Differential sensitivity of pancreatic and colon cancer to cyclosporine and alpha-difluoromethylornithine in vivo

We have previously reported that the in vitro growth of MC-26 mouse colon cancer and H2T hamster pancreatic cancer cells are inhibited by cyclosporine (CsA) and alpha-difluoromethylornithine (DFMO). The present study was designed to investigate the effects of these two drugs on the two experimental tumors (MC-26 and H2T) growing in vivo. Forty-eight male Balb/c mice or Syrian golden hamsters were inoculated with MC-26 (250,000) or H2T (500,000) cells, respectively, and then were randomized into four groups of 12 each: group I was control; group II received CsA; group III received DFMO; group IV received a combination of CsA and DFMO. MC-26 tumors were significantly more sensitive than H2T tumors to the effects of CsA and DFMO. MC-26 tumor growth and tumor weight, as well as the tumor content of DNA, RNA, and protein were all significantly more reduced by CsA and DFMO than were the H2T tumors. Our present study shows that both CsA and DFMO are potent inhibitors of MC-26 colon carcinoma growth in vivo, though DFMO is more than twice as effective as CsA. DFMO also produced greater reductions in the tumor content of DNA, RNA, and protein than did CsA. DFMO significantly decreased the concentrations of polyamines in both H2T and MC-26 tumors; the MC-26 tumors were affected to a greater degree.

Development and age-related changes in pancreatic cholecystokinin receptors and duodenal cholecystokinin in guinea pigs

We have investigated the changes associated with development and aging on the interrelationships between cholecystokinin (CCK) and the pancreas in the guinea pig. Three groups (1 month old, 1 year old, and 3 years old) of male guinea pigs were sacrificed while feeding in order to measure food-stimulated levels of CCK in blood and in duodenal mucosa by radioimmunoassay (RIA), as well as the pancreatic concentrations of CCK receptors. Systemic blood concentrations of CCK did not change with age. However, the concentration and content of CCK in duodenal mucosa increased more than 3-fold with age. A single class of high-affinity (KD less than or equal to 0.1 nM) CCK-receptor was found on the pancreatic membranes. The concentration (fmol/mg protein) of these receptors significantly diminished by one-half with increasing age. We also found an apparently similar fall in the receptor-binding affinity, but the difference was not significant. We conclude that in the guinea pig, duodenal content of CCK increases so as to compensate for the decreasing concentration of pancreatic CCK receptors, or, perhaps, vice versa. The diminished exocrine function of the pancreas, seen with increasing age, may well reflect both the diminished number of CCK-receptors and the reduction of pancreatic acinar cells.

Establishment of a human gastrinoma in nude mice

We report the first establishment and characterization of functioning gastrinoma from a human being transplanted into nude mice. Tissue was obtained at operation from a gastrinoma liver metastasis from a patient with the Zollinger-Ellison syndrome. The tumor was implanted subcutaneously in five athymic nude mice. Serum gastrin was measured by means of radioimmunoassay in specimens of mouse blood taken before and 5 minutes after intraperitoneal injection of secretin (100 micrograms/kg). In a second experiment serum gastrin was measured 30 minutes after injection of somatostatin analogue, SMS 201-995 (300 micrograms/kg). Studies were also done in 10 control mice. At passage, the fundus of each tumor-bearing mouse was weighed and examined microscopically. The gastrinoma (tumor line, PT) has been maintained for 34 months through four passages with a tumor doubling time of 37 to 45 days. The histology is similar to the original tumor. Immunocytochemistry showed that PT contained gastrin. In two mice metastasis developed 9 months after implantation. Gastrin levels in mice bearing PT have ranged from 216 to 12,000 pg/ml. Gastrin levels of control mice ranged from 0 to 63 pg/ml. Secretin increased gastrin levels in three of five mice tested and decreased gastrin levels in two mice. Repeat secretin tests showed identical results. SMS 201-995 decreased gastrin levels from basal values. Fundic weight of mice bearing PT (397 +/- 93 mg) was significantly greater than control fundic weight (180 +/- 26 mg). Gastrinomas growing in nude mice produce physiologically active gastrin as shown by elevated serum gastrin levels and by hyperplasia of the stomach. Two distinct subpopulations of gastrinoma cells respond differently to secretin. This model should provide important information on mechanisms of growth control and on gastrin release by gastrinomas in human beings.

Inhibition of gastric acid secretion by peptide YY is independent of gastric somatostatin release in the rat

The purpose of this study was to determine whether the inhibitory action of peptide YY (PYY) on gastric acid secretion is attributable to the release of gastric somatostatin in rats. Two groups of rats (six rats/group) were anesthetized with urethane and prepared with gastric fistulas and jugular catheters. Pentagastrin (18 micrograms/kg-h) was given intravenously for 150 min to stimulate gastric acid secretion. Intravenous PYY (130 micrograms/kg-h) inhibited pentagastrin-stimulated gastric acid secretion significantly (P less than 0.05). Administration of iv PYY resulted in a 41% reduction (P less than 0.05) in pentagastrin-stimulated gastric acid secretion. In another group of anesthetized rats, administration of PYY (10(-7), 10(-8) M) failed to stimulate a release of somatostatin from the isolated-perfused rat stomach. Our findings indicate that PYY can inhibit gastric acid secretion independently of release of gastric somatostatin in the rat.

Restricted feeding schedules alter the circadian rhythms of serum insulin and gastric inhibitory polypeptide

Insulin and gastric inhibitory polypeptide (GIP) have a circadian rhythm of secretion that is altered by various feeding schedules. We acclimated rats over 3 weeks to one of 6 different feeding schedules. They were then killed at intervals over one feeding cycle. Blood was collected, and their stomachs were weighed. Hormones in the serum were measured by radioimmunoassay. When highest and lowest measured concentrations were compared in ad libitum fed rats, insulin more than doubled (445 +/- 50 to 993 +/- 180 pg/ml) and GIP more than tripled (682 +/- 108 to 1964 +/- 145 pg/ml) during a 24-h period. With restricted schedules, concentrations correlated with the feeding schedule, not the light-dark cycle. Hormone levels rose higher during feeding and fell lower with fasting than in ad lib fed rats. For example, GIP in one study fluctuated from 468 +/- 22 to 6433 +/- 432 pg/ml. In another example, insulin ranged from 30 +/- 5 to 2259 +/- 406 pg/ml during a 24-h period. However, insulin did not always correlate well with stomach weight. Circadian rhythms occurred for insulin with all feeding schedules and for GIP with all schedules except fasted rats. This finding implies an endogenous insulin rhythm, whereas food intake controls GIP secretion. Thus, disruption of normal circadian cycles of feeding may yield misleading information about gut hormone secretion.

Age-related changes in gallbladder contractility and gallbladder cholecystokinin receptor population in the guinea pig

We have examined the effects of aging on guinea pig biliary motility both in vitro and in vivo. The first experiment compared contractile tension of gallbladder strips from young adult (6-12 months old) and 3-year-old guinea pigs in vitro. Contraction of gallbladder strips from the young guinea pigs was twice as forceful and was more sensitive to octapeptide of cholecystokinin (CCK-8) stimulation than the gallbladder strips from the older guinea pigs. The two groups were also studied in vivo by measuring changes in the intraluminal pressure of the gallbladder in response to exogenously administered doses of CCK-8. Young adult guinea pigs were more sensitive to CCK-8 at the lower doses tested and demonstrated gallbladder contractions that were more forceful than that of the old guinea pigs. CCK receptors were measured on gallbladder muscularis membranes from young adult and old guinea pigs. The number of receptors on gallbladder membranes decreased with age: 65.0 +/- 17.7 fmoles/mg protein on membranes from 1 year old; 7.9 +/- 2.0 fmoles/mg protein on membranes from 3 years old. The binding affinity of CCK receptors on gallbladder muscularis membranes for binding to CCK-8 was not significantly different in the two age groups studied. We conclude that age-related decreases in gallbladder responses to CCK-8 may be due to decreased concentrations of CCK receptors on gallbladder muscle cells.

The time course of beta cell dysfunction in chronic ethanol-induced pancreatitis: a prospective analysis

Insulin-glucose homeostasis was examined in 62 patients with chronic pancreatitis (CP). All patients were graded on the basis of test results from five studies: (1) endoscopic retrograde cholangiopancreatography, (2) fat-stimulated release of pancreatic polypeptide (PP), (3) NBT-bentiromide PABA test, (4) 72-hour fecal fat test, and (5) oral glucose tolerance test (OGTT). Patients with CP were graded as either mild/moderate or severe by means of a scoring system that we devised and have previously reported. Nineteen patients were graded as mild/moderate and 43 patients were graded as severe. The endocrine function of non-beta and beta islet cells was compared by assessing release of PP after fat and by release of insulin during OGTT. Release of PP was depressed in 58%, and the depressed output was found in only patients with a severe grade of CP. Forty-four of 62 patients (71%) with CP had abnormal OGTT findings; the distribution of this abnormality was not greatly different between mild/moderate and severe grades. Depressed release of insulin was seen in 58% (36 of 62)--more commonly in patients with a severe grade (10%) but also in 32% of patients with a mild/moderate grade. A subset of patients with CP sustains early beta-cell dysfunction. We conclude that decreased output of PP is a more reliable measure of functional deficit and stage in CP.

Role of Ca2+ in bombesin-stimulated release of gastrin and somatostatin from isolated perfused rat stomach

The role of calcium (Ca2+) in bombesin (BBS)-stimulated release of gastrin and somatostatin-like immunoreactivity (SLI) was examined in isolated perfused rat stomachs obtained from male rats fasted overnight. The stomachs were perfused via the celiac artery. BBS (1 nM) was perfused alone for 10 min or in combination with various Ca2+ antagonists, including 1) different doses of divalent cationic Ca2+ chelator (EGTA), 2) Ca2+ channel blockers (nifedipine, verapamil), and 3) calmodulin (Ca2+ binding protein) antagonist [trifluoperazine (TFP)]. The effluent was collected for measurement of gastrin and SLI. EGTA at doses of 2 or 5 mM blocked the BBS-mediated release of both gastrin and SLI. After removal of a low dose of EGTA from the perfusate, the release of both gastrin and SLI rebounded. On removal of a high dose of EGTA, however, SLI release remained depressed, but gastrin rebounded even more significantly. In the absence of BBS, the rebound of gastrin release was less dramatic, indicating that reexposure to Ca2+ partially contributed to the rebound phenomenon. Nifedipine (0.1-10 microM) markedly decreased BBS-stimulated release of gastrin and SLI in a dose-dependent fashion; the inhibitory effect of nifedipine on SLI release was significantly stronger than on gastrin release. Verapamil (10 microM) depressed BBS-induced SLI release but not gastrin release. TFP (50 or 100 microM) also resulted in inhibition of bombesin-elicited release of gastrin and SLI in a dose-related manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-reaction of two different somatostatin antisera with calcitonin gene-related peptide

Two different anti-somatostatin antisera, R-101 and OAL-273, cross-react with rat calcitonin gene-related peptide (1-37) (CGRP). CGRP amounts, in excess of 6.25 x 10(-9) M, cross-react with R-101 in the somatostatin radioimmunoassay. CGRP amounts, in excess of 1.6 x 10(-9) M, cross-react with OAL-273. Both CGRP displacement curves are parallel to that of synthetic somatostatin (1-14). Comparison of ID50's shows that the cross-reactivity of CGRP with R-101 and OAL-273 are 0.02 and 0.1% of somatostatin, respectively.

Operative drainage of the pancreatic duct delays functional impairment in patients with chronic pancreatitis. A prospective analysis

In a prospective study, 85 patients with chronic pancreatitis have been subjected to evaluation by morphologic analysis (endoscopic retrograde cholangiopancreatography), by exocrine function tests (bentiromide PABA and 72-hour fecal fat testing), and by endocrine function tests (oral glucose tolerance test and fat-stimulated release of pancreatic polypeptide). All patients were graded on a five-point system, with 1 point assessed for an abnormal result in each of the five tests performed. Zero score denoted mild disease; 1-2 points signaled moderate disease; and 3-5 points indicated severe disease. In 68 patients, both an initial and late (mean follow-up period of 14 months) evaluation were performed. Forty-one patients underwent modified Puestow side-to-side Roux-en-Y pancreaticojejunostomy. The Puestow procedure alone was performed in 18 patients. Eight patients also had drainage of pseudocysts, seven also had a biliary bypass, and eight had pseudocyst drainage plus bypass, in addition to the Puestow. There were no deaths. Of the 68 patients who were studied twice, 30 had operations and 38 did not. None of the patients with severe disease improved their grade during follow-up. Of 24 patients who did not undergo operation, 17 (71%) who were graded mild/moderate progressed to a severe grade at follow-up. By contrast, only three of the 19 patients operated on (16%) and who were initially graded as mild/moderate progressed to severe disease at follow-up testing. More than 75% of all of the patients had a history of weight loss. Twenty-six of 30 patients operated on (87%) (all of whom had lost weight before surgery) gained a mean 4.2 kg (range 1.4-2.7 kg) after surgery, compared with no significant weight change (range -3.6-2.7 kg) among patients not operated on. These findings support a policy of early operation for chronic pancreatitis, perhaps even in the absence of disabling abdominal pain.

Influence of endogenous prostaglandins on secretin-mediated inhibition of gastric acid secretion in dogs

The influence of endogenous prostaglandins on secretin-mediated inhibition of gastric acid secretion was examined in 6 mongrel dogs with Thomas gastric and Herrera pancreatic cannulas. The dogs were given intravenous pentagastrin (1 microgram/kg.h) during the 180-min experiment, and graded doses of secretin (0.3-1.5 micrograms/kg.h) (1-5 CU/kg.h) were infused intravenously between 60 and 120 min. In alternate, otherwise identical experiments, a prostaglandin synthesis inhibitor, either indomethacin or meclofenamate, was also administered throughout the experiment. Increasing doses of secretin led to increasing inhibition of gastric acid output with the maximum inhibition at 1 microgram/kg.h (3.3 CU/kg.h) of secretin. Both indomethacin and meclofenamate abolished the inhibitory effects of secretin on gastric acid secretion. The inhibitors of prostaglandin generation had no effect on the serotonin system. We concluded that secretin mediates its inhibitory action on gastric acid secretion, at least in part, through endogenous prostaglandins.

Effect of cyclic nucleotides on bombesin-evoked gastrin release from isolated perfused rat stomach

We and others have recently reported an involvement of calcium (Ca2+)-mediated intracellular pathways in the release of antral gastrin in response to bombesin (BBS), while cyclic adenosine 3'5'-monophosphate (cAMP) potentiated the gastrin response to BBS. In this study we examined the effect of cyclic nucleotides on BBS-induced gastrin release from isolated perfused rat stomachs. Dibutyryl cyclic AMP (dbcAMP, 1 mM), and Rolipram (a phosphodiesterase inhibitor, 0.5 microM), stimulated basal gastrin secretion and potentiated BBS-induced gastrin release. The stimulation of gastrin release by BBS was not altered by Wiptide (a cAMP dependent protein kinase inhibitor, 1.0 microM), but was surprisingly inhibited by dbcGMP (1 mM). The cAMP content in antral mucosa or in the perfusates was not changed after infusion of BBS. These findings coupled with previous results suggest that BBS-provoked gastrin release is principally coupled to a Ca2+-mediated intracellular pathway, and that an activation of the adenylate cyclase mediated pathway is not involved. Intracellular cGMP, however, may participate in the negative regulation of gastrin release induced by BBS.

Vasoactive intestinal peptide inhibits the growth of hamster pancreatic cancer but not human pancreatic cancer in vivo

We have previously shown that hamster H2T pancreatic ductal cancer has a receptor for vasoactive intestinal peptide (VIP) which is not present on a cell line of human pancreatic ductal cancer (MIA). The purpose of this study was to examine the effect of chronic administration of VIP on the growth of both H2T hamster pancreatic carcinoma and MIA human pancreatic carcinoma in vivo. The growth of H2T was studied in hamsters; a control group of six hamsters received 0.1% bovine serum albumin (BSA) in saline, and two treatment groups of six hamsters each received VIP (1 and 10 nmol/kg), all administered three times a day by i.p. injection for 35 days. Both doses of VIP inhibited the growth of H2T tumor (tumor area, weight, DNA, RNA, and protein content). The growth of MIA was studied in athymic Balb/c mice, one group of 10 received 0.1% BSA and the other 10 received VIP (1 nmol/kg), both three times a day by i.p. injection for 3 months. There was no difference in tumor growth rate between the two groups. Treatment with VIP did not have any effect on body weight or size of the normal pancreas in either the hamsters or the mice. We conclude that the differential response of hamster and human pancreatic cancer to VIP treatment may be due to the presence or absence of VIP receptors.

Calcitonin gene-related peptide inhibits gallbladder contractility

Calcitonin gene-related peptide (CGRP), a 37-amino acid peptide, is widely distributed in the gastrointestinal tract where it is colocalized with substance P. The effect of CGRP on gallbladder motility is unknown. The objective of this study was to examine the effect of CGRP on cholecystokinin-octapeptide (CCK-8) and substance P-stimulated gallbladder contraction in vivo and in vitro. In in vivo studies intragallbladder pressure was measured in response to bolus administration of CCK-8 (10(-15) to 10(-9) mol/kg) or substance P (10(-12) to 10(-7) mol/kg), either alone or with a continuous infusion of CGRP (10(-9) mol/kg/hr), in anesthetized guinea pigs. In in vitro studies the contractile force of guinea pig gallbladder muscle strips was examined in response to CCK-8 (10(-12) to 10(-7) mol/L) and substance P (10(-9) to 10(-6) mol/L), alone or with CGRP (10(-10) to 10(-6) mol/L). CGRP (10(-9) mol/kg/hr) inhibited in vivo gallbladder contraction that was stimulated by CCK-8, but not by substance P. CGRP alone produced a significant (p less than 0.05) dose-related decrease in the resting tension of gallbladder strips in vitro. CGRP (10(-6) mol/L) inhibited gallbladder muscle tension in vitro, stimulated by both CCK-8 and substance P. These studies show that CGRP can affect gallbladder motor activity by decreasing smooth muscle tone and that CGRP can antagonize the action of CCK and substance P. CGRP may be involved in the physiologic control of gallbladder emptying and refilling.

Circadian rhythms in gastrin receptors in rat fundic stomach

Circadian rhythmicity in the number of gastrin receptors in rat fundic mucosa was characterized and was related to the concentrations of gastrin in serum and in antrum. Male Sprague-Dawley rats were acclimated to 12 hr light alternating with 12 hr darkness. Subgroups of six rats each were killed at 4-hr intervals. Fundic mucosa was collected for measurement of gastrin receptors; serum and antral tissues were collected for measurement of gastrin levels by radioimmunoassay. Circadian periodicity in the data was determined by cosinor analyses. In both freely fed and fasted rats, gastrin receptors showed circadian variation (range 2.5-10 fmol/mg protein), as did serum gastrin concentrations (range in fed rats 195-407 pg/ml). The phasing of the intrinsic circadian variation in gastrin receptor level that was observed in the fasted rats was advanced by a few hours in fed rats. This shift is probably due to food-induced gastrin release, resulting in gastrin-mediated down-regulation of gastrin receptors, followed by up-regulation of gastrin receptors. Food-related effects were thus superimposed upon the intrinsic circadian rhythms in gastrin receptor levels, causing the circadian variation in gastrin receptor levels in the fed rats to be shifted forward compared to that in the fasted rats. No significant circadian rhythms, on the other hand, were found in concentrations of gastrin in the antrum. These results suggest that changes in sensitivity of target tissues to hormones are related to both intrinsic circadian rhythms in levels of hormone receptors and also to food-related changes in hormone-receptor levels mediated by changing serum hormone levels.

Polyamine levels and gastrin receptors in colon cancers

Polyamines and gastrin receptors (GR) were studied in samples of colon cancer and mucosa from 40 patients and in control mucosa from 11 patients without cancer. Polyamines (i.e., putrescine, spermidine, spermine) are essential for growth and differentiation. The concentration of polyamines is elevated in rapidly proliferating normal tissues and in some cancers. The presence of GR in human colon cancers has been previously reported. The purpose of the present study was twofold: (1) to determine whether polyamine levels are elevated in colon cancers and in adjacent normal colon mucosa compared to colon mucosa from patients without cancer; and (2) to examine the relationship between polyamine levels and GR in colon cancers. Polyamine levels in colon cancers were significantly higher than in the normal colon mucosa from the same patients. The polyamines, spermidine and spermine, were significantly higher in colon mucosa from patients with cancer compared to patients without cancer. Spermidine and the spermidine:spermine ratio, an index of cell proliferation, were increased in colon cancers with GR compared to cancers without GR. There were no significant correlations between polyamine levels and the following: patient age, CEA level, site of cancer, stage, or differentiation. Because polyamine levels are increased in colon mucosa from patients with cancer, measurement of polyamines may detect patients at risk for subsequent development of colon cancer. Increased levels of polyamines in colon cancers with GR is evidence that gastrin may play a trophic role in human colon cancers.

Peptide YY and gallbladder contraction. Studies in vivo and in vitro

The purpose of this study was to examine the effect of peptide YY on contraction of the gallbladder in vivo and in vitro and on contraction of the sphincter of Oddi in vitro. In conscious dogs that were prepared with strain-gauge force transducers implanted in the gallbladder wall, peptide YY (400 ng/kg, bolus; 800 pmol/kg.h, infusion) did not affect the resting contractile pattern of the gallbladder, nor did it inhibit cholecystokinin-octapeptide (CCK-8)-stimulated gallbladder contraction. In contrast, the cholecystokinin antagonist proglumide (5, 10, 20, 40, or 80 mg/kg), given in vivo, inhibited CCK-8-stimulated gallbladder contraction in a dose-related manner. The highest dose of proglumide (80 mg/kg) completely abolished contraction of the gallbladder stimulated by CCK-8. In vitro studies showed that peptide YY (0.25, 0.5, or 1 microgram/ml) did not affect the resting tension of rabbit gallbladder strips, and it did not inhibit CCK-8-stimulated contraction of gallbladder strips. Proglumide (0.4, 0.8, 1.6, or 3.2 mg/ml) inhibited CCK-8-stimulated tension of gallbladder strips in a dose-related manner. Peptide YY and CCK-8 had no effect on the motility of the canine sphincter of Oddi in vitro, whereas acetylcholine caused contraction and adrenergic agonists caused relaxation. These results suggest that peptide YY and pancreatone (a peptidelike substance, extracted from ileal and colonic mucosa, that inhibits CCK-8-stimulated gallbladder contraction in vivo) do not appear to be identical.

Inhibition of human gastric adenocarcinoma xenograft growth in nude mice by alpha-difluoromethylornithine

We studied the effect of inhibition of polyamine biosynthesis by alpha-difluoromethylornithine on the growth of a human gastric adenocarcinoma (CLEES) xenotransplanted in nude mice. CLEES is a well-differentiated gastric adenocarcinoma of the intestinal type. The doubling time has ranged from 7 to 10 days through 11 passages. Electron microscopic and immunohistochemical studies comparing the original tumor and xenotransplants showed similar structure and similar amounts of carcinoembryonic antigen. Polyamine biosynthesis is required for cell division. alpha-Difluoromethylornithine inhibits ornithine decarboxylase, the rate-limiting enzyme in polyamine biosynthesis. In this study, 48 athymic mice were used in two experiments. In the first experiment, two groups of 12 mice each were inoculated with CLEES tumor cells and received either tap water or a 3% alpha-difluoromethylornithine solution as drinking water. Tumor size was measured twice weekly. Tumor size was significantly decreased from controls by the fourth week of treatment and at all points of analysis thereafter for 7 wk. In the second experiment, alpha-difluoromethylornithine significantly reduced tumor concentrations of the polyamines putrescine and spermidine. In addition, the tumor content of DNA was significantly reduced in treated mice (0.64 +/- 0.16 mg) compared to controls (4.76 +/- 0.92 mg). Our data suggest that inhibition of polyamine biosynthesis may be a useful component of multidrug chemotherapy for human gastric adenocarcinoma. Establishment of tumor lines such as this gastric adenocarcinoma will facilitate further studies on the biological behavior of human gastric cancer and its response to chemotherapeutic manipulation in vivo.

Bombesin inhibits growth of human pancreatic adenocarcinoma in nude mice

Bombesin, a 14-amino acid peptide, exhibits direct and indirect effects on the gastrointestinal tract, including release of hormones, stimulation of pancreatic, gastric, and intestinal secretion and intestinal motility. Cholecystokinin (CCK) and gastrin, two of the hormones released by bombesin, have been shown to play a role in maintaining the growth of normal gastrointestinal mucosa as well as in eliciting trophic responses in normal and neoplastic tissue. We studied the effects of chronic bombesin treatment on the growth of a human ductal pancreatic adenocarcinoma (SKI) xenografted into nude mice, and on the growth of the normal nude mouse pancreas. Thirteen nude mice were implanted with SKI tumor and divided into two groups. Mice received 0.1 ml intraperitoneal injections of either bombesin (20 micrograms/kg) or the vehicle alone three times per day. Tumor areas were measured twice weekly until death (week 8), at which time the tumors and the host pancreas were excised, weighed, and assayed for protein, RNA, and DNA content. Significant inhibition of tumor growth was found in the bombesin-treated group at weeks 4, 5, 6, 7, and 8. Tumor area and weight at death (day 57) were significantly less in the bombesin-treated group (48 and 46%) as compared with control. We observed similar inhibition of tumor DNA (39%), RNA (38%), and protein (43%) content compared with controls. In contrast, bombesin significantly increased the weight (64%), protein (81%), and DNA (73%) content of the mouse pancreas compared with controls. We conclude that bombesin acts concurrently as both a trophic agent for normal host pancreas and a growth inhibitory agent in xenografted pancreatic cancer tissue.

Role of vagal hyperactivity in gastric stress ulceration after acute injury to the cervical cord

The role of vagal hyperactivity in the pathogenesis of gastric stress ulceration that occurs after acute trauma to the cervical cord is controversial. We have used a rat model of transection of the cervical cord to induce gastric stress ulceration and to examine the cause of the ulcers. Cervical cord transection did not increase gastric acid output or plasma levels of gastrin or pancreatic polypeptide, either immediately or up to eight hours later. However, gastric stress ulceration showed a time-related increase in ulceration. Vagal stimulation with 2-deoxy-glucose enhanced the gastric acid output in rats with cervical cord transection but failed to change the quantity or characteristics of the gastric ulceration. We conclude that there is no evidence to support the vagal hyperactivity hypothesis in the pathogenesis of gastric stress ulceration after acute cervical cord injury.

Mechanisms of the trophic actions of bombesin on the pancreas

Bombesin has both direct and indirect effects [mediated through release of cholecystokinin (CCK)] on pancreatic secretion. Polyamine biosynthesis, essential for DNA synthesis, is increased in the pancreas after CCK stimulation. The purpose of this study was to examine the trophic effects of bombesin and to determine whether the mechanism of bombesin-induced pancreatic growth is mediated through synthesis of polyamines. The time course of bombesin-stimulated polyamine biosynthesis was defined. Rats were studied in groups of six and received intraperitoneal (i.p.) injections every 8 h of either saline, bombesin (10 micrograms/kg), CR1409 (2.5 mg/kg) (a CCK-receptor antagonist), or both to define the effects on pancreatic growth and polyamine biosynthesis. Rats were killed at 14 days and the pancreas was excised, weighed, and analyzed for protein, RNA, and DNA content. We found that bombesin produced significant pancreatic hyperplasia (increased pancreatic weight, protein, and DNA content) after 14 days. CR1409 inhibited only bombesin-stimulated DNA content. Bombesin stimulated polyamine biosynthesis as early as 2 h after administration of bombesin, but CR1409 had no effect. The trophic actions of bombesin are both direct and indirect (mediated through CCK), and the direct effects of bombesin are mediated by polyamine biosynthesis.

Effect of peptide YY on insulin release stimulated by 2-deoxyglucose and neuropeptides in dogs

Peptide YY (PYY) is a hormone released from gut after a meal. The objective of this study was to determine the effect of PYY on insulin release stimulated by either 2-deoxyglucose (2-DG) or neuropeptides in conscious dogs with gastric and duodenal fistulas. In control experiments dogs received either 2-DG (75 mg/kg i.v. bolus) or atropine (25 micrograms/kg bolus followed by 20 micrograms/kg/h i.v.) plus 2-DG (75 mg/kg i.v.) or bethanechol (80 micrograms/kg/h i.v.) or vasoactive intestinal peptide (VIP, 4 micrograms/kg i.v. bolus) or gastrin-releasing peptide (GRP, 400 pmol/kg/h i.v.) or tetragastrin (G4, 100 micrograms/dog, i.v. bolus). On separate days, PYY was also infused intravenously in combination with one of the above stimulants. Given intravenously, PYY (200, 400 pmol/kg/h) significantly inhibited 2-DG stimulated-insulin secretion in a dose-dependent fashion. This inhibitory effect also existed in the presence of atropine. Peptide YY (400 pmol/kg/h) depressed the insulin levels in response to GRP or G4 but failed to inhibit bethanechol- and VIP-stimulated insulin release. After administration of the above stimulants, PYY did not modify the blood sugar concentrations. These results demonstrated that PYY might inhibit the cephalic phase of insulin release from dogs triggered by 2-DG and by the neuropeptides GRP and G4. Thus, PYY may play a negative feedback regulatory role on insulin release.

Regulation of the release of cholecystokinin by bile salts in dogs and humans

The objective of these studies was to investigate the role of bile salts in the regulation of release of cholecystokinin in response to nutrients in dogs and humans. In dogs, the intraduodenal administration of a bile salt sequestrant, cholestyramine (2, 4, or 8 g/h), resulted in a dose-related enhancement of the release of cholecystokinin-33/39 and pancreatic protein secretion in response to intraduodenal administration of amino acids. Intraduodenal administration of cholestyramine alone did not affect basal levels of cholecystokinin-33/39 or pancreatic protein secretion. Total diversion of bile also significantly increased the release of cholecystokinin and pancreatic protein secretion in response to intraduodenal administration of amino acids. Replacement of the bile salt pool by intraduodenal administration of taurocholate completely reversed the enhancement effect of both cholestyramine and bile diversion. In humans, oral ingestion of cholestyramine (12 g) significantly increased the release of cholecystokinin-33/39 and gallbladder contraction in response to the oral ingestion of either a triglyceride or amino acids. These results support a physiologic role of bile salts in the negative feedback regulation of release of cholecystokinin in response to luminal nutrients.

Daily variations in the formation of gastric ulcers caused by cervical cord transection in the rat

Cervical spinal cord transection is used as a model of mammalian stress ulcerogenesis. Circadian variations in gastric ulceration have been demonstrated in other animal models. We investigated whether gastric ulceration changed after cervical cord transection throughout a 24-h period by subjecting different groups of rats to cord transection. Ulcers were quantitated using an index described by Szabo and colleagues. Ulcer formation showed significant variation as a function of time of lesioning, with least severe ulceration at 8 AM. We found that cord transection, like other models of gastric ulceration, is also influenced by the circadian system.

Peptide YY antagonizes beta-adrenergic-stimulated release of insulin in dogs

Peptide YY (PYY) and neuropeptide Y (NPY) are peptides of 36 amino acids that share structural homologies with pancreatic polypeptide (PP). PP is predominantly found in the endocrine pancreas. PPY is primarily found in mucosal endocrine cells of the distal ileum, colon, and rectum, whereas NPY is found in both the peripheral and central nervous systems. Previous studies indicate that these peptides can interact with the autonomic nervous system. The objective of the present experiments was to study the effect of PYY on neurally stimulated insulin release [i.e., in response to 2-deoxy-D-glucose (2-DG), a nonmetabolizable glucose analogue] in conscious dogs. Intravenous administration of PYY (100, 200, and 400 pmol.kg-1.h-1) reduced 2-DG-stimulated insulin release in a dose-dependent manner (P less than 0.05) without affecting plasma glucose levels. Administration of NPY (800 pmol.kg-1.h-1), but not PP (400 pmol.kg-1.h-1), reduced 2-DG-stimulated release of insulin (P less than 0.05). The inhibitory action of PYY on 2-DG-stimulated insulin release persisted in the presence of atropine or phentolamine treatment; however, hexamethonium alone or phentolamine plus propranolol treatment blocked the inhibitory action of PYY. Release of insulin stimulated by the beta-agonist isoproterenol was also inhibited by PYY (P less than 0.05). These results indicate that PYY can inhibit autonomic neurotransmission by a mechanism that may involve ganglionic or postganglionic inhibition of beta-adrenergic stimulation. Our findings suggest a role for PYY and NPY in the autonomic regulation of insulin release.