CCK-B Antagonist Research Articles

Design and synthesis of novel 1,4-benzodiazepine surrogates as potential CCKA and CCKB antagonists via palladium-catalyzed three-component cascade reactions

Structurally diverse novel 1,4-benzodiazepine analogues related to selective CCKA antagonist MK-329, and CCKB antagonists L-365,260 and YM022 are prepared via palladium-catalyzed three component domino reactions involving allenylation-carbonylation-anion capture in one-pot cascade protocol in good to excellent yields.

Cholecystokinin from the entorhinal cortex enables neural plasticity in the auditory cortex

Patients with damage to the medial temporal lobe show deficits in forming new declarative memories but can still recall older memories, suggesting that the medial temporal lobe is necessary for encoding memories in the neocortex. Here, we found that cortical projection neurons in the perirhinal and entorhinal cortices were mostly immunopositive for cholecystokinin (CCK). Local infusion of CCK in the auditory cortex of anesthetized rats induced plastic changes that enabled cortical neurons to potentiate their responses or to start responding to an auditory stimulus that was paired with a tone that robustly triggered action potentials. CCK infusion also enabled auditory neurons to start responding to a light stimulus that was paired with a noise burst. In vivo intracellular recordings in the auditory cortex showed that synaptic strength was potentiated after two pairings of presynaptic and postsynaptic activity in the presence of CCK. Infusion of a CCKB antagonist in the auditory cortex prevented the formation of a visuo-auditory association in awake rats. Finally, activation of the entorhinal cortex potentiated neuronal responses in the auditory cortex, which was suppressed by infusion of a CCKB antagonist. Together, these findings suggest that the medial temporal lobe influences neocortical plasticity via CCK-positive cortical projection neurons in the entorhinal cortex.

The CCKB antagonist CI988 reduces food intake in fasted rats via a dopamine mediated pathway

Studies have shown a reduction of food intake following peripheral and brain injection of CCK. However, it remains to be established whether endogenous central CCK is involved in the regulation of food intake. We investigated the role of central CCK in the regulation of food intake by pharmacological manipulation of the CCKB (CCK2) receptor system. Intracerebroventricularly (ICV) cannulated male Sprague Dawley rats were fasted for 24h and received an ICV injection of the CCKB receptor antagonist CI988 at a dose of 10nmol or 49nmol or vehicle. Another group received two consecutive ICV injections consisting of the corticotropin-releasing factor (CRF) receptor-1 (CRF1) antagonist, CP376395 (3nmol) or the CRF2 receptor antagonist, K41498 (2nmol) alone, or followed by CI988 (49nmol). Lastly, another group of rats received an intraperitoneal (IP) injection of the dopamine antagonist, flupentixol (∼197 and ∼493nmol/kg) alone, or followed by CI988 (49nmol, ICV). Cumulative food intake was assessed for 11h. Vehicle injected rats showed a robust feeding response. CI988 at 49nmol reduced food intake by 30% starting at 2h post injection. CP376395 and K41498 had no effect on food intake. Flupentixol injected IP at a dose of 197 and 493nmol/kg alone did not modulate food intake whereas the higher dose blocked the CI988-induced reduction of feeding. During the dark phase, CI988 had no effect on food intake in unfasted rats. In summary, CCKB signaling is involved in the regulation of food intake after a fast likely by downstream dopamine signaling.

Tu1831 The CCK-B Antagonist Ci988 Reduces Food Intake in Fasted Rats via a Dopamine Mediated Pathway

Tu1831 The CCK-B Antagonist Ci988 Reduces Food Intake in Fasted Rats via a Dopamine Mediated Pathway

ChemInform Abstract: Rationally Designed “Dipeptoid” Analogues of CCK. α-Methyltryptophan Derivatives as Highly Selective and Orally Active Gastrin and CCK-B Antagonists with Potent Anxiolytic Properties.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

P.1.d.022 GABAergic synaptic coverage of principal cells in the hippocampus in the rat model of schizophrenia

We found that GH3 cells, a rat anterior pituitary tumor cell line, expressed a single class of high affinity binding sites for radiolabeled cholecystokinin octapeptide (CCK-8) with a Kd of 48 pM. The binding sites had high-affinity for CCK-8, CCK-4, gastrin I, and L-365.260 (CCK-B antagonist), and had low affinity for devazepide (CCK-A antagonist), indicating that the binding sites are CCK-B receptors. GTP and its stable analogues inhibited radiolabeled CCK-8 binding to GH3 cell membranes, suggesting a coupling of CCK-B receptors to a G-protein.

Synthesis of the Gastrin/CCK-B Receptor Antagonist (+)-AG-041R

AG-041R is an orally available ­gastrin/CCK-B antagonist that is a lead for the treatment of gastric ulcers. The synthesis depicted is noteworthy for the use of an asymmetric oxidative spiroannulation to construct the quaternary center in 3-aminooxindole structure C from the carbamate A using the rhodium catalyst B. For a related C-H insertion reaction, see: C. G. Espino, J. Du Bois Angew. Chem. Int. Ed. 2001, 40, 598.

Italian Roots

1 This Special Issue contains important primary and secondary research contributions from speakers at the XIXth National Meeting on Medicinal Chemistry (September 14–18, 2008 in Verona, Italy), along with a comprehensive Conference Report (p. 899 ff.) written by the conference organisers: Professors Livio Brasili and Luisa Mosti, and Dr. Daniele Donati, reflecting Italy's long-standing history of excellence in the field of medicinal chemistry. The Italian Chemical Society (SCI) is one of the founding societies of ChemMedChem, formed through a “transformation” of Il Farmaco, and as such the journal has Italian roots. Therefore, it was with great pleasure that we supported and attended the conference, organized by the Medicinal Chemistry Division of the SCI. 1 A highlight of this very interesting and fruitful meeting was the presentation of the prestigious Giordano Giacomello Medal to Professor Giorgio Tarzia (pictured), a ChemMedChem Editorial Board chairman, who received the award for his contributions to the advancement of medicinal chemistry throughout a long and varied career as a medicinal chemist in both the industrial and academic research spheres. Every three years, the Medicinal Chemistry Division of the SCI awards the Giordano Giacomello Medal to an Italian scientist who stands out for their original and relevant research results in the field of medicinal chemistry. Professor Tarzia graciously accepted the award presented to him in the opening ceremony by Professor Mosti, who very ably outlined his outstanding scientific career, documented by 33 patents and over 160 scientific papers published in high-standing international journals. His research efforts leading to the development of new medicinal entities such as nonsteroidal anti-inflammatory agents, prostaglandin analogues, benzodiazepine-type anti-anxiety agents, neuroleptic agents, teicoplanin derivatives, carbapenems, and CCK-B antagonists were described. Professor Tarzia's considerable contributions to the field as an educator and figurehead in the scientific community were also highlighted. He is currently the Dean of the Faculty of Pharmacy at the University of Urbino (Urbino, Italy), and a permanent member of the Scientific and Organizing Committee of the European School of Medicinal Chemistry, a titular member of the IUPAC subcommittee on Medicinal Chemistry and Drug Development, and a chairman of the Editorial Board of ChemMedChem. Former positions held by Professor Tarzia include: member of the Editorial Board of La Chimica e l’Industria (1994–2000), member (1998–2004) and vice president (2000–2004) of the Executive Council of the Medicinal Chemistry Division of the SCI, member of the Editorial Advisory Board of the Journal of Medicinal Chemistry (2003–2005), and Editor-in-Chief of Il Farmaco (2001–2005). Professor Tarzia gave a most inspiring award lecture entitled “Alkylcarbamic Acid Biphenyl-3-yl Esters as Selective Inhibitors of Fatty Acid Amide Hydrolase: A Novel Approach to Antianxiety and Antidepressant Agents”, dedicated to Professor Aurelio Romeo. Thanks go to Professor Mosti, who kindly provided the details for this Editorial, to the Conference organizers, in particular Professor Brasili, for their assistance in assembling this Special Issue, and finally, to the authors for their readiness to provide excellent research articles and other contributions. 1 1

The roles of nerve growth factor and cholecystokinin in the enhancement of morphine analgesia in a rodent model of central nervous system inflammation

Animal models of inflammatory pain are characterized by the release of inflammatory mediators such as cytokines and neurotrophic factors, and enhanced analgesic sensitivity to opioids. In this study, we examine the mechanisms underlying this effect, in particular the roles of cholecystokinin (CCK) and nerve growth factor (NGF), in an animal model of central nervous system (CNS) inflammation induced by spinal administration of lipopolysaccharide (LPS). Although spinal administration of LY-225910 (25 ng), a CCK-B antagonist, enhanced morphine analgesia in naïve rats, it was unable to do so in LPS-treated animals. Conversely, spinal CCK-8S administration (1 ng) decreased morphine analgesia in LPS-treated rats, but not in naïve animals. Further, spinal anti-NGF (3 μg) was able to reduce morphine analgesia in LPS-treated rats, but not in naïve animals, an effect that was reversed by spinal administration of LY-225910. While CCK-8S concentration was increased in spinal cord extracts of LPS animals as compared to controls, morphine-induced spinal CCK release in the extracellular space, as measured by in-vivo spinal cord microdialysis was inhibited in LPS animals as compared to controls, and this was reversed by anti-NGF pretreatment. Finally, chronic spinal administration of β-NGF (7 μg/day) for 7 days enhanced spinal morphine analgesia, possibly by mimicking a CNS inflammatory state. We suggest that in intrathecally LPS-treated rats, spinal CCK release is altered resulting in enhanced morphine analgesia, and that this mechanism may be regulated to an important extent by NGF.

Responses of human sling and clasp fibers to cholecystokinin (CCK) and gastrin through CCK receptors

Cholecystokinin (CCK) and gastrin exert their influences via CCK receptors. This research was conducted to look at the responses of the sling and clasp fibers forming the human lower esophageal sphincter (LES) to CCK and gastrin, and the role of CCK receptors in the responses. Muscle strips of sling and clasp fibers from the LES were obtained from patients undergoing subtotal esophagectomy. Isometric tension responses of the strips to CCK-8 and gastrin-17 were studied, and the maximum effect (E(max)) for each agonist was derived. CCK-A receptor antagonist, CR1409 and CCK-B antagonist, CR2945 were applied to sling and clasp fibers and their pK(B) values were calculated. Sling fibers produced significant contractions following exposure to CCK-8 and gastrin-17, while clasp fibers had less responses to the two agents. CR1409 and CR2945 inhibited responses of sling to CCK-8 in a concentration-dependent fashion. The inhibition effects of the two antagonists on clasp fibers were not measurable because there was a mild contraction of the fiber in response to CCK-8. The contractions generated by sling fibers following exposure to CCK and gastrin are greater than that produced by clasp fibers. CCK-A receptors are more important for the generation of contractions by the sling fibers, whereas both CCK-A and CCK-B receptors are involved in the functional regulation of the clasp fibers. [Corrections added after online publication 28 April 2008: in the Background and Aims section of the preceding abstract, all instances of 'CKK' were corrected to 'CCK'. In the final sentence of the abstract 'CCKA'was corrected to 'CCK-A'. In the article title '(CKK)' was corrected to '(CCK)'.].

Social defeat increases alcohol preference of C57BL/10 strain mice; effect prevented by a CCKB antagonist

In humans, social stress over long and short term can increase alcohol consumption, but the mechanisms involved are not understood. This study was conducted to examine the effects of social defeat, using the resident/intruder paradigm, on the alcohol preference of "low alcohol drinking" individuals in a colony of C57BL/10 strain mice and the effects of two anxiolytic drugs. Alcohol preference, in a two-bottle choice (8% v/v alcohol or water), was measured, in separate experiments, after either a single experience of social defeat by a resident male mouse, five consecutive daily defeat experiences or one experience per week for 4 weeks. Comparison was made with effects of repeated social defeat on the preference for dilute sucrose. In addition, the actions of the CCKB receptor antagonist, CAM1028, and of diazepam were examined on the effects of repeated defeat experiences. Five consecutive daily defeat experiences had a slow onset effect in increasing alcohol preference and consumption, compared with five daily exposures to a novel environment. A single defeat, or one defeat per week, did not significantly alter alcohol preference or intake. There were no effects of five daily defeat experiences on sucrose preference or consumption. The effect of repeated defeats on alcohol preference was significantly decreased by administration of the CCKB receptor antagonist, CAM1028, prior to each experience, but not by corresponding administration of diazepam. The results show that social stress increases alcohol intake in low alcohol preference C57BL/10 mice and suggest that CCK transmission may be involved in this effect.

Selective CCK‐A but not CCK‐B receptor antagonists inhibit HT‐29 cell proliferation: synergism with pharmacological levels of melatonin

Some data suggest that cholecystokinin (CCK) receptor agonists stimulate the growth of colon cancer. Melatonin, an endogenous indoleamine with strong antioxidant properties, displays antiproliferative and proapoptotic properties both in vivo or in vitro in several types of tumors. We used HT-29 human colon cancer cells, expressing CCK receptors, to test the antiproliferative effects of several antagonists of CCK-A and/or CCK-B and their possible synergism with melatonin. HT-29 cells were cultured in RPMI 1640 medium supplemented with fetal bovine serum at 37 degrees C. Cell proliferation was assessed by the incorporation of [3H]-thymidine into DNA. Annexin V-FITC plus propidium iodine were used for flow cytometry apoptosis/necrosis evaluation. The following drugs were tested: gastrin (CCK-B agonist); CCK-8s (CCK-A agonist); proglumide (CCK-A plus CCK-B antagonist); lorglumide (CCK-A antagonist); PD 135,158 (CCK-B antagonist and weak CCK-A agonist); devazepide or L 364,718 (CCK-A antagonist); L 365,260 (CCK-B antagonist), and melatonin. The results shown a lack of effects of gastrin on HT-29 cell proliferation, whereas CCK-8s induced proliferation at high doses. The order of the antiproliferative effect of the other drugs was devazepide > lorglumide > proglumide. These drugs produce cell death mainly inducing apoptosis. Melatonin showed strong antiproliferative effect at millimolar concentrations, and it induced apoptotic cell death. Melatonin generally enhanced the antiproliferative effects of devazepide, lorglumide and proglumide and increased the proglumide-induced apoptosis. These results suggest that melatonin and CCK-A antagonists are useful for controlling human colon cancer cell growth in culture and in combined therapy significantly increases their efficiency.

In vitro analysis of the effects of cholecystokinin on rat brain stem motoneurons

Using whole cell patch clamp in thin brain stem slices, we tested the effects of cholecystokinin (CCK) on identified gastric-projecting neurons of the rat dorsal motor nucleus of the vagus (DMV). Perfusion with the sulfated form of CCK octapeptide (CCK8s, 30 pM-300 nM, EC50 approximately 4 nM) induced a concentration-dependent inward current in 35 and 41% of corpus- and antrum/pylorus-projecting DMV neurons, respectively. Conversely, none of the fundus-projecting DMV neurons responded to perfusion with CCK8s. The CCK8s-induced inward current was accompanied by a 65 +/- 17% increase in membrane input resistance and reversed at 90 +/- 4 mV, indicating that the excitatory effects of CCK8s were mediated by the closure of a potassium conductance. Pretreatment with the synaptic blocker TTX (0.3-1 microM) reduced the CCK8s-induced current, suggesting that a portion of the CCK8s-induced current was mediated indirectly via an action on presynaptic neurons apposing the DMV membrane. Pretreatment with the selective CCK-A receptor antagonist lorglumide (0.3-3 microM) attenuated the CCK8s-induced inward current in a concentration-dependent manner, with a maximum inhibition of 69 +/- 12% obtained with 3 microM lorglumide. Conversely, pretreatment with the selective CCK-B antagonist triglumide did not attenuate the CCK8s-induced inward current; pretreatment with triglumide (3 microM) and lorglumide (1 microM) attenuated the CCK8s-induced current to the same extent as pretreatment with lorglumide alone. Immunohistochemical experiments showed that CCK-A receptors were localized on the membrane of 34, 65, and 60% of fundus-, corpus-, and antrum/pylorus-projecting DMV neurons, respectively. Our data indicate that CCK-A receptors are present on a subpopulation of gastric-projecting neurons and that their activation leads to excitation of the DMV membrane.

Synthesis and morphine enhancement activity of N-[5-(2-phenoxyphenyl)-1, 3, 4-oxadiazole-2-yl]-N'-phenylurea derivatives.

The synthesis of N-[5-(2-phenoxyphenyl)-1, 3, 4-oxadiazole-2-yl]-N'-phenylurea derivatives is reported. The structures of these compounds are supported by their IR, (1)H-NMR and mass spectra. Conformational analysis and superimposition of energy minima conformers of these compounds on L-365, 260, a known 3-ureido-1, 4-benzodiazepine CCK-B antagonist, showed that the aromatic rings fell in the same contour. Morphine analgesia enhancement evaluation of the synthesized compounds in comparison with a control group showed that compounds 8a, 8c, 8h-8j, 8l, 8o have significant effects.

Effects of cholecystokinin tetrapeptide (CCK4) and of anxiolytic drugs on GABA outflow from the cerebral cortex of freely moving rats

The effect of cholecystokinin tetrapeptide (CCK4) and of different anxiolytic drugs on GABA outflow from the cerebral cortex was investigated in freely moving rats, by using the epidural cup technique. CCK4 (3–30μg/kg, i.p.) increased GABA outflow and induced objective signs of anxiety. These neurochemical and behavioral responses were prevented by the CCKB antagonist GV150013 at 0.1μg/kg (i.p.). At higher doses (up to 30μg/kg) this compound per se reduced GABA release and caused sedation, suggesting the presence of a CCKergic positive tonic modulation on GABA interneurons. Similarly the GABAA receptors modulator, diazepam (2mg/kg, i.p.) and the 5-HT1A agonist buspirone (3mg/kg, i.p.) reduced GABA outflow and caused the expected behavioral effects (reduced muscle tone, mild 5-HT syndrome) which were prevented by the respective, selective antagonists, flumazenil (1mg/kg, i.p.) and NAN-190 (3mg/kg, i.p.). These findings support the idea that GV150013, diazepam and buspirone inhibit GABAergic cortical activity, through the respective receptors. This neurochemical effect may represent the end-effect of various anxiolytic compounds affecting the cortical circuitry.

Proinflammatory role of leptin in experimental colitis in rats Benefit of cholecystokinin-B antagonist and β3-agonist

Leptin, a hormone primarily secreted from adipocytes, plays a key role in controlling body weight homeostasis. In vitro studies indicate that it is also implicated in immune responses. Hyperleptinaemia has been reported in acute inflammation, especially during the early stages of intestinal inflammation in rats. The present study investigated the possible role of leptin in the pathogenesis of trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats. Since no specific antagonist of leptin is available, a CCK-B antagonist (YM022) and a β3 agonist (BRL37344) were used in this study to inhibit leptin secretion. Colitis was induced by intracolonic instillation of TNBS in rats. Five TNBS-groups were subcutaneously implanted with micropumps containing : placebo, YM022, BRL37344, BRL37344 and exogenous leptin simultaneously, or leptin alone. At sacrifices, colitis severity was assessed by macroscopic and histological scoring systems and by determination of tissue myeloperoxidase activity. The TNBS-induced hyperleptinaemia was significantly reduced by YM022 and BRL37344 (p<0.05). Inhibition of leptin secretion markedly reduced colonic inflammation, whatever the criteria considered (i.e. macroscopic, histological or biochemical). In contrast, administration of exogenous leptin completely abolished the beneficial effect of leptin-lowering drugs on colitis severity. These results provide the first direct evidence for an important deleterious role of leptin in the pathogenesis of experimental intestinal inflammation and suggest that a pro-inflammatory activity is attributable to leptin in vivo. Further studies are required to determine if these results have clinical significance.

The inability of CCK to block (or CCK antagonists to substitute for) the stimulus effects of chlordiazepoxide

To further examine the relationship between cholecystokinin (CCK) and GABA, the present study assessed the ability of the CCK-A antagonist devazepide and the CCK-B antagonist L-365,260 to substitute for the stimulus effects of chlordiazepoxide (CDP), as well as the ability of CCK-8s to block these effects, in female Long–Evans rats within the conditioned taste aversion baseline of drug discrimination learning. Both devazepide and L-365,260 failed to substitute for the discriminative stimulus properties of CDP, and CCK-8s failed to block its stimulus effects. The benzodiazepine diazepam did substitute for, and the benzodiazepine antagonist flumazenil did block, the stimulus effects of CDP. This suggests that the lack of substitution for, or antagonism of, CDP by the CCK antagonists and CCK-8s, respectively, was not due to the inability of the present design to assess such effects. Possible bases for the current findings, e.g., necessity of an anxiogenic baseline, drug and receptor specificity, as well as the dose–response nature of the interaction, were discussed. Given that a relationship between CCK and GABA has been reported in other designs, the present results suggest that such a relationship may be preparation specific.

The effect of a cholecystokinin agonist on masseter muscle activity in the cat.

The CCK(B) agonist, pentagastrin, has been shown to induce anxiety in human subjects. Similarly, in the cat model, pentagastrin facilitates the expression of hypothalamically activated emotional behavior. Because hypothalamically mediated emotional behavior is also accompanied by increased EMG activity in the jaw muscles, these experiments were designed to examine the combined effects of administration of pentagastrin with activation of hypothalamically mediated emotional behavior upon jaw muscle EMG activity. Electrodes were carefully lowered through previously placed guide tubes overlying the hypothalamus until a behavioral site was identified. Following the establishment of a stable threshold current for eliciting an emotional behavioral response, the skin overlying the ipsilateral masseter muscle was shaved and cleaned with alcohol, and surface electrodes were attached. The EMG was recorded, amplified, digitized, and stored in a microcomputer for analysis. Mean power frequencies (MPF) and latencies for behavior were calculated for baseline prior to infusion of all drugs. Following this, the effects of intravenous administration of pentagastrin and the CCK(B) antagonist LY288513 on the MPF were determined. The infusion of the CCK(B) agonist, pentagastrin (0.77, 1.92, and 3.84 microg/kg), decreased MPF in a time-related manner. The effects of pentagastrin 1.92 microg/kg were blocked by the CCK(B) antagonist, LY288513 (6.54 microg/kg). In addition, the infusion of LY288513 alone increased MPF. These results are surprising in that pentagastrin's anxiogenic properties would appear to make it likely to facilitate motor activity, not suppress it.

Cefaclor, a cephalosporin antibiotic, delays gastric emptying rate by a CCK-A receptor-mediated mechanism in the rat.

Studies in vitro suggest that cephalosporin antibiotics release the gut hormone cholecystokinin. Cholecystokinin is known to inhibit gastric emptying. Here we examine the effects of cefaclor on gastric emptying and intestinal motility. Male Sprague-Dawley rats were fitted with gastric cannulas. Following a 3-week recovery, the rate of gastric emptying of saline, peptone (4.5%) or cefaclor was determined after instillation into the gastric cannula, while intestinal transit was measured by using the propagation of arabic gum + charcoal mixture given intraduodenally. Gastric emptying of saline was significantly delayed by the addition of cefaclor (3, 10, 30 or 100 mM). The CCK-A antagonist SR-27897B (1 mg kg(-1), i.p.) reversed the delay induced by 10 mM cefaclor, whereas the CCK-B antagonist CI-988 (1 mg kg(-1), i.p.) had no significant effect. In capsaicin-treated rats, 10 mM cefaclor emptied more rapidly than in vehicle-treated animals. Thirty-minute intestinal transit was increased at 30 and 100 mM of cefaclor, while the gastric acid secretion following cefaclor instillation was no different than the group which received saline. The cephalosporin antibiotic cefaclor appears to be a potent stimulant of CCK release from gut endocrine cells, resembling the effects of peptone. Cefaclor delays gastric emptying via capsaicin-sensitive afferent pathways, which involve CCK-A receptor interaction.

Enhancement of Peptone-Induced Gastric Acid Secretion in Streptozotocin-Induced Diabetic Rats

We compared the acid secretory response to peptone in normal and streptozotocin-induced diabetic rats. Animals were injected with streptozotocin and used after 5 weeks of diabetes with blood glucose levels of >350 mg/dl. Under urethane anesthesia, 2 ml peptone solution (2–8%) was instilled in the stomach through an acute fistula every 30 min. Peptone increased acid secretion in a concentration-dependent manner in normal rats, the maximal response being obtained at 8%. Likewise, the increased acid response was observed in diabetic rats, yet the maximal response observed at 497o was significantly greater than that in normal rats. In both cases, this response was inhibited potently by famotidine as well as YM-022 (a CCKB antagonist) and partially inhibited by atropine. Peptone increased luminal histamine and plasma gastrin levels in both normal and diabetic rats, and the former response was significantly greater in diabetic animals. The altered acid secretion and histamine output in diabetic rats were reverted by insulin treatment. Pentagastrin- but not histamine-induced acid secretion was also increased in diabetic rats. We conclude that peptone-induced acid secretion is increased in diabetic conditions. This phenomenon is insulin-dependent and associated with an enhanced release of histamine but not with an increased sensitivity of the parietal cells.