Parasympathetic non-adrenergic, non-cholinergic transmission in rat parotid glands: effects of cholecystokinin-A and -B receptor antagonists on the secretory response

Recent studies show i.v. administered pentagastrin and cholecystokinin to evoke protein/amylase secretion from the rat parotid gland and to stimulate gland protein synthesis, the two phenomena being abolished by cholecystokinin receptor antagonists. In the rat parotid gland, non-adrenergic, non-cholinergic transmission mechanisms contribute to secretion of fluid and protein/amylase. Since cholecystokinin may act as a neurotransmitter, activation of cholecystokinin receptors of the gland might contribute to the parasympathetic nerve-evoked secretion. In this study, the parasympathetic innervation was stimulated in non-atropinized (in periods of 2 min) or atropinized (in periods of 3 min) pentobarbitone-anaesthetized rats before and after administration of the cholecystokinin-A receptor antagonist lorglumide (48 mg/kg, i.v.) and the cholecystokinin-B receptor antagonist itriglumide (5.5 mg/kg, i.v.). The non-adrenergic, non-cholinergic transmission fatigues rapidly resulting in declining responses. Therefore, atropinized rats, not receiving the cholecystokinin receptor antagonists, had to serve as controls. Neither at a stimulation frequency of 10 Hz nor of 40 Hz were the secretory responses of the atropinized rats affected by the receptor antagonists. After lorglumide, the saliva volume and the amylase output were (expressed as percentage of the response to the stimulation period before the administration of the antagonist) 98.0+/-3.8% (vs. control 91.1+/-4.0%) and 91.9+/-4.9% (vs. 87.7+/-3.7%) at 10 Hz, respectively, and 79.8+/-4.5% (vs. 77.3+/-2.1%) and 73.6+/-5.3% (vs. 71.7+/-2.3%) at 40 Hz, respectively. After itriglumide, the corresponding percentage figures for saliva volume and amylase output were, at 10 Hz, 99.5+/-8.9% (vs. 92.0+/-2.8%) and 95.8+/-11.8% (vs. 89.2+/-6.4%), respectively, and, at 40 Hz, 74.0+/-3.1% (vs. 79.6+/-2.2%) and 66.6+/-3.3% (vs. 63.9+/-6.0%), respectively. Similarly, the antagonists were without effect on the parotid secretory responses of non-atropinized rats subjected to stimulation at 10 Hz. Thus, under physiological conditions, the cholecystokinin receptors of the parotid gland are likely to be stimulated by circulating hormones rather than by nervous activity.     

Effect of the specific cholecystokinin-receptor antagonist loxiglumide on bombesin stimulated pancreatic enzyme secretion in man.

We have investigated the effects of the specific cholecystokinin (CCK) receptor antagonist loxiglumide on basal and bombesin stimulated pancreatic enzyme secretion, bilirubin output and plasma CCK release in six healthy subjects. The data were compared with those obtained in control experiments where saline was infused instead of loxiglumide. Basal amylase output (4.7 +/- 0.8 kU/45 min), trypsin output (2.9 +/- 0.8 kU/45 min) and bilirubin output (7.7 +/- 2.8 mmol/45 min) gradually declined during infusion of loxiglumide to values of 1.3 +/- 0.3 kU/45 min, 0.5 +/- 0.1 kU/45 min and 0.4 +/- 0.0 mmol/45 min, respectively, reaching statistical significance (P less than 0.05) in the 30 to 45-min period after the start of the loxiglumide infusion. In the control experiments saline infusion failed to influence basal amylase, trypsin and bilirubin output, while bombesin stimulated amylase output from 4.7 +/- 0.8 kU/45 min to 25.1 +/- 5.1 kU/45 min (P less than 0.05), trypsin output from 2.9 +/- 0.8 kU/45 min to 11.6 +/- 2.0 kU/45 min (P less than 0.05) and bilirubin output from 7.7 +/- 2.8 mmol/45 min to 68.0 +/- 16.0 mmol/45 min (P less than 0.05). Loxiglumide failed to significantly influence bombesin stimulated amylase output (36.7 +/- 9.0 kU/45 min) and trypsin output (8.3 +/- 2.9 kU/45 min), but almost abolished bilirubin output (9.7 +/- 3.6 mmol/45 min) (P less than 0.05). Basal plasma CCK (2.4 +/- 0.1 pM) was not significantly influenced by loxiglumide (2.4 +/- 0.2 pM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Acid inhibition by intestinal nutrients mediated by CCK-A receptors but not plasma CCK

We examined the role of CCK-A receptors in acid inhibition by intestinal nutrients. Gastric acid and plasma CCK and gastrin levels were measured in rats with gastric and duodenal fistulas during intragastric 8% peptone and duodenal perfusion with saline, complete liquid diet (CLD; 20% carbohydrate, 6% fat, and 5% protein), and the individual components of CLD. Acid output was significantly inhibited (50-60%) by CLD, lipid, and dextrose. Plasma CCK was significantly increased by CLD (from 2.6 +/- 0.3 to 4.8 +/- 0.5 pM) and lipid (4.6 +/- 0.5 pM). CCK levels 50-fold higher (218 +/- 33 pM) were required to achieve similar acid inhibition by exogenous CCK-8 (10 nmol x kg(-1) x h(-1) iv). Intestinal soybean trypsin inhibitor elevated CCK (10.9 +/- 2.5 pM) without inhibiting acid secretion. The CCK-A antagonist MK-329 (1 mg/kg iv) reversed acid inhibition caused by CLD, lipid, and dextrose. Peptone-stimulated gastrin (21.7 +/- 1.9 pM) was significantly inhibited by CLD (14.5 +/- 3.6 pM), lipid (12.3 +/- 2.2 pM), and dextrose (11.9 +/- 1.5 pM). Lipid and carbohydrate inhibit acid secretion by activating CCK-A receptors but not by altering plasma CCK concentrations.     

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.     

The cholecystokinin receptor antagonist CR1409 increases plasma cholecystokinin in rats

This study was undertaken to determine whether plasma cholecystokinin (CCK) levels are affected by the administration of the CCK-receptor antagonist CR1409 to rats. Infusion of 0.19, 0.94 and 4.75 mg/kg.h CR1409 for 30 min each into 6 conscious rats increased (P less than 0.05) plasma CCK from 1.3 +/- 0.5 to 6.0 +/- 1.2, 5.4 +/- 1.2, and 5.4 +/- 1.0 pM, respectively. In a subsequent study infusion of stepwise increasing lower doses of 0.3, 1.5, 7.5, 37.5 and 187.5 micrograms/kg.h CR1409 for 30 min each into 6 other rats dose-dependently increased (P less than 0.05) plasma CCK from 1.4 +/- 0.3 to 3.1 +/- 0.6, 4.1 +/- 0.8, 5.4 +/- 1.0, 5.9 +/- 0.8 and 7.1 +/- 1.1 pM, while infusion of saline did not affect plasma CCK concentrations. We therefore conclude that the CCK-receptor antagonist CR1409 increases plasma CCK in the rat.     

Cholecystokinin and peptide YY are released by fat in either proximal or distal small intestine in dogs

We tested the hypothesis that the release of cholecystokinin (CCK) and peptide YY (PYY) may be independent of the region of the small intestine exposed to fat. In five dogs equipped with duodenal and midgut fistulas, the small intestine was compartmentalized so that fat was confined to either the proximal or distal one-half of the gut. Plasma CCK and PYY levels were measured by radioimmunoassay and compared by the square root of the area under the curve (sqrt AUC), representing the plasma peptide concentration over time. CCK was released similarly whether fat was delivered into the proximal (69.9+/-4.7 pM) or distal (71.0+/-5.5 pM) gut, but significantly more CCK (88.9+/-5.6 pM; p<0.05) was released when both the proximal and distal gut were perfused simultaneously with fat. PYY was released similarly whether fat was delivered into the proximal (34.9+/-2.6 pM) or distal (40.0+/-1.2 pM) gut or both (38.6+/-2.2 pM). We conclude that CCK and PYY are released by fat in either the proximal or distal one-half of the small intestine.     

Effect of immunoneutralisation of cholecystokinin on bombesin-stimulated pancreatic enzyme secretion in the rat

Infusion of bombesin stimulates plasma cholecystokinin (CCK) and pancreatic enzyme secretion in various species, including the rat. This study was undertaken in two groups of four conscious rats with a cannulated pancreatic duct to determine the role of endogenously released CCK in mediating the effect of bombesin on pancreatic enzyme secretion. Infusion of 2 ml CCK antiserum or normal rabbit serum for 40 min was followed 10 min later by infusion of 18 pmol/kg bombesin for 30 min and after an interval of 90 min by infusion of 24 pmol/kg CCK for 30 min. After administration of control rabbit serum, pancreatic protein secretion increased by 3.2 +/- 1.0 mg/30 min during bombesin and 4.0 +/- 1.5 mg/30 min during CCK, while the plasma CCK increments were 1.7 +/- 0.5 pM and 7.0 +/- 0.9 pM for the bombesin and CCK infusions, respectively. Immunoneutralisation with the CCK antiserum did not significantly affect bombesin-stimulated pancreatic protein secretion (3.6 +/- 1.3 mg/30 min), but almost abolished the pancreatic protein response to CCK (0.5 +/- 0.2 mg/30 min). It is therefore concluded that CCK is not an important mediator of the stimulatory effect of bombesin on the pancreas in the rat.     

Effect of lorglumide (CR-1409) on pancreatic secretory and trophic response to caerulein in newborn rats.

The authors investigated whether lorglumide a specific CCK-receptor antagonist affects the pancreatic actions of caerulein in female newborn Wistar rats. Pancreatic secretory response (expressed as the decrease in specific trypsin activity in the pancreas) was studied in 11-day-old rats following acute administration of saline (control), caerulein (0.3, 1, or 3 micrograms/kg s.c.) either without or with lorglumide (10 mg/kg s.c.). Lorglumide was given 15 min before caerulein. In chronic studies rats were treated 3x/day for 10 days from the day of birth (Day 1) with caerulein and lorglumide as above. On Day 11 the rats were decapitated and exsanguinated, their pancreas removed and analyzed. Acute administration of caerulein induced a dose-dependent depletion of specific trypsin activity from the pancreas and this was antagonized by lorglumide. Chronic treatment with each dose of the peptide increased total pancreatic trypsin content. Besides, the 3 micrograms/kg dose caused to increase pancreatic protein, DNA, and amylase content and to increase plasma corticosterone level. Chronic administration of lorglumide did not influence normal pancreatic growth, while it strongly inhibited the increase in trypsin content evoked by caerulein. However, lorglumide, given alone or in combination with caerulein, induced a significant increase in pancreatic amylase content without affecting plasma corticosterone level.     

Chronic exposure to nicotine alters endothelium-dependent arteriolar dilatation: effect of superoxide dismutase.

The first goal of this study was to determine whether chronic injection of nicotine alters endothelium-dependent arteriolar dilatation. We measured the diameter of cheek pouch resistance arterioles (approximately 50 microm in diameter) in response to endothelium-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in control hamsters and hamsters treated with nicotine (2 microg. kg-1. day-1 for 2-3 wk). In control hamsters, acetylcholine (0.1 and 1.0 microM) dilated arterioles by 13 +/- 2 and 31 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by 18 +/- 1 and 30 +/- 1%, respectively. In contrast, acetylcholine (0.1 and 1.0 microM) dilated arterioles by only 5 +/- 2 and 12 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by only 7 +/- 2 and 13 +/- 3%, respectively, in animals treated with nicotine (P < 0.05 vs. response in control hamsters). Nitroglycerin produced similar dose-related dilatation of cheek pouch arterioles in control and nicotine-treated hamsters. Our second goal was to examine a possible mechanism for impaired endothelium-dependent arteriolar dilatation during chronic treatment with nicotine. We found that superfusion of the cheek pouch microcirculation with superoxide dismutase (150 U/ml) restored impaired endothelium-dependent, but did not alter endothelium-independent, arteriolar dilatation in hamsters treated with nicotine. Superfusion with superoxide dismutase did not alter endothelium-dependent or -independent arteriolar dilatation in control hamsters. We suggest that chronic exposure to nicotine produces selective impairment of endothelium-dependent arteriolar dilatation via a mechanism related to the synthesis/release of oxygen-derived free radicals.     

CCK-58 is the only detectable endocrine form of cholecystokinin in rat

CCK-58 differs from CCK-8 in patterns of expression of pancreatic secretion of fluid and amylase and gallbladder contraction. These differences have physiological relevance only if CCK-58 release is stimulated by nutrients entering the intestine and if CCK-58 circulates in sizeable amounts. In this study, we report that when radiolabeled CCK-58 is added to rat blood and plasma is formed, there is extensive loss and degradation of the radioactive peptide. Therefore, a new method was developed to minimize loss and degradation of this label. This method recovered >85% of the label with no detectable degradation. Furthermore, the optimized method recovered all unlabeled exogenous cholecystokinin molecular forms in >80% yields. Blood from fasted rats and rats in which cholecystokinin release was stimulated by the trypsin inhibitor camostat contained only CCK-58 (3.5 +/- 0.5 and 17 +/- 1.5 fmol/ml, respectively). Because CCK-58 predominates in the blood, this molecular form should be used in studies on the physiology and pathophysiology of cholecystokinin.     

Sulfated cholecystokinin octapeptide in the rat: pontomedullary distribution and modulation of the respiratory pattern.

We performed anatomical and physiological studies to determine the site and actions of sulfated cholecystokinin octapeptide (CCK8-S) on breathing. Peptide locations were determined by combined immunodetection of CCK8-S- containing synaptic varicosities and retrograde labeling of medullary neurons projecting to the ventral respiratory group. Retrogradely labeled neurons and CCK8-S immunolabeled varicosities overlapped within the nuclei of the solitary tract, ventral respiratory group, and the Kolliker-Fuse nucleus. Additional CCK8-S immunoreactive terminals were located in the rostroventrolateral medullary reticular nucleus, lateral paragigantocellular reticular nucleus, and the caudal pontine reticular nucleus. The respiratory effects of CCK8-S, which binds to CCK(A) and CCK(B) receptors, were examined by intravenous injection in adult rats and by bath application in the in vitro neonatal rat brainstem - spinal cord preparation. CCK8-S produced an increase in the mean amplitude of diaphragmatic electromyogram (EMG) of 28 +/- 35% (SD) and a decrease in mean respiratory interval of 13 +/- 4% in vivo. In vitro, CCK8-S significantly increased inspiratory duration and decreased respiratory interval, primarily by shortening expiratory duration. CCK8-unsulfated, a specific agonist for CCK(B) receptors, did not produce these effects. CCK8-S effects in the in vitro preparation were partially blocked by the CCK receptor antagonist lorglumide (final bath concentration 600 nM). These results suggest that CCK8-S modulates the respiratory rhythm via CCK(A) receptors within one or more medullary or pontine respiratory groups in both neonatal and adult rats.     

Lipids, proteins and carbohydrates stimulate the secretion of intestinal cholecystokinin in the pig

Food intake enhances the release of intestinal cholecystokinin (CCK) in the pig but the contribution of individual nutrients to the CCK response has not yet been established in this species. Six hogs (mean weight 50 kg) were fitted with a duodenal fistula for instillation of nutrients and with portal (PV) and carotid (CA) catheters for blood sampling. After a 24-h fast, the animals received 1,000 ml of isotonic solution containing 440 kcal of carbohydrate (starch hydrolysate), or of protein (casein hydrolysate) or fat (Intralipid) or a control saline solution by 60-min intraduodenal perfusion after a 60-min control period during which the animals received saline. Portal and peripheral blood samples were collected at 15-min intervals for CCK radioimmunoassay. Intraduodenal perfusion of fat provoked a sharp increase in CCK-Like immunoreactivity (CCK-LI) in PV (peak 76.6 +/- 12.2 pM from basal 10.8 +/- 1.2 pM) and in peripheral blood (peak 46.7 +/- 8.4 pM from basal 9.1 +/- 1.0 pM). The protein hydrolysate induced a transient increase in plasma CCK-LI during the first 30 min of intestinal perfusion (PV: peak 40.1 +/- 5.0 pM from basal 11.9 +/- 1.4 pM; CA: 31.8 +/- 4.0 pM from basal 8.5 +/- 0.8 pM). The transient effect of proteins on CCK release might reflect the consequence of somatostatin release from intestinal stores. Starch hydrolysate promptly raised plasma CCK-LI level to a plateau value (PV: 52.5 +/- 13.1 pM from basal 11.9 +/- 1.4 pM; CA: 35.4 +/- 8.0 from basal 8.5 +/- 0.8 pM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Does increased endogenous CCK interact with serotonin to reduce food intake in rats?

The present study was aimed to test the hypothesis that increased endogenous CCK may interact with the anorectic serotonergic agent dl-fenfluramine to reduce food intake in rats. Previous studies, using selective CCK receptor antagonists, could demonstrate CCK-dependent 5-HT-induced anorexia. In the present approach, we used protease inhibitors to increase levels of endogenous CCK instead of blocking CCK receptors by antagonists. The protease inhibitors we used were soybean trypsin inhibitor (STI) and camostate. We hypothesized that combining the anorectic serotonergic drug dl-fenfluramine with either STI or camostate should result in an enhanced hypophagic effect when compared to single drug treatment. All feeding experiments were performed in non-deprived rats during night time feeding. Given alone, STI (500 mg/kg, po), camostate (200 mg/kg po) and also fenfluramine (1–9 mg/kg ip) reduced significantly food intake, with a more pronounced effect following fenfluramine. However, the experiments do not provide evidence for any additive or synergistic action between camostate or STI and the anorectic serotonergic drug dl-fenfluramine on food intake.     

Effect of pancreatic enzyme supplementation on postprandial plasma cholecystokinin secretion in patients with pancreatic insufficiency

To test the hypothesis, based on studies in healthy man and dog, that patients with impaired digestion due to severe pancreatic insufficiency have impaired postprandial cholecystokinin (CCK) secretion that can be improved by the addition of pancreatic enzymes, we have studied plasma CCK responses to a test meal with and without addition of pancreatic enzymes in 10 patients with pancreatic insufficiency and steatorrhea, in 8 patients with chronic pancreatitis without steatorrhea, and in 6 healthy subjects. The patients with steatorrhea had a significantly (P less than 0.001) lower integrated plasma CCK response to the meal (177 +/- 23 pM.150 min) than the healthy subjects (468 +/- 41 pM.150 min), while patients with chronic pancreatitis without steatorrhea had an intermediate integrated postprandial CCK secretion (327 +/- 101 pM.150 min). Addition of pancreatic enzymes to the meal significantly augmented the integrated CCK response in both the patients with steatorrhea to 483 +/- 72 pM.150 min (P less than 0.01) and in those without steatorrhea to 480 +/- 85 pM.150 min (P less than 0.05). These values were not significantly different from those in the healthy subjects (521 +/- 86 pM.150 min). Integrated CCK secretion in the three groups during bombesin infusion was similar (patients with steatorrhea 134 +/- 23 pM.20 min, patients without steatorrhea 131 +/- 33 pM.20 min, and healthy subjects 146 +/- 28 pM.20 min), indicating a normal capacity to secrete CCK in response to a humoral stimulus. These data are in agreement with the suggestions from previous studies that digestion of nutrients by pancreatic enzymes plays an important role in the regulation of plasma CCK secretion after feeding.     

The effect of physiological doses of thyroxine on the level of cyclic adenosine-3',5'-monophosphate in pituitary and anterior hypothalamus of male rats of different age

The levels of cAMP in the pituitary and anterior hypothalamus were determined by competitive binding to protein in male rats aged 2--2.5, 6--8 and 14--18 months. The lowest level of cAMP both in the pituitary and anterior hypothalamus (1.05 +/- 0.17 and 0.85 +/- 0.23 pM) (per mg wet weight, respectively) was found in 6--8 month-old rats. Administration of T4 (2 micrograms/100 g body weight, for 8 days) was followed by a decrease in cAMP level in the pituitary of 14--18 month-old animals, which was not the case with younger rats. The obtained results agree with the earlier observation that the threshold to homeostatic suppression in the hypothalamus-pituitary-thyroid system of rats decreases with aging. It is suggested that cAMP system contributes to the mechanism of changes in hypothalamic threshold and its pharmacological correction.     

Progesterone secretion by adrenal glands of hamsters and comparison of ACTH influence in rats and hamsters.

Studies were designed to determine a) if adrenal glands of hamsters secrete progesterone (PROG), b) the effects of adrenocritocotropin (ACTH) administration on adrenocortial function of rats and hamsters under the surgical conditions necessary for collection of adrenal venous blood from the left renal vein, and c) the effects of blood loss during sample collection. PROG was quantitated by the competitive protein-binding method after extraction and separation by sephadex LH-20 column chromatography. The presence of interfering quantities of androstenedione necessitated two column chromatographic steps. Glucocorticoids (11-OHCS) were determined fluorometrically. PROG was detected in adrenal venous plasma of female hamsters. The PROG concentration and secretory rate were 91 +/- 12 ng/ml and 4 +/- 1 ng/min, respectively, while the peripheral plasma level of the same animals was 2 +/- 0.2 ng/ml, indicating that the adrenal glands of female hamsters are capable of secreting PROG. ACTH administration increased PROG secretory rates in both hamsters (3 +/- 1 to 14 +/- 3 ng/min) and rats (62 +/- 9 to 152 +/- 32 ng/min) on estrus, as well as increasing the 11-OHCS secretory rate of hamsters (16 +/- 1 to 33 +/- 4 ng/min), but not of rats. The greater increase in PRCC than in 11-OHCS secretion may be related to excess PROG formation relative to the capacity of the 17alpha- or 21-hydroxylating enzyme systems. The adrenal venous PROG concentration and secretory rate of female hamsters infused with 10% dextran while collecting adrenal venous blood did not differ significantly from those of the non-infused animals, suggesting that this amount of blood loss (1 ml) does not influence PROG secretion.     

Absence of luminal bile increases duodenal content of cholecystokinin in rats.

The effects of the removal of bile from the proximal intestine on pancreas, plasma cholecystokinin (CCK) concentration, and duodenal content of CCK were examined in rats. Bile was excluded from the duodenum and introduced into the distal ileum through a silastic cannula for 7 days. Pancreatic juice was maintained to be normally secreted into the duodenum. After 7-day bile diversion, plasma CCK concentration and duodenal CCK content were significantly increased in bile-diverted rats. Trypsin content in the proximal intestine in bile-diverted rats was one-half that in control. Pancreatic wet weight, protein content, and DNA content in the pancreas were slightly increased, and lipase content was slightly decreased, by bile diversion, but none of these changes was statistically significant. Amylase content significantly decreased and chymotrypsin content significantly increased in bile-diverted rats. Intragastric administration of camostate (trypsin inhibitor) significantly increased plasma CCK concentration in both bile-diverted and control rats, and the net increase was much greater in bile-diverted rats than in control rats. In conclusion, bile diversion increased duodenal CCK content and increased the CCK response to luminal stimulant.     

A secretin releasing peptide exists in dog pancreatic juice

Canine pancreatic juice has been shown to stimulate exocrine pancreatic secretion in the dog. In the present study we investigated whether there is a secretin-releasing peptide in canine pancreatic juice. Pancreatic juice was collected from the dogs with Thomas gastric and duodenal cannulas while pancreatic secretion was stimulated by intravenous administration of secretin at 0.5 microg/kg/h and CCK-8 at 0.2 microg/kg/h, respectively. The pancreatic juice was separated into three different molecular weight (MW) fractions (Fr) by ultrafiltration (Fr 1; MW > 10,000, Fr 2; MW=10,000-4,000 and Fr 3; MW < 4,000), respectively. All the fractions were bioassayed in anesthetized rats. Fraction 3 dose-dependently and significantly stimulated pancreatic juice flow volume from 78.0% to 99.4% (p<0.05) and bicarbonate output from 128.9% to 202.1% (p<0.01), respectively. Plasma secretin concentration also increased from 1.2 +/- 0.5 pM to 5.0 +/- 0.8 pM and 6.0 +/- 1.0 pM (p<0.05). None of these fractions increased pancreatic protein secretion or plasma CCK level. The stimulatory effect of Fraction 3 on pancreatic secretion and the release of secretin was completely abolished by treatment with trypsin (1 mg/ml for 60 min at 37 degrees C) but not by heating (100 degrees C, 10 min). Intravenous injection of a rabbit anti-secretin serum, which rendered plasma secretin almost undetectable in rat plasma, also abolished Fr 3-stimulated pancreatic secretion of fluid and bicarbonate secretion. These observations suggest that a secretin-releasing peptide exists in the canine pancreatic juice. It is trypsin-sensitive and heat-resistant. This peptide may play a significant physiological role on the release of secretin and regulation of exocrine pancreatic secretion.     

Immunochemical characterisation of somatostatin in ruminants

Following development and validation of a radioimmunoassay for somatostatin, the immunoreactivity of this peptide in the plasma of ruminants was measured and the levels in sheep were 9-31 pM (mean 18 +/- 7 pM, n = 48), in lambs 10-54 pM (mean 25 +/- 10 pM, n = 18) and in calves 5-35 pM (mean 12 +/- 6 pM, n = 22). Somatostatin-like immunoreactivity was present in sheep in high concentrations in the antrum (2342 +/- 280 pmol/g wet weight), duodenum (446 +/- 73 pmol/g) and pancreas (832 +/- 208 pmol/g). Lower concentrations (6-150 pmol/g) were found in other regions of the gastrointestinal tract. Molecular sieve chromatography on Bio-Gel P-10 showed that while most of the somatostatin in the antrum was somatostatin-14, in the duodenum about 30% of the total immunoreactivity was somatostatin-28.     

Enterostatin (APGPR) suppresses the analgesic activity of morphine by a CCK-dependent mechanism

Enterostatin (APGPR) found in the gastrointestinal tract and brain is an anorectic pentapeptide. We found that APGPR inhibited morphine-induced analgesia after intracerebroventricular administration in mice at a dose of 10nmol/mouse. The anti-analgesic effect of APGPR was inhibited by pretreatment with lorglumide and LY225910, antagonists for cholecystokinin 1 (CCK1) and cholecystokinin 2 (CCK2) receptors, respectively. The anti-analgesic effect of APGPR may be mediated by CCK release, since APGPR does not have affinity for CCK receptors.