Inhibition of Prolactin Secretion and Synthesis by Dopamine, Noradrenaline and Pilocarpine in Cultured Rat Pituitary Tumour Cells

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Abstract
Clonal strains of rat pituitary tumour cells (GH3‐cells) synthesize and secrete prolactin into a chemically defined culture medium. Short time treatment (0.5–2 hrs) of cell cultures with noradrenaline (10‐3 M) and dopamine (10‐3 M) reduced the spontaneous secretion of prolactin by 50 % and 30 %, respectively, while pilocarpine (10‐3 M) had no effect. Long‐term treatment (20 hrs) with noradrenaline (10‐3 M) or with pilocarpine (10‐3 M) inhibited prolactin synthesis by 45 % and 65 % of control cultures, respectively, Neither compounds affected cell growth. The inhibitory effect of noradrenaline, but not that of pilocarpine, was completely reversed 4 hrs after cessation of treatment. Adrenaline, dopamine and acetylcholine in concentrations up to 10‐3 M did not change prolactin synthesis. In contrast thyroliberin treatment (2×10‐8 M) caused a 45 % increase in prolactin secretion, and resulted in a 40 % increase in hormone synthesis after treatment for 20 hrs. It is concluded that both noradrenaline and dopamine are able to inhibit prolactin secretion. Prolactin synthesis could be inhibited by noradrenaline and pilocarpine. However, only the effect of noradrenaline is easily reversible on cessation of treatment.