Biomedical subjects

R Xu

Publications and source records attributed to R Xu.

At least 181 records · Page 10Linked to original sources

PubMed1998

The in vitro effect of leptin on basal and growth hormone-releasing hormone-stimulated growth hormone secretion from the ovine pituitary gland.

We have studied the direct effect of leptin on the secretion of GH from the anterior pituitary gland of the sheep. Using primary cultures of ovine pituitary cells, leptin (10(-9)-10(-7) M) treatment for 30 min did not affect basal or GHRH (10(-7) M)-stimulated GH secretion. Following treatment for 24 h, a dose of 10(-7) M leptin stimulated basal GH secretion. In contrast, doses of 10(-7) and 10(-8) M leptin inhibited GHRH-stimulated GH secretion after 24 h of treatment. These results suggest that leptin can have long-term effects on the somatotropes, but no acute effect. Furthermore, leptin appears to have opposite effects on basal and GHRH-stimulated GH secretion.

Animals↗

PubMed1998

Synthesis, antimuscarinic activity and quantitative structure-activity relationship (QSAR) of tropinyl and piperidinyl esters.

A series of tropinyl and piperidinyl esters was synthesized and evaluated for inhibitory activities on the endothelial muscarinic receptors of rat (M3) and rabbit (M2) aorta. Some of the esters (cyclohexylphenylglycolates and cyclohexylphenylpropionates) were found to be better antimuscarinic compounds than standard M2 and M3 inhibitors such as AFDX116 and 4-diphenylacetoxy-N-methylpiperidine (DAMP), with pKEC50 values in the range of 8-9. A few esters were found to be more selective M3 than M2 inhibitors, but these tended to have low activities. The hydrophobic, electronic and steric characteristics of these esters were correlated with antimuscarinic activity by using appropriate parameters representing hydrophobicity (HPLC capacity factor, log kw), size (molecular volume) and electronic character (Taft's polar substituent constant sigma * and 13C chemical shift difference delta delta). Finally, 92% of the M2-inhibitory activities of the esters could be accounted for by the size and electronic character sigma * of the side chain. In contrast, the M3-inhibitory activities of these esters were mainly attributed to the electronic nature (sigma *, delta delta) of the side chain, with good activity being associated with electron-withdrawing groups. Visualization of the comparative molecular field analysis (CoMFA) steric and electrostatic fields provided further confirmation of the structure-activity relationship (SAR) derived from traditional quantitative structure activity relationship (QSAR) approaches.

Animals↗

PubMed1998

The location of the spinal nerve root on plain radiographs of the cervical spine.

Twelve cervical spines from C2 to T1 were harvested from embalmed cadavers to study the location of the nerve root on plain radiographs. After removal of the soft tissue, the spinal nerves just lateral to the transverse processes were exposed and injected with lead oxide. Plain radiographs including anteroposterior (AP) and left and right oblique views were taken. Angular and linear measurements were performed directly on the radiographs. Results showed that the average frontal angle of the nerve root for all levels was 155 degrees on the AP view, 108 degrees on the foraminal side of the oblique view, and 153 degrees on the opposite side of the oblique view. The nerve root height for all levels averaged 4.7 +/- 0.5 mm. The interpedicular space height increased consistently from 7.8 +/- 0.7 mm at C3-C4 to 9.0 +/- 1.3 mm at C6-C7 except at C2-C3. The nerve root height with respect to the interpedicular space height was 56.2% at C2-C3, 57.8% at C4-C5, and 53.7% at C6-C7. A knowledge of the location of the cervical nerve root related to plain radiographs may enhance the value of plain radiographs in the diagnosis and treatment of cervical spinal disorders.

Aged↗

PubMed1998

Location of the sacral pedicle, foramina, and ala on the lateral aspect of the sacrum: a radiographic study.

Twenty-one adult dry-bone sacral specimens were used to quantitatively determine the location of the sacral pedicle, foramina, and ala on the lateral radiographic view of the sacrum. The anterior and posterior sacral foramina from S1 to S3, the midlines of the anterior sacrum and cephalad border of the S1 vertebral body, and the lateral limit of the lateral sacral mass were outlined with wires. A lateral radiograph was taken, and measurements were made directly from the radiograph. The average sacral pedicle height for both male and female specimens was approximately 20 mm for S1, 12 mm for S2, and 7 mm for S3. The sacral foramina height averaged approximately 13 mm for S1 and S2, and 10 mm for S3. The average ala and S1 body-ala angles were 88 degrees and 35 degrees. The distance from the ala tip to the anterior aspect of the sacrum averaged 12 mm, and the average anterior height of the S1 vertebral body above the ala was 11 mm. These measurements, in conjunction with inlet and outlet radiographs, may aid in the recognition of the vital structures of the sacrum on the lateral radiographic view and enhance the safety of dorsal sacral screw placement.

Adult↗

PubMed1998

Computed tomographic evaluation of the internal structure of the lateral mass of the lower cervical spine.

Axial computed tomography scans with a slice thickness of 2 mm taken from 12 cervical spines were used to study the internal structure of the lateral mass. Images representing the middle of zone I (Heller's classification) and the top of zone III were analyzed. The measurement of zone I involved anterior cortex thickness (ACT) while measurements of zone III included ACT, lateral cortex thickness (LCT), posterior cortex thickness (PCT), lateral mass thickness (LMT), and lateral mass width (LMW). The percentage of the ACT and PCT with respect to the LMT (ACT/LMT and PCT/LMT) were calculated. Results showed the average ACT in zone I ranged from 1.6 to 1.8 mm. In zone III, the average LMT and LMW ranged from 8 to 9 mm and 13 to 15 mm, respectively. The smallest LMT was found at C7. The average ACT and PCT for all levels ranged from 1.8 to 2 mm. The ACT with respect to the LMT (ACT/LMT) was approximately 17% to 19% for C3 to C5 and C7, and 15% for C6 separately. The PCT with respect to the LMT (PCT/LMT) was approximately 16% to 18% for C3 to C6, and 20% for C7. These results show the ventral cortex of the lateral mass is relatively thicker and support the concept of bicortical screw purchase.

Aged↗

PubMed1998

[Malignant clonogenic precursors in the peripheral blood of patients with multiple myeloma].

OBJECTIVE: To study the clonogenic potential of circulating malignant precursors in the peripheral blood of patients with multiple myeloma (MM). METHODS: A new cell culture system was used to expand putative malignant precursor clones and promote their differentiation. Meanwhile, immunocytochemical staining, Giemsa-Wright staining and scanning electron microscopy were employed to reveal the growth properties and biological features of fresh and expanded malignant precursors and plasmacytes. RESULTS: Small lymphocyte-like B cells, which were actively proliferative and grew in the form of clusters, were found at the third day after culture. They accounted for 38% +/- 14%. The cells didn't express cytoplasmic immunoglobulin (CyIg) and CD38 antigen. In addition, no typical plasmacytes were observed. At the sixth day of culture, morphologically discernible plasmacytes, which grew in the form of large clumps in this culture system, were detected and represented 58% +/- 8%. These plasmacytes strongly expressed CD38 antigen and monoclonal CyIg identical to that of the original myeloma cells. CONCLUSION: Malignant clonogenic precursor cells, which have high proliferative potential, are present in the peripheral blood of MM cases, and could proliferate and differentiate into myeloma cells.

Adult↗

PubMed1998

[Investigation of retroviral infection in human acute myeloid leukemia].

OBJECTIVE: To explore the potentiality of retroviral etiology in human acute myeloid leukemia (AML). METHODS: Cell culture techniques, direct immunogold silver staining(D-IGSS), reverse transcriptase (RT)assay, XC syncytium assay, and electron microscopy were employed to evaluate retrovirus associated antigens (RVAAgs), RT activities, CPE, and virus particles of both leukemic cells and normal hematopoietic cells. RESULTS: RVAAgs were detected by D-IGSS in 50.0% of fresh AML cell samples and 87.5% of cultured AML samples. RT assay showed that RVAAg-positive samples from 14 cases simultaneously expressed RT activities, and XC syncytium assay also revealed positive results. Electron microscopy demonstrated typical type C retrovirus particles at various maturation in 75% of cultured leukemic cell samples. In contrast, neither RVAAgs and RT activity nor syncytium and virus particles were detected in normal controls. CONCLUSIONS: AML cells harbor the entire genome(s) of retrovirus(es), which could release into extracellular spaces in intact particles via budding from the target cells stimulated in vitro by appropriate RV inducing agents. The exact relationship between these viruses and AML etiology is uncertain and needs further study.

Adult↗

PubMed1998

[E2-induced prolactin-secreting tumor of heteroplasty pituitary in renal capsule of the rats].

OBJECTIVE: A prolactin-producing tumor induced by 17-beta-estradiol (E2) in isotransplanted pituitaries under renal capsules of SD rats were studied. METHODS: Male SD rats (30 days old) were transplanted with an isologaus pituitary under renal capsule and treated with subcutaneous implantation of an empty or E2-laden silastic capsule. RESULTS: After treated with E2 for 60 days and 120 days, both the eutopic and ectopic pituitaries were more than three times heavier than those from control rats, accompanied by hyperprolactinemia, and the body weight of rats decreased significantly. The effects of E2 on the weight of eutopic pituitary and the concentration of plasma PRL were time-dependent. In situ hybridization was employed to measure the levels of PRL mRNA expression in cells from the eutopic and ectopic pituitaries 120 days after treatment of E2. The PRL mRNA contents in both the eutopic and ectopic pituitary cells were much greater than those in untreated pituitary cells. But PRL mRNA levels showed no significant difference between the eutopic and ectopic pituitary cells. CONCLUSIONS: Our previous data has shown that prolactinomas can be induced by chronic treatment of E2 in eutopic pituitaries of SD rats. In present study it appeared that E2 exerted similar effect on the ectopic pituitaries which were distant from the hypothalamus. Our results also demonstrated that E2 could promote the PRL gene expression in both the eutopic and ectopic pituitary cells, and there was no significant difference between them. Our data suggested the possibility of PRL-producing pituitary tumors could originate from anterior pituitary.

Animals↗

PubMed1998

[A preliminary investigation on causes of failure of vitreoretinal surgery for complicated rhegmatogenic retinal detachments].

OBJECTIVE: To evaluate the failure causes of vitreoretinal surgery for complicated rhegmatogenic retinal detachment. METHODS: Vitreoretinal (VR) surgery was performed on 477 cases (479 eyes) with complicated rhegmatogenic retinal detachment, the operative procedures including vitrectomy, peeling of pre-retinal membrane, fluid-air exchange, inert gas (SF(6) or C(3)F(8)) or silicone tamponade. RESULTS: On discharge, the operation was effective in 349 eyes (72.87%) and failed in 130 (27.13%) eyes. CONCLUSION: The multiple stepwise multivariate regression shows that the factors significantly influencing VR surgery are silicone tamponade, giant retinal tears, SF(6) tamponade, iatrogenic tear, anterior proliferative vitreoretinopathy (PVR), subretinal proliferation, PVR, C(3)F(8) tamponade, operative frequency and choroidal detachments.

Adolescent↗

PubMed1998

[Solid-phase extraction coupled with high-field proton nuclear magnetic resonance spectroscopy: application to the analysis of brodimoprim metabolites in rat urine].

The use of coupled solid-phase extraction and high-field proton nuclear magnetic resonance spectroscopy (SPE-1HNMR) for the detection and identification of the urinary metabolites of brodimoprim is described. Urine was obtained from Wistar rats following a dose of 200 mg.kg-1 of brodimoprim. Analysis was performed on partially purified extracts obtained by solid-phase extraction onto C-18 bonded silica gel. As each spectrum was often given by a mixture of more than two kinds of metabolites, stepwise identification of the individual metabolites was achieved by sorting out signal sets having invariant proportionality. Five kinds of metabolites of the drug were found by the analysis.

Animals↗

PubMed1998

[Transient response in electric measurement of human auricular point].

This is an experiment on the measuring E approximately t and R approximately t for human auricular point, which shows there is a transient response of electric potential E(t) and voltage drop U(t) when t < 2 tau and there is at intervals change with the time after 2 tau about R(t) and E(t). We have obtained a response function of the E(t) and U(t) by the circuit analysis. The parameter of the transient character is relaxation time tau, tau approximately RC. The mathematical model is in correspondence with the experimental result of the auricular point and TPM simulation. It indicates that the character changing with the time should be extracted after 2 tau. This experiment is of importance to understanding the electric character of the otopoint.

Acupuncture Points↗

PubMed1998

[Transient response in electric measurement of human auricular point].

This is an experiment on the measuring E-t and R-t for human auricular point, which shows there is a transient response of electric potential E(t) and voltage drop U(t) when t < 2 tau and there is at intervals change with the time after 2 tau about R(t) and E(t). We have obtained a response function of the E(t) and U(t) by the circuit analysis. The parameter of the transient character is relaxation time tau,tau approximately RC. The mathematical model is in correspondence with the experimental result of the auricular point and TPM simulation. It indicates that the character changing with the time should be extracted after 2 tau. This experiment is of importance to understanding the electric character of the otopoint.

Acupuncture Points↗

PubMed1998

The effect of atlas anterior translation and rotation on axis canal size. A computer-assisted anatomic study.

Eighteen adult paired atlas and axis specimens were used in conjunction with computer analysis to determine the average transverse canal area of the axis after different degrees of anterior translation and three types of rotation of the atlas. After each displacement, the remaining transverse canal area of the axis was calculated. The data showed that the mean transverse canal area of the axis was 351.5 +/- 8.8 mm2 for males and 276.9 +/- 8.6 mm2 for females, respectively. After a 3-, 4-, and 5-mm anterior translation of the atlas, the mean transverse canal area of the axis decreased to 300.4 +/- 5.1 mm2 (85.5%) for males and 238.0 +/- 2.1 mm2 (85.9%) for females, 283.9 +/- 5.9 mm2 (80.8%) for males and 228.5 +/- 3.1 mm2 (82.5%) for females, and 260.4 +/- 4.2 mm2 (74.1%) for males and 216.4 +/- 2.8 mm2 (78.2%) for females, respectively. After a 40 degree rotation, 40 degree rotation with 4-mm anterior translation, and 40 degree rotation with 8-mm anterior translation of the atlas, the mean transverse canal area of the axis for both sexes decreased approximately to 58%, 42%, and 23%, respectively. This study confirmed that the size of the transverse canal area of the axis was consistently correlated with the degrees of the anterior translation and rotation of the atlas.

Adult↗

PubMed1998

Computed tomographic considerations of dorsal sacral screw placement.

Axial computed tomographic scans were obtained from 40 sacrum specimens. The best scans close to the inferior portion of S1 superior facet and the middle of S2 pedicle were chosen to evaluate various screw paths. Measurements of screw paths included the screw path lengths and angulations as well as the distances between the screw and the sacral canal. The results showed that no significant differences between male and female specimens were found in any parameters, although the linear measurements were greater for male specimens than for female specimens. In S1, the greatest value of the screw path lengths was noted in screw path IV (anterolaterally directed) with an average of 36.9 +/- 7.3 mm. The mean value for screw path 1 (30 degrees anteromedially directed) was 32.5 +/- 7.2 mm, and the mean distance between screw path I and the lateral cortex of the sacral canal was 6.0 +/- 3.1 mm. For S2, the mean value (31.9 +/- 7.6 mm) of screw path II (anterolaterally directed) was significantly greater than that (24.2 +/- 4.9 mm) of screw path I (30 degrees anteromedially directed) (p < or = 0.001). The mean distance between screw path I and the lateral cortex of the sacral canal was 4.8 +/- 3.2 mm. This study showed that computed tomography (CT) scans provide more accurate information of screw path lengths. Preoperative CT evaluation of the sacral screw path angle and length is recommended.

Bone Screws↗

PubMed1998

The quantitative anatomy of the superior gluteal artery and its location.

Twenty cadaveric posterior gluteal regions were dissected to quantitatively determine the location and dimensions of the superior gluteal artery and its branches on the posterior gluteal region. Two reference lines were defined: one (transverse) was drawn from the posterior inferior iliac spine (PIIS) across the ilium to the anterior superior iliac spine (ASIS), and another (vertical) was drawn orthogonal to the transverse line at a point 8 cm from the PIIS. Results showed that the average distances from the posterior superior iliac spine (PSIS) and PIIS to the superior gluteal artery origin at the sciatic notch were 60 mm and 42 mm, respectively. The deep superior branch traveled an average of 18 mm above the transverse line at the vertical line, and averaged 54 mm from the iliac crest at the same point. This same branch inserted in the medius an average of 29 mm from the ASIS, and 11 mm above the transverse line, while providing 4 to 7 perforators to the gluteus medius and 0 to 2 to the gluteus minimus. The deep inferior branch traveled an average of 23 mm below the transverse line along the vertical line and penetrated the minimus or medius 36 mm from the ASIS, while providing 3 to 8 perforators to the medius and 1 to 3 to the minimus. The average distance from the deep inferior branch to the superior edge of the acetabulum along the vertical line was 25 mm. These data may be helpful in preventing the injury of the superior gluteal artery during the posterior gluteal approach.

Arteries↗

PubMed1998

Modified Magerl technique of lateral mass screw placement in the lower cervical spine: an anatomic study.

Twelve adult embalmed cadaveric cervical spines were used to modify the traditional Magerl technique for screw placement in the lower cervical spine. The starting point for the drill bit was 2 mm inferior to the inferiormost edge of the superior facet and 1-2 mm medial to the posterior midline of the lateral mass. The orientation of the drill bit was parallel to the superior facet in the sagittal plane, and 25-30 degrees lateral in the transverse plane. After drilling, we made direct measurements of the screw path length between the dorsal and ventral cortexes of the lateral mass and screw-path angles in both the sagittal and transverse planes. The results showed the mean screw-path length for all levels ranged from 11 to 15 mm with the smallest value at C7. The mean sagittal and transverse angles of the screw path ranged from 41 to 43 degrees and from 26 to 28 degrees. Penetration of the superior facet was found in three (2.5%) cases. Possible spinal nerve violation was seen in 13 (10.8%) cases if the drill bit was excessively overpenetrated. This study suggested that our modified Magerl technique for lateral mass screw placement be as high as possible without impinging on the facet joint, and drilling be as cranial and lateral as possible to leave the superior articular process as high and lateral as possible. This may further decrease the incidence of spinal nerve injury. Careful drilling and tapping technique is recommended to avoid overpenetration.

Adult↗

PubMed1998

Quantitative anatomy of the transverse foramen and pedicle of the axis.

Forty dry C2 cervical vertebrae were obtained to evaluate quantitatively the anatomy of the C2 transverse foramen and pedicle. Computed tomography (CT) scans and plain radiographs were also obtained of 20 specimens to evaluate the internal structure of the transverse foramen and pedicle. The results of the measurements showed that differences between male and female specimens were found to be significant for four of seven linear parameters and for one of the two angular parameters. With regard to the sides, differences were found to be significant for two of the seven linear parameters and both of the angular parameters between right and left measurements. The variation of the foramen size between sexes was more significant than that between sides, and a remarkable variation between sides and between sexes was found in the transverse foramen horizontal angle and the pedicle width. The inferior pedicle width was approximately 3 mm less than the superior pedicle width. CT scans revealed that the lateral wall of the pedicle is very thin compared with the medial wall. Considering the greater variation of the C2 foramen orientation, smaller inferior pedicle dimension, and thinner lateral pedicle wall, a screw placement as close as possible to the mediosuperior cortex is recommended to avoid violation of the transverse foramen if transpedicular screw fixation in C2 is intended.

Adult↗

PubMed1997

Epsilon subunit-containing acetylcholine receptors in myotubes belong to the slowly degrading population.

Two types of muscle acetylcholine receptors (AChRs) can be distinguished on the basis of their degradation rates and sensitivities to innervation, muscle activity, and agents elevating intracellular cAMP. The first type (Rs), is present in a stable form (degradation t1/2 = approximately 10 d) at the adult innervated neuromuscular junctions (NMJs). Rs can also exist in a less stable form (called accelerated Rs; t1/2 = approximately 3-5 d) at denervated NMJs and in aneurally cultured myotubes; agents that increase intracellular cAMP reversibly modulate Rs stability. The second type of AChR is a rapidly degrading receptor (Rr) expressed only in embryonic and noninnervated muscles. Rr can be stabilized by ATP and not by cAMP. This study tested the hypothesis that the degradation properties unique to the Rs are attributable to the presence of the epsilon subunit. Immunoprecipitation and Western blot analysis of AChRs extracted from rat muscle cells in tissue culture showed that AChRs recognized by antibodies against the epsilon subunit degraded as a single population with a half-life similar to that of the slow component, Rs, in these cells. In addition, as for Rs receptors in denervated NMJs and cultured muscle cell, the degradation rate of these epsilon-containing AChRs was stabilized by dibutyryl-cAMP. The data indicate that the epsilon-containing AChRs behave like Rs. Thus, the presence of the epsilon subunit is sufficient for selecting an AChR molecule to the Rs pool.

Animals↗