STIMULATORY EFFECT OF BOMBESIN ON PHOSPHOINOSITIDE METABOLISM IN THE RAT PINEAL-GLAND

The pineal gland is under complex peptidergic nervous control originat ing from hypothalamic nuclei. The daily rhythm of bombesin-like peptid e in the hypothalamus suggests that this neuropeptide, similarly as ot her neuropeptides, might be involved in modulation of the physiologica l activity of the pineal gland. In our experiments we studied the mech anism of signal transduction of bombesin in the isolated pineal glands of rats. The phosphoinositide signalling system was examined by measu ring P-32-labelling of phosphatidylinositol (PI), phosphatidylinositol phosphate (PIP) and phosphatidylinositol bisphosphate (PIP2), which r eflects phosphoinositide cycle activation. Bombesin induced a signific ant increase in P-32-labelling of PI, PIP and PIP2. The antagonist of this neuropeptide, (D-Phe(12)-Leu(14))-bombesin, suppressed the increa se in P-32-labelling of all phosphoinositides. Bombesin was without ef fect on cAMP dependent protein phosphorylation. The data indicate that bombesin activates the PI signalling system via specific receptors. ( C) 1997 Elsevier Science Ireland Ltd.