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Biomedical subjects

Z Y Yan

Publications and source records attributed to Z Y Yan.

35 records · Page 2Linked to original sources
PubMed1994

Role of prostaglandins in angiotensin II-induced gastric vasoconstriction.

The purpose of our study was to examine the role of prostaglandins in angiotensin II (ANG II)-induced gastric vasoconstriction. ANG II produced statistically significant, dose-related increases in vascular resistance of a mechanically perfused ex vivo stomach segment of chloralose-anesthetized dogs. We next examined the effect of cyclooxygenase inhibitors on responses to ANG II. Indomethacin (10 mg/kg), which blocked the vasodilator response to intra-arterial arachidonic acid, augmented the maximal increase in perfusion pressure during ANG II infusion. Similar results were found using a different cyclooxygenase inhibitor, meclofenamic acid. In the final experiments we used an enzyme immunoassay to measure 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) plasma concentrations. ANG II produced dose-related increases in gastric venous but not arterial levels of 6-keto-PGF1 alpha, the major metabolite of prostacyclin. Our results are consistent with the hypothesis that release of vasodilatory prostaglandins attenuates the vasoconstrictor response to ANG II in the gastric microcirculation.

6-Ketoprostaglandin F1 alpha↗
PubMed1994

[Quality control of xiaoqinglong mixture].

TLC was used to detect ephedrine, paeoniflorin, glycyrrhizic acid, cinnamic aldehyde and xixin volatile oils in Xiaoqinglong mixture. Paeoniflorin was determined by HPLC. The average recovery is 99.42%, and RSD 0.23%.

Acrolein↗
PubMed1993

Renal ultrasound using parametric imaging techniques to detect changes in microstructure and function.

RATIONALE AND OBJECTIVES: Signal processing techniques have been used to generate parametric ultrasound images that describe properties of tissue microstructure. METHODS: Images of the average scatterer size (D) and integrated backscatter coefficient (IBC) for normal dog kidneys were examined. RESULTS: With parametric ultrasound the authors identified sources of cortical backscatter and observed microanatomical changes corresponding to ischemia. In particular, scatterer size images acquired in vitro and in vivo show it is possible to rapidly assess changes and differences in the average glomerular diameter and the average arteriolar cross-sectional diameter. CONCLUSIONS: A more direct interpretation of sonographic image data is possible with this new type of imaging. Parametric imaging may have a diagnostic role as a means to differentiate among conditions producing increased cortical echogenicity and to detect important structural indicators such as glomerular hypertrophy.

Animals↗
PubMed1992

Platelet activating factor-induced changes in gastric motility and vascular resistance.

Our study evaluated the hypothesis that gastric contractions may contribute to ischemia by increasing vascular resistance. Using an ex vivo segment of the dog's stomach as the experimental model, contractions were induced with platelet activating factor (PAF) and bethanechol, a cholinergic vasodilator. Spontaneous contractions produced slight increases in luminal pressure and corresponding increases in vascular resistance. PAF caused statistically significant, dose-dependent increases in the force of gastric contractions that were highly correlated with phasic changes in vascular resistance. To ensure that the relationship between contractions and vascular resistance was independent of vascular tone, we next examined responses to bethanechol. Bethanechol stimulated contractions that also transiently increased both luminal pressure and vascular resistance. Our results demonstrate that gastric contractions markedly increase vascular resistance and support the hypothesis that hypercontractility may contribute to the development of mucosal ischemia during ulceration.

Animals↗
PubMed1992

Gastric microvascular actions of platelet-activating factor: role of leukocytes.

This study examined the effects of platelet-activating factor (PAF) on the gastric microcirculation. We measured changes in vascular resistance and filtration during intra-arterial infusion of graded doses of PAF and its metabolite, lyso-PAF, to an ex vivo gastric segment of alpha-chloralose-anesthetized dogs. PAF produced dose-related sustained increases in vascular resistance (2-150 nM; n = 6). Filtration and venous hematocrit were also both significantly increased by PAF. In contrast, there were no statistically significant changes in these measurements with lyso-PAF (n = 6). Filtration and venous hematocrit were not significantly changed by norepinephrine at doses that increased perfusion pressure to the same degree as PAF (n = 4). PAF also increased filtration in the absence of changes in perfusion pressure (during maximal vasodilation induced with papaverine). Finally, removal of leukocytes from gastric arterial blood significantly attenuated these responses to PAF. Our results suggest that PAF-induced mucosal ischemia is primarily due to vasoconstriction and may involve edema formation due to increased filtration as well. In addition, these responses to PAF appear to be largely dependent on circulating leukocytes.

Analysis of Variance↗
PubMed1992

Relative potency of endothelin analogues on changes in gastric vascular resistance.

The purpose of this study was to examine the effects of several endothelin analogues on the gastric microcirculation. We measured changes in vascular resistance of an ex vivo gastric segment of chloralose-anesthetized dogs. Changes in luminal pressure were used to quantitate contractile force. Graded doses of endothelin-2 (ET-2), endothelin-3 (ET-3), [Ala3,11]endothelin (Ala-ET), and the COOH-terminal hexapeptide (ET-C) were infused intra-arterially to the stomach. ET-2 and Ala-ET produced dose-related sustained increases in vascular resistance (10(-10) to 10(-8) M), with Ala-ET less potent than ET-2. In contrast, ET-3 was a weak vasoconstrictor while ET-C had no significant effects. There were no detectable changes in filtration with any of these analogues. However, the force of gastric contractions was significantly attenuated by both ET-2 and Ala-ET in a dose-dependent manner. We found that endothelin analogues produced sustained vasoconstriction of the gastric segment with a potency order of ET-2 greater than Ala-ET-3 much greater than ET-C. Our results suggest that endothelin analogues are potent vasoconstrictors but have little effect on filtration across the gastric vasculature.

Animals↗
PubMed1991

A three-dimensional analysis of plasma skimming at microvascular bifurcations.

This paper analyzes an important underlying mechanism for the discharge hematocrit reduction observed in microvessels, which refers to the plasma skimming from the cell-free layer near the parent tube wall in the presence of a side branch. The three-dimensional theory recently developed by the authors (Yan et al., 1991, J. Fluid Mech., in press) for treating the simple shear flow past a side branch tube in a plane wall with suction is first summarized and then extended to treat T bifurcations from parent vessels with an upstream Poiseuille flow. For unequal vessel bifurcations, a fundamental new dimensionless group, Q = 1/8(qb/qp)(Rp/Rb)3, is derived whose value determines the shape of the upstream capture tube of the plasma phase, when the partitioning qb/qp of the flow into the side branch and the ratio Rp/Rb of the radii of the parent and side branch vessels are varied. Closed form expressions are then presented for the three-dimensional fluid capture tube shape upstream of the bifurcation which are valid when Q greater than 1 or Q less than 0.2. Based on this theory and its modification for an upstream Poiseuille velocity profile, the separating surface shape, the critical minimum fractional flux for incipient cell capture, and the discharge hematocrit defect and its dependence on the flow rate are predicted. It is shown, furthermore, that for flows typical of the microcirculation, a single dimensionless number, P = 3 pi Q(Rb/gamma 2), with gamma being the cell-free layer thickness, can be defined whose value determines the discharge hematocrit defect that arises from plasma skimming. The minimum critical flow rate for any red cells to enter the side branch is then given by the criterion P = 1. Although this theory does not account for the cell screening effect arising from the hydrodynamic interaction between the cells and the tube walls, it leads to predictions which exhibit the same trends as the experimental observations and is able to explain the results of several seemingly contradictory microvascular experiments that have puzzled investigators in recent years.

Hematocrit↗
PubMed1990

[Effect of radix Salviae miltiorrhizae on gastric mucosal barrier].

The authors observed the effects of Radix Salviae Miltiorrhizae (RSM, Dan-shen) on gastric mucosa of twelve dogs with ex vivo gastric chambers. It was demonstrated that in physiological condition RSM increases gastric mucosal blood flow and potential difference, and decreased hydrogen ion back-diffusion. In this way, RSM kept the integrity of mucosal barrier, and improved its defence function. In pathological condition caused by aspirin, however, RSM could only delay the advance of mucosal lesions. According to this observation, RSM may be used as a prophylactic medicine combined with cimetidine in critical ill patients.

Animals↗
PubMed1987

Endoscopic measurements of canine colonic mucosal blood flow using hydrogen gas clearance.

We have examined the feasibility of hydrogen (H2) clearance for endoscopic measurements of colonic mucosal blood flow in anesthetized dogs. In 6 animals, measurements of H2 clearance did not differ significantly in different regions of the sigmoid colon and they were highly reproducible (p less than 0.001) on different days. In a total of 12 dogs, measurements of H2 clearance correlated closely with those obtained using radioactive microspheres under resting conditions and, in 4 dogs, during infusion of vasopressin (slope = 0.94, p less than 0.001). In 8 dogs, ligation of the major arteries supplying the sigmoid colon resulted in an acute 60% decrease in sigmoid mucosal blood flow (p less than 0.001); however, in 5 animals that survived the procedure, mucosal blood flow returned nearly to control levels as early as 3 days after operation. Endoscopic H2 clearance thus appears to be feasible for measuring mucosal blood flow in the colon. Serial measurements of H2 clearance may prove useful in characterizing the role of mucosal blood flow in the pathogenesis of various forms of human colonic disease.

Animals↗
PubMed1986

Regional gastric mucosal blood flow after parietal cell vagotomy in dogs.

In this study we used the recently validated H2 clearance method to perform endoscopic measurements of gastric mucosal blood flow (MBF) in anesthetized dogs before and after parietal cell vagotomy (PCV). Under resting conditions, MBF in the gastric corpus before PCV was 72 +/- 5 ml/min/100 gm. This was not altered significantly at 4, 8, or 16 weeks after PCV, and there were not significant long-term changes in MBF on the greater or lesser curvatures of the corpus individually. Before PCV infusion of pentagastrin (8 micrograms/kg/hr) elicited increases in corpus MBF to 104 +/- 4 ml/min/100 gm, accompanied by increases in gastric acid output from resting levels of 2.1 +/- 0.9 to 38.6 +/- 2.4 mEq/hr (p less than 0.001). PCV significantly reduced pentagastrin-stimulated acid secretion by 50%, and secretory inhibition was accompanied by significant reductions in pentagastrin-stimulated MBF in the corpus. Pentagastrin did not alter antral MBFs before or after PCV. In summary PCV does not elicit significant long-term changes in resting MBF in different regions of the gastric corpus, and PCV significantly diminishes increases in acid output and corpus MBF that are normally stimulated by pentagastrin. These observations suggest that alterations in gastric MBF after PCV may be attributable to alterations in acid secretion.

Animals↗
PubMed1985

Endoscopic measurements of gastric mucosal blood flow in dogs.

The feasibility and validity of endoscopic measurements of gastric mucosal blood flow (GMBF) using 3% H2 gas clearance were investigated in the intact stomach of anesthetized dogs. Platinum electrodes were lengthened and modified to permit passage through the instrument channel of a standard gastroscope. In five anesthetized dogs, antral mucosal blood flow (103.2 +/- 5.3 ml/min/100 g tissue) was significantly higher (P less than 0.05) than that in the corpus (66.9 +/- 7.1 ml/min/100 g tissue). Histamine stimulation selectively increased flow in the corpus to 134.5 +/- 7.5 ml/min/100 g tissue. Comparison of endoscopic GMBF measurements in these five dogs on 2 different days revealed a close correlation (r = 0.87, P less than 0.001). Endoscopic H2 clearance measurements obtained in five awake dogs were not significantly different from those obtained during pentobarbitol anesthesia. In 12 dogs, GMBF determined by endoscopic H2 gas clearance showed a good agreement (r = 0.91, P less than 0.001) with that measured by radioactive microspheres. These two methods also demonstrated comparable changes in GMBF induced by intravenous infusion of histamine and vasopressin. It was concluded that 3% H2 gas clearance can be used to accurately and reproducibly measure GMBF through the endoscope, a unique advantage of this method for potential clinical use.

Anesthesia↗
PubMed1985

Comparison of gastric mucosal blood flow as measured by H2 gas clearance and microspheres during secretory stimulation and inhibition.

H2 clearance is a recently described method of measuring gastric mucosal blood flow that has great potential for clinical use. However, the effects of luminal pH and of secretory activity of the gastric mucosa on the accuracy of H2 clearance measurements have not been systematically examined. We therefore tested the validity of H2 clearance measurements at different pHs in both in vitro and in vivo systems. In addition, we compared measurements by H2 clearance and radioactive microspheres during stimulation and suppression of acid secretion. In vitro, H2 washout was relatively constant over a range of pHs from 2.0 to 8.0. In chambered segments of canine fundus in vivo, H2 clearance was not significantly affected by pH of the luminal solutions either in the resting state or at lower blood flows induced during infusion of vasopressin. Finally, there was a close correlation (r = 0.85; p less than 0.001) between H2 clearance and microsphere measurements under resting conditions, during intravenous histamine stimulation, and after infusion of cimetidine to suppress acid secretion. In summary, H2 clearance reliably and accurately measures gastric mucosal blood flow at different luminal pHs and under conditions that stimulate or suppress acid secretion.

Animals↗
PubMed1981

The "bolus flow" solution of the plasma between the red blood cells flowing through a capillary.

In this paper, we have derived an approximate "Bolus Flow" solution between two adjacent red blood cells (RBC) in a capillary, using the Galerkin method and numerical smoothing technique, and then examined in detail the effects of the ratio lambda of the diameter of the RBC to that of the capillary and those of the leakback Q in the thin lubrication layer on the Bolus Flow. Because of the simplicity of the method employed here, only a small amount of numerical calculation is involved. Furthermore, we have rectified somewhat unreasonable formulation of the boundary conditions presented previously so as to match the Bolus Flow with the flow in the lubrication layer. The results are reasonably in agreement with other theories, providing correct boundary conditions for the determination of the deformation of RBC.

Capillaries↗
PubMedDate not supplied

Molecular dynamics simulations and the conformational mobility of blood group oligosaccharides.

Molecular dynamics simulations were carried out without explicit consideration of solvent to explore the conformational mobility of blood group A and H oligosaccharides. The potential energy force field of Rasmussen and co-workers was used with the CHARMM program on a number of disaccharide and trisaccharide models composed of fucose, galactose, glucose, N-acetyl glucosamine, and N-acetyl galactosamine chosen to represent various fragments of blood group oligosaccharides. In agreement with results of earlier studies, stable chair conformations were found for each pyranoside from which no transitions were detected in simulations as long as 800 ps. Exocyclic dihedral angles, including that of C5-C6, generally show numerous transitions on a time scale of approximately 5-30 ps. The dihedral angles of some but not all glycosidic linkages of blood group oligosaccharides show transitions on the time scale of 30-50 ps, implying that the extent of internal motion in blood group oligosaccharides depends strongly on linkage stereochemistry. For certain blood group A and H oligosaccharides that show limited internal motion in these simulations, we argue that the calculations are consistent with our previous analysis of 1H nuclear Overhauser enhancement (NOE) data that imply single conformations over a wide range of temperature and solvent conditions. While the trajectories are consistent with 13C T1 values that have been interpreted as indicating rigid conformations, measurements of 13C-NOE and T1 as a function of magnetic field strength are proposed as an improved method for experimental detection of the internal motion that is suggested for certain oligosaccharides in these simulations. The results of these simulations differ substantially from those of peptides of a similar molecular weight in that the oligosaccharides show much less internal motion.

Blood Group Antigens↗
PubMedDate not supplied

A study of effects of WGA and ConA on RBC membrane receptors using a new ektacytometric method.

With a new ektacytometry, we studied the relation between the microstructure of red blood cell (RBC) membrane and the rheological properties of RBCs in a shear flow field of low viscosity. The main contributions of this paper are as follows: 1. The hemorheological meanings of the orientation index (DI)or and the small deformation index (DI)d were explored. (DI)or is an overall rheological index depending on the deformability and morphology of RBCs. The better the physiological shape of RBCs is maintained, the greater the (DI)or is. (DI)d can be used to describe the lipid fluidity of RBC membrane. Such an explanation for the meaning of (DI)d has been forcefully supported by our experiments using electron spin resonance (ESR) and fluorescence polarization. 2. The influence of wheat germ agglutinin (WGA) of different concentrations on the lipid fluidity of membrane is different from that of concanavalin A (ConA). The lipid fluidity of membrane changes with WGA concentration treating RBCs and there is a maximum value for the membrane fluidity at a specific concentration of WGA. However, the deformability of membrane described by the integrate deformation index (IDI) monotonically decreased with the increase in WGA concentration treating RBCs. 3. It is concluded that the increase in the lipid fluidity of red cell membrane is not necessarily associated with the improvement of RBC deformability.

Animals↗