Thyrotropin-releasing hormone stimulates porcine melanotrope cells in primary culture.
The action of thyrotropin-releasing hormone (TRH) on melanotrope cells maintained in primary culture was studied with biochemical and electrophysiological techniques. TRH effects on polyphosphoinositide (PPI) breakdown was measured in [3H]myoinositol labelled cells maintained in suspension for 24 hours or in primary culture. TRH (50 nM) or its potent analogue (3Me-His2)-TRH increased total PPI levels by 50-125% in separate experiments after 30 min of treatment whereas corticotropin-releasing hormone (CRF) was without effect. The effect of TRH was dose-dependent (ED50 = 5 nM), the maximal effect being reached with 50 nM TRH. Using the patch-clamp technique in the cell-attached configuration spikes were recorded extracellularly. In 6 of the 13 cells tested, (3Me-His2)-TRH (10 nM) elicited an increase in the spontaneous spiking rate. Furthermore, TRH (50 nM) increased melanocyte-stimulating hormone (alpha-MSH) secretion 2-fold after 8 h of treatment. These results suggested that TRH activated phospholipase C and electrical activity in melanotrope cells; the resulting phosphoinositide breakdown and increase in intracellular free Ca2+ ultimately led to a stimulation of hormone release.
Trouslard
J
J
Laboratoire de Physiologie Générale (URA D0309 CNRS), Université Louis Pasteur, Strasbourg, France.
Loeffler
J P
JP
Demeneix
B A
BA
Feltz
P
P
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D008544:Melanocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000502:physiology*; D018025:Receptors, Thyrotropin-Releasing Hormone; D013403:Sugar Phosphates / Q000378:metabolism*; D013552:Swine; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D007295:Inositol Phosphates; D017981:Receptors, Neurotransmitter; D018025:Receptors, Thyrotropin-Releasing Hormone; D013403:Sugar Phosphates; D013973:Thyrotropin-Releasing Hormone