Do adenosine receptors play a role in amitriptyline-induced cardiovascular toxicity in rats?

The aim of the our study was to investigate the role of adenosine receptors on cardiovascular toxicity induced by amitriptyline, a tricyclic antidepressant agent. Therefore, the hypothesis of this study was that adenosine receptor antagonists would improve and/or prevent amitriptyline-induced hypotension and conduction abnormalities in an anesthetized rat model of amitriptyline intoxication.

Two separate experimental protocols were performed. Amitriptyline intoxication was induced by the infusion of amitriptyline 0.94 mg/kg/min until 40-45% reduction of mean arterial pressure (MAP). Sodium cromoglycate (10 mg/kg) was injected i.v. to inhibit the A3 receptor-mediated activation of mast cells. In protocol 1, after amitriptyline infusion, while control animals (n=8) were given dextrose solution, treatment groups received a selective adenosine A1 antagonist DPCPX (8-cyclopentyl-1,3-Dipropylxanthine, 20 microg/kg/min, n=8) or a selective A2a antagonist CSC (8-(3-chlorostyryl) caffeine, 24 microg/kg/min, n=8) for 60 minutes. In protocol 2, after the sodium cromoglycate, while control group of rats (n=8) recevied a dextrose solution, treatment groups of rats were administered DPCPX (20 microg/kg/min, n=8) or CSC (24 microg/kg/min, n=8) infusion to block adenosine A1 and A2a receptors for 20 minutes before amitriptyline infusion. After pretreatment with adenosine antagonists, all rats were given a dose of 0.94 mg/kg/min of amitriptyline infusion during 60 minutes. Outcome measures were mean arterial pressure (MAP), heart rate (HR), QRS duration and survival rate.

In protocol 1, amitriptyline infusion significantly reduced MAP and prolonged QRS within 15 minutes. HR was not changed significantly during the experiments. While dextrose did not improve MAP and QRS prolongation, DPCPX or CSC administration developed a significant improvement in MAP compared to the dextrose group within 10 min (88.5 +/- 2.8%, 75.6 +/- 4.7% and 50.1 +/- 14.7%, p<0.01, p<0.05, respectively). Both DPCPX and CSC decreased QRS prolongation (p<0.05) and increased median survival time significantly (log-rank test, p<0.00001). In protocol 2, pretreatment with DPCPX or CSC prevented the reduction in MAP due to amitriptyline toxicity compared to rats administered dextrose infusion (99.5 +/- 2.6%, 102.4 +/- 2.6%, 81.8 +/- 5.4, p<0.01 at 30 min; 98.0 +/- 2.9%, 93.5 +/- 6.0%, 64.9 +/- 4.7, p<0.001, p<0.01 at 40 min, respectively). Pretreatment with DPCPX or CSC also prevented the QRS prolongation (p<0.05) and increased median survival time significantly (log-rank test, p<0.0001).

Adenosine antagonists were found to be effective in improving hypotension, QRS prolongation and survival time in our rat model of amitriptyline toxicity. Additionally, amitriptyline-induced cardiotoxicity was abolished by pretreatment with adenosine receptor antagonists. These results suggest that adenosine receptors may have a role in the pathophysiology of amitriptyline-induced cardiovascular toxicity. Adenosine A1 and A2a receptor antagonists may be promising agents for reversing amitriptyline-induced cardiovascular toxicity.