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Biomedical subjects

A Semplicini

Publications and source records attributed to A Semplicini.

At least 37 records · Page 2Linked to original sources
PubMed2000

Control of vascular tone in the syndromes of Bartter and Gitelman.

Bartter's and Gitelman's syndromes can be used as models to gain insight into the mechanisms responsible for maintaining/controlling vascular tone. In fact, the study of patients with these syndromes provides important insights into mechanistic details of the most relevant pathways of vascular tone. So far, several experimental findings in patients with these syndromes point to G protein abnormalities and suggest that the intracellular signaling systems that involve the G protein complex transducing components may be defective, leading to altered vascular reactivity. These results are also of particular interest because the derangements found in Bartter's and Gitelman's syndromes are the mirror images of those involved in the pathophysiology of hypertension.

Bartter Syndrome↗
PubMed2000

Cerebral perfusion in hypertensive patients: effects of lacidipine and hydrochlorothiazide.

Previous studies have shown areas of cerebral hypoperfusion in the frontal and parietal lobes of asymptomatic hypertensives, in the absence of extracranial carotid artery stenosis. The aims of the present study were: (a) to correlate the presence of focal cortical hypoperfusion with the presence of white matter lesions (WML), lacunae and extracranial carotid artery stenosis; and (b) to compare the effects on cerebral perfusion of the dihydropyridine calcium entry blocker lacidipine and of hydrochlorothiazide (HCTZ) in hypertensive patients with carotid artery stenosis. Forty-one patients (30 males, aged 40-75) with mild to moderate essential hypertension and with negative history for cerebrovascular diseases were investigated. Twenty-four had normal extracranial carotid arteries at echo-colourDoppler examination, while 17 had at least one 50-70% stenosis of the internal carotid artery (ICA). At computed tomography (CT) scan, five patients had one or more lacunar infarctions, four WML, three lacunar infarctions and WML, and 26 a normal CT scan. Three, with old cortical infarctions, were excluded from further analysis. The prevalence of lesions was significantly higher among the patients with carotid artery stenosis (44% vs. 29%; p < 0.05). Distribution of mean relative cortical perfusion (MRCP) of regions of interest [hexamethyl-propileneamine oxime-single photon emission tomography (SPET)] was not normal, with a negative skewness in patients with lacunae. MRCP was slightly but significantly reduced in patients with lacunae in comparison with hypertensives with normal CT scan and with WML. The asymmetry index of tracer distribution was significantly greater in the patients with lacunar infarctions and WML than in the hypertensive patients with normal CT scan, irrespective of the presence of internal carotid artery stenosis. Fifteen hypertensives (13 males, aged 55-75 years) with at least one moderate stenosis of ICA at duplex scanning were treated in a double-blind, randomised, parallel study with lacidipine (4-6 mg o.d.) or HCTZ (25-50 mg o.d.) for 3 months after a 4-week single-blind placebo period. At baseline, perfusion of the cortical and basal areas was similar in the stenotic and the contralateral side. Despite the fall in pressure, both treatments increased MRCP in the stenotic side and in the contralateral side. The lower the baseline perfusion, the larger its increase with treatment. The decrease of local cerebral vascular resistance was significantly greater with lacidipine than with HCTZ. We conclude that in hypertensive patients, the distribution of cerebral flow is uneven, mostly in the presence of small asymptomatic subcortical lesions and independently from internal carotid artery stenosis. Antihypertensive treatment with lacidipine and HCTZ reduces local cerebral resistance and corrects focal hypoperfusion without inducing steal effects in patients with ICA stenosis.

Adult↗
PubMed2000

Oxidative stress and nitric oxide system in post-transplant hypertension.

BACKGROUND: CsA-induced endothelial dysfunction and CsA-induced hypertension have been attributed to CsA effects on the endothelial-derived factors controlling vasomotor tone, but the mechanisms responsible are unclear. Endothelial nitric oxide (NO) is known to maintain a state of basal vasodilation and recently a NO mediated counterregulatory mechanism protective from CsA-induced vasoconstriction has been suggested. PATIENTS AND METHODS: Our study evaluates ecNOS gene status and NO metabolites in kidney transplanted patients under chronic CsA treatment with CsA-induced hypertension. Since CsA increases superoxide production, which metabolizes NO, plasma hydroperoxides and peroxynitrite were also evaluated as index of the presence of "oxidative stress". RESULTS: Quantification of monocyte ecNOS mRNA and NO metabolites plasma level from patients and control subjects (C) demonstrated NO system up regulation in patients notwithstanding hypertension. The mean ecNOS to beta-actin ratio was 2.00 +/- 0.87 vs 0.29 +/- 0.08 in C, p < 0.04. NO metabolite plasma level was 30.03 +/- 9.62 mM vs 9.37 +/- 3.86, p < 0.001. Hydroperoxides were also increased in patients: 3.6 +/- 1.6 i.a.u. vs 1.4 +/- 0.8, p < 0.007 (from cholesterol esters) and 10.8 +/- 6.6 vs 1.5 +/- 0.9, p < 0.008 (from triglycerides) as well as peroxynitrite plasma level: 0.36+/- 0.14 mM/L vs undetectable in C. CONCLUSIONS: This study confirms a NO system up-regulation in transplanted patients. However, the counterregolatory system to CsA-induced vasoconstriction, could be cancelled by CsA induced superoxide and free radicals production which, increasing NO metabolism could contribute to CsA induced vasoconstriction and hypertension.

Humans↗
PubMed2000

Cerebral perfusion in hypertensives with carotid artery stenosis: a comparative study of lacidipine and hydrochlorothiazide.

Focal cerebral hypoperfusion is a common finding in uncomplicated hypertensives even in the absence of large vessel atherosclerosis, and neuropsychological deficits correlate with cerebral hypoperfusion in hypertensive patients with cerebral microangiopathy. We investigated the effects on cerebral perfusion of the dihydropiridine calcium antagonist lacidipine and of hydrochlorothiazide (HCTZ) in asymptomatic hypertensive patients with concomitant atherosclerosis of the carotid arteries. Fifteen essential hypertensives (including 13 males, aged 55-75 years) with at least one 30-60% stenosis of the internal carotid artery at echo-color Doppler examination were treated in a double-blind, randomized, parallel study with lacidipine (4-6 mg od) or HCTZ (25-50 mg od) for 3 months after a 4-week single-blind placebo period. Regional cerebral perfusion was assessed at baseline and at the end of the treatment period with HMPAO-SPECT. Relative perfusion of cortical and subcortical areas was calculated as the ratio between their tracer activity and that of the cerebellum. At baseline, mean relative perfusion (MRP) of the cortical and subcortical areas was similar in the stenotic and the contralateral side. Despite the fall in pressure, lacidipine increased MRP both in the cortical and in the subcortical areas, whereas HCTZ increased MRP only in the cortical areas. The mean change in local vascular resistance, adjusted for initial perfusion value, was -20 A.U. (arbitrary unit) with lacidipine and -12 A.U. with HCTZ (p < 0.001). These differential effects of antihypertensive drugs on subcortical perfusion may be of benefit in the long-term prevention of vascular dementia in hypertensive patients.

Aged↗
PubMed1999

MAPKinase and regulation of the sodium-proton exchanger in human red blood cell.

The sodium-proton exchanger is activated by various agonists, including insulin, even in human red blood cell. MAPKinase, a family of ubiquitous serine/threonine kinases, plays an important role in the signal transduction pathways which lead to sodium-proton exchanger activation. The aim of our study was to establish the existence of MAPKinase in human red blood cell and to investigate the effects of its activation by insulin and okadaic acid on the sodium-proton exchanger. Immunoblot with antiMAPK antibody revealed the presence of two isoforms, p44(ERK1) and p42(ERK2). Insulin stimulated MAPKinase activity and increased the phosphorylation of MAPK tyrosine residues, with a peak time between 3 and 5 min. Okadaic acid, an inhibitor of serine/threonine phosphatases, stimulated MAPKinase activity. In the presence of PD98059, an inhibitor of MEK, the upstream activator of MAPKinase, insulin and okadaic acid failed to stimulate MAPKinase. Insulin and okadaic acid increased the activity of the sodium-proton exchanger and this effect was abolished by PD98059. In conclusion, we first describe the presence and activity of MAPKinase in human red blood cell. Furthermore, we demonstrate that in human red blood cell, insulin modulates the sodium-proton exchanger through MAPKinase activation.

Adult↗
PubMed1999

Effect of protein kinase C and insulin on Na+/H+ exchange in red blood cells of essential hypertensives.

The kinetic properties of sodium-proton exchange are abnormal in human red blood cells of hypertensive patients and it has been demonstrated that the transport protein undergoes post-translational modifications able to affect its kinetic properties. Protein kinase C (PKC) activation decreases the affinity constant for intracellular protons while insulin increases the maximal rate of proton translocation. The present study therefore aimed to examine the relationships among PKC activity, fasting insulin levels and the kinetic behaviour of sodium-proton exchange in red blood cells from 20 normotensives and 36 hypertensives. In comparison with normotensive subjects, hypertensive patients had higher body mass index (26.2 +/- 0.7 vs 23.6 +/- 0.6 kg/m2, P < 0.05), higher fasting insulin levels (93.2 +/- 10.8 vs 38.6 +/- 2.9 pmol/L), increased maximal velocity of proton translocation (37.9 +/- 2.7 vs 27.6 +/- 1.9 mmol/L per cell x h, P < 0.05), and reduced Hill's coefficient (1.6 +/- 0.1 vs 2.0 +/- 0.1, P < 0.01) of sodium-proton exchange. Basal PKC activity of the cytosol and membrane was similar in the study groups. However, after treatment with 1 micromol/L phorbol 12-myristate 13-acetate (PMA) for 10 min, membrane PKC activity was stimulated to a larger extent in hypertensives (to 181 +/- 8 pmol/min/mg protein) than in normotensives (to 136 +/- 6 pmol/min/mg protein, P < 0.01). The PMA stimulated PKC activity was positively correlated to fasting insulin levels (r = 0.59, P < 0.01). Stimulation of membrane PKC by PMA corrected the low Hill's coefficient for H(i)+ activation of sodium-proton exchange in the hypertensives, while the constant for half maximal activation for intracellular protons (ie, the affinity for intracellular protons) decreased to a similar extent in both groups. The maximal transport rate was unaffected by PMA. These results indicate that the abnormal proton activation of red blood cell sodium-proton exchange in hypertensives reflects an abnormal regulation of PKC translocation to the cell membrane, associated to hyperinsulinaemia and probably insulin resistance. Therefore, post-translational modifications of the transport protein(s) account for the altered kinetic behaviour of sodium-proton exchange in hypertensives.

Adult↗
PubMed1999

Controlled study of the effect of angiotensin converting enzyme inhibition versus calcium-entry blockade on insulin sensitivity in overweight hypertensive patients: Trandolapril Italian Study (TRIS).

OBJECTIVE: The aim of this study was to evaluate the effect of trandolapril, an angiotensin converting enzyme inhibitor, on blood pressure, forearm blood flow and insulin sensitivity in comparison with nifedipine gastrointestinal therapeutic system. PATIENTS AND METHODS: This is a multicentre, two-way parallel-group, open-label comparative study in 90 overweight hypertensive patients, who were randomly assigned to treatment for 8 weeks with either trandolapril or nifedipine. At baseline and after treatment, all patients underwent an oral glucose tolerance test, an evaluation of their metabolic profiles and a euglycaemic hyperinsulinaemic clamp test. In a subgroup of 18 patients, a forearm study was carried out. RESULTS: Blood pressure fell by the second week of treatment and remained significantly reduced compared with baseline in both treatment groups. Plasma triglyceride levels were also significantly reduced after trandolapril therapy, but no significant changes occurred in the other metabolic parameters during treatment with either drug. During the euglycaemic hyperinsulinaemic clamp, whole-body glucose use was similar in the two treatment groups at baseline, and a moderate but statistically significant increase in insulin sensitivity was observed after trandolapril treatment (trandolapril: 5.0 +/- 0.2 versus 4.5 +/- 0.2 mg/kg per min; nifedipine: 4.1 +/- 0.3 versus 4.2 +/- 0.3 mg/kg per min; P < 0.05, versus baseline and trandolapril versus nifedipine treatment). Skeletal muscle glucose uptake was significantly higher after trandolapril than after nifedipine therapy (5.0 +/- 0.7 and 3.0 +/- 0.4 mg/min, respectively; P < 0.01). As forearm blood flow was similar in the two treatment groups at baseline and was unchanged after 8 weeks of therapy, skeletal muscle glucose extraction was significantly greater in the ACE inhibitor treated-group than in the nifedipine comparative group (trandolapril: baseline 21 +/- 2, treatment 24 +/- 3 mg/dl; nifedipine: baseline 18 +/- 3, treatment 16 +/- 2 mg/dl; P < 0.05, trandolapril versus nifedipine treatment). CONCLUSIONS: During short-term treatment, ACE inhibition with trandolapril was able to moderately improve insulin sensitivity, in comparison with calcium blockade, and this effect appeared to be independent of the haemodynamic action of the drug.

Adult↗
PubMed1999

Protein kinase C activity is acutely regulated by plasma glucose concentration in human monocytes in vivo.

Activation of protein kinase C (PKC) by hyperglycemia is implicated in the pathogenesis of long-term diabetic complications. Monocyte activation and transformation into macrophages is a key step in the atherosclerotic process. Therefore, in this study, we sought to determine 1) the effect of hyperglycemia on monocyte PKC activity and on the distribution of Ca2+-dependent and diacylglycerol-sensitive PKC isoforms; and 2) whether the effects on these parameters are determined by hyperglycemia per se, independent of the diabetic state. The studies were performed in 19 type 2 diabetic patients and 14 control subjects. Plasma glucose concentration was higher and insulin sensitivity lower (both P < 0.01) in diabetic patients than in control subjects. Monocytes from diabetic patients showed similar cytosol PKC activity to those from control subjects but higher membrane PKC activity (78+/-6 vs. 50+/-5 pmol x min(-1) x mg(-1) protein; P < 0.01). A direct correlation was observed between fasting plasma glucose and membrane PKC activity (r2 = 0.4008, P = 0.0001). In contrast, a reciprocal correlation was observed between membrane PKC activity and insulin sensitivity index (r2 = 0.28, P < 0.05). Using immunoblotting analysis, we found that membrane beta2, but not alpha, isoform of PKC was more abundant in monocytes from diabetic patients. In diabetic patients, when euglycemia was acutely induced, membrane PKC activity decreased by approximately 42% and beta2 isoform by approximately 15%. In two normal subjects in whom hyperglycemia was induced, membrane PKC increased from 63 and 57 to 92 and 128.6 pmol x min(-1) x mg(-1) protein, respectively. This increase was associated with an increase in the membrane isoform beta2; alpha isoform was unchanged. We conclude that 1) monocytes express the glucose-sensitive beta2 isoform of PKC; 2) the prevailing plasma glucose acutely regulates the activity of the membrane PKC and the content of membrane PKC beta2 isoform; and 3) this effect appears to be a direct effect of glucose per se, since the phenomenon was observed in normal control subjects when hyperglycemia was induced. Monocyte PKC activation may account for the accelerated atherosclerosis of patients with type 2 diabetes.

Blood Glucose↗
PubMed1998

Screening for primary aldosteronism with a logistic multivariate discriminant analysis.

OBJECTIVE: Primary aldosteronism (PA) is the most common endocrine cause of curable hypertension, but no single test unequivocally identifies it. Accordingly, we investigated the usefulness of a logistic multivariate discriminant analysis (MDA) approach for PA screening. DESIGN: Generation of a logistic MDA function based on retrospective analysis of biochemical tests in a large cohort of referred patients with/without confirmed Conn's adenoma (CA), followed by prospective validation of the model. PATIENTS: We investigated 574 selected hypertensives: 206 (32 with and 174 without CA) retrospectively, 48 (with a 13% prevalence of CA) prospectively for the validation of the model, and 320 referred hypertensives (with a 3.4% prevalence of CA) similarly evaluated. Patients were referred to a specialised centre for hypertension (4th Clinica Medica--University of Padua) and to a department of Internal Medicine of a regional hospital (Reggio Emilia). MEASUREMENTS: In all patients we measured several demographic and biochemical variables and performed a captopril test. A stepwise analysis of variance, based on a model fitted with several different variables, identified baseline (sALDO) and captopril-suppressed plasma aldosterone (cALDO), supine plasma renin activity (sPRA) and K+ as the most informative. Therefore, two models of logistic MDA with sPRA, K+, and either sALDO (model A) or cALDO (model B) were developed and used. ROC analysis was also performed to assess the optimal cut-off values. RESULTS: The model B of MDA provided the best performance and identified CA with 100% sensitivity and 81% accuracy. When used prospectively it showed 100% sensitivity, both in the Padua (88% accuracy) and in the Reggio Emilia series (90% accuracy). However, at both institutions most patients with idiopathic hyperaldosteronism (IHA) were also detected. CONCLUSIONS: Thus, although developed from patients with confirmed Conn's adenoma, a strategy based on multivariate discriminant analysis can be used prospectively for accurate screening for primary aldosteronism. Furthermore, it was proven to be accurate and applicable to patients tested with similar modalities at a different institution. Although this approach did not provide a clear-cut discrimination of Conn's adenoma from idiopathic hyperaldosteronism, it may avoid unnecessary and costly further testing in patients with a low probability of primary aldosteronism.

Adult↗
PubMed1998

Modulatory effect of insulin on release of calcium from human fibroblasts by angiotensin II.

BACKGROUND: Angiotensin II stimulates synthesis and deposition of collagen and might contribute to the vascular and cardiac dysfunction associated with arterial hypertension. Insulin attenuates angiotensin II-induced responses of intracellular Ca2+ concentration ([Ca2+]) in many cell types but this effect is less in insulin-resistant states. The mechanisms of the interaction between insulin and angiotensin II are still not known. OBJECTIVE: To characterize the effects of angiotensin II on intracellular [Ca2+] and the effects of insulin on the angiotensin II-induced response of intracellular [Ca2+] in human skin fibroblasts. METHODS: Spectrofluorophotometric measurements of intracellular [Ca2+] in monolayers of cultured human skin fibroblasts from 15 normotensive patients were performed using Fura-2 at 510 nm emission with excitation wavelengths of 340 and 380 nm. RESULTS: Basal intracellular [Ca2+] in quiescent (24 h serum-deprived) human fibroblasts was 75 +/- 3 nmol/l (n = 20). Administration of angiotensin II elevated intracellular [Ca2+] dose-dependently with a concentration for half-maximal effect of 20 nmol/l. Administration of 100 nmol/l angiotensin II stimulated a rapid and transient increase in intracellular [Ca2+] (from 75 +/- 3 to 130 +/- 2 nmol/l, n = 20). Removal of extracellular calcium did not change peak intracellular [Ca2+], but it did reduce the time to recovery of [Ca2+] (from 64 +/- 4 to 48 +/- 2 s, n = 10, P < 0.01), suggesting that an angiotensin II-induced transmembrane calcium influx had occurred. This hypothesis was confirmed by quenching studies with manganese. The angiotensin II-induced changes in intracellular [Ca2+] were completely blocked by administration of 100 nmol/l of the angiotensin II type 1 receptor inhibitor losartan but not by administration of 100 nmol/l of the angiotensin II type 2 receptor blocker CGP42112A. Acute (20 min) exposure to 100 nmol/l insulin did not alter basal intracellular [Ca2+] in quiescent fibroblasts, but significantly blunted angiotensin II-stimulated peak of [Ca2+] (to 101 +/- 3 nmol/l, P < 0.01, n = 18) and delayed recovery of [Ca2+] (to 99 +/- 5 s, P < 0.01). The inhibitory effect of insulin was observed both with and without extracellular Ca2+. CONCLUSIONS: Our results demonstrate that administration of angiotensin II increases intracellular [Ca2+] in human skin fibroblasts by release of Ca2+ from intracellular Ca2+ stores and by influx of Ca2+ and that administration of insulin attenuates the response of [Ca2+] to angiotensin II but prolongs the time to recovery of [Ca2+].

Angiotensin II↗
PubMed1998

Enhanced responsiveness of blood pressure to sodium intake and to angiotensin II is associated with insulin resistance in IDDM patients with microalbuminuria.

We assessed blood pressure (BP), body weight, renal hemodynamics, and insulin sensitivity (by euglycemic-hyperinsulinemic clamp) in nine normoalbuminuric and seven microalbuminuric IDDM patients after 6 days on a low-sodium diet (20 mEq) and after 6 days on a high-sodium diet (250 mEq). In microalbuminuric but not in normoalbuminuric IDDM patients, switching from a low to a high-sodium diet was associated with a significant increase in mean BP (from 92 +/- 3 to 101 +/- 4 mmHg; P < 0.001) and in body weight (2.91 +/- 0.63 vs. 1.47 +/- 0.26 kg; P < 0.05). Moreover, under high-sodium conditions, angiotensin II infusion (3 ng x kg(-1) x min(-1)) caused a greater increase in mean BP (14 +/- 2 vs. 7.4 +/- 1 mmHg; P < 0.05) and a smaller reduction in renal plasma flow (-122 +/- 29 vs. -274 +/- 41 ml x min(-1) x 1.73 m2; P < 0.05) in microalbuminuric than in normoalbuminuric IDDM patients. Under low sodium conditions, aldosterone increments after angiotensin II infusion were lower (P < 0.05) in microalbuminuric than in normoalbuminuric IDDM patients. Insulin-mediated glucose disposal was not affected by sodium dietary content, but it was lower in microalbuminuric (P < 0.05) than in normoalbuminuric IDDM patients. The salt-induced changes in mean BP were related to insulin sensitivity (r = -0.78; P < 0.001). In conclusion, in IDDM patients, microalbuminuria is associated with 1) an increased responsiveness of BP to salt intake and angiotensin II, 2) impaired modulation of renal blood flow, and 3) insulin resistance. Therefore, salt sensitivity in IDDM patients clusters with other factors that are likely to play an important role in the pathogenesis of diabetic nephropathy and its cardiovascular complications.

Adrenal Glands↗
PubMed1997

Elevated sodium-lithium countertransport activity in erythrocytes is predictive of the development of microalbuminuria in IDDM.

Pathogenetic mechanisms other than the quality of metabolic control may play a role in the development of diabetic nephropathy. Some cross-sectional studies have shown that elevated erythrocyte sodium-lithium countertransport (Na+/Li+ CT) activity may be linked to incipient or overt nephropathy in insulin-dependent diabetic (IDDM) patients. The aim of the present work was to ascertain if high erythrocyte Na+/Li+ CT activity anticipates the development of microalbuminuria in IDDM patients. Evaluation of this cation transport system was carried out in 159 normotensive, normoalbuminuric IDDM patients, who were divided into two groups: those with values above (Group A) and those with values below (Group B) the median level in the overall population (300 mumol/erythrocytes x h). A total of 79 patients in Group A and 80 in Group B underwent periodic examinations over a similar time period (5.2 years, range 3.3-7.4 years and 5.4 years, range 3.4-7.5 years, respectively). Median sodium-lithium countertransport activity was stable when evaluated after 2 and 4 years of follow-up. Only seven patients were excluded from the protocol because changes in their sodium-lithium countertransport activity placed them on the other side of the median value with respect to their baseline measurement. Thus, 152 patients completed the study (76 in Group A and 76 in Group B). Of the 76 patients in Group A, 17 developed persistent microalbuminuria (22.3%). The number of patients in Group B showing persistent microalbuminuria was significantly lower (4 of 76; 5.2%; p < 0.01). The sensitivity of erythrocyte Na+/Li+ CT in predicting the development of microalbuminuria was 85% and its specificity was 55%. Seven patients of Group A and five of Group B developed arterial hypertension. Subjects in Group A had significantly higher mean HbA1c values of twice yearly measurements than those in Group B (9.6 +/- 1.7 vs 8.3 +/- 1.7%, p < 0.002, mean +/- SD) despite similar daily insulin requirements. Systolic and diastolic blood pressure levels were also evaluated every 6 months and were significantly higher in the Group A than in the Group B patients, although on average within the normal range. The odds ratio for developing persistent microalbuminuria in IDDM with elevated baseline erythrocyte Na+/Li+ CT activity after adjustment for gender and baseline albumin excretion rate, and mean 6 monthly plasma creatinine, HbA1c and systolic and diastolic blood pressure levels was 4.2 (95% confidence intervals 2.0-11.1). It was also found that the percentage of offspring having both parents with Na+/Li+ CT activity above the median value was significantly higher in Group A than in Group B (Group A vs Group B: 35 vs 19%; p < 0.01). On the contrary the percentage of offspring whose erythrocyte Na+/Li+ CT was lower in both parents was lower in Group A than in Group B: 10 vs 38%, p < 0.01). Parents of Group A offspring had arterial hypertension more frequently than those of Group B. These results indicate that erythrocyte Na+/Li+ CT activity is a useful diagnostic tool in identifying normotensive, normoalbuminuric patients who may be predisposed to develop persistent microalbuminuria. This disorder in the cation transport system is associated with poor metabolic control, higher blood pressure, and male sex; it also appears to be, at least partly, genetically transmitted.

Adolescent↗
PubMed1997

Inhibition of furosemide-sensitive cation transport and activation of sodium-lithium exchange by endogenous circulating factor(s) in Bartter's and Gitelman's syndromes.

BACKGROUND: The nature of the cellular abnormality causing hypokalemia, hypotension, and hypovolemia in Bartter's and Gitelman's syndromes is still being debated. In fact, despite the recent descriptions of an array of nonconservative missense or point mutations in some ion transporters and in K+ channel, the lack of detectable defects in some patients suggests that other abnormalities of cell ion homeostasis may be involved in the pathophysiology of these syndromes. The study of the activity of cell ion transporters in patients with these syndromes using red blood cells (RBC) as a cellular model never investigated the role of plasma factor(s) affecting ion transport. OBJECTIVE: To evaluate the effect of plasma from patients with these syndromes on furosemide-sensitive lithium efflux (FSLE) from lithium (Li+)-loaded RBC of healthy subjects in vitro. METHODS: RBC of healthy controls were loaded with Li+ in the presence of nystatin and FSLE was evaluated in the presence of various concentrations of plasma from controls and patients with the two syndromes. RESULTS: Plasma from controls did not affect FSLE (0.08 +/- 0.02 mmol/l cells per h with 1:4 vol:vol and 0.07 +/- 0.02 mmol/l cells per h with 1:2 vol:vol plasma dilution). In contrast, doubling concentrations of plasma from patients with either syndrome in the efflux solution halved FSLE (from 0.10 +/- 0.0 mmol/l cells per h with 1:4 vol:vol to 0.05 +/- 0.01 mmol/l cells per h with 1:2 vol:vol plasma dilution, P < 0.05). Na+/Li+ exchange was significantly greater for RBC from patients with either syndrome than it was for RBC from controls (0.373 +/- 0.06 versus 0.257 +/- 0.01 mmol/l cells per h, P < 0.01), but the kinetic properties of furosemide-sensitive Na+-K+-2Cl- cotransport were similar. CONCLUSION: These data provide evidence for the hypothesis that plasma factor(s) affect ion transport in patients with these two syndromes. Since FSLE estimates Na+-K+-2Cl- cotransport the data suggest that plasma factor(s) contribute(s) to K+ wasting, hypokalemia, and hypotension by inhibiting cotransport in patients with these syndromes. The increase of Na+/Li+ exchange is most likely a secondary phenomenon associated with the hypermineralocorticoid state.

Adult↗
PubMed1997

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.

Adult↗