Doses Of CCK Research Articles

Effects of pirenzepine on CCK-stimulated canine pancreatic exocrine secretion

1. 1. The effects of the anticholinergic compound pirenzepine on pancreatic secretion stimulated by intravenous infusions of increasing doses of CCK (0.025-0.4 Ivy Dog Unit/kg/min) were investigated in fasting anaesthetized dogs. 2. 2. Pirenzepine (0.75 mg/kg i.v.) slightly reduced the increases in the pancreatic juice secretion evoked by CCK. 3. 3. Similar results were obtained with others anticholinergic compounds as atropine (3 mg/kg i.v.) and hexametonium (5 mg/kg i.v.).

Cholecystokinin in the Inhibition of Gastric Secretion and Gastric Emptying in Humans

Cholecystokinin (CCK) is known to inhibit gastric acid secretion and gastric emptying but its physiological role in the inhibition of gastric functions is not settled. In this study performed on 16 young male subjects, gastric acid secretion and emptying rate were determined after intragastric administration of 8% peptone meal alone or in combination with intravenous infusion of graded doses of CCK-8 (5-80 pmol/kg.h) or with addition of vegetable oil to meal without or with pretreatment with loxiglumide, a specific CCK antagonist. CCK-8 infusion at lower dose (5 pmol/kg.h) was ineffective but at higher doses (20-80 pmol/kg.h) it resulted in a significant reduction in acid output by 39 and 43% and a decrease in gastric emptying from 54% to 40 and 22%, respectively. Pretreatment with loxiglumide abolished almost completely the inhibition of both gastric acid and gastric emptying by CCK-8. Fat added to peptone meal reduced gastric acid secretion by 42-65% and decreased gastric emptying to 24-32%. The pretreatment with loxiglumide tended to reduce fat-induced inhibition of gastric acid secretion and gastric emptying but the difference in the inhibition of gastric functions between the tests without and with loxiglumide was not significant. This study provides evidence that exogenous CCK administered at pharmacological doses is a potent inhibitor of gastric acid secretion and gastric emptying and probably acts via specific CCK receptors. In contrast, fat induces inhibition of gastric acid secretion and gastric emptying that cannot be fully attributed to hormonally acting CCK.

The role of CCK, caerulein, and CCK antagonists in nociception

The octapeptide form of CCK predominates in the central nervous system (CNS) of mammalian species, including man. Many of the physiological roles of CCK in the CNS are unknown, but it is believed to be involved in nociception. CCK is distributed throughout cortical grey matter, periaqueductal grey matter, ventromedial thalamus and spinal dorsal horn, all of which are areas known to be associated with pain modulation. CCK receptor subtypes have been identified and may be classified according to their affinity for the sulphated and desulphated forms of CCK-8 and the recently described selective antagonist, MK-329. CCK-A receptors have high affinity for sulphated CCK-8 and for MK-329 but low affinity for desulphated CCK-8 and CCK-4 whilst CCK-B sites bind MK-329 with low affinity and discriminate poorly between sulphated and desulphated CCK-8. CCK-A receptors are found predominantly in peripheral tissues but they also exist in discrete regions of the primate CNS, including the spinal cord. CCK-B receptors are found ubiquitously throughout other regions of the neuraxis. The results of studies on the effects of CCK-8 and the decapeptide analogue caerulein on pain thresholds are conflicting. Some workers suggest that large doses of CCK-8 and caerulein induce naloxone-reversible analgesia in certain pain models. However, it appears likely that analgesia induced by large doses of CCK and caerulein in animals may be a pharmacological rather than a physiological phenomenon. Accordingly, others have found that small (and most probably, physiological) doses of CCK-8 attenuate the analgesic effects of morphine, and of endogenous opioids. Thus, it has been proposed that CCK may act as an endogenous opiate antagonist. Studies in rats with the selective CCK antagonist MK-329 have helped clarify the interaction between CCK and morphine-induced analgesia. Treatment with MK-329 enhances morphine analgesia and chronic treatment with MK-329 prevents the development of tolerance to morphine analgesia. However, the antagonist does not prevent naloxone-precipitated withdrawal symptoms in morphine-dependent rats. In man, caerulein prevents pain associated with gall-bladder contraction, probably by relaxation of the sphincter of Oddi. Caerulein has also been shown to reduce renal colic and the pain of intermittent claudication. Preliminary clinical studies with the weak, non-selective, CCK antagonist proglumide, indicate an enhancement of morphine analgesia. As yet, no studies have demonstrated analgesic effects of CCK antagonists in man when administered alone. It is possible that selective and specific CCK antagonists may have a therapeutic role in enhancing exogenous and endogenous opioid analgesia and in preventing tolerance to opioid analgesics.

Pharmacokinetics and organ catabolism of cholecystokinin octapeptide in pigs

The pharmacokinetics and organ catabolism of cholecystokinin octapeptide (CCK8) were studied in pigs. In conscious animals, intravenous infusion of increasing doses of CCK8 (2.9–232.3 pmol · kg −1 · min −1) resulted in a linear increase of plasma CCK-like immunoreactivity (CCK-LI). At the cessation of infusion of the largest dose of CCK8, plasma CCK-LI promptly returned to near basal values. The half-disappearance time ( t 1 2 ), metabolic clearance rate (MCR) and distribution volume (DV) were estimated to be 0.55 ± 0.03 min, 134.8 ± 10.8 ml · kg −1 · min −1 and 107.9 ± 13.0 ml · kg −1, respectively. In another group of anesthetized animals, infusion of CCK8 at similar doses produced higher plateau plasma CCK levels and the t 1 2 , MCR and DV were calculated to be 0.68 ± 0.06 min, 32.5 ± 3.9 ml · kg −1 · min −1 and 45.2 ± 5.6 ml · kg −1, respectively. Estimates of first-pass immunological degradation through various vascular beds were in the range 27–66%, with in decreasing order the kidney, liver, hindleg, followed by the brain and gut. These results indicate that immunoreactive CCK8 is rapidly cleared from plasma during passage through several vascular beds. The peptide is only partly inactivated during hepatic transit and so may exert hormonal effects upon its release from intestinal stores.

Role of Cholecystokinin in the Control of Food Intake

CCK appears to regulate short-term control of food intake by acting as a satiety signal. Larger doses of CCK may decrease food intake by aversive actions (malaise, nausea, cramps), presumably by effects on gastrointestinal motility. In rats and most likely humans CCK is released from the upper intestine after a mixed meal and appears to activate afferent vagal fibers by causing pyloric contraction with resultant gastric distention or directly binding to the gastric afferent vagus which courses to the nucleus solitarius with further projections to the paraventricular nucleus and ultimately the ventromedial hypothalamus. Peripherally released CCK may also bind to CNS receptors in the area postrema overlying the nucleus solitarius. Central nervous system CCK released from the paraventricular nucleus may also exert a satiety effect. The satiety effect of CCK appears to be a physiologic action of the peptide since antibodies to CCK and CCK receptor antagonists can increase food intake. CCK is probably just one of several satiety signals but can cause a profound decrease in food intake when administered exogenously in pharmacologic doses. Administration of exogenous CCK, as well as endogenous CCK released by oral protease inhibitors, can decrease food intake in humans. Studies designed to examine the effect of chronic administration of CCK on food intake will be necessary to determine if the peptide has a role in the management of obesity and bulimia.

Infusions of cholecystokinin octapeptide into the ventral tegmental area potentiate amphetamine conditioned place preferences.

Cholecystokinin (CCK) and dopamine (DA) coexist in both cell body and terminal areas of a mesolimbic pathway that projects from the ventral tegmental area (VTA) to the nucleus accumbens (N ACC). Autoradiography reveals extensive CCK binding sites in the N ACC, but not in the VTA. However, iontophoresis of CCK into the VTA results in activation or deactivation of DA neuronal firing rates, and bursting activity (depending on the dose of CCK administered). CCK could have neuromodulatory effects on mesolimbic DA neurons. In two studies, behavioral effects of infusions of CCK into the VTA were examined in the conditioned place preference (CPP) paradigm. The CPP paradigm is a behavioral test used to assess reinforcement induced by drug administration. Drugs with reinforcing properties can condition preferences for novel environments. CCK infusions into VTA (0.0, 0.04, 0.4, and 4.0 ng/cannula) potentiated amphetamine CPPs in a dose-dependent linear manner. CCK infusions by themselves did not have significant effects in the CPP paradigm. Results indicate a neuromodulatory role for CCK on the neuronal mechanisms that mediate the reinforcing effects of amphetamine. Results also implicate sites of action for CCK in the VTA.

Role of cholecystokinin in intestinal phase and meal-induced pancreatic secretion

Amylase secretion and plasma cholecystokinin (CCK) were measured in dogs in the interdigestive state and after exogenous CCK-8 and CCK-39 (12.5 to 400 pmol.kg-1.h-1), intestinal sodium oleate, tryptophan plus phenylalanine, HCl (0.74, 2.2, 6.7, 20 mmol/h), and a meat meal (20 g/kg). Interdigestive plasma CCK did not vary, although amylase output showed periodic 15-fold increases. Plasma CCK increased linearly after doubling doses of CCK-8 and CCK-39; the slope of plasma CCK-39 vs. dose was 2.8 times steeper than that of CCK-8, suggesting a longer circulating half-life. At similar plasma concentrations, CCK-8 and CCK-39 were equipotent for stimulating pancreatic secretion. Sodium oleate and tryptophan plus phenylalanine significantly increased plasma CCK and amylase secretion in a load-dependent pattern and were equipotent for both effects. HCl stimulated bicarbonate secretion but not plasma CCK or amylase secretion. Food significantly increased plasma CCK and amylase secretion. Amylase responses to intestinal stimulants and food were significantly greater than to exogenous CCK at low plasma CCK levels. Maximal amylase responses to intestinal stimulants were similar to that after CCK-39 but occurred at 10-fold lower plasma CCK levels. These results indicate that CCK and other factors interact to regulate pancreatic responses to food and intestinal stimulants in dogs.

CCK-8 injected into the nucleus accumbens attenuates the supersensitive locomotor response to apomorphine in 6-OHDA and chronic-neuroleptic treated rats.

Postsynaptic dopamine-cholecystokinin (CCK) interactions in the nucleus accumbens were studied in two behavioral preparations of DA receptor supersensitivity: chronic-neuroleptic treated and 6-hydroxydopamine (6-OHDA) denervated rats. Subcutaneous (SC) injections of apomorphine (APO; 0.15 mg/kg) in experiment 1 produced marked hyperlocomotion in rats following 12 days of pretreatment with cis-[Z]-flupenthixol (2 mg/kg; twice per day). Bilateral intra-accumbens (N.Acc.) microinjections of CCK-8 (2 ng and 2 micrograms) reliably reduced APO-stimulated hyperlocomotion. An intermediate CCK dose (20 ng) was without effect. No change in APO responsivity following chronic vehicle treatment was observed and the baseline APO response was not altered by CCK at any dose. Denervation of mesolimbic dopamine (DA) terminals by intra-N.Acc. injections of 6-hydroxydopamine (6-OHDA; 8 micrograms/side) in experiment 2 similarly resulted in intense locomotor hyperactivity after APO stimulation (0.1 mg/kg; SC). Bilateral intra-N.Acc. injections of CCK-8 (1, 10, 100 ng, and 1 micrograms) significantly attenuated the supersensitive locomotor response to APO. As in experiment 1, CCK produced "biphasic" dose-response effects with strong attenuation that persisted throughout the entire 60-min test at both high (1 microgram) and low (1 ng) doses. Intermediate CCK doses (10 and 100 ng) produced only short-term reductions in activity. Hypomotility induced by APO in SHAM-lesioned rats was not effectively reversed by CCK treatments. CCK had no effect on unstimulated baseline locomotor activity in either 6-OHDA or SHAM-lesioned rats. These results provide further evidence that CCK-8 modulates mesolimbic DA activity by functionally opposing the postsynaptic effects of DA in the region of the nucleus accumbens.

Effects of cholecystokinin octapeptide on the pancreatic exocrine secretion in the pig.

In conscious pigs, intravenous infusion of serial doses of cholecystokinin octapeptide (CCK8; 2.9-232.3 pmol.kg-1.min-1) upon a background of secretin resulted in a linear increase of plasma CCK-like immunoreactivity (CCK-LI) concentration and evoked a dose-related increase of pancreatic volume and bicarbonate and protein outputs. The threshold plasma CCK-LI concentration for significant pancreatic response was 103.8 +/- 10.2 pM using a CCK8 dose of 8.8 pmol.kg-1.min-1. The maximum pancreatic response was observed for a plasma CCK-LI level of 498.0 +/- 15.3 pM using 77.2 pmol CCK8.kg-1.min-1. In anesthetized pigs, the threshold plasma CCK-LI concentration for pancreatic response was 1500 pM (actual CCK8 dose of 60.3 pmol.kg-1.min-1). The physiological relevance of this finding was assessed by comparing the food-induced increase of pancreatic secretion with that of plasma CCK-LI. Food ingestion was followed by a sharp pancreatic response and by a progressive increase of plasma CCK-LI to a peak increment of about 15 pM. Gel chromatography of portal and peripheral plasma from fed animals revealed three major peaks in the volumes of CCK33/39 and CCK8, and in a volume intermediate between CCK33/39 and CCK8. An additional minor component eluted ahead of CCK33/39. CCK8, which is one of the CCK components released after food intake, appears to be a fairly weak pancreatic stimulant in pigs.

Blockade of morphine-induced increases in brain tryptophan hydroxylase activity by systemic pretreatment with CCK-8: no reversal by vagotomy

The treatment of rats with CCK-8 suppresses the behavioral responses to subsequent injection of opiates. We have investigated the possibility that peripherally administered CCK-8 can also suppress a neurochemical response to opiates, namely the increase in brain tryptophan hydroxylase (TrpH) activity and tissue 5-hydroxyindole acetic acid (5-HIAA) which results from morphine administration. While morphine sulfate (4 mg/kg s.c.) roughly doubled brain TrpH activity and tissue 5-HIAA 40 min after injection, pretreatment with CCK-8 (5 μg/kg i.p., 10 min prior to morphine) completely abolished this neurochemical change induced by morphine. Doses of CCK-8 as low as 1 μ/kg were effective in blunting the morphine-induced increase in cortical TrpH activity, but the desulfated form was ineffective at doses of 5 and 100 μ/kg. Subdiaphragmatic vagotomy did not prevent the effect of CCK-8.

Effects of CCK-8 in combination with natural or synthetic secretin on amylase, lipase, trypsin, and chymotrypsin secretion in rats

In the present study, we examined the interaction between CCK-8 and natural or synthetic secretin on pancreatic enzyme secretion. On anaesthetized rats, a proximal duodenal segment was continuously perfused with saline and amylase, lipase, trypsin, and chymotrypsin were determined in the perfusate. Neither during iv saline nor during iv secretin (natural or synthetic) at doses of 0.01, 0.05, or 0.1 CU/kg/h, any of the four enzymes changed significantly from basal values over a period of 100 min. Iv CCK-8 at stepwise increasing doses of 5, 10, and 20 pmol/kg/h elicited a significant increase of all four enzymes at the medium dose, with a further increase of amylase and trypsin, but not lipase and chymotrypsin at 20 pmol/kg/h. The addition of secretin at all 3 doses potentiated CCK-induced trypsin output. The effects of natural secretin were more pronounced than those of the synthetic peptide. Secretin significantly increased amylase secretion over basal at the lowest dose of CCK-8 (5 pmol/kg/h) that by itself had no effect on amylase release. Only the higher doses of natural but not synthetic secretin augmented lipase secretion during the lowest dose of CCK-8. Both forms of secretin had no further stimulatory effect on CCK-induced chymotrypsin secretion. The present data demonstrate that, first, in rats a potentiation of CCK-8-induced enzyme secretion by low doses of secretin is different for the four enzymes, which suggests a differential regulatory action of these two intestinal hormones on pancreatic enzyme release. Second, the different effects of natural secretin may represent those of contaminants suggesting that only synthetic secretin should be employed in future studies of this peptide on pancreatic enzyme secretion.

External pancreatic secretion in the rat: Supramaximal inhibition induced by the cholecystokinin octapeptide [CCK(26–33)] and analogs altered on the 28–29 bond

Supramaximal doses of cholecystokinin induce in vitro submaximal biological responses, desensitization and residual stimulation. In vivo, supramaximal inhibition and oedematous pancreatitis have been reported. The aim of this study was to analyze the in vivo response of the pancreatic secretion of the rat to a wide range of doses of CCK8 and analogs prepared by alterations of the Met(28)-Gly(29) bond, a modification that may lead to potent agonists. We used Boc-[Nle 28-Nle 31]-CCK(26–33) (1) and derivatives of (1) with the 28–29 peptide bond replaced by CH 2-NH (2), CO-CH 2 (3), CH 2-CH 2 (4), NH-CO (5). On infusions, the ED 50's (pmol/kg·min) for protein output were 4 for CCK8 and (1), 11 for (3), 40 for (2) and (4), and 860 for (5). The relative order of the in vivo potencies was near to the one determined in vitro on isolated rat acini. On bolus injections, the maximal response was observed with 300 pmol/kg of CCK8, and peaked 10–15 min after the injection. With higher doses of CCK8, the secretory peak was smaller, and was delayed relative to the monment of the injection. Supramaximal doses of CCK analogs induced the same pattern of response; however, the peak injection delay was in some cases smaller than after CCK8. Determination of the plasma CCK levels indicated that the time of peak effect after supramaximal doses of CCK8 was delayed relative to the time of effective maximal plasma CCK levels. This suggests a slow dissociation of CCK8 from one of its pancreatic binding sites in vivo. These data indicate that agonists with high in vivo potency can be obtained by altering the Met(28)-Gly(29) bond, that supramaximal doses of CCK and analogs induce both a decrease and a delay of the peak effect, and suggest that the delay may be related to the rate of dissociation of the peptides from one of their receptor sites.

Peptidergic control of male rat sexual behavior: The effects of intracerebral injections of substance P and cholecystokinin

Behavioral experiments examined the roles of substance P (SP) and cholecystokinin (CCK) in male rat copulatory behavior. Male copulatory behavior was recorded subsequent to injections of different doses of CCK and SP into the medial preoptic-anterior-hypothalamic area (MPOA-AH), caudate/putamen (CP), or the lateral ventricles (LV) in sexually experienced male rats. In the first experiment, three different doses of SP (10, 100, and 200 ng/cannula) injected bilaterally into the MPOA-AH produced marked changes in several components of male copulatory behavior. Latencies were most affected. All three doses significantly shortened the interval to initiate copulation, and the 10 and 100 ng, but not 200 ng dose also significantly reduced ejaculation latencies. Injections of 10 ng of SP into the CP did not affect sexual behavior, while injections into the LV produced changes different from those of MPOA-AH injections. These data argue for some degree of site specificity of the effects of the MPOA-AH injections. Bilateral injections of 10 ng of SP into the MPOA-AH, were incapable of inducing copulatory behavior in castrated rats deprived of testosterone. Injections of an undiluted SP antiserum (2 μl/cannula) into the MPOA-AH produced a dramatic impairment of male copulatory behavior. These injections significantly lengthened mount, intromission, and ejaculation latencies, while having no effect on the number of mounts or intromissions prior to ejaculation. In contrast, bilateral injections of CCK-8 (10, 100, and 200 ng/cannula) into the MPOA-AH failed to affect any parameter of male copulatory behavior. The results of the present study provide the first support for a role of SP in the neural regulation of male rat sexual behavior and suggest that a SP-sexually dimorphic pathway forms part of the neural circuitry important for the expression of male rat sexual behavior.

Cholecystokinin and satiation with alcohol

Release of the brain-gut peptide cholecystokinin (CCK) is stimulated by intragastric instillation of ethanol, and peripheral administration of CCK inhibits ethanol consumption. To assess the temporal specificity of the inhibitory effect of CCK on alcohol intake, water-deprived rats were given 5% ethanol at 20, 10 or 0 min after intraperitoneal injections of CCK octapeptide. Delaying access to ethanol for 20 min prevented a significant effect of CCK on intake. CCK's temporally constrained inhibitory action on alcohol consumption is consistent with an ethanol satiation effect. To test the motivational specificity of CCK's effect on fluid intake, rats were allowed a 2-bottle choice of 2% ethanol and water after CCK injections. Ethanol solution intake was suppressed by CCK, and total water intake was unaffected. The putative alcohol satiation action of CCK is appropriately specific to ethanol solution in free-choice tests. Hungry, but not fluid-deprived rats that were either ethanol experienced or naive received a 2-bottle choice of 4% ethanol or water after CCK or saline injections. CCK again specifically inhibited ethanol intake, but this effect required prior ethanol experience. Doses of CCK and naloxone, an opioid receptor blocker, combined to inhibit ethanol intake in an infra-dose-additive manner in water-deprived rats. CCK may act endogenously, in part on opioid receptor-mediated processes, as a preabsorptive satiety signal of ethanol. The full expression of this action appears to depend on prior conditioning of nutritive expectancy of the postingestive effects of alcohol.

The effect of gastrointestinal hormones on the incorporation of tritiated thymidine in the pancreatic adenocarcinoma cell line (WD PaCa).

In view of the trophic action of gastrointestinal hormones on the exocrine pancreas, the effects of secretin, octapeptide of cholecystokinin (CCK-8), and desglugastrin on the growth of hamster pancreatic well differentiated adenocarcinoma were investigated in vitro. Desglugastrin exhibited the greatest effect on thymidine incorporation into these cells after a lag period of 96 h. Doses of desglugastrin in the range from 30 to 270 ng/mL caused a significant and dose-dependent increase in thymidine incorporation. Higher doses of this peptide led to a decreased response. Secretin also increased thymidine incorporation, but the response was less than that induced by gastrin. Prolonged incubation with secretin for 96 h increased tritiated thymidine incorporation in a log-dose fashion in the range of 30 to 270 ng/mL. Doses of CCK-8 in the range of 90 to 810 ng/mL significantly increased thymidine incorporation after 48 h of incubation. Following 72 h of incubation, only the dose of 270 ng/mL continued to exhibit a significant stimulation. Our study suggests that the gastrointestinal hormones could directly increase the growth of pancreatic carcinoma cells, act synergistically with endogenous growth factors, or stimulate the local production of these factors. In any event, our results that gastrin, secretin, and CCK can stimulate the growth of pancreatic ductal tumor cells in tissue cultures, support earlier findings on normal and malignant pancreatic parenchyma.

Effect of estradiol on pancreatic amylase and cholecystokinin binding in ovariectomized guinea pigs

The effect of estradiol (E 2) on amylase content and on basal and stimulated amylase release from the pancreatic acini was examined in relation to its effects on cholecystokinin (CCK)-receptor (R) levels. Guinea pigs were ovariectomized (OVX) and a week later administered either E 2 (10 μg/kg) (Treated, T) or vehicle (corn oil) (Control, C) 0.2 ml/day s.c. After 7 days of injections, animals were killed, pancreata weighed and basal and stimulated amylase release from pancreatic acini measured. Receptors for CCK were measured on pancreatic membranes. Chronic administration of E 2 resulted in a significant decrease in: (1) pancreatic weight (0.96 ± 0.04, T vs 1.142 ± 0.046 g, C); (2) total pancreatic DNA content (5.74 ± 0.37, T vs 6.81 ± 0.16 mgs, C); (3) total amylase content in pancreata (2081 ± 307, T vs 3795 ± 442 I.U., C); (4) absolute value of basal amylase release (6.57 ± 1.4, T vs 11.8 ± 1.9 I.U./incubate, C); and (5) absolute value of amylase release stimulated by increasing doses (0.01–1000 nM) of CCK in T vs C animals. On the other hand, the amylase release in response to >0.5 nM of CCK, expressed as a percentage of the total amylase content, was significantly increased in T vs C animals, which may be related to a significant rise in the concentration (fmol/mg protein) of CCK-receptors (629.8 ± 65.9, T vs 313.4 ± 92.7 fmol, C). Concentration of DNA/unit pancreatic weight and basal amylase release expressed as a percentage of total content, however, was similar in the C and T guinea pigs, while concentration of amylase and CCK-receptors/unit pancreatic weight remained significantly different in the two groups of animals. These results suggest that E 2 may have more than one effect on the pancreas in vivo, including a significant reduction in pancreatic growth and amylase concentration/cell and an up-regulation of CCK-receptors/cell.

CCK receptor antagonism by loxiglumide and gall bladder contractions in response to cholecystokinin, sham feeding and ordinary feeding in man.

The postprandial contractions of the gall bladder result from the interaction of neurohormonal factors but their relative contribution is unknown. This study was designed to determine the role of cholecystokinin (CCK) in gall bladder contractions using a highly selective and potent CCK-receptor antagonist, CR-1505 (loxiglumide) in healthy men either infused with exogenous CCK in graded doses (1.56-50 pmol/kg/h) or subjected to modified sham feeding (MSF) and ordinary feeding tests. The gall bladder volume measured by real time ultrasonography showed dose dependent decrease in the gall bladder volume in 10 subjects when CCK8 was infused iv in graded doses reaching about 15% at 1.56 pmol/kg/h and 91% at 50 pmol/kg/h. Close correlation between the decrease in gall bladder volume and the dosage of CCK or the increments in plasma CCK-bioactivity was observed. After pretreatment with loxiglumide, CCK resulted in similar increments in plasma CCK-bioactivity but failed to affect the gall bladder volume at CCK doses up to 6.25 pmol/kg/h and caused only 53% reduction at 50 pmol/kg/h. Modified sham feeding and real feeding reduced the volume of gall bladder by 20% and 70%, respectively and loxiglumide decreased these values to 15% and 30%, respectively. This study provides evidence that loxiglumide is highly potent and selective CCK antagonist and that endogenous CCK plays an important role both in the postprandial contractions of gall bladder.

Inhibition of Acetyl- and Butyrylcholinesterase and Amylase Release from Canine Pancreas

There are two tissue-fixed cholinesterases in dog pancreas: acetylcholinesterase and butyrylcholinesterase. In the present experiments, an organophosphate that only inhibits butyrylcholinesterase (isopropylpyrophosphoramide, or iso-OMPA) was compared with echothiophate and a nonorganophosphate compound, physostigmine. The latter two agents inhibit both cholinesterases. Fresh canine pancreas from anesthetized dogs was minced into fragments and suspended in Eagle's solution gassed with 100% O2. Amylase release was measured by the Phadebas method. In 2-h dose-response studies, there was a fivefold increase in sensitivity to acetylcholine when fragments were preincubated 1 h with iso-OMPA. There was a 1,000-fold increase in sensitivity when fragments were preincubated for 1 h in echothiophate. Basal amylase release in incubates with echothiophate were also increased. In dose-response studies with CCK-8, iso-OMPA was without effect, but echothiophate treatment resulted in a greater total response to CCK-8. There was a corresponding increase in basal output with echothiophate alone. Physostigmine also potentiates the response to CCK-8. Cumulative responses up to 3 h with half-maximal acetylcholine or half-maximal CCK-8 doses showed enhanced total output in fragments preincubated with echothiophate (p less than 0.05). The enhancement effect was atropine-sensitive to hexamethonium ganglionic blockade. In calcium-free medium, the enhancement with echothiophate was greatly reduced but still present. Inhibitors of both cholinesterases in the pancreas cause a greater total amylase release to sub-maximal doses of acetylcholine and CCK-8 than agents that only inhibit butyrylcholinesterase. Though our data do not provide direct proof, the results could be explained by a greater accumulation of endogenous acetylcholine when both cholinesterases are inhibited.

Interaction of CCK-8 and somatostatin-14 in control of food intake in dogs

interactions of cholecystokinin COOH-terminal octapeptide (CCK-8) and somatostatin-14 (SS-14) on food intake in dogs were examined by administration of graded doses of these peptides alone and in combination. In animals fasted 19 h, SS-14 (2,000 or 20,000 pmol.kg-1.h-1) had no effect on food intake. In animals fasted 4 h, food intake was not affected by 40 or 400 pmol.kg-1.h-1 SS-14 but was significantly (P less than 0.05) increased by 20% after 4,000 pmol.kg-1.h-1 SS-14. Feeding responses to simultaneous infusions of CCK-8 (50 or 400 pmol.kg-1.h-1) and SS-14 (40, 400, or 4,000 pmol.kg-1.h-1) were determined in animals fasted 4 h. Given alone, the high dose of CCK-8 (400 pmol.kg-1.h-1) significantly (P less than 0.01) depressed food intake by 55%. This effect was blocked by all doses of SS-14. In the absence of CCK-8, SS-14 had no effect except at the highest dose (4,000 pmol.kg-1.h-1), which significantly (P less than 0.01) stimulated food intake by 57%. This effect was blocked by both doses of CCK-8. Simultaneous infusion of lower doses of SS-14 (40 and 400 pmol.kg-1.h-1) and CCK-8 (50 pmol.kg-1.h-1) had no effect on food intake. These results suggest that plasma levels of CCK and SS-14 after a meal are not sufficient alone or in combination to produce satiety.

Contractile response of canine gallbladder and sphincter of Oddi to substance P and related peptidesin vitro

Substance P (SP) is a neurotransmitter peptide that is widely distributed in the body. Since SP has been demonstrated in the gallbladder (GB) and bile ducts of dogs, it may have a role in biliary motility. The objective of this study was to examine the effect of SP on the GB and sphincter of Oddi (SOD) of dogs in vitro, to evaluate the structure-activity relationship of SP, and to compare the contractile effect of SP with that of cholecystokinin octapeptide (CCK-8) and acetylcholine (Ach). Isolated longitudinal strips of GB and SOD from dogs were suspended in oxygenated Krebs buffer and the isometric tension responses to various doses of CCK-8, Ach, SP, and SP homologs [SP-free acid (SPFA), Octa-SP (O-SP), physalaemin (PHY)] were measured. We found that all the SP homologs, other than SPFA, stimulated GB and SOD contractions in vitro in a dose-dependent manner. The potency of SP and its homologs on GB and SOD was SP greater than or equal to PHY greater than O-SP; SPFA was without effect. CCK-8 was significantly more effective than SP on GB contraction, but unlike SP, CCK had no effect on SOD. The maximum contraction achieved by Ach was 1.3 (SOD) to 2.3 (GB) times greater than that achieved by SP, but the ED50 of SP was approximately 100- to 200-fold lower than that of Ach. The contractile effect of SP was partially blocked by 10(-5) M atropine.(ABSTRACT TRUNCATED AT 250 WORDS)