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Biomedical subjects

H M Chung

Publications and source records attributed to H M Chung.

At least 73 records · Page 4Linked to original sources
PubMed1989

Amphibian (urodele) myotomes display transitory anterior/posterior and medial/lateral differentiation patterns.

Myotome differentiation during Mexican axolotl (Ambystoma mexicanum) somitogenesis was analyzed by employing anti-actin and anti-myosin monoclonal antibodies as molecular probes. Myotome differentiation occurs after segmentation and proceeds in the cranial-to-caudal direction along the somite file. Within individual somites myotome differentiation displays distinct polarities. Examination of the somite file at the tailbud stage revealed that soon after segmentation, actin/myosin accumulate predominantly in the anterior and medial region of the myotome initially. Subsequently, cells within the myotome differentiate in an anterior-to-posterior and medial-to-lateral direction. Experimental analysis of presomitic paraxial mesoderm grafts before segmentation revealed that this transient myotome polarity is autonomous. Comparative analyses indicate that this myotome differentiation pattern is urodele specific. Cynops pyrrhogaster undergoes myotome differentiation like the axolotl, while two anurans, Xenopus laevis and Bombina orientalis, do not.

Actins↗
PubMed1989

First identification of acute tetrodotoxin-associated food poisoning in Taiwan.

Attempt was made to elucidate the responsible toxin in fish which recently caused food poisoning in Ilan County, Taiwan. The causative fish was assayed for anatomical distribution of toxicity (as tetrodotoxin). The roe showed the highest toxicity (1200 mouse units per gram, abbreviated as MU/g), followed by the dermis (150 MU/g) and muscle (120 MU/g). The toxins were partially purified from the methanolic extracts of the fish muscle and roe by ultrafiltration and Bio-Gel P-2 column chromatography. Thin-layer chromatography, cellulose acetate membrane electrophoresis and high performance liquid chromatography analysis demonstrated that the toxins consisted of tetrodotoxin and anhydrotetrodotoxin. It was concluded that the causative agent of the above food poisoning was tetrodotoxin.

Animals↗
PubMed1987

Clinical assessment of extracellular fluid volume in hyponatremia.

Assessment of the status of extracellular fluid volume is important in evaluating the cause and selecting appropriate therapy for hyponatremic disorders. Since the sensitivity and specificity of clinical assessment of extracellular fluid volume status in hyponatremic states remain unknown, 58 non-edematous patients with serum sodium less than 130 meq/liter were prospectively evaluated. Patients were judged to be either normovolemic (no response of serum sodium to saline infusion) or hypovolemic (saline infusion significantly corrected hyponatremia). Hypovolemic patients had significantly higher plasma renin activity (5.0 +/- 1.5 versus 2.5 +/- 0.5 ng/ml per three hours, p less than 0.05) and norepinephrine (1,054 +/- 252 versus 519 +/- 55 pg/ml, p less than 0.05) concentrations than did normovolemic patients. Clinical assessment correctly identified only 47 percent of hypovolemic patients and 48 percent of normovolemic patients. Thus, clinical assessment was of limited sensitivity and specificity in identifying extracellular fluid volume status in these hyponatremic patients. However, the concentration of sodium in a spot urine sample clearly separated hypovolemic (mean UNa = 18.4 +/- 3.1 meq/liter) from normovolemic (mean UNa = 72 +/- 3.7 meq/liter, p less than 0.001) hyponatremic patients.

Extracellular Space↗
PubMed1986

Beta-adrenergic-mediated extrarenal potassium disposal in patients with end-stage renal disease: effect of propranolol.

This study was designed to investigate beta-adrenergic-mediated extrarenal potassium disposal in patients with end-stage renal disease (ESRD). Plasma potassium was measured over a period of 3 months in 20 patients with ESRD who were receiving the nonselective beta-blocker propranolol (n = 10) or not (n = 10). Both groups were virtually anuric and had a comparable plasma BUN, plasma bicarbonate, and red cell Na-K-ATPase activity. Plasma potassium measured before dialysis was higher in propranolol users than in nonusers (5.6 +/- 0.2 and 4.6 +/- 0.1 mEq/l, p less than 0.005). To examine beta-adrenergic-mediated internal potassium disposal more directly, epinephrine and epinephrine plus propranolol were acutely administered to another group of patients with ESRD and to normal subjects. Epinephrine resulted in a similar fall in plasma potassium in both groups (0.69 +/- 0.20 and 0.63 +/- 0.07 mEq/l, respectively), thereby suggesting unimpaired beta-adrenergic-mediated extrarenal potassium handling in patients with ESRD. In patients, however, the response to epinephrine was heterogeneous. In 4 of the 10 patients studied, epinephrine infusion did not result in a decrement in plasma potassium suggesting impaired beta-adrenergic responsiveness and thus blunting of this mechanism of extrarenal potassium disposal. In the remaining 6 patients, epinephrine infusion resulted in a fall in plasma potassium which was greater than that observed in normal subjects (1.13 +/- 0.14 and 0.63 +/- 0.07 mEq/l, respectively, p less than 0.01). In the presence of propranolol, the infusion of epinephrine did not result in a decrement in plasma potassium in these 6 patients or in the 6 normal subjects (0.04 +/- 0.07 and -0.02 +/- 0.06 mEq/l, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1986

Postoperative hyponatremia. A prospective study.

In the present study, we found that at least 4.4% of 1,088 prospectively studied patients developed postoperative hyponatremia (plasma sodium concentration less than 130 mEq/L). Most patients (42%) were normovolemic. Edematous states (21%), hyperglycemia (21%), volume depletion (8%), and renal failure (8%), however, were also common settings of postoperative hyponatremia. Plasma arginine vasopressin was present in all patients in whom it was measured and 94% of the patients were receiving hypotonic fluid at the time of development of hyponatremia. Hyponatremia was not associated with significant neurologic deterioration in the 48 postoperative patients in the present study. In eight patients, however, the positive water balance that resulted in hyponatremia was associated with development of pulmonary vascular congestion. We conclude that hyponatremia commonly occurs following all types of surgical procedures and is due to hypotonic fluid administration in the presence of nonosmotic secretion of arginine vasopressin.

Adult↗
PubMed1985

Interrelationship between cardiac output and vascular resistance as determinants of effective arterial blood volume in cirrhotic patients.

The effect of head-out water immersion (HWI) in decompensated cirrhotic patients to correct sodium and water excretion has been found to be incomplete and variable. The explanation may be that the efficacy of HWI in correcting a decreased effective arterial blood volume (EABV) in decompensated cirrhotic patients is limited by an accompanying decrease in systemic vascular resistance (SVR) and thus a relative increase in arterial vascular holding capacity. The present studies were undertaken to examine this possibility by maintaining SVR (dynes X sec X cm-5) nearly constant during HWI with an exogenous infusion of norepinephrine (HWI + NE). In six decompensated cirrhotic patients, neither HWI nor NE infusion alone significantly increased sodium excretion (UNaV, 13 vs. 19 and 13 microEq/min, respectively), but each maneuver increased the excretion of a 20 ml/kg water load (28 to 60 and 61%, respectively, both P less than 0.05). The combination of HWI + NE, however, significantly increased UNaV to 70 microEq/min (P less than 0.05) and percentage of water excretion to 95 (P less than 0.001), values significantly greater than those achieved with either maneuver alone. These differences were not explained by any changes in inulin clearance. With HWI alone, cardiac index (CI) increased (4.2 to 5.3 liter/min/m2, P less than 0.01), but SVR decreased (872 to 613 dynes X sec X cm-5, P less than 0.001) and mean arterial pressure (MAP) remained constant (83 vs. 78 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Specific cleavages of DNA by ascorbate in the presence of copper ion or copper chelates.

The DNA-cleavage specificity of ascorbate in the presence of copper ion is analyzed with end-labeled pBR322 DNA fragments. The nonenzymatic reaction of Cu(II)/ascorbate and DNA shows certain degrees of cleavage preference toward purine-containing short segments in the labeled DNA under mild conditions (at 0 degrees C and 10 min). The segments of pyrimidine clusters are least susceptible to cleavage. The DNA scission cannot be detected in the absence of metal ions, and is greatly diminished in the presence of EDTA and metal-chelating peptide. It is more specific than the nuclease-like scission activity induced by cuprous-phenanthroline complex. This scission activity in relation to the antiviral and antitumor activities of vitamin C reported in the literature deserves a crucial consideration.

Ascorbic Acid↗
PubMed1985

Elevated plasma norepinephrine concentrations in decompensated cirrhosis. Association with increased secretion rates, normal clearance rates, and suppressibility by central blood volume expansion.

Plasma norepinephrine concentrations are elevated in patients with decompensated cirrhosis, and correlate inversely with urinary sodium and water excretion. Increased plasma norepinephrine concentrations may result from a decreased metabolic clearance rate or an increased secretion rate, possibly in response to a decreased "effective arterial blood volume." If the latter hypothesis is correct, plasma norepinephrine might be expected to be suppressed when central blood volume is expanded by head-out water immersion. In the present study, plasma norepinephrine secretion and clearance rates were determined by infusion of tritiated norepinephrine. Norepinephrine secretion rates were elevated in eight cirrhotic patients as compared to control subjects (1.50 +/- 0.25 vs. 0.26 +/- 0.08 micrograms/m2 per min, P less than 0.001), whereas clearance rates were similar (3.13 +/- 0.48 vs. 2.60 +/- 0.28 liters/min, NS). Baseline plasma norepinephrine concentrations were markedly elevated in the cirrhotic patients (830 +/- 136 vs. 185 +/- 12 pg/ml, P less than 0.001). Head-out water immersion significantly suppressed plasma concentrations of both norepinephrine (704 +/- 72 to 475 +/- 70 pg/ml, P less than 0.005) and epinephrine (121 +/- 33 to 57 +/- 10 pg/ml, P less than 0.05) in all seven patients studied. We conclude that the high circulating catecholamine concentrations in cirrhosis are secondary to increased secretion, rather than to decreased metabolic clearance, and are suppressible by central blood volume expansion.

Adult↗
PubMed1985

Hyponatremia: a prospective analysis of its epidemiology and the pathogenetic role of vasopressin.

We prospectively evaluated the frequency, cause, and outcome of hyponatremia (plasma sodium concentration, less than 130 meq/L), as well as the hormonal response to this condition, in hospitalized patients. Daily incidence and prevalence of hyponatremia averaged 0.97% and 2.48%, respectively. Two thirds of all hyponatremia was hospital acquired. Normovolemic states (so-called syndrome of inappropriate secretion of antidiuretic hormone) were the most commonly seen clinical setting of hyponatremia. The fatality rate for hyponatremic patients was 60-fold that for patients without documented hyponatremia. Nonosmotic secretion of vasopressin was present in 97% of hyponatremic patients in whom it was sought. In edematous and hypovolemic patients, plasma hormonal responses (increases in plasma renin activity and aldosterone and norepinephrine levels) were compatible with baroreceptor-mediated release of vasopressin. Hyponatremia is a common hospital-acquired electrolyte disturbance that is an indicator of poor prognosis. Nonosmotic secretion of arginine vasopressin is a major pathogenetic factor in this electrolyte disturbance.

Adolescent↗
PubMed1985

Microgravity simulation as a probe for understanding early Xenopus pattern specification.

Pattern specification in early amphibians (Xenopus) was monitored in embryos subjected to gravity compensation (microgravity simulation) by constant low-speed rotation on a horizontal axis (clinostat). The useful range of clinostat speeds was determined empirically. The results were interpreted in terms of a set of models which account for the reorganization of the egg cytoplasm that follows fertilization and that correlates with the establishment of dorsal/ventral polarity. Large percentages of clinostated eggs displayed a positive result (normal axial structure morphogenesis). Consequently, normal development of amphibian eggs in the microgravity environment of space should be possible. Models which depend upon gravity-driven rearrangements for cytoplasmic organization (e.g. dorsal/ventral polarization) of the early embryo should, therefore, not be favoured. At several clinostat speeds symmetrization of the egg in accordance with the site of sperm penetration, a natural phenomenon, was altered. The results at those clinostat speeds indicate that models which employ sperm entrance as an obligatory feature of the cytoplasmic rearrangements that generate egg polarity are not applicable.

Animals↗
PubMed1984

Influence of clinostat rotation on fertilized amphibian egg pattern specification.

Pattern specification in fertile Xenopus eggs rotated on horizontal clinostats was monitored with respect to primary embryonic axis formation, subsequent morphogenesis, and compartmentalization of the cytoplasm. At the speeds of 1 to 24 rpm (which are believed to simulate microgravity) a large percentage of eggs developed normal axial structures. Eggs clinostated at 12 rpm showed a randomization of dorsal/ventral polarity. The cytoplasmic compartments showed some clinostat effects but no abnormal mixing, disruption or dislocation of compartments. It is predicted that Xenopus eggs fertilized and allowed to develop in space will retain normal cytoplasmic density compartments, establish primary axes and undergo normal morphogenesis in space. Their dorsal/ventral polarity may not, however be determined by the sperm entrance site (as is the case for 1g eggs).

Animals↗
PubMed1984

Acute renal failure caused by acute monofluoroacetate poisoning.

NaFA produces toxic effects by metabolic conversion to fluorocitrate, inhibits Krebs' cycle and the formation of ATP, reduces energy supply to cells, and thus causes cellular dysfunction or degeneration. All body cells are potentially affected, although with different sensitivity. Acute renal failure was found in three out of our five cases, and two were in frank uremia. The ARF was reversible and may be either oliguric or non-oliguric. The causes of ARF were not apparent, but direct nephropathy or some other factors might be involved in the pathogenesis of ARF.

Acute Kidney Injury↗
PubMed1983

Reversal of developmental competence in inverted amphibian eggs.

Inverted amphibian embryos were employed for an analysis of pattern formation in early embryogenesis. Axolotl (Ambystoma) and Xenopus eggs were inverted prior to the first cleavage division and permitted to develop upside down to the early gastrulation stage. In both cases the cleavage patterns of the animal and vegetal hemispheres were reversed. By gastrulation, however, developmental arrest began, and no inverted embryos developed beyond neurulation. The state of competence of the animal and vegetal hemisphere cells of inverted embryos was examined in a series of tissue transplantation, usually into genetically marked (albino) hosts. In all cases the developmental competence of the original animal and vegetal hemisphere cells of inverted embryos had been reversed. For example, the egg's original vegetal hemisphere developed into various neural structures. Those observations should eventually be useful in formulating models to account for the manner in which various regions of the amphibian egg cytoplasm generate early embryonic patterns.

Ambystoma↗
PubMed1981

A comparative study of the effects of egg rotation (gravity orientation) and UV irradiation on anuran vs. urodele amphibian eggs.

The response of various anuran and urodele eggs to a brief rotation prior to first cleavage were observed. In all instances, the dorsal lip formed on the side of the egg which opposed gravity during the rotation. The ability of egg rotation to prevent the series of developmental abnormalities associated with UV irradiation of the uncleaved egg was also examined. Anuran and urodele eggs responded to those manipulations in a similar fashion. These results should facilitate future studies on the mechanisms involved in the establishment of the dorsal/ventral polarity of the amphibian egg.

Animals↗
PubMed1978

Further characterization of the effects of ultraviolet irradiation of the amphibian egg.

UV-irradiation of the vegetal hemisphere of amphibian eggs leads to developmental abnormalities in neural morphogenesis. The possibility that the egg's transient sensitivity to irradiation could be due to pigmentation changes was examined in albino eggs. The tissue specificity of the effects of irradiation was analyzed by exchanging the ectoderm between irradiated and control embryos.

Animals↗