Evidence for the Autoregulation of Hormone Secretion by Prolactin*

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Abstract
The cells from the 2B8 clonal strain of pituitary cells which previously have been reported to produce only PRL were incubated with varying amounts of ovine PRL (oPRL) ranging from 0.01–1000 ng/ml. After 1 h, significantly less PRL was measured in culture media from cells incubated with all doses of oPRL employed. This inhibition was dose related. The cells were rinsed five times with Hank's balanced salt solution and subsequently placed into PRL-free media for an additional hour. Hypersecretion of hormone occurred from those cells previously exposed to 1–1000 ng/ml oPRL. The PRL in the media from cells previously exposed to 0.01–0.1 ng/ml was similar to that in the control culture. In some experiments, the cellular concentration of PRL was determined at the end of each of the two 1-h incubation periods. After the initial exposure to oPRL, an increase in intracellular hormone was observed only in those groups incubated with 1–1000 ng/ml oPRL. In contrast, after the cells were rinsed and placed into PRL-free medium, the cellular concentration of PRL was unchanged in all groups except the group previously exposed to 100 ng/ml oPRL. These data indicate that PRL can inhibit its own secretion through direct action on the lactotrophs of the anterior pituitary gland.