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Biomedical subjects

G J Williams

Publications and source records attributed to G J Williams.

At least 73 records · Page 4Linked to original sources
PubMed1986

Doppler echocardiographic characteristics of the Carpentier-Edwards xenograft.

In order to define ranges of normal velocities for the Carpentier-Edwards xenograft, 38 mitral, 24 aortic and 9 tricuspid prostheses were studied with pulsed or continuous wave Doppler at a mean interval of 38 months following surgery. All patients had clinically normal prosthetic valve function and no clinical or radiographic signs of heart failure. Mean peak velocity across aortic prostheses was 244 cm s-1 (SD 48). There was weak correlation (r = 0.54, P less than 0.01) between peak velocity and time since valve implantation, but no significant difference in peak velocity across valves of different size. In the mitral position, mean peak velocity was 164 cm s-1 (SD 24) and mean pressure half time 90 ms (SD 23). There was again no significant difference between valves of different size. There was a weak correlation between pressure half time and time since implantation (r = 0.44, P less than 0.01), but there was no relationship between the latter and peak velocity. In the tricuspid position, mean peak velocity was 150 cm s-1 (SD 12) and mean pressure half time 163 ms (SD 50). The Doppler indices of obstruction to blood flow for prostheses in the mitral and aortic positions showed a significant increase with time after implantation.

Adult↗
PubMed1985

Diastolic forward blood flow in the pulmonary artery detected by Doppler echocardiography.

The etiology of diastolic motion of the pulmonary valve seen on the M-mode echocardiogram has been the subject of much debate. To further investigate diastolic events in the pulmonary artery, the patterns of diastolic pulmonary artery blood flow velocity were studied using pulsed Doppler echocardiography in patients with a normal heart. Two diastolic waveforms were found, one in early diastole related to passive filling of the right ventricle and one in late diastole related to atrial contraction. These waveforms were also related to the two recognized phases of diastolic pulmonary valve motion detected by M-mode echocardiography. The presence of biphasic diastolic blood flow in the pulmonary artery was confirmed by electromagnetic flow velocimetry in four additional patients with various cardiac diseases and normal right heart pressures. It is concluded that both atrial contraction and passive right ventricular filling produce blood flow in the pulmonary artery.

Adolescent↗
PubMed1985

Inhibition of binding to initiation complexes of nascent reovirus mRNA by double-stranded RNA-dependent protein kinase.

A coupled, cell-free system for the transcription and translation of reovirus mRNA was developed. Activated reovirions were incubated with reticulocyte lysate and an appropriate energy mix. Active transcription was obtained, but protein synthesis was inhibited after a short lag even by low concentrations of reovirions. This inhibition was abolished by the addition of the kinase inhibitor 2-aminopurine. With this addition, the synthesis of viral proteins could be detected in reaction mixtures containing nuclease-treated reticulocyte lysate. The binding of nascent reovirus mRNA to 80S initiation complexes measured after 2 min of incubation was greatly inhibited, whereas the binding of cellular mRNA added to the same reaction mixtures for the next 2 min was not inhibited. The inhibition of reovirus mRNA binding could not be explained by the synthesis of defective templates, since most of the mRNA could be bound to 80S complexes after the addition of 2-aminopurine. These results indicate that the binding of nascent reovirus mRNA was preferentially inhibited by a protein kinase. Reovirions preincubated with reticulocyte lysate could phosphorylate initiation factor eIF-2. This phosphorylation was inhibited by the addition of high concentrations of double-stranded RNA, which are inhibitory for the eIF-2 kinase present in elevated levels in reticulocyte lysate and in interferon-treated cells. These results indicate that the translation of viral mRNA may be preferentially inhibited in interferon-treated cells by the eIF-2 kinase activated by viral transcriptional complexes containing double-stranded RNA.

Animals↗
PubMed1985

Inhibition of viral mRNA translation in interferon-treated L cells infected with reovirus.

Murine L cells were treated with interferon (IFN) concentrations which reduced by 75 to 80% the synthesis of viral mRNA after infection with reovirus. Protein synthesis was not inhibited in these cells up to 6 h after infection, but a large fraction of the viral mRNA was not associated with polyribosomes and sedimented at about 50S. In contrast, most of the reovirus mRNA was associated with polyribosomes in control infected cells. This mRNA was of similar size to non-polyribosomal mRNA from IFN-treated cells when analyzed by Northern blot hybridization with a cloned cDNA for the s2 reovirus mRNA, indicating that the non-polyribosomal mRNA was not appreciably degraded. Viral mRNA was labeled with [3H]uridine and the non-polyribosomal mRNA was isolated from IFN-treated cells. This mRNA could quantitatively bind to 80S initiation complexes when incubated in a rabbit reticulocyte cell-free system. These findings indicated that the non-polyribosomal RNA was translatable, but that its binding to functional initiation complexes was inhibited in IFN-treated cells by a discriminatory mechanism, which did not affect translation of cellular mRNA. Previous experiments showed that mRNA is blocked in 48S complexes when the alpha subunit of initiation factor eIF-2 is phosphorylated by the double-stranded RNA-dependent protein kinase induced by IFN. A localized activation of this kinase could explain the block of viral mRNA in 48S complexes. By labeling the phosphoproteins of IFN-treated cells with 32P, eIF-2 (alpha P) was shown to cosediment with non-polyribosomal mRNA, presumably in 48S complexes.

Animals↗
PubMed1985

Correctable plasma lipoprotein abnormalities in infants with choledochal cysts.

Plasma lipoproteins from two female patients--patient A, 4 wk and patient B, 19 months--were examined prior to and at 1 and 5 wk after surgical correction of biliary obstruction due to choledochal cyst. The findings were correlated with standard indices of hepatic function, namely SGPT, GGTP, 5'nucleotidase, serum bile salts, and total and conjugated bilirubin. Prior to surgery in both patients plasma cholesterol, phospholipid, and triglyceride were elevated; cholesterol esters were low; high-density lipoprotein (HDL) cholesterol and apolipoprotein A-I, the major protein constituent of HDL, were subnormal; most of the plasma lipids were contained in the low-density lipoprotein density region; lipoprotein-X was present. Patient B had had a relatively brief obstruction and suffered little secondary hepatic injury. One week after surgery, plasma lipid concentrations returned to normal; apolipoprotein A-I increased in the HDL density region and a concomitant rise in cholesterol esters to near normal, 65%, was observed; plasma lipids were contained predominantly in HDL; hepatic function improved markedly. Patient A had had intrauterine obstruction and suffered major hepatic injury with cirrhosis. One week after surgery, plasma lipid concentrations, cholesterol esters, low-density lipoprotein lipid predominance, and hepatic function remained essentially unchanged. Five weeks after surgery, the lipoprotein levels and composition and hepatic function were near normal. In conclusion, children with biliary obstruction have lipoprotein abnormalities similar to those seen in adult patients. These alterations are rapidly reversible with surgical relief and may be used as prognostic indicators of outcome.

Apolipoprotein A-I↗
PubMed1984

Active muscle migration during insect metamorphosis.

The R1 abdominal retractor muscles of the insect Tenebrio molitor change position during the course of metamorphosis. These muscles detach from the epidermal tendon cells at their anterior ends, and migrate in a posterior direction, parallel to the body axis, to form completely new attachments shortly before adult emergence. Movement is preceded by the loss of sarcomere structure, and the muscles migrate in a partially dedifferentiated condition, closely accompanied by satellite cells and haemocytes. Movement appears to result from the extension of muscle processes towards the epidermis posterior to the larval attachment sites, which contact reciprocal processes extended from the epidermis. Contacts at the new posterior sites are then reinforced, and relinquished at the anterior. This cycle is subsequently repeated. It is envisaged that migration ceases when the muscles encounter a contour in the epidermal gradient known to specify the position of the adult muscle attachment sites. This positional information may be encoded in the epidermal basal lamina. The muscles then redifferentiate, with concurrent differentiation of new epidermal tendon cells. Development of adult muscle attachments appears to require reciprocal morphogenetic interactions between muscle and epidermis.

Animals↗
PubMed1984

Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. : III. Responses of Protoplasts and Intact Chloroplasts.

Protoplasts and intact chloroplasts isolated from Agropyron smithii Rybd. were utilized in an effort to determine the limiting factor(s) for photosynthesis at supraoptimal temperatures. Saturated CO(2)-dependent O(2) evolution had a temperature optimum of 35 degrees C for both protoplasts and intact chloroplasts. A sharp decline in activity was observed as assay temperature was increased above 35 degrees C, and at 45 degrees C only 20% of the maximal rate remained. The temperature optimum for 3-phosphoglycerate reduction by intact chloroplasts was 35 degrees C. Above this temperature, 3-phosphoglycerate reduction was more stable than CO(2)-dependent O(2) evolution. Reduction of nitrite in coupled intact chloroplasts had a temperature optimum of 40 degrees C with only slight variation in activity between 35 degrees C and 45 degrees C. Reduction of nitrite in uncoupled chloroplasts had a temperature optimum of 40 degrees C, but increasing the assay temperature to 45 degrees C resulted in a complete loss of activity. Reduction of p-benzoquinone by protoplasts and intact chloroplasts had a temperature optimum of 32 degrees C when measured in the presence of dibromothymoquinone. This photosystem II activity exhibited a strong inhibition of O(2) evolution as assay temperature increased above the optimum. It is concluded that, below the temperature optimum, ATP and reductant were not limiting photosynthesis in these systems or intact leaves. Above the temperature optimum, photosynthesis in these systems is limited in part by the phosphorylation potential of the stromal compartment and not by the available reductant.

Journal Article↗
PubMed1984

Cleavage of nascent reovirus mRNA by localized activation of the 2'-5'-oligoadenylate-dependent endoribonuclease.

Addition of cell extracts prepared from untreated or interferon-treated cells reduced the yield of reovirus RNA synthesized in transcription reactions with purified virions. The reduction observed with the extract of interferon-treated cells was greater than that observed with the extract of untreated cells. The yield of reovirus RNA could be restored to the level obtained without addition of cell extracts by carrying out transcription either in the presence of an inhibitor of 2'-5'-oligoadenylate (2-5A) synthesis, 2'-dATP, or in the presence of the 3'-methyl analog of 5'-monophosphate 2-5A, which inhibits the 2-5A-dependent endoribonuclease. This enzyme was activated in a localized way since neither mRNA added to transcription reactions containing the extract of interferon-treated cells nor rRNA was appreciably degraded, whereas accumulation of reovirus mRNA was drastically inhibited. These findings provide evidence for an antiviral role of the 2-5A synthetase/endoribonuclease system, which preferentially cleaves nascent viral RNA.

2',5'-Oligoadenylate Synthetase↗
PubMed1984

Coronary sinus orifice atresia and persistent left superior vena cava. A report of two cases, one associated with atypical coronary artery thrombosis.

Fourteen previously reported cases of atresia of the coronary sinus ostium, in which the coronary venous flow entered the right atrium by a persistent left superior vena cava, the innominate vein, and the right superior vena cava, are reviewed and two new cases reported. The first new case was in a 43 year old woman with atypical chest pains in whom investigations for suspected ischaemic heart disease, including coronary arteriography, yielded normal results. She died suddenly from massive myocardial infarction due to extensive old thrombotic occlusion of a major coronary artery without any appreciable underlying disease of the vessel wall. Exercise testing is considered to be advisable in symptomatic patients with normal coronary angiograms and attention to the venous phase might be informative. The second new case occurred in a child with an atrial septal defect and complete transposition of the great arteries, who died aged 1 month.

Adult↗
PubMed1983

Calcification of glutaraldehyde-preserved porcine and bovine xenograft valves in young children.

Eight children (mean age, 7.6 years) had xenograft prosthetic valves inserted. All developed evidence of prosthetic valve obstruction requiring reoperation 18 to 55 months after insertion (mean, 32 months). At operation, all the valves were found to be heavily calcified. There were two perioperative deaths. Of two patients who had a second xenograft valve inserted, one died suddenly 12 months later. Gross calcification of the xenograft was found at postmortem examination. The other patient had evidence of mild xenograft calcification at follow-up 19 months postoperatively. Four of the ten calcified xenograft valves were of bovine origin (Ionescu-Shiley type); in these the calcific obstruction occurred significantly earlier than in the six porcine (Hancock) valves.

Aortic Valve Stenosis↗
PubMed1983

The three-point beam test for the evaluation of dental porcelain.

The three-point beam test is simple and extremely sensitive to surface conditions. It appears to be ideally suited to the evaluation of dental porcelain, but specimen fabrication is difficult. In this study, specimens of porcelain fired on platinum foil have been constructed using an alumina former. The results showed excellent specimen consistency and reproducibility. Of the surfaces investigated, the use of tin-oxide-coated platinum foil did not result in an increase in transverse strength.

Dental Porcelain↗
PubMed1982

Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. : I. FACTORS AFFECTING NET CO(2) UPTAKE IN INTACT LEAVES AND CONTRIBUTION FROM RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE MEASURED IN VIVO AND IN VITRO.

As part of an extensive analysis of the factors regulating photosynthesis in Agropyron smithii Rydb., a C(3) grass, we have examined the response of leaf gas exchange and ribulose-1,5-bisphosphate (RuBP) carboxylase activity to temperature. Emphasis was placed on elucidating the specific processes which regulate the temperature response pattern. The inhibitory effects of above-optimal temperatures on net CO(2) uptake were fully reversible up to 40 degrees C. Below 40 degrees C, temperature inhibition was primarily due to O(2) inhibition of photosynthesis, which reached a maximum of 65% at 45 degrees C. The response of stomatal conductance to temperature did not appear to have a significant role in determining the overall temperature response of photosynthesis. The intracellular conductance to CO(2) increased over the entire experimental temperature range, having a Q(10) of 1.2 to 1.4. Increases in the apparent Michaelis constant (K(c)) for RuBP carboxylase were observed in both in vitro and in vivo assays. The Q(10) values for the maximum velocity (V(max)) of CO(2) fixation by RuBP carboxylase in vivo was lower (1.3-1.6) than those calculated from in vitro assays (1.8-2.2). The results suggest that temperature-dependent changes in enzyme capacity may have a role in above-optimum temperature limitations below 40 degrees C. At leaf temperatures above 40 degrees C, decreases in photosynthetic capacity were partially dependent on temperature-induced irreversible reductions in the quantum yield for CO(2) uptake.

Journal Article↗
PubMed1982

Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. : II. CONTRIBUTION FROM ELECTRON TRANSPORT AND PHOTOPHOSPHORYLATION.

As part of an analysis of the factors regulating photosynthesis in Agropyron smithii Rydb., a C(3) grass, the response of electron transport and photophosphorylation to temperature in isolated chloroplast thylakoids has been examined. The response of the light reactions to temperature was found to depend strongly on the preincubation time especially at temperatures above 35 degrees C. Using methyl viologen as a noncyclic electron acceptor, coupled electron transport was found to be stable to 38 degrees C; however, uncoupled electron transport was inhibited above 38 degrees C. Photophosphorylation became unstable at lower temperatures, becoming progressively inhibited from 35 to 42 degrees C. The coupling ratio, ATP/2e(-), decreased continuously with temperature above 35 degrees C. Likewise, photosystem I electron transport was stable up to 48 degrees C, while cyclic photophosphorylation became inhibited above 35 degrees C. Net proton uptake was found to decrease with temperatures above 35 degrees C supporting the hypothesis that high temperature produces thermal uncoupling in these chloroplast thylakoids. Previously determined limitations of net photosynthesis in whole leaves in the temperature region from 35 to 40 degrees C may be due to thermal uncoupling that limits ATP and/or changes the stromal environment required for photosynthetic carbon reduction. Previously determined limitations to photosynthesis in whole leaves above 40 degrees C correlate with inhibition of photosynthetic electron transport at photosystem II along with the cessation of photophosphorylation.

Journal Article↗