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The presence of carbonic anhydrase (type V) was recently documented in rat and mouse pancreatic islet [3-cells by immunostaining and Western blotting. In the present study, the activity of carbonic anhydrase was measured in rat islet homogenates and shown to be about four times lower than in rat parotid cells. The pattern for the inhibitory action of acetazolamide on carbonic anhydrase activity also differed in islet and parotid cell homogenates, suggesting the presence of different isoenzymes. Na[N.sub.3] inhibited carbonic anhydrase activity in islet homogenates and both D-[U-[sup.14]C]glucose oxidation and glucose-stimulated insulin secretion. Acetazolamide (0.3-10.0 mM) also decreased glucose-induced insulin output but failed to affect adversely D-[U-[sup.14]C]glucose oxidation, although it inhibited the conversion of D-[5-[sup.3]H]glucose to [[sup.3]H]OH and that of D-[U-[sup.14]C]glucose to acidic metabolites. Hydrochlorothiazide (3.0-10.0 mM), which also caused a concentration-related inhibition of the secretory response, like acetazolamide (5.0-10.0 mM), decreased [H.sup.14]C[O.sup.-.sub.3] production from D-[U-[sup.14]C]glucose (16.7 mM). Acetazolamide (5.0 mM) did not affect the activity of volume-sensitive anion channels in [beta]-cells but lowered intracellular pH and adversely affected both the bioelectrical response to D-glucose and its effect on the cytosolic concentration of [Ca.sup.2+] in these cells. The lowering of cellular pH by acetazolamide, which could well be due to inhibition of carbonic anhydrase, might in turn account for inhibition of glycolysis. The perturbation of stimulus-secretion coupling in the [beta]-cells exposed to acetazolamide may thus involve impaired circulation in the pyruvate-malate shuttle, altered mitochondrial [Ca.sup.2+] accumulation, and perturbation of [Cl.sup.-] fluxes, resulting in both decreased bioelectrical activity and insulin release. acetazolamide; D-glucose metabolism; insulin secretion; bioelectrical activity; bicarbonate production doi: 10.1152/ajpendo.00631.2006

Abstract Background Women with rheumatoid arthritis (RA) have increased morbidity and mortality due to coronary heart disease. Chronic systemic inflammation is known to accelerate atherosclerosis and increase arterial stiffness in patients, but other mechanisms may also be involved. Biomarkers of oxidant stress, inflammation, insulinaemia and endothelial dysfunction were measured in blood and urine from 46 RA patients and 48 age-matched controls. Plaque formation and intima-medial thickness (IMT) were measured using B-mode carotid Doppler scan. Findings The prevalence of plaque was increased (p = 0.042) in RA patients between 50–59 years old compared to the same age group in controls. 8-isoprostane (p = 0.004), C-reactive protein (p < 0.001), interleukin-6 (p < 0.001), insulin (p = 0.035), adiponectin (p = 0.012), vascular cell adhesion molecule (VCAM) (p = 0.029) and E-selectin (p < 0.001) were all increased while selenium (p = 0.003) and LDL-cholesterol (p = 0.025) were both decreased in all RA patients. 8-isoprostane correlated with 10 year cardiac risk (r = 0.55, p < 0.001), VCAM with IMT (r = 0.37, p = 0.012) and E-selectin with rheumatoid factor titre (r = 0.43, p = 0.003) in RA patients. In the control group, age, carotid IMT, VCAM, systolic blood pressure and smoking status were all associated with plaque development whereas in RA patients only age was associated with plaque. Conclusion The burden of atherosclerosis is particularly increased in middle-aged women with RA. Patients with RA have increased levels of oxidant stress, inflammation, insulin and soluble adhesion molecules. As the association between classical risk factors was much weaker in RA patients compared to controls, these additional factors may be more important in the accelerated development of atheroma in RA.

Abstract The use of antipsychotic drugs is known to be associated with a number of adverse metabolic side effects, including diabetes mellitus. These side effects could be, at least in [...]

Background: Autoanalyser methods for the measurement of anti-Müllerian hormone have been introduced into clinical laboratories but few reports of paediatric reference intervals using these new assays have been published. Methods: After prior evaluation of the Roche Elecsys anti-Müllerian hormone assay against the Beckman Coulter modified second generation anti-Müllerian Hormone enzyme-linked immunosorbent assay using samples from adult females, a cohort of paediatric samples which had previously been assessed using the Beckman Coulter Access anti-Müllerian hormone assay was analysed using the Roche Elecsys anti-Müllerian hormone assay. Results: The Roche Elecsys anti-Müllerian hormone assay measured significantly lower than the Beckman Coulter modified second generation anti-Müllerian Hormone enzyme-linked immunosorbent assay. In the paediatric cohort measured with the Roche Elecsys assay, male levels are very high from birth to puberty after which they fall towards postpubertal female levels. Male results were similar to those previously obtained using the Beckman Coulter Access anti-Müllerian hormone assay on the same cohort. Roche Elecsys anti-Müllerian hormone in the females was very low in the neonatal and prepubertal years and the postpubertal trend, with a steady rise from 15 years, was smoother than previously modelled using the Beckman Coulter Access anti-Müllerian hormone assay. Conclusion: Anti-Müllerian hormone levels measured with the Roche Elecsys assay were significantly lower than the Beckman Coulter modified second generation enzyme-linked immunosorbent assay suggesting the need for new reference ranges. In the paediatric cohort, Roche Elecsys anti-Müllerian hormone levels between boys and girls showed good prepubertal delineation and small but statistically significant differences to previously measured levels using the Beckman Coulter Access anti-Müllerian hormone assay on the same sample cohort. [ABSTRACT FROM AUTHOR]

Background/aims: Pancreatic β-cell function is influenced by changes in cell volume. Such volume changes depend on water permeability of the plasma membrane, conferred in part by aquaporins. Islet cells express aquaporin 7 (AQP7), which is permeable to urea and glycerol in addition to water. We therefore investigated the effects of glycerol and urea on rat pancreatic β-cell function. Methods: Electrical activity and whole-cell current were studied using the perforated patch technique. Cell volume was measured by video-imaging and insulin release by radioimmunoassay. Aquaporin 7 expression was studied by RT-PCR, Western blot and double fluorescent immunolabelling. Results: The isosmotic addition of glycerol and urea resulted in depolarization of the plasma membrane and electrical activity, accompanied by β-cell swelling, activation of the volume-regulated anion channel (VRAC) and insulin release. However, the effects of glycerol, in contrast to urea, persisted throughout exposure to the osmolyte. Glycerol also caused β-cell activation when added hyperosmotically. A non-metabolizable glycerol analogue had comparable effects to urea on β-cells. The expression of AQP7 was demonstrated in rat β-cells. Conclusion: Glycerol and urea can activate β-cells via their rapid uptake across the β-cell plasma membrane, possibly via AQP7. This results in cell swelling, VRAC activation, electrical activity and insulin release. Glycerol appears to exert an additional effect, possibly related to its intracellular metabolism. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Background: Women with rheumatoid arthritis (RA) have increased morbidity and mortality due to coronary heart disease. Chronic systemic inflammation is known to accelerate atherosclerosis and increase arterial stiffness in patients, but other mechanisms may also be involved. Biomarkers of oxidant stress, inflammation, insulinaemia and endothelial dysfunction were measured in blood and urine from 46 RA patients and 48 age-matched controls. Plaque formation and intima-medial thickness (IMT) were measured using B-mode carotid Doppler scan. Findings: The prevalence of plaque was increased (p = 0.042) in RA patients between 50–59 years old compared to the same age group in controls. 8-isoprostane (p = 0.004), C-reactive protein (p < 0.001), interleukin-6 (p < 0.001), insulin (p = 0.035), adiponectin (p = 0.012), vascular cell adhesion molecule (VCAM) (p = 0.029) and E-selectin (p < 0.001) were all increased while selenium (p = 0.003) and LDL-cholesterol (p = 0.025) were both decreased in all RA patients. 8-isoprostane correlated with 10 year cardiac risk (r = 0.55, p < 0.001), VCAM with IMT (r = 0.37, p = 0.012) and E-selectin with rheumatoid factor titre (r = 0.43, p = 0.003) in RA patients. In the control group, age, carotid IMT, VCAM, systolic blood pressure and smoking status were all associated with plaque development whereas in RA patients only age was associated with plaque. Conclusion: The burden of atherosclerosis is particularly increased in middle-aged women with RA. Patients with RA have increased levels of oxidant stress, inflammation, insulin and soluble adhesion molecules. As the association between classical risk factors was much weaker in RA patients compared to controls, these additional factors may be more important in the accelerated development of atheroma in RA. [ABSTRACT FROM AUTHOR]

Medroxyprogesterone (MP) was used as the progestogen in randomized clinical trials of postmenopausal hormone replacement on cardiovascular risk. To attempt to understand the lack of benefit in these trials, we have examined the effects of MP and two other progestogens, the less androgenic desogestrel (DG) and the more androgenic norethisterone (NE), on cardiovascular risk factors against a background of oestrogen therapy.Thirty-four women were treated with conjugated equine oestrogens (CEE) 0·625 mg daily alone for 12 weeks, followed in random order by each of the three progestogens (DG 75 µg, MP 10 mg and NE 1 mg daily) given sequentially for three 12-week cycles while maintaining the same CEE treatment. We measured serum lipoproteins, paraoxonase activity, C-reactive protein (CRP), fibrinogen, fasting glucose and insulin levels at baseline, at the end of the oestrogen-only phase and at the end of each of the combined oestrogen and progestogen phases.The addition of progestogens to CEE maintained the oestrogen-induced reduction in apolipoprotein B (apo B) and lipoprotein (a)[Lp(a)], and further lowered total cholesterol (P < 0·01) and fibrinogen (P < 0·001). CEE raised serum triglyceride (P < 0·001) and CRP (P < 0·01) concentrations, which reverted towards pre-oestrogen levels with progestogens. Progestogens significantly reduced high density lipoprotein (HDL) cholesterol (P < 0·05). NE was associated with the greatest reduction in HDL cholesterol and apo A1, but was most effective in preserving paraoxonase activity and reducing the potentially unfavourable oestrogen-induced increases in triglycerides and CRP.Preconceptions that more androgenic progestogens necessarily have more unfavourable effects on cardiovascular risk factors may require revision. [ABSTRACT FROM AUTHOR]

The addition of the triose D-glyceraldehyde (5-20 mM) to HIT-T15 hamster insulinoma cells caused a rapid, marked depolarisation of the plasma membrane accompanied by a pronounced intracellular acidification, an increase in the cytosolic free calcium concentration [Ca2+]i and enhanced secretion of insulin. D-glyceraldehyde did not reduce the rate of efflux of 86Rb+ from loaded perifused cells. All of the above effects of D-glyceraldehyde were also observed in response to L-glyceraldehyde. The changes in membrane potential and intracellular pH (pHi) caused by D-glyceraldehyde were unaffected by the glycolytic inhibitor iodoacetate, by K+-channel blockers (tolbutamide and tetraethylammonium), or by inhibitors of the transport of lactate (alpha-fluorocinnamate), alanine (methylaminoisobutyrate) or glucose (phloretin, phlorrizin). The glyceraldehyde-induced depolarisation and acidification were also observed in the absence of extracellular Ca2+ or Na+. The increase in [Ca2+]i evoked by D-glyceraldehyde was reversed by removal of Ca2+ from the medium. The formation of lactate by HIT-T15 cells was not significantly increased by addition of 10 mM D-glyceraldehyde or L-glyceraldehyde. In contrast, 10 mM glucose caused an approximately fourfold rise in lactate production. The oxidation of D-glyceraldehyde by HIT-T15 cells was also extremely modest compared to glucose oxidation by these cells. These results suggest that the stimulation of HIT-T15 cells by either D-glyceraldehyde of L-glyceraldehyde does not require metabolism of the triose within the cell and may not involve closure of nucleotide-sensitive K+ channels. We propose that the electrogenic transport of glyceraldehyde across the plasma membrane, possibly via H+ cotransport, might lead to depolarisation and hence to Ca2+ entry into the cell. [ABSTRACT FROM AUTHOR]

Objective To determine whether the modified Beckman-Coulter 2nd-generation (Gen II) antimüllerian hormone (AMH) assay (Gen IIm) provides more consistent results following storage at room temperature and on dilution than the original Gen II assay, to compare AMH results from the modified assay with those obtained from the original assay, and to assess the relationship between new AMH values and the antral follicle count (AFC). Design Cohort. Setting Hospital fertility clinic. Patient(s) A total of 678 consecutive women (21–46 years old) investigated for subfertility. Intervention(s) None. Main Outcome Measure(s) AMH was measured by means of the Gen IIm assay protocol in women with known AFC. AMH values were obtained on a subset of serum samples by means of both original and modified assays. Result(s) Specimens analyzed by Gen IIm exhibited a proportional AMH response on dilution, and AMH values decreased by an average of 12.1% after 7 days at room temperature, in contrast to the steady increase seen with the use of the original Gen II assay. Gen IIm assay values were, on average, 51.4% higher than Gen II values. Population analysis suggested a conversion factor of 1.35 (95% CI 1.23–1.47) between the Gen IIm and historical data obtained for the Diagnostic Systems Laboratories AMH assay. The relationship between the Gen IIm AMH measurement and AFC was adequately represented by a linear function. Conclusion(s) The Gen IIm assay gave more reliable AMH results on sample dilution and storage than the original Gen II protocol. Findings obtained with the use of the original Gen II ELISA method should be treated with caution. [ABSTRACT FROM AUTHOR]

Electrical and secretory activity in the pancreatic β-cell can be elicited by hypotonic cell swelling, due largely to activation of a volume-regulated anion channel (VRAC) leading to depolarisation and electrical activity. However, β-cell responses to cell shrinkage are less well characterised. The present study has examined the effects of osmotic cell shrinkage on rat pancreatic β-cells. Electrical activity and whole-cell current were studied in isolated β-cells using the perforated patch and conventional whole-cell recording techniques. Insulin release was measured using intact islets by radioimmunoassay. Exposure to a 33% hypertonic bath solution resulted in an initial depolarisation and a period of electrical activity. In several cases, this depolarisation was transient and was followed by a hyperpolarisation. A similar pattern was observed with insulin release. In voltage-clamp experiments, osmotic shrinkage resulted in activation of a non-selective cation channel (NSCC) sensitive to inhibition by flufenamic acid and Gd3+. It is suggested that activation of this NSCC is responsible for the depolarisation evoked by hypertonic media. The secondary hyperpolarisation is likely to be the result of inhibition of VRAC activity. These opposing ionic effects could underlie the biphasic effect on insulin release following exposure to hypertonic media.

Background/aims: Pancreatic beta-cell function is influenced by changes in cell volume. Such volume changes depend on water permeability of the plasma membrane, conferred in part by aquaporins. Islet cells express aquaporin 7 (AQP7), which is permeable to urea and glycerol in addition to water. We therefore investigated the effects of glycerol and urea on rat pancreatic beta-cell function., Methods: Electrical activity and whole-cell current were studied using the perforated patch technique. Cell volume was measured by video-imaging and insulin release by radioimmunoassay. Aquaporin 7 expression was studied by RT-PCR, Western blot and double fluorescent immunolabelling., Results: The isosmotic addition of glycerol and urea resulted in depolarization of the plasma membrane and electrical activity, accompanied by beta-cell swelling, activation of the volume-regulated anion channel (VRAC) and insulin release. However, the effects of glycerol, in contrast to urea, persisted throughout exposure to the osmolyte. Glycerol also caused beta-cell activation when added hyperosmotically. A non-metabolizable glycerol analogue had comparable effects to urea on beta-cells. The expression of AQP7 was demonstrated in rat beta-cells., Conclusion: Glycerol and urea can activate beta-cells via their rapid uptake across the beta-cell plasma membrane, possibly via AQP7. This results in cell swelling, VRAC activation, electrical activity and insulin release. Glycerol appears to exert an additional effect, possibly related to its intracellular metabolism., (Copyright 2009 S. Karger AG, Basel.)

Objective: Women with systemic lupus erythematosus (SLE) have increased risk of coronary heart disease (CHD) that is not fully explained by the classic CHD risk factors. Insulin resistance is an established risk factor for CHD in the general population. We compared insulin secretion and sensitivity in patients with SLE and healthy controls, and assessed the prevalence of the metabolic syndrome in women with SLE and its relation to circulating oxidized low density lipoprotein (ox-LDL)., Methods: Fasting insulin, glucose, and lipid profiles were measured in nondiabetic women with SLE (>or= 4 revised 1997 criteria) not undergoing antimalarial therapy (n = 44), and in age matched controls recruited from the hospital staff and the local community (n = 45). Using the Homeostatic Model Assessment equations, insulin sensitivity (HOMA-S) and pancreatic beta cell function (HOMA-B) were calculated from fasting insulin and glucose. The metabolic syndrome, defined according to the Adult Treatment Panel (ATP III) criteria, was determined in a consecutive series of 61 women with SLE., Results: Patients with SLE had significantly higher fasting insulin [median (range) 10 (2.8-38) vs 6.6 (3.1-26) mU/l; p < 0.01], higher pancreatic beta cell function (HOMA-B) [165 (54-1567) vs 111 (28-653); p < 0.01], and lower insulin sensitivity (HOMA-S) [0.46 (0.09-1.9) vs 0.73 (0.16-1.3); p < 0.01]. SLE patients also had significantly higher triglycerides (p < 0.01) and lower high density lipoprotein cholesterol (p < 0.01) than controls. HOMA-S did not correlate with disease activity or steroid therapy, but was associated with components of the insulin resistance syndrome. HOMA-S showed a significant negative correlation with levels of ox-LDL in patients, but not in controls. Eleven (18%) patients had the metabolic syndrome. Again, this was not related to current steroid therapy. SLE patients with the metabolic syndrome had no difference in LDL, but had significantly higher levels of ox-LDL., Conclusion: Nondiabetic patients with SLE have evidence of significant decrease in sensitivity to insulin, and overall this population has a high prevalence of the metabolic syndrome (18%). Insulin resistance in the context of SLE was not strongly related to current or recent steroid therapy; it was, however, associated with higher levels of ox-LDL. Insulin resistance may therefore represent an additional CHD risk factor in patients with SLE.

The use of antipsychotic drugs is known to be associated with a number of adverse metabolic side effects, including diabetes mellitus. These side effects could be, at least in part, the result of impaired islet cell function, although the underlying mechanisms are unknown. We have studied the effects of the atypical antipsychotic clozapine and of the conventional drug haloperidol on electrical and secretory activity in rat pancreatic beta-cells. At a low glucose concentration (4mM), clozapine (5microM) had little or no effect on membrane potential. However, at a stimulatory glucose concentration (16mM), clozapine was found to hyperpolarize the cell membrane potential, resulting in a complete inhibition of electrical activity. In contrast, haloperidol (5microM) was found to cause a marked depolarization of the membrane potential in the presence of both low and high concentrations of glucose. Clozapine and haloperidol were found, respectively, to increase and decrease-cell input conductance, an index of K(+) permeability. Single channel recordings indicated that changes in K(ATP) channel activity contributed towards these effects. Neither clozapine nor haloperidol affected basal insulin release, although clozapine inhibited glucose-induced insulin release. It is concluded that clozapine and haloperidol exert contrasting actions on electrical activity in rat pancreatic -cells as a result of opposing effects on K(+) permeability. These findings may relate to the increased incidence of diabetes associated with clozapine treatment.

We have investigated the effects of the ethacrynic acid derivative 4-(2-butyl-6,7-dichloro-2-cyclopentyl-indan-1-on-5-yl) oxobutyric acid (DCPIB), an inhibitor of the volume-sensitive anion channel (VSAC), on electrical activity and insulin secretion in rat pancreatic beta-cells. DCPIB inhibited whole-cell VSAC currents in beta-cells with IC50 values of 2.2 and 1.7 microM for inhibition of outward and inward currents, respectively. DCPIB also inhibited the VSAC at the single channel level in cells activated by glucose. In intact cells, DCPIB caused a net increase in beta-cell input conductance and evoked an outward current that was sensitive to inhibition by tolbutamide, suggesting KATP channel activation. However, no KATP channel activation was evident under conventional whole-cell conditions, suggesting that the drug might activate the channel in intact cells via an indirect mechanism, possibly involving nutrient metabolism. DCPIB suppressed glucose-induced electrical activity in beta-cells, hyperpolarised the cell membrane potential at a substimulatory glucose concentration and prevented depolarisation when the glucose concentration was raised to stimulatory levels. The suppression of electrical activity by DCPIB was associated with a marked inhibition of glucose-stimulated insulin release from intact islets. It is concluded that DCPIB inhibits electrical and secretory activity in the beta-cell as a combined result of a reciprocal inhibition of VSAC and activation of KATP channel activities, thus producing a marked hyperpolarisation of the beta-cell membrane potential.