plus fava beans (dashed line). Arrows indicate when meals were provided. *P < 0.05, **P < 0.01, ***P < 0.001 according to Wilcoxon's matched-pairs signed-rank test. The treatment × time interaction was significant (P < 0.013) for dopa, DA, and NE by repeated-measures ANOVA. n = 13. DA, dopamine; dopa, dihydroxyphenylalanine; NE, norepinephrine.

FIGURE 4.

Mean (±SEM) urinary excretion of dopa, DA, and NE. After breakfast consisting of a fixed-sodium diet (black bars) or the fixed-sodium diet plus fava beans (gray bars), 4-h urine samples were collected at 0–4 (n = 10), 4–8 (n = 13), and 8–12 (n = 13) h. The treatment × time interaction was significant for dopa (P = 0.011) and DA (P = 0.013) but not for NE (P = 0.909) by general linear model analysis. A Wilcoxon's matched-pairs signed-rank test was used to test for significant differences between data obtained with and without fava beans during each collection period. P values are included for NE because the main effect of treatment was significant (P < 0.001). DA, dopamine; dopa, dihydroxyphenylalanine; NE, norepinephrine.

FIGURE 5.

Mean (±SEM) urinary excretion of sodium and 4-h urine volumes. After breakfast consisting of a fixed-sodium diet (black bars) or the fixed-sodium diet plus fava beans (gray bars), 4-h urine samples were collected at 0–4 (n = 10), 4–8 (n = 13), and 8–12 (n = 13) h. The treatment × time interaction was significant for volume (P = 0.020) but not for sodium (P = 0.194) by general linear model analysis. A Wilcoxon's matched-pairs signed-rank test was used to test for significant differences between data obtained with and without fava beans during each collection period. P values are included for sodium because the main effect of treatment was significant (P < 0.001).

FIGURE 6.

Effect of dietary dopa on plasma and urinary catechols and urinary sodium excretion. DA, dopamine; DA-S, dopamine sulfate; DHPG, dihydroxyphenylglycol; dopa, dihydroxyphenylalanine; DOPAC, 3,4-dihydroxyphenylacetic acid; DOPA-S, dopa sulfate; MAO, monoamine oxidase; NE, norepinephrine.