Dopaminergic regulation of prolactin and growth hormone synthesis in rat pituitary tumor cells

The dopaminergic regulation of prolactin (PRL) and growth hormone (GH) synthesis were studied in monolayer cultures of rat pituitary tumor (GH₃) cells. PRL synthesis could not be inhibited by dopamine at concentrations ranging from 10⁻⁹ to 10⁻⁵ M. Bromocriptine inhibited PRL synthesis only at the very high concentration of 10⁻⁵ M, and this effect was not reversible by metoclopramide. GH synthesis was inhibited by 10⁻⁶ and 10⁻⁵ M dopamine but not by bromocriptine, and the dopamine effect was blocked by metoclopramide. These results suggest the existence of a defective dopaminergic regulation of PRL and GH synthesis in GH₃ cells.