[Dopamine-induced up-regulation of alpha 2-adrenoceptors in crude synaptic membranes of rat brain].

After cerebral cortical membranes were incubated with 0.1-100 microM of dopamine (DA) in 50 mM Tris-HCl buffer (pH 7.7) at 37 degrees C for 30 min, [3H] clonidine binding to alpha 2-receptors was increased in a concentration-dependent manner without changing [3H] WB4101 and [3H] DHA binding to alpha 1- and beta-receptors, respectively. Scatchard analysis of [3H] clonidine binding to cortical membranes showed that DA increased the Bmax in both high- and low-affinity components. The increasing effect of DA on [3H] clonidine was dependent on incubation time and temperature, and it was antagonized by pimozide and cis-flupenthixol. The addition of GTP produced a reduction in DA-induced elevation in [3H] clonidine binding, while that of cyclic AMP did not affect the effect of DA. DA and Mn2+, though both of them increased [3H] clonidine binding, appeared to act at a different site in the membrane. Furthermore, the DA-induced increase in [3H] clonidine was found uniformly in membranes prepared from 7 other regions of the rat brain. These results suggested that DA regulates specifically alpha 2-receptor density by stimulating D1-receptors and/or via other mechanism(s).