Distinction of NPY receptors in vitro and in vivo. I. NPY-(18-36) discriminates NPY receptor subtypes in vitro.

We studied the possibility of multiple neuropeptide Y (NPY) receptor subtypes. NPY-stimulated Ca2+ mobilization in human erythroleukemia (HEL) cells was used to screen a number of NPY analogues. The potencies of three of these analogues [peptide YY (PYY), [D-Tyr-36]NPY, and NPY-(18-36)] were compared with that of NPY in the following model systems: Ca2+ mobilization and inhibition of adenosine 3',5'-cyclic monophosphate accumulation in HEL cells, potentiation of vasoconstriction in the isolated rabbit ear artery, reduction of cutaneous microvascular perfusion in the rat digit, and inhibition of [3H]serotonin release in rat brain. In each of the five models, PYY was a full agonist that exhibited a similar or slightly higher potency than NPY, whereas [D-Tyr-36]NPY and NPY-(18-36) were partial agonists with lower potencies: NPY-(18-36) had a lower potency and efficacy than [D-Tyr-36]NPY in HEL cells and the rabbit ear artery, but was more effective than [D-Tyr-36]NPY for constricting cutaneous microvasculature and inhibiting serotonin release. Because of its weak partial agonism, we also tested NPY-(18-36) as an antagonist of NPY-stimulated Ca2+ mobilization in HEL cells. NPY-(18-36) shifted the NPY concentration-response curve to the right with a KB affinity value of 297 nM. In summary, [D-Tyr-36]NPY and NPY-(18-36) are partial agonists, the relative potency of which varies between systems. These data demonstrate the presence of multiple NPY receptor subtypes. We propose a modified classification scheme of NPY receptor subtypes.