Sodium-lithium countertransport activity and its sensitivity to inhibitors with erythrocyte ageing in man

Sodium-lithium countertransport is believed to depend on a specific protein and since such proteins usually decline with erythrocyte age it would be expected to be reduced in older cells. In fact, sodium-lithium countertransport increased with ageing, whereas the rate constant of the sodium pump decreased. The increase in sodium-lithium countertransport with erythrocyte ageing was due to a phloretin insensitive component that was not present in young erythrocytes. Raised sodium-lithium countertransport in patients with essential hypertension was due mainly to an increased phloretin sensitive component but the phloretin insensitive component was also higher in middle aged erythrocytes. Amiloride had no effect upon sodium-lithium countertransport or unidirectional sodium influx in cells of any age. This suggests that sodium-lithium countertransport is not a mode of action of the sodium-proton exchanger in the erythrocyte.     

Platelet cytosolic free calcium concentration, total plasma calcium concentration and blood pressure in human twins: a genetic analysis.

1. We used path analysis and maximum-likelihood model fitting to evaluate the relative contributions of genetic and environmental factors to the relationships observed between level of blood pressure and both total plasma calcium concentration and platelet cytosolic free calcium concentration in 109 twin pairs. 2. Total plasma calcium concentration was positively associated with systolic (r = 0.26, P less than 0.001) but not diastolic blood pressure, a relationship which remained significant after adjustment for albumin, age and body mass index. A relationship between platelet cytosolic free calcium concentration and both systolic and diastolic blood pressure (r = 0.17 and r = 0.13, respectively, P less than or equal to 0.05) was no longer significant after adjustment for age and body mass index. 3. Additive genetic influences, unique environmental effects and age contributed to 60%, 30% and 10% of the variance in systolic blood pressure, respectively. Additive genetic effects explained 78% of the variance in plasma total calcium concentration and at least 48% of the variance in platelet cytosolic free calcium concentration in females and 37% in males. 4. Bivariate factor models provided evidence of genetic, but not environmental, co-variation of total plasma calcium concentration and systolic blood pressure, suggesting that a common genetic factor (or factors) contributes to their univariate relationship. In contrast, there was evidence of environmental, but not genetic, covariation of platelet cytosolic free calcium concentration and systolic blood pressure, suggesting that some of the individual experiences specific to each twin may be causing these two traits to vary together. 5. The possible confounding effects of adiposity and environmental factors should be considered in future studies investigating the role of intracellular calcium levels in the pathogenesis of hypertension.     

Hormone replacement therapy, insulin sensitivity, and abdominal obesity in postmenopausal women.

OBJECTIVE: The purpose of this study was to determine whether insulin sensitivity differs between postmenopausal women taking estradiol, women on estrogen plus progesterone hormone replacement therapy (HRT), and women not on HRT and whether differences are explained by the differences in total and/or abdominal adiposity and fat deposition in the muscle. RESEARCH DESIGN AND METHODS: We studied 28 obese, sedentary postmenopausal Caucasian women. Women taking oral estrogen (n = 6) were matched for age (57 +/- 3 vs. 58 +/- 2 years), weight (87.9 +/- 6.0 vs. 83.0 +/- 3.9 kg), and BMI (33.9 +/- 1.7 vs. 33.9 +/- 1.9 kg/m(2)) with women not on HRT (n = 6). Eight women taking oral estrogen plus progesterone were matched with eight different women not on HRT for age (59 +/- 2 vs. 60 +/- 2 years), weight (82.8 +/- 3.7 vs. 83.7 +/- 4.1 kg), and BMI (30.7 +/- 1.0 vs. 29.9 +/- 1.3 kg/m(2)). RESULTS: VO(2max) (maximal aerobic capacity), percentage of fat, total body fat mass, and fat-free mass (FFM) were similar between groups. Visceral fat, subcutaneous abdominal fat, sagittal diameter, and mid-thigh low-density lean tissue (intramuscular fat) did not differ by hormone status. Basal carbohydrate and fat utilization was not different among groups. Fasting plasma glucose and insulin did not differ by hormone use. Glucose utilization (M) was measured during the last 30 min of a 3-h hyperinsulinemic-euglycemic clamp (40 mU. m(2). min(-1)). Postmenopausal women taking oral estrogen had a 31% lower M than women not on HRT (42.7 +/- 4.0 vs. 61.7 +/- 4.7 micromol. kg(FFM). min(-1), P < 0.05). M was 26% lower in women taking estrogen plus progesterone (44.0 +/- 3.5 vs. 59.7 +/- 6.2 micromol. kg(FFM). min(-1), P < 0.05) than women not on HRT. M/I, the amount of glucose metabolized per unit of plasma insulin (I), an index of insulin sensitivity, was 36% lower in women taking estrogen compared with matched women not on HRT (P < 0.05) and 28% lower in women taking estrogen plus progesterone compared with matched women not on HRT (P < 0.05). CONCLUSIONS: Postmenopausal women taking oral estrogen or those taking a combination of estrogen and HRT are more insulin-resistant than women not on HRT, even when women are of comparable total and abdominal adiposity.     

Possible role of cytosolic free calcium concentrations in mediating insulin resistance of obesity and hyperinsulinemia.

Insulin- and glyburide-stimulated changes in cytosolic free calcium concentrations [( Ca2+]i) were studied in gluteal adipocytes obtained from six obese women (139 +/- 3% ideal body wt) and six healthy, normal weight age- and sex-matched controls. Biopsies were performed after an overnight fast and twice (at 3 and 6 h) during an insulin infusion (40 mU/m2 per min) (euglycemic clamp). In adipocytes obtained from normal subjects before insulin infusion, insulin (10 ng/ml) increased [Ca2+]i from 146 +/- 26 nM to 391 +/- 66 nM. Similar increases were evoked by 2 microM glyburide (329 +/- 41 nM). After 3 h of insulin infusion, basal [Ca2+]i rose to 234 +/- 21 nM, but the responses to insulin and glyburide were completely abolished. In vitro insulin-stimulated 2-deoxyglucose uptake was reduced by insulin and glucose infusion (25% stimulation before infusion, 5.4% at 3 h, and 0.85% at 6 h of infusion). In obese patients, basal adipocyte [Ca2+]i was increased (203 +/- 14 nM, P less than 0.05 vs. normals). The [Ca2+]i response demonstrated resistance to insulin (230 +/- 23 nM) and glyburide (249 +/- 19 nM) stimulation. Continuous insulin infusion increased basal [Ca2+]i (244 +/- 24 nM) and there was no response to either insulin or glyburide at 3 and 6 h of study. Rat adipocytes were preincubated with 1-10 mM glucose and 10 ng/ml insulin for 24 h. Measurements of 2-deoxyglucose uptake demonstrated insulin resistance in these cells. Under these experimental conditions, increased levels of [Ca2+]i that were no longer responsive to insulin were demonstrated. Verapamil in the preincubation medium prevented the development of insulin resistance.     

Effects of parathyroid hormone on cytosolic free calcium concentration in individual rabbit connecting tubules.

PTH stimulates active Ca reabsorption in isolated perfused rabbit kidney connecting tubules (CNTs). The existence of PTH-sensitive adenylate cyclase and the reproduction of increased epithelial Ca transport by dibutyryl-cAMP suggest that cAMP is the mediator. Accordingly, we studied the effects of PTH and 8-bromoadenosine 3',5'-cAMP (8-Br-cAMP) on cytosolic free calcium concentration [( Ca2+]i) in individual rabbit CNTs. [Ca2+]i was estimated by continuous epifluorescence microscopy of single fura-2-loaded tubules during dual wave-length excitation. In nonperfused controls at 37 degrees C, [Ca2+]i decreased with time. In contrast to vehicle controls, synthetic bovine (1-34) PTH (0.1 nM) increased [Ca2+]i within 4 min, produced a maximal effect in 7.2 min, and sustained its effect for at least 2 min after washout. 8-Br-cAMP (1 mM) mimicked the effect of PTH, but with an earlier onset of action. To test the hypothesis that lumen Ca is the predominant source of the rise in [Ca2+]i, we studied singly perfused CNTs. In the absence of bath and lumen Ca, PTH elicited no rise in [Ca2+]i, implying that intracellular Ca stores are not the major source. In contrast, there was a rise when Ca was replenished in both media. In the continuous presence of bath Ca, lumen Ca was estimated to contribute 65% of the total rise in [Ca2+]i in response to PTH when it was first deleted and then replenished. However, when the sequence of lumen Ca manipulation was reversed, the contributions by lumen and bath Ca were found to be essentially equal. We conclude (a) at a physiologic concentration, PTH increases [Ca2+]i in rabbit CNTs, (b) 8-Br-cAMP mimics this action, implicating cAMP as a second messenger, and (c) the PTH-stimulated rise in [Ca2+]i depends importantly on both bath and tubular luminal fluid Ca.     

Platelet cytosolic free calcium concentration and parathyroid hormone: changing relationships with haemodialysis in end-stage renal disease.

1. Twelve patients receiving haemodialysis for end-stage renal failure were studied at a single dialysis session. Platelet cytosolic calcium concentration, plasma ionized calcium concentration and serum parathyroid hormone concentration were measured before dialysis, mid-dialysis and 30 min after dialysis. 2. Plasma ionized calcium concentration increased towards dialysate calcium concentrations, falling insignificantly after cessation of dialysis. Serum parathyroid hormone concentration fell by 39% during dialysis, with incomplete recovery afterwards. There was no overall change in platelet cytosolic calcium concentration. 3. Patients were divided into two subgroups: low parathyroid hormone (serum parathyroid hormone concentration less than 10 pmol/l) and high parathyroid hormone (serum parathyroid hormone concentration greater than 10 pmol/l). Before dialysis, values of platelet cytosolic calcium concentration or plasma ionized calcium concentration were not statistically different between the subgroups, but the platelet cytosolic calcium concentration was higher in the high-parathyroid hormone subgroup during and after dialysis. 4. Before haemodialysis there was a linear correlation between plasma ionized calcium concentration and platelet cytosolic calcium concentration, which disappeared during dialysis. In contrast, there was no relationship between serum parathyroid hormone concentration and platelet cytosolic calcium concentration before dialysis, but after dialysis a hyperbolic relationship was evident. 5. These results suggest that uraemic toxins may interfere with cytosolic calcium homoeostasis, allowing passive diffusion of extracellular calcium to influence the resting concentration, and that this effect is reversible by haemodialysis.     

Effect of insulin sensitivity on SHBG levels in premenopausal versus postmenopausal obese women

This study was performed to evaluate the impact of insulin sensitivity on sex hormone-binding globulin (SHBG) and sex steroids in premenopausal and postmenopausal euthyroid obese women. A total of 227 women were eligible for this study. All were euthyroid, obese, and overweight; ages ranged from 25 to 69 years. Women were divided into premenopausal (n=151) and postmenopausal (n=76) groups. SHBG, sex steroids, thyrotropin, fasting and postprandial glucose, lipid profile, uric acid, serum insulin, and blood pressure were measured. No significant difference was found in mean SHBG levels between premenopausal and postmenopausal women. The investigators observed that during transition from premenopause to postmenopause, SHBG levels increased in insulin-sensitive women in the postmenopausal group; however, SHBG levels decreased in insulinresistant women. It was concluded that SHBG blood concentration factors are likely to change during transition from premenopause to postmenopause. The positive effect of estradiol on SHBG levels is probably stronger in premenopausal women than in postmenopausal women. It has been noted that after menopause, the impact of insulin resistance on SHBG level seems more important than the effect of estradiol.     

慢性肺原性心脏病急性加重期血浆内皮素-1与血小板功能关系的探讨

目的：探讨血浆内皮素１（ＥＴ１）、血小板聚集及血小板内游离Ｃａ２＋在慢性肺原性心脏病（肺心病）急性加重期的意义及其相互关系。方法：用放射免疫分析法测定两组（４２例慢性肺心病患者急性加重期和２５例健康者）血浆ＥＴ１含量，用比浊法测定两组血小板聚集率和用Ｆｕｒａ２／ＡＭ荧光技术测定血小板内游离Ｃａ２＋含量。结果：慢性肺心病急性加重期ＥＴ１水平明显升高（Ｐ＜０．０１），血小板聚集率增高（Ｐ＜０．０１），血小板内游离Ｃａ２＋含量显著增加（Ｐ＜０．０１）。另外还观察到ＡＤＰ诱导的血小板聚集率与血小板内游离Ｃａ２＋含量之间呈正相关（ｒ＝０．７３８，Ｐ＜０．０１），而血浆ＥＴ１水平与血小板聚集率和血小板内游离Ｃａ２＋含量之间无明显相关性。结论：血浆ＥＴ１在慢性肺心病急性加重期的发病中可能起一定作用。此期血小板的功能处于活跃状态，易于聚集，形成血栓，加重病情；而血浆ＥＴ１对血小板功能可能无影响。     

血清单核细胞趋化蛋白1浓度与葡萄糖钳夹试验中胰岛素敏感性的关系

目的评价单核细胞趋化蛋白1(MCP-1)与正常糖耐量者、2型糖尿病患者葡萄糖钳夹试验中胰岛素敏感性的关系。方法分别对15例正常糖耐量者和20例2型糖尿病患者进行高胰岛素-正葡萄糖钳夹试验,以钳夹稳态期胰岛素介导的葡萄糖利用率(Rd)来判定周围组织胰岛素敏感性。同时用酶联免疫吸附测定(ELISA)法测定血清MCP-1水平,并测定其他临床指标,分析各指标之间的相关性及与胰岛素敏感性的关系。结果与正常糖耐量者相比,2型糖尿病患者外周血MCP-1水平明显升高(P<0.01),Rd值明显降低(P<0.01),其中MCP-1(65.64±17.67)ng/Lvs(144.39±61.63)ng/L,Rd(10.05±2.24)mg·kg-1.min-1vs(6.33±2.41)mg·kg-1.min-1,两者呈负相关(P<0.001)。Rd值、MCP-1均与体质量指数、腰围呈中度相关。偏相关分析和多元逐步回归分析显示,MCP-1是胰岛素敏感性的独立影响因素。结论外周血MCP-1与胰岛素抵抗、2型糖尿病关系密切。既独立于体质量、腰围、血脂等因素影响胰岛素抵抗的发生,又与之紧密相关,促进胰岛素抵抗的进展。     

Heart rate in relation to insulin sensitivity and insulin secretion in nondiabetic subjects

OBJECTIVE: Elevated heart rate has been predictive of cardiovascular disease and has been proposed as a global index of the autonomic nervous system influence on the heart. Hyperinsulinism has been shown to trigger sympathetic activity experimentally; however, the clinical and epidemiological data on the association of heart rate with hyperinsulinism and insulin resistance are conflicting. RESEARCH DESIGN AND METHODS: Insulin sensitivity (S(I)) and the acute insulin response (AIR) to glucose were assessed by a frequently sampled intravenous glucose tolerance test and related to resting heart rate in the tri-ethnic nondiabetic population (n = 1,000) of the Insulin Resistance Atherosclerosis Study. RESULTS: Heart rate was related to fasting insulin (r = 0.20), intact proinsulin (r = 0.15), split proinsulin (r = 0.17), and AIR (r = 0.18), and an inverse relation was found between heart rate and S(I) (r = -0.19) (all P values <0.0001, adjusted for age, sex, ethnicity, glucose tolerance status, and smoking). In a multiple linear regression analysis (adjusting for age, sex, ethnicity, clinical center, glucose tolerance status, and smoking), heart rate was significantly and independently associated with AIR, proinsulin, and S(I). CONCLUSIONS: Proinsulin, acute insulin secretion, and S(I) are associated with heart rate in nondiabetic subjects.     

Platelet cytosolic free calcium in essential hypertension: responses to vasopressin

1. Resting and stimulated free calcium concentrations have been measured in platelets loaded with the fluorescent probe quin2 from 30 patients with essential hypertension and from 30 age-matched controls. 2. Cytosolic free calcium concentrations were 94.6 +/- 2.7 (mean +/- SEM) in the hypertensive group and 91.7 +/- 2.8 nmol/l in the normotensive group, the difference was not significant. 3. Arginine vasopressin caused a transient increase in platelet free calcium concentration in all subjects. In the presence of extracellular calcium the increase was significantly higher in the control subjects than in the hypertensive patients (P = 0.005). In the absence of extracellular calcium, arginine vasopressin caused much smaller increases, and there was then no difference between the responses of the two groups. 4. Platelet free calcium concentrations were measured again in 13 patients after 8 weeks treatment with either verapamil (n = 6) or atenolol (n = 7). The reductions in systolic pressure after drug treatment were correlated with the changes in cytosolic free calcium concentrations (r = 0.75, P less than 0.01).     

Dynamic association between artery shear flow condition and platelet cytosolic free Ca2+ concentration in human hypertension

1. Blood cells and vascular endothelial cells are subjected to a wide range of haemodynamically generated shear stress forces. In vitro, membrane stretching or shear stress have been observed to activate ion channels and cell metabolism and to facilitate erythrocyte and platelet aggregation. 2. The present study was designed to evaluate the participation of shear stresses in the control of apparent platelet cytosolic free Ca2+ concentration in hypertensive patients. 3. Shear conditions and platelet cytosolic free Ca2+ concentration in vitro were studied after a dynamic perturbation induced by 3 months of double-blind treatment with one of two beta-antagonists, carteolol and atenolol. Brachial artery wall shear rate and stress were estimated by means of a pulsed Doppler velocimeter, and blood viscosity was measured by a co-axial viscometer at a shear rate of 96 s-1. Platelet cytosolic free Ca2+ concentration was simultaneously measured by using the Quin-2 fluorescent chelator. The direct effect of atenolol and carteolol on platelet cytosolic free Ca2+ concentration in vitro was also measured after addition of the beta-blockers to platelet-rich plasma. 4. Atenolol and carteolol decreased blood pressure similarly but their effects on shear rate (P less than 0.02), shear stress (P less than 0.01) and platelet cytosolic free Ca2+ concentration (P less than 0.05) differed after 3 months of therapy. In contrast, neither of the drugs significantly altered platelet cytosolic free Ca2+ concentration, in vitro per se. 5. In the overall population, strong positive correlations existed not only between changes in platelet cytosolic free Ca2+ concentration and those in shear rate (r = 0.81, P less than 0.001) and shear stress (r = 0.83, P less than 0.001), but also between their absolute values, suggesting a possible haemodynamic shear-dependent modulation of transmembrane Ca2+ transport.     

Reductions in plasma cytokine levels with weight loss improve insulin sensitivity in overweight and obese postmenopausal women

OBJECTIVE: The purpose of this study was to determine whether improvements in insulin sensitivity with weight loss are mediated by changes in inflammation in obese, postmenopausal women. RESEARCH DESIGN AND METHODS: We studied 58 sedentary, overweight, and obese (BMI 33 +/- 1 kg/m(2), means +/- SEM) postmenopausal (58 +/- 1 year) women at baseline and 37 women who completed 6 months of weight loss induced by diet and exercise. The women underwent 3-h hyperinsulinemic-euglycemic clamps (40 mU x m(-2) x min(-1)) to determine glucose utilization (M). Insulin sensitivity was determined as M/I, the amount of glucose metabolized per unit of plasma insulin (I). Visceral adipose tissue (VAT) and plasma concentrations of C-reactive protein (CRP), cytokines interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha, as well as their soluble receptors, were measured. RESULTS: At baseline, CRP concentration was a predictor of both glucose utilization and insulin sensitivity, independent of adiposity, race, and aerobic fitness (M: partial r = -0.30, P = 0.03, and M/I: partial r = -0.32, P = 0.02). Weight loss resulted in significant reductions in body weight, fat mass, VAT, and fasting glucose and insulin levels (P < 0.05). Both glucose utilization and insulin sensitivity increased by 16% (P < 0.05). CRP, IL-6, and soluble TNF receptor (sTNFR)-1 concentrations decreased (P < 0.05), but concentrations of TNF-alpha, sTNFR-2, and soluble IL-6 receptor (IL-6sR) did not change. In stepwise regression models to predict changes in glucose homeostasis, changes in VAT and sTNF-R1 independently predicted changes in glucose utilization (r = -0.49 and cumulative r = -0.64, P < 0.01), while changes in VAT and IL-6 were both independent predictors of changes in insulin sensitivity (r = -0.57 and cumulative r = -0.68, P < 0.01). CONCLUSIONS: Improvements in glucose metabolism with weight loss programs are independently associated with decreases in cytokine concentrations, suggesting that a reduction in inflammation is a potential mechanism that mediates improvements in insulin sensitivity.     

A cross-sectional study of basal platelet intracellular free calcium concentration in normotensive and hypertensive primigravid pregnancies

1. The intracellular free calcium concentration ([Ca2+]i) in washed human platelets was measured using the fluorescent indicator, fura-2, in a cross-sectional study of 36 normotensive, primigravid volunteers, 12 in each trimester of pregnancy and a further 12 at 6 weeks post partum. The results were compared with those obtained from 30 normal female volunteers not using oral contraception. 2. The mean basal [Ca2+]i in the platelets of the pregnant women in the first two trimesters (115.6 +/- 6.7 and 120.1 +/- 5.7 nmol/l, respectively) was not shown to differ significantly from that of normal non-pregnant volunteers (112.3 +/- 2.9 nmol/l). However, during the third trimester a significant increase in [Ca2+]i was noted (134.0 +/- 4.9 nmol/l; P less than 0.05), with a return to normal values in the post-partum period (108.2 +/- 6.1 nmol/l). 3. [Ca2+]i was also measured in the platelets of a group of 12 primigravid pregnant women in the third trimester whose pregnancies were complicated by gestational hypertension (pregnancy-induced hypertension and pre-eclampsia). A significant rise in basal [Ca2+]i was noted in the platelets of primigravidae whose pregnancies were complicated by pre-eclampsia (163.6 +/- 8.8 nmol/l) as compared with normotensive, third-trimester primigravidae (P less than 0.02). However, no correlation could be demonstrated between [Ca2+]i and systemic blood pressure.     

氯通道阻断剂对血小板胞浆游离钙和血小板聚集的影响

目的　探讨氯通道在血小板胞浆游离钙和血小板聚集功能调节中的作用。方法　新鲜分离人血小板,以凝血酶为诱导剂,观察氯通道阻断剂DIDS、NFA和钙通道阻断剂SK&F96365、Nife dipine对血小板胞浆游离钙和血小板聚集的单独作用和相互作用。结果　氯通道阻断剂DIDS、NFA可以浓度依赖性地抑制凝血酶 ( 1U/ml)诱导的血小板聚集,对静息血小板胞浆游离钙无明显影响;DIDS、SK&F96365、Nifedipine可以明显降低凝血酶诱导的血小板聚集、钙释放和钙内流,与对照组比较,P<0. 05;DIDS与SK&F96365联合,对凝血酶诱导的血小板聚集、钙释放和钙内流的抑制比各自单独抑制作用明显增高(P<0. 05),两者的作用相互增强;DIDS与Nifedipine联合,对凝血酶诱导的血小板钙释放的抑制比各自单独抑制作用明显增高 (P<0. 05 ),两者可相互增强;NFA与SK&F96365联合,对凝血酶诱导的血小板钙释放的抑制比各自的单独作用明显降低 (P<0. 05 ),两者可相互减弱;NFA与Nifedipine联合,对凝血酶诱导的血小板聚集、钙释放和钙内流的抑制比各自的单独作用明显降低(P<0. 05),两者可相互减弱。结论　氯通道阻断剂DIDS、NFA对人静息血小板胞浆钙浓度无影响;DIDS可抑制凝血酶诱导的血小板聚集、钙释放和钙内流,NFA仅抑制凝血酶诱导的钙释放;氯通道阻断剂和     

LDL particle size in relation to insulin, proinsulin, and insulin sensitivity. The Insulin Resistance Atherosclerosis Study.

OBJECTIVE: LDL particles are heterogeneous in terms of size and density; small dense LDL particles are considered more atherogenic than larger LDL particles. The aim of this study was to investigate the interrelationships among LDL size, insulin, proinsulin (intact and split), and insulin sensitivity in a tri-ethnic population with varying degrees of glucose tolerance (n = 1,549) in the Insulin Resistance Atherosclerosis Study. RESEARCH DESIGN AND METHODS: Insulin sensitivity was assessed by a frequently sampled intravenous glucose tolerance test with minimal model analysis. Proinsulin levels were measured using highly sensitive assays without detectable cross-reactivity with insulin, and LDL size was determined by gradient-gel electrophoresis. RESULTS: In univariate analyses, LDL size was related to various features of the insulin resistance syndrome, including fasting insulin (r = -0.18), intact proinsulin (r = -0.24), split proinsulin (r = -0.24), the proinsulin-to-insulin ratio (r = -0.14), and insulin sensitivity (r = 0.21; all P < 0.0001). In a multivariate regression model (adjusted for age, BMI, ethnicity, and clinic), triglyceride levels (P = 0.0001), HDL cholesterol (P = 0.0001), sex (P = 0.002), and proinsulin (P = 0.01) were significantly related to LDL size. In the same model stratified by sex, LDL size was significantly inversely related to proinsulin in men (P = 0.005 and P = 0.04 after further adjustment for the glucose tolerance status), but not in women (P > 0.15). CONCLUSIONS: We found an inverse relation of proinsulin to LDL particle size in a large tri-ethnic population with varying degrees of glucose tolerance. This relation was independent of age, BMI, and triglyceride and HDL cholesterol concentrations, and was more pronounced in men than in women.     

Evidence for role of cytosolic free calcium in hypoxia-induced proximal tubule injury.

The role of cytosolic free Ca2+ ([Ca2+]i) in hypoxic injury was investigated in rat proximal tubules. [Ca2+]i was measured using fura-2 and cell injury was estimated with propidium iodide (PI) in individual tubules using video imaging fluorescence microscopy. [Ca2+]i increased from approximately 170 to approximately 390 nM during 5 min of hypoxia. This increase preceded detectable cell injury as assessed by PI and was reversible with reoxygenation. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA; 100 microM) reduced [Ca2+]i under basal conditions (approximately 80 nM) and during hypoxia (approximately 120 nM) and significantly attenuated hypoxic injury. When [Ca2+]i and hypoxic cell injury were studied concurrently in the same individual tubules, the 10 min [Ca2+]i rise correlated significantly with subsequent cell damage observed at 20 min. 2 mM glycine did not block the rise in [Ca2+]i, yet protected the tubules from hypoxic injury. These results indicate that in rat proximal tubules, hypoxia induces an increase of [Ca2+]i which occurs before cell damage. The protective effect of BAPTA supports a role for [Ca2+]i in the initiation of hypoxic proximal tubule injury. The glycine results, however, implicate calcium-independent mechanisms of injury and/or blockade of calcium-mediated processes of injury such as activation of phospholipases or proteases.     

Effects of growth factors on cytosolic free calcium concentration and DNA synthesis in cultured rat aortic smooth muscle cells

Proliferation of vascular smooth muscle cells (SMCs) has been considered to be an important process in the development of atherosclerosis. This study was conducted to investigate the role of cytosolic free calcium in DNA synthesis of SMCs stimulated by growth factors. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and somatomedin-C (Sm-C) increased [3H]thymidine incorporation, an index of DNA synthesis, and cell number of rat aortic SMCs after 36 hr of incubation. Cytosolic free calcium concentration [( Ca++]i) in quiescent SMCs, measured by using quin 2, was 178 +/- 18 nM (n = 15). Both PDGF and EGF provoked a rapid and transient rise in [Ca++]i, while Sm-C did not alter [Ca++]i. Nifedipine (3 X 10(-6) M) suppressed the rise in [Ca++]i provoked by PDGF and EGF. On the other hand, nifedipine suppressed the enhancement of DNA synthesis provoked by EGF, but did not suppress those by PDGF and Sm-C. These results suggest that the transient rise in [Ca++]i plays an important role in the proliferation of SMCs stimulated by EGF, while the rise in [Ca++]i is not involved in the mechanism of proliferation of SMCs provoked by Sm-C. The role of cytosolic free calcium in the proliferation of SMCs provoked by Sm-C. The role of cytosolic free calcium in the proliferation of SMCs provoked by PDGF was not definitive.