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Biomedical subjects

T Yang

Publications and source records attributed to T Yang.

At least 289 records · Page 16Linked to original sources
PubMed1985

Sustained increases in heart rate induced by timed repetition of vagal stimulation in dogs.

We determined the influence of the "free-running cycle length" (tau FR) on chronotropic responses to one burst of right vagal stimuli per cardiac cycle in anesthetized dogs (tau FR, cycle length that prevailed in absence of right vagal stimulation). We varied tau FR by the following methods: 1) tonic left vagal stimulation in pentobarbital-anesthetized animals; 2) tonic left vagal stimulation plus sinus node cooling in pentobarbital-anesthetized animals; and 3) anesthesia with fentanyl, droperidol, and pentobarbital. When tau FR was less than a critical value [1,019 +/- 60 (SE) ms], right vagal stimulus bursts always had the expected negative chronotropic effect. However, when the tau FR was increased beyond critical value, right vagal stimulus bursts delivered within a specific portion of cardiac cycle actually had a positive chronotropic effect; i.e., cycle lengths diminished to values below tau FR. As tau FR was progressively increased beyond critical value, positive chronotropic response became greater and could be evoked by stimulus bursts delivered within a greater fraction of cardiac cycle. The right vagal stimuli that elicited the maximum positive chronotropic effect were those that were given approximately 235 ms prior to beginning of next atrial depolarization. This critical time probably occurs near the end of the period of phase 4 depolarization of sinus node automatic cells.

Acetylcholine↗
PubMed1985

Parasitism by Placobdella multilineata (Hirudinoidea: Glossiphoniidae) and its first record from Asia.

Placobdella multilineata (Hirudinoidea: Glossiphoniidae) a temporary, bloodsucking ectoparasite, was previously recorded only from the southern United States, with turtles and the American alligator (Alligator mississipiensis) as hosts. This is the first record of P. multilineata from Asia (Beijing, People's Republic of China) and also a new host record for the estuarine crocodile (Crocodylus porosus). The introduction of P. multilineata to Asia occurred as a result of the transfer of American alligators. All 34 specimens of P. multilineata collected in Beijing were non-clitellate but blood in their guts indicated that feeding had occurred on the host.

Alligators and Crocodiles↗
PubMed1984

Sex chromosome positions in human interphase nuclei as studied by in situ hybridization with chromosome specific DNA probes.

Two cloned repetitive DNA probes, pXBR and CY1, which bind preferentially to specific regions of the human X and Y chromosome, respectively, were used to study the distribution of the sex chromosomes in human lymphocyte nuclei by in situ hybridization experiments. Our data indicate a large variability of the distances between the sex chromosomes in male and female interphase nuclei. However, the mean distance observed between the X and Y chromosome was significantly smaller than the mean distance observed between the two X-chromosomes. The distribution of distances determined experimentally is compared with three model distributions of distances, and the question of a non-random distribution of sex chromosomes is discussed. Mathematical details of these model distributions are provided in an Appendix to this paper. In the case of a human translocation chromosome (Xqter----Xp22.2::Yq11----Yqter) contained in the Chinese hamster X human hybrid cell line 445 X 393, the binding sites of pXBR and CY1 were found close to each other in most interphase nuclei. These data demonstrate the potential use of chromosome-specific repetitive DNA probes to study the problem of interphase chromosome topography.

Cell Nucleus↗
PubMed1984

Synchronization of automatic cells in S-A node during vagal stimulation in dogs.

In anesthetized, open-chest dogs, one burst of stimuli was delivered to the left or right vagus nerve each cardiac cycle. The timing of the stimulus bursts relative to the cardiac cycle was varied by a constant, small amount on successive cardiac cycles, until the entire cardiac cycle was scanned. The level of vagal activity was changed by varying the number of stimulus pulses in each burst; two levels of activity were used in each experiment. For a given level of vagal activity, the mean cardiac cycle length and the amplitude of the phase-response curve were significantly greater during right than during left vagal stimulation. These response characteristics increased as the level of vagal activity was augmented. The minimum-to-maximum phase differences of the phase-response curve were less during right than during left vagal stimulation and when the level of vagal activity was increased. The disparities between the minimum-to-maximum phase differences for the right and left vagi are probably ascribable to the associated differences in the overall magnitudes of the chronotropic responses, rather than to any fundamental difference in the innervation of the effector cells by nerve fibers originating from the right and left sides.

Action Potentials↗
PubMed1984

The phase-dependency of the cardiac chronotropic responses to vagal stimulation as a factor in sympathetic-vagal interactions.

We determined the effects of the timing of repetitive bursts of vagal stimulation on the positive chronotropic responses of the heart to trains of cardiac sympathetic nerve stimulation in open-chest anesthetized dogs. Trains of sympathetic stimulation alone, at frequencies of 2 and 4 Hz, decreased the cardiac cycle length by 176 +/- 19 msec (mean +/- SE) and 190 +/- 22 msec, respectively. When bursts of vagal stimuli were given once each cardiac cycle and they were placed at their least effective time in the cycle, sympathetic stimulation at frequencies of 2 and 4 Hz decreased cardiac cycle length by only 107 +/- 8 and 120 +/- 8 msec, respectively. However, when the bursts of vagal stimuli were delivered at their most effective time in each cycle, the same levels of sympathetic stimulation elicited much larger reductions in cardiac cycle length (285 +/- 32 and 330 +/- 32 msec, respectively). Therefore, the effects of sympathetic stimulation were significantly attenuated by the vagal stimuli when the vagal bursts were relatively ineffective. Conversely, the chronotropic effects of the sympathetic stimulation were exaggerated substantially when the vagal stimulus bursts were initially positioned at their most effective time in the cardiac cycle. This latter response is contrary to the characteristic "accentuated antagonism," wherein the effect of any given level of sympathetic stimulation is diminished as the level of vagal activity is increased. This vagally mediated enhancement of the positive chronotropic response to sympathetic stimulation occurs because the phase dependency of the response of the automatic cells to the bursts of vagal stimulation is altered by the increased sympathetic activity.

Animals↗
PubMed1983

Prospective immunological assessment of arthritis induced by rubella vaccine.

A prospective study was carried out to correlate the development of joint symptoms after rubella immunization with pre- and post-immunization rubella-specific immunological responses. Arthralgia or arthritis or both occurred in 10 of 37 adult female volunteers at a mean time of 17.0 days after immunization with the RA 27/3 rubella vaccine. All individuals studied before immunization were seronegative for rubella by either the hemagglutination inhibition or the single radial hemolysis technique. In contrast, rubella enzyme-linked immunosorbent assay or lymphoproliferative responses or both were positive in 27 of 37 (73%) individuals tested before receiving the vaccine. Rubella enzyme-linked immuno-sorbent assays carried out before immunization were positive at high levels (mean E = 0.536) in four individuals who developed recurrent episodes of arthritis after administration of the vaccine while remaining at low levels preimmunization in subjects who developed transient arthralgia (E = 0.238) or no joint manifestations at all (E = 0.288). These data provide preliminary evidence suggesting that rubella vaccine-associated arthritis may occur as a consequence of secondary, rather than primary, infection with rubella virus and that the presence of circulating, nonneutralizing rubella antibody may enhance the development or severity (or both) of the associated postinfection joint manifestations. Assessment of rubella hemagglutination inhibition, hemagglutination inhibition (immunoglobulin M), and enzyme-linked immunosorbent assay serological responses at 6 weeks and 6 months post-immunization revealed no significant differences between patients who developed and those who did not develop joint manifestations. Rubella lymphoproliferative responses were elevated at 6 weeks post-immunization in the group developing arthralgia or arthritis or both, with no difference between the groups observed at 6 months post-immunization.

Adult↗
PubMed1982

Tetramethyl-p-phenylenediamine oxidase of Pseudomonas aeruginosa.

An oxidase complex has been solubilized and partially purified from the membrane particle of Pseudomonas aeruginosa grown under limited oxygen condition. The oxidase consists of two major cytochrome components, cytochrome c554 and cytochrome o (b561), with a molar ratio of about 9:1 in terms of c-heme to protoheme content. Ninety percent of the cytochrome c+o complex, corresponding to all of the cytochrome c554, is reducible by reduced N,N,N',N'-tetramethyl-p-phenylenediamine. This partially purified oxidase exhibited a maximal specific activity about 5 mumol O2 uptake x min-1 x mg protein-1, with a Km (of reduced N,N,N',N'-tetramethyl-p-phenylenediamine) = 7.2 x 10(-4) M at 30 degrees C. The oxidase is sensitive to KCN, NaN3 and NaNO2. Oxidation-reduction potentiometric titration shows that cytochrome c554 has a midpoint potential of 289 mV and cytochrome o of + 25 mV at pH 7.2 in the partially purified oxidase preparation. The purity of the preparation has been estimated to be about 85--90% by gel electrophoresis.

Cell Membrane↗
PubMed1981

Oxidation-reduction titration of cytochrome components in the electron transport chaim of Azotobacter vinelandii.

The multiple cytochrome components in the electron transport particle of Azotobacter vinelandii were resolved and their oxidation-reduction midpoint potentials were determined by a simultaneous potentiometric and absorption measurements under anaerobic condition with or without CO. The midpoints of the individual cytochrome component corresponding to the membrane-bound types were also determined in the solubilized fractions prepared by a differential detergent solubilization of the membrane particles of A vinelandii. Two cytochromes of b type, one with an absorption maximum measured at 559 nm and another at 561 nm in the membrane particle, were resolved and their Em, 7.4 values determined to be - 30 mV and +122mV, respectively. Cytochrome b 559 reacted in both membrane-bound and solubilized forms, however, cytochrome b561 was inert to CO treatment. Only one cytochrome of c type (c4) measured at 575-551 nm was resolved, its midpoint potential at pH 7.4 was +322mV in the membrane-bound form and +278mV in the solubilized form. This c-type cytochrome had no CO reactivity. Cytochrome d, a CO-reactive component, had a midpoint of +270mV in the membrane fraction. The midpoint of cytochrome a1 in its membrane-bound form could not be measured accurately because of its low concentration. However, in the solubilized preparations, cytochrome a1 apparently had a red shift with an absorption maximum at 613 nm, with an estimated Em, 7.4 of - 45 mV, while cytochrome d was no longer detected, possibly because of denaturation.

Azotobacter↗
PubMed1979

The oxidation-reduction potentials of cytochrome o + c4 and cytochrome o purified from Azotobacter vinelandii.

Oxidation-reduction titrations of Azotobacter vinelandii cytochrome o + c4 and cytochrome o were performed with simultaneous potential and absorbance measurements under anaerobic conditions. Cytochrome c4 has a midpoint potential (Em, 7.4) of 260mV and purified cytochrome o has an Em, 7.4 of -18mV. Little change in the midpoint potential of cytochrome o was observed when titrated in the pH range 6.2--9.8.

Azotobacter↗
PubMed1977

Biological effects of high-LET particles on corn-seed embryos in the Apollo-Soyuz Test Project--Biostack III experiment.

High-LET particle hits in embryos of Zea mays corn seeds, flown as part of Biostack III in the Apollo-Soyuz Test Project, were determined via plastic nuclear track detectors. Based on etched particle-track measurements, 41 embryos were hit in seed layer 1 which contained 80 seeds, and 49 hits occurred in layer 2 which contained 79 seeds. The mean LET value and range of atomic numbers of recorded hits is, respectively, 210 +/- 57 keV micrometers -1 and 9 < or approximately Z < or approximately 26. Detailed analysis of one particular seed showing marked growth anomalies revealed two hits in the central region of the embryo. These two hits had LET values in the region of 100-150 keV micrometers-1, and Z > or approximately 20.

Collodion↗
PubMedDate not supplied

Modulation of coronary vascular resistance in female rabbits by estrogen and progesterone.

OBJECTIVE: To study the roles of estradiol and various progestins on the regulation of coronary flow in female rabbits. METHODS: Ovariectomized adult female rabbits were treated with estradiol, with progesterone (or one of the following synthetic progestins: megace, norethindrone, or medroxyprogesterone acetate), or with both an estradiol and a progestin. Hearts were isolated and perfused at constant pressure by a modified Langendorff technique. Changes in coronary flow were determined at baseline and in response to direct infusion into the coronary circulation of NG-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide (NO) synthase. RESULTS: Coronary flow rates were 40-50% greater in hearts of animals treated with estradiol than in control hearts of animals not treated with the hormone. Treatment of the animals with progestin alone had little effect on coronary flow. However, when administered with estradiol, it abrogated the estradiol-related increase in coronary flow. The increments in coronary flow evoked by estradiol were virtually abolished by L-NNA, an inhibitor of NO synthase. In hearts of animals treated with estradiol plus progesterone, L-NNA had no additional inhibitory effect on coronary flow to that of progesterone. CONCLUSION: Estradiol decreases coronary vascular resistance (CVR) and hence increases coronary flow. Progestins attenuate this effect of estradiol.

Animals↗
PubMedDate not supplied

Beneficial effects of estrogen on cardiac stunning in female rabbits.

OBJECTIVE: To determine the effect of estrogen treatment on the contractile, relaxation, and chronotropic responses of hearts of female rabbits to cessation of perfusion. METHODS: Adult female rabbits were treated either with estradiol or with the vehicle (control). The hearts were then isolated and perfused at constant pressure by the Langendorff technique. A saline-filled balloon connected to a pressure transducer was inserted in the left ventricle in order to assess the mechanical function of the isolated heart. Cardiac stunning was induced by halting the perfusion of the coronary vasculature for four successive periods of 1, 3, 5, and 5 minutes, followed by reperfusion between nonperfusion periods. Changes in cardiac function induced by the cessation of perfusion were assessed by monitoring the changes in heart rate and in left ventricular pressure ([dP/dt]max as an index of ventricular contractility and [dP/dt]min as an index of ventricular relaxation). Changes in coronary flow were determined at baseline and following reperfusion. RESULTS: Halting coronary perfusion decreased (dP/dt)max, and (dP/dt)min and slowed left ventricular contractions both in control and in estrogen-treated hearts. The depressant effects of flow cessation on left ventricular (dP/dt)max and (dP/dt)min were smaller in estrogen-treated hearts than in control hearts. Treatment with estrogen had no effect on the changes on the heart rate in responses to cessation of flow and to reperfusion. Treatment with estrogen increased coronary flow by 40%. Coronary reperfusion increased coronary flow transiently, but the effects did not differ significantly between control and estrogen-treated hearts. CONCLUSION: Short-term treatment of adult female rabbits with doses of estrogen that are physiologic for the rabbit exerts a protective effect on cardiac contractility from repetitive periods without perfusion.

Animals↗