Hypospadias Prevalence and Trends in International Birth Defect Surveillance Systems, 1980-2010.

BACKGROUND: Hypospadias is a common male birth defect that has shown widespread variation in reported prevalence estimates. Many countries have reported increasing trends over recent decades. OBJECTIVE: To analyze the prevalence and trends of hypospadias for 27 international programs over a 31-yr period. DESIGN, SETTING, AND PARTICIPANTS: The study population included live births, stillbirths, and elective terminations of pregnancy diagnosed with hypospadias during 1980-2010 from 27 surveillance programs around the world. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: We used joinpoint regression to analyze changes over time in international total prevalence of hypospadias across programs, prevalence for each specific program, and prevalence across different degrees of severity of hypospadias. RESULTS AND LIMITATIONS: The international total prevalence of hypospadias for all years was 20.9 (95% confidence interval: 19.2-22.6) per 10000 births. The prevalence for each program ranged from 2.1 to 39.1 per 10000 births. The international total prevalence increased 1.6 times during the study period, by 0.25 cases per 10000 births per year (p<0.05). When analyzed separately, there were increasing trends for first-, second-, and third-degree hypospadias during the early 1990s to mid-2000s. The majority of programs (61.9%) had a significantly increasing trend during many of the years evaluated. Limitations include known differences in data collection methods across programs. CONCLUSIONS: Although there have been changes in clinical practice and registry ascertainment over time in some countries, the consistency in the observed increasing trends across many programs and by degrees of severity suggests that the total prevalence of hypospadias may be increasing in many countries. This observation is contrary to some previous reports that suggested that the total prevalence of hypospadias was no longer increasing in recent decades. PATIENT SUMMARY: We report on the prevalence and trends of hypospadias among 27 birth defect surveillance systems, which indicate that the prevalence of hypospadias continues to increase internationally.

Gastroschisis and associated defects: an international study.

Our objective was to evaluate the frequency and type of malformations associated with gastroschisis in a large pool of international data, to identify malformation patterns, and to evaluate the role of maternal age in non-isolated cases. Case-by-case information from 24 registries, all members of the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR), were evaluated. After the exclusion of other abdominal wall defects cases were classified as: (a) isolated; (b) recognizable syndrome, chromosomal or not; (c) multiple congenital anomalies (MCA). Our results showed that out of 3,322 total cases 469 non-isolated cases were registered (14.1%): 41 chromosomal syndromes, 24 other syndromes, and 404 MCA. Among MCA four groups of anomalies were most frequent: CNS (4.5%), cardio-vascular (2.5%), limb (2.2%), and kidney anomalies (1.9%). No similar patterns emerged except two patterns resembling limb-body wall complex and OEIS. In both of them the gastroschisis could be however misclassified. Chromosomal trisomies and possibly non-syndromic MCA are associated with an older maternal age more than isolated cases. On consideration of our data and the most valid studies published in the literature, the best estimate of the proportion of gastroschisis associated with major unrelated defects is about 10%, with a few cases associated to recognizable syndromes. Recognized syndromes with gastroschisis seem to be so exceptional that the well documented and validated cases are worth being published as interesting case report. An appropriate case definition in etiological studies should include only isolated gastroschisis after an appropriate definition of isolated and non-isolated cases and a thorough case-by-case review.

Protein kinase C activation stimulates calcium transport in adrenal zona glomerulosa cells.

Adrenal zona glomerulosa (ZG) cells produce aldosterone in response to angiotensin II and extracellular potassium through different mechanisms which involve changes in cytosolic free calcium (Cai). Protein kinase C (PKC) activation is part of the angiotensin II signalling cascade but its effects on Cai are unknown. PKC activation with 1 microM phorbol 12-myristate 13-acetate (PMA) and 8 mM Ko significantly increased the rate of calcium influx (P < 0.001). Both the PKC- and the Ko-induced calcium influx occurred via a nifedipine-sensitive pathway. When both were combined, PKC activation and 8 mM Ko were not additive over either agent alone. PKC activation and 8 mM Ko also stimulated calcium efflux (P < 0.01). When combined together PKC activation and 8 mM Ko had additive effects on calcium efflux (P < 0.05). PKC activation did not increase Cai nor the exchangeable calcium pool in contrast to 8 mM Ko which significantly increased both (P < 0.001). Thus, PKC activation in ZG cells induces a pattern of calcium transport characterized by accelerated calcium recycling across the cell membrane without increasing cell calcium content.

Stimulation of membrane serine-threonine phosphatase in erythrocytes by hydrogen peroxide and staurosporine.

Indirect evidence has suggested that K-Cl cotransport in human and sheep erythrocytes is activated physiologically by a serine-threonine phosphatase. It is activated experimentally by H2O2 and by staurosporine, a kinase inhibitor. Activation by H2O2 and staurosporine is inhibited by serine-threonine phosphatase inhibitors, suggesting that the activators stimulate the phosphatase. The present study shows that sheep and human erythrocytes contain membrane-associated as well as cytosolic serine-threonine phosphatases, assayed from the dephosphorylation of 32P-labeled glycogen phosphorylase. In cells from both species, the relatively low sensitivity of the membrane enzyme to okadaic acid suggests it is type 1 protein phosphatase. The cytosolic phosphatase was much more sensitive to okadaic acid. Membrane-associated phosphatase was stimulated by both H2O2 and staurosporine. The results support earlier conclusions that the membrane-associated type 1 phosphatase identified here is regulated by phosphorylation and oxidation. The results are consistent with the phosphatase, or a portion of it, being responsible for activating K-Cl cotransport.

Effects of PKC alpha activation on Ca2+ pump and K(Ca) channel in deoxygenated sickle cells.

We have previously shown that a pretreatment with phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), reduced deoxygenation-induced K+ loss and Ca2+ uptake and prevented cell dehydration in sickle anemia red blood cells (SS cells) (H. Fathallah, E. Coezy, R.-S. De Neef, M.-D. Hardy-Dessources, and F. Giraud. Blood 86: 1999-2007, 1995). The present study explores the detailed mechanism of this PMA-induced inhibition. The main findings are, first, the detection of PKC alpha and PKC zeta in normal red blood cells and the demonstration that both isoforms are expressed at higher levels in SS cells. The alpha-isoform only is translocated to the membrane and activated by PMA and by elevation of cytosolic Ca2+. Second, PMA is demonstrated to activate Ca2+ efflux in deoxygenated SS cells by a direct stimulation of the Ca2+ pump. PMA, moreover, inhibits deoxygenation-induced, charybdotoxin-sensitive K+ efflux in SS cells. This inhibition is partly indirect and explained by the reduced deoxygenation-induced rise in cytosolic Ca2+ resulting from Ca2+ pump stimulation. However, a significant inhibition of the Ca2+-activated K+ channels (K(Ca) channels) by PMA can also be demonstrated when the channels are activated by Ca2+ plus ionophore, under conditions in which the Ca2+ pump is operating near its maximal extrusion rate, but swamped by Ca2+ plus ionophore. The data thus suggest a PKC alpha-mediated phosphorylation both of the Ca2+ pump and of the K(Ca) channel or an auxiliary protein.

Na+/Li+ and Na+/H+ countertransport activity in hypertensive non-insulin-dependent diabetic patients: role of insulin resistance and antihypertensive treatment.

We measured erythrocyte Na+/Li+ and Na+/H+ countertransport (CT) activity (millimoles per liter per cell per hour) in 10 healthy control subjects (age, 38 +/- 4 years; body mass index, 25 +/- 1 kg/m2) and in 25 hypertensive patients with non-insulin-dependent diabetes mellitus ([NIDDM] age, 49 +/- 3 years; body mass index, 29 +/- 1 kg/m2; fasting plasma glucose, 157 +/- 12 mg/dL) 4 weeks after discontinuation of previous antihypertensive treatment. Na+/Li+ CT was significantly increased in hypertensive NIDDM patients compared with controls (0.56 +/- 0.04 v 0.30 +/- 0.03, P < .01), whereas Na+/H+ CT was similar to control levels (21 +/- 1 v 20 +/- 2). A positive correlation was found between Na+/Li+ CT and the severity of insulin resistance (r = .69, P < .01), mean arterial pressure ([MAP] r = .64, P < .01), plasma triglyceride concentration (r = .46, P < .05), and plasma total cholesterol (r = .41, P < .05). An inverse correlation was found between Na+/Li+ CT activity and plasma insulin concentration (r = -.47, P < .05). No relationship was observed between Na+/Li+ CT activity and either creatinine clearance or proteinuria. Stepwise multiple regression analysis for all metabolic variables and blood pressure showed that only the severity of insulin resistance was positively correlated with increased Na+/Li+ CT activity. Na+/H+ and Na+/Li+ CT activity were not altered by 3 hours of euglycemic physiologic hyperinsulinemia (84 +/- 3 microU/mL). Hypertensive NIDDM subjects were treated for 3 months with captopril, nifedipine, or doxazosin. After captopril, a reduction of Na+/H+ CT was observed (22 +/- 4 v 13 +/- 2, P < .05); Na+/Li+ CT decreased after doxazosin (0.56 +/- 0.06 v 0.45 +/- 0.05, P < .05) and nifedipine (0.52 +/- 0.06 v 0.42 +/- 0.05, P < .05). In conclusion, in hypertensive NIDDM subjects, (1) Na+/Li+ CT is increased and is correlated with the level of insulin resistance and the MAP; (2) acute physiologic hyperinsulinemia does not affect Na+/Li+ or Na+/H+ CT activity; and (3) Na+/H+ CT activity is reduced by captopril, and Na+/Li+ CT is decreased by doxazosin and nifedipine.

Red blood cells of a transgenic mouse expressing high levels of human hemoglobin S exhibit deoxy-stimulated cation flux.

Deoxy-stimulated cation fluxes have been implicated in the generation of the dense and irreversibly sickled red blood cells (RBCs) in patients homozygous for hemoglobin S (SS). We now report on the effect of short term deoxygenation on K+ and Na+ transport in RBCs from control mice (C57Bl/6J) and a transgenic (alphaHbetaS[betaMDD]) mouse line that expresses high levels of human alphaH and betaS-chains and has a small percent dense cells but does not exhibit anemia. In transgenic mouse RBCs (n = 5) under oxygenated conditions, K+ efflux was 0.22 +/- 0.01 mmol/L cell x min and Na+ influx was 0.17 +/- 0.02 mmol/L cell x min. Both fluxes were stimulated by 10 min deoxygenation in transgenic but not in control mice. The deoxy-stimulated K+ efflux from transgenic mouse RBCs was about 55% inhibited by 5 nm charybdotoxin (CTX), a blocker of the calcium activated K+-channel. To compare the fluxes between human and mouse RBCs, we measured the area of mouse RBCs and normalized values to area per liter of cells. The deoxy-simulated CTX-sensitive K+ efflux was larger than the CTX-sensitive K+ efflux observed in RBCs from SS patients. These results suggest that in transgenic mice, deoxygenation increases cytosolic Ca2+ to levels which open Ca2+-activated K+ channels. The presence of these channels was confirmed in both control and transgenic mice by clamping intracellular Ca2+ at 10 microM with the ionophore A23187 and measuring Ca2+-activated K+ efflux. Both types of mouse had similar maximal rates of CTX-sensitive, Ca2+-activated K+ efflux that were similar to those in human SS cells. The capacity of the mouse red cell membrane to regulate cytosolic Ca2+ levels was examined by measurements of the maximal rate of calmodulin activated Ca2+-ATPase activity. This activity was 3-fold greater than that observed in human RBCs thus indicating that mouse RBC membranes have more capacity to regulate cytosolic Ca2+ levels. In summary, transgenic mouse RBCs exhibit larger values of deoxy-stimulated K+ efflux and Na+ influx when compared to human SS cells. They have a similar Ca2+-activated K+ channel activity to human SS cells while expressing a very high Ca2+ pump activity. These properties may contribute to the smaller percent of very dense cells and to the lack of adult anemia in this animal model.

K:Cl cotransport in red cells of transgenic mice expressing high levels of human hemoglobin S.

K:Cl cotransport is involved in generating dense red blood cells (RBCs) in homozygotes for HbS (SS). We report on the properties of this transport system in RBCs from control and transgenic mice expressing high levels of human alpha(H) and beta(S) chains. Unlike human SS RBCs, mouse RBCs incubated in isotonic media exhibited a Cl(-)-dependent K+ efflux and therefore have a different set-point for activation. This basal efflux was slightly stimulated by cell swelling to values five times smaller than that in human SS cells; in addition, the delay time for activation was shorter in transgenic than in control mice, but fourfold longer than that of human SS cells. These properties cast doubt on the physiological impact of the mouse K:Cl cotransporter on RBC volume regulation in the mouse and suggest that there are intrinsic differences between the human K:Cl cotransporter and the putative transporter in mice.

Protein kinase C and insulin regulation of red blood cell Na+/H+ exchange.

Insulin activation of red blood cell (RBC) Na+/H+ (NHE) and Na+/Li+ (NLiE) exchanges is mimicked by okadaic acid, thus suggesting that it may change the state of phosphorylation of serine/threonine NHE residues. To investigate the role of the serine/threonine protein kinase C (PKC) in insulin regulation, we evaluated the effect of phorbol 12-myristate 13-acetate (PMA; 1 microM) and insulin on PKC activity, membrane protein phosphorylation, and the activation kinetics of both exchangers. Our studies revealed that PMA decreased cytosolic PKC activity (4.1 +/- 0.6 to 2.3 +/- 0.5 pmol x mg protein(-1) x min(-1), n = 9, P < 0.001), increased membrane PKC activity (42.3 +/- 5 to 132 +/- 12 pmol x mg protein(-1) x min(-1), n = 11, P < 0.001), and enhanced serine phosphorylation of bands 3, 4.1, and 4.9 membrane proteins. PMA markedly reduced the Michaelis constant (Km) for intracellular H+ (415 +/- 48 to 227 +/- 38 nM, n = 11, P < 0.01) but had no effect on the maximal transport rate (Vmax) of NHE and the Km for Na+ of NLiE. NHE activation and PKC activity were affected differently by insulin (100 microU/ml) and PMA. Insulin increased the Vmax of NHE and the Km for Na+ of NLiE but had no effect on the Km for intracellular H+ and membrane PKC activity. These findings lead us to conclude that in the human RBC, NHE is modulated by PKC and insulin through different biochemical mechanisms.

Sodium-lithium countertransport is associated with insulin resistance and urinary albumin excretion in young African-Americans.

Increased activity of the sodium transporter, sodium-lithium countertransport (SLC), is reported in hypertensive white patients with evidence of cardiac and renal injury. The purpose of this study was to determine whether increased SLC activity detects risk for nephropathy or vascular disease in nondiabetic, young adult African-Americans. We examined 85 African-Americans aged 25 to 33 years with measurement of blood pressure, an oral glucose tolerance test to measure insulin response to glucose challenge, and an insulin clamp for insulin sensitivity (M). Fasting plasma lipids were measured, and the Vmax and Km for Na+ were assayed on red blood cells. Urinary albumin excretion (UAE) was measured on timed collections. There was a statistically significant correlation of the Vmax for SLC with M (r = -0.26, P = 0.02) and with UAE (r = 0.25, P = 0.02). The Km for Na+ to activate SLC was also elevated in the subgroup of subjects with elevated Vmax of SLC. There was no significant correlation of SLC with blood pressure in bivariate analysis. Step-wise multiple linear regression analysis of all variables on the Vmax SLC demonstrated that plasma triglyceride, UAE, body mass index, systolic blood pressure, M, and fasting insulin were step-wise selected into the linear regression model (F-ratio = 3.2, df = 77, R = 0.46, P < 0.009). In this young adult African-American population, elevated SLC activity is detected in association with metabolic and lipid alterations typical of insulin resistance. Elevated SLC activity is also associated with higher rates of UAE, suggesting possible evidence of early renal injury.

Elevated lymphocyte cytosolic calcium in a subgroup of essential hypertensive subjects.

Abnormalities of intracellular calcium homeostasis and sodium-proton exchange have been implicated in the pathophysiology of essential hypertension. To further define the nature of cytosolic calcium abnormalities and whether they relate to increased sodium-proton exchange in hypertension, we have studied peripheral lymphocytes from normotensive and hypertensive subjects. Lymphocyte cytosolic calcium was significantly increased (P < .01) in hypertensive compared with normotensive subjects while consuming a high salt diet. Using maximum likelihood analysis, we found that cytosolic calcium levels in our study population were not normally distributed and observed three modes (P < .02). The means of the first mode and the two upper modes were separated (+/-2 SD) at a cytosolic calcium level of 120 nmol/L. We conducted further analysis in the subgroups with cytosolic calcium levels > 120 nmol/L or < 120 nmol/L. The majority of the normotensive subjects (86%) and half of the hypertensive subjects (52%) had levels < 120 nmol/L. Clinical characteristics of the two subgroups did not differ. Subjects with levels < 120 nmol/L had a rise in cytosolic calcium when changed to a low salt diet; those with levels > 120 nmol/L did not show a change in cytosolic calcium but their blood pressure fell significantly with salt restriction. Hypertensive subjects also had increased sodium-proton exchange activity compared with normotensive subjects when both groups were studied in a high salt balance. A positive correlation between sodium-proton exchange and cytosolic calcium was observed in subjects with levels < 120 nmol/L. There was insufficient power to draw conclusions on this relationship in subjects with levels > 120 nmol/L. Thus, many hypertensive subjects have increased cytosolic calcium, but this abnormality is not associated with sodium-proton exchange activity in all individuals. The salt-induced change in cytosolic calcium in subjects with levels < 120 nmol/L and its link to sodium-proton exchange suggest regulation by factors involved in salt-volume homeostasis. Individuals with cytosolic calcium > 120 nmol/L, most of whom were hypertensive, may have abnormalities in this regulation, contributing to hypertension.

Effect of alpha-adrenergic blockers, ACE inhibitors, and calcium channel antagonists on renal function in hypertensive non-insulin-dependent diabetic patients.

In the present study we investigated the effect of a selective alpha 1-adrenergic blocker (doxazosin), an angiotensin-converting enzyme (ACE) inhibitor (captopril), and a calcium channel antagonist (nifedipine) on renal function in hypertensive non-insulin-dependent diabetic patients. 30 NIDD hypertensive patients (age = 50 +/- 3 years; BMI = 30 +/- 1 kg/m2) (mean +/- SEM) were studied before and after a 12-week period of antihypertensive treatment. Ten patients were treated with doxazosin (Cardura) (2-8 mg once daily or 8 mg b.i.d.), 9 with captopril (Capoten) (25-50 mg b.i.d.), and 11 with nifedipine (Procardia-XL) (30-60 mg once daily). Blood pressure, creatinine clearance, 24-hour urinary protein excretion, fasting plasma glucose concentration and glycosylated hemoglobin were measured before and after drug treatment. Fasting plasma glucose and glycosylated hemoglobin (HbA1c) were similar in all three groups prior to the start of antihypertensive therapy and did not change significantly from baseline in any treatment groups. In the doxazosin group creatinine clearance rose from 99 +/- 8 to 122 +/- 8 ml/1.73 m2.min (p < 0.01), while 24-hour urinary protein excretion declined from 2.66 +/- 0.05 to 1.76 +/- 0.02 mg/day/ml/1.73 m2.min (p < 0.01). In diabetics treated with captopril creatinine clearance rose from 93 +/- 6 to 109 +/- 9 ml/1.73 m2.min (p < 0.05), while the 24-hour urinary protein excretion fell from 2.70 +/- 0.05 to 2.03 +/- 0.04 mg/day/ml/1.73 m2.min (p < 0.05). In patients treated with nifedipine creatinine clearance did not change (97 +/- 6 vs. 94 +/- 7 ml/1.73 m2.min), while 24-hour urinary protein excretion decreased from 2.84 +/- 0.04 to 1.95 +/- 0.03 mg/day/ml/1.73 m2.min. Systolic and diastolic blood pressure were similar in doxazosin (150 +/- 3/95 +/- 2 mm Hg), captopril (153 +/- 3/93 +/- 1), and nifedipine (155 +/- 4/93 +/- 1) groups prior to the start of antihypertensive therapy and declined to 143 +/- 3/84 +/- 3 (doxazosin), 139 +/- 3/82 +/- 3 (captopril), and 141 +/- 3/84 +/- 1 (nifedipine) mm Hg (all p < 0.01 vs. pretreatment). In summary, both doxazosin and captopril treatment were associated with significant rises in GFR, while all three antihypertensive agents caused a significant decline in proteinuria. These results indicate that alpha-adrenergic blockers, ACE inhibitors, and calcium channel antagonists can safely and effectively be used in the clinical management of non-insulin-dependent diabetic patients with hypertension.

Activity and expression of the Na+/H+ exchanger in human endothelial cells cultured in high glucose.

Establishing whether high ambient glucose affects the plasma membrane Na+/H+ exchanger is relevant to understanding the adverse effects of high glucose on cell replication and the mechanisms of the increased exchanger activity encountered in diabetic patients with nephropathy. In 8 primary and 15 first-passage isolates of human endothelial cells cultured in 30 mmol/l glucose for 8.7 +/- 2.3 and 15.8 +/- 2.3 days, respectively, we determined Na+/H+ exchanger activity and mRNA levels. Activity was determined by measuring 22Na+ influx in the presence or absence of dimethylamiloride (DMA) after intracellular acidification. We also measured fibronectin mRNA because fibronectin provides signals for cell replication through the Na+/H+ antiporter. Control cells grown in 5 mmol/l glucose showed at morphologic confluency a total Na+ influx (in nmol.mg protein-1.min-1) of 10.1 +/- 3.2 in primary and 11.7 +/- 2.2 in first subculture, which was reduced to 5.3 +/- 0.3 in the presence of DMA. Paired cultures exposed to 30 mmol/l glucose and exhibiting pHi and cell densities identical to controls showed in both primary and first subculture a reduction in total Na+ influx (delta = -0.98 +/- 0.93 nmol.mg protein-1.min-1 p < 0.005) whereas DMA-resistant Na+ influx was identical to that of control. Neither chronic hypertonicity nor acute exposure to high glucose mimicked the effects of chronic high glucose. The level of the Na+/H+ exchanger isoform 1 (NHE-1) mRNA was unchanged by high glucose whereas fibronectin mRNA levels were increased 1.5-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of angiotensin-converting enzyme inhibitors, Ca2+ channel antagonists, and alpha-adrenergic blockers on glucose and lipid metabolism in NIDDM patients with hypertension.

We compared the effects of captopril, nifedipine, and doxazosin on glucose and lipid metabolism in 30 hypertensive non-insulin-dependent diabetes mellitus (NIDDM) patients (age = 50 +/- 3 years; body mass index = 30 +/- 1 kg/m2). Of these patients, 9 were treated with captopril, 11 with nifedipine, and 10 with doxazosin for 12 weeks. Blood pressure, fasting plasma glucose (FPG) concentration, HbA1c, oral glucose tolerance test (OGTT), euglycemic insulin clamp, and plasma lipids were measured before and after a 3-month period. Mean arterial blood pressure (114 +/- 2 mmHg) was similar in all groups before initiating antihypertensive therapy and declined to 102 +/- 2 (captopril), 103 +/- 1 (nifedipine), and 103 +/- 2 (doxazosin) mmHg (P < 0.001). Baseline FPG (148 +/- 11 mg/dl) and HbA1c (6.3 +/- 1%) were similar in all groups and did not change significantly with treatment. Plasma glucose, insulin, and free fatty acid (FFA) concentrations during the OGTT were similar in all groups before antihypertensive treatment and did not change with captopril and nifedipine; after doxazosin, plasma glucose and FFA concentrations during the OGTT decreased (both P < 0.05) without change in plasma insulin response. Insulin-mediated glucose uptake (144 +/- 11 mg.m-2.min-1), glucose oxidation (76 +/- 4 mg.m-2.min-1), and nonoxidative glucose disposal (71 +/- 6 mg.m-2.min-1) were similar in all groups before the start of antihypertensive treatment and did not change in captopril and nifedipine groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Albuminuria in association with insulin and sodium-lithium countertransport in young African Americans with borderline hypertension.

The purpose of this study was to determine whether early nephropathy, evidenced by urinary albumin excretion, can be detected in young African American subjects with only borderline hypertension, and whether there is a relationship of albuminuria with insulin resistance and with sodium-lithium countertransport activity. Clinically well young African American men and women including normotensive (blood pressure < 135/85 mm Hg, n = 41) and borderline hypertensive (blood pressure > or = 135/85 mm Hg, n = 26) individuals were studied. Each subject underwent an oral glucose tolerance test and euglycemic hyperinsulinemic clamp study. Albuminuria was measured on timed urine collections. Sodium-lithium countertransport activity was assayed in fresh red blood cells at 280 mmol/L Na+ for full saturation of external Na+ sites. The sum of insulin levels during glucose tolerance was significantly greater in the borderline hypertensive compared with the normotensive subjects (P = .014), and insulin-stimulated glucose utilization during the clamp was significantly lower in borderline hypertensive compared with normotensive subjects (P = .016). Albuminuria was greater in borderline hypertensive compared with normotensive subjects (P = .002). Albuminuria was significantly correlated with fasting plasma insulin concentration (r = .44, P < .002) and the sum of insulins during the glucose tolerance test (r = .45, P < .002). Sodium-lithium countertransport correlated with albuminuria (r = .31, P < .05) as well as significantly with insulin-stimulated glucose utilization during the clamp (r = .44, P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-lithium countertransport has low affinity for sodium in hyperinsulinemic hypertensive subjects.

We recently reported that incubation of red blood cells with insulin markedly decreases the affinity for external Na+ and increases the maximal transport rate (Vmax) of Na(+)-Li+ countertransport. The association of hypertension with insulin resistance and its compensatory hyperinsulinemia led us to investigate the relationship between insulin levels in vivo and the Na+ activation kinetics of this antiporter. We studied normotensive (n = 28) and hypertensive (n = 25) subjects after they had fasted overnight and determined their plasma glucose and insulin concentrations. Insulin levels were higher in the hypertensive subjects (11.7 +/- 1.5 microU/mL, mean +/- SEM) than in the normotensive subjects (8.2 +/- 1.2 microU/mL), but glucose levels were similar and within normal limits. Antiporter activity was measured as sodium-stimulated Li+ efflux by a new procedure that uses isosmotic conditions to raise external Na+ to 280 mmol/L. In normotensive subjects, Vmax was reached between 50 and 100 mmol/L Na+, whereas in most hypertensive subjects, Na+ concentrations higher than 150 mmol/L were needed. This different kinetic behavior was because the Na+ concentration for half-maximal activation (Km) was twofold higher in hypertensive subjects (58.9 +/- 5.3 mmol/L) than in normotensive subjects (29.8 +/- 2.6 mmol/L, P < .001). Hypertensive subjects with fasting insulin levels greater than 10 microU/mL (n = 12) had a higher Km for Na+ than subjects with insulin levels less than 10 microU/mL (n = 13) (73.4 +/- 8.7 versus 45.6 +/- 3.9 mmol/L, respectively, P < .01) and similar Vmax (0.57 +/- 0.05 versus 0.41 +/- 0.05 mmol.L-1.h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of angiotensin converting enzyme inhibitor (lisinopril) on insulin sensitivity and sodium transport in mild hypertension.

The purpose of this study was to determine whether antihypertensive therapy with the angiotensin converting enzyme inhibitor lisinopril would alter cell Na+ transport kinetics, metabolic parameters associated with insulin resistance, or both in young adults with mild hypertension. Sixteen young adults (mean age 29 +/- 4 years) were treated with placebo for 8 weeks, then with lisinopril for 12 weeks. Metabolic risk factors examined included plasma lipid levels, plasma insulin concentration during an oral glucose tolerance test, and insulin sensitivity determined by an euglycemic hyperinsulinemic clamp procedure. Red blood cells were assayed for Na+/H+ exchange, Na+/Li+ exchange, Na(+)-K+ pump activity, and Na(+)-K(+)-Cl- cotransport before and during treatment. Blood pressure decreased from 142 +/- 4/98 +/- 2 mm Hg before treatment to 131 +/- 3/85 +/- 1 mm Hg during lisinopril treatment (P < .001). During lisinopril treatment, there was a significant reduction in total cholesterol (from 177 +/- 8 to 161 +/- 8 mg/dL, P < .008), in low density lipoprotein-cholesterol (from 107 +/- 7 to 91 +/- 7 mg/dL, P < .002), and in insulin at 60 min into the oral glucose tolerance test (from 132 +/- 18 to 99 +/- 15 microU/mL, P < .05). There was a marginally significant increase in insulin sensitivity during lisinopril treatment (P < .08). The assays of cell Na+ transport showed a significant reduction in maximal activity (Vmax) for Na+/H+ exchange (from 33.7 +/- 3.8 to 19.7 +/- 2.6 mmol/L cell/h, P < .003).(ABSTRACT TRUNCATED AT 250 WORDS)

Red cell sodium-lithium countertransport and cardiovascular risk factors in essential hypertension.

Human red blood cells possess a Na (+)H (+) antiporter in the plasma membrane that can exchange external Na(+) for intracellular H(+) when the intracellular pH falls below 7.0. The antiporter can also exchange Na(+) for Li(+) and that is named Na (+)Li (+) countertransport (SLC). This antiporter activity has been extensively investigated in essential hypertension and diabetes by clinical, epidemiologic, and genetic studies. Elevated values are found in patients with essential hypertension and diabetic nephropathy. In vitro studies in red cells of fasted individuals have demonstrated that physiologic doses of insulin increase the maximal transport rate and the K(m) for Na(+) of both Na (+)Li (+) and Na (+)H (+) exchanges. Ex vivo, SLC also exhibits elevated maximal activity and low affinity for Na(+) in insulin-resistant hypertensives. Patients with elevated antiporter activity manifest metabolic abnormalities (for example, high fasting insulin levels, hyperlipidemia, increased total body exchangeable Na(+), and renal and cardiac hypertrophy) that are part of the syndrome characterized by resistance to insulin-stimulated body glucose disposal. The coexistence of hypertension with insulin resistance and elevated SLC has suggested that a link between the metabolic and ion transport abnormalities may be mediated through chronic elevation of insulin levels. The association between circulating insulin concentrations and prevalence and severity of cardiovascular disease has been documented in many prospective population studies. Insulin modulation of this Na(+) antiporter might be an intermediate risk factor for cardiovascular disease that monitors chronic alterations of Na(+) homeostasis observed in hypertension and diabetes.

Rate of activation and deactivation of K:Cl cotransport by changes in cell volume in hemoglobin SS, CC and AA red cells.

Red blood cells (RBC) of subjects homozygous for hemoglobin A (AA), C (CC) and S (SS) exhibit different cell volumes which might be related to differences in cell volume regulation. We have investigated how rapidly K:Cl cotransport is activated and deactivated to regulate the cell volume in these cells. We measured the time course of net K+ efflux after step changes in cell volume and determined two delay times: one for activation by cell swelling and a second for deactivation by cell shrinkage. Cell swelling induced by 220 mOsm media activated K+ efflux to high values (10-20 mmol/liter cell x hr) in CC and SS; normal AA had a threefold lower activity. The delay time for activation was very short in blood with a high percentage of reticulocytes (retics): (SS, 10% retics, 1.7 +/- 0.3 min delay, n = 8; AA, 10% retics, 4 +/- 1.5 min, n = 3; CC, 11.6% retics, 4 +/- 0.3, n = 3) and long in cells with a smaller percentage of reticulocytes: (AA, 1.5% retics, 10 +/- 1.4 min, n = 8; CC whole blood 6% retics, 10 +/- 2.0 min, n = 10, P < 0.02 vs. SS). The delay times for deactivation by cell shrinking were very short in SS (3.6 +/- 0.4 min, n = 8, P < 0.02) and AA cells with high retics (2.7 +/- 1 min, n = 3) and normal retics (2.8 +/- 1 min, n = 3), but 8-15-fold longer in CC cells (29 +/- 2.8 min, n = 9). Density fractionation of CC cells (n = 3) resulted in coenrichment of the top fraction in reticulocytes and in swelling-activated cotransport (fourfold) with short delay time for activation (4 +/- 0.3 min) and long delay for deactivation (14 +/- 4 min). The delay time for activation, but not for deactivation, increased markedly with increasing cell density. These findings indicate that all CC cells do not promptly shut off cotransport with cell shrinkage and high rates of cellular K+ loss persist after return to isotonic conditions. In summary, (i) K:Cl cotransport is not only very active in young cells but it is also very rapidly activated and deactivated in young AA and SS cells by changes in cell volume. (ii) Delay times for cotransport activation markedly increased with RBC age and in mature cells with low cotransport rates, long delay times for activation were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Erythrocyte sodium-lithium countertransport: another link between essential hypertension and diabetes.

Erythrocyte Na+/Li+ countertransport has been extensively investigated in human essential hypertension in numerous clinical, epidemiologic, and genetic studies and through these studies has emerged as the best-characterized intermediate phenotype. Patients with elevated antiporter activity manifest high total body exhangeable Na+ levels, renal and cardiac hypertrophy, and metabolic abnormalities which are part of the syndrome characterized by resistance to insulin-stimulated body glucose disposal. The coexistence of hypertension with insulin resistance and elevated Na+/Li+ countertransport has suggested that a link between the metabolic and ion transport abnormalities may be mediated through elevated insulin levels. In vitro studies in erythrocytes of fasted individuals have demonstrated that physiologic doses of insulin increased the maximal transport rate and the concentration for half-maximal transport for Na+ of both the Na+/Li+ and Na+/H+ exchanges. In vivo, Na+/Li+ exchange also exhibits a low affinity for Na+ in insulin-resistant hypertensive patients and in patients with insulin-dependent diabetes mellitus complicated by nephropathy. Insulin modulation of this antiporter may play a role in the chronic alterations in Na+ homeostasis observed in hypertension and diabetes.