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S O Svensson

Publications and source records attributed to S O Svensson.

At least 19 recordsLinked to original sources
PubMed1997

Calibration and application of an X-ray image intensifier/ charge-coupled device detector for monochromatic macromolecular crystallography.

Charge-coupled device (CCD)-based X-ray detectors allow data to be collected much more quickly (approximately 10 times) than with current on-line imaging-plate systems. At the ESRF, X-ray image intensifier/CCD detector systems have been developed. These have great potential as fast read-out detectors for macromolecular and other forms of crystallography. They are relatively large sensitive X-ray detectors but have two inherent weaknesses: convex detection surfaces leading to spatial distortion and non-uniformity of intensity response, and susceptibility to small changes in magnetic fields. A large improvement has been made to the accuracy obtained by non-uniformity of response calibration and correction, using fluorescence from doped lithium borate glasses. Monochromatic macromolecular crystallography demonstration experiments with external user groups have shown that high-quality results may be obtained under real experimental conditions.

Journal Article↗
PubMed1997

Time-resolved X-ray powder diffraction using a large-area CCD-based detector and Rietveld refinement: solid-state polymerization of S2N2 to (SN)x.

A kinetic study of the solid-state polymerization of disulfur dinitride (S2N2) to polysulfur nitride [(SN)x] has been performed, combining monochromatic high-energy (lambda = 0.3263 A) synchrotron radiation X-ray powder diffraction, a large-area (ø = 220 mm) CCD-based X-ray image-intensifier detector and Rietveld refinement. Recently developed techniques for detector calibration and reduction of two-dimensional images to one-dimensional diffraction patterns have been employed for data processing/analysis. Good fits were obtained after Rietveld refinement [Rp = 8.4%, wRp = 9.4%, sin(theta(max))/lambda = 0.585 A(-1)] of diffraction patterns of S2N2 from images with 2 s exposure time. The solid-state polymerization of S2N2 to (SN)x, was followed at a maximum rate of two diffraction images per minute. Scale factors and cell parameters for S2N2 and beta-(SN), as functions of time were readily obtained after Rietveld refinement of the diffraction patterns obtained from each individual image throughout the polymerization. The polymerization was preceded by a lattice distortion of S2N2, and at 50% conversion the a axis had decreased by about 1% and the c axis had increased about 1%. The polymerization yielded not only the expected polymer beta-(SN)x, but also a small amount of a compound that could be another phase of (SN)x.

Journal Article↗
PubMed1996

A Novel Technique for Accurate Intensity Calibration of Area X-ray Detectors at Almost Arbitrary Energy.

A novel intensity uniformity calibration method for area X-ray detectors is described. In diffraction experiments, amorphous lithium glass plates, containing doping elements chosen for their K edges just below the energy of the main beam, replace the crystallographic samples for the calibration measurement. The fluorescent emission excited by the X-ray beam is almost isotropic. It has exactly the same geometry as the diffracted radiation, and can be obtained at the same wavelength by proper selection of the element and excitation energy. A sample 2theta scan allows the emission distribution as a function of angle to be characterized with an accuracy of a fraction of a percent. This allows a flat-field correction of similar accuracy. The quality of crystallographic data collected with an X-ray image intensifier/CCD detector was significantly improved by flat-field correction using an Sr-doped lithium tetraborate glass. This technique can be applied to X-ray energies from 5 to 50 KeV; the calibration sample is small, stable and easily handled.

Journal Article↗
PubMed1980

Reduction of serum gastrin response to insulin hypoglycemia by selective vagotomy with pyloroplasty in duodenal ulcer patients.

We have previously demonstrated that insulin hypoglycemia releases antral gastrin by a pH sensitive mechanism in duodenal ulcer (DU) patients. The effect of vagotomy per se on the hypoglycemic release of gastrin therefore might be obscured by alterations in antral pH. In the present study on 11 DU patients, the gastric acid response to intravenously administered insulin (0.2 units/kg-1) was determined before and after selective vagotomy with pyloroplasty (SV + PP). In another preoperative and postoperative test on each patient, the serum gastrin test, the serum gastrin response (radioimmunoassay) to insulin was determined during gastric perfusion with citrate-phosphate buffer pH 7.0. By adjusting the perfusion rate, the intragastric pH was maintained at 5.0 or higher. SV + PP abolished the acid response to insulin in four and reduced the response by 80% to 95% in another six patients. Gastric buffer perfusion or SV + PP did not alter the basal serum gastrin level. The increase of serum gastrin level after insulin was significantly (P less than 0.01) reduced by SV + PP. Before operation the integrated serum gastrin response to insulin was significant (P less than 0.01). SV + PP reduced the response to one-third. The effect of SV + PP on the hypoglycemic release of gastrin varied among the patients but no relationship was found to the effect on the acid response, nor to the variations of the volume or pH of the perfusate (pH range, 5.0 to 7.5). It is concluded that insulin hypoglycemia releases antral gastrin by a vagal and probably also by a nonvagal mechanism and that both mechanisms are pH sensitive.

Adult↗
PubMed1979

Significance of antral pH for gastrin release by insulin hypoglycemia in duodenal ulcer patients.

The significance of antral pH for the basal serum level of immunoreactive gastrin and for the release of gastrin during insulin hypoglycemia has been studied in duodenal ulcer (DU) patients. To permit paired comparisons, 14 DU patients underwent two or three tests with insulin. Venous blood samples were collected at fixed intervals for determination of gastrin (radioimmunoassay). In the first insulin test, the gastric juice was aspirated; in the second test, the stomach was perfused with citrate-phosphate buffer, pH 7.0; and in the third test the stomach was perfused with 0.1M HCl, pH 1.0. The rate of buffer or acid perfusion was adjusted, and the pH of the perfusate was kept above 5.0 and below 1.3, respectively. Gastric perfusion with buffer or acid for 1 hour did not affect the basal serum gastrin level, nor did perfusion with buffer for 3 hours. Insulin hypoglycemia stimulated acid secretion and produced a significant integrated serum gastrin response during gastric aspiration, but the gastrin response was four times greater during buffer perfusion. Acid perfusion abolished the gastrin response. From our previous and present findings, it is concluded that the gastrin in serum during basal conditions is of extra-antral origin and is independent of antral pH. Insulin hypoglycemia releases antral gastrin by a pH-sensitive mechanism in DU patients; the release is suppressed at pH 1.3 or less and also is markedly inhibited when the gastric juice is aspirated.

Adult↗
PubMed1979

Parietal cell structure and acid secretion in the vagally innervated stomach and the vagally denervated fundic pouch in cats.

In seven cats provided with gastric fistula (GF) of the main stomach and a denervated Heidenhain pouch (HP) the structure of the innervated and denervated mucosa was examined by light and electron microscopy. In four of these cats dose-response curves for acid output to pentagastrin were determined before and after vagal denervation of the fundic pouch. Vagal denervation reduced the acid response to pentagastrin by decreasing both the secretory capacity and the sensitivity of the oxyntic glands. Accordingly, in the same cat the parietal cells of the HP were less sensitive to pentagastrin than the cells of the innervated main stomach. Light and electron microscopic investigations revealed that the fundic mucosa was thinner, and the size and proportion of the parietal cells was smaller in the HP than in the GF. It is likely that the morphological changes in the pouch were caused by the vagal denervation rather than by the loss of mucosal contact with food. The secretory and morphological changes produced by the vagotomy are not necessarily related.

Animals↗
PubMed1977

Acid secretory responses to histamine, pentagastrin, and feeding before and after vagal denervation of fundic pouches in cats.

Dose-response curves for acid output to histamine, pentagastrin and feeding were determined in cat before and after vagal denervation of the fundic pouch. Before denervation, the maximal response to the three stimulants was equal. Denervation reduced the acid response to histamine by decreasing the secretory capacity, and to pentagastrin by decreasing both the secretory capacity and sensitivity of the oxyntic glands. In this respect the effect of local and truncal vagotomy is equal in cats. The reduction of the response to feeding was greater than to histamine and pentagastrin. In the denervated pouch, the maximal response to feeding amounted to two-thirds of that to histamine and pentagastrin. This demonstrates that feeding does not release enough gastrin to induce maximal rate of acid secretion in the absence of vagal impulses. Nevertheless, feeding and pentagastrin produced equal maximal responses before denervation. This suggests that vagal impulses during feeding produce greater enhancement than basal vagal tone of the acid response to submaximal doses of gastrin.

Animals↗
PubMed1977

Effect of methacholine on acid and pepsin responses to pentagastrin in cats with innervated and denervated fundic pouches.

The effect of threshold dose of methacholine on gastric secretion stimulated by pentagastrin (PG) was studied in two groups of cats, four with Pavlov pouches (PP) and four with Heidenhain pouches (HP). In the PP group methacholine did not alter the maximal response (MR) and the dose producing half of the maximal response (D50) for PG. In the HP group the highest acid response to PG combined with methacholine was greater than the MR to PG alone. Methacholine decreased the D50 for PG in the HP group to that in the PP group with and without methacholine. Methacholine increased the pepsin response to all doses of PG both in the PP and the HP groups. The effect was more pronounced in the HP group. In both types of pouches, the percentage increase of pepsin secretion was larger at low than at high doses of PG. Methacholine increased the pepsin/acid (P/A) ratio for PG in the HP group to that in the PP group with and without methacholine. Accordingly, methacholine sensitized the oxyntic glands and increased the pepsin response to PG in the HP group as did basal vagal tone in the PP group. Methacholine did not further sensitize the innervated oxyntic glands to gastrin but increased the response of the peptic glands.

Animals↗
PubMed1976

Cholinergic release of gastrin by feeding in cats.

The effect of atropine on acid secretion and serum gastrin level after feeding was studied in 8 cats with denervated fundic pouches (Heidenhain pouch, HP). Serum gastrin concentration was measured by radioimmunoassay. In the control experiments, the mean peak acid response occurred 45 min after feeding and the mean peak gastrin concentration 15 min after feeding. After the 1st postprandial hr, acid secretion declined but the gastrin level remained elevated. Atropine, 0.1 mg per kg intravenously 5 min before feeding, depressed both acid secretion and the increase in serum gastrin concentration during the 1st postprandial hr. In both the control and atropine experiments, acid secretion and serum gastrin level were correlated significantly during the 1st postprandial hr, but no correlation was found later in the experiments. The reduction by atropine of the acid and serum gastrin responses varied among the cats but were correlated significantly. It is concluded that a cholinergic mechanism is implicated in the release of gastrin by feeding in cats during the 1st postprandial hr. Atropine reduces the HP acid response to feeding at least in part by depressing the release of gastrin.

Animals↗
PubMed1976

Gastric acid and serum gastrin responses to insulin and 2-deoxy-d-glucose in duodenal ulcer patients before and after partial gastrectomy.

Gastric acid and serum gastrin (radioimmunoassay) responses to insulin (0.2 U/kg i.v.) and 2-deoxy-D-glucose (2DG) (50 mg/kg i.v.) were determined in 11 male duodenal ulcer patients before and after partial gastrectomy involving complete antral resection. In 8 of the patients the acid response to pentagastrin (6 mug/kg subc.) was also determined. Before operation, 2DG produced higher acid and gastrin responses than insulin. Partial gastrectomy reduced basal acid secretion by 54% but did not alter the basal gastrin level, suggesting that this gastrin is of extra-antral origin. Partial gastrectomy reduced the acid responses to insulin and 2DG by 66% and 78%, respectively; after operation the acid responses to these stimulants were equal. The ratio for the acid response to insulin and pentagastrin was 65% before and 56% after partial gastrectomy; corresponding ratios for 2DG and pentagastrin were 112% and 48%. Partial gastrectomy abolished the peak gastrin response to insulin hypoglycemia and reduced that to 2DG by 64%. The integrated gastrin response to insulin and 2DG was insignificant in the operated patients. Both insulin and 2DG release mainly antral gastrin which appears to be of greater importance for the acid response to 2DG than insulin.

Adult↗