Effects of ergots on adenylate cyclase activity in the corpus striatum and pituitary

Adenylate cyclase activity was determined in homogenates of the corpus striatum and pituitary gland. Dopamine and several ergots stimulated cyclic AMP synthesis in the striatum, but no stimulation was seen in the pituitary gland. None of the ergots tested were as active as dopamine itself, and all were able to partially inhibit the dopamine-induced activation of adenylate cyclase. Lergotrile, a simple ergoline derivative which displays dopamine agonist activities in the pituitary gland and striatum, did not stimulate adenylate cyclase in either tissue. These findings show that the $\text{in vivo}$ dopaminergic activity of ergots is not reflected in the dopamine-dependent adenylate cyclase assay using either the corpus striatum or the pituitary gland. It is suggested that those dopamine receptors in the pituitary gland which mediate prolactin release are not associated with adenylate cyclase.