Comparative study of the dopamine-sensitive adenylate cyclase in the striatum and hypothalamus of rat brain

Stimulation by dopamine of adenylate cyclase in homogenates of rat brain striatum was enhanced in the presence of ATP (0.6--3 mM) and GTP (10--100 micrometer). The stimulation by dopamine appeared to be the result of its antagonism of inhibition of adenylate cyclase by GTP or higher concentrations of ATP. Stimulation of the enzyme by dopamine was also dependent on MgCl2, and was maximal at MgCl2 concentrations of at least two fold excess over ATP. While ATP did not inhibit adenylate cyclase in homogenates of the ventral hypothalamus, GTP (10--100 micrometer) significantly stimulated it. Dopamine stimulated the adenylate cyclase in the hypothalamus. This action was blocked by chlorpromazine (10 micrometer) and phentolamine (100 micrometer) but not by an analogue of chlorpromazine having no neuroleptic activity or by propranolol (100 micrometer).