Plasticity of cardiovascular nucleoside transporters following chronic dipyridamole treatment

Dipyridamole (37.5 mg/kg, s.c., b.i.d.), a potent inhibitor of nucleoside transport, was administered to guinea pigs for 14 days in order to investigate the effects of: 1) chronic dipyridamole treatment on [3H]nitrobenzylthioinosine ([3H]NBMPR) binding: 2) chronically released endogenous adenosine on adenosine A1 and A2 receptors. Comparisons of the binding capacities (Bmax) and equilibrium dissociation constants (Kd) in vehicle-treated (VTA) and dipyridamole-treated animals (DTA), revealed a 100 percent increase in Kd of [3H]NBMPR binding in the kidney of DTA but not in heart or brain. There were no changes in adenosine A1 or A2 receptor activities in kidney and brain as measured by [3H]R-phenylisopropyladenosine and [3H]5'-N-ethyl-carboxamidoadenosine binding, respectively. The data suggest that cardiac and central nucleoside transporters may be either less susceptible to chronic dipyridamole administration or have a different adaptive mechanism. Also, endogenous adenosine, which may be chronically released upon dipyridamole treatment, has no effect on adenosine receptors.