Search PubMed⌕ Search

Biomedical subjects

J C Chan

Publications and source records attributed to J C Chan.

At least 343 records · Page 19Linked to original sources
PubMed1987

Aluminum deposition in the central nervous system. Preferential accumulation in the hippocampus in weanling rats.

Simultaneous administration of 1,25-dihydroxyvitamin-D3, citrate, and aluminum-containing phosphate binders is frequently used in patients with chronic renal failure. In order to investigate whether citrate may represent a risk factor of aluminum intoxication, 16 Sprague-Dawley weanling rats were randomly assigned to four groups: 1,25-dihydroxyvitamin-D3 at 16 ng/kg/day was given to all groups except the control; in addition, two groups received either aluminum hydroxide at 160 mg elemental aluminum/kg/day, or aluminum citrate at 160 mg elemental aluminum/kg/day, respectively. The control group received only the vehicle. Extremely high aluminum concentrations were detected in the hippocampus of rats receiving aluminum compounds. This content of aluminum (microgram/g dry weight) was far higher than that found in other brain areas of the same animals (146.40 +/- 51.23 versus 4.49 +/- 0.62, P less than 0.001) as well as that detected in the hippocampus of the control animals (2.73 +/- 0.40). Thus, in non-uremic, weanling rats supplemented with 1,25-dihydroxyvitamin-D3, the administration of aluminum favors selective accumulation in the hippocampus. No differences between aluminum hydroxide and aluminum citrate administration were observed.

Aluminum↗
PubMed1986

Monoclonal antibody detection of transformation associated protein (TAP) in ts110 Moloney murine sarcoma virus transformed 6M2 cells that are different from the mos gene product.

By the use of a highly specific monoclonal antibody (designated MC), we were able to detect three radiolabeled bands with molecular weights of 60,000, 63,000, and 66,000 daltons in the ts-110 Moloney murine sarcoma virus mutant-transformed rat kidney cells known as 6M2. Expression of transformation properties as well as these three bands in 6M2 cells was found to be temperature sensitive. Therefore, MC detected factors that are apparently associated with the transformation of 6M2 cells. These factors are tentatively referred to as transformation associated proteins. These transformation proteins were found in two other Moloney murine sarcoma virus-transformed rat cell lines. These proteins were found to differ from known gene products of the ts-110 Moloney murine sarcoma virus mutant and do not have kinase activity. The transformation associated proteins may represent rat cellular factors activated during the transformation of rat cells by Moloney murine sarcoma virus.

Animals↗
PubMed1986

Hypercalciuria associated with long-term administration of calcitriol (1,25-dihydroxyvitamin D3). Action of hydrochlorothiazide.

Urine calcium excretion was evaluated in 19 patients before and after calcitriol (1,25-dihydroxyvitamin D3) treatment that was followed up for a five- to seven-year period. The effects of increases of calcitriol dosage and modifications of calciuria with hydrochlorothiazide were systematically examined. The urine calcium excretion before calcitriol therapy was 2.3 +/- 0.8 mg/kg/day (mean- +/- SEM) and the urine calcium-creatinine concentration ratio was 0.12 +/- 0.04. With the dose of calcitriol at 23 ng/kg/day, these values increased to 3.2 +/- 0.8 mg/kg/day and 0.19 +/- 0.04, respectively. Following double dose of calcitriol (44 ng/kg/day), increments in calciuria and urinary calcium/creatinine concentration of 1.4 +/- 0.6 mg/kg/day and 0.10 +/- 0.03, respectively, were observed. With concomitant administration of hydrochlorothiazide (1 to 2 mg/kg/day) therapy at maintenance dose and calcitriol (31 ng/kg/day), the urine calcium excretion effectively decreased by 1.3 +/- 0.6 mg/kg/day and the urine calcium-creatinine concentration ratio by 0.05 +/- 0.02. The results suggest that children with calcium-phosphate disorders who require long-term treatment with calcitriol must be carefully monitored in terms of urine calcium excretion, especially when the dosages are increased to achieve maximal therapeutic efficacy. Calciuria induced by calcitriol administration is effectively reversed by addition of hydrochlorothiazide to the treatment regimen.

Adolescent↗
PubMed1986

Bone disease induced by anticonvulsant therapy and treatment with calcitriol (1,25-dihydroxyvitamin D3).

To evaluate the effects of calcitriol (1,25-dihydroxyvitamin D3) therapy for the bone disease induced by long-term treatment with anticonvulsants, we reviewed the medical records of 330 institutionalized oligophrenic children and young adults under 26 years of age to identify the 144 children who required anticonvulsant therapy. Of this latter group, 52 children were found to have serum alkaline phosphatase levels elevated more than 2 SDs above normal and were enrolled into this prospective three-year study. To achieve rapid resolution of the bone disease, we elected to use calcitriol at 0.25 to 0.75 micrograms/d. After 1195 patient-months of treatment, our data suggest that the dystrophic process was reversed in 42.3% of the cases, as judged by decreases in serum alkaline phosphatase levels at six months, 65.4% of cases at 12 months, and 83.3% of cases at 13 to 18 months. By 30 months of follow-up, all patients showed significant lowering of serum alkaline phosphatase levels. The improvements were slow and gradual. Twenty-six patients in the treatment series of 52 patients initially showed signs of rickets or osteomalacia on roentgenograms of the wrists. Of these 26 patients, 12 (46%) showed improvement on roentgenograms within 24 months of the beginning of treatment. With reference to complications, hypercalcemia (calcium level, greater than 11 mg/dL [2.74 mmol/L]) was encountered at the rate of one episode per 44 patient-months of treatment. Our results strongly suggest that calcitriol is effective in healing anticonvulsant-related osteomalacia among children and youths, with a low incidence of complications.

Acid Phosphatase↗
PubMed1986

A double-blind randomized study comparing ofloxacin and amoxicillin in treating infective episodes in bronchiectasis.

32 hospitalized adult patients with infective episodes of bronchiectasis were enrolled in an ongoing double-blind, placebo-controlled study comparing ofloxacin with amoxicillin. They were randomized to receive either 200 mg ofloxacin or 1 g amoxicillin, both t.i.d. orally for ten days. In the ofloxacin group (15 patients), clinical response was excellent (clinical cure) in 11 and fair (clinical improvement or early reinfection) in three patients with one failure. In the amoxicillin group (17 patients), clinical response was excellent in six, fair in five, and poor (treatment failure) in six patients. Ofloxacin levels at 2 h (day 5) were 2.3 to 8.2 mg/l (mean 3.9 mg/l) for serum and 1.3 to 15 mg/l (mean 4.5 mg/l) for sputum. Sputum: serum ratio was 1.2:1. Amoxicillin levels at 2 h were 10 to 40 mg/l (mean 19.9 mg/l) for serum and 0 to 1.5 mg/l (mean 0.3 mg/l) for sputum, with no amoxicillin detected in sputum in 10 of 17 patients. Sputum: serum ratio was 0.02:1. One patient in the ofloxacin group had nausea. In the amoxicillin group, four patients had nausea and stomach pain, one had vertigo and one had transient peripheral eosinophilia. Ofloxacin thus yielded higher sputum concentration and appeared to be more effective and better tolerated than amoxicillin in infective episodes of bronchiectasis.

Adult↗
PubMed1986

Central nervous system disease in acquired immunodeficiency syndrome: prospective correlation using CT, MR imaging, and pathologic studies.

A prospective study compared the abilities of high-resolution computed tomography (HRCT) and magnetic resonance (MR) imaging in detection and evaluation of central nervous system disease in neurologically symptomatic patients with acquired immunodeficiency syndrome (AIDS). Eighteen CT scans and 19 MR images in 14 patients were compared. HRCT images with contrast material enhancement were superior to unenhanced 0.35-T MR images for differentiating a lesion from surrounding edema, discriminating between lesions in close proximity, locating lesions for biopsy, judging lesion activity, detecting small cortical lesions with minimal edema, and spatial resolution. MR imaging was superior to CT scanning in evaluation of white-matter lesions and detection of small lesions surrounded by edema. MR imaging exhibited higher contrast resolution and greater sensitivity. Complementary uses of MR and CT imaging are suggested.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. I. Responses to wideband noise.

We examined the responses of low-frequency neurons in the central nucleus of the inferior colliculus (ICC) of the cat to interaurally delayed, wideband noise stimuli. The stimuli were pseudorandom noise signals that were generated digitally with a nominal bandwidth of 60-4,000 Hz. We also compared the responses to noise with those obtained from interaural phase differences of pure tones. We studied 144 neurons with characteristic frequencies below 2.5 kHz. Eighty-five percent (85%) of these were sensitive to changes in both interaural time differences (ITDs) of noise and interaural phase differences of pure tones, only 2% were sensitive to one stimulus but not the other, and the remainder were insensitive to both stimuli. For most cells the discharge rate was modulated in an approximately cyclic fashion by changes in ITDs of the wideband noise stimuli. The maximal spike counts often occurred near zero ITD, and there was considerable variability in the nature of the cycling, though it usually disappeared for ITDs greater than +/- 4,000 microseconds. The position of the central peak was usually (65%) within the physiologically relevant range of +/- 400 microseconds, and most (80%) occurred at positive ITDs, which corresponded to delays to the ipsilateral stimulus. In general, the shapes of the responses were not affected by changes in stimulus level above threshold. As long as identical noises were delivered to both ears, the responses were not sensitive to the particular noise stimulus used. When uncorrelated noises were delivered to the two ears, there was no sensitivity to ITDs. Composite curves were computed by linear summation of the responses to ITDs of pure tones at frequencies spaced at equal intervals throughout each cell's response area. The shapes of composite curves were similar to the responses of the same cell to ITDs of wideband noise stimuli. The positions of the central peaks of these two functions were highly correlated (r = 0.91, slope = 0.97). The values of characteristic delay and characteristic phase computed from the tonal responses were found to be good indicators of the shapes of the noise delay curves. Characteristic phases (CPs) near zero were associated with noise delay curves symmetric about the central peak, CPs near 0.5 cycles with those symmetric about the trough, while CPs between 0 and 0.5 or between 0.5 and 1.0 had noise delay curves that were asymmetric with a prominent trough to the left or right, respectively, of the central peak.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Renal tubular acidosis in children. Diagnosis, treatment and prognosis.

To delineate the spectrum of clinical expressions of distal, type 1 renal tubular acidosis in children and to update progress in diagnosis, therapy, and prognosis, the medical records of 14 girls and 10 boys, seen over a 7 year period, who met the following criteria, were examined: persistent urinary pH more than 6, net acid excretion less than 70 microEq/min/1.73 m2, simultaneous serum total CO2 less than 17.5 mEq/1, and normal or mild impairment of the glomerular filtration rate. The mean age at diagnosis was 8 months. The presenting signs and symptoms were failure to thrive (50%), vomiting and/or diarrhea (37.5%), dehydration (12.5%), and poor feeding (8.3%). Mean values +/- SD of serum calcium (9.8 +/- 0.8 mg/dl), inorganic phosphate (5.6 +/- 0.8 mg/dl), and alkaline phosphatase (222.6 +/- 96.1 U/l) were normal. Hyperkalemia (serum potassium above 5.0 mEq/l) was present at diagnosis in 13 children. Type 4 renal tubular acidosis was ruled out by the inability to achieve a minimum urine pH. With a mean follow-up period of 28.1 +/- 25.3 months, after alkali therapy at 3.3-3.5 mEq/kg/day had been administered for at least 12 months, the growth parameters improved as follows: the percentile weight (mean +/- SD) increased from the initial 11.8 +/- 7.5 to the final 27.6 +/- 31.3 (p less than 0.003), and the length/height percentile increased from 11.5 +/- 7.3 to 29.7 +/- 24.2 (p less than 0.03). The relationship between urine calcium/creatinine ratio and serum total CO2 showed poor correlation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis, Renal Tubular↗
PubMed1986

The application of "Bi-Digital O-Ring Test" in the diagnosis and treatment of urinary tract infection in symptomatic and asymptomatic patients.

"Bi-Digital O-Ring Test" was used as the basis to diagnose abnormality in the urinary bladder, to detect the presence of infection, to choose the effective antibiotic for therapy, to follow up patients after treatment and to evaluate the therapeutic effect. Confirmation of urinary tract infection was done by using the "Bacturcult" urine culture system. This study of 45 patients reveals the value of "Bi-Digital O-Ring Test" in the early and inexpensive diagnosis and treatment of urinary tract infection.

Acupuncture Therapy↗
PubMed1985

Binaural interactions in cortical area AI of cats reared with unilateral atresia of the external ear canal.

Binaural interactions were recorded in auditory cortical (AI) neurons of anesthetized adult cats that had unilateral atresias created shortly after birth by surgically ligating and cutting one external ear canal. At the time of the recording experiment, the atresia and associated debris were removed and tones were delivered to both tympanic membranes via a sealed and calibrated acoustic system. The majority of neurons recorded were in the cortex ipsilateral to the previously occluded ear. Thresholds for monaural stimulation of either the operated or unoperated ear were within normal range although thresholds to stimulation of the previously operated ear tended to occupy the upper end of the normal distribution. Monotonic and nonmonotonic spike count-vs-intensity functions derived from responses to monaural stimulation of the atretic ear were indistinguishable in their shape from those recorded in normal cats. All binaural classes were represented in our sample in proportions similar to those reported in cats with two normal ears. The forms of the functions relating spike count to interaural intensity differences and interaural phase differences were essentially the same as those seen in normal animals. The main binaural deficit observed under these conditions was a shift in the interaural intensity difference to which an AI neuron was most sensitive. The intensity needed for a stimulus to the atretic ear to participate in the binaural response was as much as 50 dB higher than that at the opposite normal ear in contrast to the nearly equal SPLs required for binaural interactions in cats with two ears intact. It was suggested that elevated thresholds at the previously operated ear could account for much of the shift observed.

Action Potentials↗
PubMed1985

Calcium and phosphate metabolism in children with idiopathic hypoparathyroidism or pseudohypoparathyroidism: effects of 1,25-dihydroxyvitamin D3.

Two children with congenital hypoparathyroidism and two children with pseudohypoparathyroidism were given maintenance doses of 15 to 45 ng/kg/day 1,25-dihydroxyvitamin D3 for a total of 255 months. The urinary calcium excretion showed an upward elevation after the first 2 years of treatment but was not significantly higher than that in 10 normal control subjects. The renal threshold for phosphate excretion stayed within the normal ranges compared with control values. Two hypercalcemic and two hypocalcemic episodes occurred during this period of treatment. Hypercalcemia was reversed within 1 week after withdrawal of 1,25-dihydroxyvitamin D3. Hypocalcemia was countered by increasing the dose of 1,25-dihydroxyvitamin D3. Renal functions were not adversely affected, as estimated by creatinine clearance and reciprocals of serum creatinine concentrations. The mean serum calcium concentration during 1,25-dihydroxyvitamin D3 treatment was significantly higher (P = 0.001) compared with that obtained during vitamin D2 treatment at a dose of 500 to 3000 IU/kg/day. These data provide additional support for the long-term use of 1,25-dihydroxyvitamin D3 in idiopathic hypoparathyroidism and pseudohypoparathyroidism.

Calcitriol↗
PubMed1985

Risk of tuberculous infection among house staff in an urban teaching hospital.

Physicians in training in our medical center were found to have a higher risk of tuberculous infection than other hospital employees. Their annual tuberculin conversion rate was 3.96%; in two of the 15 recent converters, active disease developed. There is a significant linear relationship between the acquisition of tuberculous infection and the duration of training in an urban teaching hospital. Their compliance rate to annual tuberculin testing and chemoprophylaxis is less than 50%.

Attitude of Health Personnel↗