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Biomedical subjects

Y D Chen

Publications and source records attributed to Y D Chen.

16 recordsLinked to original sources
PubMed1992

[Studies on the establishment of malarial animal model of short-term relapse. I. Asynchronous growth of exoerythrocytic schizonts of Plasmodium cynomolgi].

A monkey was infected with sporozoites of Plasmodium cynomolgi from Vietnam. Parasitemia was detected on the 8th day with a starting density of 17/100 white blood cells. 22 hours after that time, many EE schizonts appeared with an average density of 3.74 +/- 0.66 per mm3 hepatic tissue in liver biopsy specimens from the monkey. Most of the EE schizonts were immature and grew at an uneven rate, having an average diameter of 34.22 +/- 7.28 microns but some of them even remained 15.75 +/- 2.47 microns in diameter similar to the EE schizonts on the 6th day. The results showed that the EE schizonts of Plasmodium cynomologi were asynchronous in growth. The authors suggest that the release of merozoites from liver might be a successive process for many times, and not to be completed at a time.

Animals↗
PubMed1979

Characterization of a model of dietary-induced hypertriglyceridemia in young, nonobese rats.

Healthy, nonobese, young rats developed hypertriglyceridemia (mean triglyceride levels of 250 mg/dl) following consumption of a sucrose-lard diet. The hypertriglyceridemia was apparent three days after start of the diet and persisted throughout the 4-week experimental period. Body weight, liver weight, and serum glucose levels were similar in animals eating either the sucrose-lard diet or standard rat chow. On the other hand, serum free fatty acid levels were slightly increased and serum insulin levels were substantially increased in animals eating the sucrose-lard diet. Determination of very low density lipoprotein turnover revealed that total triglyceride secretion in rats eating the sucrose-lard diet was significantly (P < 0.01) increased over that of rats eating standard chow. Direct measurement of hepatic and intestinal very low density lipoprotein secretion indicated that the observed rise in total triglyceride secretion was secondary to increased secretion of very low density lipoproteins by the liver. Finally, lipoprotein lipase activity of adipose tissue from rats eating the sucrose-lard diet was equal to, or greater than (depending upon sampling time), the activity of the enzyme from adipose tissue of rats eating the control diet. These data indicate that young, nonobese, rats develop hypertriglyceridemia when they ingest a sucrose-lard diet, and that the rise in plasma triglyceride levels results from an increase in hepatic very low density lipoprotein secretion. The dietary-induced hypertriglyceridemia is associated with elevated serum insulin levels, and, as such, may provide a useful animal model to use in studies aimed at defining the pathogenesis of endogenous hypertriglyceridemia in man.-Reaven, G. M., T. R. Risser, Y-D. I. Chen, and E. P. Reaven. Characterization of a model of dietary-induced hypertriglyceridemia in young, nonobese rats.

Animals↗
PubMed1978

Interacting enzyme systems at steady state: further Monte Carlo calculations on two-state molecules.

In this work, Monte Carlo calculations were made on a 10 x 10 lattice of two-state, steady-state enzyme molecules in two special cases for which the Bragg-Williams (mean field) approximation had earlier produced some very interesting phase-transition properties. The Monte Carlo results proved to be similar to Bragg-Williams in some respects but not in others. The discrepancies are attributed primarily to; (i) inadequate treatment by Bragg-Williams of strong negative cooperativity; and (ii) the finite size of the 10 x 10 lattice used in the exact calculations.

Enzymes↗
PubMed1978

Interacting enzyme systems at steady state: location of the phase transition in approximations of the mean field type.

We consider a phase transition "loop," obtained from a mean field type of approximate treatment of a closed steady-state Ising system. Where is the cut (stable path) across the loop located? The general procedure, in answering this question, is to pass to an open version of the same system and use the cut that appears automatically in this case (no loop is possible in an open system). This is equivalent to finding the point at which the two phases have equal total probability in the open system. It is shown here that this procedure, when applied to a system of two-state enzyme molecules, is formally equivalent to well-known thermodynamic methods (Maxwell's theorem, etc.). These can be applied directly to the closed system without considering the open system explicitly. However, for enzyme molecules with more than two states, the "thermodynamic" method generally fails and one must fall back on the open system procedure mentioned above. Practical implementation of this procedure is not easy.

Enzymes↗
PubMed1977

Steroid and FSH action on LH receptors and LH-sensitive testicular responsiveness during sexual maturation of the rat.

This study examines the effect of FSH, testosterone and estradiol on testicular LH receptors and in vitro testicular responsiveness to LH in immature rats under various conditions. FSH treatment of 15-day-old immature rats significantly increased the number of LH receptors but did not alter testicular responsiveness. FSH treatment of hypophysectomized immature rats increased the number of LH receptors and markedly increased testicular responsiveness. Treatment of hypophysectomized rats with testosterone proprionate for 4 days, followed by a 5-day treatment with FSH, enhanced the effect of FSH on the number of LH receptors but did not increase the effect of FSH on testicular responsiveness. In contrast, treatment with estradiol for 4 days before FSH treatment had no effect on the FSH-induced increase in LH receptors but completely inhibited the FSH-induced increase in testicular responsiveness. These observations suggest that during male sexual maturation (1) regulation of LH receptors is distinct from regulation of testicular responsiveness to LH, (2) estradiol may be a factor in the regulation of testicular responsiveness to LH, and (3) testosterone may enhance the FSH-induced increase of LH receptors.

Animals↗
PubMed1977

Pituitary regulation of Leydig cell function in the adult male rat.

The effects of hypophysectomy on serum testosterone, 125I-labelled hCG binding to testicular membranes and on testicular responsiveness were studied in adult rats. Serum testosterone decreased rapidly over the first 6 h after hypophysectomy. LH receptors were determined (pmol/testis) by measuring the specific binding of 125I-labelled hCG in membrane preparations of testes of rats hypophysectomized 1, 2, 3, 6, 9, or 15 days earlier. Hypophysectomy did not result in a decrease in 125I-labelled hCG binding on day 1 but this had decreased to 40% of that in intact controls by day 2. A gradual decline was found between days 2 and 6 at which time hCG binding had decreased to 15%. No further decrease occurred between days 6 and 15. Scatchard analysis indicated that the decline in hCG binding was due to a decreaffinity. FSH, testosterone, dihydrotestosterone, and oestradiol were unable to prevent the decline in hCG binding. Although serum testosterone, testicular testosterone content, and 125I-labelled hCG binding decreased rapidly after hypophysectomy, testicular responsiveness to LH was biphasic. The intraperitoneal administration of 25 microgram LH 2 h before decapitation increased testosterone in the circulation to a greater extent extent in animals hypophysectomized for 1 day than in intact controls while hCG binding affinities and capacities had not changed. Two or three days after hypophysectomy testicular responsiveness to LH was similar to that of intact controls even though hCG binding in hypophysectomized animals had decreased to 40 and 28% of intact controls respectively. It is concluded that (1) the testis is dependent on anterior pituitary hormones for maintenance of testicular LH receptors and testosterone secretion, (2) FSH, testosterone, dihydrotestosterone, or oestradiol cannot prevent the decline in testicular LH receptors resulting from hypophysectomy, and (3) steroidogenic capacity of the testis persists significantly longer than the hCG binding capacity of the testis.

Animals↗
PubMed1977

Testicular receptors for luteinizing hormone after immunoneutralization of gonadotrophin releasing hormone in the male rat.

The effects of immunoneutralization of endogenous gonadotrophin releasing hormone (GnRH) on the serum concentrations of testosterone and gonadotrophins and the binding of 125I-labelled human chorionic gonadotrophin (HCG) to testicular membrane fractions were studied in adult male rats. Four days after the administration of 1 ml anti-GnRH serum, the level of testosterone in the serum decreased to 44% of the concentration before the injection, whereas administration of normal rabbit serum had no effect. Multiple injections of anti-GnRH serum for 4 days dramatically suppressed the secretion of gonadotrophins in rats orchidectomized 2 months earlier. In intact male rats treated identically, immunoneutralization of GnRH decreased the level of serum testosterone to 32% of the concentration present in saline-treated controls, but did not decrease the number of testicular binding sites for HCG (LH). Administration of testosterone or oestradiol for 3 or 6 days caused a marked reduction in the concentration of serum gonadotrophins but did not decrease the number of LH receptors. This study provides further support for the concept that one releasing hormone governs secretion of both FSH and LH. In addition, these studies indicate that selective reduction of gonadotrophins for 3-6 days has no effect on the number of testicular LH receptors. This suggests that pituitary hormones other than gonadotrophins may be important in the maintenance of testicular receptors for LH.

Animals↗
PubMed1976

Differentiation of channel models by noise analysis.

Differentiation of membrane channel models based on fluctuation (or noise) analysis is discussed. The theory is particularly useful in distinguishing a single-conductance model (Hodgkin-Huxley formalism) from a multiconductance model. When applied to the frog node of Ranvier, it seems likely that the potassium channels of the membrane may have multiconductance states.

Animals↗
PubMed1975

Some self-consistent two-state sliding filament models of muscle contraction.

The general formalism required to treat two-state sliding filament models of muscle contraction, including free energy considerations, is first reviewed and amplified. This formalism is then used to examine, and modify as needed, three models studied previously by Podolsky and Nolan, in which cross-bridge attachment-detachment and ATP turnover are not tightly coupled. No attempt is made here to establish an optimal, self-consistent model of this type because our interest is primarily in methadology rather than in fitting experimental results. But it appears from this preliminary study that such a model, with satisfactory mechanical and thermodynamic properties, could be found. An extremely simple but unrealistic two-state model is also studied which is of interest because it demonstrates the fact that it is possible, in principle at least, for sliding filament models to work with very high thermodynamic efficiencies (50-100 percent). An appendix is included that is concerned with the form of the dependence of certain first-order rate constants on the concentrations of ATP, ADP, and P.

Adenosine Diphosphate↗
PubMed1975

Matrix method for fluctuations and noise in kinetic systems.

In a series of papers we were concerned with the question of how to calculate the concentration noise power spectra of an ensemble of multi-state linear kinetic systems when the rate constants of the systems are assumed to be known. We have used a standard eigenvalue-eigenfunction method to solve the differential equations which govern the regression of the means and derived the noise power spectrum as a function of the eigenvalues and eigenfunctions of the relaxation matrix of the system. In this paper, we have obtained an equation which relates the noise spectrum matrix of the fluctuations directly to the relaxation matrix of the means. As a result, the noise power spectrum can be calculated through matrix operations without the necessity of an eigenvalue-eigenfunction calculation. The present formalism is particularly useful in the evaluation of kinetic rate constants when the noise spectrum data of concentration fluctuations are given. Possible applications to biochemical systems are briefly discussed.

Kinetics↗
PubMed1975

Stochastics of cycle completions (fluxes) in biochemical kinetic diagrams.

Over a long time period, the rate constants for cycle completions (one-way fluxes) in steady-state biochemical diagrams can be expressed explicitly in terms of the elementary rate constants for transitions between states of the diagram. These cycle rate constants determine the mean one-way fluxes in the diagram and also fluctuations about the means. These properties are confirmed by Monte Carlo computer simulations on special cases. Two other topics are considered briefly: the effect of the starting state or states on the numbers of cycle completions in computer simulation runs; and the more detailed stochastic approach required if individual cycle completions are to be followed (i.e., if the "long time" restriction is removed).

Computers↗