NEUROPEPTIDE-Y INHIBITS CA2-AMP, AND SECRETION IN MELANOTROPE CELLS OF XENOPUS-LAEVIS VIA A Y-1 RECEPTOR( OSCILLATIONS, CYCLIC)

The melanotrope cells in the pituitary gland of Xenopus laevis are inn ervated by neurons containing neuropeptide Y (NPY). In the present stu dy, the mechanism of action of NPY on the melanotropes has been invest igated. NPY inhibited in vitro secretion from melanotropes in intact n eurointermediate lobes as well as from isolated, single melanotropes. Inhibition of secretion from neurointermediate lobes was mimicked by t he NPY analogues PYY and [Leu(31), Pro(34)]NPY, whereas NPY(13-36) was inactive. Secretion from isolated melanotropes was inhibited by [Leu( 31), Pro(34)]NPY and NPY (13-36), but NPY(13-36) was 10-fold less pote nt than [Leu(31),Pro(94)]NPY. Studies on isolated cells revealed that NPY and its analogues inhibited the occurrence of intracellular Ca2+ o scillations with the same potency as they inhibited secretion from iso lated cells. In addition to inhibiting basal secretion and spontaneous Ca2+ oscillations, NPY inhibited the basal production of cyclic AMP. On the basis of these results it is proposed that NPY inhibits secreti on from Xenopus melanotropes by inhibiting cyclic AMP-dependent sponta neous Ca2+ oscillations through a Y-1-like receptor.