EFFICACY OF INTRAVENOUS GRANISETRON IN SUPPRESSING THE BRADYCARDIA AND HYPOTENSION ASSOCIATED WITH A RABBIT MODEL OF THE BEZOLD-JARISCH REFLEX

This study investigated whether granisetron, a 5-HT3 receptor antagoni st, can alter the Bezold-Jarisch reflex (i.e., hypotension and inappro priate heart rate slowing). A hemorrhagic rabbit model that has been s hown to induce the Bezold-Jarisch reflex was used. In 11 rabbits (3.8 kg), catheters were placed in the carotid arteries one day before expe rimental hemorrhage. On the day of the study, the rabbits were given i ntravenous granisetron (50 mu g/kg) or an equal volume of saline. Five minutes after administration of granisetron or saline, hemorrhage was induced by continuous blood withdrawal at 5 mL/min and blood pressure (BP) and heart rates were obtained at frequent intervals until systol ic BP declined to 80 mmHg. Six rabbits received saline and five granis etron. An average of 77.6 mL +/- 16.4 mL of blood was removed in the g roup receiving granisetron (compared with 56.5 mL +/- 13.1 mL for the saline group) before achieving the target systolic BP of 80 mmHg. The group receiving granisetron demonstrated the same ability to increase their heart rate from baseline as the saline group. However, the grani setron group had a final heart rate that was closer to their maximal h eart rate than the saline group. In this animal model, granisetron rt as significantly more effective at preventing inappropriate heart rate slowing and allowed significantly more blood to be removed before rea ching the target blood pressure. This implies that granisetron may be effective in preventing vasovagal syncope, although further study shou ld be carried out to verify these potentially interesting findings.