Position paper: recommendations for a digital mammography quality assurance program V4.0

In 2001 the ACPSEM published a position paper on quality assurance in screen film mammography which was subsequently adopted as a basis for the quality assurance programs of both the Royal Australian and New Zealand College of Radiologists (RANZCR) and of BreastScreen Australia. Since then the clinical implementation of digital mammography has been realised and it has become evident that existing screen-film protocols were not appropriate to assure the required image quality needed for reliable diagnosis or to address the new dose implications resulting from digital technology. In addition, the advantages and responsibilities inherent in teleradiology are most critical in mammography and also need to be addressed. The current document is the result of a review of current overseas practice and local experience in these areas. At this time the technology of digital imaging is undergoing significant development and there is still a lack of full international consensus about some of the detailed quality control (QC) tests that should be included in quality assurance (QA) programs. This document describes the current status in digital mammography QA and recommends test procedures that may be suitable in the Australasian environment. For completeness, this document also includes a review of the QA programs required for the various types of digital biopsy units used in mammography. In the future, international harmonisation of digital quality assurance in mammography and changes in the technology may require a review of this document. Version 2.0 represented the first of these updates and key changes related to image quality evaluation, ghost image evaluation and interpretation of signal to noise ratio measurements. In Version 3.0 some significant changes, made in light of further experience gained in testing digital mammography equipment were introduced. In Version 4.0, further changes have been made, most notably digital breast tomosynthesis (DBT) testing and QC have been addressed. Some additional testing for conventional projection imaging has been added in order that sites may have the capability to undertake dose surveys to confirm compliance with diagnostic reference levels (DRLs) that may be established at the National or State level. A key recommendation is that dosimetry calculations are now to be undertaken using the methodology of Dance et al. Some minor changes to existing facility QC tests have been made to ensure the suggested procedures align with those most recently adopted by the Royal Australian and New Zealand College of Radiologists and BreastScreen Australia. Future updates of this document may be provided as deemed necessary in electronic format on the ACPSEM's website ( https://www.acpsem.org.au/whatacpsemdoes/standards-position-papers and see also http://www.ranzcr.edu.au/quality-a-safety/radiology/practice-quality-activities/mqap ).

Modulation of hippocampal synaptic transmission by the kynurenine pathway member xanthurenic acid and other VGLUT inhibitors

Xanthurenic acid (XA), an endogenous kynurenine, is a known vesicular glutamate transport (VGLUT) inhibitor and has also been proposed as an mGlu2/3 receptor agonist. Changes in these systems have been implicated in the pathophysiology of schizophrenia and other psychiatric disorders; however, little is known of how XA affects synaptic transmission. We therefore investigated the effects of XA on synaptic transmission at two hippocampal glutamatergic pathways and evaluated the ability of XA to bind to mGlu2/3 receptors. Field excitatory postsynaptic potentials (fEPSPs) were recorded from either the dentate gyrus (DG) or CA1 region of mouse hippocampal slices in vitro. Addition of XA to the bathing medium (1-10 mM) resulted in a dose-related reduction of fEPSP amplitudes (up to 52% reduction) in both hippocampal regions. In the DG, the VGLUT inhibitors Congo Red and Rose Bengal, and the mGlu2/3 agonist LY354740, also reduced fEPSPs (up to 80% reduction). The mGlu2/3 antagonist LY341495 reversed the LY354740 effect, but not the XA effect. LY354740, but not XA, also reduced DG paired-pulse depression. XA had no effect on specific binding of 1 nM [(3)H]LY341495 to membranes with human mGlu2 receptors. We conclude that XA can modulate synaptic transmission via a mechanism that may involve VGLUT inhibition rather than activation of mGlu2/3 receptors. This could be important in the pathophysiology of nervous system disorders including schizophrenia and might represent a target for developing novel pharmacological therapies.

Interim recommendations for a digital mammography quality assurance program

In 2001 the ACPSEM published a position paper on quality assurance in screen film mammography which was subsequently adopted as a basis for the quality assurance programs of both the Royal Australian and New Zealand College of Radiologists (RANZCR) and of BreastScreen Australia. Since then the clinical implementation of digital mammography has been realised and it has become evident that existing screen-film protocols were not appropriate to assure the required image quality needed for reliable diagnosis or to address the new dose implications resulting from digital technology. In addition, the advantages and responsibilities inherent in teleradiology are most critical in mammography and also need to be addressed. The current document is the result of a review of current overseas practice and local experience in these areas. At this time the technology of digital imaging is undergoing significant development and there is still a lack of full international consensus about some of the detailed Quality Control tests that should be included in quality assurance (QA) programs. This document describes the current status in digital mammography QA and recommends test procedures that may be suitable in the Australasian environment. For completeness, this document also includes a review of the QA programs required for the various types of digital biopsy units used in mammography. In the future, international harmonisation of digital quality assurance in mammography and changes in the technology may require a review of this document. Accordingly, updates of this document will be provided as deemed necessary in electronic format on the ACPSEM's website (see http://www.acpsem.org.au/au/subgroup/radiology/RadiologySG_index.html).

Automatic technique parameter selection on a digital mammography system: an evaluation of SNR and CNR as a function of AGD on a GE Senographe DS

There are obvious differences in the automatic selection of kVp, anode, and filter between a digital mammography system and the equivalent film/screen system for the same thickness of PMMA absorber. To investigate the reason for these changes, a large number of images were acquired using 2, 4, 6, and 8 cm thick PMMA absorbing slabs, and various combinations of kVp, mAs, anode, and filter. The SNR and CNR were calculated using two different contrast test objects and plotted as a function of AGD. The results can be summarized as follows: 1) For any given AGD with 4, 6, and 8 cm thick PMMA absorbers, SNR(Rh/Rh) > SNR(Mo/Rh) > SNR(Mo/Mo), 2) For any given AGD: At 4 cm thickness, CNR(Mo/Mo) > CNR(Mo/Rh) > CNR(Rh/Rh), At 6 cm thickness, CNR(Rh/Rh) approximately CNR(Mo/Rh) > CNR(Mo/Mo), At 8 cm thickness, CNR(Rh/Rh) > CNR(Mo/Rh), 3) For any given absorber thickness and target/filter combination, CNR is approximately proportional to SNR, 4) For any given absorber thickness and target/filter combination, SNR (and hence CNR) is approximately proportional to (AGD)0.3 rather than the expected (AGD)(0.5), 5) CNR measured using 0.1 mm thick aluminium foil as the contrast object is more dependent on choice of kVp than using a 1 mm deep hole in a PMMA slab.

Measurement of CT scanner dose profiles in a filmless department

The measurement of the FWHM of the slice thickness radiation dose profile of a CT scanner using a prototype low sensitivity CR imaging plate has been investigated, as an alternative to the traditional method using envelope-packed industrial film. Using a standard Agfa clinical CR system to acquire the image, the FWHM of the dose profile can be accurately measured using readily available Public Domain software. An Agfa 18 x 24 cm CR cassette gives a pixel pitch of 113.5 microm, but with interpolation, the measurement accuracy can be less than 1 pixel. For a nominal 10 mm collimation, 15 successive measurements of the FWHM using CR gave an average width of 10.00 mm with a standard deviation of 0.02 mm. This may be compared with 4 successive measurements using film and a dual exposure technique to define the optical density at half peak height, yielding an average width of 9.98 mm with a SD of 0.03 mm. This prototype NDT plate is not a commercial product, but a radiotherapy plate with a similar sensitivity is available commercially and should give similar results.

Characterization of the intracellular signalling pathways that underlie growth-factor-stimulated glucose transport in Xenopus oocytes: evidence for ras- and rho-dependent pathways of phosphatidylinositol 3-kinase activation

The stimulation of glucose transport is one of the early cellular responses to growth factors and is essential for cell proliferation, yet the molecular processes that underlie this response are poorly defined. The aim of this study was to characterize the role of the low-molecular-mass G-proteins, Ras and Rho, and their downstream targets, Raf protein kinase and phosphatidylinositol 3-kinase, in the regulation of glucose transport in Xenopus oocytes by two distinct growth-factor receptors: the insulin-like growth factor I (IGF-I) tyrosine kinase receptor and the heterotrimeric G-protein-coupled lysophosphatidic acid (LPA) receptor. Microinjection of a neutralizing anti-Ras antibody partially blocked IGF-I-stimulated deoxyglucose uptake but was without effect on LPA-stimulated deoxyglucose uptake. In contrast, microinjection of the C3 coenzyme of botulinum toxin, which selectively ADP-ribosylates and inactivates Rho, inhibited LPA-stimulated, but not IGF-I-stimulated, deoxyglucose uptake. Similarly, LPA- but not IGF-I-stimulated deoxyglucose uptake was attenuated in oocytes expressing a dominant negative rho construct. Cells expressing a dominant negative mutant of Raf protein kinase exhibited markedly reduced sensitivity to both LPA and IGF-I, consistent with a role for endogenous Raf in glucose uptake by both growth factors. Furthermore, expression of a constitutively activated form of raf-1 resulted in a growth-factor-independent increase in deoxyglucose uptake. Measurements of phosphatidylinositol 3-kinase activity in microinjected cells support the hypothesis that the IGF-I receptor stimulates glucose transport by a Ras-dependent activation of phosphatidylinositol 3-kinase, whereas the G-protein-coupled LPA receptor controls this response by a pathway that involves Rho-dependent activation of a distinct phosphatidylinositol 3-kinase. Thus we provide evidence for clear differences in the signalling pathways that control glucose transport by G-protein-coupled and tyrosine kinase growth-factor receptors. Furthermore this is the first demonstration that active Rho is involved in the signalling pathways that regulate glucose uptake in response to some growth factors.

Phosphatidylinositol 3'-kinase, but not p70 ribosomal S6 kinase, is involved in membrane protein recycling: wortmannin inhibits glucose transport and downregulates cell-surface transferrin receptor numbers independently of any effect on fluid-phase endocytosis in fibroblasts

The exposure of 3T3-L1 fibroblasts to growth factors results in a 2-to-3-fold increase in 2-deoxyglucose transport and a approximately 50% to 80% increase in cell-surface transferrin receptor levels. We sought to determine the role of phosphatidylinositol-3'-kinase and p70 ribosomal S6 kinase in these stimulations, using selective inhibitors of these enzymes. Both basal and growth factor-stimulated deoxyglucose transport are blocked by wortmannin, but with different IC50 values (65 nM vs. 15 nM, respectively), suggesting a functional difference between these two states. This is accompanied by the accumulation of glucose transporters in intracellular locations. Both basal and growth factor-stimulated cell-surface transferrin receptor levels are downregulated by wortmannin, but with identical IC50 values (approximately 15 nM). These two proteins are known to recycle between an intracellular site and the plasma membrane in these cells, thus implying a functional role for phosphatidylinositol-3'-kinase in membrane recycling. In an effort to determine whether the effect of wortmannin was selective for the protein component of this recycling, we examined fluid-phase endocytosis of radiolabeled mannitol. Wortmannin was without effect on the fluid phase accumulation of mannitol, suggesting that the effects on membrane traffic are limited to the protein component of recycling membranes. Rapamycin, an inhibitor of p70 ribosomal S6 kinase, was without effect on any of these parameters, but both rapamycin and wortmannin inhibit growth factor-stimulated p70 ribosomal S6 kinase activity. These data support an important role for phosphatidylinositol-3'-kinase, but not p70 ribosomal S6 kinase, in the regulation of membrane protein traffic. We suggest that this enzyme may be involved in sorting of membrane proteins during trafficking.

Lysophosphatidic acid stimulates glucose transport in Xenopus oocytes via a phosphatidylinositol 3'-kinase with distinct properties

Lysophosphatidic acid (LPA) stimulated the transport of deoxyglucose into oocytes isolated from Xenopus laevis. This stimulation was accounted for entirely by an increase in the Vmax for transport. Various LPAs with different acyl groups in the sn-1 position and phosphatidic acid stimulated deoxyglucose (deGlc) transport in these cells with a rank order potency of 1-oleoyl-LPA > 1-palmitoyl-LPA > phosphatidic acid = 1-stearoyl-LPA > 1-myristoyl-LPA. The phosphatidylinositol 3'-kinase inhibitor LY294002 completely blocked LPA-stimulated deoxyglucose uptake (IC50 approximately 2 microM). In marked contrast, wortmannin, which can completely block both insulin-like growth factor-I (IGF-I)-stimulated deGlc uptake in oocytes and phosphatidylinositol 3'-kinase activation at concentrations as low as 20 nM [Gould, Jess, Andrews, Herbst, Plevin and Gibbs (1994) J. Biol. Chem. 269, 26622-26625], was a relatively poor inhibitor of LPA-stimulated deGlc transport, even at concentrations as high as 100 nM. We further show that LPA stimulates phosphatidylinositol 3'-kinase activity(s) that can phosphorylate both phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate, and that this stimulation is inhibited by LY294002 but is relatively insensitive to wortmannin, again in marked contrast to IGF-I-stimulated phosphatidylinositol 3'-kinase activity. Antibodies against the p85 regulatory subunit of phosphatidylinositol 3'-kinase or antiphosphotyrosine antibodies immunoprecipitated IGF-I-stimulated but not LPA-stimulated phosphatidylinositol 3'-kinase activity. We conclude that LPA stimulates glucose uptake in Xenopus oocytes by a mechanism that may involve activation of a form of phosphatidylinositol 3'-kinase that is distinguished from other isoforms by its resistance to wortmannin and by its substrate specificity. Since the LPA-activated form of phosphatidylinositol 3'-kinase is pharmacologically and immunologically distinct from that which is involved in IGF-I-stimulated glucose transport in these cells, we suggest that distinct isoforms of this enzyme are able to function with the same biological effect, at least in the regulation of sugar transport.

Three-dimensional CT angiography in the detection and characterization of intracranial berry aneurysms

PURPOSE

To assess the accuracy of three-dimensional CT angiography (CTA) in the detection and characterization of intracranial aneurysms and to help determine its role as a screening test for aneurysms in the asymptomatic population and as an adjunct to angiography in subarachnoid hemorrhages and in the follow-up of untreated aneurysms.

METHODS

In a blinded, prospective study, the 3-D CTA studies in 80 patients with symptomatic aneurysms were analyzed for the presence and morphology of aneurysms. Angiography or surgery acted as the control.

RESULTS

Ninety-four aneurysms were found in 63 patients. Negative findings at angiography were noted in 17. Sensitivity and specificity of 3-D CTA for all aneurysms, all patients, and aneurysms 5 mm or smaller were 90.4% and 50%, 98.4% and 82.4%, and 78.8% and 51.9%, respectively.

CONCLUSION

Three-dimensional CTA may have a role in noninvasive screening for asymptomatic aneurysms in the general population, but caution is advocated when data obtained from symptomatic patients are extrapolated to the asymptomatic population who harbor smaller aneurysms. Also, 3-D CTA may be useful as an adjunct to angiography in the characterization of berry aneurysms and in the follow-up of untreated aneurysms.

The activation of distinct mitogen-activated protein kinase cascades is required for the stimulation of 2-deoxyglucose uptake by interleukin-1 and insulin-like growth factor-1 in KB cells

The uptake of 2-deoxyglucose into KB cells was stimulated about 2-fold by interleukin-1 (IL1), anisomycin or insulin-like growth factor-1 (IGF1). Stimulation by IL1 and anisomycin was prevented by SB 203580, a specific inhibitor of the mitogen-activated protein (MAP) kinase homologue termed 're-activating kinase' [RK; also known as p38, p40 and CSBP (cytokine synthesis anti-inflammatory-drug-binding protein)], but was unaffected by PD 98059, a specific inhibitor of the activation of the classical MAP kinase pathway. In contrast, the stimulation of 2-deoxyglucose uptake by IGF1 was blocked by PD 98059 and unaffected by SB 203580. Consistent with these observations, IL1 and anisomycin were potent activators of MAP kinase-activated protein (MAPKAP) kinase-2, a physiological substrate of RK, whereas IGF1 was only a very weak activator of MAPKAP kinase-2. Conversely, IGF1 was a stronger activator of p42 MAP kinase than IL1 or anisomycin. These results imply that the activation of distinct MAP kinase pathways is required for the stimulation of glucose transport by IL1/anisomycin and IGF1 in KB cells, and suggest that the combined use of SB 203580 and PD 98059 is a powerful new approach to explore the roles of different MAP kinase cascades in cell regulation.

Purification of a phosphatidic-acid-hydrolysing phospholipase A2 from rat brain

A phosphatidic-acid-hydrolysing phospholipase A2 was purified from rat brain and characterized. This phospholipase A2 was purified by sequential cation, hydrophobic, heparin and gel-filtration chromatography. The purified protein had a mass of approximately 58 kDa as assayed by SDS/PAGE, had a pH optimum of 6.0, and was Ca(2+)-independent. This enzyme was apparently phosphatidic-acid-selective and had little measurable catalytic activity when phosphatidylcholine, phosphatidylethanolamine or diacylglycerol was used as substrate. On the basis of its physical and catalytic properties, we conclude that this phospholipase A2 is unique from those previously purified, and we speculate that it may be important for the production of the bioactive lipid lysophosphatidic acid.

Evidence for a role of phospholipase A2 in the mechanism of LHRH priming in rat anterior pituitary tissue

The phospholipase A2 (PLA2) inhibitors, quinacrine, p-bromophenacyl bromide, ONO-RS-082, aristolochic acid and chloracysine blocked the priming effect of LHRH, but not acute LHRH-induced gonadotrophin release measured in anterior pituitary pieces in pro-oestrous rats in vitro. These results suggest that the intracellular mechanisms underlying LHRH priming are distinct from those which mediate LH release in the present circumstances in that they involve PLA2. Furthermore, neither LHRH-induced LH release from preprimed tissue nor Ca(2+)-induced LH release were attenuated by quinacrine, indicating that this inhibitor does not interfere with the general Ca(2+)-dependent secretory apparatus of the gonadotroph and that the critical period for its action is in the induction of priming. LHRH induced the release of [3H]arachidonic acid ([3H]AA) from [3H]AA-prelabelled anterior pituitary tissue from pro-oestrous rats; a response which was sensitive to inhibitors of PLA2, of protein kinase C (PKC) and of protein synthesis. Activation of PKC also resulted in [3H]AA release which was inhibited with exactly the same pharmacological profile as the response to LHRH. Both gonadotrophin secretion and [3H]AA release responses to LHRH and to phorbol ester varied in parallel during the oestrous cycle and in ovariectomized/oestradiol-17 beta-replaced animals, as did their sensitivity to quinacrine and the protein synthesis inhibitor cycloheximide. These results indicate that LHRH priming is dependent on a hormonally regulated cascade involving a distinct form of PKC acting through a protein synthesis-dependent step to release AA by means of PLA2 activity. The priming effect was mimicked (at least in part) by conditioning preincubation with AA, confirming the functional relevance of this signalling cascade. Results using standard inhibitors of lipoxygenase/epoxygenase pathways were equivocal as to whether these pathways were critically involved, whilst cyclo-oxygenase inhibitors were completely without effect. The steps downstream from AA (and its possible metabolites) by which stimulus-secretion coupling is up-regulated in priming remain to be clarified.

Identification and characterization of a lysophosphatidic acid receptor

A specific binding site for 1-[3H]stearoyl-lysophosphatidic acid (stearoyl-LPA) was identified and characterized in membranes prepared from rat brain and Swiss 3T3 fibroblasts. Specific binding of [3H]LPA to these sites was protein dependent, was saturable, reached equilibrium in 15 min, and was displacable by the addition of excess unlabeled LPA. Scatchard analysis of saturation binding experiments indicated that these sites had affinities of 2.0 +/- 0.5 nM and 5.4 +/- 2.6 nM and densities of 19 +/- 3 fmol/micrograms of protein and 38 +/- 6 fmol/micrograms of protein in rat brain and 3T3 cell membranes, respectively. Various LPAs, with different acyl groups in the sn-1-position, competed with [3H]LPA for these binding sites, with a rank order of potency of 1-oleoyl-LPA > 1-stearoyl-LPA = 1-palmitoyl-LPA > 1-myristoyl-LPA. Phosphatidic acid also bound to these sites, but with lower affinity than any LPA tested. Neither lysophosphatidylcholine, lysophosphatidylethanolamine, nor any free fatty acid competed with [3H]LPA for these binding sites. Binding of [3H]LPA to these sites was regulated by nonhydrolyzable guanine nucleotides in both rat brain and 3T3 cell membranes. Furthermore, in 3T3 cells, these sites were regulated by cell density. It was subsequently determined that LPA induced a transient increase in intracellular Ca2+ levels in 3T3 cells. The concentrations required for this response, as well as the rank order of potency of the various LPAs and phosphatidic acid, correlated with the affinity of these compounds for the [3H]LPA binding site. These results suggest that the specific, high affinity, binding sites for [3H]LPA are G protein-coupled receptors.

Activation of serum response element-regulated genes by lysophosphatidic acid

Lysophosphatidic acid (LPA) is an important constituent of serum and shares its mitogenic activity. Serum induction of several genes is regulated, at least in part, by sequences related to the c-fos serum response element (SRE). A Rat-2 fibroblast cell line containing the beta-galactosidase reporter gene under SRE control was treated with LPA. Lysophosphatidic acid induced a time- and dose-dependent increase in beta-galactosidase activity. After 5 hours of treatment with 1-oleoyl-LPA a 3-fold increase in beta-galactosidase activity was observed. In contrast, endogenous alkaline phosphatase activity did not change in parallel with the beta-galactosidase activity indicating that the induction was specific. Various LPAs with different acyl groups in the sn-1 position induced beta-galactosidase activity with a rank order potency of 1-oleoyl-LPA > 1-palmitoyl-LPA > or = 1-myristoyl-LPA > 1-stearoyl-LPA. Phosphatidic acid was approximately equal to 1-stearoyl-LPA. Neither the calcium ionophore (A23187) nor 12-O-tetradecanoylphorbol 13-acetate, induced beta-galactosidase activity. These data suggest that LPA may exert some of its effects by regulation of SRE controlled genes.

Activation of MAP kinase associated with the priming effect of LHRH

A MAP kinase activity assay was developed to determine whether the LHRH receptor could activate this enzyme (particularly during LHRH priming). In anterior pituitary tissue from prooestrous rats LHRH caused concentration-dependent activation of MAP kinase after 5-10 min and continued for up to 60 min of incubation. The magnitude of this response correlated with that of LHRH priming on various days of the oestrous cycle but not with the magnitude of 1st hour (unprimed) LHRH-induced LH release. The response to LHRH was mimicked by a phorbol ester but not by ionomycin and was blocked with high potency by GF 109203X but not by H7 (in a similar manner to the PKC species that mediates LHRH priming). Neither the tyrosine kinase inhibitor lavendustin A nor the protein synthesis inhibitor cycloheximide blocked LHRH-induced MAP kinase activation. The possible functional significance of MAP kinase activation in gonadotrophs is considered with respect to LHRH priming.

The clinical diagnosis of sensory neuropathy in elderly people

Minor abnormalities in sensory perception are common in elderly people but the significance of these findings is uncertain. In order to define the most relevant clinical tests for the diagnosis of significant neuropathy in the elderly diabetic patient, quantified perception of vibration, temperature, pain, and light touch was assessed in 200 (100 hospitalized, 100 community) consecutive non-diabetic elderly subjects without apparent neurological disease, using an established scoring system. The changes in sensory perception were similar in the two groups and data were pooled for further analysis. Progressive loss of peripheral sensation was apparent with increasing age (neuropathy deficit score vs age: r = .04, p < 0.0001). Loss of vibration perception was particularly marked; deficit scores for vibration were significantly lower in the < 70 years age group than in all the older age groups (vibration score: < 70 years vs 80-84 years mean (95% CI) 0.89 (0.54) vs 3.02 (0.6), p < 0.0001). In contrast, perception of light touch and pain was relatively preserved in old age. Assessment of vibration perception is of limited value in elderly people since the distinction between 'normal ageing' and significant neuropathy is unclear. Perception of light touch and pain are likely to be the most reliable clinical indicators of significant neuropathy in an elderly diabetic population.

Differential involvement of phospholipase A2 in phorbol ester-induced luteinizing hormone and growth hormone release from rat anterior pituitary tissue

The protein kinase C (PKC) activator, phorbol 12,13-dibutyrate (PDBu) induced the release of both luteinizing hormone (LH) and growth hormone (GH) from proestrous rat anterior pituitary pieces in vitro. Phorbol 12,13-dibutyrate-induced LH, but not GH release was readily inhibited by the phospholipase A2 (PLA2) inhibitors, quinacrine, aristolochic acid, ONO-RS-082 and chloracysine. Furthermore, PDBu induced release of [3H]arachidonic acid ([3H]AA) from pre-labelled anterior pituitary tissue that was prevented in the presence of quinacrine, aristolochic acid and ONO-RS-082 but not the diglyceride lipase inhibitor RHC 80267. The effect of PDBu was completely inhibited by staurosporine and the selective PKC inhibitor Ro 31-8220 but only partially by low concentrations of H7; consistent with the involvement of both H7-sensitive and H7-resistant forms of PKC in the activation of PLA2 by PDBu. The protein synthesis inhibitor cycloheximide inhibited the release of both [3H]AA and LH that had been induced by PDBu, whereas LH release induced by the PLA2 activator mellitin was cycloheximide-insensitive. These results suggest that PKC activators may induce LH but not GH release from anterior pituitary tissue by a mechanism involving activation of a PLA2, brought about by a process which is reliant on protein synthesis.

The involvement of dihydropyridine-sensitive calcium channels in phorbol ester-induced luteinizing hormone and growth hormone release

We examined the role of voltage-activated, L-type, Ca2+ channels in phorbol ester-induced luteinizing hormone (LH) and growth hormone (GH) release from rat anterior pituitary tissue. The L-type Ca2+ channel inhibitor, nimodipine (NMD), inhibited phorbol 12,13-dibutyrate (PDBu)-induced GH release but had no significant effect on LH release. The L-type Ca2+ channel activator BAY K 8644 had no effect on PDBu-induced GH release but potentiated PDBu-induced LH release. In contrast, 60 mM K(+)-induced LH and GH release were inhibited by NMD, whereas BAY K 8644 had no effect. When PDBu and either K+ or BAY K 8644 were used together, they acted synergistically to evoke levels of LH release greater than addition of release caused by each secretagogue alone. However, the release of GH was additive with PDBu and either K+, BAY K 8644. The protein kinase C (PKC) inhibitor staurosporine inhibited both PDBu-induced LH release and GH release. A structurally different PKC inhibitor, H7, significantly inhibited PDBu-induced LH release but had no effect on PDBu-induced GH release. Both staurosporine and H7 inhibited LH release induced by PDBu and BAY K 8644 together. In contrast, although staurosporine inhibited GH release induced by PDBu and BAY K 8644, H7 significantly potentiated this response. A difference in the action of these two inhibitors was also apparent on K(+)-induced hormone release where staurosporine partially blocked K(+)-induced LH and GH release but H7 had no effect on the release of either hormone. Data obtained in 45Ca2+ influx experiments further suggested that a staurosporine-sensitive, but H7-resistant, PKC-like kinase may tonically maintain L-channels in a voltage-sensitive state, as down-regulation of PKC in dispersed anterior pituitary cells by long term PDBu treatment caused a significant reduction in K(+)-induced 45Ca2+ influx. We conclude that phorbol ester-induced GH release, but not LH release, is a result of L-type Ca2+ channel activation which may occur by means of alterations in the channel itself to increase its responsiveness to a given depolarisation.

The differential effects of protein kinase C activators and inhibitors on rat anterior pituitary hormone release

We investigated the possibility that various protein kinase C (PKC) activators and inhibitors may differentially affect luteinizing hormone (LH) and growth hormone (GH) release from rat anterior pituitary tissue, incubated in vitro. Activators of PKC induced LH release with the following order of potency: mezerein > phorbol 12,13-dibutyrate (PDBu). Mezerein and PDBu were equipotent on GH release. A range of PKC inhibitors (including compounds highly selective for PKC) potently and completely inhibited PKC activator-induced LH and GH release. Chelerythrine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7) were less potent inhibitors of PDBu-induced GH release than of LH release. A component of PDBu- and mezerein-induced LH release was inhibited by H7 with high potency, but a second H7-insensitive component was detected. Mezerein- and PDBu-induced GH release consisted of an H7-resistant component only. When the regulatory domain of PKCs from different sources was investigated by displacement of [3H]PDBu binding, the affinity for mezerein was 3-5-fold greater than that for PDBu at PKCs from cerebral cortex, lung and alpha and beta isoforms extensively purified from brain. Anterior pituitary PKCs were unusual in showing closely matched affinity for mezerein and PDBu, reminiscent of their equivalent potency on GH release. In order to investigate the potency of the catalytic domain inhibitor H7 on PKCs from different sources, enzyme activity assays were carried out on partially purified cytosolic PKCs from midbrain and anterior pituitary and on extensively purified PKC alpha and PKC beta. The Ca(2+)-independent component of PDBu-induced (phosphatidylserine-dependent) activity from anterior pituitary alone showed unusually low potency of inhibition by H7 but was potently inhibited by staurosporine and Ro 31-8220. In contrast, the Ca(2+)-dependent PKC activity in anterior pituitary was inhibited by H7, staurosporine and Ro-31-8220 with high potency as in all other preparations. These results are consistent with the presence and active role in secretion of pharmacologically distinct forms of PKC (or PKC-like kinases) in rat anterior pituitary cells.

Evidence that protein kinase C alpha has reduced affinity towards 1,2-dioctanoyl-sn-glycerol: the effects of lipid activators on phorbol ester binding and kinase activity

The effect of 1,2-diacylglycerols on specific binding of [3H]phorbol 12,13-dibutyrate to cytosolic protein kinase C (PKC) was investigated in tissues reported to contain different proportions of PKC isoforms. In lung, frontal cerebral cortex and cerebellum cytosols (enriched in PKC alpha, beta and gamma, respectively) displacement of specific binding by phorbol 12,13-dibutyrate or diacylglycerols containing unsaturated acyl chains was of similar potency for each tissue. A range of 1,2-diacylglycerols containing saturated acyl chains exhibited varying affinities for [3H]phorbol 12,13-dibutyrate binding sites in each tissue; defining an optimal acyl chain length of around 14 carbons in each case. However, the affinities of saturated diglycerides were consistently lower in lung cytosol than in frontal cerebral cortex and cerebellum cytosols, with the greatest differences occurring at lower acyl chain lengths, especially with 1,2-dioctanoyl-sn-glycerol. Furthermore, a mixed micelle assay of PKC activity showed that 1,2-dioctanoyl-sn-glycerol displayed reduced potency at PKC alpha partially-purified from COS 7 cell cytosol compared to the mixture of PKC isoforms present in rat midbrain cytosol. Both low potency of 1,2-dioctanoyl-sn-glycerol as a displacer of [3H]phorbol 12,13 dibutyrate binding and the ability of arachidonic acid to act as an allosteric enhancer of binding, correlated with the proportional PKC alpha content of a range of tissues reported in the literature. In PKC enzyme activity assays, 1,2-dioctanoyl-sn-glycerol, but not phorbol 12,13-dibutyrate, was correspondingly a much poorer activator of PKC alpha from COS 7 cells than of the broad consensus of isoforms in rat midbrain. When alpha and beta isoforms were extensively-purified on DEAE-cellulose then hydroxyapatite, both the low affinity of 1,2-dioctanoyl-sn-glycerol for [3H]phorbol 12,13-dibutyrate binding sites and their allosteric regulation by arachidonic acid were confirmed to be characteristic of the alpha rather than the beta isoforms.

Oestradiol-17 beta modulates the actions of pharmacologically distinct forms of protein kinase C in rat anterior pituitary cells

Phorbol ester-induced release of LH and GH from rat anterior pituitary tissue in vitro is differentially inhibited by some, but not other, inhibitors of protein kinase C (PKC), suggesting that pharmacologically distinct species of PKC may have different functional roles in these cells. Since stimulus-induced anterior pituitary hormone release can be enhanced by oestradiol-17 beta (OE2) pretreatment, we investigated the effect of OE2 treatment of long-term (4 weeks) ovariectomized rats on the amount, activity and cellular actions of pharmacologically distinct PKC species in rat anterior pituitary tissue. Here we report that OE2 treatment enhanced phorbol 12,13-dibutyrate (PDBu)-induced LH but not GH release measured in vitro. This effect of OE2 on LH release may involve synthesis of additional PKCs that are not targeted by the synthetic diacylglycerol, 1,2-dioctanoyl-sn-glycerol (DOG). Measurements of anterior pituitary PKC activity and [3H]phorbol ester-binding studies suggested that the facilitatory action of OE2 on LH release may occur, at least in part, by altering the quantity and activity of PKC(s). Our results also demonstrate that the OE2-induced PKC(s) which facilitate LH release may be of the type that are not dependent upon raised intracellular Ca2+ for their activation and display distinct pharmacological properties (being readily activated by PDBu, but not by DOG, and are staurosporine-sensitive but H7-insensitive). This facilitatory action of OE2 on PKC-induced LH release does not appear to involve OE2-induced changes in the affinity of existing PKC(s) for PDBu, or changes in the amount of releasable LH in the pituitary prior to the stimulus.

The threshold effect: consequence of change in the frequency of food intake in the presence of a functional threshold

Studies on diseases thought to be diet-induced have so far assumed that the effect of a food depends solely on the amount ingested. When the metabolism of a food derivative is dependent on a threshold-dependent mechanism this single variable assumption is invalid, as the net effect of the derivative will also depend on intake frequency. In this paper the consequences of varying intake frequency in the presence of a notional threshold are analysed mathematically. It is shown that at the low frequency end of the scale relevant to human diet, if a metabolic threshold exists then the net effect of a food will be critically dependent on intake frequency, and that the effect of changing frequency may exceed that produced by even substantial changes in quantum. It is concluded that epidemiological studies which have not included data on frequency of intake involve a potential error and could be misleading.

Can elderly diabetic patients co-operate with routine foot care?

Foot care education is widely promoted as a preventive strategy for reducing foot ulceration in diabetes. We describe a simple method of assessing the ability of elderly diabetic patients to co-operate with foot care advice. Using small self-adhesive red spots, foot lesions can be simulated and patients advised and prompted to detect and inspect these 'lesions'. Nineteen young non-diabetic volunteers and three groups of 14 elderly patients were assessed: diabetic patients with a foot ulcer, diabetic patients with no history of foot ulceration and non-diabetic patients. Eleven (39%) of the diabetic patients were unable to reach their toes and remove the lesions and only 6 (14%) of all elderly patients could respond to plantar lesions. It is therefore unlikely that unsupported foot care education can be effective in reducing the morbidity of foot problems in the elderly diabetic patient.

The priming effect of luteinizing hormone-releasing hormone (LHRH) but not LHRH-induced gonadotropin release, can be prevented by certain protein kinase C inhibitors

The priming effect of LHRH in vitro (which results in increased responsiveness of gonadotropes to both LHRH receptor-mediated and receptor-independent stimuli) is brought about by an unknown mechanism. The present results indicate that induction of the LHRH priming effect is inhibited in a concentration-dependent manner by the protein kinase C (PKC) inhibitors staurosporine, K252a, H7 and by the novel highly-selective PKC inhibitor, Ro 31-8220. In contrast, a range of other compounds that are relatively selective inhibitors of other kinases such as tyrosine kinases and Ca2+/calmodulin-dependent kinases were unable to prevent priming. The PKC inhibitors prevented priming without affecting initial LHRH-induced gonadotropin secretion. Thus, the priming-elicited increment in secretion was selectively removed, restoring hormone release to the level measured during an initial response to LHRH. Similar results were obtained on different days of the estrous cycle where the magnitude of the priming effect varies. Experiments on the time course of PKC inhibitor action revealed that the critical period was in the induction of the priming effect, not its expression. The PKC inhibitors had neither acute nor delayed effects on gonadotropin secretion induced by ionomycin. Staurosporine, K252a and Ro 31-8220 inhibited LHRH priming with identical potencies to their inhibition of phorbol ester-induced gonadotropin secretion. The reduced potency of H7 seen on LHRH priming compared to phorbol ester-induced gonadotropin release parallels results seen with this inhibitor on phorbol ester-induced secretion of growth hormone (Johnson and Mitchell (1989) Biochem. Soc. Trans. 17, 751-752) and on the pharmacological characteristics of PKCs partially purified from anterior pituitary tissue. In all aspects of this study, effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion appeared to be entirely similar.

Quantitative vibration perception testing in elderly people: an assessment of variability

The variability of vibration perception threshold measured by the Biothesiometer for three consecutive readings on a single occasion and 18 sequential readings over 7 days was assessed in 20 elderly convalescent subjects. The coefficient of variation for three consecutive readings at the great toe was high [right great toe: median (range) 15 (6-260%]. The median coefficients of variation for sequential readings were higher than those for consecutive readings at both toes [right great toe: median (range) 26 (5-71)% versus 15 (6-26)%, p = 0.0001]. Thus quantitative tests of sensory function are not reliable in elderly people, even when the subjects have no acute medical problem. Screening for neuropathy in elderly patients should probably rely on clinical examination or electrophysiological tests.

Pulmonary infarction, myocardial infarction, and acute disseminated intravascular coagulation

Pulmonary and myocardial damage are frequently cited as manifestations of disseminated intravascular coagulation (DIC), but rarely as causes. Three elderly cases of severe DIC due to pulmonary and myocardial infarction are reported. All three patients died. Necropsy showed extensive pulmonary emboli in each case with large pulmonary infarcts in cases 1 and 2 and a ventricular aneurysm containing thrombus in cases 2 and 3. Early diagnosis and treatment of pulmonary embolism requires a high degree of clinical suspicion but may prevent progression to the irreversible stage of severe DIC.

Lack of knowledge of symptoms of hypoglycaemia by elderly diabetic patients

The knowledge of symptoms of hypoglycaemia of 45 consecutive elderly diabetic patients was assessed during a structured interview and compared with that of an age-matched non-diabetic control group. Twenty-three (88%) patients taking oral hypoglycaemic agents (OHAs) and six (32%) insulin-treated patients denied any knowledge of hypoglycaemia. There was no significant difference in knowledge of 14 symptoms of hypoglycaemia between the non-diabetic controls and the combined diabetic (OHA and insulin) groups, but insulin-treated patients were slightly more knowledgeable than patients taking OHAs. Fourteen (54%) of the OHA group were taking either glibenclamide or chlorpropamide which have been associated with severe and prolonged hypoglycaemia. Elderly diabetic patients are unlikely to respond to the warning symptoms of hypoglycaemia and caution should therefore be exercised when prescribing for these patients.

Inhibition of depolarisation-induced calcium influx into GH3 cells by arachidonic acid: the involvement of protein kinase C

The influx of 45Ca2+ induced in GH3 cells by exposure to 60 mM K+ medium was inhibited by arachidonic acid (AA) in a concentration-dependent manner. This action of AA was not prevented by inhibitors of its metabolism but was reversed by the inhibitors of protein kinase C (PKC), H7 and staurosporine but not their less active congeners HA 1004 and K252a, respectively. Presumed down-regulation of PKC by pretreatment with phorbol 12,13-dibutyrate (PDBu) also greatly diminished the effect of AA. Experiments to assess effects of AA on 45Ca2+ efflux and on cytosolic Ca2+ concentrations indicated that an additional PKC-independent action of AA involving the release of intracellularly stored calcium was present. Both direct activation of certain PKC isoform(s) by AA and the synergistic influence on PKC activity by its concomitant raising of intracellular Ca2+ concentrations, may be physiologically important in the regulation of depolarisation-induced Ca2+ entry.

The threshold effect: consequences of change in the frequency of food intake in the presence of a functional threshold

Studies on diseases thought to be diet-induced have so far assumed that the effect of a food depends solely on the amount ingested. When the metabolism of a food derivative is dependent on a threshold-dependent mechanism this single variable assumption is invalid, as the net effect of the derivative will also depend on intake frequency. In this paper the consequences of varying intake frequency in the presence of a notional threshold are analysed mathematically. It is shown that at the low frequency end of the scale relevant to human diet, if a metabolic threshold exists then the net effect of a food will be critically dependent on intake frequency, and that the effect of changing frequency may exceed that produced by even substantial changes in quantum. It is concluded that epidemiological studies which have not included data on frequency of intake involve a potential error and could be misleading.

Frequency multiplexer for ultrasonic Doppler blood flow signals

An instrument is described which uses single-sideband techniques to combine two channels of Doppler flow signals into a form suitable for simultaneous processing by a single-channel real-time spectral analyzer. The maximum input frequency range is 50 Hz to 10 kHz.

Influence of fixation conditions on the performance of glutaraldehyde-treated porcine aortic valves: towards a more scientific basis

To maintain optimum mechanical properties in glutaraldehyde-treated heart-valve tissue the full collagen crimp geometry originally present in the relaxed fresh tissue should be retained. By varying the pressure at which glutaraldehyde fixation is carried out, considerable alterations to this crimp geometry can be achieved. The mechanical stiffness of the preserved tissue is consequently affected, and this in turn has a striking influence on both the opening behaviour of the valve and the degree of strain localisation in the leaflet tissue. A pressure of 100 mmHg eliminated the collagen crimp geometry entirely, and this resulted in the formation of sites of local strain or kinks in the valve leaflets during opening. It is expected that this strain localisation phenomenon will influence the long-term fatigue durability of the treated tissue. Pressures even as low as 4 mmHg result in significant reductions of crimp geometry. Fresh valves should therefore be fixed under a positive head of pressure sufficient only to ensure that the leaflets seal along their coapting free margins. A pressure of less than 1 mmHg was sufficient to achieve this. Leaflets of the commercially available Hancock valve show features similar to valves fixed in glutaraldehyde at about 100 mmHg pressure.

Experimental evaluation of aortic homograft valves mounted on flexible support frames and comparison with glutaraldehyde-treated porcine valves

The durability of the aortic homograft valve, when mounted in a rigid support frame, has been limited in some cases by aortic wall detachment from the frame in the commissure buttress area. To investigate the effects of frame flexibility, a stent was designed which was suitable for canine aortic valves of selected sizes. Of the two materials tested, acetal copolymer was found to be superior to polypropylene, as stents made from the latter material were permanently deformed as a result of polymer creep under the action of a cyclic load. Observations of a commercially available glutaraldehyde-treated heterograft mounted on a polypropylene frame indicated that stent flexibility was less important than had been suggested in earlier reports. It is considered that the glutaraldehyde preservation and the method of mounting this valve in the frame are major factors in prolonging the life of the implant.

The glutaraldehyde-treated heterograft valve: some engineering observations

Two commercially prepared, glutaraldehyde-treated porcine heterograft valves mounted on flexible stents have been tested in a pulsatile-flow water tunnel. Measurements of the radial deflections of the stent posts have been made for various applied pressures across the valve. A previous claim of 90 percent reduction in leaflet stress as a result of stent flexibility is of doubtful validity because the measurement technique used was inappropriate for the magnitude of strain involved. Photographs of the valve at various steady forward flow rates show that the leaflets do not open as readily as the antibiotic-treated homograft valve.

Rock-Type Discrimination from Ratioed Infrared Scanner Images of Pisgah Crater, California

The radiances in two thermal infrared channels of an airborne scanner system were ratioed to produce images that recorded compositionally diagnostic emittance variations for several silicate rock types near Pisgah Crater, California.