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Biomedical subjects

W Chan

Publications and source records attributed to W Chan.

At least 163 records · Page 9Linked to original sources
PubMed1979

alpha-Ketoisocaproate stimulates branched-chain amino acid transaminase in kidney and muscle.

We have reported that branched-chain amino acid transaminase (BATase) activity of isolated rat kidney is stimulated by perfusion with alpha-ketoisocaproate (KL). This study examines the mechanism of this effect in kidney and documents that stimulation occurs in intact skeletal muscle. Increased activity was not attributable to synthesis of enzyme because it occurred in the presence of cycloheximide. The in vivo degradation rate of BATase estimated from sequential measurements of activity following intravenous cycloheximide was longer than 90 min, whereas during in vitro perfusion stimulation could be detected within 5 min. Incubation of supernatant from kidney homogenate with KL stimulated BATase; incubation with alpha-keto-beta-methylvalerate (KI), alpha-ketoisovalerate (KV), leucine (leu), or isovaleryl CoA did not. Perfusion of rat hindquarter with KL increased muscle BATase activity; perfusion with acetoacetate, KI, KV, or leu did not. Again, cycloheximide studies indicated a direct effect of KL on muscle BATase. These findings suggest that alpha-ketoisocaproate can increase BATase activity and thus may be involved in regulation of its activity.

Amino Acids, Branched-Chain↗
PubMed1979

Plasma biochemistry changes in thoroughbred foals during the first 4 weeks of life.

Changes in plasma sodium, potassium, chloride, total carbon dioxide, urea, creatinine, glucose, total bilirubin, iron, total protein, albumin, alkaline phosphatase (AP), aspartate amino transferase (AST), calcium, inorganic phosphorus, cholesterol and triglycerides were studied in 45 Thoroughbred foals 15 min to 28 days after birth. The results were analysed in 3 groups; Group 1 (0--12 h), Group 2 (12--36 h), Group 3 (1--4 weeks). When Group 2 was compared to Group 1, there were significant reductions of sodium, creatinine, iron and calcium and elevations of total protein and bilirubin. When Group 3 was compared to Group 1 there were significant reductions of sodium, chloride, urea, creatinine, bilirubin, iron and AP. Significant elevations occurred in glucose, total protein, AST, inorganic phosphorus and triglycerides.

Age Factors↗
PubMed1979

Tubular secretion and metabolism of dopamine, norepinephrine, methoxytyramine and normetanephrine by the rat kidney.

The fate of catecholamines released in rat kidneys was examined by microinjecting tritiated norepinephrine (NE), normetanephrine (NMN), dopamine (D) and 3-methoxytyramine (3MT) into proximal and distal tubule lumina and peritubular capillaries. [14C] Inulin included in the injectate served as a reference standard. After injection of NE, D, NMN and 3MT at 0.1 to 4.0 pg/min for 4 to 10 min into proximal tubules, 87 to 94% was recovered in the urine of the injected kidney. Less than 10% of the amines was chemically altered during passage through the nephron. After injection into capillaries, percentages secreted in the first passage through the kidney were: D, 25 +/- 5; 3MT, 47 +/- 3; NE, 13 +/- 2; and NMN, 4 +/- 3. After D capillary injections, excretion of 3MT and D from the microinjected was twice that from the contralateral kidney. Acidic metabolites, homovanillic acid and dihydroxyphenylacetic acid were excreted equally by both kidneys. There was no appreciable difference in the products excreted from left and right kidneys after NE injections. In summary, D released into the peritubular space is converted to 3MT and both compounds are secreted avidly. NE released into the peritubular circulation is converted to NMN and both compounds are secreted but to a much smaller extent than occurs with D and 3MT.

Animals↗
PubMed1978

Identification of neuro-epithelial bodies in rabbit fetal lungs by scanning electron microscopy: a correlative light, transmission and scanning electron microscopic study.

In the present study, neuro-epithelial bodies (NEB) were identified by scanning electron microscopy (SEM) within the bronchial epithelium of near-term rabbit fetuses. The surface features and topography of NEB were correlated by light and transmission electron microscopy. In SEM, the surfaces of NEB were easily visualized in smaller peripheral airways because of paucity of ciliated cells in these regions. The NEB formed crater-like pits, which were lined with microvilli and had smooth-surfaced nonciliated cells around the rim. Stereo-pair photographs revealed that the latter cells protruded above adjacent bronchiolar mucosa. The SEM also revealed that NEB were preferentially located near or at bronchiolar bifurcations. This is the first report of the three-dimensional structure of pulmonary NEB. Their direct contact with the airway lumen, as well as their strategic location in bronchiolar mucosa, support the suggestion that they are intrapulmonary receptors and help to regulate air-flow in peripheral airways.

Animals↗
PubMed1978

Effect of branched-chain keto-acids and dietary protein content on the activity of branched-chain amino acid transferase in rat tissues.

Rats fed branched-chain keto-acids in place of branched-chain amino acids exhibited increased specific activity of branched-chain amino acid transferase (BATase) in muscle, intestine, brain and liver as compared with controls fed sufficient diet to achieve comparable weight gain. This increase was observed whether or not methionine and phenylalanine were also replaced by their N-free analogues. Kidney BATase was unaffected. Rats fed a protein-free diet exhibited higher BATase specific activity in kidney, brain, liver and intestine than rats fed diets containing 6% casein; but little change in specific activity in these organs was seen as casein intake was progressively increased from 6% to 18%. Muscle BATase specific activity was the same between 0 and 18% dietary casein. The results show that branched-chain keto-analogues augment BATase in several tissues, including muscle. In contrast, varying casein intake from 6% to 18% had little effect, although protein-feeding augments BATase in some organs.

Amino Acids↗
PubMed1978

Transamination of branched-chain keto acids by isolated perfused rat kidney.

Isolated rat kidney perfused without substrate released serine, glycine, and taurine, and substantially smaller amounts of other amino acids. When branched-chain keto acids were added, the corresponding amino acids were released at rates amounting to 15-25% of keto acid disappearance. Perfusion with 2 mM alpha-keto-isovalerate or alpha-keto-beta-methylvalerate caused an increased glucose release amounting to 18-23% of keto acid disappearance. The activity of branched-chain amino acid transferase (BATase) was significantly stimulated by perfusion with the analogue of leucine, but not by perfusion with alpha-ketoglutarate, the analogues of valine or isoleucine, or with leucine itself. These findings document that the kidney converts branched-chain keto acids in part to the corresponding amino acids and suggest that the keto analogue of leucine may be involved in the control of renal BATase activity, thereby indirectly regulating the metabolism of branched-chain amino acids.

Amino Acids↗
PubMed1978

Echocardiographic demonstration of tricuspid valvulitis and right atrial thrombus complicating an infected artificial pacemaker:a case report.

A right ventricular artificial demand pacemaker was implanted into a 59-year-old man with supra-Hisian complete heart block. His postoperative course was complicated by Staphylococcal aureus septicemia, which was controlled with antibiotics. A year later, S. aureus was again isolated from the blood. Echocardiography showed thickening of the tricuspid valve leaflet and multiple echoes in the right atrium. Autopsy findings included tricuspid leaflet thickening and an overlying right atrial thrombus. The echocardiogram is thus useful in localizing an infected valve in bacterial endocarditis and in demonstrating the presence of the thrombus.

Echocardiography↗
PubMed1977

Less common side effects of methyldopa.

A patient with methyldopa-induced hyperpyrexia who also developed positive antinuclear factors, LE cells and ocular disturbance is described. These side effects disappeared when the drug was withdrawn. The incidence of these side effects is reviewed. Methyldopa should be withdrawn when these side effects appear, as less troublesome antihypertensive drugs are now readily available.

Aged↗
PubMed1977

Primary amyloidosis with cardiac involvement diagnosed by left ventricular endomyocardial biopsy.

A case of primary amyloidosis is described. The patient presented with the nephrotic syndrome and later developed heart failure. Left ventricular endomyocardial biopsy was performed and haemodynamic data were recorded. The findings were those of a 'restrictive' cardiomyopathy. Histology of the biopsy was pathognomonic of amyloid involvement of the heart. The patient was started on chemotherapy consisting of prednisone, penicillamine, melphalan and fluoxymesterone. This case demonstrates the ability of endomyocardial biopsy in arriving at a definitive diagnosis in this patient.

Amyloidosis↗
PubMed1977

The non-invasive recognition of left atrial enlargement: comparison of electro- and echocardiographic measurements.

The aim of this study was to compare the ability of electro- and echocardiography to detect enlargement of the left atrium. Seventy-four patients, divided into three groups (eighteen normal, thirty-six valvular disease, twenty hypertension and/or coronary artery disease) were studied. The P wave terminal force in lead V1 (PTF-V1) was measured from a standard 12 lead electrocardiogram, and the internal left atrial dimension (LAD) was measured from time-motion echocardiograms. Linear regression analysis showed a small but significant linear correlation between PTF-V1 and LAD (r = 0-32, P less than 0-01). Both methods would separate patients with diseases known to cause left atrial enlargement from normals, but echocardiography showed greater "specificity" (100% v. 94+) and "sensitivity" (75% v. 67%). It was much superior to the ECG in detecting milder grades of left atrial enlargement and for following serial changes.

Cardiomegaly↗
PubMed1976

A case of self-induced digoxin poisoning: with His bundle studies of the site of heart block.

A case of digoxin overdose was described. Despite vigorous gastric lavage, the serum digoxin which was 0.8 ng/ml on admission rose to 7 ng/ml four hours later. The main side-effects were symptoms of nausea and anorexia and conduction defects including complete atrioventricular dissociation requiring pacemaker insertion. Opportunity was taken to study the site of heart block with His bundle electrography during the conduction disturbances. This showed that the site of block was situated above the His-Purkinje system in the atrioventricular (A-V) node.

Aged↗
PubMed1976

Vitamin A metabolism during the repletion of zinc deficient rats.

The experiments reported here were designed to determine if the low plasma vitamin A levels observed in zinc deficient rats are reversible as well as to examine the time required for any response. In experiment 1, rats previously zinc deficient were repleted for 6 days with a zinc sufficient diet, fed either ad libitum, or pair-fed the amount consumed by a zinc deficient group. After repletion, plasma vitamin A concentration for the zinc sufficient group returned to within normal range while the pair-fed group had a plasma vitamin A concentration intermediate between the zinc sufficient ad libitum and zinc deficient groups. The zinc sufficient ad libitum group had a lower concentration but higher total liver content of vitamin A than the other two groups. In experiment 2, the response of zinc deficient rats to intraperitoneal zinc repletion was examined daily for 7 days. There was a 3 day lag period before plasma vitamin A began to increase significantly following zinc treatment. By the fifth day, plasma vitamin A concentration increased to within the normal range. The data suggest that adequate food intake as well as zinc appears necessary to totally reverse low plasma vitamin A concentrations in zinc deficiency. Possible mechanisms are discussed.

Animals↗
PubMed1976

Alterations in vitamin A metabolism during zinc deficiency and food and growth restriction.

The purpose of these experiments was to further elucidate the effect of the trace element, zinc, on vitamin A metabolism. Three experiments were conducted at two different locations using different sources of animals. A total of 95 rats were used; 71 specific pathogen free and 24 germfree. The results indicate that plasma vitamin A is depressed in zinc deficient animals or animals severely restricted in food and growth. Liver stores of vitamin A were adequate in both groups. Thus, the normal mechanism for maintaining plasma vitamin A appears to be altered by either zinc deficiency and/or severe food and growth restriction.

Animals↗
PubMed1975

Ultrastructure and fluorescence histochemistry of endocrine (APUD-type) cells in tracheal mucosa of human and various animal species.

This study describes distrinctive cells with ultrastructural and histochemical features of APUD-type endocrine cells within the tracheal epithelium of human fetuses, newborns and children as well as different animal species. These cells referred to as Kultschitzky cells (K cells) were found to be argyrophilic, but not argentaffin, and are considered analogous to the same type of cells in lung and gastro-intestinal tract. Fluorescence histochemistry demonstrated the presence of intracellular amine within tracheal K cells, but only after in-vitro or in-vivo administration of amine precursor (L-DOPA). Ultrastructurally, these cells are characterized by the presence of numerous cytoplasmic granules (dense core vesicles) which show species related morphologic variations. Two different types of K cells were found in trachea of lamb and armadillo, each type possessing morphologically different dense core vesicles. In human and rabbit tracheas, only one type of K cell was identified. K cells in the trachea are distributed as single cells between other epithelial cells; neuroepithelial bodies such as those found in bronchial mucosa were not identified. Well differentiated K cells were found in tracheas of early human fetuses and throughout gestation, infancy, and childhood. Preservation of K cells in human autopsy material and widespread occurence of these cells in various laboratory animals will permit further studies into the nature and function of tracheobronchial endocrine cells.

Animals↗