INTERACTION OF METAIODOBENZYLGUANIDINE WITH CARDIOACTIVE DRUGS - AN IN-VITRO STUDY

Metaiodobenzylguanidine (MIBG), an analogue of noradrenaline, is used to explore the functional integrity of sympathetic nerve endings in th e human heart. Various drugs inhibit noradrenaline transport systems a nd may block the uptake of MIBG. As in vivo studies of the effect of t hese drugs on myocardial [I-123]MIBG uptake are often difficult to per form, we used an in vitro human blood platelet model for this purpose. A platelet preparation from healthy volunteers was incubated with [I- 125]MIBG alone or different concentrations of drugs currently used in cardiology. Labetalol and propranolol inhibited [I-125]MIBG uptake, wh ereas all other drugs tested (other beta-blockers, calcium inhibitors, digoxin and amiodarone) had no effect even at doses exceeding 50 mu M . The labetalol dose inhibiting 50% of [I-125]MIBG uptake was lower th an the plasma concentration of this drug in treated patients, whereas the propranolol dose was higher. This in vitro study of the effect of- drugs on MIBG uptake by human blood platelets is predictive of their i n vivo effect on myocardial uptake of [I-123]MIBG in treated patients, provided that plasma concentration is taken into account.