Activation of somatostatin receptor subtype 2 inhibits acid secretion in rats

Somatostatin is a potent inhibitor of gastric acid secretion. Recently, at least five distinct somatostatin receptor subtypes (SSTR) have been characterized and evaluated using relatively selective peptide analogues of somatostatin. We sought to determine which somatostatin receptor subtypes are involved in peripheral regulation of gastric acid secretion. Fasted, male Sprague-Dawley rats were anesthetized and were implanted with a double-lumen cannula in the stomach. Acid secretion was measured in gastric samples collected every 10 min by backtitration to pH 7. After a 30-min basal period, a 2-h intravenous infusion of pentagastrin (24 micrograms.kg-1.h-1 i.v.) was started. During the second pentagastrin hour, a 1-h intravenous infusion of either vehicle (0.1% canine serum albumin in 0.9% saline) or somatostatin receptor agonists was begun. The somatostatin receptor agonists included peptides with relative specificity for SSTR1-5 (somatostatin-14; 10 nmol.kg-1.h-1); SSTR2, SSTR3, and SSTR5 [SMS-(201-995); 10 nmol.kg-1.h-1]; SSTR2 (1-1,000 nmol.kg-1.h-1); SSTR3 (10-1,000 nmol.kg-1.h-1); and SSTR5 (10-1,000 nmol.kg-1.h-1). The SSTR2 agonist decreased pentagastrin-stimulated acid secretion dose dependently, from 82 +/- 7% of maximum acid output at 1 nmol.kg-1.h-1 to 4 +/- 7% of maximum at 100 nmol.kg-1.h-1. At 10 nmol.kg-1.h-1, the SSTR2 agonist inhibited acid secretion (40 +/- 7% of maximum) similarly to somatostatin (37 +/- 4% of maximum) and SMS-(201-995) (31 +/- 4% of maximum). The SSTR2 agonist inhibited acid secretion approximately 10- to 100-fold more potently than either the SSTR3 or the SSTR5 agonist. These results indicate that somatostatin regulates gastric acid secretion by activation of SSTR2 receptors.

Interaction of galanin fragments with galanin receptors on isolated smooth muscle cells from guinea pig stomach: identification of a novel galanin receptor subtype

From structure-function studies it has been proposed that two subtypes of receptors may mediate galanin's actions in the gastrointestinal tract and other tissues and their effects can be either direct or neurally mediated. We have recently demonstrated that isolated gastric smooth muscle cells possess high-affinity galanin receptors, activation of which increases AMP and causes relaxation. Because this cell system contains no neural elements, contains a single class of galanin receptors and allows binding to be correlated with function, it is a good system to investigate peptide requirements for cell activation. Porcine galanin (p-Gal) and rat galanin (r-Gal) were equipotent to the NH2-terminal fragments r,p-Gal(1-10), r,p-Gal(1-15), r,p-Gal(1-20), p-Gal(2-29) and p-Gal(3-29) at inhibiting binding of 125I-galanin to gastric smooth muscle cells from guinea pig (Kd 5-8 nM). The midmolecule fragment p-Gal(9-25) and the long COOH-terminal fragment r-Gal(9-29) were equipotent and 25-fold less potent than p-Gal. Acetylation of r-Gal(9-29) increased potency to that of p-Gal. The short COOH-terminal fragment, p-Gal(21-29) and r-Gal(21-29), had very low affinity (Kd 3 microM). Each peptide alone (1 microM) caused no effect on cell length, but inhibited carbachol-induced contraction. The inhibition was 81% to 92% for r-Gal or p-Gal, r,p-Gal(1-10), r,p-Gal(1-15), r,p-Gal(1-20), p-Gal(2-29), p-Gal(3-29) and Ac-r-Gal(9-29); 47% for p-Gal(9-25) and r-Gal(9-29); and 16% to 17% for p-Gal(21-29).(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of feeding inhibition by neuromedin B using a selective receptor antagonist

The ability of a selective neuromedin B receptor antagonist, D-Nal-cyclo[Cys-Tyr-D-Trp-Orn-Val-Cys]-Nal-NH2 (BIM-23127), to block suppression of food intake produced by the mammalian bombesin-like peptides neuromedin B and neuromedin C was examined. BIM-23127 completely blocked suppression of intake produced by neuromedin B but not by neuromedin C. These results suggest an independent role for neuromedin B receptors in suppression of food intake by bombesin-like peptides and demonstrate the utility of this group of antagonists for in vivo experiments.

Specific inhibition of rat pancreatic insulin or glucagon release by receptor-selective somatostatin analogs

A group of new peptide ligands displaying high selectivity for binding to somatostatin receptor subtypes 2, 3 or 5 have been used to characterize somatostatin receptor involvement in the inhibition of glucagon secretion in rats. It was found that NC-8-12 and DC-25-100, which have high affinity for SSTR2 and much less affinity for the type 5 receptor, were by far the most potent inhibitors of glucagon secretion with EC50s of 48 and 18 nmole, respectively, relative to somatostatin itself (EC50 131 nmole). These two analogs were actually much less potent than somatostatin in inhibiting glucose-stimulated insulin release. In contrast, DC-23-99 (a type 5 receptor selective analog), which was previously found to be a more potent inhibitor of insulin secretion than somatostatin, had considerably less potent (EC50 410 nmole) effects on glucagon release. The SSTR3-specific ligands, DC-25-12 and DC-25-20, were not effective at the doses tested. The differing spectra of activities of these analogs suggest that inhibition of insulin and glucagon secretion in rats is mediated by entirely different somatostatin receptor populations.

Gastrin releasing peptide-preferring bombesin binding sites in human lung

Characterization of bombesin binding sites in healthy human lung was performed through direct binding techniques. There was limited binding in the absence of trypsin and chymotrypsin inhibitors, suggesting important activities of both enzymes in human lung and/or increased sensitivity of the bombesin sites toward them. In human lung membranes, bombesin, gastrin releasing peptide (GRP) and GRP-preferring bombesin receptor antagonists displaced [125I-Tyr4]bombesin binding with high affinities (36-177 nM), whereas neuromedin B possessed a lower affinity of 2878 nM. [D-F5Phe6,D-Ala11]bombesin-(6-13)-methyl ester, the most active GRP-preferring bombesin antagonist as yet reported, had the highest affinity among all antagonists tested whereas neuromedin B had the lowest affinity. These data demonstrate that the bombesin binding sites in the human lung are of the GRP-preferring type.

The somatostatin receptor subtype on rat enterochromaffinlike cells

BACKGROUND/AIMS

Gastric enterochromaffinlike (ECL) cells play an important role in peripheral regulation of acid secretion. This study investigated the somatostatin receptor subtype on ECL cells.

METHODS

ECL cells were isolated from rat fundic mucosa to a purity of 90%-95% by combining enzymatic digestion, elutriation, density gradient centrifugation, and culture.

RESULTS

Polymerase chain reaction performed with templates from an ECL cell complementary DNA library and primers specific to each of the five known somatostatin receptor subtypes showed that the somatostatin receptor type 2 was significantly enriched in ECL complementary DNA. Single cell videoimaging of highly purified ECL cells in culture showed that only the somatostatin receptor type 2 selective agonist, DC 32-87, inhibited the gastrin-induced calcium signal at 10(-11) mol/L. The type 3 and type 4 selective agonists, DC 25-12 and DC 32-92, and also somatostatin 14 required 100-1000 times higher concentrations (10(-8) mol/L). The somatostatin receptor type 2 analogue also inhibited gastrin-stimulated histamine release with a 50% inhibitory concentration (IC50) value of 2 x 10(-12) mol/L, whereas somatostatin 14 and the type 3 and 4 analogues showed IC50 values of 1 to 5 x 10(-9) mol/L.

CONCLUSIONS

The predominant somatostatin receptors on rat gastric ECL cells are of the somatostatin receptor 2 subtype; they inhibit histamine secretion by interfering with the gastrin-induced calcium signal.

Comparison of responses to adrenomedullin and calcitonin gene-related peptide in the pulmonary vascular bed of the cat

Pulmonary vascular responses to the newly discovered hypotensive peptide, adrenomedullin, were compared with responses to the structurally related peptides, calcitonin gene-related peptide (CGRP) and amylin, in the intact-chest cat. Under conditions of controlled blood flow, when tone in the pulmonary vascular bed had been raised to a high steady level, intralobar injections of adrenomedullin (0.03-1 nmol), CGRP (0.1-3 nmol), and amylin (0.1 and 0.3 nmol) caused dose-related decreases in lobar arterial pressure without changing left atrial pressure. In terms of relative vasodilator activity in the pulmonary vascular bed, the dose of the peptide that decreased lobar arterial pressure 7.5 mm Hg (ED7.5 mm Hg) was significantly lower for adrenomedullin than for CGRP. The duration of the pulmonary vasodilator responses to CGRP was longer than for adrenomedullin, and both peptides decreased systemic arterial pressure when injected into the perfused lobar artery in the higher doses studied. The present data demonstrate that synthetic human adrenomedullin and CGRP have potent but relatively short-lasting vasodilator activity in the pulmonary vascular bed. These data show also that amylin, a structurally related pancreatic peptide, also has significant pulmonary vasodilator activity.

Chief cells possess somatostatin receptors regulated by secretagogues acting through the calcium or cAMP pathway

Inhibition both in vivo and in vitro of pepsinogen secretion by somatostatin (SS) and the histological demonstration that fundic D-cells contain long cytoplasmic processes extending to chief cells suggest a possible direct effect of SS on chief cell function. The aim of the present study was to determine whether SS interacts directly with receptors on isolated gastric chief cells and, if so, how SS alters cell function. Binding of 125I-[Tyr11]SS14 to chief cells was saturable, time and temperature dependent, and was inhibited by both SS14 (Ki 1.6 nM) and SS28 (Ki 5.2 nM). SMS-201-995 was 1,300-fold less potent than SS14. Calcium-mobilizing secretagogues reduced binding of 125I-[Tyr11]SS14 with efficacies of cholecystokinin octapeptide (CCK-8) > carbachol > gastrin. Adenosine 3',5'-cyclic monophosphate (cAMP)-activating secretagogues also inhibited binding with efficacies of secretin > vasoactive intestinal polypeptide (VIP). 12-O-tetradecanoylphorbol 13-acetate (TPA) or A-23187 also decreased binding. Analyses demonstrated that CCK-8 and TPA were decreasing the affinity of SS receptors for 125I-[Tyr11]SS14 without affecting their binding capacity. Both SS14 and SS28 at a maximally effective concentration inhibited cAMP production caused by VIP or secretin (20-30%) but did not alter cytosolic calcium ([Ca2+]i), inositol phosphates, or pepsinogen release. We conclude that chief cells possess SS receptors with a high affinity for both SS14 and SS28 but low affinity for SMS-201-995 and thus resemble the SSB receptors described in the rat cerebral cortex. Although occupation of these receptors by SS has no effect on pepsinogen release induced by secretagogues acting through either the calcium or the cAMP pathway, SS receptor occupation is regulated by agents activating phospholipase C, adenylate cyclase, protein kinase C, and [Ca2]i.

Smooth muscle cells from guinea pig stomach possess high-affinity galanin receptors that mediate relaxation

Galanin-like immunoactivity occurs in nerves and plexi in muscle layers throughout gastrointestinal tract including the stomach. Galanin can affect gastric emptying and contraction or relaxation of gastric muscle in different species. The aim of this study was to investigate the direct effect of galanin on dispersed gastric smooth muscle cells and to characterize any galanin receptors that mediated any effect. Dispersed gastric smooth muscle cells were prepared from guinea pig stomach by collagenase digestion. Porcine galanin (p-galanin; 1 microM) did not stimulate contraction when present alone; however, p-galanin (1 microM) inhibited carbachol-induced contraction with a half-maximal effect at 7 nM. p-Galanin (1 microM) increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content by 10 s and caused a maximal increase of 80% over basal. 125I-galanin (porcine) bound to dispersed cells in a time- and temperature-dependent manner. Binding was saturable, reversible, and specific. Binding of 125I-galanin was inhibited almost equally by porcine and rat galanin (Ki = 6-8 nM) but was not inhibited by the galanin-associated peptide [preprogalanin-(108-123)]. The fragment galanin-(1-16) was equally potent to rat galanin; however, the fragment galanin-(9-29) was 56-fold less potent (Ki = 370 nM). Computer analysis demonstrated there were two binding sites for p-galanin on gastric smooth muscle cells, a high-affinity site (Kd = 2.6 nM) with low capacity (Bmax = 175 fmol/mg protein) and a low-affinity site (Kd = 150 nM) with large capacity (Bmax = 3,611 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)

Synthetic human adrenomedullin and adrenomedullin 15-52 have potent short-lived vasodilator activity in the hindlimb vascular bed of the cat

Responses to synthetic human adrenomedullin, a novel hypotensive peptide isolated from human pheochromocytoma cells, and the carboxy terminal 15-52 amino acid fragment of adrenomedullin (ADM15-52) were investigated in the hindlimb vascular bed of the cat under constant flow conditions. Intraarterial injections of the peptides in doses of 0.01-0.3 nmol caused dose-related decreases in hindlimb perfusion pressure. When compared on a nmol basis, adrenomedullin and ADM15-52 were similar to bradykinin in vasodilator potency and were approximately 10 fold less potent than acetylcholine. The half-life of the vasodilator response to adrenomedullin and ADM15-52 ranged from 55 to 80 sec and was greater than the half-life of vasodilator responses to bradykinin in doses of 0.01-0.3 nmol and acetylcholine in doses of 0.01-0.3 nmol. The present data demonstrate that synthetic human adrenomedullin and ADM15-52 have potent but relatively short-lasting vasodilator activity in the hindlimb vascular bed of the cat. These data suggest that amino acid residues 15-52 of adrenomedullin are important for the expression of vasodilator activity in the hindlimb vascular bed of the cat.

Bombesin receptor subtype mediation of gastroenteropancreatic hormone secretion in rats

Bombesin is a potent releaser of many gut and pancreatic hormones including gastrin, glucose-dependent insulinotropic polypeptide (GIP), pancreatic polypeptide (PP), cholecystokinin (CCK), enteroglucagon, and insulin. Three mammalian bombesin-like peptides, gastrin-releasing peptide (GRP), neuromedin C (NMC or GRP-10), and neuromedin B (NMB), and two bombesin receptor subtypes, GRP preferring and NMB preferring, have been characterized. We used a highly potent, selective antagonist of the GRP-preferring receptor, [D-Phe6]bombesine(6-13)-methylester ([D-Phe6]Bn(6-13)OMe), to determine the receptor subtype mediating bombesin-induced secretion of gastrin, GIP, PP, peptide YY (PYY), and insulin, as well as the importance of endogenous bombesin-like peptides in controlling basal secretion of these hormones. Unanesthetized rats received femoral vein infusion of saline, bombesin (10 nmol/kg/h), [D-Phe6]Bn(6-13)OMe (1000 nmol/kg/h), or bombesin plus [D-Phe6]Bn(6-13)OMe. Blood was withdrawn from jugular vein catheters before and 30 min after the start of infusions. Plasma gastrin, GIP, PP, PYY, and insulin were measured by specific radioimmunoassays. [D-Phe6]Bn(6-13)OMe alone reduced basal insulin levels by 28% (p < 0.05) but did not alter basal levels of plasma PP, GIP, PYY, or gastrin (p > 0.05 for each). Bombesin infusion significantly increased plasma levels of each hormone (p < 0.0001 for each). [D-Phe6]Bn(6-13)OMe completely blocked bombesin-induced increases in PP, insulin, and gastrin, and almost completely blocked increases in GIP and PYY (p < 0.01 for each). Our results suggest that (a) exogenous bombesin significantly stimulates PP, insulin, GIP, PYY, and gastrin secretion, (b) bombesin-induced secretion of these hormones is primarily mediated by the GRP-preferring receptor, and (c) an endogenous bombesin-like peptide acting at this receptor subtype plays an important physiological role in control of basal secretion of insulin but not PP, GIP, PYY, or gastrin.

Effects of an LHRH antagonist on the time of occurrence and amplitude of the preovulatory LH surge, progesterone and estradiol secretion, and ovulation in superovulated Holstein heifers

Beginning on Day 10 or 11 of the estrous cycle, mature Holstein heifers were given a superovulatory regimen of twice-daily injections of porcine FSH, together with injections of PG with the fifth and sixth FSH injections. Every 12 h from 24 to 60 h after PG administration, the animals received im injections of different doses of the LH releasing hormone antagonist [N-Ac-D-Nal(2)(1), D-pCl-Phe(2), D-Trp(3), D-Arg(6), D-Ala(10)]-LHRH or vehicle. Follicular development was monitored by transrectal ultrasonography every 12 h from 24 to 120 h after PG administration. All animals were given hCG at 72 h after PG injection, and were artificially inseminated. At Day 7 of gestation, the corpora lutea were counted by ultrasonography, and embryos were collected by nonsurgical flushing of the uterus. Treatment with the antagonist resulted in a dose-dependent decrease in the amplitude of the LH surge and in delays in the time of occurrence of the LH surge, ovulation and the shift from estradiol to progesterone production. These results indicate that LHRH antagonists can be used to delay the LH surge and ovulation in superovulated heifers. This finding may be beneficial to studies in the superovulation of cattle.

Characterization of somatostatin receptor subtypes controlling rat gastric acid and pancreatic amylase release

An examination of the binding characteristics of a large number of somatostatin analogues with respect to the five known somatostatin receptor subtypes has recently resulted in the discovery of several peptides with some selectivity for types 2, 3, and 4 and little affinity for type 1 or 5 receptor. A panel of these peptides has thus far implicated type 2 receptors in the inhibition of release of pituitary growth hormone and type 4 receptors in inhibiting pancreatic insulin release. In the present article, we have examined the inhibitory effects of the same group of peptides on in vivo rat gastric acid and pancreatic amylase release and binding to rat pancreatic acinar cells. The type 2-selective ligand NC-8-12 was a potent inhibitor of gastric acid release (EC50s in the 1.5 nM region) whereas the type 4-selective ligand, DC-23-99, elicited little response. However, some involvement of type 3 receptors could not be ruled out because the type 3-selective analogue, DC-25-20, exhibited inhibitory effects at higher dose levels (EC50 > 10 nM). Conversely, the type 4 analogue was a potent inhibitor of amylase release (EC50 1.1 nM) whereas the type 3 analogue had no significant effects at doses tested. DC-23-99 also bound with high affinity to rat acinar cells (EC50 3.8 nM), whereas DC-25-20 exhibited more than 10-fold less affinity. Thus, these two major biological functions of somatostatin appear to be controlled by different receptors and, furthermore, effects on both endocrine and exocrine pancreas appear to be type 4 receptor mediated.

Galanin-induced relaxation in gastric smooth muscle cells is mediated by cyclic AMP

Galanin has numerous effects on gastrointestinal motility in different species; however, its cellular basis of action in mediating these effects is unclear. Dispersed gastric smooth muscle cells have been shown to possess high-affinity galanin receptors that increase cAMP and cause relaxation. Recent studies show some smooth muscle relaxants such as VIP cause relaxation by both cAMP-dependent and -independent mechanisms. It is unknown if galanin's cellular basis of relaxation is similar or different from that of VIP. To investigate galanin's relaxant effect and compare it to VIP's effect, dispersed smooth muscle cells from guinea pig stomach were prepared by collagenase digestion. The mean length in resting cells was 110 +/- 2 microns and, with carbachol treatment, contracted to 89 +/- 2 microns. VIP and galanin alone had no effect on cell length, but each caused a dose-dependent inhibition of carbachol-induced contraction and both had an EC50 of 3-7 nM. Galanin (1 microM) and VIP (1 microM) increased cellular cAMP from 118 +/- 10 pmol/10(6) cells in control to 212 +/- 14 and 214 +/- 12 pmol/10(6) cells, respectively. The protein kinase A inhibitor, Rp-cAMPS, at 100 microM, completely inhibited the relaxant effect of an EC50 concentration of galanin (3 nM), but only inhibited that by VIP by 80% (p < 0.05). Adding the nitric oxide inhibitor, L-NNA (NG-nitro-L-arginine), at 100 microM did not alter the length of resting cells or inhibit carbachol-induced contraction. However, L-NNA (100 microM) decreased VIP-induced relaxation by 45%, whereas it had no effect on galanin-induced relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

A chimeric VIP-PACAP analogue but not VIP pseudopeptides function as VIP receptor antagonists

The ability to assess the importance of VIP in different physiological processes is limited by the lack of specific potent antagonists. In the present study, we have adopted two different approaches used successfully with other peptides in an attempt to identify new VIP receptor antagonists. One involves the formation of pseudopeptides by insertion of reduced peptide bonds in the NH2-terminus from position 2 to 8 of VIP. The other methodology involves the formation of a COOH-terminal chimeric analogue by combining VIP(6-28) and PACAP(28-38). The ability of each of these peptides to function as an antagonist was compared with reported VIP antagonists. All of the peptides inhibited [125I]VIP binding to VIP receptors on guinea pig pancreatic acini. For the pseudopeptides the affinities were: [psi 3-4]VIP (0.2 microM) = 4 x [psi 4-5]VIP = 8 x [psi 8-9]VIP = 14 x [psi 6-7]VIP, [psi 2-3]VIP = 25 x [psi 5-6]VIP. Each nonpseudopeptide analogue also inhibited VIP binding with relative potencies of VIP(6-28)-PACAP(28-38) (1 microM) = 2.5 x [4-Cl-D-Phe6,Leu17]VIP, VIP(10-28), neurotensin(6-11)-VIP(7-28) = 6 x [Ac-Tyr1,D-Phe2]GRF. All pseudopeptides were agonists with relative potencies: [psi 3-4]VIP > [psi 6-7], [psi 4-5]VIP > [psi 5-6] > [psi 8- 9]VIP > [psi 2-3]VIP. The reported VIP receptor antagonist, neurotensin(6-11)-VIP(7-28), was also an agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-activity relationships for relaxation of smooth muscle by VIP

Utilizing VIP and five VIP analogues, concentration-response curves for relaxation of rat mesenteric artery and rat gastric longitudinal muscle were determined for comparison with our previously published radioligand binding data on rat smooth muscle and other tissues. The biological potency of the VIP analogues in the present study compared more closely with their potency for VIP receptor binding in smooth muscle tissue (arteries) vs. other tissues (pituitary, brain, liver).

Synthetic human adrenomedullin and ADM15-52 have potent short-lasting vasodilator activity in the pulmonary vascular bed of the cat

Responses to synthetic human adrenomedullin, a novel hypotensive peptide localized in several organ systems, including the lung, and the carboxy terminal 15-52 amino acid fragment of adrenomedullin (ADM15-52) were investigated in the pulmonary vascular bed of the intact-chest cat. Under constant flow conditions when baseline tone in the pulmonary vascular bed was raised to a high steady level, injections of adrenomedullin and ADM15-52 into the perfused lobar artery in doses of 0.1-1 nmol, caused significant dose-related decreases in lobar arterial pressure. Since left atrial pressure was unchanged, the decreases in lobar arterial pressure reflect decreases in pulmonary lobar vascular resistance. Adrenomedullin and ADM15-52 exhibited similar vasodilator activity and were approximately 3-fold more potent than bradykinin in the pulmonary vascular bed of the cat. Pulmonary vasodilator responses to adrenomedullin and ADM15-52 were rapid in onset and lasted for 150-200 sec, depending on the dose of the peptide injected. The present results demonstrate that synthetic human adrenomedullin and ADM15-52 possess potent, short-lasting vasodilator activity in the pulmonary vascular bed of the cat and suggest that amino acids 15-52 in the peptide are important for the expression of vasodilator activity in the pulmonary vascular bed of the cat.

Cyclic lactam analogues of ovine pituitary adenylate cyclase activating polypeptide (PACAP): discovery of potent type II receptor antagonists

Binding of [125I]PACAP-38 to rat liver membranes was investigated. It was rapid at 37 degrees C, reversible, and saturable, and it was time, concentration, and temperature dependent. Scatchard plots showed that [125I]PACAP-38 bound to single noninteracting site(s), and [125I]VIP bound to high- and low-affinity binding site(s). The order of potency of displacing [125I]PACAP-38 from rat liver membranes was: PACAP-38 > PACAP-27 > VIP (IC50 = 5, 180, and 350 nM, respectively). Surprisingly, the order of potency of displacing [125I]VIP was also the same (IC50 = 1, 8, and 52 nM, respectively). The order of potency of stimulating adenylate cyclase to release cyclic AMP was: PACAP-27 > VIP > PACAP-38 (EC50 = 0.06, 1, and 6 nM, respectively). Modification of PACAP-27 or PACAP-38 structures either through deletions, substitutions, or cyclization involving amino acid residues, Asp3, Asp8, Lys15, Lys20, or Lys21 indicated that the N-terminal region of the molecule is important for both binding and transduction. Of the various lactam analogues synthesized, cyclo[Asp3,Lys15]PACAP-38 and cyclo[Asp8,Lys15]PACAP-38 appear to be competitive receptor antagonists of the release of cAMP by PACAP-38. The results presented suggest that liver membranes possess distinct PACAP and VIP receptors, and that the PACAP receptor(s) is probably similar, but not identical, to type I receptor(s) characteristic of the brain.

GRP-preferring bombesin receptor subtype mediates contractile activity in cat terminal ileum

Mammalian bombesin-like peptides, such as gastrin-releasing peptide and neuromedin B, are known to increase motility of different segments in the gut. The present study was carried out to identify the receptor subtype mediating these contractions of ileal longitudinal muscles in cats, in vitro. Both gastrin-releasing peptide (GRP) and neuromedin B (NMB) evoked concentration-dependent contractions of the strips. [D-Phe6]Bombesin(6-13)-methyl-ester, a highly selective GRP-preferring receptor antagonist, competitively inhibited contractions induced by either agonist. On the other hand, D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2, a selective NMB receptor antagonist, did not affect the actions of either gastrin-releasing peptide or neuromedin B. Our results suggest that bombesin-like peptides contract cat terminal ileum via activating GRP receptors.

Potent inhibitory effects of a type four receptor-selective somatostatin analog on rat insulin release

A total of 5 somatostatin (SS) receptors have been characterized, cloned, and transfected into various cell types which have recently been used to discern peptide ligands displaying high degrees of selectivity for binding to types 2, 3, and 4. These have now allowed us to examine which receptor(s) is involved in SS inhibition of glucose-stimulated rat pancreatic insulin release. The type 4 selective ligand, DC-23-99, which had little affinity for receptor types 1, 2, or 5, was at least equipotent to SS in preventing insulin release. In contrast, the type 3 selective peptide, DC-25-20, was totally devoid of inhibitory effects. Peptides, such as NC-8-12, which have extremely high affinity for type 2 receptors but far less for types 1, 3, 4 and 5, were considerably less potent than SS in this assay. Thus, 2 major inhibitory physiological functions of SS on GH (type 2) and insulin release appear to be mediated by entirely different receptor types.

Effect of [(CH2NH)4,5]secretin on pancreatic exocrine secretion in guinea pigs and rats

[psi 4,5]Secretin was shown to be a secretin receptor antagonist that inhibits secretin-stimulated increase in adenosine 3',5'-cyclic monophosphate in isolated pancreatic acini of the guinea pig. To determine whether it inhibits pancreatic exocrine secretion in vivo, we have studied the effect of [psi 4,5]secretin on the pancreatic secretion stimulated by secretin in anesthetized guinea pigs and rats. In basal state, [psi 4,5]secretin given intravenously for 2 or 3 h in varying doses of 1.6-32.7 nmol.kg-1.h-1 dose dependently increased pancreatic secretion of both fluid and bicarbonate during the 1st h, but it returned gradually to basal level within 2 or 3 h. On the other hand, [psi 4,5]secretin significantly inhibited the pancreatic secretion stimulated by either exogenous or endogenous secretin in a dose-related manner. The inhibitory effect of [psi 4,5]secretin in guinea pigs was greater than that in rats. However, it did not completely block the secretin-stimulated pancreatic secretion, whereas a rabbit antisecretin serum suppressed it completely. We conclude that 1) in the unstimulated state, [psi 4,5]secretin is a partial agonist of pancreatic exocrine secretion of both fluid and bicarbonate; and 2) when pancreatic secretion is stimulated by secretin, unlike an antisecretin serum, it is a partial inhibitor in intact guinea pigs and rats.

Comparison of responses to pituitary adenylate cyclase activating peptides 38 and 27 in the pulmonary vascular bed of the cat

Responses to pituitary adenylate cyclase activating polypeptide (PACAP)-38 were investigated and compared with responses to PACAP-27 and vasoactive intestinal polypeptide (VIP) in the pulmonary vascular bed of the intact-chest cat under constant flow conditions. Under low resting tone baseline conditions, injections of PACAP-38 had little or no effect on lobar arterial pressure; however, when tone in the pulmonary vascular bed was raised to a high steady level (35-40 mm Hg) with U46619, intralobar injections of PACAP-38 caused dose-related decreases in lobar arterial pressure without altering left atrial pressure. The peptide induced biphasic changes in systemic arterial pressure. PACAP-38 was more potent than VIP in decreasing lobar arterial pressure, and both peptides were significantly less potent than PACAP-27 in dilating the pulmonary vascular bed. The present data show that PACAP-38 has significant vasodilator activity in the pulmonary vascular bed of the cat, and that the 27 amino acid form of the peptide is approximately 3-fold more potent than PACAP-38.

Discovery of a novel class of neuromedin B receptor antagonists, substituted somatostatin analogues

Bombesin-related peptides have widespread activities in the central nervous system and peripheral tissues. Recent studies show two subtypes of receptors; a gastrin-releasing peptide (GRP) receptor subtype and a neuromedin B (NMB) receptor subtype exist. In contrast to the GRP receptor, no antagonists exist for the NMB receptor. In the present study we report that certain somatostatin (SS) octapeptide analogues function as selective NMB receptor antagonists. The most potent analogue, D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2, inhibited binding of 125I-[D-Tyr degree]NMB to NMB receptor-transfected 3T3 cells and C6 cells. This analogue had 100-fold lower affinity for GRP receptors. Structure-function studies were performed by synthesizing 18 structurally related SS octapeptide analogues; each of these analogues, but not native SS-14 or SS-28, also inhibited binding to NMB receptors. The stereochemistry at positions 1, 2, 7, and 8, the hydrophobicity and ring size of the substitution in positions 1, 3, and 4, and the basicity of the group in position 5 were all important in determining NMB receptor affinity. No SS octapeptide analogue increased [3H]inositol phosphates in NMB receptor-transfected cells; however, each analogue inhibited NMB-stimulated increases. The most potent analogue, D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2, caused a parallel rightward shift of the NMB dose-response curve, the Schild plot slope was not significantly different from unity, and the affinity was 230 nM. SS octapeptide analogues also interacted with SS receptors and mu-opioid receptors; however, there was no correlation between the affinities of the analogues for these receptors and their affinities for NMB receptors, demonstrating that these activities can be separated. The results demonstrate for the first time a class of antagonists with > 100-fold selectivity for NMB versus GRP receptors. Because the structural requirements for determining NMB, SS, and mu-opioid receptor activity differ, it is likely that highly selective, specific, high affinity NMB receptor antagonists can now be developed that will be useful in defining the role of NMB in various physiological processes.

Angiopeptin enhances acetylcholine-induced relaxation and inhibits intimal hyperplasia after vascular injury

The effects of the somatostatin analogue, angiopeptin (BIM-23014), on neoendothelial function, as evidenced by formation of prostaglandin (PG) I2 and by acetylcholine-induced relaxation (formation of endothelial-derived relaxing factor), were investigated in the rabbit aorta. A balloon catheter injury of the thoracic and abdominal aorta was induced in New Zealand White rabbits. Animals treated with angiopeptin for 2 or 4 wk were compared with untreated rabbits at 2 or 4 wk after the induction of injury, as well as to sham-operated controls. When the rabbits were killed, vascular rings were assessed for arachidonic acid-stimulated PGI2 formation, acetylcholine-induced relaxation, and the degree of intimal hyperplasia. Vascular rings from animals treated with angiopeptin exhibited enhanced acetylcholine-induced relaxation; however, angiopeptin treatment had no effect on arachidonic acid-stimulated PGI2 formation. Intimal hyperplasia in treated animals was reduced by 36%. Treatment with another somatostatin analogue, BIM-23030, did not enhance relaxation or inhibit intimal hyperplasia. These data suggest that treatment with angiopeptin may inhibit intimal hyperplasia in part by its beneficial effect on neoendothelial function.

Pituitary adenylate cyclase activating polypeptide: a neuropeptide with potent inotropic and coronary vasodilatory effects in neonatal pig hearts

Cardiac effects of the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) have not previously been reported. We investigated the influence of PACAP, vasoactive intestinal polypeptide (68% homology with PACAP) and the beta-adrenergic receptor agonist isoproterenol on contractile function and coronary vascular tone in isolated piglet hearts (1 to 5 d of age). Paced (180 beats/min) isovolumically beating hearts underwent retrograde aortic perfusion at constant coronary flow (approximately 3 mL.min-1.g-1) with an erythrocyte-enriched (hematocrit 15 to 20%) solution (37 degrees C). Agonists were injected into the aortic root of hearts, and the positive (+) and negative (-) changes in maximum rate of change of systolic pressure with respect to time (dP/dtmax) and in coronary perfusion pressure (that reflected alterations in vascular tone) were measured. PACAP (n = 8, 0.1 and 0.5 nmol) increased (+) dP/dtmax from 944 +/- 59 to 1519 +/- 206 mm Hg/s and from 867 +/- 40 to 2010 +/- 226 mm Hg/s (p < 0.05); increased (-) dP/dtmax from 1114 +/- 41 to 1439 +/- 95 mm Hg and from 999 +/- 37 to 1668 +/- 145 mm Hg/s (p < 0.05); and decreased perfusion pressure from 61.4 +/- 3.1 to 48.9 +/- 2.3 mm Hg and from 60.5 +/- 2.4 to 43.9 +/- 2.3 mm Hg (p < 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Galanin: structure-dependent effect on pancreatic amylase secretion and jejunal strip contraction

Rat and porcine galanin and their fragments inhibited cholecystokinin-8 (CCK-8)-stimulated amylase secretion with the following activities: rat galanin-(1-29) = porcine galanin-(1-29) = galanin-(1-15) = rat galanin-(3-29) > rat galanin-(2-29) = porcine galanin-(2-29) > galanin-(1-10). Fragments of rat galanin-(9-29) and N alpha-acetyl-galanin-(9-29) were able to inhibit CCK-8-stimulated pancreatic amylase secretion but only at higher dose levels. Porcine galanin-(15-29) and rat galanin-(21-29) were unable to produce significant inhibition. Rat and porcine galanin-(1-29), galanin-(1-15) and rat N alpha-acetyl-galanin-(9-29) also inhibited basal pancreatic amylase secretion. In the rat jejunal strip contraction model, rat galanin-(1-29) and porcine galanin-(1-29) have similar potencies. Galanin-(1-15) and galanin-(1-10) stimulate rat jejunal strip contraction with decreasing potencies. Elimination of Gly1 from the N-terminus of both rat and porcine galanin had no significant effect either on pancreatic amylase secretion or on jejunal strip contraction. The rat galanin-(3-29) and (9-29) are not active in the stimulation of rat jejunal strip contraction. Acetylation of porcine galanin-(9-29) created a peptide that was a powerful stimulator of rat jejunal strip contraction. The present data indicate that N-terminal rat galanin amino acid residues are crucial for rat jejunal strip contraction but are not required for inhibition of pancreatic amylase. These results suggest that the galanin amino acid sequence contains several specific domains, which can be recognized by specific galanin receptor subsets.

Chimeric galanin analogs that function as antagonists in the CNS are full agonists in gastrointestinal smooth muscle

Galanin has numerous effects on gastrointestinal smooth muscle. However, because of the lack of specific inhibitors, it is not known which are physiological and which are pharmacological. This study investigates the ability of two chimeric galanin analogs, [# 1-galantide = (M-15) = [galanin (1-13)-substance P(5-11)] and #2-M-35[galanin(1-13)bradykinin (2-9)], which were recently reported to function as galanin-receptor antagonists in the CNS, to interact with galanin receptors on rat jejunal muscle strips or dispersed smooth muscle cells from guinea pig stomach. In both systems each chimeric analog had agonist activity and was as efficacious as galanin. Cross-desensitization experiments demonstrated that in the jejunal muscle strips, both chimeric analogs were causing muscle contraction by interacting with the galanin receptor. In dispersed smooth muscle cells, galanin, as well as each chimeric analog, caused muscle relaxation, whereas substance P and bradykinin both caused muscle contraction. Each chimeric analog was equipotent to galanin in inhibiting binding of 125I-galanin, and there was close agreement between their abilities to occupy the galanin receptor and cause relaxation. Each chimeric analog also activated adenylate cyclase and increased cAMP characteristic of relaxants. These studies demonstrate these chimeric analogs will not be useful for defining the physiological role of galanin in altering gastrointestinal motility, because they function as full galanin-receptor agonists instead of as galanin-receptor antagonists.

The new pharmacology of somatostatin and its multiple receptors

A large number of somatostatin analogs taken from several major families of peptides has been examined for binding to three newly discovered somatostatin receptors (SSTR1, 2 and 3) transfected and expressed in various cell membrane preparations. Extremely potent octapeptide analogs related to and including octreotide (SMS 201-995) were found to bind with high affinity to SSTR2 receptors, which appear to be primarily of a pituitary type, and indeed affinities correlated extremely well with inhibitory potencies for inhibition of GH release from rat pituitary cells. Several new octapeptides were discovered with affinities and in vitro potencies greater than previously reported analogs. Whereas all of the octapeptides had much lower affinity for SSTR1 and SSTR3 receptors, which appear to be primarily present in the CNS, high affinity and highly specific ligands for the latter were found within a series of linear somatostatin analogs. No analogs were found which had high affinity for SSTR1 receptors. These studies confirm the feasibility of designing ligands which are specific for the various somatostatin receptors. These should provide useful tools for delineating the physiological roles of these receptors, specifically labeling certain receptors, and developing therapeutically interesting compounds targeted towards specific physiological events.

Cloned somatostatin receptors: identification of subtype-selective peptides and demonstration of high affinity binding of linear peptides

The recent molecular cloning of the genes encoding three somatostatin (SRIF) receptor subtypes has allowed for the individual expression of these receptors in mammalian cells and characterization of their respective pharmacological profiles. In the present study, we have investigated the affinities of a battery of SRIF analogues to bind to SRIF receptor subtypes SSTR1 (cloned somatostatin complex), SSTR2, and SSTR3, as well as their abilities to inhibit the release of growth hormone from anterior pituitary cells in vitro. We labeled SSTR1 and SSTR3 receptors expressed in Chinese hamster ovary and COS-1 cells, respectively, with the metabolically stable SRIF analogue 125I-CGP 23996. SSTR2 receptors expressed in Chinese hamster ovary cells were labeled with the SSTR2-specific radioligand 125I-MK-678. Inhibition studies were performed using SRIF analogues of differing structures, including hexapeptide analogues similar to MK-678, octapeptide analogues similar to SMS 201-995, pentapeptide analogues similar to c[Ahep-Phe-D-Trp-Lys-Thr(Bzl)] (SA), and linear SRIF analogues. SSTR1 bound SRIF and SRIF-28 with high affinity and the peptide SA and its structural analogues with low affinity. The hexapeptides did not interact with SSTR1 at concentrations as high as 1 microM, and only a few of the octapeptides or linear peptides bound, with very low affinities. In contrast, 125I-MK-678 binding to SSTR2 was potently inhibited by the hexapeptides, octapeptides, and some of the linear compounds, whereas SA and its analogues did not bind to SSTR2. The potencies of the various SRIF agonists to inhibit growth hormone release in vitro was highly correlated with their potencies to inhibit radioligand binding to SSTR2, but not to SSTR1 or SSTR3. SSTR3 bound analogues of each class but with moderate to low affinities, with the exception of several linear peptides and one of the octapeptides. We report for the first time the binding affinities of linear analogues of SRIF, some of which display subnanomolar affinities and are highly selective for SRIF receptor subtypes. Most importantly, these studies identify several peptide analogues that are highly potent, specific, and selective for individual subtypes of SRIF receptors. Such information, coupled with the knowledge of the distribution of these receptor subtypes in normal and pathological tissues, will be critical for more specific experimental and therapeutic interventions.

Interaction of ovine pituitary adenylate cyclase-activating peptide (PACAP-38) with rat lung membranes

The binding of ovine pituitary adenylate cyclase-activating peptide (PACAP-38) to rat lung membranes was investigated using [125I]PACAP-38 as radioligand. Binding was rapid at 37 degrees C, reversible, saturable, and time, concentration, and temperature dependent. Kinetic parameters derived from saturation experiments revealed a Kd = 100 +/- 15 pM, Bmax = 310 +/- 36 fmol/mg protein, and a Hill slope factor (nH) of 1.17 +/- 0.12. Various chemically synthesized analogues of PACAP-38, as well as related peptides, were tested for their ability to displace [125I]PACAP-38. Of those that had an IC50 < 0.2 microM, the following order of potency was determined: PACAP-38 (IC50 = 25 nM) > or = [Ile2]PACAP-38 (IC50 = 31 nM) > PACAP-27 (IC50 = 54 nM) > [Tyr1]PACAP-38 (IC50 = 104 nM) > GHRH(1-29)NH2 (IC50 = 108 nM) > PHI (IC50 = 181 nM) > [Ser2]PACAP(2-38) (IC50 = 198 nM). Glucagon, PHM, secretin, and GIP exhibited little affinity in the same binding assay. Vasoactive intestinal peptide (VIP) had an IC50 in excess of 1 microM. When [125I]VIP was used as radioligand, PACAP-27 had an IC50 = 0.2 nM > PACAP-38 (IC50 = 0.5 nM) > VIP (IC50 = 16 nM). A novel analog of PACAP-38, [4-Cl-D-Phe6,Leu17]PACAP-38, was able to displace [125I]VIP very efficiently (IC50 = 1 nM), but had little potency in displacing [125I]PACAP-38 (IC50 = 320 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Production of immunoreactive pituitary adenylate cyclase activating polypeptide (PACAP) by human neuroblastoma cells, IMR-32: detection and characterization with monoclonal and polyclonal antibodies against different epitopes of PACAP

Sensitive and specific two-side enzyme immunoassays (two-site EIAs) for pituitary adenylate cyclase activating polypeptides, PACAP38, and PACAP27, have been established using six monoclonal antibodies against PACAP38, and a rabbit antibody against a C-terminal portion of PACAP27. In extracts of rat hypothalamus, these EIAs detected not only PACAP38 and PACAP27 but also an immunoreactive (ir-) PACAP lacking an epitope of a monoclonal antibody, PA-1C, which recognizes the C-terminal portion of PACAP38. By the use of these EIAs, it was found that one of the human neuroblastoma cell lines, IMR-32, produced ir-PACAP. In reverse-phase (RP-)HPLC, intracellular and extracellular ir-PACAPs were separated into two peaks, of which one was eluted at a position close to that of PACAP38 and the other in rather hydrophobic fractions. Those ir-PACAPs also lacked PA-1C epitope of PACAP38. SDS-PAGE and immunoblot analysis of the two peaks of the RP-HPLC indicated that they consisted of several components including those with apparent molecular weights of 6.5 k and 10 k for the first peak ir-PACAP, and 14 k and 20 k for the second peak ir-PACAP. These results indicate that IMR-32 produces a precursor of PACAP and related peptides generated in various processing steps. Although the significance of the modification in the C-terminus of PACAP38 is unknown, IMR-32 may be a cell line useful for studying the regulation of the biosynthesis of PACAP.

Characterization of bombesin receptors using a novel, potent, radiolabeled antagonist that distinguishes bombesin receptor subtypes

Bombesin (Bn)-related peptides affect numerous cell functions; however, receptor characterization by radiolabeled ligands is limited because only radiolabeled agonists exist. In the present study we demonstrate that [D-Tyr6]Bn(6-13)methyl ester [[D-Tyr6]Bn(6-13)ME] functions as a Bn receptor antagonist with high affinity. The binding of both the radiolabeled agonist 125I-[Tyr4]Bn and the radiolabeled antagonist 125I-[D-Tyr6]Bn(6-13)ME to AR42J cells, murine 3T3 cells, and dispersed guinea pig pancreatic acini was time and temperature dependent, saturable, and reversible. Binding of the antagonist more rapidly reached equilibrium and was more rapidly reversible. Guanine nucleotides did not affect binding of the radiolabeled antagonist, whereas guanosine-5'-(beta,gamma-imido)triphosphate decreased agonist binding by decreasing Bn receptor affinity. Acid stripping studies demonstrated that the radiolabeled agonist, but not the antagonist, was internalized in each cell system. Bn receptor affinities for various Bn receptor agonists or antagonists in each cell system were identical when computed from an analysis of inhibition curves for binding of radiolabeled agonist or antagonist. However, with AR42J cells and 3T3 cells the radiolabeled agonist demonstrated a > 2-fold higher number of Bn receptors than did the radiolabeled antagonist. Binding studies using cell membranes, in contrast to cells, showed equal numbers of Bn receptors with either radiolabeled ligand. The radiolabeled agonist demonstrated high affinity binding to both rat pancreatic acinar and esophageal muscularis mucosa membranes, whereas the radiolabeled antagonist interacted with high affinity only with the gastrin-releasing peptide-preferring subtype of Bn receptors on pancreatic tissue. These results demonstrate that 125I-[D-Tyr6]Bn(6-13)ME is a high affinity radiolabeled antagonist that interacts specifically with Bn receptors. In contrast to the radiolabeled agonist, binding of the antagonist is not affected by guanine nucleotides and it is not internalized, which allows quantitation of only Bn cell surface receptors. Furthermore, the radiolabeled antagonist can distinguish Bn receptor subtypes, whereas the radiolabeled agonist does not. This ligand should prove useful for characterizing Bn receptors as well as studying their regulation.

Bombesin receptor antagonists differentiate receptor subtypes in rat brain

Previous studies have shown that various bombesin receptor antagonists can distinguish between bombesin receptor subtypes in peripheral tissues. To determine whether these antagonists would be useful in differentiating bombesin receptor subtypes in the rat central nervous system, we used in vitro receptor autoradiography to examine the binding affinities of several bombesin receptor antagonists for two brain regions we had characterized as possessing distinct bombesin receptor subtypes. Our results demonstrate that, consistent with peripheral bombesin receptors, bombesin receptor subtypes in the rat brain can be differentiated by various bombesin receptor antagonists.

Solubilization and purification of bombesin/gastrin releasing peptide receptors from human cell lines

Bombesin/gastrin releasing peptide (BN/GRP) receptors were solubilized and purified from human glioblastoma (U-118) and lung carcinoid cell lines (NCI-H720). The U-118 cells, when extracted with CHAPS/cholesterol hemisuccinate (CHS), bound (125I-Tyr4)BN with high affinity (Kd = 2 nM) to a single class of sites (Bmax = 150 fmol/mg protein). Specific (125I-Tyr4)BN binding was inhibited with high affinity by BN, GRP, GRP14-27, and receptor antagonists such as (D-Phe6)BN6-13methylester(ME) and (D-Phe6)BN6-13 propylamide(PA) (IC50 = 2, 22, 3, 1 and 2 nM, respectively) but not GRP1-16 or BN1-12. The solubilized and cellular receptor bound peptides with similar affinity. The solubilized receptor was purified using (Lys0, Gly1-4, D-Ala5)BN and (Lys3, Gly4,5, D-Tyr6)BN3-13 PA affinity resins. When eluted from the affinity resins by NaCl, the receptor bound (125I-D-Tyr6)BN6-13ME with high affinity. The NCI-H720 BN/GRP receptor was purified 86,000-fold after extraction with CHAPS/CHS and purification using both affinity resins. SDS-PAGE analysis indicated that major 65 and 115 kDa proteins were purified. These data indicate that BN/GRP receptors can be solubilized from human cells and purified using affinity chromatography techniques with retention of ligand binding activity.

Effect of bombesin antagonist D-Phe6-BN(6-13)OMe on vagally induced gastrin release from perfused rat stomach

The aim of the present study was to evaluate the effect of the bombesin antagonist D-Phe6-BN(6-13)OMe (BN-antagonist) on vagally stimulated gastrin release from the isolated rat stomach, which was perfused via the celiac artery with Krebs-Ringer buffer. Vagal stimulation was performed for 10 minutes with 1 ms, 10 V and 10 or 2 Hz, respectively. Gastrin secretion increased significantly during stimulation with 10 and 2 Hz. BN-antagonist was added to the perfusate at the concentration of 10(-6) M, which induced a significant reduction of vagally stimulated gastrin release at 10 Hz (619 +/- 65 vs. 252 +/- 62 pg/10 min, p < 0.05), but not at 2 Hz (564 +/- 117 vs. 493 +/- 113 pg/10 min, p > 0.05). In contrast, atropine (10(-7) M) reduced significantly the gastrin response at 2 Hz (270 +/- 78 pg/10 min, p < 0.01), but not at 10 Hz (446 +/- 87 pg/10 min, p > 0.05). The combination of BN-antagonist and atropine elicited an inhibition of vagally stimulated gastrin release similar to each substance when given alone. Basal gastrin release was not changed by the BN-antagonist. The present data suggest, that in the rat stomach endogenously released bombesin-related peptides contribute to the noncholinergic stimulation of gastrin release at higher stimulation frequencies (10 Hz), however, bombesin-related peptides are not involved, when lower stimulation frequencies (2 Hz) are employed. At both stimulation frequencies additional mechanisms are activated which are noncholinergic and not related to bombesin peptides.

Analysis of systemic and pulmonary vascular responses to PACAP and VIP: role of adrenal catecholamines

Systemic and pulmonary vascular responses to pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide with 68% sequence homology to vasoactive intestinal peptide (VIP), were investigated in the anesthetized cat. Intravenous injections of PACAP in doses of 0.1-3.0 nmol/kg produced decreases in arterial pressure (AP) at low doses and biphasic changes (decreases followed by increases) at higher doses, which were accompanied by increases in central venous pressure (CVP) and cardiac output (CO), and decreases and biphasic changes in systemic vascular resistance (SVR). In contrast, VIP in doses of 0.1-3.0 nmol/kg produced only dose-dependent decreases in AP and SVR and produced little change in CVP and CO. PACAP produced increased pulmonary arterial pressure (PAP), left atrial pressure (LAP), and increases in pulmonary vascular resistance (PVR). PACAP increased heart rate (HR) and right ventricular contractile force (RVCF), while VIP had no effect. Increases in AP and SVR in response to PACAP were changed to decreases following the administration of phentolamine or after adrenalectomy. Under constant flow conditions, PACAP and VIP produced dose-dependent decreases in lobar arterial pressure when tone was elevated, with PACAP being threefold more potent than VIP. Meclofenamate and nitro-L-arginine methyl ester (L-NAME) had no effect on pulmonary responses to the peptides. PACAP produced dose-dependent biphasic changes in hindquarters perfusion pressure, whereas VIP produced only decreases that were unchanged by indomethacin, L-NAME, and glibenclamide. Phentolamine and adrenalectomy eliminated the hindquarters pressor response to PACAP and D-Phe2-VIP, a VIP antagonist, reduced responses to VIP but not to PACAP. These data suggest that responses to PACAP and VIP are mediated by distinct receptors and that pressor responses to PACAP are due to the release of catecholamines from the adrenal gland.

Neuromedin B receptors retain functional expression when transfected into BALB 3T3 fibroblasts: analysis of binding, kinetics, stoichiometry, modulation by guanine nucleotide-binding proteins, and signal transduction and comparison with natively expressed receptors

The receptor that interacts with the mammalian bombesin-related peptide neuromedin B (NMB) is ubiquitous in the gastrointestinal tract and central nervous system. However, little is known regarding its cellular mechanisms of action. This receptor has been recently cloned, sequenced, and stably transfected into BALB 3T3 fibroblasts, permitting detailed study of the pharmacology and coupled biological activities of this receptor. In the present study, we compare the ability of transfected receptors to alter cell function with that of receptors natively expressed in small numbers by the rat glioblastoma cell line C6. NMB inhibited binding of 125I-[D-Tyro]NMB with high affinity in transfected cells (Ki = 3.08 +/- 0.14 nM) and in C6 cells (Ki = 1.90 +/- 1.10 nM), whereas the bombesin-related agonists gastrin-releasing peptide (GRP) and [D-Phe6, D-Ala11, Leu14]bombesin(6-16) (GRP analogue) had 100- and 300-fold lower affinities, respectively, for NMB receptors in either cell type. For both cell systems, maximal binding was observed between 5 and 15 min at 22 degrees. Both cell types internalized NMB at similar rates, with > 70% of bound ligand being internalized by 60 min at 22 degrees. The nonhydrolyzable guanosine analogue guanosine 5'-(beta,gamma-imido)triphosphate was equipotent in causing a decrease in binding of 125I-[D-Tyro]NMB due to decreased receptor affinity in both cell types, without a change in receptor number, demonstrating that the NMB receptor remained coupled to a guanine nucleotide-binding protein in both native and transfected cells. In both cell systems, NMB increased inositol monophosphate, inositol bisphosphate, and inositol trisphosphate in a time-dependent fashion. Inositol phosphates were increased in a dose-dependent fashion, with similar half-maximal values being obtained for NMB in both cell types (transfected, 1.01 +/- 0.09 nM; C6, 2.09 +/- 0.15 nM) and for the GRP analogue (transfected, 1855 +/- 140 nM; C6, 2129 +/- 250 nM). NMB mobilized intracellular Ca2+ in both cell systems, and the dose-response curves were superimposible (EC50 for transfected, 0.10 +/- 0.08 nM; C6, 0.11 +/- 0.02 nM). These data demonstrate that activation of the receptor for NMB stimulates phospholipase C and increases intracellular Ca2+. These results also demonstrate that transfected and native NMB receptors behave similarly, suggesting that the transfected cell line will be useful in future studies investigating ligand-receptor interactions, as well as in molecular biological studies of the structure-function relationship of the receptor.

Neuromedin B binds with high affinity, elevates cytosolic calcium and stimulates the growth of small-cell lung cancer cell lines

Previously, gastrin-releasing peptide (GRP) receptors were identified on small-cell lung cancer (SCLC) cells and GRP functioned as a SCLC autocrine growth factor. Here the effects of neuromedin B (NMB) on SCLC cells were investigated. [125I-Tyr0]NMB bound with high affinity to three of seven SCLC cell lines examined. [125I-Tyr0]NMB bound to SCLC cell line NCI-H209 and NCI-H345 in a time-dependent and reversible manner. [125I-Tyr0]NMB bound with high affinity (Kd = 1 nM) to a single class of sites (Bmax = 800/cell). Specific [125I-Tyr0]NMB binding was inhibited with high affinity by NMB (IC50 = 1 nM) and moderate affinity by bombesin, GRP and [D-Arg1, D-Pro2, D-Trp7,9, Leu11]substance P ([APTTL]SP) but not GRP1-16 (IC50 = 50, 100, 1,000 and > 10,000 nM, respectively). In Fura 2 AM loaded NCI-H345 cells, NMB elevated cytosolic calcium in a concentration-dependent manner. NMB (10 nM) elevated the cytosolic calcium from 150 to 180 nM and calcium was released from intracellular pools. The increase in cytosolic calcium caused by 10 nM NMB was reversed by 1 microM [APTTL]SP but not 1 microM [D-Phe6]bombesin6-13methylester, a GRP receptor antagonist. Also, NMB stimulated the clonal growth of NCI-H209 and NCI-H345 in a concentration-dependent manner. The increase in the clonal growth caused by NMB was reversed by 1 microM [APTTL]SP. These data suggest that NMB receptors may regulate the proliferation of some SCLC cells.

Activation of neuromedin B-preferring bombesin receptors on rat glioblastoma C-6 cells increases cellular Ca2+ and phosphoinositides

Recent cloning studies confirm the presence of two subtypes of bombesin (Bn) receptors. In contrast to the gastrin-releasing peptide (GRP)-preferring subtype, which has been widely studied, nothing is known about the cellular mechanisms of the neuromedin B (NMB)-preferring subtype, which occurs widely in the central nervous system and gastrointestinal tissues, partially because of the lack of a cell line with functional receptors. In the present study we have investigated Bn receptors on the rat glioblastoma cell line C-6, reported to contain mRNA of the NMB receptor subtype. Binding of 125I-[D-Tyr0]NMB to these cells was time- and temperature-dependent, saturable, reversible, and only inhibited by Bn receptor agonists or antagonists. For Bn receptor agonists the relative potencies were: NMB (1.7 nM) approximately equal to litorin (3 nM) greater than ranatensin (8 nM) greater than Bn (19 nM) greater than neuromedin C (NMC) (210 nM) greater than GRP (500 nM). These relative affinities were almost identical to those for the NMB receptor subtype on rat oesophageal tissue and for Balb 3T3 cells stably transfected with the NMB receptor subtype. These potencies differed from those for the GRP receptor subtype on rat pancreatic acini [Bn approximately equal to litorin (4 nM) greater than ranatensin, NMC, GRP (15-20 nM) much greater than NMB (351 nM)]. The relative potencies of four different classes of Bn receptor antagonists were compared. Results from C-6 tumour cells agreed closely with those for binding to the NMB receptor subtype on rat oesophageal tissue and in Balb 3T3 cells stably transfected with this receptor, and differed markedly from those for binding to the GRP receptor subtype on rat pancreatic acini. Four Bn receptor antagonists had a higher affinity for the GRP subtype ([D-Phe6]Bn-(6-13)ethyl ester (500 x), [D-Phe6][psi 13-14,Cpa14]Bn- (6-14) (70 x) (where psi 13-14 refers to the replacement of the -CONH- peptide bond between Leu13 and Met14 by -CH2NH2) [psi 13-14,Leu14]Bn, [D-Phe6]Bn-(6-13) propylamide (30 x)] and two had a higher affinity for the NMB subtype on C-6 cells and transfected cells ([D-Pro4,D-Trp7,9,10] substance P-(4-11) (9 x) and [Tyr4,D-Phe12]Bn (18 x)]. In C-6 tumour cells, Bn receptor agonists caused an increase in cytosolic Ca2+ and the generation of inositol phosphates. For both responses, NMB was more than 50-fold more potent than GRP. Neither NMB nor GRP increased cyclic AMP. These results demonstrate that the rat glioblastoma cell line C-6 possesses functional NMB-preferring Bn receptors, and agonist occupation activates phospholipase C, thus increasing cytosolic Ca2+ and inositol phosphate formation. Because the interaction of Bn-related peptides with C-6 cell receptors is identical with that reported in other tissues containing the mRNA for the NMB subtype, this cell line should prove useful in exploring further the cellular basis of action of the peptides that interact with this receptor in the central nervous system and various other tissues.

Identification and initial characterization of a putative neuromedin B-type receptor from rat urinary bladder membranes

Receptor binding site(s) on the rat urinary bladder membranes were characterized using a biologically active analog of bombesin, [Tyr4,Leu14]bombesin, and a 50,000 x g total particulate preparation. The binding was specific, reversible, saturable, time- and concentration-dependent. A dissociation curve showed that both bombesin and neuromedin B equally displaced the radioligand in the first 10 min after saturation. From the rate constant of association K + 1 = 7.60 x 10(9) M-1 min-1, and the rate constant of dissociation k-1 = 0.050 min-1, the apparent equilibrium dissociation constant Kd = 6.57 +/- 1.09 pM was determined. A linear Scatchard plot of the specific binding of 125I-[Tyr4,Leu14]bombesin to the membranes revealed that the radioligand bound with high affinity, Kd = 6.38 +/- 0.86 pM, to a single class of sites (Bmax = 2.3 fmol/mg protein). The Hill coefficient of the same binding data was 1.05 +/- 0.21, indicating that the radioligand was binding to a single population of noninteracting binding sites. Both bombesin and neuromedin B displaced the radioligand dose dependently (IC50 = 0.3 nM). Neurokinin A and neurokinin B were less potent (IC50 = 20 and 110 nM, respectively). Substance P, or the specific bombesin receptor antagonists [D-Phe6]bombesin-(6-13) methyl ester, [D-F5Phe6,D-Ala11]bombesin-(6-11) methyl ester, [D-Phe6]bombesin-(6-13) propylamide, [D-Phe6,Leu13psi(CH2NH)Leu14]bombesin or [D-Cpa6,Phe14(psi13-14)]bombesin-(6-14) had an IC50 greater than 1 microM. The results presented suggest the presence of neuromedin B receptor sites on the rat urinary bladder membranes that can be occupied also by some other peptides, notably bombesin, neurokinin A and neurokinin B.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of [D-Phe6] bombesin (6-13) methylester, a bombesin receptor antagonist, towards bombesin-induced contractions in the guinea-pig and rat isolated urinary bladder

1. The effect of [D-Phe6] bombesin (6-13) methylester (OMe), a newly developed potent antagonist of bombesin receptors, has been investigated against bombesin-induced contractions of the guinea-pig and rat isolated urinary bladder. 2. Bombesin (0.1 nM-10 microM) produced a concentration-dependent contraction of the guinea-pig isolated bladder which approached the same maximum response as KCl (80 mM). The response to bombesin was antagonized in a competitive manner (rightward shift of the concentration-response curve without depression of the maximal response) by [D-Phe6] bombesin (6-13) OMe (0.3-10 microM). Degree of antagonism was concentration-dependent between 0.3 and 3 microM (dose ratios = 2.4, 9 and 39 in the presence of 0.3, 1, 3 microM of the antagonist). However, a larger concentration (10 microM) of the antagonist was not more effective (dose ratio = 36) than 3 microM. 3. Neither the action of bombesin nor the activity of the antagonist was influenced by peptidase inhibitors (bestatin, captopril and thiorphan 3 microM each) or by atropine, indomethacin, chlorpheniramine and desensitization of P2x purinoceptors by alpha, beta methylene ATP. 4. The bombesin antagonist was ineffective against contraction of the guinea-pig urinary bladder produced by the NK-1 tachykinin receptor-selective agonist, [Sar9] substance P sulphone. The action of the NK-1 receptor agonist was antagonized by L 668, 169 (3 microM), a cyclic peptide tachykinin antagonist. L 668, 169 had no effect toward bombesin-induced contraction. 5. The bombesin antagonist (1-10 microM) had no effect against the non-adrenergic non-cholinergic response of the guinea-pig isolated urinary bladder to electrical field stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a potent bombesin receptor antagonist with prolonged in vivo inhibitory activity on bombesin-stimulated amylase and protein release in the rat

Of the various types of potent bombesin(Bn)/gastrin releasing peptide receptor antagonists that have been discovered, the desMet14-methyl ester peptides are devoid of residual agonist activity and are among the most potent in terms of in vitro receptor blockade and also in terms of their prolonged inhibition of bombesin-stimulated amylase and protein release in the rat. We have now examined the in vitro and in vivo properties of a new series of methyl ester analogues, [D-Phe6]Bn(6-13)OMe, [D-Phe6,D-Ala11]Bn(6-13)OMe, N alpha-propionyl-[D-Ala24]GRP(20-26)OMe, and [D-pentafluoro-Phe6,D-Ala11]Bn(6-13)OMe, which have an additional D-amino acid substituent and some highly lipophilic moieties at the N-terminus. All analogues were able to potently antagonize the ability of Bn to stimulate amylase release from rat acinar cells, with IC50 values of 2.4, 2.5, 0.6, and 1.3 nM, respectively. The four peptides were found to have binding affinities for these cells comparable to Bn itself, with K(i)s of 10.3, 2.8, 5.5, and 3.6 nM, respectively, but all had little or no affinity for neuromedin B receptors on murine C6 cells. Single bolus IV injections of these peptides were found to potently inhibit amylase and protein release caused by IV infusion of bombesin into the rat. Generally the peptides containing the D-Ala substituent were longer acting than [D-Phe6]Bn(6-13)OMe, so that [D-Phe6,D-Ala11]Bn(6-13)OMe and N alpha-propionyl-[D-Ala24]GRP(20-26)OMe displayed significant inhibitory effects for up to 1.5 h after administration.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the clearance of ovine and human corticotrophin-releasing hormone (CRH) in man and sheep: a possible role for CRH-binding protein

A specific binding protein for human corticotrophin-releasing hormone (hCRH), which does not bind to the ovine hormone (oCRH), has recently been demonstrated in human plasma. No such binding protein has been found in sheep plasma. We have investigated the half-life of human and ovine CRH in man and in sheep. Peptides were measured directly in plasma with two-site immunoradiometric assays, as these assays are unaffected by the presence of inactivated peptide fragments. In man, the half-life of hCRH (30.5 +/- 3.3 min; mean +/- S.E.M.) was significantly (P less than 0.001) less than that of oCRH (42.8 +/- 6.4 min). In sheep, there was no significant difference between the half-life of hCRH (46.5 +/- 7.2 min) and that of oCRH (39.8 +/- 10.1 min); these half-lives were also significantly (P less than 0.001) longer than that of hCRH in man. One possible explanation for the shorter half-life of hCRH in man is that the clearance of hCRH is enhanced by CRH-binding protein, although other binding proteins often have the opposite effect. Peak ACTH and cortisol responses occurred earlier in sheep than in man, although no differences were found in the response times to oCRH or hCRH within either species. The responses were more sustained in sheep than in man, and the previously reported biphasic response was only seen in some of the sheep and not in man. Absolute responses to either peptide were greater in sheep than in man; however, in man an 8.1-fold rise in ACTH was measured in response to oCRH, while hCRH gave a significantly (P = 0.043) smaller 4.4-fold response.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptone stimulates gastrin secretion from the stomach by activating bombesin/GRP and cholinergic neurons

The mechanism by which partly digested protein (peptone) stimulates gastrin secretion was examined in isolated antral tissues with intact intramural innervation. In the isolated vascularly perfused rat stomach, luminal perfusion with 0.5% peptone increased gastrin (62 +/- 14 pg/min; P less than 0.01) and decreased somatostatin (74 +/- 19; P less than 0.01) secretion. The axonal blocker tetrodotoxin (TTX) abolished the gastrin and somatostatin responses indicating that the responses were neurally mediated. Atropine partly inhibited the gastrin response (50%) and converted the somatostatin response to an increase above basal level. The selective bombesin/gastrin-releasing peptide (GRP) antagonist [Leu13-psi(CH2NH)-Leu14]-bombesin partly inhibited the gastrin response (65%) and caused a further decrease in somatostatin secretion. A combination of atropine and the bombesin/GRP antagonist, like TTX, abolished the gastrin and somatostatin responses. The pattern of response to peptone in superfused antral segments was identical to that in the vascularly perfused stomach. In fundic segments that do not secrete gastrin, the somatostatin response to peptone alone and with various antagonists was identical to that in antral segments. The results indicate that peptone stimulates gastrin secretion by activating stimulatory cholinergic and bombesin/GRP neurons. Cholinergic neurons stimulate gastrin directly as well as indirectly by eliminating the inhibitory paracrine influence of somatostatin.

Pituitary adenylate cyclase-activating polypeptide relaxes rat gastrointestinal smooth muscle

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a new member of the secretin/glucagon peptides family, being most homologous to vasoactive intestinal peptide (VIP). The present study was designed to investigate a possible effect of PACAP on the rat gastrointestinal smooth muscle in vitro. We demonstrated that 1) PACAP reduced basal smooth-muscle contractions in all portions of the gastrointestinal tract, but the effect of VIP was region-specific. The inhibitory effect of PACAP in midcolon was approximately 100 times greater than that of VIP. 2) PACAP significantly inhibited smooth-muscle contractions induced by acetylcholine or carbachol. The inhibitory effect of PACAP was not affected by hexamethonium and was additive to the inhibitory effect of atropine and pirenzepine. 3) PACAP inhibited smooth-muscle contractions induced by substance P, cholecystokinin, and galanin, even after atropine treatment. Although the exact mechanism of the inhibitory action of PACAP remains to be clarified, PACAP appears to exert its effect in the rat at a site other than muscarinic receptors, probably through a direct effect on gastrointestinal smooth muscle in vitro.

Reduced gastric acid inhibitory effect of a pGIP(1-30)NH2 fragment with potent pancreatic amylase inhibitory activity

Gastric inhibitory polypeptide (GIP) strongly stimulates insulin secretion in the presence of glucose and also stimulates somatostatin release from gastric mucosa. It was reported recently that both stimulatory activities can be dissociated by removing the C-terminal 12 amino acid residues. Since insulin and somatostatin are involved in regulation of exocrine pancreatic and gastric secretion in rats, we compared the inhibitory effects of pGIP and the pGIP(1-30)NH2 fragment on pancreatic amylase and gastric acid secretion. pGIP(1-30)NH2 displayed full activity on inhibition of bombesin (BN)-stimulated amylase release relative to GIP itself, but was about 10-fold less potent in inhibiting gastric acid secretion. These results suggest that the receptors involved in these two events have quite different ligand binding requirements and that more specific analogues of GIP can be designed which should be of value in elucidating the physiological roles of this hormone.

Actions of somatostatins on gastric smooth muscle cells

The effects of somatostatin-28, somatostatin-14, and a synthetic somatostatin octapeptide analogue, D-Phe-Cys-Tyr-D-Trp-Lys-Thr-Cys-Nal-NH2 (cyclo SS-8) were examined on contraction of dispersed gastric smooth muscle cells from guinea pigs. The somatostatins did not cause contraction of gastric smooth muscle cells, nor did they inhibit carbachol-stimulated contraction. However, they reversed vasoactive intestinal peptide (VIP)-induced inhibition (relaxation) of carbachol-stimulated contraction. Somatostatin-28 had a half-maximal effect (EC50) at 1.6 +/- 0.8 nM, cyclo SS-8 at 0.6 +/- 0.3 nM, but somatostatin-14 had no effect even when used in concentrations as high as 1 microM. Incubation of muscle cells with peptidase inhibitors phosphoramidon (1 microM) plus amastatin (10 microM) had no effect on the EC50 of somatostatin-28 or cyclo SS-8 but increased the potency of somatostatin-14 greater than 1,000-fold. When peptides were incubated with muscle cells and the products applied to high-performance liquid chromatography, cyclo SS-8 was not degraded, but somatostatin-14 was rapidly degraded when present alone, and the addition of peptidase inhibitors partially inhibited the degradation. Cyclo SS-8 had its maximal effect at 0.5-1 min and inhibited relaxation induced by VIP, isoproterenol, glucagon, or dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP). Cyclo SS-8 partially inhibited the increase in VIP-stimulated cAMP. Preincubation with pertussis toxin blocked the inhibitory action of cyclo SS-8 on VIP or DBcAMP-induced relaxation. These results indicate that gastric smooth muscle cells rapidly degrade somatostatin-14 and suggest that muscle cell peptidases could have a major effect on the actions of somatostatin-14.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural requirements for galanin inhibition of pentagastrin-stimulated gastric acid secretion in conscious rats

The effects of rat galanin, together with a number of its N- and C-terminal fragments, on pentagastrin-stimulated gastric acid secretion were studied in conscious rats equipped with chronic gastric fistulas. Similarly to its porcine counterpart studied previously, at a dose of 3 nmol/kg per h rat galanin was a potent inhibitor of gastric acid secretion. The N-terminal fragments, rat galanin-(1-10) and -(1-15), retained about 60% of the inhibitory potency of the whole galanin sequence whilst the C-terminal fragments, rat galanin-(2-29), -(3-29) and -(9-29), were unable to produce significant inhibition over comparable dose ranges. Surprisingly, however, simply acetylating the alpha-amino group in position 9 of rat galanin-(9-29) restored almost full gastric acid inhibitory activity in a homologous rat model. We speculate that this could be due to a favorable conformational effect on the C-terminal region produced by alpha-acetylation. These results also suggest that structural features within either the N-terminal or C-terminal regions of rat galanin are able to elicit this particular biological response. One possible explanation for this could be the involvement of more than one rat galanin receptor having different ligand recognition requirements.

D-Ala2,F5Phe4-dynorphin amide, an opiate with analgesic and toxic properties

A novel analog of dynorphin (1-13), D-Ala2,F5Phe4-dynorphin amide, was prepared and its pharmacological spectrum of activity was investigated. In a hot plate test on Swiss Webster and C57Bl mice, a 20 micrograms intracerebroventricular (icv) dose of the analog produced analgesia, which was greater in potency and duration than the parent dynorphin. This action of D-Ala2,F5Phe4-dynorphin amide was antagonized by the opiate receptor antagonist naloxone (2 mg/kg ip), administered either before or after the peptide. In addition to its analgesic action in mice, D-Ala2,F5Phe4-dynorphin amide produced a Straub tail and a catatonic-like state, both of which were also attenuated by naloxone. On the electrically-stimulated mouse vas deferens preparation, in vitro, D-Ala2,F5Phe4-dynorphin amide inhibited contractile activity and had an IC50 of 108.2 +/- 34.7 nM (SEM), about 4-fold weaker than that of dynorphin. This action was also attenuated by naloxone. An icv dose of 150 micrograms of D-Ala2,F5Phe4-dynorphin amide in mice, and a cumulative series of icv doses up to 2600 micrograms in anesthetized rats, failed to produce a lethal effect. No pathological changes were observed in mouse liver and kidney at 24 h after a 50 mg/kg dose of the peptide analog. In rats anesthetized with diallylbarbital (70 mg/kg ip) and urethane (280 mg/kg ip), D-Ala2,F5Phe4-dynorphin amide did not modify blood pressure, heart rate and respiratory rate. However, when mice were injected peripherally with single doses of D-Ala2,F5Phe4-dynorphin amide, convulsive episodes were produced, and lethal effects were observed with an LD50 of 60.0 mg/kg (95% confidence limits: 49.7-70.2 mg/kg) at 48 h. This action of D-Ala2,F5Phe4-dynorphin amide was not attenuated by naloxone (2.0 mg/kg, ip). Although analgesic and behavioral effects of D-Ala2,F5Phe4-dynorphin amide (e.g. Straub tail and catatonic-like state) are opiate-like, the lethal effect may be the consequence of actions of the peptide on non-opiate systems, Thus, the novel fluorinated dynorphin analog, D-Ala2,F5Phe4-dynorphin amide, may be a useful chemical tool for the study of opiate systems and their occasionally unanticipated biological or toxic actions.