PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 3982961

Sinus slowing and pacemaker shift caused by adenosine in rabbit SA node.

G A West·L Belardinelli
View original source ↗Export metadata ↓

Abstract

Adenosine has a negative chronotropic effect in a number of species. The studies reported here were undertaken to characterize further the effects of adenosine using isolated perfused rabbit hearts and isolated SA node tissue. In the isolated perfused hearts (n = 9) the threshold doses for slowing by adenosine and 2-chloroadenosine, an adenosine analog, were 1 X 10(-5) M and 1 X 10(-7) M, respectively. In the isolated hearts adenosine, in addition to slowing sinus rate, also caused a change in the activation pattern of the right atrium. During adenosine infusion the earliest site of activation shifted from the SA node region to the right atria near the crista terminalis. The pacemaker shift was reversible upon washout of adenosine. The adenosine -induced shift in pacemaker could also be demonstrated using microelectrode recordings in the isolated SA node preparation that included the crista terminalis and some of the surrounding tissue. During control the activation of SA node preceded that of the crista terminalis (CT) by 44 +/- 4.1 ms (n = 11). Adenosine infusion caused an increase in cycle length and, in addition shifted the earliest site of activation from the SA node region to CT, i.e., in the presence of adenosine CT preceded SA node activation by 26.68 +/- 3.2 ms. All the effects were reversible after washout of adenosine. Adenosine also caused conduction block within the sinus node. No effect on the action potentials or on conduction in the CT was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Explore related subjects

2-ChloroadenosineAdenosineAnimalsDose-Response Relationship, DrugHeartHeart Conduction SystemIn Vitro TechniquesPerfusionRabbitsSinoatrial NodeJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

G A West, L Belardinelli. 1985. Sinus slowing and pacemaker shift caused by adenosine in rabbit SA node.. https://doi.org/10.1007/bf00583284

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2006

Modulation of ischaemic contracture in mouse hearts: a 'supraphysiological' response to adenosine.

While inhibition of ischaemic contracture was one of the first documented cardioprotective actions of exogenously applied adenosine, it is not known whether this is a normal function of endogenous adenosine generated during ischaemic stress. Additionally, the relevance of delayed contracture to postischaemic outcome is unclear. We tested the ability of endogenous versus exogenous adenosine to modify contracture (and postischaemic outcomes) in C57/Bl6 mouse hearts. During ischaemia, untreated hearts developed peak contracture (PC) of 85 +/- 5 mmHg at 8.9 +/- 0.8 min, with time to reach 20 mmHg (time to onset of contracture; TOC) of 4.4 +/- 0.3 min. Adenosine (50 microm) delayed TOC to 6.7 +/- 0.6 min, as did pretreatment with 10 microm 2-chloroadenosine (7.2 +/- 0.5 min) or 50 nm of A(1) adenosine receptor (AR) agonist N(6)-cyclohexyladenosine (CHA) (6.7 +/- 0.3 min), but not A(2A)AR or A(3)AR agonists (20 nm 2-[4-(2-carboxyethyl) phenethylamino]-5' N-methylcarboxamidoadenosine (CGS21680) or 150 nm 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA), respectively). Adenosinergic contracture inhibition was eliminated by A(1)AR gene knockout (KO), mimicked by A(1)AR overexpression, and was associated with preservation of myocardial [ATP]. This adenosine-mediated inhibition of contracture was, however, only evident after prolonged (10 or 15 min) and not brief (3 min) pretreatment. Ischaemic contracture was also insensitive to endogenously generated adenosine, since A(1)AR KO, and non-selective and A(1)AR-selective antagonists (50 microm 8-sulphophenyltheophylline and 150 nm 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX), respectively), all failed to alter intrinsic contracture development. Finally, delayed contracture with A(1)AR agonism/overexpression or ischaemic 2,3-butanedione monoxime (BDM; 5 microm to target Ca(2+) cross-bridge formation) was linked to enhanced postischaemic outcomes. In summary, adenosinergic inhibition of contracture is solely A(1)AR mediated; the response is 'supraphysiological', evident only with significant periods of pre-ischaemic AR agonism (or increased A(1)AR density); and ischaemic contracture appears insensitive to locally generated adenosine, potentially owing to the rapidity of contracture development versus the finite time necessary for expression of AR-mediated cardioprotection.

2-Chloroadenosine↗
PubMed2006

Long-term stimulation of adenosine A2b receptors begun after myocardial infarction prevents cardiac remodeling in rats.

BACKGROUND: Adenosine inhibits proliferation of cardiac fibroblasts and hypertrophy of cardiomyocytes, both of which may play crucial roles in cardiac remodeling. In the present study, we investigated whether chronic stimulation of adenosine receptors begun after myocardial infarction (MI) prevents cardiac remodeling. METHODS AND RESULTS: MI was produced in Wistar rats by permanent ligation of the left anterior descending coronary artery. One week after the onset of MI, animals were randomized into 8 groups: vehicle, dipyridamole (DIP; the adenosine uptake inhibitor, 50 mg/kg), 2-chroloadenosine (CADO; the stable analogue of adenosine, 2 mg/kg), and CADO in the presence of the nonselective adenosine receptor antagonist 8-sulfophenyltheophylline (8-SPT) or the selective antagonist for adenosine A1, A2a, A2b, or A3 receptor. Three weeks after treatment, hemodynamic and echocardiographic parameters in the DIP and CADO groups were significantly improved compared with the vehicle group. These hemodynamic and echocardiographic improvements were blunted by either 8-SPT or the selective adenosine A2b antagonist MRS1754 but not by the selective antagonists for other subtypes of adenosine receptors. The collagen volume fraction was smaller, and gene expression of the molecules associated with cardiac remodeling such as matrix metalloproteinase in noninfarcted areas was reduced in the DIP and CADO groups compared with the vehicle group, both of which were attenuated by either 8-SPT or MRS1754. CONCLUSIONS: Long-term stimulation of adenosine A2b receptors begun after MI attenuates cardiac fibrosis in the noninfarcted myocardium and improves cardiac function. Drugs that stimulate adenosine A2b receptors or increase adenosine levels are new candidates for preventing cardiac remodeling after MI.

2-Chloroadenosine↗
PubMed2006

Mechanism of 2-chloroadenosine toxicity to PC3 cell line.

BACKGROUND: 2-CADO inhibits the growth of several types of cells and causes apoptosis by a mechanism which involves adenosine receptors or cellular uptake or both. METHODS: Androgen-independent (PC3) prostate cancer cells were used in the study and proliferation, cell-cycle progression, and apoptosis analyzed. Deoxy-and ribonucleoside triphosphate pools were determined by HPLC. The molecular mechanism was examined by assessing the involvement of DNA synthesizing enzymes in the cellular response. RESULTS: 2-CADO treatment dramatically reduced the number of prostate cancer cells and permanently stopped cell-cycle progression in the S-phase. The role of 2-CADO in prostate cancer cells is uptake-mediated and followed by sequential phosphorylations to 2-Cl-ATP that irreversibly inhibits several key-enzymes for DNA biosynthesis. CONCLUSIONS: Arrest of DNA synthesis responsible for toxicity of 2-CADO to PC3 cells is due to the lack of substrates for DNA polymerization caused by irreversible inhibition of purine/pyrimidine ribo-and 2-deoxyribonucleotides salvage enzymes.

2-Chloroadenosine↗