VIP enhances TRH-stimulated prolactin secretion of pituitary tumours. Studies with 31P NMR.
Intravenous thyrotrophin releasing hormone (TRH) caused a 6.5-fold increase in plasma prolactin (PRL) in rats carrying implanted pituitary tumours. Vasoactive intestinal polypeptide (VIP) had no effect, but TRH given after VIP raised TRH stimulated secretion 13-fold above basal. 31P NMR spectroscopy showed that VIP caused a decrease in high energy metabolites (depleted phosphocreatine, elevated inorganic phosphate and lowered intracellular pH). TRH alone caused a similar but smaller effect; given after VIP, it caused no detectable depletion. We suggest that the changes in high energy metabolite concentrations reflect increased cellular energy consumption consistent with a priming process (stage 1) in PRL secretion, followed by hormone release (stage 2). VIP induces stage 1 whereas RTH induced both stages.
D000818:Animals; D004347:Drug Interactions; D005260:Female; D009682:Magnetic Resonance Spectroscopy; D009368:Neoplasm Transplantation; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects
D014660:Vasoactive Intestinal Peptide; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin