Phospholipases and melatonin signal transduction in the ovine pars tuberalis.
The potential role of phospholipases in mediating melatonin-dependent inhibition of adenylyl cyclase was investigated in pars tuberalis (PT) cultures. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) stimulated the release of choline metabolites and increased the transphosphatidylation reaction. The calcium ionophore A23187 stimulated the release of arachidonic acid from cultures. These observations demonstrate phospholipase A and D activities within PT. Phosphatidic acid inhibited forskolin-stimulated production of cyclic AMP both in PT cells and in membrane preparations. This indicates that melatonin could inhibit adenylyl cyclase by increasing phosphatidic acid levels through activation of cellular phospholipases. Melatonin did not stimulate the release of arachidonic acid or choline from PT cultures, nor did it increase intracellular levels of hydrophobic second messengers or stimulate transphosphatidylation. Therefore melatonin does not stimulate phospholipase A and D pathways in PT cells. However, these pathways are present in the PT and their activation could potentially modulate the cellular actions of melatonin.
McNulty
S
S
Department of Anatomy, University of Cambridge, UK.
Morgan
P J
PJ
Thompson
M
M
Davidson
G
G
Lawson
W
W
Hastings
M H
MH
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002478:Cells, Cultured; D002794:Choline / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D005260:Female; D008246:Lysophospholipids / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000494:pharmacology / Q000502:physiology*; D008563:Membrane Lipids / Q000378:metabolism; D010712:Phosphatidic Acids / Q000494:pharmacology; D010740:Phospholipases / Q000502:physiology*; D010743:Phospholipids / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000502:physiology*; D015290:Second Messenger Systems; D012756:Sheep; D015398:Signal Transduction / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D008246:Lysophospholipids; D008563:Membrane Lipids; D010712:Phosphatidic Acids; D010743:Phospholipids; D005576:Colforsin; D016718:Arachidonic Acid; D000001:Calcimycin; D000242:Cyclic AMP; D010740:Phospholipases; D000262:Adenylyl Cyclases; D008550:Melatonin; D002794:Choline; D013755:Tetradecanoylphorbol Acetate