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Biomedical subjects

H Sun

Publications and source records attributed to H Sun.

At least 469 records · Page 26Linked to original sources
PubMed1990

Pattern formation in an immobilized bienzyme system. A morphogenetic model.

Experimental and theoretical studies of a reaction-diffusion model of two immobilized enzymes participating in the cellular acid-base metabolism, namely glutaminase and urease, are presented. The system shows an unstable steady state at pH 6.0, where any perturbation will drive the system towards a more alkaline or more acidic pH, owing to the autocatalytic behaviour with respect to pH exhibited by both enzymes. When diffusion is coupled to reaction by means of immobilization, different patterns of the internal pH profile appear across the membrane. If the bienzymic membrane is subjected to a perturbation at its boundaries, of the same amplitude but in opposite directions, the internal pH evolves through an asymmetric pattern to attain a nearly symmetric distribution of pH. The pH value at the final steady state is more acidic or more alkaline than the initial state according to the initial and boundary conditions. The final nearly symmetric state is attained more rapidly when less enzyme is immobilized (1.8 x 10(-4) M.s-1 as against 3.3 x 10(-4) M.s-1 of total enzyme activity in the membrane volume). The experimental results agree rather well qualitatively with numerical predictions of the model equations.

Diffusion↗
PubMed1990

Platelet-activating factor and hyperacute rejection. The effect of a platelet-activating factor antagonist, SRI 63-441, on rejection of xenografts and allografts in sensitized hosts.

The pathogenesis of hyperacute transplantation reactions includes the activation of a cascade of nonspecific inflammatory reactions that precipitates the destruction of the target organ. Platelet-activating factor (PAF) represents an important component of these inflammatory cascades, and we have examined the influence of a specific PAF receptor antagonist (SRI 63-441) on the inhibition of hyperacute rejection in two experimental models, the rejection of rat cardiac allografts by presensitized recipients and guinea pig-to-rat and mouse-to-rat cardiac xenografts. Our results demonstrate that inhibition of PAF function by SRI 63-441 has a variable effect on the survival of cardiac allografts in presensitized rat recipients. In the ACI to sensitized BN cardiac allograft model, the use of SRI 63-441 alone, or in combination with CsA, FK506, or prostaglandin E2 (PGE2), does not prolong graft survival. As we have previously reported, SRI 63-441 does act as a single agent to prolong the survival of ACI to sensitized LEW grafts, and this survival effect is synergistic when combined with CsA. Here we extend these results to demonstrate that this survival is also extended when FK506 is used in the ACI-to-LEW model. Concordant mouse-to-rat cardiac xenografts are also relatively resistant to prolongation of graft survival following treatment with SRI 63-441 alone or in combination with CsA or FK506. Discordant xenografts appear to be more susceptible to inhibition of the rejection reaction with SRI 63-441. When either donor or recipient animals were treated with SRI 63-441 alone, or in combination with CsA or FK506, there was significant prolongation of guinea pig-to-rat cardiac xenograft survival. These results are consistent with our earlier description of the effectiveness of SRI 63-441 in preventing the rejection of cat-to-rabbit kidney xenografts. We believe that these results demonstrate that the use of the SRI 63-441 to specifically interfere with the function of PAF has the effect of prolonging graft survival in those systems in which performed antibody and/or complement activation are important components of the hyperacute reaction. This synthetic drug is representative of a family of compounds whose structure can be modified to balance their therapeutic and toxicity activities, and may prove to be important components of a polytherapeutic approach to the control of graft rejection in sensitized patients or following discordant xenografting.

Animals↗
PubMed1990

Liver allograft rejection: an overview of morphologic findings.

Recent improvements in patient survival has resulted in widespread use of liver transplantation as therapy for end stage liver disease. The pathologist plays a critical role in the pre- and post-operative care of these patients, and the core needle biopsy of the allograft has become a fairly reliable method of diagnosing acute cellular rejection. Most of the non-rejection related causes of graft dysfunction produce morphologic manifestations similar to those seen in nontransplanted livers (e.g., duct obstruction resembles duct obstruction). Many pathologists are, however, unfamiliar with the histologic changes of the various types of rejection. The following article is an attempt to acquaint pathologists with the morphologic features of liver allograft rejection. As a backdrop to understanding the events in humans, observations in untreated experimental animals are presented and reviewed briefly.

Animals↗
PubMed1990

[Pharmacokinetics and distribution of isotetrandrine in rats].

A reversed-phase HPLC method for determination of isotetrandrine (ITD) in biological specimens was developed. The mobile phase composed of 0.2% (w/v) SDS, 47% acetonitrile and 53% distilled water (pH 2), at a flow rate of 1.5 ml/min with determination wavelength of 230 nm. The drug concentration-time curves of ITD in rats after iv of 12.5, 25 and 50 mg/kg were shown to fit a two-compartment open model with half-lives of 67.1 +/- 6.22 68.0 +/- 2.57 and 97.6 +/- 14.6 min, respectively. At doses of 12.5 and 25 mg/kg, the elimination of the drug from plasma was found to be in accord with linear kinetics, but when the dosage was 50 mg/kg, a non-linear kinetics was observed. Following ig ITD 100 and 250 mg/kg, the plasma concentration-time curves exhibited two marked peaks. Half-lives of elimination after ig doses was much longer than after iv administration, with mean values of 9.35 +/- 3.24 h (100 mg/kg) and 9.01 +/- 3.02 h (250 mg/kg). Distribution of the drug in rats was extensive, highest level of the drug was found in the lung and lowest in plasma after iv administration. Following ig administration, highest level of the drug was found in the liver and lowest in plasma.

Alkaloids↗
PubMed1990

The time to reach steady state after the administration of intravenous bolus, constant infusion, and oral immediate-release and sustained-release preparations.

Based on one-compartment pharmacokinetic model, the equations to calculate the specific fractional steady-state of drug level achieved at any time (FSS) after administration of intravenous bolus, constant infusion, and oral immediate-release preparations are reviewed. Also the equation to calculate FSS after administering an oral sustained-release dosage form is derived. From these equations, it can be shown that the drug FSS after these routes of administration is dependent primarily on the elimination rate constant (K). However, for a sustained-release preparation, the FSS is dependent on K, drug release rate constant (Kr), as well as the fraction of sustained release (Fs) of the dosage form. Using the new derived equation for FSS, several simulations were performed to evaluate the effects of Kr K, and Fs. These indicate that the time to achieve a given FSS is prolonged as Kr or K becomes smaller and as Fs becomes large.

Administration, Oral↗
PubMed1989

Double-strand breaks at an initiation site for meiotic gene conversion.

It has been proposed that the initiation of meiotic recombination involves either single-strand or double-strand breaks in DNA. It is difficult to distinguish between these on the basis of genetic evidence because they give rise to similar predictions. All models invoke initiation at specific sites to explain polarity, which is a gradient in gene conversion frequency from one end of a gene to the other. In the accompanying paper we describe the localization of an initiation site for gene conversion to the promoter region of the ARG4 gene of the yeast Saccharomyces cerevisiae. Here, we show that a double-strand break appears at the ARG4 recombination initiation site at the time of recombination, and that the broken DNA molecules end in long single-stranded tails.

Gene Conversion↗
PubMed1989

Characterization of the larval olfactory response in Drosophila and its genetic basis.

Drosophila larvae are attracted to a wide variety of chemical stimuli. The olfactory response to ethyl acetate, a powerful attractant, was found to be surprisingly well conserved across a variety of different wild-type strains. Strain differences are documented, however, both in attraction to ethyl acetate and in another chemosensory behavior: avoidance of an aversive stimulus. As a means of analyzing the extent of genetic heterogeneity within strains, one wild-type population, Canton-S, was screened for variant X chromosomes. An enrichment procedure was characterized and used to make the screening more efficient. Lines homozygous for individual X chromosomes were established, and all were found to exhibit a strong olfactory response, although evidence was found for variation among them. The olfactory response was found to be conserved through an extended period of larval development, including the final period during which larvae leave the culture medium in preparation for metamorphosis. The results are discussed in terms of the genetic basis of the response and the use of single-gene mutations as a means of dissecting olfactory system function.

Animals↗
PubMed1989

Genetic analysis of olfactory behavior in Drosophila: a new screen yields the ota mutants.

A simple means of measuring Drosophila olfactory response is described, and the behavior which it measures is characterized. The assay was used to screen for X-linked mutants defective in olfactory function. Six ota mutants were isolated and characterized (ota = olfactory trap abnormal). Four of the mutants were found to be abnormal in another chemosensory behavior as well. Two of the mutant phenotypes extend to include another sensory system: they are defective in visual system physiology. All were normal, however, in a test of giant fiber system physiology. Two of the mutations are dominant, and the recessive mutations define two complementation groups. Mutations representing each complementation group, as well as one of the dominant mutations, were mapped. For the mutants with defective visual system physiology, the visual defects were shown to cosegregate with olfactory phenotypes.

Analysis of Variance↗
PubMed1989

[24-hour ambulatory blood pressure monitoring in normal and hypertensive subjects].

24-hour ambulatory blood pressures (BP) of 172 normal subjects and 167 hypertensive patients recorded by automatic ambulatory monitoring device (A method) and standard mercury sphygmomanometer (B method) were studied. The results show: (1) 66% of normal subjects and 78% hypertensive patients have an evident circadian rhythm BP during 24-hours, BP readings during sleep and noon time are lower. (2) There is no significant difference between times at work and at home readings (P greater than 0.05), but the mean BP during sleeping time is the lowest (P less than 0.01). (3) The correlative coefficient of 24-hour average BP and casual clinic BP is low (r = 0.38-0.74). (4) The validity and accuracy of ambulatory BP monitoring by A and B methods were compared.

Adult↗
PubMed1986

Organization and evolution of D region class I genes in the mouse major histocompatibility complex.

Chromosome walking has been used to study the organization of the class I genes in the D and Qa regions of the MHC of the BALB/c mouse and in the D region of the AKR mouse. Five and eight class I genes are found in the D and Qa regions of the BALB/c mouse, respectively, while the AKR mouse contains only a single class I D region gene that has been identified by transfection as the Dk gene. Restriction map homologies and crosshybridization experiments suggest that the multiple class I genes in the D region of the BALB/c mouse have been generated by unequal crossing-over involving class I genes from the Qa region. The expanded D region of BALB/c and other H-2d haplotype mouse strains appears to be metastable, since evidence for gene contraction in the Dd region has been found in two mutant strains. Thus the D region and also the Qa region class I genes are in a dynamic state, evolving by gene expansion and contraction.

Animals↗