The comparative strengths of commercial glass-ionomer cements with and without metal additions

Metal reinforced glass-ionomer cements are said to possess superior mechanical properties when compared to non-metal reinforced glass-ionomer cements. However, the literature to date does not always support this view, owing to the variety of materials and test methods employed. In this study the mechanical properties of three reinforced and three standard materials were tested using the standard specification tests of compressive and diametral strength in addition to tensile strength using the four point bend test. The tensile strength was also measured using the shell test in order that this test, which on theoretical grounds is more suited to these materials, may be evaluated. Six specimens of each material were prepared for each of the test modalities resulting in the conclusion that the addition of metal to glass-ionomer cements can markedly increase the strength of the materials. However, the method of fusing the metal to the glass rather than by simple addition does not produce any advantages in strength. In this evaluation one reinforced material was significantly stronger than all other materials in all four test modalities. The compressive strength test which appears in most standards does not appear to be very discriminatory. Of the tensile tests, which have more clinical significance, the results of the diametral strength tests, which are included in some standards, appear to be at variance with the other two tensile tests, suggesting that the flexural or shell test would be more appropriate.

Identification of a novel 5-HTN (nematoda) receptor from Ascaris suum muscle

1. The abilities of various serotonergic drugs to bind with the 5-HT receptor of Ascaris suum muscle and to affect cyclic AMP levels in muscle tissue were examined. 2. Ligands which selectively interact with either the 5-HT1 or the 5-HT2 receptor in mammalian systems interact with the 5-HT receptor from A. suum muscle and increase cyclic AMP levels. 3. No binding of 5-HT3 ligands to 5-HT receptors from A. suum muscle was observed. 4. The 5-HT receptor of A. suum muscle should be called the 5-HTN (for Nematoda) receptor because its pharmacological and biochemical behaviors were different from those of mammalian 5-HT receptors.

Regulation of [Ca2+]i by secretagogue stimulation of canine gastric parietal cells

The ability of gastrin, histamine, and carbachol to stimulate acid secretion by direct action on gastric parietal cells is well established but the role of intracellular Ca2+ concentration ([Ca2+]i) in mediating these effects is the subject of some controversy. To examine this issue further, secretagogue-mediated changes in [Ca2+]i in single isolated canine gastric parietal cells were examined by microspectrofluorometry of fura-2-loaded cells. Resting [Ca2+]i in single parietal cells was 63 +/- 6 (SE) nM. Carbachol, 10(-5) M, induced a maximum elevation in [Ca2+]i with an initial transient rise of 178 +/- 24 (SE) nM, which was maintained in the absence of extracellular Ca2+ and a sustained plateau of 112 +/- 20 (SE) nM, which was abolished by removal of extracellular Ca2+. Both effects were reversed by the muscarinic receptor antagonist atropine. Gastrin (10(-9)-10(-7) M) also induced a bimodal rise in [Ca2+]i with a maximal initial transient rise of 206 +/- 14 nM and a sustained plateau of 94 +/- 9 nM. Both components of the [Ca2+]i response to gastrin were reversed by the gastrin specific antagonist L 365260. Lower concentrations of gastrin (10(-10) M) induced repetitive transient increases (oscillations) in cytosolic Ca2+. The amplitude of the first spike was less than 50% of the transient rise in [Ca2+]i stimulated by 10(-8) M gastrin. The oscillations occurred at a rate of 0.9/min, gradually decreasing in amplitude within 15 min of secretagogue administration. Histamine (10(-4) M) led to a minimal rise in [Ca2+]i (less than 5% of control) in less than 10% of the canine parietal cells tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Low molecular mass GTP-binding proteins in subcellular fractions of the pancreas: regulated phosphoryl G proteins

Low molecular mass guanine nucleotide-binding proteins [small guanosine 5'-triphosphate (GTP)-binding proteins] and phosphoproteins of the pancreatic acinar cell were compared by two-dimensional gel electrophoresis. [35S]GTP alpha S blotting analysis of the total cell protein revealed 20 GTP-binding proteins ranging in molecular mass from 20 to 28 kDa and pI of 4.8-6.4. Analysis of 32P-labeled total cell protein revealed over 300 phosphoproteins. The subcellular distribution of the small GTP-binding proteins was examined: 17 were located in the rough endoplasmic reticulum (RER) fraction, 19 in the smooth microsome fraction, 14 in the zymogen granule membrane fraction, and 11 in the cytosolic fraction, with overlap between fractions. Of the GTP-binding proteins, two were also found to be phosphoproteins, one located on the RER and one on the zymogen granule membrane. The phosphorylation of both small GTP-binding proteins was increased by secretagogue stimulation of the cells but with different time courses. The RER small GTP-binding protein demonstrated a rapid and transient increase in 32P labeling, whereas the granule membrane small GTP-binding protein showed an increase at longer times (30 min). Two of the cytosolic small GTP-binding proteins were also seen in particulate fractions, especially in the zymogen granule membrane fraction, suggesting the possibility of cycling between cytosolic and membrane-associated forms.

Regulation of phospholipid hydrolysis in streptolysin-O-permeabilized rat pancreatic acini

To investigate the mechanism of phospholipid hydrolysis in pancreatic acinar cells, the effects of Ca2+, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and cholecystokinin (CCK) on both polyphosphoinositide (PI) and phosphatidylcholine (PC) hydrolysis were studied in rat pancreatic acini permeabilized with the bacterial toxin, streptolysin-O. When acini were prelabeled with myo-[3H]inositol, permeabilized, and then incubated with various concentrations of free Ca2+ for 15 min, Ca2+ stimulated [3H]inositol phosphate release at a concentration of 100 nM and was maximally effective at 100 microM. Both GTP gamma S and CCK enhanced Ca(2+)-induced [3H]inositol phosphate release, although these agents had no effect in the absence of Ca2+. At a physiological concentration of Ca2+ (100 nM), CCK stimulated [3H]inositol phosphate release which was further enhanced by GTP gamma S. When acini were similarly prelabeled with [3H]choline before permeabilization, [3H]choline phosphate release was also stimulated by free Ca2+ over the concentration range from 100 nM to 10 microM. In contrast to PI hydrolysis, however, neither GTP gamma S, CCK, or GTP gamma S plus CCK had an additional effect on [3H]choline phosphate release stimulated by 100 nM-100 microM free Ca2+. Furthermore, Ca(2+)-induced [3H]choline phosphate release appeared to be due to the redistribution from cell to the medium rather than to an increase in choline phosphate production. Therefore, choline phosphate release following prelabeling with [3H]choline is not useful as an indicator of PC hydrolysis in permeabilized acini.

Quantitative comparison of radiolabeled antibody therapy and external beam radiotherapy in the treatment of human glioma xenografts

Using 90Yttrium radiolabeled antibodies, radioimmunotherapy was compared to fractionated external beam radiotherapy in the treatment of human glioma xenografts. Antibody treatments required administration of an approximately threefold greater total dose compared to external beam treatments to achieve the same tumor regrowth delay. Following multi-fraction external beam radiation treatments, tumor regrowth delay demonstrated a large fractionation effect (alpha/beta = 2.3 Gy, 95% confidence limits 0.4-4.2 Gy), suggesting that much of the ineffectiveness of the antibody treatments could be caused by a large dose-rate effect in this system. Despite the large fractionation effect, the regrowth delay was small for a large single-fraction external beam irradiation, possibly because of tumor hypoxia. When compared to external beam radiation, radiolabeled antibody treatments resulted in a comparatively diminished tumor bed effect, suggesting radioimmunotherapy spares normal tissue surrounding the tumor.

In vitro erosion of 20 commercial glass ionomer cements measured using the lactic acid jet test

The lactic acid jet test has been proposed for incorporation in international standards for dental cements, since results correlate well with in vivo erosion. In the literature, jet test results have been reported on only six glass ionomer cements. This study examines three types of glass ionomer, restorative, luting and metal reinforced, twenty materials from six manufacturers. A wide range of erosion rates was found particularly for restorative cements. The hypotheses put forward by previous workers to explain differences in erosion rates found on their limited range of glass ionomers do not apply to the wider range that we tested.

Solubilization and affinity purification of the Y2 receptor for neuropeptide Y and peptide YY from rabbit kidney

Neuropeptide Y (NPY) is an important neuropeptide in both central and peripheral neurones whereas peptide YY (PYY) is a gut hormone present in endocrine cells in the lower bowel. Both peptides interact with multiple binding sites that have been further classified into Y1 and Y2 receptors. We have solubilized native Y2 receptors both from basolateral membranes of proximal convoluted tubules from rabbit kidney and from rat hippocampal membranes. Solubilization of functional Y2 receptors was obtained with both 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) and digitonin and resulted in each case in a single class of high affinity binding sites. The soluble receptor retained the binding specificity for different peptides and long C-terminal fragments of NPY exhibited by membrane preparations. Gel filtration of solubilized receptors resulted in a single peak of specific PYY binding activity corresponding to Mr = 350,000 whereas affinity labeling revealed a major band of Mr = 60,000. Since this binding activity was inhibited by guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) the Y2 receptor is probably solubilized as a receptor complex containing a G-protein along with the ligand binding protein. Y2 receptor binding sites from kidney tubular membranes were purified to homogeneity by a three-step procedure employing Mono S cation-exchange adsorption, affinity chromatography on wheat germ lectin-agarose beads, and affinity chromatography on NPY-Affi-Gel. Electrophoresis and silver staining of the final receptor preparation revealed a single protein with Mr = 60,000 whereas gel filtration showed a single peak at approximately Mr = 60,000. The purified protein can be affinity labeled with [125I-Tyr36]PYY, indicating that the Mr = 60,000 protein contains the ligand binding site of the Y2 receptor, and this binding is not affected by GTP gamma S. Scatchard transformation of binding data for the purified Y2 receptors was compatible with a single class of binding sites with Kd = 76 pM. The purified Y2 receptors retain their binding properties with regard to affinity and specificity for different members of the pancreatic polypeptide-fold peptide family. The specific activity of purified Y2 receptors was calculated to approximately 14.7 nmol of ligand binding/mg of receptor protein, which is consistent with the theoretical value (16.6 nmol/mg) for a pure Mr = 60,000 protein binding one PYY molecule. Purification to homogeneity thus reveals the Y2 receptor as an Mr = 60,000 glycoprotein.

A novel substrate for assays of gene expression using chloramphenicol acetyltransferase

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The interfacial region of the tooth/glass ionomer restoration: a confocal optical microscope study

The dynamic interactions between the tooth tissues and a glass ionomer cement were investigated, using fluorescent markers incorporated into components of glass ionomer restorations. A confocal optical microscope was used to examine the tooth/restoration interface. Samples were examined at specific intervals after restoration to determine the effect of maturation of the glass ionomer matrix. Loss of fluorescent dye from the glass ionomer restoration into the subjacent dentin indicated fluid movement across the interface during maturation. To determine the effect of shrinkage from water loss on the integrity of the tooth/restoration interface, restored teeth were maintained fully hydrated and then allowed to dry. Substantial cracking at the enamel margins after drying of the set restoration indicated the strength of the attachment to enamel and also cautioned against excessive clinical drying.

Control of Drosophila wing and haltere development by the nuclear vestigial gene product

The Dipteran flight appendages, the wings and halteres, develop from larval imaginal discs that also produce other sections of the second and third thoracic adult body segments. Loss of vestigial (vg) function in Drosophila selectively eliminates wing and haltere formation. Here, we show that vg expression is spatially restricted to the presumptive wing and haltere regions of these imaginal discs. An intronic regulatory element mediates this restriction and may elaborate upon cues that activate vg expression in the embryonic disc primordia. The nuclear vg protein lacks any recognized nucleic acid-binding motif but is comprised of two putative functional domains, one of which bears similarity to part of the Deformed homeotic protein and may mediate protein-protein interactions. These results suggest that vg is directly involved in determining which thoracic imaginal disc cells will form wings and halteres, perhaps by interacting with other nuclear regulatory proteins.

Growth and differentiation of pancreatic acinar cells: independent effects of glucocorticoids on AR42J cells

Dexamethasone (DEX) inhibits growth and induces differentiation in rat pancreatic acinar AR42J cells. We wished to determine whether growth and differentiation are mutually exclusive in AR42J cells and whether DEX effects on growth and differentiation are mutually dependent or independent. Inhibition of DNA synthesis, assessed by [3H]thymidine incorporation, was detectable after 6 h, half-maximal after 12 h, and complete after 18-h DEX treatment, at which time incorporation was reduced to 9.0% of control. The half-maximal effective dose for inhibition of DNA synthesis was 0.5 nM, and maximal inhibition was achieved with 10 nM DEX. This dose-response was similar to that previously reported for DEX-induced parameters of differentiation. The rank order of potency for inhibition of DNA synthesis by various steroid hormones was DEX greater than corticosterone greater than aldosterone greater than progesterone. Hydroxyurea or serum starvation inhibited growth to the same extent as DEX but did not induce differentiation. Moreover, hydroxyurea or serum starvation did not block the ability of DEX to induce differentiation. Addition of either EGF or insulin significantly reversed the growth inhibitory effects of submaximal (1 nM) DEX. In cultures released from growth inhibition, 1 nM DEX increased cellular amylase content 5.9- to 6.5-fold, similar to the amylase increase in growth-inhibited cultures. Therefore, growth inhibition and differentiation are independent delayed events regulated by DEX in AR42J cells.

Binding, internalization, and processing of bombesin by rat pancreatic acini

The binding and subsequent fate of 125I-labeled bombesin was studied in rat pancreatic acini. At both 37 degrees C and 4 degrees C binding occurred to a single saturable site, with Kd equal to 1.7 nM. The amount of steady-state tracer binding was reduced at 4 degrees C (5.7%/mg protein) compared with 37 degrees C (8.7%/mg), with a similar relative change in calculated binding capacity. With the use of an acid wash procedure to remove surface bound ligand, 55% of cell-associated 125I-bombesin was internalized in the steady state at 37 degrees C but only 5% at 4 degrees C. Preincubation at 4 degrees C followed by an increase to 37 degrees C led to rapid internalization of bound bombesin, which was blocked by the metabolic inhibitor antimycin. 125I-bombesin was found to be degraded by two acinar systems. One was not related to receptor binding but could be inhibited with bacitracin. The other occurred after internalization and was partially blocked with chloroquine. Thus, after binding, bombesin is internalized, and the degradation products are released from the cell. Exposure to bombesin is also accompanied by a subsequent decrease in cell surface binding (54% after 1 h exposure to 100 nM bombesin), suggesting that the bombesin receptor may also be internalized in a ligand-dependent manner.

Intracellular mediators of bombesin action on rat pancreatic acinar cells

The effects of bombesin on physiological responses (amylase secretion, protein synthesis) and intracellular mediators [inositol 1,4,5-trisphosphate (1,4,5-IP3), [Ca2+]i, and diacylglycerol] were studied in isolated rat pancreatic acini and compared with the actions of cholecystokinin (CCK). Bombesin stimulated amylase secretion to the same extent as CCK. However, it failed to reproduce the inhibition of amylase secretion by high concentrations of CCK and likewise did not inhibit incorporation of [3H]leucine into protein in contrast to high concentrations of CCK. Low concentrations of bombesin (1-100 pM) induced repetitive oscillations in [Ca2+]i, whereas higher concentrations of bombesin (1-10 nM) induced a large transient increase in [Ca2+]i followed by a small sustained plateau. Bombesin (1-100 nM) induced an early peak of 1,4,5-IP3 at 5-15 s but was without measurable effect at lower concentrations. These effects on [Ca2+]i and 1,4,5-IP3 were similar to those seen with CCK except that bombesin was approximately 10-fold less potent than CCK. Bombesin induced an increase in acinar 1,2-diacylglycerol with a biphasic time course similar to CCK. However, the magnitude of the response to bombesin was much smaller than the response to CCK. The results suggest that bombesin receptors initiate similar intracellular messengers as does CCK. However, CCK induces a larger increase of diacylglycerol and probably an as yet unidentified messenger responsible for its inhibitory effects.

Mastoparan induces oscillations of cytosolic Ca2+ in rat pancreatic acinar cells

Microfluorimetry of fura-2 was used to monitor [Ca2+]i in single cells stimulated with the G-protein activating agent mastoparan. Mastoparan induced the generation of [Ca2+]i oscillations, which in contrast to oscillations induced by low concentrations of CCK were acutely dependent on the presence of extracellular Ca2+. Oscillations were inhibited by phorbol ester. Sodium fluoride, a known activator of G-proteins, gave similar results. Both mastoparan and CCK induced turnover of inositol phosphates, at concentrations higher than necessary to induce oscillations.

A quantitative study of the coincidence of blood vessels and A4 protein deposits in Alzheimer's disease

The spatial relationship between A4 protein deposits and blood vessels in the brains of 6 elderly cases of Alzheimer's disease has been investigated. Sections were taken from medial temporal cortex and were double immunostained for A4 protein and type IV collagen, the latter being employed as a marker of blood vessels. By comparing the observed area of vessel overlying A4 deposit with that predicted from the product of A4 deposit and blood vessel area fractions it is shown that, contrary to expectations, the likelihood of a vessel co-inciding with an A4 deposit is less than would be expected by chance. It would therefore appear that the previously described positive association between A4 deposits and blood vessels reflects the abundance of A4 and the high vascularity of the cortex rather than any specific correlation between the two features.

Pulpal response to two semihydrous glass ionomer luting cements

This study compared the pulpal responses to two innovative semihydrous glass ionomer luting cements (STA and ZIN) with those previously obtained for a conventional anhydrous glass ionomer luting cement, Aquacem. ZIN contained zinc oxide in the formulation. The study was conducted according to the BSI (1989) recommendations for testing restorative materials in vivo. ZIN was associated with minimal pulpal changes and microbial microleakage, and differed little from the control material, Kalzinol. The pulpal response to STA was similar to that observed for Aquacem, but was associated with less microbial microleakage. The statistical model demonstrated a significant association between bacterial presence within the experimental cavity and pulpal inflammation. The closer that bacteria were to the pulp, the more severe was the ensuing inflammation.

Ligand interaction energies and molecular recognition by chloramphenicol acetyltransferase

The apparent binding energy for the interaction of the 3-hydroxyl group of chloramphenicol (CM) with the proposed general base (His-195) in chloramphenicol acetyltransferase (CAT) was determined by comparison of the dissociation constants of CM and 3-deoxyCM with CAT. The delta Gapp for this hydrogen bond to the N-3 of the imidazole ring is 1.5 kcal mol-1. Extending the use of modified ligands, in an approach which is complementary to that of site-directed mutagenesis, the binding affinity of each of a family of 3-halo-3-deoxychloramphenicol derivatives was observed to increase in the series F less than Cl less than Br less than I and is dominated by hydrophobic considerations. There is a linear free energy relationship between the dissociation constants for binding to CAT and an empirical hydrophobicity scale derived from reverse-phase HPLC retention times. The existence of such a relationship allows a true estimate of the total energetic contribution of interactions between the 3-hydroxyl group of CM and its contacts at the active site of CAT to be made on the basis of a regression analysis. The calculated value of delta Gbind (2.7 kcal mol-1) must include not only the hydrogen bond but also some favorable van der Waals interactions. The results demonstrate some of the advantages of an analysis of the energetics of ligand binding using modified ligands, in an approach that is formally analogous with and complementary to the use of site-directed mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Alternative binding modes for chloramphenicol and 1-substituted chloramphenicol analogues revealed by site-directed mutagenesis and X-ray crystallography of chloramphenicol acetyltransferase

Leucine-160 of chloramphenicol acetyltransferase (CAT) has been replaced by site-directed mutagenesis to investigate enzyme-ligand interactions at the 1-hydroxyl substituent of the substrate chloramphenicol. The consequences of the substitution of Leu-160 by glutamine and by phenylalanine were deduced from the steady-state kinetic parameters for acetyl transfer from acetyl-CoA to the 3-hydroxyl of chloramphenicol and its analogues 1-deoxychloramphenicol and 1-acetylchloramphenicol. The acetyl group of the latter, which is a substrate both in vivo and in vitro, could potentially bind in a similar position to the 1-hydroxyl of chloramphenicol, in close proximity to the side chain of Leu-160. In the case of Gln-160 CAT, large increases in Km for the three acetyl acceptors were accompanied by small decreases in kcat and in apparent affinity for acetyl-CoA. Such results are consistent with the introduction of the relatively hydrophilic amide in place of the delta-methyl groups of Leu-160. The kinetic properties of Phe-160 CAT were unexpected in that Km for each of the three acetyl acceptors was unchanged or reduced, compared to the equivalent parameters for the wild-type enzyme, whereas kcat fell significantly (44-83-fold) in each case. The ratios of specificity constants (kcat/Km) for the acetylation of chloramphenicol compared with the alternative acyl acceptors were similar for wild-type and mutant enzymes. As the residue substitutions for Leu-160 do not result in enhanced discrimination against the binding and acetylation of 1-acetylchloramphenicol, it appears unlikely that the 1-acetyl group binds to the CAT active site in the same position as that occupied by the 1-hydroxyl of chloramphenicol.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in compressive strength of glass ionomer restorative materials with respect to time periods of 24 h to 4 months

This study investigated whether long-term changes occur in the compressive strength of a number of glass ionomer restorative materials, in view of the fact that little information is available from the manufacturers, and any variations with time might affect suitability for clinical use. It was found that, over the period of 24 h to 4 months, some materials, namely those based on polyacrylic acid, maintained or even showed a slight increase in their strength, whereas others based on copolymers of acrylic acid first increased in strength, but thereafter showed deterioration. In one case the strength decreased by nearly 50% compared to that at 24 h.

Localization of Y1 receptors for NPY and PYY on vascular smooth muscle cells in rat pancreas

To localize binding sites for peptide YY (PYY) in the pancreas we utilized a slide-mount autoradiographic technique on frozen sections of rat pancreas incubated with 125I-Tyr36-PPY. Saturable autoradiographic labeling was located over pancreatic blood vessels, whereas islets, acinar cells, ducts, and neural elements did not appear to be specifically labeled. Isolated vascular fragments were prepared by collagenase digestion of rat pancreas. Binding experiments with 125I-Tyr36-PYY showed saturable binding to the fraction enriched in blood vessels but not to acini. Inhibition of 125I-Tyr36-PYY binding by nonradioactive neuropeptide Y (NPY) and PYY were similar, with half-maximal inhibition at 31.2 +/- 5 pM (n = 6); the potency of pancreatic polypeptide (PP) was 10,000 times lower. The binding site was classified as belonging to a Y1 type of NPY and/or PYY receptors, since [Leu31,Pro34]NPY, a specific Y1-receptor agonist, inhibited binding similar to NPY. To further localize the bound [125I-Tyr36]PYY within the blood vessels, light- and electron-microscopic autoradiographs were prepared and quantitated. Autoradiographic grains were located predominantly over vascular smooth muscle cells, although saturable localization was also seen over endothelial cells. It is concluded that in the pancreas Y1 receptors are predominantly located on vascular smooth muscle cells.

Secretagogue-induced Ca2+ oscillations in isolated canine gastric chief cells

Agonist-induced changes in cytoplasmic free Ca2+ concentration [( Ca2+]i) of isolated canine gastric chief cells were evaluated by microspectrofluorometry of superfused fura-2 loaded cells. Application of high concentrations of carbachol (CCh, 10(-5) M) or cholecystokinin octapeptide (10(-8) M) resulted in biphasic Ca2+ mobilization comprising an initial large transient followed by a small sustained elevation above the prestimulation level. Submaximal concentrations of CCh (10(-6) M) or cholecystokinin (10(-9) M) led to either a transient series of large amplitude Ca2+ spike(s) or a higher frequency of sustained Ca2+ oscillations of smaller amplitude. Cholecystokinin at 10(-10) M induced only sustained Ca2+ oscillations. Elimination of Ca2+ from the medium had no immediate effect on oscillations indicating an intracellular source of Ca2+. Thus the Ca2+ signalling mode in chief cells is dependent on agonist concentrations.

Interactions of intracellular mediators of amylase secretion in permeabilized pancreatic acini

Mouse pancreatic acini were permeabilized with streptolysin O to investigate amylase secretion stimulated by various intracellular mediators and the kinetics of secretion as a function of temperature. Amylase secretion was temperature dependent in that the initial rate of Ca2(+)-stimulated secretion increased with increasing temperature. In addition, there was no enhancement of Ca2(+)-stimulated secretion by GTP[gamma S] at 14 degrees C, while enhancement was maximal at 30 degrees C. GTP[gamma S]-mediated enhancement of secretion at a given temperature was mostly due to sustained secretion with a small increase in secretory rate. At 30 degrees C Ca2(+)-stimulated secretion was also enhanced by cAMP and phorbol ester (TPA) to similar extents as by GTP[gamma S]. The maximally effective concentration of cAMP was 1-10 microM in the presence of 0.1 mM isobutylmethylxanthine. The enhancements of Ca2(+)-stimulated amylase secretion by all combinations of cAMP (100 microM plus 0.1 mM isobutylmethylxanthine), TPA (1 microM), and GTP[gamma S] (30 microM) were fully additive. In Ca2(+)-free buffer, cAMP, TPA or GTP[gamma S] individually had no effect on amylase secretion. Together, TPA and GTP[gamma S] stimulated Ca2(+)-independent secretion, which was 187 +/- 38% of basal. Cyclic AMP together with TPA and GTP[gamma S] in the absence of Ca2+ stimulated 329 +/- 30% of basal secretion. Ca2(+)-stimulated amylase secretion was decreased about 50% by metabolic inhibition, while the enhancement by cAMP, TPA or GTP[gamma S] was totally blocked by metabolic inhibitors. These data demonstrate that amylase secretion in the acinar cell is mediated by multiple intracellular pathways which act in parallel and probably converge at a distal step in the exocytotic process.

Efficacy of tiamulin against experimentally induced Streptococcus suis type-2 infection in swine

Eighteen 4-week-old pigs were used in a study to evaluate tiamulin in drinking water for control of experimentally induced Streptococcus suis type-2 infection. Pigs in groups A and B (n = 6 pigs/group) were aerosolized with a logarithmic-growth phase culture of S suis type 2, whereas pigs in group C (n = 6 pigs) served as noninfected and nonmedicated controls. After exposure to S suis, pigs in group B were given 180 mg of tiamulin/L of drinking water for 5 days. Pigs in group B consumed more feed (P = 0.009) and gained body weight faster (P = 0.02) than did pigs in group A. Pigs in group A had higher rectal temperature (P = 0.05) for up to 7 days after S suis exposure, higher clinical sign scores (P = 0.008), higher serum cortisol concentration on days 7 and 14, higher gross lesion scores (P = 0.03), and higher microscopic lesion scores (P = 0.01) than did pigs in groups B and C. Gross and microscopic lesions in pigs of groups A and B included meningitis, pneumonia, pleuritis, pericarditis, peritonitis, and synovitis of variable severity. Streptococcus suis type 2 was recovered from tissue specimens of 2 group-A pigs and 1 group-B pig. Data indicated that tiamulin administered via drinking water significantly reduced the effects of S suis type-2 infection.