Integrative systems biology reveals NKG2A-biased immune responses correlate with protection in infectious disease, autoimmune disease, and cancer

Infection, autoimmunity, and cancer are principal human health challenges of the 21st century. Often regarded as distinct ends of the immunological spectrum, recent studies hint at potential overlap between these diseases. For example, inflammation can be pathogenic in infection and autoimmunity. T resident memory (TRM) cells can be beneficial in infection and cancer. However, these findings are limited by size and scope; exact immunological factors shared across diseases remain elusive. Here, we integrate large-scale deeply clinically and biologically phenotyped human cohorts of 526 patients with infection, 162 with lupus, and 11,180 with cancer. We identify an NKG2A+ immune bias as associative with protection against disease severity, mortality, and autoimmune/post-acute chronic disease. We reveal that NKG2A+ CD8+ T cells correlate with reduced inflammation and increased humoral immunity and that they resemble TRM cells. Our results suggest NKG2A+ biases as a cross-disease factor of protection, supporting suggestions of immunological overlap between infection, autoimmunity, and cancer.

Acute cholecystitis, obesity, and steatohepatitis constitute the lethal triad for bile duct injury (BDI) during laparoscopic cholecystectomy

OBJECTIVE

The most feared complication during laparoscopic cholecystectomy remains a bile duct injury (BDI). Accurately risk-stratifying patients for a BDI remains difficult and imprecise. This study evaluated if the lethal triad of acute cholecystitis, obesity, and steatohepatitis is a prognostic measure for BDI.

METHODS

A retrospective review of the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) registry was performed. All laparoscopic cholecystectomy cases within the main NSQIP database for 2012-2019 were queried. Two study cohorts were constructed. One with the lethal triad of acute cholecystitis, BMI ≥ 30, and steatohepatitis. The other cohort did not have the full triad present. Multivariate analysis was performed via logistic regression modeling with calculation of odds ratios (OR) to identify independent factors for BDI. An uncontrolled and controlled propensity score match analysis was performed.

RESULTS

A total of 387,501 cases were analyzed. 36,887 cases contained the lethal triad, the remaining 350,614 cases did not have the full triad. 860 BDIs were identified resulting in an overall incidence rate 0.22%. There were 541 BDIs within the lethal triad group with 319 BDIs in the other cohort and an incidence rate of 1.49% vs 0.09% (P < 0.001). Multivariate analysis identified the lethal triad as an independent risk factor for a BDI by over 15-fold (OR 16.35, 95%CI 14.28-18.78, P < 0.0001) on the uncontrolled analysis. For the controlled propensity score match there were 29,803 equivalent pairs identified between the cohorts. The BDI incidence rate remained significantly higher with lethal triad cases at 1.65% vs 0.04% (P < 0.001). The lethal triad was an even more significant independent risk factor for BDI on the controlled analysis (OR 40.13, 95%CI 7.05-356.59, P < 0.0001).

CONCLUSIONS

The lethal triad of acute cholecystitis, obesity, and steatohepatitis significantly increases the risk of a BDI. This prognostic measure can help better counsel patients and potentially alter management.

T cell receptor sequences are the dominant factor contributing to the phenotype of CD8+ T cells with specificities against immunogenic viral antigens

Antigen-specific CD8+ T cells mediate pathogen clearance. T cell phenotype is influenced by T cell receptor (TCR) sequences and environmental signals. Quantitative comparisons of these factors in human disease, while challenging to obtain, can provide foundational insights into basic T cell biology. Here, we investigate the phenotype kinetics of 679 CD8+ T cell clonotypes, each with specificity against one of three immunogenic viral antigens. Data were collected from a longitudinal study of 68 COVID-19 patients with antigens from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), cytomegalovirus (CMV), and influenza. Each antigen is associated with a different type of immune activation during COVID-19. We find TCR sequence to be by far the most important factor in shaping T cell phenotype and persistence for populations specific to any of these antigens. Our work demonstrates the important relationship between TCR sequence and T cell phenotype and persistence and helps explain why T cell phenotype often appears to be determined early in an infection.

Large libraries of single-chain trimer peptide-MHCs enable antigen-specific CD8+ T cell discovery and analysis

The discovery and characterization of antigen-specific CD8+ T cell clonotypes typically involves the labor-intensive synthesis and construction of peptide-MHC tetramers. We adapt single-chain trimer (SCT) technologies into a high throughput platform for pMHC library generation, showing that hundreds can be rapidly prepared across multiple Class I HLA alleles. We use this platform to explore the impact of peptide and SCT template mutations on protein expression yield, thermal stability, and functionality. SCT libraries were an efficient tool for identifying T cells recognizing commonly reported viral epitopes. We then construct SCT libraries to capture SARS-CoV-2 specific CD8+ T cells from COVID-19 participants and healthy donors. The immunogenicity of these epitopes is validated by functional assays of T cells with cloned TCRs captured using SCT libraries. These technologies should enable the rapid analyses of peptide-based T cell responses across several contexts, including autoimmunity, cancer, or infectious disease.

Multiple early factors anticipate post-acute COVID-19 sequelae

Post-acute sequelae of COVID-19 (PASC) represent an emerging global crisis. However, quantifiable risk factors for PASC and their biological associations are poorly resolved. We executed a deep multi-omic, longitudinal investigation of 309 COVID-19 patients from initial diagnosis to convalescence (2-3 months later), integrated with clinical data and patient-reported symptoms. We resolved four PASC-anticipating risk factors at the time of initial COVID-19 diagnosis: type 2 diabetes, SARS-CoV-2 RNAemia, Epstein-Barr virus viremia, and specific auto-antibodies. In patients with gastrointestinal PASC, SARS-CoV-2-specific and CMV-specific CD8+ T cells exhibited unique dynamics during recovery from COVID-19. Analysis of symptom-associated immunological signatures revealed coordinated immunity polarization into four endotypes, exhibiting divergent acute severity and PASC. We find that immunological associations between PASC factors diminish over time, leading to distinct convalescent immune states. Detectability of most PASC factors at COVID-19 diagnosis emphasizes the importance of early disease measurements for understanding emergent chronic conditions and suggests PASC treatment strategies.

Artificial image objects for classification of breast cancer biomarkers with transcriptome sequencing data and convolutional neural network algorithms

BACKGROUND

Transcriptome sequencing has been broadly available in clinical studies. However, it remains a challenge to utilize these data effectively for clinical applications due to the high dimension of the data and the highly correlated expression between individual genes.

METHODS

We proposed a method to transform RNA sequencing data into artificial image objects (AIOs) and applied convolutional neural network (CNN) algorithms to classify these AIOs. With the AIO technique, we considered each gene as a pixel in an image and its expression level as pixel intensity. Using the GSE96058 (n = 2976), GSE81538 (n = 405), and GSE163882 (n = 222) datasets, we created AIOs for the subjects and designed CNN models to classify biomarker Ki67 and Nottingham histologic grade (NHG).

RESULTS

With fivefold cross-validation, we accomplished a classification accuracy and AUC of 0.821 ± 0.023 and 0.891 ± 0.021 for Ki67 status. For NHG, the weighted average of categorical accuracy was 0.820 ± 0.012, and the weighted average of AUC was 0.931 ± 0.006. With GSE96058 as training data and GSE81538 as testing data, the accuracy and AUC for Ki67 were 0.826 ± 0.037 and 0.883 ± 0.016, and that for NHG were 0.764 ± 0.052 and 0.882 ± 0.012, respectively. These results were 10% better than the results reported in the original studies. For Ki67, the calls generated from our models had a better power for prediction of survival as compared to the calls from trained pathologists in survival analyses.

CONCLUSIONS

We demonstrated that RNA sequencing data could be transformed into AIOs and be used to classify Ki67 status and NHG with CNN algorithms. The AIO method could handle high-dimensional data with highly correlated variables, and there was no need for variable selection. With the AIO technique, a data-driven, consistent, and automation-ready model could be developed to classify biomarkers with RNA sequencing data and provide more efficient care for cancer patients.

Artificial image objects for classification of schizophrenia with GWAS-selected SNVs and convolutional neural network

In this article, we propose a new approach to analyze large genomics data. We considered individual genetic variants as pixels in an image and transformed a collection of variants into an artificial image object (AIO), which could be classified as a regular image by CNN algorithms. Using schizophrenia as a case study, we demonstrate the principles and their applications with 3 datasets. With 4,096 SNVs, the CNN models achieved an accuracy of 0.678 ± 0.007 and an AUC of 0.738 ± 0.008 for the diagnosis phenotype. With 44,100 SNVs, the models achieved class-specific accuracies of 0.806 ± 0.032 and 0.820 ± 0.049, and AUCs of 0.930 ± 0.017 and 0.867 ± 0.040 for the bottom and top classes stratified by the patient's polygenic risk scores. These results suggest that, once transformed to images, large genomics data can be analyzed effectively with image classification algorithms.

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Introduce a technique to transform genomics data into AIOs

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Apply CNN algorithms to classify genomics derived AIOs

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Showcase the technique with GWAS-selected SNVs to classify schizophrenia diagnosis

Genome-wide association studies have discovered many genetic variants that contribute to human diseases. However, it remains a challenge to effectively utilize these variants to facilitate early and accurate diagnosis and treatment. In this report, we propose a new approach that transforms genetic data into AIOs so that they can be classified by advanced artificial intelligence and machine learning algorithms. Using schizophrenia as a case study, we demonstrate that genetic variants can be transformed into AIOs and that the AIOs can be classified by CNN algorithms consistently. Our approach can be applied to other omics data and combine them to jointly model disease risks and treatment responses.

Untangle the Structural and Random Zeros in Statistical Modelings

Count data with structural zeros are common in public health applications. There are considerable researches focusing on zero-inflated models such as zero-inflated Poisson (ZIP) and zero-inflated Negative Binomial (ZINB) models for such zero-inflated count data when used as response variable. However, when such variables are used as predictors, the difference between structural and random zeros is often ignored and may result in biased estimates. One remedy is to include an indicator of the structural zero in the model as a predictor if observed. However, structural zeros are often not observed in practice, in which case no statistical method is available to address the bias issue. This paper is aimed to fill this methodological gap by developing parametric methods to model zero-inflated count data when used as predictors based on the maximum likelihood approach. The response variable can be any type of data including continuous, binary, count or even zero-inflated count responses. Simulation studies are performed to assess the numerical performance of this new approach when sample size is small to moderate. A real data example is also used to demonstrate the application of this method.

The Trypanosoma brucei dihydroxyacetonephosphate acyltransferase TbDAT is dispensable for normal growth but important for synthesis of ether glycerophospholipids

Glycerophospholipids are the most abundant constituents of biological membranes in Trypanosoma brucei, which causes sleeping sickness in humans and nagana in cattle. They are essential cellular components that fulfill various important functions beyond their structural role in biological membranes such as in signal transduction, regulation of membrane trafficking or control of cell cycle progression. Our previous studies have established that the glycerol-3-phosphate acyltransferase TbGAT is dispensable for growth, viability, and ester lipid biosynthesis suggesting the existence of another initial acyltransferase(s). This work presents the characterization of the alternative, dihydroxyacetonephosphate acyltransferase TbDAT, which acylates primarily dihydroxyacetonephosphate and prefers palmitoyl-CoA as an acyl-CoA donor. TbDAT restores the viability of a yeast double null mutant that lacks glycerol-3-phosphate and dihydroxyacetonephosphate acyltransferase activities. A conditional null mutant of TbDAT in T. brucei procyclic form was created and characterized. TbDAT was important for survival during stationary phase and synthesis of ether lipids. In contrast, TbDAT was dispensable for normal growth. Our results show that in T. brucei procyclic forms i) TbDAT but not TbGAT is the physiologically relevant initial acyltransferase and ii) ether lipid precursors are primarily made by TbDAT.

Contemporary Pharyngeal and Invasive emm1 and Invasive emm12 Group A Streptococcus Isolates Exhibit Similar In Vivo Selection for CovRS Mutants in Mice

Group A Streptococcus (GAS) causes diverse infections ranging from common pharyngitis to rare severe invasive infections. Invasive GAS isolates can have natural mutations in the virulence regulator CovRS, which result in enhanced expression of multiple virulence genes, suppressed the expression of the protease SpeB, and increased virulence. It is believed that CovRS mutations arise during human infections with GAS carrying wild-type CovRS and are not transmissible. CovRS mutants of invasive GAS of the emm1 genotype arise readily during experimental infection in mice. It is possible that invasive GAS arises from pharyngeal GAS through rare genetic mutations that confer the capacity of mutated GAS to acquire covRS mutations during infection. The objective of this study was to determine whether contemporary pharyngeal emm1 GAS isolates have a reduced propensity to acquire CovRS mutations in vivo compared with invasive emm1 GAS and whether emm3, emm12, and emm28 GAS acquire CovRS mutants in mouse infection. The propensity of invasive and pharyngeal emm1 and invasive emm3, emm12, and emm28 SpeB^A+ isolates to acquire variants with the SpeB^A- phenotype was determined during subcutaneous infection of mice. The majority of both invasive and pharyngeal emm1 SpeB^A+ isolates and two of three emm12 isolates, but not emm3 and emm28 isolates, were found to acquire SpeB^A- variants during skin infection in mice. All analyzed SpeB^A- variants of emm1 and emm12 GAS from the mouse infection acquired covRS mutations and produced more platelet-activating factor acetylhydrolase SsE. Thus, contemporary invasive and pharyngeal emm1 GAS isolates and emm12 GAS have a similar capacity to acquire covRS mutations in vivo. The rarity of severe invasive infections caused by GAS does not appear to be attributable to a reduced ability of pharyngeal isolates to acquire CovRS mutations.

The Glycerol-3-Phosphate Acyltransferase TbGAT is Dispensable for Viability and the Synthesis of Glycerolipids in Trypanosoma brucei

Glycerolipids are the main constituents of biological membranes in Trypanosoma brucei, which causes sleeping sickness in humans. Importantly, they occur as a structural component of the glycosylphosphatidylinositol lipid anchor of the abundant cell surface glycoproteins procyclin in procyclic forms and variant surface glycoprotein in bloodstream form, that play crucial roles for the development of the parasite in the insect vector and the mammalian host, respectively. The present work reports the characterization of the glycerol-3-phosphate acyltransferase TbGAT that initiates the biosynthesis of ester glycerolipids. TbGAT restored glycerol-3-phosphate acyltransferase activity when expressed in a Leishmania major deletion strain lacking this activity and exhibited preference for medium length, unsaturated fatty acyl-CoAs. TbGAT localized to the endoplasmic reticulum membrane with its N-terminal domain facing the cytosol. Despite that a TbGAT null mutant in T. brucei procyclic forms lacked glycerol-3-phosphate acyltransferase activity, it remained viable and exhibited similar growth rate as the wild type. TbGAT was dispensable for the biosynthesis of phosphatidylcholine, phosphatidylinositol, phosphatidylserine, and GPI-anchored protein procyclin. However, the null mutant exhibited a slight decrease in phosphatidylethanolamine biosynthesis that was compensated with a modest increase in production of ether phosphatidylcholine. Our data suggest that an alternative initial acyltransferase takes over TbGAT's function in its absence.

Effect of siRNA targeting HER2/neu on the proliferation and viability of prostate cancer PC-3M cells

The aim of this study was to investigate the effect of a small interfering RNA (siRNA) targeting human epidermal growth factor receptor 2 (HER2/neu) on the proliferation and viability of prostate cancer PC-3M cells. Chemically synthesized siRNA targeting HER2/neu was transfected into PC-3M cells by using liposomes, and cells transfected with empty liposomes, a negative siRNA sequence, or nothing (untransfected) were used as controls. mRNA and protein levels of HER2/neu were detected using reverse transcription-polymerase chain reaction and western blot, respectively. The inhibitory action of HER2/neu siRNA on the in vitro growth of PC-3M cells was assessed by the cholecystokinin 8 assay and apoptosis was detected using flow cytometry. Cells transfected with HER2/neu siRNA showed decreased mRNA and protein levels of HER2/neu compared to control groups (P < 0.05). The survival rate of PC-3M cells decreased significantly after transfection with HER2/neu siRNA compared to that of untransfected cells (55.39 ± 1.60 and 81.42 ± 0.80%, respectively; P < 0.05). The apoptosis rate in cells transfected with HER2/neu siRNA was quite high (45.60 ± 0.70%) compared to that of blank control, empty liposome, and negative siRNA sequence groups (P < 0.05). In conclusion, siRNA targeting HER2/neu inhibits HER2/neu expression in PC-3M cells, resulting in an inhibition in proliferation and an induction of apoptosis.

Pulse-modulation imaging-review and performance analysis

In time-domain or pulse-modulation (PM) imaging, the incident light intensity is not encoded in amounts of charge, voltage, or current as it is in conventional image sensors. Instead, the image data are represented by the timing of pulses or pulse edges. This method of visual information encoding optimizes the phototransduction individually for each pixel by abstaining from imposing a fixed integration time for the entire array. Exceptionally high dynamic range (DR) and improved signal-to-noise ratio (SNR) are immediate benefits of this approach. In particular, DR is no longer limited by the power-supply rails as in conventional complementary metal-oxide semiconductor (CMOS) complementary metal-oxide semiconductor active pixel sensors, thus providing relative immunity to the supply-voltage scaling of modern CMOS technologies. In addition, PM imaging naturally supports pixel-parallel analog-to-digital conversion, thereby enabling high temporal resolution/frame rates or an asynchronous event-based array readout. The applications of PM imaging in emerging areas, such as sensor network, wireless endoscopy, retinal prosthesis, polarization imaging, and energy harvesting are surveyed to demonstrate the effectiveness of PM imaging in low-power, high-performance machine vision, and biomedical applications of the future. The evolving design innovations made in PM imaging, such as high-speed arbitration circuits and ultra-compact processing elements, are expected to have even wider impacts in disciplines beyond CMOS image sensors. This paper thoroughly reviews and classifies all common PM image sensor architectures. Analytical models and a universal figure of merit - image quality and dynamic range to energy complexity factor are proposed to quantitatively assess different PM imagers across the entire spectrum of PM architectures.

Dose-Time-Response Cumulative Multinomial Generalized Linear Model

In toxicological and pharmaceutical experiments, a type of quantal bioassay experiment is designed in which a response, such as mortality, in a group of animals is recorded over time points under different dose levels in the course of the experiment. The application of the typical logit and probit analyses is no longer valid in this situation because it neglects the dependency on time and also the possible interaction of time and dose concentration on the response in the experiment. In this paper, a dose-time-response model is proposed for this type of experiment and a cumulative multinomial generalized linear model that incorporates time and the other experimental conditions as covariates is developed by the theory of maximum likelihood estimation. Both the point estimator and confidence bands for ED50(t), the concentration of a toxicant that will kill 50% of the animals by a specific time, t; as well as LT50(d), the time to 50% mortalities for a specific concentration, d, is then formulated in closed form from the newly proposed dose-time-response model. Finally, the newly proposed model is considered for a real data set to demonstrate the application.

Interactive toxicity of simple chemical mixtures of cadmium, mercury, methylmercury and trimethyltin: model-dependent responses

Scientific and societal interest in the analysis of aggregate toxicity derives from the fact that people are seldom exposed to single chemicals, but rather to multiple agents from different sources and even to mixtures of agents from a single source. Many descriptive terms and mathematical, graphical, and statistical models have been used to evaluate the toxicity of simple mixtures. It is not very easy to distinguish clearly the intrinsic differences, distinctions and limitations of these models when applied to characterizing interactive toxicity. A series of experiments were performed to illustrate model-dependent consistencies and differences in interactive toxicity. Cultured murine renal cortical cells, target cells for metal toxicity, were treated with selected concentrations of one metal or binary mixtures of metals to give conditions of dose-additivity, response additivity, or with only one toxic member of the binary mixture. The cytotoxicity was determined at 24h by lactate dehydrogenase release. The data were analyzed graphically and mathematically by (a) Carter's statistical isobologram, (b) Barton's non-linear, and (c) Kodell and Pounds' linear models to characterize the interaction. These models were compared and contrasted for robustness, and consistency using these common data sets. The models gave generally consistent conclusions, but each model has limitations and strengths for assessing particular mixtures scenarios. This comparison illustrates the complexity of extrapolating conclusions between models, and difficulty of public health assessment from exposures to multiple chemicals in the environment.

[Study of helical CT low-contrast resolution and its influencing factors]

This paper studies the helical CT low-contrast resolution and its influencing factors by experimental analysis. The CT low-contrast resolution increased with mA, kV, slice thickness, scan time and FOV, and decreased with matrix, pitch and thickness of the scanned objective. The reconstruction algorithm of high resolution results lower low-contrast resolution. Mostly helical image low-contrast resolution is slightly lower than axial image. It's very important for us to understand CT low-contrast resolution and its influencing factors for the correct evaluation of the performance of CT scanner.

Empirical Bayes estimation for combinations of multivariate bioassays

This article presents a new empirical Bayes estimator (EBE) and a shrinkage estimator for determining the relative potency from several multivariate bioassays by incorporating prior information on the model parameters based on Jeffreys' rules. The EBE can account for any extra variability among the bioassays, and if this extra variability is 0, then the EBE reduces to the maximum likelihood estimator for combinations of multivariate bioassays. The shrinkage estimator turns out to be a compromise of the prior information and the estimator from each multivariate bioassay, with the weights depending on the prior variance.

Effects of perindopril, propranolol, and dihydrochlorothiazide on cardiovascular remodelling in spontaneously hypertensive rats

AIM

To investigate the effects of perindopril, propranolol, and dihydrochlorothiazide on artery wall thickening, left ventricular hypertrophy, and cardiac fibrosis in spontaneously hypertensive rats (SHR).

METHODS

After measurement of systolic blood pressure (SBP), 16-wk-old Male SHR were randomly divided into 3 groups (each n = 10), given perindopril (Per, 5 mg.kg-1.d-1), propranolol (Pro, 40 mg.kg-1.d-1), dihydrochlorothiazide (DCT, 100 mg.kg-1.d-1) respectively by gavage for 12 wk. Sex-, age-, and number-matched untreated SHR and normotensive Wistar Kyoto rats (WKY) served as controls. When the treatment finished, body weights (BW) and SBP were measured before decapitation of the rats. The heart was excised rapidly, the left ventricle was weighed and then subjected to collagen content analysis. Vascular wall and lumen ratio from aorta, renal arteries and branch III vessels of mesenteric arteries were determined morphometrically.

RESULTS

Treated rats in 3 groups showed a lower SBP and the ratio of left ventricle weight to body weight (LVW/BW) compared with WKY. Artery wall thickening was similarly inhibited in the treated groups. Per and Pro inhibited cardiac fibrosis, but collagen concentration increased in DCT treated SHR [collagen volume fraction (CVF): 19 +/- 4 vs SHR 14 +/- 4, P < 0.05; perivascular collagen fraction(PVCF): 84 +/- 7 vs SHR 79 +/- 5, P < 0.05].

CONCLUSION

Per and Pro inhibited, but DCT promoted, cardiac fibrosis.

A nonlinear isobologram model with Box-Cox transformation to both sides for chemical mixtures

The linear logistical isobologram is a commonly used and powerful graphical and statistical tool for analyzing the combined effects of simple chemical mixtures. In this paper a nonlinear isobologram model is proposed to analyze the joint action of chemical mixtures for quantitative dose-response relationships. This nonlinear isobologram model incorporates two additional new parameters, Ymin and Ymax, to facilitate analysis of response data that are not constrained between 0 and 1, where parameters Ymin and Ymax represent the minimal and the maximal observed toxic response. This nonlinear isobologram model for binary mixtures can be expressed as [formula: see text] In addition, a Box-Cox transformation to both sides is introduced to improve the goodness of fit and to provide a more robust model for achieving homogeneity and normality of the residuals. Finally, a confidence band is proposed for selected isobols, e.g., the median effective dose, to facilitate graphical and statistical analysis of the isobologram. The versatility of this approach is demonstrated using published data describing the toxicity of the binary mixtures of citrinin and ochratoxin as well as a new experimental data from our laboratory for mixtures of mercury and cadmium.

Inhibitory effects of captopril on c-myc expression during left ventricular hypertrophy

AIM

To study the molecular mechanism of captopril (Cap) on the inhibition of left ventricular hypertrophy (LVH), disclose the expression and distribution of c-myc in different cell types in left ventricle (LV) in spontaneously hypertensive rats (SHR).

METHODS

Cap 100 mg.kg-1.d-1 was given p.o. to SHR. Systolic blood pressure (SBP), left ventricular weight (LVW), and body weight (BW) were measured at 16-wk old. The level of angiotensin II (Ang II), c-myc mRNA, and oncoprotein were determined by immunohistochemical method, Northern blot, and Western blot, respectively.

RESULTS

Cap reduced SBP, LVW/BW in SHR, with a decrease of Ang II and c-myc expression in LV. Local cardial Ang II mainly distributed in cardiomyocytes. Cap inhibited cardial Ang II production and c-myc expression (histochemical staining intensity index, 0.49 +/- 0.04 vs 0.83 +/- 0.24, P < 0.01). The c-myc oncoprotein was prevailingly located in cardiac fibroblasts. The c-myc oncoprotein in Cap treated SHR was lower than that of WKY.

CONCLUSION

High expression of c-myc in fibroblasts played an important role in the development of LVH in SHR. Inhibitory effects of Cap on LVH was associated with a decreased myocardial Ang II and interstitial fibroblasts c-myc expression. The c-myc oncoprotein post-transcriptional translation was also interrupted by Cap.

Effect of chronic captopril treatment on circulating and tissue renin-angiotensin system in SHR rats

AIM

To study the effect of captopril treatment and its withdrawal on the circulating and tissue peptidyl-dipeptidase A, angiotensinogen (AGT), and angiotensin II (A II), in relation to left ventricular hypertrophy (LVH) and systolic blood pressure (SBP).

METHODS

SHR male rats were given captopril 100 mg.kg-1.d-1 [SHRcap, number (n) = 43] orally in mixture with milk powder as vehicle from intrautero period of 16 wk of age. Rats were killed at 16 (n = 19) and 40 (n = 24) wk of age, respectively. Male, age-matched untreated SHR and WKY rats served as controls. SBP, left ventricular mass/body weight (LVM/BW) ratio, left ventricular (LV) myocardium and plasma A II concentration, aortic and serum peptidyl-dipeptidase A activity, AGT mRNA level in kidney and liver, renal renin mRNA level were determined.

RESULTS

Captopril treatment decreased SBP and reduced LVM/BW at 16 and 40 wk of age, and persistently inhibited LV myocardium A II, aortic peptidyl-dipeptidase A activity, and AGT gene expression in kidney even after the treatment was removed. Nevertheless, no changes were found in plasma A II concentration, serum peptidyl-dipeptidase A activity, and AGT mRNA level in liver by captopril therapy. Renal renin mRNA level was low in SHR and WKY rats, but it was increased by captopril treatment. Tissue renin-angiotensin system (RAS) such as AGT mRNA in kidney, aortic peptidyl-dipeptidase A activity, and LV myocardium A II, rather than circulating RAS (AGT mRNA in liver, renin mRNA in kidney, serum peptidyl-dipeptidase A activity and plasma A II), were persistently inhibited by early captopril treatment, even after the withdrawal of the treatment.

CONCLUSION

The long-term inhibition of tissue RAS is one of the mechanisms of the persistent hypotensive effect of captopril treatment.

Disparate effects of captopril on hypertension and blood vessel

AIM

To study whether the effect of captopril (Cap) on vascular structure and function may be seperated from its effect on blood pressure.

METHODS

Captopril treatment (group Cap A and B, 20 and 100 mg.kg-1.d-1) was given to SHR rats during pregnancy, weaning, and up to 16 wk of age. Study performed at 40 wk. Blood pressure (BP) was measured by tail-cuff sphygmomanometer, and wall/lumen ratio of mesenteric artery 3rd grade branch was assessed by morphometric assay. Resistance vessel properties were determined by hindquarter perfusion pressure responses to incremental doses of phenylephrine, in the presence of N omega nitro-L-arginine methyl ester (L-NAME) or the L-arginine, the precursor of nitric oxide synthesis.

RESULTS

Both doses of Cap prevented hypertrophy of blood vessels to an extent comparable to that of the untreated WKY rats (wall/lumen ratio of mesenteric artery, Cap A: 0.38 +/- 0.08, Cap B: 0.29 +/- 0.05 vs WKY: 0.34 +/- 0.11, P > 0.05, respectively). The parameters derived from hindquarter perfusion pressure curves in Cap treated group were almost identical to that of WKY, significantly different from that of untreated SHR (EC50, Cap B 4.05 +/- 2.58 vs SHR 1.15 +/- 0.96 mL.L-1, P < 0.01; vs WKY 5.13 +/- 1.97 mL.L-1, P > 0.05). Addition of L-NAME or L-arginine in the perfusate augmented or attenuated the vasoconstriction responses in the Cap treated group.

CONCLUSION

Cap initiated from intrauterine period normalized the vascular structure and vasoconstrictive responses in SHR when BP still sustained at a higher level vs WKY.

Mechanisms responsible for sustained hypotension after captopril treatment

OBJECTIVE

To investigate new aspects of the relationship between sustained reduction of blood pressure and alteration of cardiovascular structure and function after cessation of early captopril treatment.

METHODS

Spontaneously hypertensive rats (SHR) were given captopril 20 mg/kg per day (n = 13) or 100 mg/kg per day (n = 12) from the intra-uterine period to age 16 weeks and then the treatment was stopped. Age-matched untreated SHR (n = 16) and Wistar-Kyoto (WKY) rats (n = 17) served as controls. The experiments were carried out at 40 weeks.

RESULTS

Withdrawal of captopril treatment resulted in a rapid rebound of SBP to a level close to that of untreated SHR in the low-dose group, whereas a persistently lower SBP was maintained in the high-dose group. Both doses of captopril treatment completely prevented wall hypertrophy either of arteriolar resistance vessels or of muscular vessels. Captopril decreased left ventricular mass:body weight ratio dose-dependently. High-dose captopril improved the resting and stress systolic and diastolic function. Thoracic angiotensin converting enzyme levels were dose-dependently reduced by captopril treatment. The curves of perfusion pressure response to incremental doses of phenylephrine shifted to the right in both captopril treatment groups compared with those of the control SHR. Addition of L-NAME and L-arginine to the perfusate augmented or attenuated the vasoconstrictor activity in all of the rats, whereas high-dose captopril totally restored the abnormal hypersensitivity to L-NAME and caused less attenuation in response to L-arginine in the control SHR.

CONCLUSIONS

The persistent lower blood pressure caused by early captopril treatment was ascribed mainly to its sustained normalization of structure and function of resistance vessels, which may be partly mediated by the improvement of endothelial cell function. The persistent reduction of angiotensin converting enzyme activity in blood vessel wall attenuated left ventricular hypertrophy, and the improvement of cardiac systolic and diastolic function may also contribute to the sustained hypotensive effect.

[Relationship between CENP-B gene expression and the cell cycle]

The centromere/kinetochore is a specialized structure at the primary constriction of mammalian chromosomes. It participates in and is necessary for the mitotic chromosome movement. Centromere Protein B(CENP-B) is a highly conserved protein located at the centromere/kinetochore region. In this article, we explore the relationship between CENP-B expression and cell proliferation. HeLa cells were synchronized at different phases of the cell cycle and the synchronized cells were examined by flow cytometry and 3H-TdR labelling. ACA immunostaining showed the discrete single spots in nuclei of the cells at G1 and S phase, and spots in pairs mostly in those at G2 phase. Dot blot and Northern blot indicated that CENP-B gene was expressed at all phases of the cell cycle, but the expression level very much different with the highest at G2 phase and the lowest at S phase. Interestingly relatively high expression of CENP-B gene was also found in M phase, showing the continuity of the CENP-B gene expression during the cell cycle. This continuity implies a possibility that the assembly of the new centromere/kinetochore can not occur until centromere proteins reach a critical concentration when cells enter S phase and G 2 phase. Also, the continuous expression of centromere proteins may be necessary for the centromere/kinetochore function. In addition, the relationship between CENP-B gene expression and the nuclear skeleton was investigated. The nuclear skeleton-associated DNA extracted after Bam HI digestion were hybridized with 32P-labelled cDNA of CENP-B gene by means of Southern blot technique. The results that there stronger positive hybridization reaction in G 2 phase than in S phase indicated that CENP-B gene was more closely associated with the nuclear skeleton in G 2 phase cells than in S phase cells, which was in consistence with the level of the CENP-B gene expression at G 2 and S phase cells.

Inhibition of left ventricular hypertrophy and expression of proto-oncogenes c-myc other than c-fos in myocardium by early captopril treatment in SHR rats

AIM

To explore the mechanisms by which angiotensin converting enzyme inhibitor (ACEI) prevents the development of left ventricular hypertrophy (LVH).

METHODS

Captopril (Cap 100 mg.kg(-1).d(-1)) was given orally to male spontaneously hypertensive rats from intrauterine period to 16 wk of age. Experiments were performed at 40 wk of age. SBP, left ventricular weight to body weight ratio (LVW/BW) were assessed. The levels of c-myc and c-fos mRNA in the left ventricle were measured by Northern blot.

RESULTS

Early-onset Cap therapy significantly decreased SBP. After discontinuance of treatment for 24 wk, SBP of SHRcap was still maintained at a lower level. LVW/BW in SHRcap was markedly reduced. The expression of myocardial c-myc mRNA was decreased by 72% in SHRcap compared with that in the untreated SHR, but the expression of myocardial c-fos mRNA was not different between the untreated SHR, SHRcap, and WKY rats.

CONCLUSION

Early Cap treatment may permanently prevent the development of hypertension, inhibit LVH. Furthermore, the prevention of LVH is associated with a decrease in c-myc mRNA levels, and the development and regression of left ventricular hypertrophy may be irrelevant to c-fos expression.

[Mechanism of inhibition in left ventricular hypertrophy by captopril treatment in spontaneously hypertensive rats]

To explore the mechanisms by which angiotensin converting enzyme inhibitor (ACEI) prevents the development of left ventricular hypertrophy (LVH), captopril (Cap 100 mg.kg-1/d was administered orally to male spontaneously hypertensive rats from intrauterine period to 16 weeks of age. Male and age-matched untreated WKY rats and SHR were used as controls. Experiments were performed at 40 weeks of age. SBP, left ventricular weight to body weight ratio (LVW/BW), myocardial hydroxyproline (Hypro) and norepinephrine (NE) were determined. The levels of c-myc and c-fos mRNA in the left ventricle were measured by Northern blot. Early-onset Cap therapy significantly decreased SBP at 16 weeks of age. After discontinuance of treatment for 24 weeks, SBP of SHRcap was still maintained at a level lower than that of untreated SHR. LVW/BW and Hypro in SHR cap were markedly reduced. The expression of myocardial c-myc mRNA (n = 5) was decreased by 72% in SHRcap compared with that in the untreated SHR, but the expression of c-fos mRNA (n = 7) and NE was not different between the untreated SHR, SHRcap and WKY rats. These results indicate that early Cap treatment may permanently prevent the development of hypertension, inhibit myocardial hypertrophy (MH), and interstitial fibrosis. Furthermore, the prevention of MH is associated with a decrease in myocardial c-myc mRNA levels, and the development and regression of MH may be irrelevant to proto-oncogene c-fos expression.

Effects of captopril and clonidine on resting and stress cardiac performance of left ventricle in spontaneously hypertensive rats

Captopril (Cap) 20 mg.kg-1.d-1 and clonidine (Clo) 300 micrograms.kg-1.d-1 were given po to SHR from their parents mating day to 24 wk of age, with untreated, age-matched SHR and WKY as controls. Stress cardiac function was assessed by the development of LVdp/dtmax in response to incremental pressure load (phenylephrine, Phe) and volume load (dextran, Dex). The slope of delta HR/delta MAP relationship curve was used as an index of baroceptor sensitivity. Results showed that both Cap and Clo caused decreases in BP in SHR. Cap not only reduced markedly the left ventricular mass/body weight (LVM/BW), (mg.g-1, 2.7 +/- 0.4 vs SHR 3.5 +/- 0.3, P < 0.01), but also normalized the LVdp/dtmax, -LVdp/dtmax, T value, and the stress cardiac function. Clo neither decreased the LVM/BW (mg.g-1, 3.4 +/- 0.5 vs SHR 3.5 +/- 0.3, P > 0.05), nor improved the resting and stress cardiac function. The results suggested that attenuation of the left ventricular hypertrophy (LVH) is beneficial not only to the resting but also stress cardiac performance.

Sympatholytic effect of captopril in regression of cardiovascular remodeling in spontaneously hypertensive rats

Fifty-eight spontaneously hypertensive rats (SHR) at 12 wk of age were divided into 3 groups: A) captopril (Cap) 20 mg.kg-1.d-1; B) clonidine (Clo) 30 micrograms.kg-1.d-1; C) Clo 30 micrograms.kg-1.d-1 + Cap 20 mg.kg-1.d-1 orally for 24 wk. Concomitant administration of Cap and Clo did not result in more lowering of the systolic blood pressure (SBP) than that by Cap alone. Regression of left ventricular hypertrophy (LVH) were remarkable in Groups A and C, but not to the extent in that of WKY. No significant difference between these two groups was found. Cap alone resulted in a greater decrease of myocardial norepinephrine (NE) than that of Groups B and C. The wall/lumen ratio and the number of smooth muscle cell (SMC) layers of renal artery decreased in Groups A and C, but little difference was found between them. It seemed that combined blockade of renin-angiotensin-aldosterone (RAA) system and sympathetic nervous system (SNS) did not produce more significant BP reduction and reversal of cardiovascular remodeling than Cap alone did. The sympathetic inhibitory effect of angiotensin converting enzyme inhibitor (ACEI) was not enhanced by sympatholytic treatment.

[Effects of clonidine on estrus, estradiol, gonadotropin, graafian follicle, and corpus luteum in rats]

Effects of clonidine (Clo) on female reproductive system were studied in rats. Blood FSH, LH, progesterone, testosterone, and estradiol were measured by radioimmunoassay and the development of secondary follicles and corpus luteum in ovary were investigated by morphometry. After Clo po 0.3 mg.kg-1.d-1 x 14 d, the estrus of rats was prolonged; FSH, LH, and progesterone increased significantly; while estradiol reduced. The development of secondary follicles in ovary was blocked at the stage of prematuration and the numerical density of corpus luteum decreased. After clonidine po 28 d, FSH and LH sustained at high levels, but the estrous cycle, estradiol and progesterone recovered.

[Possible involvement of atrial natriuretic factor and vasopressin in antihypertensive mechanism of clonidine in humans]

To appreciate the role of some neuropeptides in the antihypertensive mechanism of clonidine, 17 patients with essential hypertension were given po clonidine 150 micrograms tid for 3 d. Plasma atrial natriuretic factor (ANF), vasopressin (Vas), and dynorphin A (Dyn A) were measured by radioimmunoassay. After the treatment, mean blood pressure (MBP), heart rate and 24 h urine norepinephrine, epinephrine were decreased, but no change was found in plasma Dyn A. The magnitudes of increased ANF and decreased Vas were correlated with the decreased MBP (r = -0.57 and 0.53, respectively, P < 0.05). These results suggest that both ANF and Vas are involved in the antihypertensive mechanism of clonidine.

Increased pressor responsiveness of femoral arteries to exogenous norepinephrine in renal hypertensive dogs mediated through alpha 2 adrenoceptors

Changes of perfusion pressure induced by femoral arterial perfusion of norepinephrine (NE) were studied in renal hypertensive dogs made with the method of wrapping both kidneys. The NE threshold dose which induced perfusion pressure increase was lower in hypertensive dogs than that in normotensive dogs. The NE pressor response in low concentration (1, 2, 10 ng.kg-1) was increased in hypertensive dogs, after alpha 2 adrenoceptors antagonized by idazoxan this increased response had been eliminated. These suggested that increased vasoconstriction by exogenous NE in hypertensive dogs was mediated through the increased reactivity of postsynaptic alpha 2 adrenoceptors to NE.

A point mutation in the MyoD basic domain imparts c-Myc-like properties

MyoD and c-Myc, members of the large "basic-helix-loop-helix" family of proteins, regulate diverse aspects of both normal and neoplastic growth and specific gene regulation. These two proteins differ at 9 of the 14 amino acids that comprise the basic domains necessary for DNA binding and transcriptional control. Individual amino acids in the MyoD basic domain were mutated to those found at the analogous positions in c-Myc. Four classes of mutants were obtained: (i) those with no effects on MyoD-site binding or activation of MyoD-responsive genes, (ii) those with no effect on MyoD-site binding but with a loss of activation potential, (iii) those with a loss of both DNA binding and activation potential, and (iv) one mutant (mut 9, Leu122----Arg) that left MyoD-site binding unaffected but imparted a new c-Myc-site binding capability. mut 9 competed with wild-type protein for the activation of MyoD-responsive reporter genes but could, like c-Myc, also suppress the adenovirus major-late promoter, which contains a c-Myc binding site. Our studies thus identify specific amino acid residues in the MyoD basic domain that are important for its activity as a DNA-binding transcriptional activator. Most significantly, our results with mut 9 indicate that Leu122 of MyoD is a critical determinant of specific DNA binding and that mutation at this residue can alter this specificity.

Nifedipine pharmacodynamics and pharmacokinetics in treatment of congestive heart failure

In 22 of 27 cases of congestive heart failure (CHF) treated with nifedipine (NIF), significant improvements in resting hemodynamics were noticed. The higher the basal systemic vascular resistance (SVR) and pulmonary artery end diastolic pressure (PAEDP), the greater the magnitude of reduction was achieved (r = 0.84 and 0.77, P less than 0.01, respectively). Exercise hemodynamic investigation showed that NIF lowered SVR, PAEDP and pulmonary vascular resistance (PVR), with an increase in stroke volume (SV) at the serum concentration of 5-10 ng/ml. Maximum effect was observed at the concentration of 20 ng/ml. No further vasodilation was attainable with serum concentrations above 20 ng/ml. No remarkable deviation of NIF pharmacokinetic parameters from the normal ranges was found in CHF patients. The plasma norepinephrine level decreased markedly 2 and 7 hours after the use of NIF. It is concluded that oral NIF is beneficial to severe CHF patients with low cardiac output and high SVR.

[Modulation of norepinephrine release in sympathetic nerve endings in renal hypertensive dogs]

Experimental renal hypertensive and normal dogs with femoral arteries constantly perfused were studied. Cocaine was used to block the presynaptic norepinephrine (NE) reuptake and tyramine to initiate the release of NE in sympathetic nerve endings. NE spillover and infusion pressure were measured under basic conditions and during intraarterial infusion of cocaine, tyramine and in combination with alpha 1 and alpha 2 adrenoceptor antagonists. The extent of NE spillover increase induced by infusion of tyramine, the increased infusion pressure by cocaine and tyramine, and the reduced infusion pressure by prazosin were all greater in hypertensive dogs than those in normal dogs, but adrenoceptor antagonist idazoxan further increased tyramine-induced NE spillover in normal dogs only. It was suggested that reduced-regulation of presynaptic alpha 2 adrenoceptors to NE release and increased responsiveness of postsynaptic alpha 1 adrenoceptors to NE were present in hypertensive dogs.

[Clonidine stimulates central nervous alpha 2 adrenoceptors not mediating Ca2+ channels]

Seven renal hypertensive (2 kidneys--2 clipped) and 8 normotensive conscious dogs were given icv clonidine. After the medication the mean arterial blood pressure (MAP) were lowered and the heart rate (HR) and plasma norepinephrine (NE) were decreased. The magnitude of the decrease of MAP was greater than normotensive dogs; while no differences of decrease of NE was found. Nicardipine (10 micrograms/kg) icv caused significant increases of MAP and HR in both hypertensive and normotensive groups. The decrease of MAP induced by clonidine was not changed by the pretreatment of nicardipine icv in both groups. It is thus concluded that clonidine stimulates central nervous alpha adrenoceptors not mediating Ca2+ channels.

Alpha-adrenergic effects of dopamine and dobutamine on the coronary circulation

After beta-adrenergic blockade, dopamine causes coronary vasoconstriction that is blocked by non-selective alpha-adrenergic antagonists. This study was carried out to determine the relative importance of alpha 1- and alpha 2-adrenoceptors in mediating coronary vasoconstriction in response to dopamine. Because dobutamine has been reported to cause alpha-adrenergic stimulation, the response to dobutamine was also examined. The circumflex coronary artery was cannulated and perfused at a constant blood flow rate in 14 dogs; coronary vasomotor responses were assessed from changes in perfusion pressure. Central effects were eliminated by vagotomy and stellate ganglionectomy; propranolol (1 mg/kg i.v.) was administered to block beta-adrenergic effects. The coronary responses to intracoronary bolus doses of dopamine and dobutamine were determined; the effects of selective alpha 1-blockade with prazosin (600 micrograms/kg i.v.) and selective alpha 2-blockade with idazoxan or rauwolscine (1-5 micrograms/kg per min intracoronary for 10 min) were examined. Dopamine produced dose-related coronary vasoconstriction; this response was not significantly altered by alpha 1-blockade with prazosin, but was abolished by the addition of alpha 2-adrenergic blockade with idazoxan or rauwolscine. Dobutamine did not produce coronary vasoconstriction at any dose tested. These data demonstrate that coronary vasoconstriction produced by dopamine is mediated through postjunctional alpha 2-adrenergic receptors.

[Pharmacodynamics and pharmacokinetics of nifedipine in patients with congestive heart failure]

Twenty-seven cases of congestive heart failure (CHF) were treated with nifedipine (Nif) 20 mg po. Significant improvements in resting hemodynamics were found in 22 cases. The higher the basal systemic vascular resistance (SVR) and pulmonary artery end diastolic pressure (PAEDP) were, the greater the magnitudes of reduction found (r = 0.84 and 0.77, P less than 0.01, respectively). Exercise hemodynamic investigation showed that Nif led to a lowering of SVR, PAEDP and pulmonary vascular resistance (PVR), with increases in SV and concentration of 5-10 ng/ml, with a maximum being observed at the concentration of 20 ng/ml. No further vasodilation was found when the plasma concentration exceeded 20 ng/ml. No remarkable deviations from the normal ranges of Nif pharmacokinetics were found in CHF patients. The plasma norepinephrine level decreased markedly 2 and 7 h after Nif. Thus, it is concluded that oral Nif is beneficial in severe CHF patients having low cardiac output and high SVR.

Postsynaptic adrenoceptor-mediated vasoconstriction in coronary and femoral vascular beds

This study examined the response to intra-arterial norepinephrine and sympathetic nerve stimulation on perfusion pressure of cannulated dog femoral and left circumflex coronary arteries perfused at constant flow rates. Sympathetic nerve stimulation was delivered through the decentralized inferior cardiac nerve and the lumbar sympathetic chain; beta-adrenergic blockade was maintained with propranolol. In the coronary artery, the vasoconstrictor response to norepinephrine was blunted by alpha 1-adrenergic blockade with prazosin but was abolished by alpha 2-adrenergic blockade with rauwolscine, indicating postsynaptic alpha 2-adrenoceptor-mediated vasoconstriction. In the femoral artery, prazosin decreased norepinephrine-induced vasoconstriction by 20-40%; the subsequent addition of rauwolscine completely abolished vasoconstriction, indicating that both alpha 1- and alpha 2-adrenoceptors contributed to vasoconstriction. Sympathetic nerve stimulation produced frequency-dependent increases of perfusion pressure in both coronary and femoral vascular beds. Prazosin caused approximately 50% reduction in the vasoconstrictor response of the coronary vascular bed and approximately 30% reduction in the femoral bed. The addition of rauwolscine completely blocked the response to sympathetic nerve stimulation in coronary and femoral vascular beds. These studies demonstrate that postsynaptic alpha 2-adrenoceptor-mediated mechanisms participate in vasoconstriction in response to both exogenous norepinephrine and sympathetic nerve stimulation in the canine coronary and femoral vascular beds.

Effects of atrial natriuretic peptide in the canine coronary circulation

Atriopeptin II has been reported to cause profound coronary vasoconstriction in the isolated perfused guinea pig heart and in the blood perfused canine heart. Consequently, this study was carried out to examine possible mechanisms by which vasomotor effects of human atrial natriuretic peptide (ANP) occur in the canine coronary circulation. Bolus dosages of ANP were administered into the left circumflex coronary artery of in situ dog hearts perfused at constant flow rate. ANP produced dose-related coronary vasodilation with a threshold dosage of 2 ng/kg; a dosage of 2 micrograms/kg caused a 27 +/- 4% decrease in coronary vascular resistance. Coronary vasodilation produced by ANP was not altered by beta-adrenergic blockade with propranolol (1 mg/kg i.v.). In addition, neither adenosine receptor blockade with 8-phenyltheophylline (5 mg/kg i.v.) nor cyclooxygenase inhibition with indomethacin (5 mg/kg i.v.) significantly altered the response to intra-arterial ANP. These data demonstrate that in the in vitro blood perfused canine heart, ANP administered intra-arterially results in coronary vasodilation that does not utilize adenosine-dependent or prostaglandin-dependent mechanisms.

Postsynaptic alpha 1- and alpha 2-adrenergic mechanisms in coronary vasoconstriction

This study examined the relative importance of postsynaptic alpha 1- and alpha 2-adrenoceptors in mediating coronary vasoconstriction in open chest dogs in which the left circumflex coronary artery was cannulated and perfused at a constant rate. The cervical vagus nerves and central connections of the stellate ganglia were transected, and beta-adrenergic blockade was produced with propranolol. Coronary vasoconstriction occurred in response to intraarterial administration of both the alpha 1-agonist phenylephrine and the alpha 2-agonist BHT 933. The response to phenylephrine was partially blocked with prazosin and nearly completely eliminated by yohimbine. The response to BHT 933 was resistant to prazosin, but almost completely blocked by yohimbine. Coronary vasoconstriction produced by norepinephrine was resistant to prazosin, but was blunted by alpha 2-adrenergic blockade with yohimbine or idazoxan. Prazosin produced some blunting of coronary vasoconstriction in response to small doses of epinephrine, while yohimbine markedly attenuated epinephrine-induced vasoconstriction at all doses used. Measurements of regional myocardial blood flow with radioactive microspheres demonstrated no transmural redistribution of perfusion during vasoconstriction produced by either alpha 1- or alpha 2 stimulation. Thus, although stimulation of both alpha 1- and alpha 2-adrenoceptors is capable of causing coronary vasoconstriction, vasoconstriction in response to norepinephrine and epinephrine is mediated principally by postsynaptic alpha 2-adrenoceptors.