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Neuropeptide Y (NPY) binds to a family of G-protein coupled receptors termed Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). The use of various receptor subtype-selective agonists and antagonists has facilitated identification of the receptor subtypes responsible for mediating many of the biological effects of NPY. For example, the potent orexigenic activity of NPY is believed to be mediated by both the Y(1) and Y(5) receptor subtypes. Several selective Y(5) receptor agonists that stimulate food intake in rodents are available, but no selective Y(1) receptor agonist has been reported. We have identified several NPY analogs that bind the NPY Y(1) receptor with high affinity and exhibit full agonist activity, measured as inhibition of forskolin-stimulated cAMP production in cells expressing the cloned NPY Y(1) receptor. [D-Arg(25)]-NPY, [D-His(26)]-NPY, Des-AA(10--17)[Cys(7,21),Pro(34)]-NPY, Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac)]-NPY, Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac),Pro(34)]-NPY, Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac),D-His(26)]-NPY and Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac),D-His(26), Pro(34)]-NPY bind the NPY Y(1) receptor with K(i) values of 0.9 +/- 0.2, 2.0 +/- 0.3, 0.2 +/- 0.05, 0.7 +/- 0.1, 0.2 +/- 0.01, 2.2 +/- 0.3, and 1.2 +/- 0.3 nM, respectively, and inhibit forskolin-stimulated cAMP production with EC(50) values of 0.2 +/- 0.02, 0.5 +/- 0.04, 0.3 +/- 0.03, 0.5 +/- 0.05, 0.4 +/- 0.16, 5.3 +/- 0.32, and 5.1 +/- 0.97 nM, respectively. These peptides are highly selective for the NPY Y(1) receptor relative to the NPY Y(2), Y(4), and Y(5) receptors. [D-Arg(25)]-NPY, [D-His(26)]-NPY and Des-AA(11--18)[Cys(7,21), D-Lys(9)(Ac),D-His(26),Pro(34)]-NPY stimulate food intake dose-responsively in Long-Evans rats for at least 4 h after intracerebroventricular administration. Although the involvement of Y(1) receptors in several physiological activities, such as vasoconstriction and anxiolysis, remains to be investigated, adequate tools are now available.

We previously showed that the somatostatin receptor 5 (sst(5))-preferring agonist BIM-23052 injected intracisternally (i.c. ; 0.8 nmol/rat) stimulated gastric emptying of a non-nutrient meal in conscious rats. In this study, we investigated the neural pathways and specificity of BIM-23052 action. BIM-23052 (0.4, 0.8, and 1.2 nmol/rat i.c.) stimulated gastric transit; values of gastric emptying were 65.5 +/- 6.5, 77.4 +/- 5.3, and 77.7 +/- 1.9%, respectively, compared with 43.2 +/-3.2% in i.c. saline group. Intravenous injection of BIM-23052 (0.8 nmol/rat) had no effect. BIM-23052 (0.8 nmol/rat i.c.) action was prevented by subdiaphragmatic vagotomy or atropine. Medullary thyrotropin-releasing hormone (TRH) is known to play a physiological role in the vagal stimulation of gastric motor function. TRH receptor antisense oligodeoxynucleotides injected i.c. with a regimen that prevented TRH (0.3 nmol/rat i.c.)-induced enhanced gastric emptying did not influence BIM-23052 stimulatory action. Somatostatin-28 (0.2-1.2 nmol/rat i.c.), which possesses a higher affinity than somatostatin-14 for sst(5), and the cyclic octapeptide des-AA(1,2,4,5,12,13)[D-Trp(8)]somatostatin (0.2-1.2 nmol/rat i.c.), an oligo-somatostatin analog that shares similar brain actions as somatostatin-28, induced a dose-related stimulation of gastric emptying. Somatostatin-14 and the preferring peptide agonists for sst(1), CH-275; sst(2), DC-32-87; sst(3), BIM-23056 and L-796,778; and sst(4), L-803,087 had no significant effect on gastric emptying when injected i.c. at 0.8 nmol/rat. These results show that BIM-23056 injected i.c. acts in the brain independently from medullary TRH to induce a vagal cholinergic stimulation of gastric emptying through the sst(5) receptor subtype.

The effect of the corticotropin-releasing factor (CRF) receptor antagonists astressin and D-Phe CRF(12-41) injected i.v. on CRF-induced delayed gastric emptying (GE) was investigated in conscious rats. Gastric transit was assessed by the recovery of methyl cellulose/phenol red solution 20 min after its intragastric administration. The 55% inhibition of GE induced by CRF (0.6 microgram i.v.) was antagonized by 87 and 100% by i.v. astressin at 3 and 10 microgram, respectively, and by 68 and 64% by i.v. D-Phe CRF(12-41) at 10 and 20 microgram, respectively. CRF (0.6 microgram)-injected intracisternally (i.c.) induced 68% reduction of GE was not modified by i.v. astressin (10 microgram) whereas i.c. astressin (3 or 10 microgram) blocked by 58 and 100%, respectively, i.v. CRF inhibitory action. Abdominal surgery with cecal manipulation reduced GE to 7.1 +/- 3.1 and 27.5 +/- 3.3% at 30 and 180 min postsurgery, respectively, compared with 40.3 +/- 4.3 and 59.5 +/- 2.9% at similar times after anesthesia alone. Astressin (3 microgram i.v.) completely and D-Phe CRF(12-41) (20 microgram i.v.) partially (60%) blocked surgery-induced gastric stasis observed at 30 or 180 min. The CRF antagonists alone (i.v. or i.c.) had no effect on basal GE. These data indicate that CRF acts in the brain and periphery to inhibit GE through receptor-mediated interaction and that peripheral CRF is involved in acute postoperative gastric ileus; astressin is a potent peripheral antagonist of CRF when injected i.v. whereas i.c. doses >/=3 microgram exert dual central and peripheral blockade of CRF action on gastric transit.

The influence of central injection of a new corticotropin releasing factor (CRF) antagonist, astressin, [cyclo(30-33)[D-Phe12,Nle21,38,Glu30,Lys33]r/ hCRF12-41)], on exogenous and endogenous CRF-induced gastric ileus and stimulation of bowel discharges was investigated in conscious rats. Intracisternal (ic) CRF (0.6 microg) reduced gastric emptying of a noncaloric solution to 17.1 +/- 4.9% compared with 50.1 +/- 4.6% in control group injected i.c. with vehicle. Astressin (1,3 and 10 microg, i.c.) dose dependently prevented ic CRF-induced delayed gastric emptying by 33, 100 and 100%, respectively, and had no effect on basal gastric emptying. Abdominal surgery with cecal manipulation (1 min) reduced gastric emptying to 19.8 +/- 5.5% 3 hr postsurgery compared with 59.9 +/- 5.2% after anesthesia alone plus i.c. vehicle. Astressin (1,3 and 10 microg, i.c.) prevented postoperative gastric ileus by 56, 93 and 92%, respectively. Intracerebroventricular CRF (0.6 microg) and water-avoidance stress stimulated pellet output (number/60 min) to 5 +/- 1 and 11 +/- 2, respectively, compared with no fecal pellet output after i.c.v. vehicle and no exposure to stress. Astressin (3 and 10 microg, i.c.v.) blocked exogenous CRF action by 47 and 63%, respectively, and colonic response to stress by 0 and 54%, respectively. These data indicate that astressin injected into the CSF at low doses (1-10 microg) has an antagonistic action against CRF and stress-related alterations of gastrointestinal motor function, without an intrinsic effect in these in vivo systems. Astressin may be a useful tool to explore functional CRF-dependent physiological pathways in specific brain nuclei.