Effect and site of action of hypothalamic neuropeptides on prolactin release in sheep

Gregory B. Thomas, James T. Cummins, Nicola Griffin, Iain J. Clarke

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In an attempt to identify a physiological prolactin-releasing factor in the sheep, ovariectomized ewes were given intracarotid injections (10-8-10-7 mol/animal) of thyrotropin-releasing hormone (TRH), vasoactive intestinal polypeptide (VIP), peptide histidine-isoleucine amide (PHI), oxytocin (OT), arginine vasopressin (AVP), substance P (SP), bombesin (BB), neurotensin (NT) and neuropeptide Y (NPY). Administration of TRH, AVP, NT and OT resulted in immediate and significant increases in plasma prolactin concentrations, the greatest stimulatory effect being obtained after TRH; other peptides had no effect in ovariectomized hypothalamo-pituitary intact ewes. AVP, NT and OT failed to release prolactin in ovariectomized ewes that had been subjected to hypothalamo-pituitary disconnection (HPD). Injection of TRH (3 × 10-9–3 × 10-7 mol/animal) resulted in a significant dose-dependent increase in plasma prolactin concentrations in ovariectomized HPD ewes. These results suggest that (1) AVP, NT and OT may act via the hypothalamus to regulate prolactin secretion in hypothalamo-pituitary intact ewes; (2) VIP, PHI, SP, BB and NPY appear to have no direct roles at the pituitary level to control prolactin secretion in sheep, and (3) TRH stimulates prolactin secretion in ovariectomized ewes by a direct pituitary action.

Original languageEnglish
Pages (from-to)252-257
Number of pages6
Issue number3
Publication statusPublished - 1 Jan 1988
Externally publishedYes


  • Arginine vasopressin
  • Bombesin
  • Neuropeptide Y
  • Neurotensin
  • Oxytocin
  • Peptide histidine-isoleucine amide
  • Prolactin
  • Prolactin-releasing factor
  • Substance P
  • Thyrotropin-releasing hormone
  • Vasoactive intestinal polypeptide

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