atrial-natriuretic-factor and 2--7--bis(carboxyethyl)-5(6)-carboxyfluorescein

Estrogen has been shown to protect the heart and attenuate myocardial hypertrophy and left ventricular remodelling through as yet to be defined mechanisms. In the present study we examined concentration-dependent effects of estrogen on hypertrophy of adult rat cardiomyocytes, potential underlying mechanisms related to intracellular pH (pHi) and possible sex-dependent responses. Cardiomyocytes were isolated from adult male and female Sprague-Dawley rats and used immediately for pHi determinations or cultured and subsequently treated for 24 h with 17beta-estradiol to assess hypertrophic responses. Fluorometric measurements with the pHi-sensitive dye BCECF demonstrated that at 1 pM 17beta-estradiol increased pHi (+0.05 pH units in females and +0.12 pH units in males, P<0.05) by a rapid non-genomic mechanism that was blocked by the sodium-hydrogen exchange isoform 1 (NHE-1) specific inhibitor AVE-4890 (AVE, 5 microM). Treatment with 1 pM 17beta-estradiol for 24 h increased cell size (females: 20%, P<0.05; males: 29%, P<0.05) and ANP expression (females: 414%, P<0.05; males: 497%, P<0.05) in a NHE-1-, and ERK1/2 MAPK-dependent manner. At 1 nM, 17beta-estradiol decreased pHi (females: -0.24 pH units, P<0.05; males: -0.07 pH units, P<0.05) which was also prevented by AVE, although at this concentration the hormone had no direct hypertrophic effect but instead prevented hypertrophy induced by phenylephrine. Our results show that low levels of estrogen produce cardiomyocyte hypertrophy through ERK/NHE-1 activation and intracellular alkalinization whereas an antihypertrophic effect is seen at high concentrations. These effects may further our understanding of the role of estrogen in heart disease particularly associated with hypertrophy.

Topics: Adrenergic alpha-Agonists; Animals; Atrial Natriuretic Factor; Cardiomegaly; Cells, Cultured; Dose-Response Relationship, Drug; Enzyme Activation; Estradiol; Estrogens; Female; Fluoresceins; Fluorescent Dyes; Heart Ventricles; Hydrogen-Ion Concentration; Male; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Myocytes, Cardiac; Phenylephrine; Rats; Rats, Sprague-Dawley; Sex Characteristics; Sodium-Hydrogen Exchanger 1; Sodium-Hydrogen Exchangers; Time Factors

While the in vivo diuretic and antihypertensive effects of the newly-developed drug Candoxatril (UK-79300), a prodrug of a selective atriopeptidase inhibitor UK-73967 (API) are well established, the mechanism of its diuretic action is not yet fully understood due to the lack of information about its direct effects on proximal tubules. To elucidate whether this atriopeptidase inhibitor has any direct effects on proximal tubules, we examined the effect of API on intracellular pH (pHi) of the in vitro microperfused proximal S2 segment of rabbit kidney, using the pH-sensitive fluorescent dye, (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein (BCECF). In the steady-state condition, pHi was 7.13 +/- 0.02 (n = 19). Atriopeptidase inhibitor (API) at 100 microM added to the bath changed pHi by only 0.02 +/- 0.07 unit (n = 7, p > 0.05) in 10 min. The same concentration of API in the lumen changed pHi by 0.03 +/- 0.02 unit (n = 6, p > 0.05). To test whether the synergistic effects of API on the luminal and basolateral transport systems prevented the apparent change in pHi, we also examined the effect of API in the presence of amiloride in the lumen. The inhibition of Na+/H+ antiporter by the addition of 1 mM of amiloride to the lumen caused no change in pHi response to basolateral API application. API was without effect on pHi also in the presence of atrial natriuretic polypeptide (ANP). These results suggest that API per se has no significant effect on the process of proximal acidification over a short time period.

Topics: Animals; Atrial Natriuretic Factor; Diuretics; Female; Fluoresceins; Fluorescent Dyes; Hydrogen-Ion Concentration; In Vitro Techniques; Indans; Kidney Tubules, Proximal; Neprilysin; Perfusion; Propionates; Rabbits