A2 Adenosine Receptor Subtypes Overproduction in Atria of Perioperative Atrial Fibrillation Patients Undergoing Cardiac Surgery: A Pilot Study

Objective: Although atrial fibrillation is a common cardiac arrhythmia in humans, the mechanism that leads to the onset of this condition is poorly elucidated. Adenosine is suspected to be implicated in the trigger of atrial fibrillation (AF) through the activation of its membrane receptors, mainly adenosine receptor (AR) subtypes A₁R and A₂R. In this study, we compared blood adenosine concentration (BAC), and A₁R, A_2AR, and A_2BR production in right (RA) and left atrium (LA), and on peripheral blood mononuclear cells (PBMCs) in patients with underlying structural heart disease undergoing cardiac surgery with or without peri-operative AF (PeOpAF).

Methods: The study group consisted of 39 patients (30 men and 9 women, mean age, range 65 [40–82] years) undergoing cardiac surgery and 20 healthy patients (8 women and 12 men; mean age, range 60 [39–72] years) as controls were included. Among patients, 15 exhibited PeOpAF.

Results: Blood adenosine concentration was higher in patients with PeOpAF than others. A_2AR and A_2BR production was higher in PBMCs of patients compared with controls and was higher in PeOpAF patients than other patients. In LA and RA, the production of A_2AR and A_2BR was higher in patients with PeOpAF than in other patients. Both A_2AR and A_2BR production were higher in LA vs. RA. A₁R production was unchanged in all situations. Finally, we observed a correlation between A₁R, A_2AR, and A_2BR production evaluated on PBMCs and those evaluated in LA and RA.

Conclusions: Perioperative AF was associated with high BAC and high A_2AR and A_2BR expression, especially in the LA, after cardiac surgery in patients with underlying structural heart disease. Whether these increases the favor in triggering the AF in this patient population needs further investigation.

Adenosine and Its Receptors: An Expected Tool for the Diagnosis and Treatment of Coronary Artery and Ischemic Heart Diseases

Adenosine is an endogenous nucleoside which strongly impacts the cardiovascular system. Adenosine is released mostly by endothelial cells and myocytes during ischemia or hypoxia and greatly regulates the cardiovascular system via four specific G-protein-coupled receptors named A₁R, A_2AR, A_2BR, and A₃R. Among them, A₂ subtypes are strongly expressed in coronary tissues, and their activation increases coronary blood flow via the production of cAMP in smooth muscle cells. A_2A receptor modulators are an opportunity for intense research by the pharmaceutical industry to develop new cardiovascular therapies. Most innovative therapies are mediated by the modulation of adenosine release and/or the activation of the A_2A receptor subtypes. This review aims to focus on the specific exploration of the adenosine plasma level and its relationship with the A_2A receptor, which seems a promising biomarker for a diagnostic and/or a therapeutic tool for the screening and management of coronary artery disease. Finally, a recent class of selective adenosine receptor ligands has emerged, and A_2A receptor agonists/antagonists are useful tools to improve the management of patients suffering from coronary artery disease.

Pharmacological properties of a new fluoroquinolone on the central nervous system in rodents

The pharmacological effects of the novel fluoroquinolone 7-(1R,4R-2,5-diazebicyclo[2.2.1]heptan-2-yl)-1-(1,1-dimethyl )ethyl-6-fluoro - 4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid (BMY-40062, CAS 116143-32-9) on central nervous system were investigated in mice and rats, in comparison in some cases with those of reference quinolones. BMY-40062 showed no effect on general behavior, spontaneous activity, body temperature and neuromuscular coordination in rats at the doses of 1000 and 250 mg/kg. None of the quinolones tested including BMY-40062 modified the seizures induced by bicuculline, a specific GABA A antagonist. BMY-40062 and ciprofloxacin did not consistently influence the pentetrazol-induced convulsions. On the contrary, pefloxacin exhibited a marked convulsivant activity. In the fenbufen (non-steroidal anti-inflammatory drug)-induced seizure model, BMY-40062 showed no effect. Enoxacin, norfloxacin followed by ciprofloxacin elicited a convulsivant effect in presence of fenbufen. Under these experimental conditions, BMY-40062 had no effect on the central nervous system compared to the other tested quinolones in rodents.

A radiotelemetry system for chronic measurement of blood pressure and heart rate in the unrestrained rat validation of the method

Chronic measurements of systemic arterial blood pressure and heart rate via a chronically implanted telemetric transmitter in unrestrained rats, was validated in a three-phase study. In the first part, week-to-week variability of systolic, diastolic, and mean arterial pressures, and heart rate was found to be minimal over the course of nine weeks. In the second part, the reproducibility of cardiovascular response to three successive administration of sotalol, an antihypertensive agent, was studied. In the last part, cardiovascular parameters determined by telemetry were compared to those obtained by direct arterial catheterization and showed a good linear correlation between those two methods.

Fluoronaphthyridines as antibacterial agents. 6. Synthesis and structure-activity relationships of new chiral 7-(1-, 3-, 4-, and 6-methyl-2,5-diazabicyclo[2.2.1]heptan-2-yl)naphthyridine analogues of 7-[(1R,4R)-2,5- diazabicyclo[2.2.1]heptan-2-yl]-1-(1,1-dimethylethyl)-6-fluoro-1,4-dihy dro-4-oxo-1,8-naphthyridine-3-carboxylic acid. Influence of the configuration on blood pressure in dogs. A quinolone-class effect

A series of novel chiral 7-(1-, 3-, 4-, and 6-methyl-[(1R,4R)-2,5- diazabicyclo[2.2.1]heptan-2-yl]-substituted naphthyridines has been prepared with the aim of obtaining good in vitro and in vivo antibacterial agents with a decrease of the pseudoallergic type reaction when compared to that observed with 7[(1R,4R)-2,5-diazabicyclo[2.2.1]heptan-2-yl]-1-(1,1-dimethylethyl )1,4- dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid (1a) (BMY 40062). The derivatives 7-[(1R,4R,6S)-6-methyl-2,5-diazabicyclo[2.2.1]heptan-2-yl]- 1-(1,1-dimethylethyl)-6-fluro-1,4-dihydro-4-oxo-1,8-naphthyridine- 3-carboxylic acid (41) and 7-[(1R,4R,6S)-6-methyl-2,5-diazabicyclo[2.2.1]heptan-2- yl]-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxy lic acid (49) showed potent in vitro and in vivo antibacterial activity against Gram-positive and Gram-negative bacteria. The derivative 49 displayed a less marked decrease in blood pressure (MAP), compared to that of 1a, after intravenous infusion in dogs and was selected as a potential candidate for preclinical trials.

[Experimental study of the hypotensive effect of apomorphine]

The effects of central (intracisternal: i.c.) and peripheral (intravenous: i.v.) administration of apomorphine (200 micrograms/kg) were compared in chloralose anaesthetized dogs. I.v. or i.c. apomorphine induced a decrease in blood pressure (BP) and an increase in heart rate (HR). However, the decrease in BP was more marked after i.c. route. This effect was due to an activation of presynaptic dopaminergic receptors since it is suppressed by i.v. haloperidol of i.v. phentolamine. I.v. atropine abolished the induced-tachycardia. I.v. but not i.c. domperidone suppressed the hypotensive response to i.v. or i.c. apomorphine. The decrease in BP induced by apomorphine was not found in dogs deprived of adrenal medulla. These results confirm the hypotensive properties of apomorphine and suggest the involvement of peripheral dopaminergic mechanisms in this effect. Dopaminergic agonists may represent a new class of antihypertensive drugs.

Renal effect of clonidine during acute hypobaric pressure breathing in normal and diabetes insipidus rats

The renal effects of clonidine (100 and 500 micrograms/kg s.c.) during acute hypobaric pressure breathing (i.e. a protocol which induces an increase in intrathoracic blood volume) were studied in normal and diabetes insipidus rats. In normal rats, clonidine enhanced the increase in urine flow and urea concentration elicited by hypobaric breathing without change in urinary creatinine level. By contrast, in Brattleboro diabetes insipidus rats, clonidine reinforced the hypoxia-induced mechanisms: oliguria, decrease in both urinary urea and creatinine excretions. During normobaric and hypobaric conditions in normal rats administration of clonidine induced an increase in electrolytes (Na+, K+, Cl-) excretion. In Brattleboro rats, clonidine potentiated the decrease in electrolytes excretion elicited by the hypobaric pressure breathing. Since the diuretic reflex elicited by the hypobaric pressure breathing is due to an inhibition of vasopressin release, the present data show that clonidine induces an inhibition of vasopressin release. However, it is suggested that beside this property clonidine also possesses direct vasoconstrictor actions during hypobaric pressure breathing.

Naloxone reduces diuretic responses induced by water, alcohol or congenital lack of vasopressin in rats

The effects of naloxone (2 and 10 mg kg-1 s.c.) were compared in several kinds of experimental polyuria: alcohol- or water-loaded rats and Brattleboro rats (i.e. animals with congenital lack of vasopressin). In normal rats, both water and alcohol increased urine flow and decreased urinary osmolality. Alcohol induced a more marked diuretic response than water. In normally hydrated rats, naloxone (2 and 10 mg kg-1 s.c.) failed to modify urine flow, urinary osmolality, Na+ and K+ urinary excretion, and urine creatinine concentration. The two doses of naloxone decreased urine flow and increased osmolality in both water- and alcohol-loaded rats. In Brattleboro rats, naloxone (10 mg kg-1 s.c.) reduced urine flow and urinary creatine whereas the low dose (2 mg kg-1 s.c.) was without effect. Since it is well known that the mechanism of water- or alcohol-induced diuresis is an inhibition of vasopressin release, the present results suggest that naloxone could prevent this inhibition. They indicate that endogenous opioid peptides may exert an inhibitory control on vasopressin release.

[Effect of clonidine on polyuria induced by alcohol, water or the lack of vasopressin in the rat]

1. The effects of two doses of clonidine (100 and 500 micrograms/kg sc) were compared on several types of experimentally induced diuresis (total value during 4 hours): alcohol or water loaded rats and Brattleboro rats (i.e. animals with congenital lack of vasopressin). 2. The two doses of clonidine alone increased the values of urine flow (fig. 1 and 3). 3. Clonidine, at a low dosage (100 micrograms/kg sc), potentiated the increase in urine flow induced by water overloading but remained ineffective in alcohol--loaded rats (fig. 1). 4. Clonidine, at a higher dosage (500 micrograms/kg sc) reduced alcohol--or water--induced diuresis (fig. 3). 5. In Brattleboro rats, clonidine decreased urine flow (100 micrograms/kg sc) or was without effect (500 micrograms/kg sc) (fig. 2). 6. These results suggest that relatively high doses of clonidine may be useful in treatment of alcohol with drawal in man: the drug could act as a sympatholytic and sedative central agent but could also decrease alcohol--induced diuresis by inhibition of vasopressin release.