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Biomedical subjects

J C Liu

Publications and source records attributed to J C Liu.

At least 73 records · Page 4Linked to original sources
PubMed1999

Origin of innervation in the feline ophthalmic artery.

In this study, we investigate the innervation to the feline ophthalmic artery by the horseradish peroxidase (HRP) tracing method. Five adult cats with body weights ranging between 2.0 and 3.0 kg were used. Under microscopic dissection, the ophthalmic artery was identified and isolated. A gelfoam (Upjohn Co.), 1 x 3 mm in size, containing 0.1 ml of HRP was applied to the prepared artery segment for 2 h. The cat was sacrificed 3 days later. The trigeminal, stellate, superior cervical, middle cervical and nodal ganglia, and oculomotor, trochlear and abducens nuclei were removed, sectioned and stained for HRP-positive cells. HRP-labeled neurons were found in the ipsilateral trigeminal (TRG) and superior cervical ganglia (SCG). The middle cervical, stellate, Edinger-Westphal, trochlear and abducens nuclei were all deemed negative for HRP-labeled cells. In the TRG, HRP-labeled neurons ranged from 21 to 250 (mean +/- SE = 93.8 +/- 42.5/ganglion). The labeled neurons were distributed primarily in the ophthalmic branch. In the SCG, the HRP-labeled neurons were distributed evenly in the ganglion, ranging from 6 to 180 (mean +/- SE = 91.6 +/- 31.5/ganglion). Two additional cats having received a sham operation revealed a negative finding. The feline ophthalmic artery is innervated by the ipsilateral TRG and SCG. Such innervation may play a role in regulating blood flow to the optic nerve.

Animals↗
PubMed1999

Effects of losartan on the sexual behavior of male rats.

Many commonly used antihypertensive drugs such as diuretics and beta-blockers can interfere with sexual function in both sexes, causing loss of libido, impairment of erectile function and ejaculation in men, and delay or prevent orgasm in women. Newly developed antihypertensive drugs should ideally not interfere with the patients' quality of life including sexual function. This study examined the effects of losartan, a nonpeptide, specific antagonist for type I angiotensin II receptors, on the male sexual behavior of rats. Spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats were treated with losartan 30 mg/ kg/day or saline control for 7, 30 and 90 days. Dark-cycle video recording was used to analyze the male sexual activities of the rats. No significant alteration in male sexual performance was observed after 7 and 30 days of treatment with losartan. In contrast, SHRs treated with propranolol 5 mg/kg/day showed increases in intromission latency, ejaculation latency and postejaculatory period indicating decreased libido and erectile and ejaculatory function. Upon completion of 90 days of losartan administration, the mount latency of the SHR was significantly increased, suggesting a decrease in libido although other parameters were unchanged and there was no effect in WKY rats. It is therefore concluded that losartan may have an advantage in preservation of sexual function when used clinically for the treatment of hypertensive disorders.

Animals↗
PubMed1999

The antihypertensive effect of the berberine derivative 6-protoberberine in spontaneously hypertensive rats.

Berberine is a natural isoquinoline alkaloid found in plants of the Ranunculaceae and Berberidaceae families. Extracts from berberine-containing plants have been used as traditional Chinese folk remedies for centuries. The antihypertensive effects of the berberine derivative 6-protoberberine (PTB-6) were studied in spontaneously hypertensive rats (SHRs). In conscious SHRs, PTB-6 lowered the systolic blood pressure in a dose-dependent manner (6-PTB: 5 mg/kg, -31.1 +/- 1.6 mm Hg; 10 mg/kg, -42.4 +/- 3.1 mm Hg). Cardiac output using the thermodilution method was reduced in PTB-6-treated anesthetized SHRs with a tendency to decrease in heart rate. Injection of PTB-6 into the intracerebral ventricles of SHRs lowered the systolic arterial blood pressure and heart rate. The berberine derivative PTB-6 is an effective antihypertensive agent. The mechanism of the antihypertensive effect of PTB-6 is probably through a central sympatholytic effect.

Animals↗
PubMed1999

[Changes and its measurement of intracellular Ca2+ during exposure to hyperbaric oxygen].

Objective. To investigate the rule of change of intracellular Ca2+ and its measurement method during exposure to hyperbaric oxygen (HBO). Method. Microfluorescence method was used to measure the changes of intracellular Ca2+ concentration in co-cultured endothelial cells (EC) and smooth muscle cells (SMC) in a specially designed miniature oxygen chamber. Result. (1) [Ca2+]i changes during HBO exposure can be clearly observed directly in the chamber. (2) Within 5 min during 0.2 MPa and 0.3 MPa HBO exposure, EC[Ca2+]i and SMC[Ca2+]i showed a tendency, to increase at first and then decrease with time throughout the exposures, especially the SMC[Ca2+]i. The EC ruptured under exposure to 0.4 MPa HBO. Conclusion. During HBO exposure, EC[Ca2+]i and SMC[Ca2+]i showed biphasic changes, which increased at first and then decreased. The technique and method used were reliable and suitable for investigating of intracellular [Ca2+]i changes under HBO.

Animals↗
PubMed1998

Free radicals are involved in methylmethacrylate-induced neurotoxicity in human primary neocortical cell cultures.

Methylmethacrylate monomer (MMA), a highly volatile material, has been extensively used for the construction of complete or partial dental prostheses. While previous studies have indicated a variety of complications and untoward side-effects associated with its use, the possible neurotoxicity induced by this monomer has not been addressed. In this study, we have investigated the MMA-produced neuronal injury in human neuron-enriched primary culture. Embryonic brain tissue (8-10 weeks postconception) was used for the primary neuron-enriched culture. Phase-contrast microscopy was used to evaluate morphological changes of cultured neurons. Extracellular concentrations of lactate dehydrogenase (LDH) and nitrite was measured from the culture medium to assess the magnitude of neuronal damage and nitric oxide formation, respectively. Neocortical neurons exposed to the monomer (1/200, Vmonomer/Vglycerol) for two days resulted in a significant increase in the LDH level but monomer (1/20000, 1/2000, or 1/200; Vmonomer/Vglycerol) failed to increase the nitrite level. Morphologically, the neurons subjected to monomer treatment exhibited irregular shrunken cell bodies with dystrophic and/or fragmented neurities, or even cell lysis. Moreover, superoxide dismutase plus catalase or vitamin C pretreatment protected against monomer-induced neurotoxicity. Our results suggest that this neurotoxicity can not likely be attributed to the cytotoxic effects of nitric oxide but may be mediated through the toxicity of superoxide and other free radicals. This is the first time, to our knowledge, that neurotoxicity induced by MMA has been demonstrated in human cortical neurons.

Ascorbic Acid↗
PubMed1998

Apoptosis is induced in aging SV40 T antigen-transformed human fibroblasts through p53- and p21CIP1/WAF1-independent pathways.

When comparing SV40 T antigen-transformed human fibroblasts of a younger generation (24 population doubling) and aging stage (58 population doubling), we found that detachment of cells from the culture surface occurred more frequently in aging cells. DNA fragmentation and chromatin condensation which are typical findings of apoptosis occurred more frequently in aging cells as compared to cells of a younger generation. There is no increase in the p53 level or decrease in the SV40 T antigen level in aging cells as compared to cells of a younger generation. Retinoic acid treatment which can effectively suppress p21 gene expression did not prevent apoptosis. These findings indicate that apoptosis that occurs due to aging-transformed human fibroblasts is mediated through p53- and p21-independent pathways.

Antigens, Polyomavirus Transforming↗
PubMed1998

Neuronal supernumerary and dendritic sprouting of the nucleus ambiguus after chronic alteration of peripheral targets in cats.

Anatomic changes of neuronal profiles in response to chronic alteration of peripheral targets were investigated in the nucleus ambiguus (NA) of cats. Unilateral vagal-hypoglossal nerve anastomosis was performed by suturing the transected proximal stump of the vagus nerve to the transected distal stump of the hypoglossal nerve. After comparing horseradish peroxidase (HRP)-labeled neurons on the ipsilateral operated side of the NA with the contralateral unoperated NA and the NA following transection and reuniting to the vagus itself, a remarkable ramification and elongation of the dendritic trees was observed in the HRP-positive neurons on the ipsilateral NA. Quantitative analysis of neuronal profiles revealed that the number of the medium and large neurons on the ipsilateral NA was greater than the contralateral NA and the NA following autologous suturing of the vagus. Comparisons of variable dendritic lengths of the medium and large neurons on the ipsilateral NA revealed longer distances and more branches of the tertiary and perisomatic dendrites than those of the contralateral NA and the NA ipsilateral to autologous reunion. Our results suggest that remarkable sprouting and elongation of the dendritic trees as well as cell supernumerary occurred in the dominant NA motoneurons ipsilateral to the nerve anastomosis. In conclusion, there is a trophic influence in the tongue musculature, which was retrogradely transported to the NA neurons via the regenerating axons and caused the morphological changes in the NA in response to the rerouting of efferents from the vagus nerve to the hypoglossal nerve to innervate intimate tongue musculature.

Animals↗
PubMed1998

Identification of a potential substrate binding domain in the mammalian peptide transporters PEPT1 and PEPT2 using PEPT1-PEPT2 and PEPT2-PEPT1 chimeras.

The mammalian peptide transporters PEPT1 and PEPT2 are energized by a transmembrane electrochemical H+ gradient and exhibit similar broad substrate specificity. These transporters however differ in their affinity for substrates, PEPT1 being a low-affinity transporter and PEPT2 being a high-affinity transporter. To identify the substrate binding domain in PEPT1 and PEPT2 which is responsible for the differing affinities, we constructed a series of PEPT1-PEPT2 and PEPT2-PEPT1 chimeras using an in vivo restriction site-independent procedure and determined their substrate affinities. A comparison of these kinetic data for different chimeras with those of the wild-type PEPT1 and PEPT2 in conjunction with the specific structural PEPT1/PEPT2 crossover regions in these chimeras has led to the identification of a putative substrate binding site, which is comprised of the transmembrane domains 7, 8 and 9 of the transporters.

Animals↗
PubMed1998

The effect of stevioside on blood pressure and plasma catecholamines in spontaneously hypertensive rats.

Stevioside is a sweet-tasting glycoside, composed of stevia, a diterpenic carboxylic alcohol with three glucose molecules, mainly used as a substitute for non-alcoholic sweetener. It has previously been shown to reduce blood pressure in studies in animals and human. The effect of intravenous stevioside on the blood pressure was studied in spontaneously hypertensive rats (SHR). The hypotensive effect on both systolic and diastolic blood pressure was dose-dependent for intravenous doses of 50, 100 and 200 mg/kg in conscious SHR. The maximum reductions in systolic and diastolic blood pressure were 31.4 +/- 4.2% and 40.8 +/- 5.6% (mean +/- SEM) respectively and the hypotensive effect lasted for more than 60 min with a dose of 200 mg/kg. Serum dopamine, norepinephrine and epinephrine levels were not changed significantly 60 min after intravenous injection of stevioside 100 mg/kg in anesthetized SHR. The present data show that stevioside given intravenously to conscious SHR was effective in blood pressure reduction and there was no change in serum catecholamines in anaesthetized animals with this natural compound.

Animals↗
PubMed1998

Recognition of the universally conserved 3'-CCA end of tRNA by elongation factor EF-Tu.

Escherichia coli tRNA(Val) with pyrimidine substitutions for the universally conserved 3'-terminal adenine can be readily aminoacylated. It cannot, however, transfer valine into polypeptides. Conversely, despite being a poor substrate for valyl-tRNA synthetase, tRNA(Val) with a 3'-terminal guanine is active in in vitro polypeptide synthesis. To better understand the function of the 3'-CCA sequence of tRNA in protein synthesis, the effects of systematically varying all three bases on formation of the Val-tRNA(Val):EF-Tu:GTP ternary complex were investigated. Substitutions at C74 and C75 have no significant effect, but replacing A76 with pyrimidines decreases the affinity of valyl-tRNA(Val) for EF-Tu:GTP, thus explaining the inability of these tRNA(Val) variants to function in polypeptide synthesis. Valyl-tRNA(Val) terminating in 3'-guanine is readily recognized by EF-TU:GTP. Dissociation constants of the EF-Tu:GTP ternary complexes with valine tRNAs having nucleotide substitutions at the 3' end increase in the order adenine < guanine < uracil; EF-Tu has very little affinity for tRNA terminating in 3' cytosine. Similar observations were made in studies of the interaction of 3' end mutants of E. coli tRNA(Ala) and tRNA(Phe) with EF-Tu:GTP. These results indicate that EF-Tu:GTP preferentially recognizes purines and discriminates against pyrimidines, especially cytosine, at the 3' end of aminoacyl-tRNAs.

Escherichia coli↗
PubMed1998

Neutron fluence and energy spectra around the Varian Clinac 2100C/2300C medical accelerator.

We have simulated the head geometry of a Varian Clinac 2100C/2300C medical accelerator in a Monte Carlo calculation to produce photoneutrons and transport them through the head shielding into a typical therapy room (modeled by a test cell at Varian Associates). The fast neutron leakage fluence and energy spectra have been calculated at 7 positions around the linac head for typical beam operation at 10, 15, 18 and 20 MV. The results of these calculations have been compared with limited measurements made using the same model accelerator operating in a Varian test cell. Calculations were also made for the fluence and energy spectra outside the head with no surrounding concrete walls, floor or ceiling to eliminate the effects of scattering from concrete. Comparisons were also made with calculations using a much simplified head geometry. The results indicate that the calculations using the complex head geometry compare, within the uncertainties, with the measurements. The simple head geometry leads to differences of a factor of 2 from the complex geometry. Results of these calculations can be used to calculate fast neutron transmission through various shielding configurations and through labyrinths.

Monte Carlo Method↗
PubMed1997

Role of acceptor stem conformation in tRNAVal recognition by its cognate synthetase.

Although the anticodon is the primary element in Escherichia coli tRNAValfor recognition by valyl-tRNA synthetase (ValRS), nucleotides in the acceptor stem and other parts of the tRNA modulate recognition. Study of the steady state aminoacylation kinetics of acceptor stem mutants of E.coli tRNAValdemonstrates that replacing any base pair in the acceptor helix with another Watson-Crick base pair has little effect on aminoacylation efficiency. The absence of essential recognition nucleotides in the acceptor helix was confirmed by converting E.coli tRNAAlaand yeast tRNAPhe, whose acceptor stem sequences differ significantly from that of tRNAVal, to efficient valine acceptors. This transformation requires, in addition to a valine anticodon, replacement of the G:U base pair in the acceptor stem of these tRNAs. Mutational analysis of tRNAValverifies that G:U base pairs in the acceptor helix act as negative determinants of synthetase recognition. Insertion of G:U in place of the conserved U4:A69 in tRNAValreduces the efficiency of aminoacylation, due largely to an increase in K m. A smaller but significant decline in aminoacylation efficiency occurs when G:U is located at position 3:70; lesser effects are observed for G:U at other positions in the acceptor helix. The negative effects of G:U base pairs are strongly correlated with changes in helix structure in the vicinity of position 4:69 as monitored by19F NMR spectroscopy of 5-fluorouracil-substituted tRNAVal. This suggests that maintaining regular A-type RNA helix geometry in the acceptor stem is important for proper recognition of tRNAValby valyl-tRNA synthetase.19F NMR also shows that formation of the tRNAVal-valyl-tRNA synthetase complex does not disrupt the first base pair in the acceptor stem, a result different from that reported for the tRNAGln-glutaminyl-tRNA synthetase complex.

Anticodon↗
PubMed1997

Localization of the major ethidium bromide binding site on tRNA.

Binding of ethidium bromide to Escherichia coli tRNAVal and an RNA minihelix based on the acceptor stem and T-arm of tRNAVal was investigated by 19F and 1H NMR spectroscopy of RNAs labeled with fluorine by incorporation of 5-fluorouracil. Ethidium bromide selectively intercalates into the acceptor stem of the tRNAVal. More than one ethidium bromide binding site is found in the acceptor stem, the strongest between base pairs A6:U67 and U7:A66. 19F and 1H spectra of the 5-fluorouracil-substituted minihelix RNA indicate that the molecule exists in solution as a 12 base-paired stem and a single-stranded loop. Ethidium bromide no longer intercalates between base pairs corresponding to the tRNAVal acceptor stem in this molecule. Instead, it intercalates between base pairs at the bottom of the long stem-loop structure. These observations suggest that ethidium bromide has a preferred intercalation site close to the base of an RNA helical stem.

Base Sequence↗
PubMed1997

Alport syndrome with neurofibromatosis type-I: a case report.

We report a 9-year-old boy with repeated fractures of the tibia from age 6 months and microscopic hematuria from age 2 years. His maternal family has a history of nephritis and his paternal family has neurofibromatosis type-I (NF-I). The boy's renal biopsy revealed an irregular attenuation and splitting of the glomerular basement membrane. The skin biopsy was stained with monoclonal antibody against the alpha 5 chain of type IV collagen; the epidermal basement membrane was negative in the boy and segmentally positive in the boy's mother. We conclude that the patient inherited Alport syndrome from his mother and NF-I from his father. We postulate this was a chance association and that this case does not suggest any relationship between the two diseases.

Child↗
PubMed1997

Blunt cardiac trauma: atrioventricular valve disruption and ventricular septal defect.

Nonpenetrating cardiac trauma resulting in cardiac chamber or valvar rupture is uncommon, requiring a high degree of suspicion for diagnosis. A case involving avulsion of the tricuspid and mitral papillary muscles with resultant interventricular septal rupture is reported. This case illustrates the importance of transesophageal echocardiography in the rapid diagnosis of blunt cardiac trauma. Surgical treatment of this condition is also discussed.

Accidents, Traffic↗
PubMed1997

Neutron sources in the Varian Clinac 2100C/2300C medical accelerator calculated by the EGS4 code.

The photoneutron yields produced in different components of the medical accelerator heads evaluated in these studies (24-MV Clinac 2500 and a Clinac 2100C/2300C running in the 10-MV, 15-MV, 18-MV and 20-MV modes) were calculated by the EGS4 Monte Carlo code using a modified version of the Combinatorial Geometry of MORSE-CG. Actual component dimensions and materials (i.e., targets, collimators, flattening filters, jaws and shielding for specific accelerator heads) were used in the geometric simulations. Calculated relative neutron yields in different components of a 24-MV Clinac 2500 were compared with the published measured data, and were found to agree to within +/-30%. Total neutron yields produced in the Clinac 2100/2300, as a function of primary electron energy and field size, are presented. A simplified Clinac 2100/2300C geometry is presented to calculate neutron yields, which were compared with those calculated by using the fully-described geometry.

Computer Simulation↗
PubMed1997

Glucocorticoid remediable aldosteronism: a case report.

Glucocorticoid remediable aldosteronism (GRA) is a hereditary cause of mineralocorticoid hypertension. The most common presentation is asymptomatic hypertension. Hypokalemia, hyperaldosteronism and suppressed plasma renin activity are other forms of primary hyperaldosteronism. However, the aldosterone secretion in these patients is regulated by adrenocortico-tropic hormone (ACTH) rather than the reninangiotension system. Here, we report a patient with a 12-year history of hypertension without response to any treatment until dexamethasone was administered. The diagnosis of GRA was confirmed by elevated plasma level of 18-oxocortisol, which is a unique steroid biochemical abnormality of this disease. In GRA, hybrid steroids (18-oxocortisol and 18-hydroxycortisol) are synthesized at the C-18 carbon of cortisol in a similar way as when corticosterone is converted to aldosterone. The gene duplication defect is on chromosome 8 codes for a chimerical 11 beta-hydroxylase/aldosterone synthase enzyme, causing ectopic expression of aldosterone synthase in zona fasiculata. Because this hypertension is remediable by exogenous glucocorticoid, this case was reported to raise attention about treatable aldosteronism.

Adrenocorticotropic Hormone↗