Neurotensin stimulation of prolactin secretion in vitro

Neurotensin stimulated prolactin (PRL) secretion from incubated rat hemipituitaries. Under the same conditions, the secretion of growth hormone, luteinizing hormone and follicle-stimulating hormone was not affected. The stimulation of PRL was dose dependent, with an apparent affinity of neurotensin of 0.56 +/- 0.12 nM and a maximal stimulation of 56.5 +/- 6.7%. The effect of neurotensin seemed to be independent of that of other PRL releasing factors. In fact, the stimulation of neurotensin and thyrotropin-releasing hormone (TRH) and also of neurotensin and vasoactive intestinal peptide were additive. The action of neurotensin on PRL cells does not appear to involve either dopamine or gamma-aminobutyric acid receptors, since antagonists to these transmitters were found ineffective on PRL stimulation by neurotensin. PRL-releasing factor activity distinct from TRH has been described in fractions of hypothalamic extracts. Neurotensin, which is present in high amounts in the median eminence and has been measured in the adenohypophysis, is a candidate as a physiological PRL-releasing factor distinct from TRH.