Pituitary lactotrophs: endocrine, paracrine, juxtacrine, and autocrine interactions.

The synthesis and release of PRL by the lactotrophs is subjected to multiple regulators that are classified into four categories: endocrine, paracrine, juxtacrine, and autocrine. Endocrine agents originate from the hypothalamus, gonads, and the posterior pituitary. Paracrine factors are produced by cells of the intermediate and anterior lobes. Juxtacrine transmitters arise from extracellular matrix and cells adjacent to the lactotrophs. Autocrine agents are synthesized by the lactotrophs themselves. Consequently, the overall secretory activity of the lactotrophs reflects a balance between local and distant releasing and inhibiting factors.