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Biomedical subjects

F Sun

Publications and source records attributed to F Sun.

At least 145 records · Page 8Linked to original sources
PubMed1991

[The structure and absolute configuration of isorupestonic acid from Artemisia rupestris L].

A new sesquiterpene compound named isorupestonic acid was isolated from Artemisia rupestris and its absolute stereostructure was elucidated as 3B by spectral and X-ray crystallographic methods. Interestingly, the isorupestonic acid is based upon an unusual 6, 7 membered ring skeleton differing from the 5, 7 membered ring rupestonic acid although both have the same absolute configuration at C-1. The biogenesis of isorupestonic acid most likely involves breaking the C4-C5 bond of rupestonic skeleton and forming the C5-C14 bond. The absolute configuration of rupestonic acid was also determined as 4C by X-ray analysis and CD data.

Azulenes↗
PubMed1989

Frequency analysis of accommodation: single sinusoids.

We present an experimental frequency analysis of a neurological control system, the accommodation system, using single sinusoids. Also, by means of continual experimental calibration full coverage of one subject's dynamic range, we demonstrate an AC nonlinearity saturation, which probably lies in the motor-response portion of the system; in contrast to the switching-mode nonlinearity, which probably lies in the sensory-processing portion. We offer our findings as a basis for further models. In addition, our results can be compared with studies using multiple sinusoids and transients to document how the different aspects of the accommodation system are realized given their different input conditions.

Accommodation, Ocular↗
PubMed1989

[Effects of l-tetrahydropalmatine on isolated rabbit arterial strips].

The effects of l-tetrahydropalmatine (THP) on isolated rabbit aortic, renal and superior mesenteric arterial strips were studied in comparison with verapamil (Ver). THP and Ver shifted the KCl, CaCl2, norepinephrine (NE) and 15-methyl prostaglandin F2 alpha dose-response curves to the right in a non-parallel fashion, and decreased the maximal response, showing noncompetitive antagonism. THP was less potent in dilating arterial strips than Ver. THP and Ver obviously inhibited the intracellular Ca2+-dependent component of NE-induced contraction of the aorta, but only slightly decreased the extracellular Ca2+-dependent component when the concentration of THP or Ver was very high (THP 0.1 mmol/L, Ver 10 mumol/L). The results suggest that THP, similar to Ver, mainly inhibits potential-operated calcium channels. THP and Ver were more potent in dilating renal and superior mesenteric arterial strips than aortic strips. The results indicate that the vasodilation effect of THP is similar to that of Ver and that THP probably has a calcium antagonistic effect.

Alkaloids↗
PubMed1988

Human pupillary response to ramp changes in light intensity.

The dynamic behavior of the pupillary system was explored using different velocity ramp changes in light intensity. Ramp stimuli ranged in velocity from 0.02 to 8.00 log units/s and the responses were recorded from three subjects. For ramp velocity below 0.066 log units/s, the responses were mainly ramps. Above 1.0 log units/s ramp velocity, the responses were mostly steps. In the stimulus velocity range of 0.066 to 1.0 log units/s, the primary responses were step-ramps. The amplitudes of the initial step movement in step-ramp responses were found to be proportional to stimulus ramp velocity. Thus the pupillary system appears either to convert the total energy in a time interval or the rate of change of intensity of the ramp stimulus into a step signal for driving the pupillary plant output.

Humans↗
PubMed1986

Dynamics of accommodation: measurements for clinical application.

Accommodation dynamics have not been used in clinical diagnosis as have eye movement and pupillary dynamics; the difficulty of clinical observation is matched by limitations in measurement methods. An instrument suitable for clinical use is described that allows measurement of step response latencies and especially time constants. With computer analysis, phase plane trajectories, and noise spectra can be quickly obtained also. The utility of these dynamical parameters for clinical diagnosis is illustrated by a study of changes of time constants with age in prepresbyopia.

Accommodation, Ocular↗
PubMed1984

Prostaglandin formation in the isolated human ductus arteriosus, aorta, pulmonary and umbilical arteries.

The prostaglandins comprise a large family of substances that includes primary prostaglandins, prostacyclin and thromboxane, all of which exhibit some vascular activity. The activity of each prostaglandin may be species - and organ - dependent, and the type of prostaglandin produced in a tissue is often dependent on the presence of terminal enzyme systems in that tissue. The prostaglandin endoperoxide PGH2 serves as a common intermediate for the enzymatic production of prostaglandins, thromboxanes and prostacyclin. We have obtained information on the biosynthesis of these compounds by the human ductus arteriosus, aorta, pulmonary and umbilical arteries in vitro. Vascular tissue samples were obtained from two fetuses of 16 to 18 weeks of gestation, two newborns of 26 and 35 weeks of gestation and in nine term infants. The vascular tissue samples were incubated with [1-14C]-arachidonic acid and/or [1-14C]-prostaglandin endoperoxide (PGH2). The study demonstrates the formation of prostaglandins and prostacyclins from all the vascular tissues and the formation of thromboxanes from the umbilical artery. The study implies that the above vessels contain "prostaglandin synthetase" enzymes as early as 16 weeks of gestation.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

A systems model for the pupil size effect. I. Transient data.

The human pupillary control system is a paradigm for linearized biological control systems. It also exhibits a series of interesting nonlinear behaviors, particularly asymmetry, "pupillary escape," and "pupillary capture." We present a nonlinear model in which a signal dependent upon pupil size is fed back internally to cause a change in system parameters related to gains and rates of light adaptation. The model was simulated on a digital computer, a variety of experimental data was well matched, and improvements over previous pupil models demonstrated. A candidate physiological mechanism for adaptive components of the model might have the form of an inverse "Henneman coded" neuronal pool.

Animals↗
PubMed1983

Dynamic pupillary response controlled by the pupil size effect.

Pupillary escape has been described as an initial contraction followed by a slow redilatation, occurring in response to a step stimulus of low-intensity light. When the initial pupil size is small, the response to the same step stimulus is pupillary capture, a steady and sustained contraction. In this experiment a comparison was made between three modes of controlling pupil size and thereby of regulating the pupillary response: contralateral light background level, ipsilateral light background level, and accommodative level with which there is no change in retinal adaptation. All three level setting modes showed similar results in illustrating the pupil size effect. In addition, an inhibitory effect was found with both ipsilateral and contralateral light backgrounds that is independent of Weber's Law in the contralateral case. Our results lead to the formulation of a binocular model, featuring an internal parameter control whereby a signal dependent on the static pupil size regulates the gains of the parallel phasic and tonic pathways, the former responsive to transient changes of light, and the latter to background levels of light and accommodative levels. Our findings also raise interesting questions concerning the loci of these complex interactions in the simple neuroanatomy of the pupillary pathways.

Humans↗
PubMed1983

Pupillary escape intensified by large pupillary size.

Pupil responses to light are greatly influenced by initial pupil size. Small pupils, operating under photopic conditions, show tonic responses to step increases of light and high gains; thus the pupil is a good regulator of light. Large pupils, operating under mesopic or scotopic conditions show phasic responses, "pupillary escape", and smaller gains; the pupil only transiently influences retinal flux. By using accommodation level to set the size of the pupil, the mechanism of the "pupil size effect" is shown to be dependent on retinal light level only so far as retinal activity sets pupil size.

Accommodation, Ocular↗
PubMed1983

Human airway monohydroxyeicosatetraenoic acid generation and mucus release.

The effects of 5-, 8-, 9-, 11-, 12-, and 15-monohydroxyeicosatetraenoic acid (HETE) (0.1-100 nM) on mucous glycoprotein release from cultured human airways were determined. Each of the HETE was an active secretagogue of mucus at concentrations greater than 1-10 nM with 12- and 15-HETE, the most active. Both 5- and 9-hydroperoxyeicosatetraenoic acid (HPETE) were also active as secretagogues at 100 nM, although of somewhat lower potency. As cultured airways were capable of responding to HETE with mucous glycoprotein release, it was of interest to identify and quantitate airway HETE formation. Accordingly, airways were incubated with tracer quantities of [14C]arachidonate for 16-48 h, and the spontaneous formation of 5-, 12- and 11- and/or 15-HETE was measured by high-pressure liquid chromatography. Indeed, sizeable quantities of 11- and/or 15- greater than 5- greater than 12-HETE were generated. This HETE generation was increased by the addition of 25 micrograms/ml of arachidonate and was reduced somewhat after 18-21 d in continuous tissue culture. Reversed anaphylaxis of human airways using anti-human IgE markedly increased the HETE formation, resulting in the production of micromolar concentrations of 5- and 11- and/or 15-HETE. Thus, human airways not only are capable of responding to the presence of HETE with mucous glycoprotein release, but also generate (both spontaneously and in response to anaphylaxis) at least three species of HETE, and do so in quantities capable of acting as mucus secretagogues.

Anaphylaxis↗
PubMed1982

Lipoxygenase activity in rat kidney glomeruli, glomerular epithelial cells, and cortical tubules.

We examined the possibility that renal glomerular and cortical tubular tissue has lipoxygenase activity in addition to the well established cyclo-oxygenase pathway of arachidonic acid metabolism. Homogenized rat kidney glomeruli, in the presence of meclofenamate (33 microM) and divalent cation ionophore A23187 (3 microM), metabolized octatritiated arachidonic acid to 12-hydroxyeicosatetraenoic acid and lesser amounts of 80 and/or 9-hydroxyeicosatetraenoic acid. These products were identified by thin layer chromatography, high performance liquid chromatography, and gas chromatography-mass spectroscopy. In order to rule out the synthesis of hydroxylated fatty acids by platelets and leukocytes entrapped in the glomeruli, we studied lipoxygenase products in glomerular epithelial cells after 9 days in cell culture. Homogenized glomerular epithelial cells converted octatritiated arachidonic acid to 12-hydroxyeicosatetraenoic acid solely. The lipoxygenase activity in cortical tubules was substantially less than in glomeruli and only 12-hydroxyeicosatetraenoic acid was synthesized. The production of hydroxyeicosatetraenoic acid by lipoxygenase inhibitors, nordihydroguaiaretic acid, 5,-homogenized glomeruli, glomerular epithelial cells, and cortical tubules was inhibited by three 8,11,14-eicosatetraynoic acid, and 1-phenyl-3-pyrazolidone. These data demonstrate that there is lipoxygenase activity in rat kidney glomeruli, glomerular epithelial cells and to a lesser extent cortical tubules, and may imply a role of the lipoxygenase products in the regulation of normal glomerular function and inflammatory disease of the kidney.

Animals↗