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

The melanotrope cells in the pituitary gland of Xenopus laevis are innervated by neurons containing neuropeptide Y (NPY). In the present study, the mechanism of action of NPY on the melanotropes has been investigated. NPY inhibited in vitro secretion from melanotropes in intact neurointermediate lobes as well as from isolated, single melanotropes. Inhibition of secretion from neurointermediate lobes was mimicked by the 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 potent than [Leu(31),Pro(94)]NPY. Studies on isolated cells revealed that NPY and its analogues inhibited the occurrence of intracellular Ca2+ oscillations with the same potency as they inhibited secretion from isolated 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 secretion from Xenopus melanotropes by inhibiting cyclic AMP-dependent spontaneous Ca2+ oscillations through a Y-1-like receptor.