Neuropeptide Y receptor in pig spleen: binding characteristics, reduction of cyclic AMP formation and calcium antagonist inhibition of vasoconstriction.
Specific, high-affinity binding sites for 125I-porcine neuropeptide Y (NPY) were demonstrated in membranes from the pig spleen. The equilibrium dissociation constant (KD) of the receptor 125I-NPY complex was 532 +/- 87 pM and the maximal number of specific binding sites (Bmax) 23 +/- 3 fmol/mg protein. The Scatchard plot for 125I-NPY binding under equilibrium conditions showed a best-fit to a straight line, whereas the dissociation appeared biphasic. 125I-NPY binding was unaffected by adrenoceptor antagonists and was inhibited by the guanosine triphosphate (GTP) analogue guanylylimidodiphosphate, suggesting regulation by a GTP binding protein. A series of NPY analogues showed a good correlation between binding, inhibition of forskolin-induced cyclic adenosine monophosphate (cAMP) formation and vasoconstrictor activity in vivo. A large carboxyl terminal portion of NPY and the carboxyl terminal amide were essential for binding, inhibition of cAMP formation and vasoconstrictor effects. The NPY fragment 13-36, which has been reported to act only on prejunctional NPY receptors, showed only a 10-fold lower potency than NPY-(1-36) both in binding to splenic membranes and vasoconstrictor activity in vivo. Phenylephrine increased phosphatidyl inositol turnover whereas NPY-(1-36) or -(13-36) did not induce formation of inositol phosphates. The calcium antagonists felodipine and nifedipine attenuated the splenic vasoconstrictor response to NPY in vivo but not the NPY-evoked inhibition of cAMP accumulation or the specific binding of 125I-NPY.(ABSTRACT TRUNCATED AT 250 WORDS)
Lundberg
J M
JM
Department of Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Hemsén
A
A
Larsson
O
O
Rudehill
A
A
Saria
A
A
Fredholm
B B
BB
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D000242:Cyclic AMP / Q000096:biosynthesis*; D006801:Humans; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D009478:Neuropeptide Y / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D017476:Receptors, Neuropeptide Y; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013154:Spleen / Q000378:metabolism*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects*
D002121:Calcium Channel Blockers; D007457:Iodine Radioisotopes; D009478:Neuropeptide Y; D010716:Phosphatidylinositols; D017476:Receptors, Neuropeptide Y; D017981:Receptors, Neurotransmitter; D001285:Atropine; D000242:Cyclic AMP