Are 5-HT1A receptors involved in the control of reflex bradycardia induced by intracoronary injection of contrast medium in humans?

RESUMO

Transient vagal bradycardia occuring during coronary arteriography (CA) immediately following intracoronary injection of ionic contrast medium is believed to be a component of the von Bezold-Jarisch reflex (BJ). Data obtained from experimental animals using buspirone (BSP) and other 5-HT1A receptor ligands suggest that these serotonergic receptors modulate the excitability of cardiac vagal motoneurones (CVM). This is a preliminary investigation of the possible effects of BSP in altering the bradycardia of patients submitted to CA for diagnostic purpose. Patients were divided into two age-and racematched groups control (CN=45, age 58.6 + 1.6 years, mean arterial blood pressure (MAP) 109 + 2.4 mmHg, heart rate (HR) 79 + 2.9 bpm) and BSP-treated (BN=14, age 58.9 + 2.1 years, MAP 111 + 4.5 mmHg, HR 76 + 3.4 bpm). The prevalent underlying pathology was coronary artery disease. Patients with acute angina, congestive heart failure, symptomatic arrhythmia and patients requiring atropine were excluded. CA was performed by a standard procedure using diatrizoate (MD-76() as contrast agent. The left and then the right coronary ostia were selectively catheterized and 8 ml of contrast medium was injected (over a period of 3 sec). HR was measured from ECG tracing before and after contrast injection into the left (LC) and right (RC) coronary arteries. Peak bradycardia was measured as the longest R-R interval during the first 15 sec after the injection minus the pre-injection R-R value, and reported as deltaR-R. Group B patients received BSP tablets 48 and 24 h before the examination (30 mg/day po). There was no statistically significant difference (P>0.05) in bradycardia between groups (CLC=-147 + 23,RC=-155+25; BLC=-143 + 44,RC=-234 + 56 msec). These results suggest that, in contrast to experimental animals, the central 5-HT1A receptors of humans are not relevant for modulating the excitability of CVM in the BJ reflex. However, since drugs and diseases can affect the responses, further studies are necessary to clarify this issue.