ARE 5-HT1A RECEPTORS INVOLVED IN THE CONTROL OF REFLEX BRADYCARDIA INDUCED BY INTRACORONARY INJECTION OF CONTRAST-MEDIUM IN HUMANS

Transient vagal bradycardia occurring during coronary arteriography (C A) immediately following intracoronary injection of ionic contrast med ium is believed to be a component of the von Bezold-Jarisch reflex (BJ ). Data obtained from experimental animals using buspirone (BSP) and o ther 5-HT1A receptor ligands suggest that these serotonergic receptors modulate the excitability of cardiac vagal motoneurones (CVM). This i s a preliminary investigation of the possible effects of BSP in alteri ng the bradycardia of patients submitted to CA for diagnostic purposes . Patients were divided into two age- and race-matched groups: control (C: N = 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 (B : N = 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 arrh ythmia acid patients requiring atropine were excluded. CA was performe d by a standard procedure using diatrizoate (MD-76(R)) as contrast age nt. The left and then the right coronary ostia were selectively cathet erized and 8 mi of contrast medium was injected (over a period of 3 se c), HR was measured from ECG tracings before and after contrast inject ion into the left (LC) and right (RC) coronary arteries. Peak bradycar dia was measured as the longest R-R interval during the first 15 sec a fter the injection minus the pre-injection R-R value, and reported as Delta R-R. Group B patients received BSP tablets 48 and 24 h before th e examination (30 mg/day po). There was no statistically significant d ifference (P > 0.05) in bradycardia between groups (C: LC = -147 +/- 2 3, RC = -155 +/- 25; B: LC = -143 +/- 44, RC = -234 +/- 56 msec). Thes e results suggest that, in contrast to experimental animals, the centr al 5-HT1A receptors of humans are not relevant for modulating the exci tability of CVM in the BJ reflex. However, since drugs and diseases ca n affect the responses, further studies are necessary to clarify this issue.