[A novel hormone found in circulation--endogenous ouabain].

Endogenous ouabain (EO) is a recently found hormone that may be secreted from adrenal cortex. As an endogenous mammalian analogue of cardiac glycosides and an inhibitor of the sodium pump, it regulates the body fluid balance, urine sodium extraction and vasoconstrictive tone, and thus plays an important role in the pathogenesis of hypertension and some other cardiovascular disorders. This articke reviews its biological features, receptor and antibody, detection, effects on diseases and relationship with endothelial cells.

New ouabain-conjugated peptide found from phage displayed peptide library.

BACKGROUND: Recently, numerous investigations have shown that endogenous ouabain plays an important role in primary and secondary hypertension. The purpose of this study was to find ouabain-conjugated peptides (OCP) to block or to antagonize actions between endogenous ouabain (EO) and sodium pump, to serve as theoretical and experimental bases of EO in hypertension. METHODS: The study involved screening the phage displayed 12-peptide library by biopanning for OCP. The DNA sequence of each selected peptide was determined and the amino acid sequences were deduced. The highest consistent of the polypeptide was synthesized by peptide synthesizer. Synthetic OCP was identified, its binding activity determined by radioligand binding assay, and bioactivity of ouabain conjugated peptide was measured by erythrocyte 86Rb uptake. RESULTS: Three kinds of peptides were identified. Peptide A (12 peptide, Leu-Leu-Ala-Asp-Thr-Thr-His-His-Arg-Pro-Trp-Thr) was the highest consistence of peptide sequences, occupied in 66.7% (8/12). Peptide A was synthesized. The results verified that there was binding activity between synthetically OCP and 3H-ouabain, and that OCP was capable of suppressing the inhibition action between ouabain and sodium pump on the surface of erythrocyte. The results showed that efficacy was in a dose-dependent manner. CONCLUSION: It is important that the results not only obtain distinctive OCP, but also supply valuable experimental data in detection of ouabain and therapy in hypertension.

11-hydroxylation in the biosynthesis of endogenous ouabain: multiple implications.

Accumulating evidence indicates that mammals use steroidal glycosides with "digitalis-like" activity. An endogenous ouabain (EO) has been described and is linked with long-term changes in sodium balance and cardiovascular structure and function. In the adrenal gland, the biosynthesis of EO and similar compounds appears to involve cholesterol side-chain cleavage with sequential metabolism of pregnenolone and progesterone. The more distal events in the biosynthesis have not been elucidated. Preliminary work using primary cell cultures from the bovine adrenal cortex suggests that the biosynthesis of EO is affected by inhibitors of 11beta-hydroxylase. Direct participation of 11-hydoxylase in EO synthesis would lead to an 11beta isomer of ouabain in mammals and, in vivo, an 11beta-oriented hydroxyl group would spontaneously form a mixture of two 11-19 hemiketal isomers. The latter isomers would likely be converted back to a single 11beta isomer of ouabain during isolation. The existence of an additional ring in the hemiketals, along with reduced flexion of the steroidal A, B, and C rings, raises the possibility that their in vivo physiological targets and actions differ from the isolated form of EO.

[Role of renal sympathetic nerves in renal sodium transport in ouabain-hypertensive rats].

OBJECTIVE: To investigate the role of renal sympathetic nerves in renal sodium transport in ouabain-hypertensive rats (OHR). METHODS: Sixteen male SD rats with sham renal denervation (Sham-RDNX) and 16 with renal denervation (RDNX) were randomly into normal control group and ouabain group to receive intraperitoneal injection of normal saline (1 ml/kg) and ouabain (27.8 µg/kg) once a day, respectively. Systolic blood pressure (SBP), heart rate and body weight were recorded weekly. Food consumption of the rats was determined twice a week. After a 4-week treatment, blood and 24 h urine samples were collected to measure the serum and urinary concentration of sodium, trace lithium and creatinine. Endogenous creatinine clearance rate (Ccr), fractional excretions of sodium (FENa), fractional excretions of lithium (FELi) and fractional reabsorption of sodium in the postproximal tubules (FDRNa) were calculated. Plasma renin activity was determined by radioimmunoassay. Norepinephrine was extracted from the renal tissue and assayed for norepinephrine content by HPLC. RESULTS: The body weight, food intake and heart rate showed no significant difference among the 4 groups (P > 0.05). After 4 weeks, the SBP of control RDNX group (CDNX) was significantly lower than that of the control Sham-DNX group (Csham)(P < 0.05); the SBP of ouabain RDNX group (ODNX) was also significantly lower than that of ouabain Sham-DNX group (Osham) (P < 0.05); RNDX lowered SBP by about 10 mmHg in both ouabain groups and control groups. The SBP was significantly higher in Osham and ODNX groups than in the corresponding control groups (P < 0.01), also significantly higher in ODNX group than in Csham group (P < 0.01). Ccr showed no significant difference among the 4 groups(P > 0.05). FENa, FELi and FDRNa were significantly lower in ouabain groups than in the corresponding control groups (P < 0.05, P < 0.01, P < 0.05), but FENa, FELi and FDRNa of ODNX group were similar with those of Osham group (P > 0.05); FENa , FELi and FDRNa were similar between CDNX and Csham groups (P > 0.05). The plasma renin activity was comparable between the 4 groups (P > 0.05). Renal norepinephrine level was markedly reduced in RDNX group compared with that in Sham-RDNX group in both ouabain and control groups (P < 0.01). CONCLUSION: The increase of proximal tubule sodium reabsorption in OHR is not dependent on the renal sympathetic nerve.

[Changes in renal sodium transport during hypertension development in ouabain-hypertensive rats].

OBJECTIVE: To investigate the changes in renal sodium transport during development of hypertension in ouabain-hypertensive rats (OHR) and further elucidate the role of ouabain in the pathogenesis of hypertension. METHODS: Eighty male SD rats weighing 80-100 g were randomized equally into normal control and ouabain groups and treated with intraperitoneal injection of normal saline (1 ml/kg) and ouabain (27.8 microg/kg) once daily, respectively. Systolic blood pressure (SBP) and body weight of the rats were recorded weekly. One week before sacrifice scheduled at weeks 2, 4, 6 and 8, respectively, the rats were individually housed in metabolic cages to determine food consumption twice. Blood and 24-hour urine samples were collected to measure serum and urine concentration of sodium, trace lithium and creatinine. Endogenous creatinine clearance rate (Ccr), fractional excretions of sodium (FENa), fractional excretions of lithium (FELi) and fractional reabsorption of sodium in the distal tubules (FDRNa) were calculated. RESULTS: The body weight and food intake between ouabain groups and control groups were comparable during the experiment (P>0.05). Blood pressure was also comparable in the two groups after 2 weeks (P>0.05). At week 4, however, blood pressure of ouabain group was significantly higher than that of the control group (P<0.001) and increased in a dose-dependent manner. The SBP in ouabain group appeared to reach a plateau at week 7. Ccr and plasma sodium (PNa) were similar in the 2 groups during the experiment (P>0.05). FELi was significantly lower at weeks 2, 4 and 6 in ouabain group than in the control group (P<0.01), and FELi decrement in ouabain group was accompanied by reduced sodium excretion. FENa was significantly lower at week 4 in ouabain group than in the control group (P<0.05), but this difference was not significant in weeks 2 and 6 (P>0.05). At weeks 2, 4 and 6, ouabain group showed significantly lower FDRNa than the control group (P<0.05), suggesting the compensation of the distal nephron segments. After 8 weeks, FENa, FELi and FDRNa were similar between the two groups (P>0.05). CONCLUSIONS: Ouabain can increase renal proximal tubule reabsorption of sodium and consequently decrease renal sodium excretion in OHR, which can contribute to alteration of the pressure-natriuresis relationship in OHR, and play an important role in the development and maintenance of hypertension of OHR.

[Contribution of endothelin and its receptors to ouabain-induced hypertension in rats].

OBJECTIVE: To investigate the effect of endothelin and its receptors on ouabain-induced hypertension in rats. METHODS: Male Sprague-Dawley (SD) rats were treated with ouabain or saline for 6 weeks and their systolic blood pressure (SBP) were recorded weekly. At the end of 2, 4 and 6 weeks, respectively, the plasma and left ventricle endothelin contents were measured by radio-immunoassay, and real-time quantitative RT-PCR was employed to determine the mRNA level of endothelin type A receptor (ETAR) and type B receptor (ETBR) in the left ventricle, and the protein expressions of ETAR and ETBR were examined by immuno-histochemistry. RESULTS: After 4 weeks of intraperitoneal ouabain injection, the mean SBP in ouabain group increased till reaching a level significantly higher than that in the control group after 6 weeks (P<0.001). The plasma and left ventricle endothelin contents were significantly increased after 2 weeks of ouabain injection (P<0.01), and similarly, increased ETAR mRNA was observed. After 4 weeks of treatment, ETAR mRNA was increased continuously and the protein expression of ETAR upregulated in ouabain group as compared with the control group. The transcription and protein expression of ETBR were not altered by ouabain treatment. CONCLUSION: Before detectable blood pressure elevation occurs, endothelin concentration and ETAR can be already upregulated in ouabain-induced hypertensive rats, suggesting that endothelin might be involved in the cardiovascular effects of ouabain via an action on ETAR.

[Effect of ouabain on cardiac function and myocardium ultrastructure of rat].

OBJECTIVE: To investigate the changes in rat cardiac function and myocardium ultrastructure in response to ouabain treatment. METHODS: Twenty-four male SD rats were randomized into two equal groups to receive daily intraperitoneal injection of ouabain or saline for 4 consecutive weeks, and their systolic blood pressure (SBP) was recorded weekly. After 4 weeks of injection, echocardiography was performed and the hemodynamic parameters were measured by invasive cardiac catheterization, and the changes in myocardium ultrastructure observed using transmission electron microscopy. RESULTS: After 4 weeks of ouabain injection, no significant changes in the mean SBP occurred in comparison with the saline group, but echocardiographic examination showed significant increases in the left ventricular end-diastolic and end-systolic diameters, septum thickness, posterior wall thickness, left ventricular mass and isovolumetric relaxation time but significantly lowered E/A ratio, ejection fraction and fractional shortening after ouabain treatment (P<0.05). Invasive monitoring revealed significant attenuation of the left ventricular developed pressure, rate of pressure development (+dp/dt) and rate of pressure decay (-dp/dt), and increment of the left ventricular end diastolic pressure. Myofibrillar fragmentation, swelling of the cardiac myocytes, absence of the Z line, increases of the mitochondria and collagen fibers were found in ouabain group by transmission electron microscopy. CONCLUSION: Ouabain can induce left ventricular enlargement, cardiac wall thickening, myocardial ultrastructural alterations, systolic and diastolic dysfunction in rats before blood pressure elevation is detected, indicating that ouabain can directly cause cardiac damage in rats.

Ouabain at pathological concentrations might induce damage in human vascular endothelial cells.

AIM: To examine the time- and dose-dependent effects of ouabain on human umbilical vein endothelial cells (HUVEC) in vivo, and the changes in aortic endothelium and the different expression levels of Kv4.2 in vitro. METHODS: The proliferation of HUVEC and cell death were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, the incorporation of [3H]TdR, trypan blue staining, and lactate dehydrogenase (LDH) release. The response of endothelial cells to ouabain was explored with a complementary DNA microarray and a candidate gene was found. Ouabain-sensitive hypertensive rats were established by chronic administration of ouabain. Changes in the aortic endothelium were observed by electron microscopy, and the expression level of Kv4.2 in different animals was studied by using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Ouabain stimulated the proliferation of HUVEC at physiological concentrations (0.3-0.9 nmol/L). Ouabain at pathological concentrations (0.9-1.8 nmol/L) inhibited proliferation and induced cell death. mRNA profile analysis indicated that 340 genes were differentially expressed after ouabain treatment: 145 were upregulated, of which 6 were upregulated significantly, including KCND2 (encoding the potassium voltage-gated channel shal-related subfamily member 2). The upregulated genes were mainly related to cell metabolism and transcription. In ouabain-sensitive hypertensive rats, the aortic endothelium was damaged and Kv4.2 (coded by KCND2) was over-expressed. CONCLUSION: The physiological role of ouabain in HUVEC might involve the control of growth and metabolism. Ouabain at pathological concentrations might affect the structure and function of the vascular endothelium by modification of expression of the KCND2 gene, and participate vascular remodeling in hypertension.

[An epidemiological study on essential hypertension in northern and western areas of China].

OBJECTIVE: To understand the epidemiological characteristics of essential hypertension in the northern and western areas of China. METHODS: A community-based sampling survey. RESULTS: Rates of awareness, treatment and control were 78.6%, 59.7% and 5.9%, respectively. About half of the diagnosed and treated patients took antihypertensive medicine irregularly before the survey was carried out. CONCLUSION: It is necessary to carry out education, prevention and control on hypertension and to establish a series of standards for the management and treatment on cases of hypertension.