Single-tooth implants and the soft tissue relationship.
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Dental Implants↗
Biomedical subjects
P C Ryan
Publications and source records attributed to P C Ryan.
The effects of acute and chronic JJ stent placement on upper urinary tract motility and calculus transit.
OBJECTIVE: To determine the pathophysiological changes in upper urinary tract motility and calculus transit which may occur following JJ stent insertion. MATERIALS AND METHODS: The acute and chronic effects of JJ stent placement were studied in 24 canine renal units. Intrarenal and intraureteric pressures and motility were measured, in addition to transit times for complete passage of synthetic calculi from the upper ureter into the bladder. RESULTS: Acute effects included raised renal intrapelvic pressure, reduced pelvic and ureteric motility and delayed calculus transit time. Prolonged JJ stent placement was associated with return of intrapelvic pressure to normal but persistent changes in both renal and ureteric motility and also calculus transit time. CONCLUSION: In situ JJ stents impair upper urinary tract motility and experimental calculus transit time and may delay passage of ureteric calculi or calculus fragments following extracorporeal shock wave lithotripsy.
Animals↗
Ischaemia-reperfusion injury in the rat kidney: effect of a single dose of sodium bicarbonate.
The protective effect of intravenous 8.4 per cent sodium bicarbonate on renal function after ischaemia was evaluated in rats subjected to 45 or 90 min warm unilateral renal ischaemia. Two groups of control animals received normal or 3 per cent saline. All solutions were given by bolus injection 3 h before ischaemia. Renal function was significantly protected in animals receiving bicarbonate. Vascular congestion of the inner stripe of the renal medulla was prevented. The survival rate in the group undergoing 90-min ischaemia was 70 per cent for animals receiving bicarbonate and nil in those given saline. Preoperative alkalinization confers significant functional and morphological protection in the ischaemic kidney.
Animals↗
The ureter in vitro: normal motility and response to urinary pathogens.
The effects of bacteria on in vitro ureteric contractility were studied, using a model which allowed selective exposure of organisms to the ureteric mucosa and smooth muscle, respectively. A cannula attached to a pressure transducer was ligated into the proximal lumen of 2.5-cm segments of canine ureter. The distal ureter was ligated to form a closed pressure monitored system, and the segment suspended in a 20-ml organ bath containing Krebs Henseleit buffer at physiological pH and temperature. Following onset of spontaneous activity, broths of Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa and Staphylococcus aureus were added to either the buffer solution or ureteric lumen in doses of > 10(6) organisms/ml. Experiments were repeated using heat-killed organisms, bacterial filtrates and E. coli endotoxin. Ureteric contractility was stimulated by organisms added to the buffer medium, but reversibly inhibited by bacteria placed in the ureteric lumen. Heat-killed organisms, endotoxin and live filtrates had no effect on normal motility when exposed to either the ureteric mucosa or muscularis respectively. These findings reflect the conflicting changes in ureteric motility seen in vivo when bacteria are administered systemically or directly into the ureteric lumen.
Animals↗
Pharmacological options for the treatment of acute ureteric colic. An in vitro experimental study.
The effects of opiate and non-steroidal anti-inflammatory agents on the in vitro canine ureter were compared using a new model for the assessment of ureteric pharmacology. A pressure measuring catheter attached to a pressure transducer and pre-calibrated pen recorder was ligated into the lumen of 2.5 cm segments of normal canine ureter. The segments were immersed in an organ bath at physiological pH and temperature and spontaneous contractility was observed in 90% of them. Morphine had a spasmogenic effect on ureteric activity which was unaffected by naloxone. This effect was similar to that of histamine and prostaglandin F2 alpha and was abolished by chlorpheniramine but not by cimetidine. Pethidine produced a transient stimulation followed by inhibition of ureteric activity which was unaffected by naloxone. Both indomethacin and diclofenac produced an abrupt inhibition which was reversible with prostaglandin F2 alpha. These data suggest that pethidine or a non-steroidal anti-inflammatory agent may by virtue of their spasmolytic effects be a superior choice of therapy for the acutely obstructed ureter.
Acute Disease↗
Recovery of ureteric motility following complete and partial ureteric obstruction.
Complete and partial ureteric obstruction was created in 2 groups of 10 mongrel dogs by placing a ligature around, or inserting a fine bore plastic stent into, the lower end of the left ureter (Groups 1 and 2). After 4 weeks the ligature or stent was removed, a 2.5-cm segment of ureter was harvested for in vitro analysis and the ureter reimplanted into the bladder. Pelvic and ureteric pressures and motility were recorded before, during and after the period of obstruction via a subcutaneously placed nephrostomy tube. Pre-obstruction resting intra-ureteric pressure was 2.1 +/- 0.3 mm Hg (mean +/- SEM), with regular contractions 8.9 +/- 0.7/min of 36.2 +/- 1.2 mm Hg amplitude. After 4 weeks of obstruction, contractility was abolished in Group 1 but increased in Group 2, 71.5 +/- 3.3 mm Hg, with irregular multiphasic contractions seen following diuresis. Intra-ureteric pressure was 16.3 + 1.2 mm Hg in Group 1 and 9.3 + 1.2 mm Hg in Group 2. In vitro experiments confirmed the patterns of contractility seen in vivo. Eight weeks after reimplantation the ureter returned to normal rhythm and rate in Group 1, but increased contractility persisted both in vivo and in vitro in Group 2.
Animals↗
Recognition of the highly conserved GTPase center of 23 S ribosomal RNA by ribosomal protein L11 and the antibiotic thiostrepton.
The antibiotic thiostrepton, a thiazole-containing peptide, inhibits translation and ribosomal GTPase activity by binding directly to a limited and highly conserved region of the large subunit ribosomal RNA termed the GTPase center. We have previously used a filter binding assay to examine the binding of ribosomal protein L11 to a set of ribosomal RNA fragments encompassing the Escherichia coli GTPase center sequence. We show here that thiostrepton binding to the same RNA fragments can also be detected in a filter binding assay. Binding is relatively independent of monovalent salt concentration and temperature but requires a minimum Mg2+ concentration of about 0.5 mM. To help determine the RNA features recognized by L11 and thiostrepton, a set of over 40 RNA sequence variants was prepared which, taken together, change every nucleotide within the 1051 to 1108 recognition domain while preserving the known secondary structure of the RNA. Binding constants for L11 and thiostrepton interaction with these RNAs were measured. Only a small number of sequence variants had more than fivefold effects on L11 binding affinities, and most of these were clustered around a junction of helical segments. These same mutants had similar effects on thiostrepton binding, but more than half of the other sequence changes substantially reduced thiostrepton binding. On the basis of these data and chemical modification studies of this RNA domain in the literature, we propose that L11 makes few, if any, contacts with RNA bases, but recognizes the three-dimensional conformation of the RNA backbone. We also argue from the data that thiostrepton is probably sensitive to small changes in RNA conformation. The results are discussed in terms of a model in which conformational flexibility of the GTPase center RNA is functionally important during the ribosome elongation cycle.
Base Composition↗
Detection of a key tertiary interaction in the highly conserved GTPase center of large subunit ribosomal RNA.
Searches of ribosomal RNA sequences for compensatory base changes preserving Watson-Crick base pairing have led to detailed models of the conserved secondary structures of these RNAs. In principle, tertiary interactions can also be detected by searches for phylogenetically covariant bases. Within a highly conserved region of the large subunit ribosomal RNA termed the "GTPase center," the bases G-1056-U-1082.A-1086 are found in all eubacteria (Escherichia coli numbering), while A-1056.C-1082.G-1086 are found at the homologous positions in eukaryotes; archaebacteria fall into either category with some exceptions. Either sequence can potentially form a similar set of hydrogen bonds connecting the 3 bases. To determine the contribution of these 3 bases to RNA tertiary structure, sequence variants were made in RNA fragments covering the GTPase center. Correct folding of the RNA fragments was assayed by measuring the binding affinities of two different ligands that recognize the RNA tertiary structure: the highly conserved ribosomal protein L11, which is normally associated with the GTPase center RNA, and the peptide antibiotic thiostrepton, which inhibits the GTPase activity of eubacterial and some archaebacterial ribosomes. The results strongly support the existence of a base pair between positions 1082 and 1086: single mutations at either position weaken both L11 and thiostrepton binding by approximately 10-fold or more, while compensatory double mutations bind the ligands nearly as well as the wild-type E. coli sequence. Variants at position 1056 have little effect on either L11 or thiostrepton binding; a 3-base interaction is therefore not supported by these experiments. A base pair between positions 1082 and 1086 strongly constrains the geometry with which three helical segments join in the middle of the GTPase center.
Base Sequence↗
Changes in regional renal perfusion following ischemia/reperfusion injury to the rat kidney.
Post-ischemic renal failure is associated with a zone of vascular hyperaemia in the outer medulla of the kidney. The effect of this lesion on regional renal perfusion is, however, unclear. Acute unilateral renal ischemia was applied to four groups of ten adult male Wistar rats for a period of 60 min, followed by revascularisation for 0, 15, 30 or 60 min. The aorta was then clamped and Microfil was injected at a standard pressure to fill the renal vasculature. Gross and histological examinations of the renal parenchyma and vasculature were then performed. Regional renal Microfil perfusion was quantified by examination of unstained histological sections, giving rise to a vascular perfusion index (VPI) for each vascular region of the kidney. The VPIs were similar in control and ischemic kidneys that were not subjected to reflow (group 1). In contrast, the VPI was markedly decreased in the inner stripe and inner medulla in animals in which revascularisation had occurred (groups 2-4), and the vasculature in these regions was histologically shown to be packed with red blood cells. Post-ischemic renal failure is associated with hyperperfusion of the medulla resulting from blockage of the vasculature that occurs during revascularisation.
Acute Kidney Injury↗
Acute and chronic bioeffects of single and multiple doses of piezoelectric shockwaves (EDAP LT.01).
Piezoelectric second generation lithotriptors are an established means of administering extracorporeal shockwave lithotripsy (ESWL) enabling treatment to be performed without anaesthesia or analgesia, but higher shockwave doses and multiple or staged treatment are frequently required. The bioeffects of this modality of ESWL, therefore, require further assessment. Seven experimental groups of adult male rabbits were treated using the EDAP LT.01 in order to determine the acute and chronic bioeffects of clinical dose, excess dose, divided excess dose, high frequency and multiple treatment (X10) piezoelectric shockwaves (PSW). Renal function was measured before and after treatment using mercaptoacetyltriglycine (MAG 3) scans. Gross and histological morphological changes were assessed at one and 30 days following application of PSW. Application of single clinical dose PSW was not associated with any significant functional or morphological renal injury. Excess dose PSW caused transient gross renal contusion, which resolved in the majority of animals with no persistent microscopic abnormality. Divided excess dose PSW resulted in no gross or microscopic damage. High frequency PSW was associated with mild histological abnormality. Multiple PSW treatments caused small discrete fibrotic lesions in all cases, without any change in renal function.
Animals↗
Cholecystokinin provocation test.
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Biliary Tract Diseases↗
An experimental technique for renal intrapelvic access.
This study describes an experimental technique for insertion of an indwelling cannula into the canine renal pelvis, and demonstrates its use in the measurement of pelviureteric pressure and motility, creatinine clearance, Whitaker tests, nephrostograms and nephrostomy drainage. The system, which consists of cannula, Heplock and plastic fixation disc, has been inserted into 53 canine kidneys (48) dogs, and percutaneous needle passage into the subcutaneously placed Heplock was used to gain access to the renal pelvis. This technique was successful in virtually all cases (131 separate procedures), and there were few complications. The indwelling intrapelvic cannula is a simple, cheap and reliable method of gaining longterm renal intrapelvic access in the dog, and has many experimental applications.
Animals↗
Ultrasonic imaging for extracorporeal shockwave lithotripsy: analysis of factors in successful treatment.
The emergence of real-time ultrasonic imaging for extracorporeal shockwave lithotripsy poses questions regarding the factors and techniques which facilitate stone imaging for clinicians with no previous practical experience in ultrasonography. The ability of these clinicians to assess when stone disintegration has been achieved also needs to be confirmed. A wide range of data was recorded from each of 2688 lithotripsy treatments performed over a 2-year period using the EDAP LT.01 ultrasound-imaged piezoelectric lithotriptor. An analysis of these data was performed using a comprehensive microcomputer-based statistics package. The mean time taken for stone imaging and positioning was reduced from 11.2 to 7.5 min over the 2-year period. Obese patients and those with renal pelvic stones were best imaged in a lateral position. Overall there was no difference in percentage stone disintegration or clearance between treatments in the supine or lateral positions, but a significant reduction in the clearance of small caliceal stones resulted when the lateral position was used. Factors associated with a significantly greater percentage of stone disintegration and clearance included pain experienced by the patient during fine adjustment of the processing head during treatment, acoustic focus attenuation and widening and acoustic shadow widening as detected by the urologist at the end of treatment. Among the factors not associated with significant alterations in the percentage of stone disintegration or clearance were the lithotriptor operator, the side or site of the calculus, obesity and shockwave frequency or power. This study confirmed the ability of urologists to develop expertise in ultrasonography for renal stone imaging and to interpret successfully the subtle signs of stone disintegration.
Adolescent↗
Use of the double pigtail stent in stone retrieval following unsuccessful ureteroscopy.
Insertion of a double pigtail stent is known to cause ureteric dilatation. We analysed the effect of an indwelling double pigtail stent on the success rate of calculus extraction by second ureteroscopy when the initial ureteroscopy fails. Over a 12-month period, a first ureteroscopy failed in 42 patients; 30 were then treated by ureteroscopy combined with a ureteric stent and 12 were treated without a ureteric stent. The group with an indwelling stent had a successful second ureteroscopy or spontaneously passed the calculus in 24 cases (84%) compared with 5 unstented cases (45%). Ureterolithotomy was necessary in 2 patients with a stent and 3 with no stent. It was concluded that following failed ureteroscopic manipulation of calculi, insertion of a double pigtail stent was associated with a higher subsequent success rate for removal of stone by ureteroscopy and a consequent lower rate of ureterolithotomy.
Adult↗
Thermodynamics of protein-RNA recognition in a highly conserved region of the large-subunit ribosomal RNA.
Ribosomal protein L11 from Escherichia coli specifically binds to a highly conserved region of 23S ribosomal RNA. The thermodynamics of forming a complex between this protein and several different rRNA fragments have been investigated, by use of a nitrocellulose filter binding assay. A 57-nucleotide region of the RNA (C1052-U1108) contains all the protein recognition features, and an RNA fragment containing this region binds L11 10(3)-10(4)-fold more tightly than tRNA. Binding constants are on the order of 10 microM-1 and are only weakly dependent on K+ concentration (delta log K/delta log [K+] = -1.4) or temperature. Binding requires multivalent cations; Mg2+ is taken up into the complex with an affinity of approximately 3 mM-1. Other multivalent cations tested, Ca2+ and Co(NH3)63+, promote binding nearly as well. The pH dependence of binding is a bell-shaped curve with a maximum near neutral pH, but the entire curve is shifted to higher pH for the smaller of two RNA fragments tested. This result suggests that the smaller fragment favors a conformation stabilizing protonated forms of the RNA recognition site and is potentially relevant to a hypothesis that this rRNA region undergoes an ordered series of conformational changes during the ribosome cycle.
Base Sequence↗
Endoscopic treatment of urinary tract calculi.
Removal of urinary tract calculi by endourological techniques is now widely practised and has reduced the indications for open surgical removal to a minority of cases. A review of 270 consecutive patients who presented to the Meath Hospital Urology department with urinary tract calculi and were treated by percutaneous or transurethral endoscopy is herein reported. The rates of successful clearance of renal (95%) and ureteric (78%) calculi compare well with previous reports. The majority of complications were minor and a low overall complication rate was experienced at ureterorenoscopy. In our experience, endourological treatment of urinary tract calculi is successful, efficient and safe and is the recommended approach to urinary tract calculi that require surgical intervention.
Adult↗
Renal injury and recovery in partial ureteric obstruction.
Partial ureteric obstruction was produced by insertion of an obstructing stent into the left ureter of 21 mongrel dogs and the duration of obstruction was varied as follows: Group A (n = 7) for 60 days; Group B (n = 7) for 28 days; Group C (n = 7) for 14 days. Intrapelvic pressure monitoring confirmed that obstruction had been produced by stent insertion and relieved by reimplantation of the left ureter following the designated obstruction period. The extent of recovery of renal function was assessed by creatinine clearance, with group C maintaining normal function, group B recovering 31% and group A recovering 8% of control function. Methyl-methacrylate extrusion casts of the renal microvasculature were made in group B and C kidneys and studied by scanning electron microscopy. During obstruction there was evidence of arteriolar constriction. These changes provide a morphological basis for the renal functional alterations and support the concept that post-obstructive renal failure is a vascular injury.
Animals↗
The Whitaker test: experimental analysis in a canine model of partial ureteric obstruction.
The Whitaker test has been described as a means of reaching a diagnosis in equivocal upper urinary tract obstruction, but there has been conflicting evidence regarding the validity of this test. The present study assesses the reliability of the test in an experimental model which creates an accurate and predetermined degree of partial obstruction of the ureter. The Whitaker test was performed using the standard perfusion rate of 10 ml./min. in male adult dogs using a long-term indwelling renal intrapelvic cannula before and after application of ureteric obstruction, and after one month. Control animals underwent a sham procedure. Results of in vivo and in vitro perfusion studies were compared. Perfusion studies at multiple flow rates were also performed. The Whitaker test reliably detected the presence of ureteric obstruction and the degree of partial obstruction could be determined. Multiple flow rate studies did not significantly improve test results. Provoked pressures in the highest grade of obstruction were less than expected and this may be due to pyelovenous reflux.
Animals↗