Endothelin: a potent stimulus of atrial natriuretic peptide secretion by superfused rat atria and its dependency on calcium

Endothelin, a hormone secreted by endothelial cells, has potent vasoconstrictive properties. Due to its potential paracrine nature, we examined the effect of endothelin-I on atrial natriuretic peptide (ANP) secretion in vitro. Isolated superfused rat left atria, paced at 2 Hz, were used for study. Endothelin (1-100 nM) increased ANP secretion in a dose-dependent manner from 1.6- to 6.7-fold above baseline. Spontaneously beating right atria increased ANP secretion by 2.3-fold in response to 10 nM endothelin without a change in beat frequency. However, the right atrial ANP secretory response was less than the 3.8-fold increase seen by left atria, and the time to peak response was slower. The calcium dependency of endothelin-stimulated ANP secretion was examined using paced left atria. The dependency of endothelin-stimulated secretion on calcium influx was examined by lowering the superfusate calcium from 1.8 to 0.2 mM. The ANP secretory response to 10 nM endothelin was reduced by 65% with 0.2 mM calcium. Influx of calcium through voltage-dependent calcium channels was examined by superfusion with 50 microM nitrendipine. Nitrendipine decreased endothelin-stimulated ANP secretion by 51% without affecting endothelin binding. The role of intracellular calcium release from the sarcoplasmic reticulum (SR) was examined by superfusion with 1 microM ryanodine, an inhibitor of SR calcium release. Ryanodine had no effect on endothelin-stimulated ANP secretion. We conclude: 1) Endothelin is a potent stimulus of ANP secretion in vitro. 2) The relative secretory response of right atria to endothelin expressed as a function of basal secretion is less and the time to peak secretion delayed relative to left atria. 3) Enhanced calcium influx, primarily through voltage-dependent calcium channels, plays a significant role in endothelin-stimulated secretion. 4) Release of intracellular calcium from the SR does not participate in the secretory response. 5) Part of the stimulatory signal appears to be independent of calcium influx or intracellular calcium release. Thus, endothelin may be an important secretagogue or modulator of ANP secretion in vivo; however, its physiological role in regulating ANP secretion in vivo remains to be determined.     

Flexible tantalum stents implanted in aortas and iliac arteries: effects in normal canines

Vascular endoprostheses made of knitted tantalum wire and expanded over angioplasty balloons were placed into aortas or iliac arteries of 14 normal dogs. Twelve stents were placed into the infrarenal abdominal aorta and two stents in the left common iliac arteries by the left carotid artery approach. To firmly expand the stent against the vascular wall, nominal stent sizes 0.5-1.0 mm larger than the measured arterial diameter were required. Arteriography performed at specified follow-up intervals showed no evidence of thrombi or emboli; all side branches (lumbar arteries) covered by the stents remained patent. Vascular diameter decreased minimally at 8 and 26 weeks, associated with histopathologic evidence of neointimal buildup. This buildup was highest at 8 weeks (mean, 313 microns) and was slightly less at 26 weeks (mean, 223 microns). Almost complete coverage by endothelium was seen as early as 3 weeks. It is concluded that the flexible tantalum wire stents are well tolerated by the arterial wall and become quickly endothelialized. No excessive neointimal buildup was observed during the 6-month study.     

Endothelin binding to cultured calf adrenal zona glomerulosa cells and stimulation of aldosterone secretion.

Endothelins are a group of potent vasoconstrictors whose structure was deduced from genomic DNA. ET-1 was first isolated from culture supernatants from porcine endothelial cells and ET-3 was identified from a rat DNA library. We report on the binding of 125I-ET-1 to zona glomerulosa cells in culture and on its ability to stimulate aldosterone secretion. Cultured calf adrenal zona glomerulosa cells have saturable, high affinity [Kd = 1.00 +/- 0.17 X 10(-10) M (SEM)] receptors which bind ET-1 in a temperature and time dependent manner. Binding was specific and angiotensin II, vasopressin, ANP, BNP, apamin, calcium channel agonists or antagonists did not interact with the receptor. ET-3 displaced 125I-ET-1 from the receptor with a relative potency of 0.39 +/- 0.1% (SEM) that of ET-1. ET-1 incubated with cultured glomerulosa cells stimulated aldosterone secretion in a dose dependent manner but it was less potent than angiotensin II. ET-3 had less than 1% the relative potency of ET-1 stimulating aldosterone secretion. This data suggest that ET-1 is an independent stimulator of aldosterone secretion and we are speculating that it might be important in those situations, like in malignant hypertension, where endothelial damage might result in increased ET-1 production.     

血管闭合器应用的现况与展望

股动脉径路是冠状动脉及外周血管介入诊疗的主要途径。然而,股动脉径路穿刺的围术期血管并发症仍是每个介入医生时常面对的问题。研究显示,与压迫止血比较,血管闭合器可减少围术期血管并发症,缩短患者制动时间,增加患者舒适度。现就相关内容及最新进展进行简要综述。     

Maternal hypertension and progeny blood pressure: role of aldosterone and 11beta-HSD.

Epidemiological and experimental evidence suggests that gestational events modulate the level of blood pressure that will be "normal" for the individual as an adult. Glucocorticoid excess during gestation is associated with low birth weight, a large placenta, and adult hypertension in humans and animals. It has been proposed that the deficiency in placental 11beta-hydroxysteroid dehydrogenase activity in humans produces a gestational hormonal milieu, notwithstanding normal circulating levels of glucocorticoids, that predisposes the adult progeny to hypertension. Animal studies indicate that maternal hypertension, excess glucocorticoids, and hydroxysteroid dehydrogenase inhibition program adult blood pressure. Blood pressures of Sprague-Dawley rat dams were manipulated during gestation with continuous intracerebroventricular infusions of vehicle, aldosterone, 11alpha-hydroxyprogesterone, or carbenoxolone at doses known to produce hypertension with no renal effects or with subcutaneous infusions of larger, equally hypertensinogenic doses that produce systemic effects. Blood pressures of all treated dams were significantly greater (P<0.01) during gestation than those of the vehicle ICV control rats but not significantly different from each other. The blood pressures of both male and female progeny (n>/=6 per group, comprising representatives from at least 4 litters) were measured after 6 weeks of age. No significant difference was found in the blood pressure of the pups regardless of the maternal gestational blood pressure or treatment with an enzyme inhibitor, even after high-salt diet challenge.     

Echicetin: a snake venom protein that inhibits binding of von Willebrand factor and alboaggregins to platelet glycoprotein Ib

Echicetin, a new protein isolated from Echis carinatus venom by reverse phase and ion exchange chromatography specifically inhibited agglutination of fixed platelets induced by several platelet glycoprotein Ib (GPIb) agonists, such as bovine von Willebrand factor (vWF), alboaggregins, and human vWF in the presence of botrocetin. Unlike alboaggregins, echicetin bound to GPIb but did not induce agglutination of washed or fixed platelets. In contrast to disintegrins, it did not block adenosine 5'-diphosphate (ADP)-induced platelet aggregation in the presence of fibrinogen. The apparent molecular weight of echicetin measured on sodium dodecyl sulfate (SDS) gel electrophoresis was 26 Kd under nonreducing conditions. On reduction, echicetin showed 16 and 14-Kd subunits suggesting that the molecule is a dimer. Reduced echicetin retained its binding activity and its inhibitory effect on the agglutination of fixed platelets induced by bovine vWF. 125I-echicetin bound to fixed platelets with high affinity (kd = 30 +/- 1.8 nmol/L) at 45,000 +/- 2,400 binding sites per platelet. The binding was selectively inhibited by a monoclonal antibody to the 45-Kd N-terminal domain of platelet GPIb, but not by monoclonal antibodies to other regions on GPIb. Binding of 125I-bovine vWF to fixed platelets was strongly inhibited by echicetin. In contrast, bovine vWF showed a much weaker inhibitory activity on binding of 125I-echicetin to platelets. The half life of echicetin in blood was approximately 170 minutes with no detectable degradation. Echicetin significantly prolonged the bleeding time of mice, suggesting that it may inhibit vWF binding to GPIb in vivo as well as in vitro.     

Effect of surfaces on fluid-phase prekallikrein activation

The activation of prekallikrein by factor XII fragments (XIIf), during incubation in plastic tubes was previously noted to be increased by high molecular weight (HMW) kininogen as well as other plasma proteins. In this report, we investigated the mechanism responsible for this increase. Although we confirmed that HMW kininogen, bovine serum albumin, fibrinogen, cold insoluble globulin, and mixed phospholipids apparently increased prekallikrein activation, we found that the product of prekallikrein activation (kallikrein) lost substantial activity in less than 0.5 min after exposure to a variety of fresh surfaces. This loss was partially prevented by the presence of various proteins and phospholipids. Similar protection against inactivation of XIIf, the enzyme in this reaction, was also found. In contrast, no loss of the substrate, prekallikrein, was observed during incubation. The loss of kallikrein activity was found to be proportional to the surface area of the incubation vessel as well as the concentration of kallikrein. Further loss of kallikrein activity could also be prevented by pretreating the vessel with kallikrein. We therefore conclude that various substances apparently affect prekallikrein activation in a purified system by preventing the enzyme and product in the reaction mixture from losing activity due to adsorption to a surface.