cyclic-gmp and daidzein

Isoflavones, such as daidzein, are proposed to possess vasculoprotective properties, perhaps through a mechanism similar to estrogen. Our experiments aimed to test the hypothesis that daidzein and 17 beta-estradiol enhance endothelium-dependent relaxation through an increase in NO synthesis due to an increase in activity or expression of endothelial nitric oxide synthase (eNOS). Male rats were treated with daidzein (0.2 mg/kg per day sc), 17 beta-estradiol (0.1 mg/kg per day sc), or vehicle for 7 days and reactivity of isolated aortic rings was then determined. ACh-induced relaxation was significantly enhanced in aortic rings from rats treated with daidzein or 17 beta-estradiol but the relaxant responses to the endothelium-independent dilators sodium nitroprusside or isoprenaline were not different. Nitrite production and the level of cGMP were significantly greater in aortae from daidzein and 17 beta-estradiol compared with vehicle-treated rats. Daidzein and 17 beta-estradiol did not alter eNOS protein in endothelium-intact aortae but reduced expression of caveolin-1 and increased expression of calmodulin, changes that would account for an increase in eNOS activity. There were no differences between groups in the expression of calmodulin and caveolin-1 in arteries when the endothelium was removed. Daidzein or 17 beta-estradiol treatment selectively enhances endothelium-dependent relaxation in male rats through an increase in eNOS activity. The increase in eNOS activity is associated with a decreased expression of caveolin-1 and an increased expression of calmodulin in endothelial cells.

Topics: Acetylcholine; Animals; Aorta; Body Weight; Calmodulin; Caveolin 1; Caveolins; Cyclic GMP; Drug Synergism; Endothelium, Vascular; Estradiol; Fulvestrant; Gene Expression; Injections, Subcutaneous; Isoflavones; Isoproterenol; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Nitroprusside; Organ Size; Phenoxybenzamine; Rats; Rats, Sprague-Dawley; Testis

Recently, we described a splice variant of the human natriuretic peptide receptor type B (NPR-Bi) in human proximal tubule cells [immortalized human kidney epithelial cells (IHKE-1) that lacks a functional guanylate cyclase domain (Hirsch JR, Meyer M, Mägert HJ, Forssmann WG, Mollerup S, Herter P, Weber G, Cermak R, Ankorina-Stark I, Schlatter E, and Kruhøffer M. J Am Soc Nephrol 10: 472-480, 1999). Its signaling pathway does not include cGMP, cAMP, or Ca2+ but leads to inhibition of K+ channels. In patch-clamp experiments, effects of tyrosine kinase receptor blockers on C-type natriuretic peptide (CNP)-mediated depolarizations of membrane voltages (Vm) of IHKE-1 cells were tested. The epidermal growth factor (EGF) receptor blocker genistein (10 microM) abolished the effect of CNP (0.2 +/- 0.4 mV, n = 7), and comparable results were obtained with 10 microM daidzein (n = 8). Aminogenistein (10 microM, n = 5) and tyrphostin AG1295 (10 microM, n = 5) had no significant effects. EGF (1 nM) hyperpolarized cells by -5.3 +/- 0.8 mV (n = 5). This effect was completely blocked by genistein or daidzein. The Cl- channel blocker NPPB (10 microM, n = 5) inhibited the EGF-mediated hyperpolarization. mRNA expression of NPR-B and NPR-Bi shows reversed patterns along the human nephron. NPR-B is highly expressed in glomeruli and proximal tubules, whereas NPR-Bi shows strong signals in the distal nephron. Expression of NPR-Bi in the cortical collecting duct was also confirmed with immunohistochemistry. In other human tissues, NPR-Bi shows strongest expression in pancreas and lung, whereas in the heart and liver NPR-B is the dominating receptor. In conclusion, CNP inhibits an apical K+ channel in IHKE-1 cells independently of cGMP and so far this effect can only be blocked by genistein and daidzein. Tyrosine phosphorylation might be the missing link in the signaling pathway of CNP/NPR-Bi.

Topics: Cell Line, Transformed; Cyclic GMP; Enzyme Inhibitors; Estrogens, Non-Steroidal; Gene Expression; Genistein; Guanylate Cyclase; Humans; Isoflavones; Kidney Tubules; Natriuretic Peptide, C-Type; Patch-Clamp Techniques; Potassium; Receptors, Atrial Natriuretic Factor; RNA Splicing; Signal Transduction; Tyrphostins