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Biomedical subjects

X Guo

Publications and source records attributed to X Guo.

At least 415 records · Page 23Linked to original sources
PubMed1994

Exocytosis from a single rat chromaffin cell by cholinergic and peptidergic neurotransmitters.

Secretion of catecholamines from chromaffin cells is mediated by cholinergic and peptidergic neurotransmitters. The cholinergic transmitter acetylcholine activates both nicotinic and muscarinic receptors to trigger catecholamine secretion in rat adrenal medulla. Vasoactive intestinal polypeptide (VIP) has been identified as the peptidergic transmitter in rat adrenal medulla and may also be the non-cholinergic transmitter in bovine adrenal. Pituitary adenylate cyclase activating polypeptide (PACAP), a VIP-like secretin peptide, is also found in the adrenal, and is a potent secretagogue. Thus, PACAP may be another peptidergic transmitter at the adrenal synapse. A most intriguing property of rat chromaffin cells is that stimulation of nicotinic, muscarinic, VIP or PACAP receptors are each able to produce robust catecholamine secretion on their own. This raises the question of whether a single chromaffin cell can respond to each of the above agonists or whether the secretion is due to subpopulations of chromaffin cells. This issue was addressed by using electrochemical techniques to monitor exocytosis from individual chromaffin cells in culture. We demonstrate that acetylcholine, nicotine, muscarine, VIP and PACAP are each able to evoke catecholamine secretion from a single chromaffin cell. Some cells only responded to acetylcholine. Furthermore, each agonist produced a distinct pattern of exocytosis. Muscarine-evoked secretion exhibited a latency of 0.5-2 s, but exocytosis persisted up to 30 s following 500 ms stimulation. Nicotine produced an immediate response which usually ended within 10 s. The secretory pattern following acetylcholine appeared to be the sum of the nicotinic and muscarinic patterns, showing both rapid onset and longer duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Immunohistochemistry of cyclin D1 in human breast cancer.

Cyclin D1/PRAD 1, a cell cycle-related gene mapped to chromosome 11q13, has been found to be amplified in some breast cancers and squamous cell carcinomas of the head and neck, and esophagus. In this study, overexpression of cyclin D1/PRAD1 gene was demonstrated immunohistochemically in 35 of 43 (81.3%) cases of human breast cancer, with a newly available anticyclin D antibody. Neither normal epithelial components nor glandular structures from samples of fibrocystic disease, were reactive. Amplification of the gene was detected in 4 of 23 (17%) cases by Southern analysis. Increased gene dosage does not seem to be the only mechanism that resulted in increased protein expression as detected by immunohistochemistry. Because the less differentiated high grade tumors exhibited a more intense nuclear stain and non-neoplastic epithelial components were not stained, the use of cyclin D1/PRAD1 has potential as a tumor marker.

Blotting, Southern↗
PubMed1994

Sex determination and polyploid gigantism in the dwarf surfclam (Mulinia lateralis Say).

Mulinia lateralis, the dwarf surfclam, is a suitable model for bivalve genetics because it is hardy and has a short generation time. In this study, gynogenetic and triploid M. lateralis were successfully induced. For gynogenesis, eggs were fertilized with sperm irradiated with ultraviolet light and subsequently treated with cytochalasin B to block the release of the second polar body (PB2). Triploidy was induced by blocking PB2 in normally fertilized eggs. The survival of gynogenetic diploids was very low, only 0.7% to 8 days post-fertilization (PF), compared with 15.2% in the triploid groups and 27.5% in the normal diploid control. Larvae in all groups metamorphosed at 8-10 days PF, and there was no significant post-larval mortality. At sexual maturation (2-3 months PF), all gynogenetic diploids were female, and there was no significant difference (P > 0.05) in sex ratio between diploids and triploids. These results suggested that the dwarf surfclam may have an XX-female, XY-male sex determination with Y-domination. Compared with diploids, triploids had a relative fecundity of 59% for females and 80% for males. Eggs produced by triploid females were 53% larger (P < 0.001) in volume than those from diploid females. In both length and weight measurements at three months PF, the gynogenetic diploids were not significantly (P > 0.33) different from normal diploid females, suggesting that inbreeding depression was minimal in meiosis II gynogens. Triploid clams were significantly larger (P < 0.001) than normal diploids. We hypothesize that the increased body-size in triploids was caused by a polyploid gigantism due to the increased cell volume and a lack of cell-number compensation.

Animals↗
PubMed1994

Genome size and organization in the ixodid tick Amblyomma americanum (L.).

We used DNA reassociation kinetics to determine genome size and organization in the ixodid tick Amblyomma americanum. We calculated the genome size of A. americanum to be approximately 1.08 pg or 1.04 x 10(9) base pairs and to consist of 35.8% unique DNA, 4.2% foldback sequences, 17.9% highly repetitive sequences, and 42.1% moderately repetitive sequences. Comparison of the reassociation kinetics of long and short fragments revealed repetitive sequences to be distributed in a pattern of long period interspersion, a feature that, to date, has been associated with arthropod genomes that lack a high percentage of repetitive DNA.

Animals↗
PubMed1994

Effects of cocaine on P3B in cocaine abusers.

Little is known about the effects of cocaine on cognitive tasks. Event-related potentials (ERP) were recorded in 7 cocaine abusers during the performance of the auditory oddball task before and after the intravenous injections of saline and cocaine (60-80 mg). The P3B and slow wave components of the ERP were significantly larger 60-210 min after the cocaine than after the placebo injection. The results suggest that cocaine abusers have difficulty in maintaining optimal stimulus processing during extended testing. Cocaine blocks this decrement in stimulus processing.

Adult↗
PubMed1994

[Treating old facial nerve paralysis of 260 cases with the acupuncture treatment skill of pause and regress in six parts].

With the acupuncture treatment skill of pause and regress in six parts, we have treated facial paralysis of 260 cases. The other 50 cases were treated with the uniform reinforcing-reducing method as control. The result shows that the effectiveness of the former is better than the latter (P < 0.01). The acupuncture treatment skill of pause and regress in six parts is a new way developed from the reducing method of the traditional reinforcing-reducing method of lifting and thrusting the needle and nine-six reinforcing-reducing method. In addition, the acupuncture points were chosen in the area of the main distribution of the facial nerve. Through the clinical practice, the acupuncture treatment skill is an effective way for treating old facial paralysis.

Acupuncture Therapy↗
PubMed1994

The body mass index of Chinese adults in the 1980s.

Patterns and trends in the body composition of Chinese adults are studied with data from the 1982 China Nationwide Nutrition Survey (CNS-82) and the 1989 China Health and Nutrition Survey (CHNS-89). The CNS-82 showed rural inhabitants were approximately 3 kg lighter than urban residents and approximately 2.2 cm shorter. Males were heavier (55.2 +/- 7.4 vs 50.7 +/- 8.0 kg) and taller (165.3 +/- 7.3 and 153.5 +/- 6.3 cm). Using a cut-off for underweight of a body mass index (BMI: kg/m2) < 18.5 and for obesity of > 25, 11.6% and 12.9% of the urban and rural sample were underweight and 9.8% and 6.9% respectively were overweight. The CHNS-89 surveyed 5138 adults aged 20-45 in eight selected provinces. The proportion of underweight in both urban and rural samples declined slightly (approximately 1.3%) but the proportion of obesity increased considerably (4.8% for the urban sample and 2% for the rural one). Increased income was significantly associated with reduced low body mass index (BMI: kg/m2) in the urban sample while, for the rural and overall samples, the opposite was found for obesity. Provincial patterns in energy intake were not associated with the distribution of BMI while occupation was. In particular, government officials and housewives were much more likely to be obese as also were subpopulation groups consuming greater proportions of energy from animal sources. Over 80% of the population fell in the normal BMI range (18.5-25). This may relate to the relatively even distribution of food in China during the past several decades.

Adult↗
PubMed1994

[Effects of high iodine and high fluorine on children's intelligence and the metabolism of iodine and fluorine].

An investigation on children's intelligence and the metabolism of iodine and fluorine in high iodine and fluorine regions was carried out. The results were as follows. In high iodine and high fluorine areas, the thyroid enlargement prevalence rate among inhabitants and that among children were 3.8% and 29.8%, respectively. The dental fluorosis prevalence rate among inhabitants and that among children was 35.48% and 72.9%, respectively. The pupils' average intelligence quotient (IQ) was 76.67 +/- 7.75, slightly lower than the control point, but that of low intelligent pupils was 16.7%. The urinary iodine and urinary fluoride were 816.25 +/- 1.80 micrograms/L and 2.08 +/- 1.03 mg/L, respectively, markedly higher than the control point. The thyroid iodine-131 (131I) uptake rate was markedly lower than the control point. The values at 3 h and 24 h were 9.36 +/- 1.55% and 9.26 +/- 4.63%, respectively. The serum TSH was obviously higher than the control point. These results indicate that high iodine and high fluorine exert severe damage to human body.

Adolescent↗
PubMed1994

Regression of cardiac hypertrophy and myosin isoenzyme patterns by losartan and captopril in renovascular hypertensive rats.

To test the effect of losartan and captopril on cardiac hypertrophy and myosin isoenzyme, two-kidney, one-clip (2K 1C) renovascular hypertensive rats (RHR) were used. Eight weeks after the onset of hypertension, losartan 5 mg.kg-1.d-1 and captopril 50 mg.kg-1.d-1 were administered p.o. to 2 groups of RHR, respectively for 8 wk. The results showed that captopril significantly decreased the cardiac mass (607 +/- 169 mg vs 1029 +/- 132 mg) and total protein content (120 +/- 38 mg vs 198 +/- 31 mg), concomitant with significant decrease of arterial blood pressure (BP) (15.4 +/- 5.2 kPa vs 28.5 +/- 4.9 kPa). Losartan also induced a significant decrease in cardiac mass (671 +/- 116 mg vs 1029 +/- 132 mg) and protein content (142 +/- 29 mg vs 198 +/- 31 mg), as well as significantly lowered the BP (15.2 +/- 2.1 kPa vs 28.5 +/- 4.9 kPa). It is important to be note that both drugs normalized the shift of myosin isoenzyme in RHR. These results indicated that both drugs, having potent antihypertensive effects, can effectively reverse the cardiac hypertrophy and abnormal distribution of myosin isoenzyme patterns.

Angiotensin Receptor Antagonists↗
PubMed1994

[The flow-limiting segment (FS) of the nasal airway].

A modified anterior rhinomanometry and electromyography of the alar muscle were introduced to investigate the site and function of the FS. It was determined that the FS was confined to the area of nasal pathway 2.5 cm in length from the nostril. The location and limitation of this region, which accounted for 78.8% of overall nasal airway resistance, could not be altered by topical vasoactive agents. The most resistive site in the FS averaged 1.75cm distant from the nostril. In normal subjects, alar muscles constricted isometrically during respiration so as to keep the vestibular airway stable. On the contrary, the deformities and abnormalities of the FS could obliterate the nasal airway easily, leading to the symptom of nasal obstruction. Clinically, it is imperative to pay much attention to lesions in the FS in the diagnosis and treatment of nasal stuffiness. Furthermore, it is essential to protect the structural integrity of the FS in the daily rhinosurgery.

Adult↗
PubMed1994

[Immunoelectron microscopic studies on the process of tumor cytolysis mediated by lymphokine activated NK cells].

The second fraction (F2) cells isolated from PBL by discontinuous Percoll density gradient centrifugation were used as the enriched natural killer (NK) cells. After being incubated with rIL2, the activated F2 cells (F2 LAK) acquired the cytolytic ability upon NK resistant tumor cell lines. In F2 LAK, about 45% of the cells were CD16+, therefore F2 LAK were used as the enriched CD16+LAK cells (or lymphokine activated NK cells). The cytolysis process of lung adenocarcinoma LTEPa-2 or K562 tumor cells mediated by CD16+LAK cells were investigated with colloidal gold labelled Ab via scanning and transmission immunoelectron microscopy. The results showed that the CD16+LAK cells extended their protrusions deep into the target cells. Crypts of various diameter and depth were observed on the surface of the target cells with membrane injury at the bottom of the crypts. It was found that the cytoplasmic granules and vacuoles of CD16+LAK cells were concentrated in the area close to the E-T conjugated side, and sometimes the granules were found within the LAK protrusions. The attacked target cells died by apoptosis and necrosis. This study provided direct evidence that lymphokine activated NK cells are effectors of LAK cells.

Adenocarcinoma↗
PubMed1993

Inhibition of hepatocyte gap junctional communication by 25-hydroxycholesterol may be mediated through free radicals.

25-Hydroxycholesterol, an autoxidation product of cholesterol, has been shown to inhibit gap junctional communication between rat hepatocytes. In this study, we investigated whether free radicals are responsible for the effect of 25-hydroxycholesterol on hepatocytes. Addition of superoxide dismutase, hydroxyl radical scavenger mannitol, or the antioxidants diphenylphenylenediamine and alpha-tocopherol markedly decreased the inhibitory effect of 25-hydroxycholesterol. However, addition of catalase or the catalase inhibitor aminotriazole did not influence the inhibition of gap junctional communication by 25-hydroxycholesterol. Data from this study suggest that free radicals other than hydrogen peroxide are involved in the mechanism of 25-hydroxycholesterol-induced inhibition of gap junctional communication.

Animals↗
PubMed1993

Salmonella typhimurium neuraminidase acts with inversion of configuration.

When the time course of the hydrolysis of identical solutions of p-nitrophenyl N-acetyl-alpha-D-neuraminide by Salmonella typhimurium neuraminidase is monitored by u.v. and by its optical rotation, the rotation change is synchronous with, or even marginally in advance of, the absorbance change. In experiments under the same conditions with influenza-virus neuraminidase, known to react with retention of configuration [Chong, Pegg, Taylor and von Itzstein (1992) Eur. J. Biochem. 207, 335-343], the rotation change is much slower than the absorbance change. The inverting, presumably single-displacement, mode of action of the S. typhimurium enzyme follows from these observations, and the position (92.5% beta) of the slowly established mutarotational equilibrium of N-acetylneuraminic acid [Friebolin, Kunzelmann, Supp, Brossmer, Keilich and Ziegler (1981) Tetrahedron Lett. 22, 1383-1386].

Kinetics↗
PubMed1993

A kinetic-isotope-effect study of catalysis by Vibrio cholerae neuraminidase.

Michaelis-Menten parameters for hydrolysis of seven aryl N-acetyl alpha-D-neuraminides by Vibrio cholerae neuraminidase at pH 5.0 correlate well with the leaving-group pKa (delta pK 3.0; beta 1g (V/K) = -0.73, r = -0.93; beta 1g (V) = -0.25; r = -0.95). The beta-deuterium kinetic-isotope effect, beta D2(V), for the p-nitrophenyl glycoside is the same at the optimum pH of 5.0 (1.059 +/- 0.010) as at pH 8.0 (1.053 +/- 0.010), suggesting that isotope effects are fully expressed with this substrate at the optimum pH. For this substrate at pH 5.0, leaving group 18O effects are 18(V) = 1.040 +/- 0.016 and 18(V/K) = 1.046 +/- 0.015, and individual secondary deuterium effects are beta proRD(V) = 1.037 +/- 0.014, beta proSD(V) = 1.018 +/- 0.015, beta proRD(V/K) = 1.030 +/- 0.017, beta proSD(V/K) = 1.030 +/- 0.017. All isotope effects, and the beta 1g(V/K) value are in accord with the first chemical step being both the first irreversible and the rate-determining step in enzyme turnover, with a transition state in which there is little proton donation to the leaving group, the C-O bond is largely cleaved, there is significant nucleophilic participation, and the sugar ring is in a conformation derived from the ground-state 2C5 chair. The apparent conflict between the beta 1g (V) value of -0.25 with all the kinetic-isotope-effect data can be resolved by the postulation of an interaction between the pi system of the aglycone ring and an anionic or nucleophilic group on the enzyme.

Catalysis↗
PubMed1993

BIBW 22, a dipyridamole analogue, acts as a bifunctional modulator on tumor cells by influencing both P-glycoprotein and nucleoside transport.

BIBW 22, a phenylpteridine analogue of dipyridamole (DPM), enhanced vincristine cytotoxicity approximately 10 times more than DPM in a multidrug-resistant (MDR) KB V20C cell line. Using rhodamine 123 accumulation in KB V20C cells as an indicator of MDR phenotype, BIBW 22 was shown to be about 100 times more potent than DPM in inhibiting the MDR-associated efflux of rhodamine 123. Photolabeling of P-glycoprotein in KB V20C plasma membranes with 0.2 microM [3H]azidopine was strongly inhibited by 1 microM BIBW 22, indicating that this compound reverses the MDR phenotype by interfering with MDR-associated P-glycoprotein. In addition, BIBW 22 at 1 microM could also enhance the cytotoxicity of 5-fluorouracil in KB cells about 20-fold. Its potency in inhibiting nucleoside transport is 7-fold more potent than that of DPM. These results suggest that BIBW 22 is a potent bifunctional modulator which influences both P-glycoprotein and nucleoside transport in tumor cells. Potential use of this compound as a modulator of combination chemotherapy involving antimetabolites and drugs affected by MDR should be explored.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

The activation of bone marrow macrophages 24 hours after thermal injury.

We determined the effect of thermal injury on the in vitro production of the immunoactive substances tumor necrosis factor, interleukin 1, prostaglandin E2, and complement component C3 by lipopolysaccharide-stimulated guinea pig bone marrow macrophages and on the cytotoxicity of these cells. Macrophages from burned animals produced different amounts of these mediators compared with unburned animals at certain culture times, suggesting that thermal injury could program the bone marrow cells to respond differently from normal cells to in vitro stimulation with lipopolysaccharide. Also, the macrophages from burned animals displayed greater cytotoxicity towards L929 target cells. These results suggest that there is a complex interaction among cellular secretory products, especially after thermal injury, that may be important in host defense.

Animals↗