José O. Alda

Renal and vascular actions of equol in the rat.

Background The urinary isoflavonoid equol inhibits membrane Na–K–Cl cotransporters at similar concentrations to those at which furosemide inhibits them, but the significance of this action is not known. Objective To investigate the potential salidiuretic and vascular actions of equol in the rat. Methods Renal functioning was assessed in vitro in the isolated perfused kidney and in vivo in conscious rats. The vascular contractility of isolated aorta was assessed. Results In the isolated perfused kidney equol was concentrated 50- to 70-fold in the urinary fluid, it was 3–4 times less potent than furosemide at increasing diuresis, natriuresis and kaliuresis (the difference was due to its higher protein-binding affinity), and it induced a modest but significant increase in glomerular filtration rate. In vivo, orally administered equol was a modest natriuretic agent, about 8-fold less potent than orally administered furosemide (in molar terms). In isolated aortic rings precontracted by administration of phenylephrine, administration of equol relaxed the contracted aorta at 10-fold lower concentrations (concentration for half-maximal activity 58.9 ± 16 μmol/l, n = 3) than did furosemide (concentration for half-maximal activity 633 ± 145 μmol/l, n = 3). Conclusions Equol is a modest natriuretic and vasorelaxant agent in the rat. Further studies are required in order to investigate the potential natriuretic and perhaps hypotensive actions of dietary equol precursors (daidzein).

Endothelium-independent vasorelaxation by the selective alpha estrogen receptor agonist propyl pyrazole triol in rat aortic smooth muscle

Objectives This study investigated the signalling mechanism of the relaxant responses to the estrogen receptor alpha (ERα) agonist PPT (propyl pyrazole triol) in endothelium‐denuded rat aortic rings.

Salidiuretic Action by Genistein in the Isolated, Perfused Rat Kidney

The urinary isoflavonoid genistein inhibits membrane Na-K-Cl cotransporters at similar concentrations as furosemide, but the significance of this action is unknown. Genistein was therefore investigated in rats for its potential salidiuretic actions. In the isolated, perfused rat kidney, genistein induced a maximal salidiuretic action similar to that of furosemide but was 3 to 5 times less potent than furosemide in terms of active doses (natriuresis EC50, 237+/-92 versus 56+/-20 micromol/L for genistein and furosemide, respectively). Genistein and furosemide had no additive salidiuretic actions. Genistein had no significant effect on glomerular filtration rate but was able to significantly reduce renal vascular resistance with respect to vehicle isolated perfused kidney. Indomethacin (10 micromol/L), a blocker of prostaglandin biosynthesis, reduced salidiuresis and renal vasorelaxation by genistein. Subcutaneous genistein (15 mg/kg) induced a statistically significant increase in diuresis and natriuresis with respect to vehicle during the first 6 hours of administration in rats. In conclusion, genistein compares well with furosemide in vitro for its salidiuretic profile and potency in the isolated perfused rat kidney and is also natriuretic by the subcutaneous route in the rat. Further studies are required to investigate potential natriuretic and perhaps hypotensive actions of dietary genistein.

Protein kinase A signalling is involved in the relaxant responses to the selective β-oestrogen receptor agonist diarylpropionitrile in rat aortic smooth muscle in vitro.

Objectives  The oestrogen receptor β (ERβ) selective agonist diarylpropionitrile (DPN) relaxes endothelium‐denuded rat aorta, but the signalling mechanism is unknown. The aim of this study was to assess whether protein kinase A (PKA) signalling is involved in DPN action.

Antioxidant intracellular activity of genistein and equol.

Antioxidant effects of isoflavonoids have recently been described. To learn whether the isoflavonoids genistein and equol have actions on the intracellular free radicals, human neutrophils and J774 monocyte-macrophage cell line were used to measure the intracellular production of O(2) (superoxide anion) and H(2)O(2) (hydrogen peroxide) by flow cytometry. The results shown significatives decrease in O(2) and H(2)O(2) production after 1 hour of incubation with equol and genistein. The phagcytic oxidant production decreased owing to the effects of both isoflavonoids in a concentration-dependent manner.

Inhibition of Na-K-Cl cotransport fluxes and salidiuretic action by an urinary extract of salt-loaded rats

We previously found a potent inhibitor of the Na-K-Cl cotransport system in urines from salt-loaded rats (C.I.F. = cotransport inhibitory factor, ref. 1). Here we extracted an urinary fraction (≈ 1 ‰ urine dry weight), free from immunoreactive A.N.P. and digoxine activity, which: (i) potently inhibited cotransport fluxes in MDCK (Madin and Darby canine kidney] cells and in human erythrocytes, (ii) inhibited Na+-dependent chloride/bicarbonate exchange with 2–3 times less potency than cotransport and (iii) strongly increased natriuresis and diuresis after i.v. infusion in rats with no significant change in kaliuresis (salidiuretic action reduced by probenecid). Therefore, C.I.F. seems to be a new natriuretic factor with part, but not all the biological profile of loop diuretic drugs.

Natriuretic Effect of Equol

A furosemide-sensitive Na-K-Cl cotransporter (NKCC2 isoform) accounts for almost all luminal NaCl reabsorption in the thick ascending limb of Henles loop (TALH). The activity of this transport protein is regulated by humoral factors known as cotransport inhibitory factors. One family of these compounds is represented by the urinary phytoestrogens equol and genistein, which inhibit cotransport fluxes at concentrations similar to furosemide. Moreover, they possess salidiuretic potency similar to furosemide in the isolated perfused rat kidney, but are less potent than furosemide (in vivo). Thus, dietary phytoestrogens can be responsible, at least in part, for the low blood pressure of vegetarians.

Molybdenum uptake through the anion exchanger in human erythrocytes

Human red blood cells were incubated in the presence of Na2MoO4 and the initial rate of molybdenum uptake was measured by using inductively coupled plasma emission spectroscopy. About 99% of molybdenum uptake was inhibited by DIDS or by SITS. DIDS-sensitive molybdenum uptake was inhibited by external chloride, bicarbonate, sulphate and phosphate in the range of concentrations previously described for anion carrier fluxes. Trace elements, previously described to be translocated by the anion carrier, i. e. copper, zinc and cadmium, slightly inhibited molybdenum uptake. Molybdenum uptake was strongly stimulated by acidification, suggesting that the monovalent HMoO4−anion species, which is formed in acidic media (pK≈4.1), can be more rapidly translocated than the divalent anion complex MoO42−, which is the predominant form at physiological pH. In conclusion, the anion carrier can catalyse rapid molybdenum movements across red cells membranes. This supports previous reports of an enterohepatic circulation of molybdenum, with red blood cells acting as molybdenum carrier between the intestine and the liver.