Biomedical subjects

A Salehi

Publications and source records attributed to A Salehi.

At least 19 recordsLinked to original sources

PubMed2006

Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells.

AIMS/HYPOTHESIS: The mechanisms by which glucose regulates glucagon release are poorly understood. The present study aimed to clarify the direct effects of glucose on the glucagon-releasing alpha cells and those effects mediated by paracrine islet factors. MATERIALS AND METHODS: Glucagon, insulin and somatostatin release were measured from incubated mouse pancreatic islets and the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) recorded in isolated mouse alpha cells. RESULTS: Glucose inhibited glucagon release with maximal effect at 7 mmol/l. Since this concentration corresponded to threshold stimulation of insulin secretion, it is unlikely that inhibition of glucagon secretion is mediated by beta cell factors. Although somatostatin secretion data seemed consistent with a role of this hormone in glucose-inhibited glucagon release, a somatostatin receptor type 2 antagonist stimulated glucagon release without diminishing the inhibitory effect of glucose. In islets exposed to tolbutamide plus 8 mmol/l K(+), glucose inhibited glucagon secretion without stimulating the release of insulin and somatostatin, indicating a direct inhibitory effect on the alpha cells that was independent of ATP-sensitive K(+) channels. Glucose lowered [Ca(2+)](i) of individual alpha cells independently of somatostatin and beta cell factors (insulin, Zn(2+) and gamma-aminobutyric acid). Glucose suppression of glucagon release was prevented by inhibitors of the sarco(endo)plasmic reticulum Ca(2+)-ATPase, which abolished the [Ca(2+)](i)-lowering effect of glucose on isolated alpha cells. CONCLUSIONS/INTERPRETATION: Beta cell factors or somatostatin do not seem to mediate glucose inhibition of glucagon secretion. We instead propose that glucose has a direct inhibitory effect on mouse alpha cells by suppressing a depolarising Ca(2+) store-operated current.

Animals↗

PubMed2005

Free fatty acid receptor 1 (FFA(1)R/GPR40) and its involvement in fatty-acid-stimulated insulin secretion.

Free fatty acids (FFA) have generally been proposed to regulate pancreatic insulin release by an intracellular mechanism involving inhibition of CPT-1. The recently de-orphanized G-protein coupled receptor, FFA(1)R/GPR40, has been shown to be essential for fatty-acid-stimulated insulin release in MIN6 mouse insulinoma cells. The CPT-1 inhibitor, 2-bromo palmitate (2BrP), was investigated for its ability to interact with mouse FFA(1)R/GPR40. It was found to inhibit phosphatidyl inositol hydrolysis induced by linoleic acid (LA) (100 muM in all experiments) in HEK293 cells transfected with FFA(1)R/GPR40 and in the MIN6 subclone, MIN6c4. 2BrP also inhibited LA-stimulated insulin release from mouse pancreatic islets. Mouse islets were subjected to antisense intervention by treatment with a FFA(1)R/GPR40-specific morpholino oligonucleotide for 48 h. Antisense treatment of islets suppressed LA-stimulated insulin release by 50% and by almost 100% when islets were pretreated with LA for 30 min before applying the antisense. Antisense treatment had no effect on tolbutamide-stimulated insulin release. Confocal microscopy using an FFA(1)R/GPR40-specific antibody revealed receptor expression largely localized to the plasma membrane of insulin-producing cells. Pretreating the islets with LA for 30 min followed by antisense oligonucleotide treatment for 48 h reduced the FFA(1)R/GPR40 immunoreactivity to background levels. The results demonstrate that FFA(1)R/GPR40 is inhibited by the CPT-1 inhibitor, 2BrP, and confirm that FFA(1)R/GPR40 is indeed necessary, at least in part, for fatty-acid-stimulated insulin release.

Animals↗

PubMed2005

Chitinase gene transformation through Agrobacteriumand its explanation in soybean in order to induce resistance to root rot caused by Rhizoctonia solani.

Chitinase gene (chi) of bean which has been cloned in recombinant binary plasmid vector, pBI121 with 35s promoter of Cauliflower mosaic virus (CaMV), were used for transformation of soybean using strain LBA4404 of Agrobacterium. The plasmid contained nptII gene that is a resistant gene to kanomycin as selector marker and Gus gene as reporter. Cotyledon explants of Williams and Clark cultivars were inoculated by Agrobacterium suspension with pBI121 and were cultured in regeneration medium. After complete regeneration of explants to seedling in B5 medium amended with kanomycin, polymerase chain reaction analysis were conducted to ensure conjugation of nptII, Gus, CHN genes in transformants seedling of soybean. Results showed that some lines of soybean contained Gus and CHN genes. More ever, chitinase activity in leaf extract of transformed soybean lines was significantly more than untransformed soybean, exception one sample. Bioassay of chitinase activity of transgenic lines on in vitro condition prevented mycelial growth of Rhizoctonia solani in comparison with untransformed control leaf extract.

Chitinases↗

PubMed2004

Alzheimer's disease and NGF signaling.

Age-related degeneration of basal forebrain cholinergic neurons (BFCNs) occurs early and contributes significantly to cognitive decline in Alzheimer's disease (AD). Proper function and morphology of BFCNs depends on the supply of nerve growth factor (NGF) from the cortex and the hippocampus. A large number of experiments have shown that decreased supply of NGF at the level of BFCN cell bodies leads to loss of neuronal markers and shrinkage, mimicking what is observed in AD. The delivery of sufficient amounts of NGF signal to BFCN cell bodies depends on the effective participation of several factors including sufficient synthesis and release of NGF, adequate synthesis and expression of NGF receptors by BFCNs, normal signaling and retrograde transport of NGF-receptor complex, and finally effective induction of gene expression by NGF. In the past few years it has become clear that decreased amounts of NGF at the level of BFCN cell bodies is largely due to failed retrograde transport rather than decreased synthesis, binding or expression of NGF receptors in the BFCN terminals. We will discuss in vivo evidence supporting decreased retrograde transport of NGF in a mouse model with BFCN degeneration, and will attempt to match these findings with our studies in postmortem human AD brain. We will speculate about the possible mechanisms of failed NGF retrograde transport and its relationship to AD pathology.

Alzheimer Disease↗

PubMed2003

Total parenteral nutrition-stimulated activity of inducible nitric oxide synthase in rat pancreatic islets is suppressed by glucagon-like peptide-1.

Long-term total parenteral nutrition (TPN) is associated with elevated plasma lipids and a marked decrease of glucose-stimulated insulin release. Since nitric oxide (NO) has been shown to modulate negatively the insulin response to glucose, we investigated the influence of TPN-treatment on isoforms of islet NO-synthase (NOS) activities in relation to the effect of glucagon-like peptide-1 (GLP-1), a known activator of glucose-stimulated insulin release. Isolated islets from TPN rats incubated at basal glucose (1 mmol/l) showed a modestly increased insulin secretion accompanied by an enhanced accumulation of islet cAMP and cGMP. In contrast, TPN islets incubated at high glucose (16.7 mmol/l) displayed an impaired insulin secretion and a strong suppression of islet cAMP content. Moreover, islet inducible NOS (iNOS) as well as islet cGMP content were greatly increased in these TPN islets. A dose-response study of GLP-1 with glucose-stimulated islets showed that GLP-1 could overcome and completely restore the impaired insulin release in TPN islets, bringing about a marked increase in islet cAMP accumulation concomitant with heavy suppression of both glucose-stimulated increase in islet cGMP content and the activities of constitutive NOS (cNOS) and iNOS. These effects of GLP-1 were mimicked by dibutyryl-cAMP. The present results show that the impaired insulin response of glucose-stimulated insulin release seen after TPN treatment is normalized by GLP-1. This beneficial effect of GLP-1 is most probably exerted by a cAMP-induced suppression of both iNOS and cNOS activities in these TPN islets.

Animals↗

PubMed2001

Somatostatin inhibits exocytosis in rat pancreatic alpha-cells by G(i2)-dependent activation of calcineurin and depriming of secretory granules.

1. Measurements of cell capacitance were used to investigate the molecular mechanisms by which somatostatin inhibits Ca(2+)-induced exocytosis in single rat glucagon-secreting pancreatic alpha-cells. 2. Somatostatin decreased the exocytotic responses elicited by voltage-clamp depolarisations by 80 % in the presence of cyclic AMP-elevating agents such as isoprenaline and forskolin. Inhibition was time dependent and half-maximal within 22 s. 3. The inhibitory action of somatostatin was concentration dependent with an IC(50) of 68 nM and prevented by pretreatment of the cells with pertussis toxin. The latter effect was mimicked by intracellular dialysis with specific antibodies to G(i1/2) and by antisense oligonucleotides against G proteins of the subtype G(i2). 4. Somatostatin lacked inhibitory action when applied in the absence of forskolin or in the presence of the L-type Ca(2+) channel blocker nifedipine. The size of the omega-conotoxin-sensitive and forskolin-independent component of exocytosis was limited to 60 fF. By contrast, somatostatin abolished L-type Ca(2+) channel-dependent exocytosis in alpha-cells exposed to forskolin. The magnitude of the latter pool amounted to 230 fF. 5. The inhibitory effect of somatostatin on exocytosis was mediated by activation of the serine/threonine protein phosphatase calcineurin and was prevented by pretreatment with cyclosporin A and deltamethrin or intracellularly applied calcineurin autoinhibitory peptide. Experiments using the stable ATP analogue AMP-PCP indicate that somatostatin acts by depriming of granules. 6. We propose that somatostatin receptors associate with L-type Ca(2+) channels and couple to G(i2) proteins leading to a localised activation of calcineurin and depriming of secretory granules situated close to the L-type Ca(2+) channels.

Adenosine Triphosphate↗

PubMed2001

Failed retrograde transport of NGF in a mouse model of Down's syndrome: reversal of cholinergic neurodegenerative phenotypes following NGF infusion.

Age-related degeneration of basal forebrain cholinergic neurons (BFCNs) contributes to cognitive decline in Alzheimer's disease and Down's syndrome. With aging, the partial trisomy 16 (Ts65Dn) mouse model of Down's syndrome exhibited reductions in BFCN size and number and regressive changes in the hippocampal terminal fields of these neurons with respect to diploid controls. The changes were associated with significantly impaired retrograde transport of nerve growth factor (NGF) from the hippocampus to the basal forebrain. Intracerebroventricular NGF infusion reversed well established abnormalities in BFCN size and number and restored the deficit in cholinergic innervation. The findings are evidence that even BFCNs chronically deprived of endogenous NGF respond to an intervention that compensates for defective retrograde transport. We suggest that age-related cholinergic neurodegeneration may be a treatable disorder of failed retrograde NGF signaling.

Aging↗

PubMed2001

TPN-evoked dysfunction of islet lysosomal activity mediates impairment of glucose-stimulated insulin release.

We examined the relation between nutrient-stimulated insulin secretion and the islet lysosome acid glucan-1,4-alpha-glucosidase system in rats undergoing total parenteral nutrition (TPN). During TPN treatment, serum glucose was normal, but free fatty acids, triglycerides, and cholesterol were elevated. Islets from TPN-infused rats showed increased basal insulin release, a normal insulin response to cholinergic stimulation but a greatly impaired response when stimulated by glucose or alpha-ketoisocaproic acid. This impairment of glucose-stimulated insulin release was only slightly ameliorated by the carnitine palmitoyltransferase 1 inhibitor etomoxir. However, in parallel with the impaired insulin response to glucose, islets from TPN-infused animals displayed reduced activities of islet lysosomal enzymes including the acid glucan-1,4-alpha-glucosidase, a putative key enzyme in nutrient-stimulated insulin release. By comparison, the same lysosomal enzymes were increased in liver tissue. Furthermore, in intact control islets, the pseudotetrasaccharide acarbose, a selective inhibitor of acid alpha-glucosidehydrolases, dose dependently suppressed islet acid glucan-1,4-alpha-glucosidase and acid alpha-glucosidase activities in parallel with an inhibitory action on glucose-stimulated insulin secretion. By contrast, when incubated with intact TPN islets, acarbose had no effect on either enzyme activity or glucose-induced insulin release. Moreover, when acarbose was added directly to TPN islet homogenates, the dose-response effect on the catalytic activity of the acid alpha-glucosidehydrolases was shifted to the right compared with control homogenates. We suggest that a general dysfunction of the islet lysosomal/vacuolar system and reduced catalytic activities of acid glucan-1,4-alpha-glucosidase and acid alpha-glucosidase may be important defects behind the impairment of the transduction mechanisms for nutrient-stimulated insulin release in islets from TPN-infused rats.

Acarbose↗

PubMed2001

Total parenteral nutrition modulates hormone release by stimulating expression and activity of inducible nitric oxide synthase in rat pancreatic islets.

The expression and activities of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) in relation to insulin and glucagon secretory mechanisms were investigated in islets isolated from rats subjected to total parenteral nutrition (TPN) for 10 d. TPN is known to result in significantly increased levels of plasma lipids during the infusion time. In comparison with islets from freely fed control rats, islets taken from TPN rats at d 10 displayed a marked decrease in glucose-stimulated insulin release (4.65 +/- 0.45 ng/[islet x h] vs 10.25 +/- 0.65 for controls) (p < 0.001) accompanied by a strong iNOS activity (18.3 +/- 1.1 pmol of NO/[min x mg of protein]) and a modestly reduced cNOS activity (11.3 +/- 3.2 pmol of NO/[min x mg of protein] vs 17.7 +/- 1.7 for controls) (p < 0.01). Similarly, Western blots showed the expression of iNOS protein as well as a significant reduction in cNOS protein in islets from TPN-treated rats. The enhanced NO production, which is known to inhibit glucose-stimulated insulin release, was manifested as a strong increase in the cyclic guanosine 5'-monophosphate content in the islets of TPN-treated rats (1586 +/- 40 amol/islet vs 695 +/- 64 [p < 0.001] for controls). Moreover, the content of cyclic adenosine monophosphate (cAMP) was greatly increased in the TPN islets (80.4 +/- 2.1 fmol/islet vs 42.6 +/- 2.6 [p < 0.001] for controls). The decrease in glucose-stimulated insulin release was associated with an increase in the activity of the secretory pathway regulated by the cAMP system in the islets of TPN-treated rats, since the release of insulin stimulated by the phosphodiesterase inhibitor isobutylmethylxanthine was greatly increased both in vivo after iv injection and after in vitro incubation of isolated islets. By contrast, the release of glucagon was clearly reduced in islets taken from TPN-treated rats (33.5 +/- 1.5 pg/[islet x h] vs 45.5 +/- 2.2 for controls) (p < 0.01) when islets were incubated at low glucose (1.0 mmol/L). The data show that long-term TPN treatment in rats brings about impairment of glucose-stimulated insulin release, that might be explained by iNOS expression and a marked iNOS-derived NO production in the beta-cells. The release of glucagon, on the other hand, is probably decreased by a direct "nutrient effect" of the enhanced plasma lipids. The results also suggest that the islets of TPN-treated rats have developed compensatory insulin secretory mechanisms by increasing the activity of their beta-cell cAMP system.

1-Methyl-3-isobutylxanthine↗

PubMed2000

P75 neurotrophin receptor in the nucleus basalis of meynert in relation to age, sex, and Alzheimer's disease.

In a previous study we showed that the staining of tyrosine kinase receptors (trks), which are high-affinity neurotrophin receptors (NTRs), is strongly diminished in the nucleus basalis of Meynert (NBM) of Alzheimer's disease (AD) patients, which may explain the lack of effect of NGF therapy in AD patients so far. Since the literature regarding the expression of low-affinity NTRs was rather controversial, the aim of the present study was to examine (i) possible changes in the staining of low-affinity NTRs, i.e., p75 in the human NBM, an area that is severely affected in AD; and (ii) alterations of these receptors in relation to risk factors for AD, e. g., age, sex, and menopause. Brain material of 31 controls and 30 AD patients was obtained at autopsy, embedded in paraffin, and stained immunocytochemically. Using an image analysis system, we quantified p75 immunoreactivity in both cell bodies and fibers at the level of the NBM. Our results showed a significant diminishment of p75 immunoreactivity in both cell bodies and fibers of NBM neurons in AD. We did not find any relationship between age or sex and the expression of p75 receptor in cell bodies. However, there was a clearly positive relationship between age and fiber staining in AD patients which suggests the occurrence of a p75 transport disorder as an early event in the process of AD. These observations and the earlier reported decreased staining of trk receptors show that degeneration of NBM neurons in AD is associated with a decreased neurotrophin responsiveness of NBM neurons in AD and that therapeutic strategies should be directed toward upregulation of receptors or facilitation of transport before an effect of neurotrophins in AD may be expected.

Age Factors↗

PubMed2000

Sex- and age-related P75 neurotrophin receptor expression in the human supraoptic nucleus.

The human supraoptic nucleus (SON) is the main production site of plasma vasopressin. Previously, using the Golgi apparatus and cell size as measures for neuronal metabolic activity, an activation of vasopressinergic neurons was found during ageing in the human SON in women but not in men. We hypothesized that the low-affinity neurotrophin receptor p75 (p75(NTR)) might be involved in the mechanism of activation of vasopressin neurons in postmenopausal women, since this receptor was found to be expressed in the SON neurons of aged individuals, and because p75(NTR) expression was shown to be suppressed by estrogens. Therefore, we investigated whether p75(NTR) immunoreactivity in the SON neurons was age- and sex-dependent. For this purpose, we studied paraffin sections of the SON in 32 postmortem brains of control patients ranging in age from 29 to 94 years with an anti-p75(NTR) antibody and determined the area of p75(NTR) immunoreactivity per neuron using an image analysis system. To study whether the p75(NTR) might also participate in the activation of SON neurons, we related Golgi apparatus size to the area of p75(NTR) immunoreactivity per cell in the same patients. We found that the area of p75(NTR) immunoreactivity per cell correlated indeed significantly with age and with Golgi apparatus size only in women but not in men. Therefore, our results suggest that p75(NTR) is involved in postmenopausal activation of vasopressinergic neurons in the human SON.

Adult↗

PubMed2000

Nitric oxide, islet acid glucan-1,4-alpha-glucosidase activity and nutrient-stimulated insulin secretion.

The mechanism of nutrient-evoked insulin release is clearly complex. One part of that mechanism is postulated to be the activation of the glycogenolytic enzyme acid glucan-1,4-alpha-glucosidase. As nitric oxide (NO) has been found to be a potent inhibitor of glucose-stimulated insulin secretion, we have now investigated a possible influence of exogenous NO and inhibition of endogenous NO production on islet acid glucan-1,4-alpha-glucosidase activity in relation to insulin release stimulated by glucose and l-arginine. In isolated islets, NO derived from the intracellular NO donor hydroxylamine inhibited the activation of acid glucan-1, 4-alpha-glucosidase and its isoform acid alpha-glucosidase in parallel with inhibition of glucose-stimulated insulin release. In comparison, other lysosomal enzymes were largely unaffected. Similarly, the spontaneous NO donor sodium nitroprusside, as well as NO gas, when added to islet homogenates, suppressed the activities of these acid alpha-glucosidehydrolases and, to a lesser extent, the activities of other lysosomal enzymes. Finally, in the presence of the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester, insulin release from isolated islets stimulated by glucose or l-arginine was markedly potentiated in parallel with an accompanying increase in the activities of acid glucan-1,4-alpha-glucosidase and acid alpha-glucosidase. Other lysosomal enzymes and neutral alpha-glucosidase were not influenced. We propose that an important inhibitory effect of NO on the insulin secretory processes stimulated by glucose and l-arginine is exerted via inactivation of islet acid glucan-1,4-alpha-glucosidase, a putative key enzyme in nutrient-stimulated insulin release.

Animals↗

PubMed1999

Gastrectomy induces impaired insulin and glucagon secretion: evidence for a gastro-insular axis in mice.

1. Mice were subjected to gastrectomy (GX) or food deprivation (24 h). The release of insulin and glucagon in response to different secretagogues was monitored in vivo and in isolated islets 3-4 weeks after surgery. 2. GX animals responded to glucose with an impaired glucose tolerance and a poor increase in plasma insulin. Islets from GX or food-deprived mice displayed impaired insulin release to high glucose and enhanced glucagon release at low glucose. 3. After GX the insulinogenic index, Delta insulin (microU ml-1)/Delta glucose (mg ml-1), was suppressed by 65% after oral glucose and by 59% after i.v. glucose. The integrated insulin response after oral glucose was reduced by 90% in GX mice. After i.v. glucose the reduction was 67%. 4. Carbachol-induced insulin release in vivo was reduced after food deprivation and exaggerated after GX. Carbachol-stimulated glucagon secretion was suppressed after GX and after food deprivation. A similar pattern was found in vitro. 5. Cyclic AMP activation (by the phosphodiesterase inhibitor isobutylmethylxanthine or the adenylate cyclase stimulator forskolin) induced a greater insulin response in GX or food-deprived mice than in sham-operated, fed mice. A similar pattern was found in vitro. The glucagon response was enhanced in vitro but not in vivo. 6. Crude extracts of rat oxyntic mucosa enhanced basal as well as glucose-induced insulin release from isolated islets, whereas glucagon release was markedly inhibited. The effects were dose dependent, the inhibition of glucagon release being achieved at lower concentrations than the potentiation of glucose-induced insulin release. The active principle was inactivated by incubation with trypsin or leucine aminopeptidase. 7. The data suggest that a circulating agent, probably a peptide, from gastric oxyntic mucosa stimulates glucose-induced insulin secretion. It also suppresses glucagon secretion. The GX-evoked impairment of the insulin (and glucagon) response to glucose is partly compensated for by an enhanced insulin response to cholinergic and/or cyclic AMP activation.

1-Methyl-3-isobutylxanthine↗

PubMed1999

Diminished neuronal metabolic activity in Alzheimer's disease. Review article.

An increasing number of studies have appeared in the literature suggesting that Alzheimer's disease (AD) is a hypometabolic brain disorder. Decreased metabolism in AD has been revealed by a variety of in vivo and postmortem methods and techniques including positron emission tomography and glucose metabolism. We used the size of the Golgi apparatus (GA) and cell profile area as indicators of neuronal activity in postmortem material. Using an antibody against MG-160, a sialoglycoprotein of the medial cisternae of the GA, we were able to visualize and quantify the GA area. In a series of experiments, we tried to relate neuronal metabolism to different hallmarks of AD, i.e. plaques and tangles, and also to genetic risk factors for AD like age and (apolipoprotein E) ApoE polymorphism. Our results showed that in AD there is indeed a clear reduction in brain metabolism in several severely affected brain regions including the nucleus basalis of Meynert (NBM), the CA1 area of the hippocampus and the hypothalamic tuberomamillary nucleus. However, the reduction in neuronal activity did not seem to be caused by the presence of neuropathological hallmarks of AD, i.e. plaques and tangles. There was, however, a clear relationship between the presence of ApoE epsilon4 alleles and a decrease in GA size. Our data suggest that decreased neuronal activity and neuropathological hallmarks of AD, such as plaques and tangles, are basically independent phenomena. Moreover, ApoE epsilon4 may participate in the pathogenesis of AD by decreasing neuronal metabolism. The main implication of these findings is that therapeutic strategies in AD should be focussed on reactivation of neuronal metabolism.

Age Factors↗

PubMed1999

Activity of vasopressinergic neurones of the human supraoptic nucleus is age- and sex-dependent.

In the human hypothalamus, arginine-vasopressin (AVP) is produced for a major part by the neurones of the supraoptic nucleus (SON). Since plasma AVP levels in men were reported to be higher than those of women and we did not find a sex difference in the neurone number, a higher vasopressinergic neurone activity was supposed to be present in the SON of men. Therefore we studied the size of the Golgi-apparatus (GA), which has been demonstrated previously to be a sensitive parameter for protein synthetic ability of neurones, in 15 men and 17 women ranging in age from 29 to 94 years. A polyclonal antibody against immunoaffinity purified MG-160, a sialoglycoprotein of the medial cisternae of the GA was applied on paraffin-embedded sections containing the dorsolateral SON (dl-SON) from which 90-95% of neurones are vasopressinergic. SON areas that contain oxytocin (OT) cells were excluded on the basis of adjacent sections stained with a monoclonal antibody against OT. By means of an image analysis system the size of the GA and the cellular profile area were determined in dl-SON neurones with a nucleolus. Our results showed indeed an age-dependent sex difference in the size of the GA that appeared to be twice as large in young men (< or = 50 years old) than in young women of the same age. The size of the GA increased with age in women but not in men. In addition, the mean cell profile area, another measure for neuronal activity, was significantly larger in young men than in young women and was in old women larger than in young women. In conclusion, these data show the presence of a sex-dependent age-difference in the activity of vasopressinergic neurones in dl-SON which may relate to differences in AVP and sex hormone levels and kidney AVP receptors.

Adult↗

PubMed1999

Photoelastic analysis of stresses produced by different acetabular cups.

Porous-coated acetabular components can provide long-term biologic fixation to bone. However, the periacetabular stress patterns and mechanisms by which different types of cementless acetabular cups obtain initial stability is not clear. In the current study, periacetabular stresses produced by different cementless acetabular cup geometries were quantitated using a three-dimensional photoelastic model. The cup geometries consisted of trispiked, finned, hemispherical, and nonhemispherical (wider than a hemisphere at the periphery) geometries. The cup models were loaded incrementally in the photoelastic material to simulate periacetabular stress distributions at the time of implantation during surgery rather than under physiologic weightbearing loads. The peripheral stress distributions and their magnitudes induced by the trispiked and oversized hemispherical cups were similar, but the trispiked cup induced localized high stress regions where the spikes penetrate the bone model. The fins separated the periacetabular material into quadrants, which was associated with decreased peripheral stresses. A nonhemispherical geometry with a wider diameter at the rim than a hemisphere increased peripheral stresses more than an oversized hemispherical geometry and required less force to seat the implant. Although various cementless acetabular cups can perform well clinically, they produce different periacetabular stresses and appear to obtain initial fixation by different mechanisms.

Acetabulum↗

PubMed1999

Dysfunction of the islet lysosomal system conveys impairment of glucose-induced insulin release in the diabetic GK rat.

Accumulated evidence links an important signal involved in glucose-stimulated insulin release to the activation of the islet lysosomal glycogenolytic enzyme acid glucan-1,4-alpha-glucosidase. We have analyzed the function of the lysosomal system/lysosomal enzyme activities in pancreatic islets of young (6-8 weeks), spontaneously diabetic, GK (Goto-Kakizaki) rats and Wistar control rats in relation to glucose-induced insulin release. The insulin secretory response to glucose was markedly impaired in the GK rat, but was restored by the adenylate cyclase activator forskolin. Islet activities of classical lysosomal enzymes, e.g.. acid phosphatase, N-acetyl-beta-D-glucosaminidase, beta-glucuronidase, and cathepsin D, were reduced by 20-35% in the GK rat compared with those in Wistar controls. In contrast, the activities of the lysosomal alpha-glucosidehydrolases, i.e.. acid glucan-1,4-alpha-glucosidase and acid alpha-glucosidase, were increased by 40-50%. Neutral alpha-glucosidase (endoplasmic reticulum) was unaffected. Comparative analysis of liver tissue showed that lysosomal enzyme activities were of the same magnitude in GK and Wistar rats. Notably, in Wistar rats, the activities of acid glucan-1,4-alpha-glucosidase and acid alpha-glucosidase were approximately 15-fold higher in islets than in liver. Other lysosomal enzymes did not display such a difference. Normalization of glycemia in GK rats by phlorizin administered for 9 days did not influence either the lysosomal alpha-glucosidehydrolase activities or other lysosomal enzyme activities in GK islets. Finally, the pseudotetrasaccharide acarbose, which accumulates in the lysosomal system, inhibited acid glucan-1,4-alpha-glucosidase activity in parallel with its inhibitory action on glucose-induced insulin release in intact Wistar islets, whereas no effect was recorded for either parameter in intact GK islets. In contrast, acarbose inhibited the enzyme activity equally in islet homogenates from both GK and Wistar rats, showing that the catalytic activity of the enzyme itself in disrupted cells was unaffected. We propose that dysfunction of the islet lysosomal/vacuolar system is an important defect impairing the transduction mechanisms for glucose-induced insulin release in the GK rat.

Acarbose↗

PubMed1999

Islet constitutive nitric oxide synthase and glucose regulation of insulin release in mice.

We have studied, by a combined in vitro and in vivo approach, the relation between the inhibitory action of N(G)-nitro-l-arginine methyl ester (L-NAME), a selective inhibitor of nitric oxide synthase (NOS), on the activity of islet constitutive NOS (cNOS) and glucose regulation of islet hormone release in mice. The cNOS activity in islets incubated in vitro at 20 mM glucose was not appreciably affected by 0.05 or 0.5 mM L-NAME, but was greatly suppressed (-60%) by 5 mM L-NAME. Similarly, glucose-stimulated insulin release was unaffected by the lower concentrations of L-NAME but greatly enhanced in the presence of 5 mM of the NOS inhibitor. In incubated islets inhibition of cNOS activity resulted in a modestly enhanced insulin release in the absence of glucose, did not display any effect at physiological or subphysiological glucose concentrations, but resulted in a markedly potentiated insulin release at hyperglycaemic glucose concentrations. In the absence of glucose, glucagon secretion was suppressed by L-NAME. The dynamics of glucose-induced insulin release and (45)Ca(2+) efflux from perifused islets revealed that L-NAME caused an immediate potentiation of insulin release, and a slight increase in (45)Ca(2+) efflux. In islets depolarized with 30 mM K(+) in the presence of the K(+)(ATP) channel opener, diazoxide, L-NAME still greatly potentiated glucose-induced insulin release. Finally, an i.v. injection of glucose to mice pretreated with L-NAME was followed by a markedly potentiated insulin response, and an improved glucose tolerance. In accordance, islets isolated directly ex vivo after L-NAME injection displayed a markedly reduced cNOS activity. In conclusion, we have shown here, for the first time, that biochemically verified suppression of islet cNOS activity, induced by the NOS inhibitor L-NAME, is accompanied by a marked potentiation of glucose-stimulated insulin release both in vitro and in vivo. The major action of NO to inhibit glucose-induced insulin release is probably not primarily linked to changes in Ca(2+) fluxes and is exerted mainly independently of membrane depolarization events.

Analysis of Variance↗