Dopamine-induced inhibition of prolactin release from cultured adenohypophysial cells: spare receptors for dopamine

There have as yet been few studies concerning the characteristics of receptor sites for substances which inhibit prolactin secretion. We have looked for the presence of spare receptors for dopamine using the approach of Nickerson, which utilizes a β-haloalkylamine, irreversible receptor blocking agent.Cultured adenohypophysial cells were washed before and after phenoxybenzamine (3 × 10^?8 ? 10^?6 M) pretreatment, and then incubated with dopamine for 4 hr. Increasing concentrations of phenoxybenzamine (10^?7 ? 10^?6 M) produced parallel shifts to the right of the subsequent dose-response curve for dopamine. However, there were no changes in the magnitude of the maximal response. The results indicate that phenoxybenzamine does irreversibly block receptors responsive to dopamine and that there are spare receptors for dopamine on prolactin cells.