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Biomedical subjects

S L Howell

Publications and source records attributed to S L Howell.

At least 19 recordsLinked to original sources
PubMed1995

Protein phosphorylation in the regulation of insulin secretion: the use of site-directed inhibitory peptides in electrically permeabilised islets of Langerhans.

We have used electrically permeabilised rat islets of Langerhans to investigate the role of protein phosphorylation in the regulation of insulin secretion using pseudosubstrate inhibitory peptides for cyclic AMP-dependent protein kinase (PKA) and for protein kinase C (PKC). The protein kinase inhibitor (PKI) peptide, PKI(6-22), completely inhibited the effects of cyclic AMP on islet PKA activity in vitro, on endogenous protein phosphorylation and on insulin secretion. This peptide had no significant effect on islet PKC activity in vitro, on Ca(2+)-induced protein phosphorylation and on secretory responses to Ca2+ or to the PKC activator, 4 beta-phorbol myristate acetate (PMA). The PKC pseudosubstrate inhibitory peptide, PKC(19-36), caused a marked inhibition of islet PKC activity in vitro and inhibite PMA-induced insulin secretion without affecting secretory responses to cyclic AMP and Ca2+. These results demonstrate that PKA- and PKC-induced protein phosphorylation is obligatory for cyclic AMP- and PMA-stimulated insulin secretion, respectively, and suggest that there is little "crosstalk" between the response elements of the secretory pathways to the different second messengers, at least after the generation of the messengers within the beta-cells.

Adenosine Triphosphate↗
PubMed1995

Insulin secretion from islets of GK rats is not impaired after energy generating steps.

Insulin secretory responses of intact and electrically permeabilised islets of Goto-Kakizaki (GK) rats, a novel model of non-insulin dependent diabetes mellitus, and Wistar (control) rats were compared to investigate the mechanism of the impairment of insulin secretion from pancreatic islets of GK rats. Insulin secretion from intact islets in response to glucose, glyceraldehyde, succinate monomethylester and tetramethyl p-phenylenediamine, which reduces cytochrome c directly, was significantly impaired in GK rats compared to control rats (P < 0.05, P < 0.01, P < 0.05 and P < 0.05, respectively). However, Ca(2+)-induced insulin release from electrically permeabilised islets of GK rats was higher than that of control rats. Moreover, insulin secretion from intact islets in response to 50 mM KCl, which depolarises islet cells, was not impaired in GK rats. These results indicate that insulin secretion from islets of GK rats is not impaired after energy generating steps of metabolism.

Animals↗
PubMed1995

Severity-adjusted differences in hospital utilization by gender.

Gender-based differences in hospital use may result from biological differences or may suggest problems of access to health services and quality of care. We hypothesized that there should be no difference in hospital care between men and women, given the same diagnosis. Hospitalizations were characterized by severity of illness, as this may indicate the timeliness of hospital care. Hospitalizations may be too late (with higher severity of illness) resulting in long stays and high costs, or too early (with lower severity of illness) resulting in care that could be given in alternative treatment settings. Three abdominal conditions were examined which could be misdiagnosed or confused with other diseases involving the female reproductive system: appendicitis, diverticulitis, and cholecystitis. The National Hospital Discharge Survey (NHDS) was used for analysis. Disease staging was used to assign a severity of illness indicator, ranging from stage 1 (conditions with no complications) to stage 3 (multiple site involvement, poor prognosis). For each disease, the percentage of discharges and the age-adjusted discharge rate per 1000 population was examined by stage of illness and gender. For appendectomy, there was a significantly greater percentage of men at stage 1 (lower severity) compared to women (73% versus 67%). For diverticular disease, women had higher proportions of stage 2/3 discharges than men for both medical and surgical hospitalizations. For cholecystitis, women had a greater percentage of hospitalizations at stage 1 than men, notably for surgical treatment (63% compared with 38%), although more men were admitted at stage 2 for both medical and surgical treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic Tests, Routine↗
PubMed1994

Regulation of insulin secretion: the role of second messengers.

This review summarises briefly studies performed in the last 5-6 years concerning the role of second messengers in the regulation of insulin secretion, using intact and electrically permeabilized rat islets of Langerhans. It is concluded that cyclic AMP (through protein kinase A), calcium (through calcium-calmodulin dependent protein kinases) and diacylglycerol (through protein kinase C) may be important second messengers in modulating the effects of specific secretagogues on insulin release. However, recent studies strongly suggest that neither protein kinase A nor protein kinase C are directly involved in the regulation of insulin secretion by glucose. The possible involvement of other second messengers, nitric oxide and arachidonic acid, in the regulation of secretion is also briefly reviewed.

Animals↗
PubMed1994

Natural/alternative health care practices used by women with chronic pain: findings from a grounded theory research study.

Findings from a grounded theory research study provide insights into making health care practices more beneficial for the needs and concerns of women with chronic pain. This article focuses on how healthy women advantageously used natural/alternative health care and pain management practices. The "healthiest" women primarily used self-care with a wide, holistic range of natural/alternative modalities.

Adult↗
PubMed1993

The mechanism of arachidonic acid-induced insulin secretion from rat islets of Langerhans.

The stimulation of rat pancreatic islets by glucose leads both to the secretion of insulin, and the production of arachidonic acid (AA). We have previously shown that exogenous AA can stimulate insulin secretion and that this secretion was not dependent upon extracellular Ca2+ nor upon the activation of protein kinase C. We have now demonstrated that AA-induced insulin secretion was a saturable and reversible process. AA-stimulated insulin secretion was slow in onset from intact islets but immediate from electrically permeabilized islets. In permeabilized islets AA-induced insulin secretion was not dependent on changes in intracellular Ca2+ or ATP and was not inhibited by noradrenaline. These results suggest that AA affects insulin secretion at a late stage in the exocytotic process.

Animals↗
PubMed1993

Activation of protein kinase C partially alleviates noradrenaline inhibition of insulin secretion.

The sympathetic neurotransmitter noradrenaline (NA) fully inhibited both phases of glucose-stimulated insulin secretion from rat islets of Langerhans. The secretory response to the protein kinase C (PKC) activator, 4 beta-phorbol myristate acetate (4 beta PMA), in the absence of exogenous glucose was also abolished by NA. However, at 20 mM glucose 4 beta PMA partially alleviated the inhibitory effect of NA both on insulin release and on cyclic AMP generation. Inhibition of insulin release by NA, albeit much decreased, was still observed in the presence of maximal stimulatory concentrations of both 4 beta PMA and dibutyryl cyclic AMP. The relieving effect of 4 beta PMA on the inhibition of insulin secretion by NA was not overcome by the competitive antagonist of cyclic AMP-dependent protein kinase, Rp-adenosine 3',5'-cyclic phosphorothioate. Down-regulation of islet PKC activity by overnight exposure to 4 beta PMA did not affect the inhibitory capacity of NA. These results suggest that NA inhibits insulin release independently of interaction with PKC, but that activation of this enzyme decreases the inhibitory effect of NA at stimulatory concentrations of glucose. This protective effect of 4 beta PMA could not be attributed to a decrease in NA inhibition of cyclic AMP generation.

1-Methyl-3-isobutylxanthine↗
PubMed1993

The role of protein kinase C in insulin biosynthesis.

Activation of protein kinase C (PKC) by the phorbol ester 4 beta-phorbol myristate acetate (4 beta-PMA) stimulated (pro)insulin biosynthesis in collagenase-isolated rat islets of Langerhans, as assessed by measuring the incorporation of [35S]cysteine into proinsulin and insulin after fractionation by high performance liquid chromatography. The stimulatory effects of 4 beta-PMA were observed at a substimulatory concentration of glucose (2 mM) but were not additive to the stimulatory effects of 20 mM glucose on insulin biosynthesis. Prolonged exposure to 4 beta-PMA caused a marked down-regulation of PKC activity in islets. PKC-depleted islets showed a much reduced biosynthetic response to 20 mM glucose, but this was caused, at least in part, by an enhanced basal rate of (pro)insulin synthesis. These elevations in the basal rate of insulin synthesis were not secondary to an increase in the amount of preproinsulin mRNA in PKC-depleted islets since Northern blot analysis showed that prolonged exposure to 4 beta-PMA, and the subsequent loss of PKC activity, did not detectably alter basal levels of preproinsulin mRNA. These results suggest that the activation of PKC stimulates (pro)insulin synthesis in rat islets by enhancing translation of existing preproinsulin mRNA, and that this may play some part in the biosynthetic responses of beta-cells to glucose.

Animals↗
PubMed1993

Staurosporine inhibits protein kinases activated by Ca2+ and cyclic AMP in addition to inhibiting protein kinase C in rat islets of Langerhans.

Staurosporine has been used in several studies to investigate the role of protein kinase C (PKC) in secretory responses of islets of Langerhans to insulin secretagogues. We have assessed the effect of staurosporine on: [i] islet PKC activity in vitro; [ii] the stimulation of insulin secretion by nutrient secretagogues and [iii] the stimulation of protein phosphorylation and insulin secretion in electrically permeabilised islets. All experiments were carried out on rat isolated islets of Langerhans, either intact or permeabilised by high voltage discharge (3.4 kV/cm). The activity of PKC partially purified from rat islets was inhibited by staurosporine (1.6-400 nM) in a concentration-dependent manner. Staurosporine also inhibited insulin secretion stimulated by both glucose and glyceraldehyde, with maximal effects at 50 nM. After prolonged exposure of islets to the tumour-promoting phorbol ester, 4 beta phorbol myristate acetate (4 beta PMA), a procedure which depletes islet PKC activity, staurosporine still inhibited both glucose- and glyceraldehyde-stimulated insulin release. In electrically permeabilised islets, staurosporine inhibited both Ca(2+)- and cyclic AMP-stimulated protein phosphorylation and insulin secretion. These results suggest that staurosporine should not be used as a selective inhibitor of PKC in rat islets.

Alkaloids↗
PubMed1993

Arachidonic acid-induced insulin secretion from rat islets of Langerhans is not mediated by protein phosphorylation.

Arachidonic acid (AA) stimulated protein phosphorylation in electrically permeabilised islets, most notably of an islet protein of approximate molecular weight 18 kDa. This protein did not appear to be a substrate for cAMP-dependent protein kinase. The AA-induced protein phosphorylation was mediated by unmetabolised AA since the lipoxygenase inhibitor, nordihydroguaretic acid (NDGA), or the cyclooxygenase inhibitor, indomethacin, did not significantly reduce AA-induced phosphorylation. Although saturated fatty acids did not stimulate phosphorylation of islet proteins, a number of cis-unsaturated fatty acids, other than AA, induced 32P incorporation into an 18 kDa protein. However, some fatty acids which stimulated protein phosphorylation had no effect on insulin secretion in experiments where AA clearly stimulated insulin secretion. AA stimulated protein kinase C (PKC) activity extracted from islets but several fatty acids which induced protein phosphorylation had no significant effect on PKC activity in vitro. 50 nM staurosporine had no effect on AA-induced protein phosphorylation but this concentration of staurosporine markedly inhibited PKC activity. 200 nM staurosporine caused complete inhibition of the AA-induced phosphorylation without having any effect on AA-induced insulin secretion. These results suggest that AA and some other fatty acids can promote 32P incorporation into islet proteins, independently of PKC activation, and that AA-induced phosphorylation is not required for insulin secretory responses to AA.

Alkaloids↗
PubMed1993

Effects of midazolam on insulin secretion from isolated rat pancreatic islets of Langerhans.

Isolated, cultured rat pancreatic islets of Langerhans were incubated in medium containing glucose 2 or 20 mmol litre-1 and with glucose supplemented with midazolam 10, 100 or 1000 ng ml-1. Glucose 20 mmol litre-1 with the addition of noradrenaline 10 mumol litre-1 was used as a control. In contrast with noradrenaline, midazolam did not inhibit glucose-induced insulin secretion. Noradrenaline 10 mumol litre-1 inhibited secretion to basal values in response to glucose 20 mmol litre-1 (P < 0.001).

Animals↗
PubMed1993

Isoflurane inhibits insulin secretion from isolated rat pancreatic islets of Langerhans.

We have investigated the effects of isoflurane on insulin secretion in vitro from rat isolated islets of Langerhans and found a significant, dose-related and reversible inhibition of insulin secretion. Isoflurane 2% decreased insulin secretion stimulated by glucose 20 mmol litre-1 to basal, nonstimulated values. In other studies to identify the stage in the stimulus secretion pathway for insulin at which the anaesthetic may exert an inhibitory action, we have stimulated insulin release using glyceraldehyde and a phorbol ester. Insulin secretion induced by these secretagogues was also blocked by isoflurane. This suggests that the inhibitory effect of the anaesthetic agent may be at a site distal to stimulation of insulin secretion by glyceraldehyde and phorbol esters.

Anesthesia, Inhalation↗
PubMed1992

Ca2(+)-induced insulin secretion from electrically permeabilized islets. Loss of the Ca2(+)-induced secretory response is accompanied by loss of Ca2(+)-induced protein phosphorylation.

Increasing the cytosolic Ca2+ concentration of electrically permeabilized rat islets of Langerhans caused rapid increases in insulin secretion and in 32P incorporation into islet proteins. However, the secretory responsiveness of permeabilized islets was relatively transient, with insulin secretion approaching basal levels within 20-30 min despite the continued presence of stimulatory concentrations of Ca2+. The loss of Ca2(+)-induced insulin secretion was accompanied by a marked reduction in Ca2(+)-dependent protein phosphorylation, but not in cyclic AMP-dependent protein phosphorylation. Similarly, permeabilized islets which were no longer responsive to Ca2+ were able to mount appropriate secretory responses to cyclic AMP and to a protein kinase C-activating phorbol ester. These results suggest that prolonged exposure to elevated cytosolic Ca2+ concentrations results in a specific desensitization of the secretory mechanism to Ca2+, perhaps as a result of a decrease in Ca2(+)-dependent kinase activity. Furthermore, these studies suggest that secretory responses of B-cells to cyclic AMP and activators of protein kinase C are not dependent upon the responsiveness of the cells to changes in cytosolic Ca2+.

Adenosine Triphosphate↗
PubMed1992

Arachidonic acid induces phosphorylation of an 18 kDa protein in electrically permeabilised rat islets of Langerhans.

Arachidonic acid (AA) was shown to induce concentration-dependent, calcium-independent, in situ phosphorylation of a protein of approximate molecular weight 18 kDa in electrically permeabilised rat islets of Langerhans. This protein did not appear to be a substrate for protein kinase C (PKC) since stimulation of PKC by 4 beta phorbol myristate acetate (4 beta PMA) did not result in 32P incorporation into an 18 kDa protein, and since AA-induced phosphorylation was observed in islets in which PKC had been down-regulated by prolonged exposure of islets to 4 beta PMA. These results suggest that AA stimulates protein phosphorylation by a mechanism other than PKC activation.

Animals↗
PubMed1992

Nitric oxide is not involved in the initiation of insulin secretion from rat islets of Langerhans.

The involvement of nitric oxide as an intracellular messenger in the control of insulin secretion from pancreatic Beta cells was studied in rat islets of Langerhans by measuring: (i) nitric oxide generation in response to physiological insulin secretagogues; (ii) the effects of inhibitors of nitric oxide synthesis on insulin secretory responses to physiological secretagogues, and on insulin synthesis; (iii) changes in islet cyclic guanosine monophosphate in response to secretagogues; (iv) the effects of exogenous cyclic guanosine monophosphate and dibutyryl cyclic guanosine monophosphate on insulin secretion from electrically permeabilised islets and from intact, respectively. These studies produced no evidence that nitric oxide generation is required for the initiation of insulin secretion by common secretagogues. However, the results of our experiments suggest that the generation of nitric oxide may be involved in long-term, glucose-dependent increases in cyclic guanosine monophosphate content of islet cells, although the physiological relevance of these changes requires further investigation.

Amino Acid Oxidoreductases↗
PubMed1992

Insulin secretion and protein phosphorylation in PKC-depleted islets of Langerhans.

Protein kinase C (PKC)-dependent phosphorylation of endogenous substrates was measured in electrically permeabilised rat islets of Langerhans. The PKC-activating phorbol ester, 4 beta-phorbol myristate acetate (PMA), caused a slow but prolonged increase in insulin secretion from permeabilised islets, which was accompanied by increased 32P incorporation into several islet proteins of apparent M.W. 30-50 kDa. Depletion of islet PKC by prolonged exposure to PMA abolished subsequent secretory and phosphorylating responses to the phorbol ester. However, PKC-depleted islets did not show diminished responses to glucose, suggesting that PKC-mediated phosphorylation of these proteins is not essential for nutrient-induced insulin secretion.

Animals↗
PubMed1992

Arachidonic acid-induced insulin secretion from rat islets of Langerhans.

There is growing evidence that arachidonic acid (AA) and/or its metabolites may be involved in the control of insulin secretion. We have now investigated the effect of AA on insulin secretion from rat islets, and the possible involvement of protein kinase C (PKC) in this process. Exogenous AA stimulated insulin secretion from intact islets at a substimulatory concentration of glucose (2 mM), but did not further enhance glucose-induced (20mM) insulin secretion. AA-induced insulin secretion was temperature dependent. The secretory responses seen at 37 degrees C were totally abolished by reducing the incubation temperature to less than or equal to 34 degrees C. AA-induced insulin secretion was not dependent upon extracellular Ca2+ and was potentiated by omission of Ca2+ or bovine serum albumin from the media. PKC in rat islets can thus be stimulated by AA, but the stimulation of PKC is not required for AA-induced insulin secretion.

Animals↗