Effects of some neurokinin A analogues on tachykinin-induced contraction of guinea pig trachea.

A series of analogues of neurokinin A (NKA) has been synthesized and characterized by testing for their abilities, in vitro, to contract guinea pig tracheal smooth muscle or to antagonize NKA-, NKB- and SP-induced contraction of this tissue. Substitution of NKA residues Gly8 or Leu9 by conformationally restricting amino acids produced peptides that were antagonists of NKA action, but the type and specificity of the antagonism depended on the size of the peptide. Thus, while [Ala5, Aib8, Leu10]NKA(2-10) showed no agonism and was a specific, competitive antagonist of NKA, [Ala5, Aib8, Leu10]NKA(4-10) was a noncompetitive antagonist of NKA and substance P (SP) and was itself a weak agonist at concentrations above 10(-7) M.     

Effect of indomethacin on opioid-induced gastric protection in cold-restrained stress

Morphine and the synthetic opioid met-enkephalin analog [D-Ala2, MePhe4, Met(0)5ol] enkephalin (FK 33-824) injected intraperitoneally to rats at doses of 5-20 and 0.5-2 mg/kg respectively showed a protective effect on gastric lesion induced by cold-restraint stress. This protective effect was abolished by pretreatment with indomethacin. This suggests a role for prostaglandins in the protection, induced by opioids of the gastric mucosa against the development of stress-induced ulcers.     

Structure-activity studies at the rat tachykinin NK2 receptor: effect of substitution at position 5 of neurokinin A.

A series of analogues of neurokinin A(4-10) was synthesized using solid phase techniques with Chiron pins, and purified by HPLC. The potencies of 10 peptides with substitution at Ser5 were assessed at rat fundus NK2 receptors. In membrane binding studies with [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), all compounds except [Asp5]NKA(4-10) showed reasonable affinity, and analogues with Lys and Arg substitutions were five-fold more potent than NKA(4-10). In functional studies, all peptides were able to contract the rat isolated fundus strips. Analogues with Phe, His and Asn substitutions were substantially weaker in functional than in binding studies, whereas there was an excellent correlation (r = 0.95) between binding and functional potency for the remaining seven peptides. [Phe5]NKA(4-10) is in fact neurokinin B(4-10) and this residue may be critical in determining selectivity between NK2 and NK3 receptors. Analogues with a basic residue (Lys, Arg) at position 5 showed both increased affinity and functional potency, whereas the neutral [Asn5]NKA(4-10) was equally as weak in contractile studies as the acidic [Asp5]NKA(4-10). However, [Glu5]NKA(4-10) and [Gln5]NKA(4-10) were no different from NKA(4-10). Our results could indicate the presence of a negative charge on the NK2 receptor, close to position 5 of NKA. This would facilitate interaction with positively charged side chains and impede interaction with negatively charged side chains, particularly the inflexible side chain of aspartic acid. Thus, not only the charge, but also the length of the side chain of the residue at position 5, seems to be important for interaction with the rat NK2 receptor.     

Tachykinins protect against ethanol-induced gastric lesions in rats

Subcutaneous pretreatment of rats with neurokinin (NK) A or the fragment NKA(4-10) reduced the degree of gastric lesions induced by oral administration of 96% ethanol. The protective effect of NKA(4-10) was dose-dependent. Arg-NKB, the water soluble derivative of NKB, was less effective than NKA or NKA(4-10) while [Me-Phe7]NKB, substance P (SP) and SP-methyl-ester were inactive. The NKA(4-10) antilesion effect was reversed by pretreatment with N-ethyl-maleimide, suggesting a possible involvement of sulphydryls in its action. Among the nonmammalian tachykinins, kassinin significantly reduced ethanol-induced lesions while eledoisin and physalaemin at equivalent molar doses were inactive. These results provide, for the first time, evidence that tachykinins and their derivatives exert gastroprotective activity toward ethanol-induced haemorrhagic lesions. Assuming a receptor-mediated mechanism, NK-2 sites could be involved.     

Conformation-activity relationship of tachykinin neurokinin A (4-10) and of some [Xaa8] analogues.

NKA (4-10), the C-terminal heptapeptide fragment (Asp-Ser-Phe-Val-Gly-Leu-Met-NH2) of tachykinin NKA, is more active than the parent native compound in the interaction with the NK-2 receptor. Substitution of Gly8 with the more flexible residue beta-Ala8 increases its selectivity with respect to other two known receptors (NK-1 and NK-3), whereas substitution with either D-Ala8 or GABA8 deprives the peptide of its biological activity. These findings can be interpreted by a conformational analysis based on NMR studies in DMSO-d6 and in a DMSO-d6/H2O cryoprotective mixture combined with internal energy calculations. NKA(4-10) is characterized by a structure containing a type I beta-turn extending from Ser5 to Gly8, followed by a gamma-turn centered on Gly8, whereas for [beta-Ala8]NKA(4-10) is possible to suggest a type I beta-turn extending from Ser5 to beta-Ala8, followed by a C8 turn comprising beta-Ala8 and Leu9 and by another beta-turn extending from beta-Ala8 to the terminal NH2. The preferred conformation of [beta-Ala8]NKA(4-10) is not compatible with models for NK-1 and NK-3 agonists proposed on the basis of rigid peptide agonists [Levian-Teitelbaum et al. (1989) Biopolymers 28, 51-64; Sumner & Ferretti (1989) FEBS Lett. 253, 117-120]. The preferred solution conformation of [beta-Ala8]NKA(4-10) may thus be considered as a likely bioactive conformation for NK-2 selective peptides.     

Characterization of the tachykinin NK2 receptor subtype in the rabbit pulmonary artery.

Contractile responses to neurokinin A (NKA), neuropeptide gamma(NP gamma), and the NK2 receptor-selective analogs [Lys5,MeLeu9,Nle10]NKA(4-10) and MDL 28,564 were determined in the endothelium-denuded rabbit pulmonary artery. Responses to NKA, NP gamma, and [Lys5,MeLeu9,Nle10]NKA(4-10) were antagonized by the NK2 receptor antagonist MDL 29,913, with pA2 values of 6.67, 6.46, and 7.32, respectively. Autoradiographic studies failed to demonstrate any specific binding sites for [125I]-iodohistidyl NKA (INKA) over the pulmonary artery. These data suggest the presence in rabbit pulmonary artery of an unusual "nonclassical" NK2 receptor subtype, which appears to lack affinity for INKA.     

Effect of prostaglandin synthesis inhibitors on neurotensin and sodium salicylate-induced gastric cytoprotection in rats

Sodium salicylate (SA) has been reported to inhibit the formation of gastric ulcerations induced by aspirin, indomethacin, and absolute ethanol. In this study, SA dose-dependently inhibited gastric ulcers induced by three hours of cold-restraint stress (CRS); SA-induced cytoprotection was prevented by both acetylsalicylic acid (aspirin) and indomethacin pretreatment. Neurotensin (NT), which has previously been demonstrated to prevent the development of CRS-induced gastric ulcerations after intracisternal administration, was found to be ineffective in animals pre-treated with aspirin, and with indomethacin, as previously described. These data suggest that in the CRS model both NT- and SA-induced gastric cytoprotection require a functionally intact gastrointestinal prostaglandin synthetic pathway.     

Monocyte chemotactic protein-1 regulates leukocyte recruitment during gastric ulcer recurrence induced by tumor necrosis factor-alpha

TNF-alpha has numerous biological activities, including the induction of chemokine expression, and is involved in many gastric injuries. C-C chemokines [monocyte chemotactic protein (MCP)-1 and macrophage inflammatory protein (MIP)-1alpha] and C-X-C chemokines [MIP-2 and cytokine-induced neutrophil chemoattractant (CINC)-2alpha] mediate chemotaxis of monocytes and neutrophils, respectively. We examined the roles of TNF-alpha and dynamics of chemokine expression in gastric ulceration including ulcer recurrence and indomethacin-induced injury. Rats with healed chronic gastric ulcers received intraperitoneal TNF-alpha to induce ulcer recurrence. Some rats were given neutralizing antibodies against neutrophils or MCP-1 together with TNF-alpha. In a separate experiment, rats were orally administered 20 mg/kg indomethacin with or without pretreatment with pentoxifylline (an inhibitor of TNF-alpha synthesis) or anti-MCP-1 antibody. TNF-alpha (1 microg/kg) induced gastric ulcer recurrence after 48 h, which was completely prevented by anti-neutrophil antibody. TNF-alpha increased the number of macrophages and MCP-1 mRNA expression in scarred mucosa from 4 h, whereas it increased MPO activities (marker of neutrophil infiltration) and mRNA expression of MIP-2 and CINC-2alpha from 24 h. Anti-MCP-1 antibody inhibited leukocyte infiltration with reduction of the levels of C-X-C chemokines and prevented ulcer recurrence. Indomethacin treatment increased TNF-alpha/chemokine mRNA expression from 30 min and induced macroscopic erosions after 4 h. Pentoxifylline inhibited the indomethacin-induced gastric injury with reduction of neutrophil infiltration and expression of chemokine (MCP-1, MIP-2, and CINC-2alpha). Anti-MCP-1 antibody also inhibited the injury and these inflammatory responses but did not affect TNF-alpha mRNA expression. In conclusion, increased MCP-1 triggered by TNF-alpha may play a key role in gastric ulceration by regulating leukocyte recruitment and chemokine expression.     

Nitroxides prevent exacerbation of indomethacin-induced gastric damage in adjuvant arthritis rats

Nonsteroidal anti-inflammatory drugs are the drugs of choice in the treatment of rheumatoid arthritis (RA) because of their rapid analgesic effect. However, they induce severe gastric damage in RA patients and animals by a process mediated by reactive oxygen species (ROS). Nitroxides (nitroxyl radicals) are widely used as imaging agents and antioxidants to explore the role of ROS generation in the pathogenesis of disease. In this study, the effectiveness of the newly synthesized nitroxides 8-aza-7,7,9,9-tetramethyl-1,4-dioxaspiro[4.5]undecan-8-oxyl (compound 1) and 4-oxo-2,2,6,6-tetraethylpiperidine-1-oxyl (compound 2) in the prevention of gastric ulcers in adjuvant arthritis rats treated with indomethacin was evaluated by monitoring the reaction of reactive oxygen species in gastric tissue with Overhauser-enhanced magnetic resonance imaging (OMRI). Pretreatment with all tested nitroxides suppressed the ulcers induced by indomethacin treatment in arthritic rats. OMRI using compounds 1 and 2 as well as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) demonstrated a redox imbalance in the stomach of these rats. Lipid peroxide and interleukin (IL)-1β levels in the gastric mucosa were significantly suppressed by compound 1 and TEMPOL, whereas CINC/gro, a member of the IL-8 family, was significantly suppressed by compound 1 only. These results suggest that the preventive effects of nitroxides on gastric ulcers may operate by different mechanisms.     

A potent and selective agonist for NK-2 tachykinin receptor

Replacement of the glycine in position 8 of the C-terminal heptapeptide NKA(4-10) with beta-alanine give rise to a potent and selective agonist for the NK-2 tachykinin receptor. The affinity of [beta-Ala8]-NKA(4-10) to the NK-2 receptor is enhanced by almost one order of magnitude as compared to NKA(4-10), while affinity decreases at about the same extent at NK-1 and NK-3 receptors, respectively. Synthesis and biological activities of a series of NKA(4-10) analogues systematically replaced in each position with beta-alanine are also reported.     

Protective effects of steroid saponins from Paris polyphylla var. yunnanensis on ethanol- or indomethacin-induced gastric mucosal lesions in rats: structural requirement for activity and mode of action

The methanolic extract from the rhizomes of Paris polyphylla SM. var. yunnanensis (FR.) H-M. was found to potently inhibit ethanol-induced gastric lesions in rats. Through bioassay-guided separation, four known spirostanol-type steroid saponins, pennogenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-arabinofuranosyl(1-->4)]-beta-D-glucopyranoside (1), pennogenin 3-O-alpha-L-rhamnopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->4)-[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (2), diosgenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-arabinofuranosyl(1-->4)]-beta-D-glucopyranoside (3), and diosgenin 3-O-alpha-L-rhamnopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->4)-[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (4), and a new furostanol-type steroid saponin, parisaponin I (5), together with two known furostanol-type steroid saponins, trigofoenoside A (6) and protogracillin (7), were isolated from the active fraction. Compounds 1-4 (1.25-10 mg/kg, po) strongly inhibited gastric lesions induced by ethanol and indomethacin. With regard to structural requirement of steroid saponins, the 3-O-glycoside moiety and spirostanol structure were found to be essential for the activity and the 17-hydroxyl group in the aglycon part enhanced the protective effects against ethanol-induced gastric lesions. The protective effects of 1 and 3 against ethanol-induced gastric lesions were attenuated by pretreatment with indomethacin and N-ethylmaleimide. Compounds 1 and 3 weakly inhibited acid secretions in pylorus-ligated rats. These findings suggested that endogenous prostaglandins and sulfhydryl compounds were involved in the protective activity.     

Relative bronchoconstrictor activity of neurokinin A and neurokinin A fragments in guinea pigs.

We examined the effect of rapid intravenous infusion of neurokinin A (NKA) and selected COOH-terminal NKA fragments on pulmonary conductance (GL) and dynamic compliance in anesthetized mechanically ventilated guinea pigs. The rank order of the dose of peptide required to reduce GL by 50% (ED50GL) was NKA = NKA2-10 = NKA3-10 = NKA4-10 less than NKA5-10 much less than NKA6-10. The time course of bronchoconstriction induced by NKA2-10, NKA3-10, and NKA4-10 was similar to that induced by NKA, whereas NKA5-10 and NKA6-10 each had a shorter duration of action than NKA for a similar induced maximal change in GL. To determine whether degradation of these NKA fragments by neutral endopeptidase (NEP) modulates their bronchoconstrictor activity as it does for native NKA, we examined the effect of the NEP inhibitor SCH32615 on NKA3-10-, NKA5-10-, and NKA6-10-induced changes in GL. We have previously reported that the ED50GL for NKA was approximately 20-fold lower in animals pretreated with SCH32615 (1 mg/kg) than in control guinea pigs. SCH32615 caused a 16-fold decrease in ED50GL for NKA3-10 (P less than 0.001) but had no effect on airway responses to NKA5-10 or NKA6-10. The results demonstrate that the magnitude and duration of bronchoconstriction induced by potential aminopeptidase degradation products of NKA are similar to those of the native peptide. Aminopeptidases do not, therefore, have the capacity to modulate the bronchoconstriction induced by this peptide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of key residues that cause differential gallbladder response to PACAP and VIP in the guinea pig

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have opposite actions on the gallbladder; PACAP induces contraction, whereas VIP induces relaxation. Here, we have attempted to identify key residues responsible for their interactions with PACAP (PAC1) and VIP (VPAC) receptors in the guinea pig gallbladder. We synthesized PACAP-27/VIP hybrid peptides and compared their actions on isolated guinea pig gallbladder smooth muscle strips using isotonic transducers. [Ala4]- and [Val5]PACAP-27 were more potent than PACAP-27 in stimulating the gallbladder. In contrast, [Ala4, Val5]- and [Ala4, Val5, Asn9]PACAP-27 induced relaxation similarly to VIP. [Asn9]-, [Thr11]-, or [Leu13]PACAP-27 had 20-70% contractile activity of PACAP-27, whereas [Asn24,Ser25,Ile26]PACAP-27 showed no change in the activity. All VIP analogs, including [Gly4,Ile5,Ser9]VIP, induced relaxation. In the presence of a PAC1 receptor antagonist, PACAP(6-38), the contractile response to PACAP-27 was inhibited and relaxation became evident. RT-PCR analysis revealed abundant expressions of PAC1 receptor, "hop" splice variant, and VPAC1 and VPAC2 receptor mRNAs in the guinea pig gallbladder. In conclusion, PACAP-27 induces contraction of the gallbladder via PAC1/hop receptors. Gly4 and Ile5 are the key NH2-terminal residues of PACAP-27 that distinguish PAC1/hop receptors from VPAC1/VPAC2 receptors. However, both the NH2-terminal and alpha-helical regions of PACAP-27 are required for initiating gallbladder contraction.     

Reactive oxygen species mediate arachidonic acid-induced dilation in porcine coronary microvessels

Reactive oxygen species (ROS) have been proposed to mediate vasodilation in the microcirculation. We investigated the role of ROS in arachidonic acid (AA)-induced coronary microvascular dilation. Porcine epicardial coronary arterioles (110 +/- 4 microm diameter) were mounted onto pipettes in oxygenated Krebs buffer. Vessels were incubated with vehicle or 1 mM Tiron (a nonselective ROS scavenger), 250 U/ml polyethylene-glycolated (PEG)-superoxide dismutase (SOD; an O2- scavenger), 250 U/ml PEG-catalase (a H2O2 scavenger), or the cyclooxygenase (COX) inhibitors indomethacin (10 microM) or diclofenac (10 microM) for 30 min. After endothelin constriction (30-60% of resting diameter), cumulative concentrations of AA (10(-10)-10(-5)M) were added and internal diameters measured by video microscopy. AA (10-7 M) produced 37 +/- 6% dilation, which was eliminated by the administration of indomethacin (4 +/- 7%, P < 0.05) or diclofenac (-8 +/- 8%, P < 0.05), as well as by Tiron (-4 +/- 5%, P < 0.05), PEG-SOD (-10 +/- 6%, P < 0.05), or PEG-catalase (1 +/- 4%, P < 0.05). Incubation of small coronary arteries with [3H]AA resulted in the formation of prostaglandins, which was blocked by indomethacin. In separate studies in microvessels, AA induced concentration-dependent increases in fluorescence of the oxidant-sensitive probe dichlorodihydrofluorescein diacetate, which was inhibited by pretreatment with indomethacin or by SOD + catalase. We conclude that in porcine coronary microvessels, COX-derived ROS contribute to AA-induced vasodilation.     

Naltrexone-sensitive behavioral actions of the ACTH 4-9 analog (Org 2766)

The effects of the ACTH 4-9 analog (Org 2766) and the COOH-terminal tripeptide of Org 2766 (Phe-D-Lys-Phe; PDLP) on retrieval of one-trial learning passive avoidance behavior were compared with those of beta-endorphin, [Met5]-enkephalin, [D-Ala2,Met5]-enkephalin, des-Tyr1-[Met5]-enkephalin and des-enkephalin-gamma-endorphin (DE gamma E). Amounts of intracerebroventricularly administered Org 2766, PDLP, [Met5]-enkephalin, [D-Ala2,Met5]-enkephalin and DE gamma E, which induced a comparable attenuation of passive avoidance behavior were determined. Pretreatment with the opiate antagonist naltrexone prevented the attenuating effect of these peptides on passive avoidance behavior except that of DE gamma E. The attenuating effect of Org 2766 and of [Met5]-enkephalin was reversed to facilitation of passive avoidance behavior in the presence of naltrexone. Subcutaneous treatment with Org 2766 and [D-Phe7]-ACTH 4-10 decreased electrical self-stimulation behavior elicited from the medial septal area. Naltrexone prevented the inhibitory effect of Org 2766 on this behavior, but not that of [D-Phe7]-ACTH 4-10. Although the attenuating effect of PDLP on passive avoidance behavior was not reduced by pretreatment with [Met5]-enkephalin- or beta-endorphin-antiserum, and PDLP induced neither analgesia nor excessive grooming, the data suggest that the inhibitory effect of Org 2766 and PDLP on passive avoidance behavior and electrical self-stimulation are mediated by endorphin systems in the brain.     

Hypotensive mechanism of [Leu13]motilin in dogs in vivo and in vitro.

The effects of [Leu13]motilin were examined in vivo after its intravenous administration into anesthetized dogs and in vitro with isolated preparations of canine mesenteric artery. [Leu13]Motilin (0.1-10 nmol x kg(-1), i.v.) induced both strong and clustered phasic contractions in the gastric antrum and duodenum. At doses of over 1 nmol x kg(-1), [Leu13]motilin also produced transient decreases in arterial blood pressure, left ventricular pressure, maximum rate of rise of left ventricular pressure, and total peripheral resistance, and an increase in aortic blood flow and heart rate. A selective motilin antagonist, GM-109 (Phe-cyclo[Lys-Tyr(3-tBu)-betaAla] trifluoroacetate), completely abolished the gastric antrum and duodenal motor responses induced by [Leu13]motilin. In contrast, hypotension induced by [Leu13]motilin (1 nmol x kg(-1)) was unchanged in the presence of GM-109. In isolated mesenteric artery preparations precontracted with U-46619 (10(-7) M), [Leu13]motilin (10(-8)-10(-5) M) induced an endothelium-dependent relaxation, and this was inhibited by a pretreatment with N(omega)-nitro-L-arginine, a competitive inhibitor of NO synthase (10(-4) M). A high dose (10(-4) M) of GM-109 slightly decreased [Leu13]motilin-induced relaxation, and shifted the concentration-response curve of [Leu13]motilin to the right. However, the pA2 value (4.09) of GM-109 for [Leu13]motilin in the present study was conspicuously lower than that previously demonstrated in the rabbit duodenum (7.37). These results suggest that [Leu13]motilin induces hypotension via the endothelial NO-dependent relaxation mechanism and not through the receptor type that causes upper gastrointestinal contractions.     

Role of endogenous prostacyclin in gastric ulcerogenic and healing responses--a study using IP-receptor knockout mice.

Endogenous prostaglandins (PGs) play an important role in the cytoprotective and healing responses in the stomach, by altering various functions, i.e., an increase of the mucosal blood flow, yet the role of prostacyclin (PGI(2)) and its receptor (IP-receptor) in these responses remains unclarified. In the present study, we used IP-receptor knockout mice [IP (-/-)] and examined the importance of IP-receptors in gastric ulcerogenic, cytoprotective and healing responses in these animals. The studies included the ulcerogenic response to cold-restraint stress, the cytoprotective response to a mild irritant (20 mM taurocholate: TC) and capsaicin, and the healing response of chronic gastric ulcers induced by thermo-cauterization. We first checked the absence of IP-receptors by examining the effect of cicaprost (a PGI(2) agonist, topical mucosal application) on gastric mucosal blood flow and found that this agent increased the mucosal blood flow in wild-type [WT (+/+)] mice but not in IP (+/-) mice. Cold-restraint stress (4 h) induced gastric lesions in both groups of mice, but the severity of damage was significantly greater in IP (-/-) mice. Prior p.o. administration of both TC and capsaicin exhibited a marked cytoprotection against HCl/ethanol-induced gastric damage in WT (+/+) mice, both responses being significantly mitigated in the presence of indomethacin. The adaptive cytoprotection induced by TC was similarly observed in IP (-/-) mice, while the capsaicin protection was totally attenuated in the animals lacking IP receptors. On the other hand, the healing of gastric ulcers was significantly delayed by daily administration of indomethacin in WT (+/+) mice. However, this process was not altered in IP (-/-) mice. These results suggest that endogenous PGI(2) is involved in the gastric ulcerogenic response to stress, but not in the healing of pre-existing gastric ulcers. In addition, PGI(2) and its receptors may play a crucial role in capsaicin-induced gastric protection but not in the adaptive cytoprotection-induced by mild irritants.     

Effects of trigeminal neurotransmitters on piglet pial arterioles.

We investigated effects of calcitonin gene-related peptide (CGRP), substance P (SP), and neurokinin A (NKA) on pial arterioles in newborn pigs. Pial arteriolar diameter was determined using a closed cranial window and intravital microscopy. Initial diameters were approximately 100 microns. Calcitonin-gene related peptide dilated pial arterioles by 22 +/- 8% at 10(-9)M and by 34 +/- 6% at 10(-8)M (n = 8), and this response was not significantly altered by prior administration of indomethacin (5mg/kg, iv) (n = 6) or administration of NG-methyl-L-arginine (5mg/kg, iv, and 10(-3)M in CSF) (n = 10). Substance P dilated arterioles at 10(-10)M through 10(-5)M (maximal response = 23 +/- 3%) (n = 6), and this response was unaffected by indomethacin administration (n = 6). In contrast, NG-methyl-L-arginine blocked much of the pial arteriolar dilation to SP. Unlike the other two peptides, NKA did not change pial arteriolar diameter. Radioimmunoassay determinations indicated that cerebrospinal fluid levels of 6-keto-prostaglandin F1 and prostaglandin E2 did not change appreciably during application of CGRP or SP. We conclude that CGRP and SP but not NKA are dilator stimuli in the piglet pial circulation. Dilation by CGRP probably involves direct activation of receptors on vascular smooth muscle, while SP probably partially dilates pial arterioles via release of an endothelium-dependent relaxing factor.     

Activation of central opioid receptors may induce gastric mucosal defence in the rat.

The effect of different opioid peptides on acidified ethanol- and indomethacin-induced gastric mucosal lesions was studied following intracerebroventricular (i.c.v.) administration. It was found that both the selective delta opioid receptor agonists--deltorphin II, [D-Ala(2), D-Leu(5)]-enkephalin (DADLE), [D-Pen(2), D-Pen(5)]-enkephalin (DPDPE)-, mu-opioid receptor agonist--[D-Ala(2), Phe(4), GlyT-ol]-enkephalin (DAGO)--as well as beta-endorphin inhibited the mucosal damage induced by both ethanol and indomethacin in pmolar dose range. In contrast, the gastric acid secretion was not influenced by DADLE in the dose of 16 nmol/rat and only a slight reduction (40%) was induced by DAGO in the dose of 1.9 nmol/rat. The protective effect was abolished in both ulcer models by bilateral cervical vagotomy. N(G)-nitro-L-arginine, an inhibitor of NO synthase, reduced the protective action in ethanol-induced, but not in indomethacin-induced gastric damage. The results suggest that activation of supraspinal delta and mu-opioid receptors resulted in inhibition of gastric mucosal lesions elicited by ethanol or indomethacin. The gastroprotective action is independent from the effect of opioids on acid secretion. Vagal nerve is involved in conveying the central action to the periphery. The mechanism of the gastroprotective effect of opioids is different in ethanol- and indomethacin-ulcer models: prostaglandins and nitric oxide are likely to be involved in the protective action of opioid peptides in ethanol-, but not in the indomethacin-ulcer model.     

The biochemical and pharmacological properties of a newly synthesized H+-K+ ATPase inhibitor, 2-dimethylamino-4,5-dihydrothiazolo[4,5:3,4]pyridol-[1,2-a]benzimidazol e

This study was designed to determine the effect of a newly synthesized proton pump inhibitor, 2-dimethylamino-4,5-dihydrothiazolo[4,5:3,4]pyridol[1,2-a]be nzimidazole (YJA20379-2), on gastric H(+)-K(+) ATPase activity, acid secretion, and experimental gastroduodenal lesions or ulcers in rats. YJA20379-2 inhibited in a concentration-dependent manner the proton pump (H(+)-K(+) ATPase) activity in isolated hog gastric mucosal microsomes, therefore, confirming its classification as a proton pump inhibitor. The inhibitory efficacy of YJA20379-2 on the proton pump was about eight times higher than that of omeprazole at pH 7.4. The activity of the inhibited enzyme was not restored by dilution and washout method, so this implied that the inhibition of YJA20379-2 is not reversible. YJA20379-2, given intraduodenally or orally, potently suppressed acid secretion in pylorus-ligated rats, with ED50 values of 3.6 and 7.7 mg.kg(-1), respectively. Pretreatment with YJA20379-2 dose dependently protected the gastric mucosa from damage induced by absolute ethanol, water-immersion stress, indomethacin, and the duodenal mucosa from damage induced by mepirizole in rats, with ED50 values of 11.0, 21.0, 0.5, and 18.7 mg.kg(-1), respectively. Repeated administration of YJA20379-2 also dose dependently accelerated spontaneous healing of acetic acid induced gastric ulcers. These results suggest that YJA20379-2 has potent antisecretory and antiulcer effects, which are exerted by suppression of H(+)-K(+) ATPase activity in gastric parietal cells, such that YJA20379-2 may be useful for the clinical treatment of peptic ulcer diseases.