Gut 1993; 34: 321-328

Cholecystokinin in the control of gastric acidsecretion in man

J W Konturek, R Stoll, S J Konturek, W Domschke

AbstractThis study was designed to determine the roleof cholecystokinin in the control gastric acidsecretion in men using loxiglumide, a specificcholecystokinin receptor blocker. Threegroups of healthy subjects (A, B, and C) wereused; group A - for studies with postprandialgastric secretion, group B - for studies withexogenous gastric secretagogues and group C -for 12 hour intragastric pH-metry. Cephalicphase stimulated by modified sham feeding ingroup A subjects increased gastric acid secre-tion to about 50% of pentagastrin maximumand the treatment with loxiglumide in a stan-dard dose (20 [tmolIkg iv loading dose plusinfusion of 20 iumol/kg/h afterwards) failed toaffect this secretion. Gastric acid response to a5% peptone meal instilled intragastricallygreatly enhanced gastric acid secretion andplasma gastrin concentration but the additionof loxiglumide in the standard dose resulted infurther increase in both gastric acid and plasmagastrin responses to peptone meal. Infusion ofcaerulein in gradually increasing doses (15-120pmollkg/h) and gastrin releasing peptide(25-200 pmol/kg/h) resulted in a dose depen-dent stimulation of gastric acid secretionreaching about 35% and 25% of maximumattained with pentagastrin. When loxiglumidewas added in a standard dose, the acidresponses to caerulein and gastrin releasingpeptide were further increased two to threefold attaining the peak reaching, respectively,about 100% and 50% ofpentagastrin maximum.In group C subjects, 12 hour pH-metryrevealed the usual increase in gastric pH aftereach meal in tests with placebo. Loxiglumide(1200 mg tablets tid, po) resulted in signifi-cantly lower pH after each meal and this wasaccompanied by significantly higher gastrinresponses than in placebo tests. We concludethat cholecystokinin released by peptone meal,ordinary meals or gastrin releasing peptideexerts a potent inhibitory influence on gastricacid secretion and gastrin release in menand this inhibition involves subtype Acholecystokinin receptors.(Gut 1993; 34: 321-328)

Gastric acid secretion depends upon the interplayof many stimulatory and inhibitory influencesthat arise within the central nervous system andthe gastrointestinal tract resulting in thecephalic, gastric, and intestinal phases of thissecretion.'

Cholecystokinin is one of major gut hormones2that has also been implicated in the control ofgastric secretion. Exogenous cholecystokinin orits natural analogue, caerulein, administered

alone in fasted humans or in dogs` caused partialstimulation of gastric acid secretion but whencombined with gastrin it inhibited gastrin in-duced secretion. The inhibitory action of chole-cystokinin could not be, however, confirmed onthe isolated canine parietal cells which respond togastrin and cholecystokinin with equal stimula-tion of acid production.6 This discrepancybetween the in vivo inhibition and in vitrostimulation by cholecystokinin of acid secretionhas been explained that cholecystokinin in vivomay release a local inhibitor of parietal cells suchas somatostatin." Indeed, using a highly selec-tive and potent cholecystokinin receptor blockersuch as L-364,718, it was recently found indogs9 '° that cholecystokinin released by a proteinor fat meal exerts a tonic inhibitory influence ongastric acid secretion and this effect may bemediated, at least in part, by somatostatin."'

This study was designed to use the selec-tive antagonist of type A cholecystokininreceptors, loxiglumide," 12 to evaluate the role ofcholecystokinin in the control ofgastric secretionand gastrin release in man under physiologicalconditions such as cephalic or gastrointestinalphase of this secretion as well as followingstimulation with exogenous secretagoguesincluding pentagastrin, caerulein or gastrinreleasing peptide.

Methods

SUBJECTSStudies were carried out on three groups (A, B,and C) ofyoung healthy men (mean age 22 years,range 19-37; mean weight 71 kg, range 59-76).Group A subjects underwent modified shamfeeding and peptone meal tests with or withoutadministration of loxiglumide. Group B subjectswere used in tests with the infusion of penta-gastrin, caerulein or gastrin releasing peptidewith or without addition ofloxiglumide. Group Csubjects were used for the intragastric recordingofpH during 12 hours ofnormal activities with orwithout oral administration of loxiglumide. Thisstudy was approved by the Human ResearchReview Committee and informed consent wasobtained from each subject.

STUDIES ON THE EFFECTS OF LOXIGLUMIDE ONMODIFIED SHAM FEEDING AND PEPTONE MEALINDUCED GASTRIC SECRETIONIn group A (eight subjects), modified shamfeeding and intragastric peptone meal were usedto induce, respectively, cephalic vagal andgastrointestinal phases of gastric secretion asdescribed before.'" '" Briefly, for modified shamfeeding, a double lumen Dreiling tube was

Institute of Physiology,University MedicalSchool, Krakow, Poland,andDepartment of Medicine,University of Munster,Munster, GermanyJW KonturekR StollS J KonturekW DomschkeCorrespondence to:Prof Dr S J Konturek,Institute of Physiology,31-531 Krakow, ul.Grzegorzecka 16, Poland.Accepted for publication14 July 1992

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MSF

MSF + LOX

M

1I30 Minute periods

Figure 1: Plasma gastrin concentrations and gastric acid outputs under basal conditions andafter modified sham feeding in group A subjects with or without administration of loxiglumidtMean (SEM) ofeight tests on eight subjects.

passed under fluoroscopic control for the aspiration of gastric juice as described previously.Residual gastric contents were discarded and thgastric aspirates were collected by a suctiopump in 15 minute periods. After 45 minutebasal period, the subjects were served an appetising meal of 250 g beef steak, 150 g frencpotatoes, with about 250 ml water to drink thfood was tested, chewed and spat out for 1

minutes. The aspiration of gastric juice wacarried out during modified sham feeding an

during consecutive 105 minute period. Thepentagastrin (2 nmol/kg/h) was infused for 6minutes and the aspiration of gastric juice wacontinued to determine maximal acid output ithese subjects. All meals were prepared inseparate room so that subjects could not see

smell the food until the time of modified sharfeeding and each subject was trained in a prnliminary study not to swallow food during cheuing. In different test day the modified sharfeeding was performed while loxiglumide (kindlprovided by Dr L Rovati, Rotta Labs, MilancItaly) was infused intravenously starting withloading dose of 20 imol/kg given during fivminutes at the beginning of the test followed byconstant iv dose of 20 Fmol/kg/h throughout thstudy period.

Six subjects of group A were then used fcintragastric peptone meal test (to mimic th

gastrointestinal phase of gastric secretion) per-formed alone or in combination with loxiglumide.On the first test day, 5% peptone solution(Bactoprotone, Difco Labs, Detroit, Michigan,USA) adjusted to pH 5-5 (with 1 M NaOH) andosmolarity ofabout 300 mOsm/l (with 1 M NaCl)

T was administered during six consecutive 30minute meals. On a second test day, loxiglumidewas administered iv in a loading dose of 20 itmol/kg followed by a constant dose of 20 [tmol/kg/hstarting with the fourth 30 minute peptone meal.All tests with peptone meal started after an

5 overnight fast. A double lumen tube was intro-duced into the stomach and basal gastric acidsecretion was quantified by suction aspiration fora 30 minute period. Peptone meal was introducedinto the stomach in the volume of 300 ml at thestart ofeach of six consecutive 30 minute periods.The stomach was emptied completely before theadministration of the next 300 ml meal. Gastriccontent was continuously mixed with the aspira-tion perfusion system and the meal stimulatedacid secretion was measured by intragastric titra-tion with the end point of pH 5-5 using 50 mM

u Na(OH) as described previously.'4 IS

o STUDIES ON THE EFFECTS OF LOXIGLUMIDE ONCAERULEIN, PENTAGASTRIN ANDGASTRINRELEASING PEPTIDE INDUCED GASTRIC SECRETIONGroup B subjects were also intubated with adouble lumen Dreiling tube and gastric acidsecretion was stimulated using caerulein (Farm-

6 italia, Milano, Italy) infused iv in graduallyincreasing doses (15-120 pmol/kg/h), each dosebeing infused for 30 minutes and then doubledwith or without addition of loxiglumide (20

e. mol/kg in a loading dose at the start of the studyfollowed by 20 [tmol/kg/h) given throughout theperiods of caerulein administration. After with-

i- drawal ofinfusion ofcaerulein, the gastric aspira-14 tion was continued for 60 minutes and thenLe pentagastrin (2 6 nmol/kg/h) was infused for 60In minutes with or without administration of loxi-s glumide (20 [tmol/kg/h) to achieve maximals- secretory response to this peptide. In six group Bh subjects, pentagastrin was also infused in sepa-.e rate test day in a constant dose (0 65 [tmol/kg/h)5 to elicit submaximal secretory response. Whenis gastric acid output in response to pentagastrind reached a well sustained plateau, caerulein wasn added to iv infusion in a constant dose of 30.0 pmol/kg/h with or without addition of loxi-1S glumide (20 Rmol/kg/h). In control tests, penta-n gastrin alone was administered for the entire 150a minutes.)r The same six subjects of group B were alsom used in different occasions in tests with iv

infusion of gradually increasing doses (25-200v- pmol/kg/h) of gastrin releasing peptide (gift ofm Professor N Yanaihara, Shizuoka, Japan) with orIy without the administration of loxiglumide in a, standard dose as used in the feeding experiments.a7ea STUDIES ON THE EFFECT OF LOXIGLUMIDE ONie 12 HOUR INTRAGASTRIC pH

Subjects of group C (eight men) underwent two)r 12 hour recording tests in a placebo controlledie randomised crossover study. Each subject was

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CCK and gastric secretion

5% Peptone pH 5 5r _

Loxiglumider~

I

Peptone alone

I

Peptone alone

B 1 2 3

30 minute periods4

Figure 2: Plasma gastrin and gastric acid responses to intragastric peptone meal without orwith iv administration ofloxiglumide. Mean ofsix tests on B subjects. Asterisk indicatessignificant increase above the control value obtained with peptone meal alone.

n = 8

B 15 30 60 120

Caerulein (pmol/kg/h)

Figure 3: Gastric acid outputs in response to gradually increasing ofdoses of caerulein alone(15-120 pmol/kglh) or caerulein combined with a constant background dose ofloxiglumide.For comparison maximal gastric acid response to pentagastrin alone (2-6 nmollkglh) andpentagastrin combined with loxiglumide is in these subjects also presented. Mean (SEM) ofeight tests on eight subjects ofgroup B.

given either placebo or loxiglumide (1200 mg)three times daily 30 minutes before standardliquid meals (Fresubin, Frezenius, Munster,Germany) taken at fixed times: breakfast at 0830

* hours, lunch at 1330 hours and supper at 1800hours. The composition (protein, 3-8%; aminoacids, 0-6%; fat, 3-4%; carbohydrates, 14%;minerals, vitamins and water 84%) of each mealwas similar and contained about 1 kcal/ml. Thevolume of breakfast and supper meal was 300 mland that of lunch meal was 500 ml. Recording ofintragastric pH was assessed during 12 hoursstarting early morning (prebreakfast) by meansofan intraluminal system, including an antimonyelectrode (Monocrystal model 91-0215, Synec-tics AB, Sweden) connected to the portableapparatus, which permitted the pH recording tobe sampled every four seconds (DigitrapperMKII, 6200, Synectics AB, Sweden). The an-timony electrode used an external reference onthorax with contact jelly (Hellige 217, FritzeHellige, FRG). At the beginning and at the endof each examination the antimony electrodeswere accurately calibrated at 21°C with pH 7-01and pH 1 07 (buffers 5001 and 5002, SynecticsAB, Sweden) and a temperature correction forintragastric reading (37°C) was performed. ThepH electrodes were passed through an anaes-thetised nostril and were positioned in the gastriccorpus under fluoroscopic control approximately5 cm below the lower oesophageal sphincter. Theconnecting wires were fixed to the nares withadhesive tape. The data recorder of intragastricminielectrodes was carried in a small bag so thatit did not interfere with normal daily life. The pHrecordings started at 0810 and lasted for 12hours. Patients were instructed not to lie downduring the day or to take additional meals oralcoholic drinks and carbonated beveragesduring the examination period.The data of intragastric pH monitoring were

transferred to IMB compatible computer (PCAT12) programmed with Gastrogram version5.50 serial No E1024 (Gastrosoft Inc, Sweden)for calculating median pH values for each 12hour test. Data from all eight subjects treatedwith placebo and loxiglumide were analysed withthe use of program STAT pHAC II/PHARM,version 2.16D3 (Gastrosoft Inc, Sweden). Gastricacidity was expressed aspH and values from eachsubject were transferred into 10 minute medianvalues. The median and mean 12 hour intra-gastric pHs were predefined for comparisonbetween study days using the Wilcoxon's signedrank test. Box whisker plots of median and meanintragastric pH in eight subjects were performedfor 12 hour period and separately for the 120minute period after each standard meal. Statis-tics of pH profile were calculated and comparedin medians and means with significance level ofless than 0-05.

RADIOIMMUNOASSAY

Venous blood samples were obtained fromperipheral vein under basal conditions and at 30minute intervals in tests with modified shamfeeding, peptone meal, and gastrin releasingpeptide infusion. In tests with 12 h pH-metry,the blood samples were taken 30 and 60 minutes

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Pentagastrin (0-65 nmol/kg h)

Caerulein (30 pmol/kg-h)

Pentagastrin + caerulein + LOX

before and 30, 60, and 90 minutes after eachmeal. Plasma gastrin was determined using gas-trin antiserum 4562 kindly donated by ProfessorJ F Rehfeld of Aarhus, Denmark, and used in afinal dilution of 1:140000. Each sample wasassayed in duplicate. The sensitivity of thegastrin measurement in the present assay was 2- 5pmol/ml serum equivalent to human G- 17 asdescribed previously. 1

M STATISTICAL ANALYSISPentagastrin + caerulein -t I Results are expressed as means (SEM). Statistical

significance was determined by both theWilcoxon's signed-rank test and the paired t test.

B 1 2 3 4 5 6 Significance was accepted with p value less than- --. 0-05.

30 Minute periods

Figure 4: Gastric acid response to pentagastrin infused iv in a dose (0-65 nmollkglh)producing submaximal stimulation ofgastric acid secretion in tests with or without additiocaerulein alone (30 pmollkglh) or combined with loxiglumide. Means (SEM) ofsix testsGsix subjects ofgroup B. Asterisk indicates significant change as compared with the controlvalue obtained with pentagastrin alone without caerulein or loxiglumide.

n - 6

GRP alone

B 25 50

GRP (prnol/kg.n)

100

Figure 5: Plasma gastrin and gastric acid responses to graded doses ofgastrin releasing pe(25-200 pmollkglh) in six subjects ofgroup B. Mean (SEM) ofsix tests on six subjects.Astenrsk indicates significant increase above the values obtained with gastrin releasing pelalone.

)n of ResultsFigure 1 shows gastric acid response to modifiedsham feeding in groupA subjects with or withoutinfusion of loxiglumide. The mean acid outputreached peak in the first 30 minute period afterthe start ofmodified sham feeding reaching about50% of pentagastrin induced maximal acid out-put (about 26 4 (2-8) mmol/15 minutes) in thesesubjects and then declined towards the basalvalue within consecutive three 30 minute periodsof examination. In tests with iv infusion of loxi-glumide both basal and modified sham feedinginduced peak acid outputs tended to increaseabove the control values but this increase was notstatistically significant. Mean plasma gastrin con-centrations also tended to increase after modifiedsham feeding, particularly in tests with loxi-glumide but, again, this rise over premodifiedsham feeding values did not reach statisticalsignificance.

Intragastric administration of 5% peptonecaused several fold increase in gastric acid secre-tion over basal value and after 60 minutes acid

-' secretion reached a well sustained plateauthroughout the consecutive 30 minute periods(Fig 2). Loxiglumide added to iv infusion

T resulted in a significant augmentation of acidresponse to peptone meal and this increaseaveraged about 30% ofthe control value obtained

*4ba with peptone meal alone. Plasma gastrin rosefrom basal value ofabout 25 pmol/l to the plateauof about 80 pmol/l after peptone meal and thiswas further significantly increased when loxi-glumide was added to iv infusion.

Caerulein infused iv in gradually increasingdoses ranging from 15 to 120 pmol/kg/h resultedin a small but significant stimulation of gastricacid secretion reaching peak at a dose of 30 pmol/kg/h and amounting to about 35% ofpentagastrininduced maximal acid outputs in these subjects(Fig 3). At a dose of 60 and 120 pmol/kg/h, acidoutputs tended to decline but remained signifi-cantly higher than basal acid secretion. Wheninfusion of caerulein was combined with a con-stant background dose of loxiglumide, gastric

200 acid outputs were significantly higher at all dosesof caerulein. The maximal acid response tocaerulein combined with loxiglumide was

'ptide attained at a dose of 120 pmol/kg/h and it was notptide significantly different from that induced with

pentagastrin in these subjects. For comparison,

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CC,K and gastric secretion

7

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Figure 6: Median intragastric pH in subjects treated with placebo (upper paloxiglumide (lower panel). Medians ofeight tests on eight subjects. The shadthe range ofpH monitoring.

the maximal acid response to pentwas not significantly different frongastrin combined with loxiglumicsubjects (Fig 3).When caerulein (30 pmol/kg/h)

infusion of a constant dose of peidose 0-62 nmol/kg/h producing sulsecretion, a significant reduction irwas observed. This reduction w

reversed when the infusion ofcombined with loxiglumide (Fig 4

In the third series oftests with gapeptide in group B subjects, inpeptide in gradually increasingpmol/kg/h) resulted in a dose depe.tion ofacid secretion reaching pealof pentagastrin maximum (Fig 5).

ofa standard dose ofloxiglumide augmented acidoutputs at all doses of gastrin releasing peptideand the maximal response to gastrin releasingpeptide was achieved at a dose of 100 pmol/kg/hreaching about 50% of pentagastrin maximum.

Gastrin releasing peptide infusion caused adose dependent increment in plasma gastrinconcentrations and the peak gastrin response togastrin releasing peptide alone was achieved at adose of 200 pmol/kg/h. Addition of loxiglumidecaused further significant increase in plasmagastrin concentrations at all dose levels of gastrinreleasing peptide reaching peak at a dose of 50pmol/kg/h (Fig 5).

Figures 6 and 7 show the median daytime pHprofile in the same eight subjects treated withplacebo or with loxiglumide (1200 mg tid po).For most ofthe time, the pH was between 1 and 2during the interdigestive periods and the medianpH was not significantly different betweenplacebo and loxiglumide treatments. Withmeals, the pH rose to 4-6 and this rise lasted forabout 90-180 minutes in subjects treated withplacebo. In subjects ingesting loxiglumide, how-ever, the rise in pH after each of the standardmeals was significantly smaller and lasted onlyabout 60-90 minutes. The median and meanpostprandial pH values (for a two hour periodafter the meal) were significantly lower in testswith loxiglumide as compared with placebotreatments (Fig 8). Plasma gastrin levels betweenmeals in placebo-treated subjects were similar tothose in loxiglumide treated subjects but thepostprandial increments in plasma gastrin withloxiglumide were significantly higher than inplacebo controls (Table).

DiscussionThis study provides evidence that cholecysto-kinin exerts a tonic inhibitory action on gastricacid secretion and gastrin release in response toordinary meals, gastric peptone or gastrin releas-ing peptide in man and that these effects aremediated by the type A cholecystokininreceptors.

18 20 Cephalic phase of gastric secretion elicited inthe present study by modified sham feeding isassumed to be mediated by vagal nerves stimulat-

nel) and ing directly the oxyntic cells and activating therelease of gastrin and histamine.'6 The reportsconcerning the rise in plasma gastrin aftermodified sham feeding in man are controversial,

agastrin alone, confirmed by some investigators'7" and ques-a that to penta- tioned by others.'3'9 The present study showsle in the same only a small and insignificant increment

in plasma hormone concentration after thewas added to modified sham feeding. The release of chole-

ntagastrin at a cystokinin was observed only in anaesthetisedbmaximal acid dogs with electrically stimulated vagal nerves20n acid response but usual cephalic stimulation in conscious dogsras completely attained by sham feeding or insulin hypo-caerulein was glycaemia failed to result in any significant

change in plasma cholecystokinin concentra-istrin releasing tions.2' Our results in man show that the pretreat-fusion of this ment with loxiglumide did not affect significantlydoses (25-200 gastric acid secretion or plasma gastrin responsendent stimula- to modified sham feeding indicating that cephalick ofabout 25% vagal excitation does not involve cholecysto-. The addition kinin. This is in keeping with the recent finding

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CL1 6 -2 1 61

o.2

omae wPlaceboco*

4 -

2 -*

Loxiglumide

12 14 16 18

Time of day (10 min steps)

Figure 7: Median intragastric pH values in tests with placebo and loxiglumide beforafter breakfast, lunch, and supper meals. Asterisk indicates significant (p<0O05) chccompared with placebo control.

showing that vagotomy in man did not ir

the release of cholecystokinin but onlyitsthe sensitivity of target organs to this ho

In this study loxiglumide failed to affe

gastric acid outputs and plasma gastrintrations suggesting that cholecystokininplay any role in the control of basal

secretion.

The gastrointestinal phase of gastric ac:

tion was reproduced in this study by ti

gastric instillation of 5% peptone meal k~constant pH 5 -5 in the stomach by intr

titration technique.'4"' Such a proceduvented the usual fall in the intragastric plmeal and resulted in a well sustained stin

|- Median ....... Mean * p7

a)

ICl

Total time Lunch08.30-20.30 09.00-11.00 14.00-16.00 18.c

Figure 8: Box-whisker plots ofmedian with interquartile range and mean postprandeight subjects as determined for tzwo hours after ingestion of standard meal. Asterisk isignificant (p<0O05) difference as compared with placebo control.

of gastric acid secretion reaching about 50% ofpentagastrin maximum in these subjects. It wasaccompanied by several fold increase in plasmagastrin concentrations probably reflecting anexcessive release of antral hormone as a result ofgastric distention by the meal and the action ofpeptic digests at high pH on the antral G-cells. 4The question remains whether such artificial

gastrointestinal meal composed ofprotein digestsstimulates the release of cholecystokinin in manand whether the amounts of hormone releasedare sufficient to affect gastric acid secretion. Inour previous study with a similar gastric peptonemeal in man, plasma cholecystokinin rose severalfold over basal value and exogenous cholecysto-kinin in a dose as low as 20 pmol/kg/h causedsignificant inhibition of gastric acid secretion inresponse to this meal. As the pretreatment withloxiglumide completely abolished the inhibitoryeffect of exogenous cholecystokinin on mealinduced gastric acid secretion we assumed thatcholecystokinin induced gastric acid secretionwas mediated by type A cholecystokinin recep-tors. The gastric acid secretion induced bypeptone meal itself, however, was not affected bythe loxiglumide in that study probably because of

20 the relatively low dose of loxiglumide (800 mg poplus iv infusion of 1 mg/kg/h) used. Also the

reand failure of the MK-329, another potent type Aange as cholecystokinin receptor blocker, to affect

the peptone meal induced gastric acid secretionin dogs9 was probably related to the in-

nfluence sufficient dose of the blocker used intra-ncreased gastrically. In the present study we decided tormone.22 use loxiglumide in larger intravenous dose (20ct basal Ftmol/kg loading dose plus 20 [tmol/kg/h infusedconcen- iv afterwards) because our dog experimentsdoes not revealed that the bioavailability of loxiglumidegastric from the gastrointestinal tract was only about

40%23 and because other reports showed thatid secre- higher doses of this blocker in humans are safehe intra- and well tolerated.2429 Such large dose of loxi-kept at a glumide applied iv did not influence basal gastricragastric acid secretion or basal plasma gastrin concentra-ure pre- tion (see Figure 6) but greatly augmented theH aftera peptone stimulated gastric acid secretion andrnulation significantly raised the postprandial plasma gas-

trin concentrations indicating that, indeed,cholecystokinin released by this peptone has atonic inhibitory influence on both gastric acidsecretion and gastrin release in man.Peptone solution applied intragastrically is,

however, highly artificial meal because itinvolves the constant neutralisation of secretedacid by intragastric titration and prevents theusual rise in the intragastric acidity after themeal. Therefore, we also used the most physio-logical assessment of intragastric acidity bycontinuous pH-metry using intraluminal pHelectrode that has been recently validated in

_ healthy subjects and peptic ulcer patients'"2 andused to monitor the action of various drugs ongastric acid secretion.2 Loxiglumide given orallythree times daily before each meal did notinfluence the interdigestive pH but resulted in a

;upper significantly lower intragastric pH after eachDo-20.00 meal indicating an overall increase in the post-liapH in prandial gastric acid secretion. Yet, despite theindicates enhanced gastric acid secretion and lower intra-

gastric pH, the plasma gastrin response to the

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Plasma gastrin concentrations as determined 60 and 30 minutes before each meal and 30, 60, and 90 minutes after each meal(breakfast, lunch, and supper) during 12 hour pH-metry tests in placebo and loxiglumide treated subjects. Means (SEM) ofeight tests on eight subjects

Placebo LoxiglumideGastrin (pmolll) Gastrin (pmolll)Time (min) Time (min)

-60 -30 30 60 90 -60 -30 30 60 90

Breakfast 22 8 23-2 32-0* 29-4* 29-0* 23-0 21-4 42-6*t 38.4*t 33-6*(1-4) (1-6) (2-6) (1 0) (1-8) (1-2) (1-8) (2 4) (2 6) (2 8)

Lunch 22 8 21-2 27-4* 29-0* 31-6* 22-8 23-0 48.2*t 47.0*t 49.2*t(1 0) (1-2) (1-8) (1-6) (2 8) (1-8) (1-6) (44) (2 7) (1-9)

Supper 23-6 22-2 28-4* 29-2* 27-2 25-0 24-8 45-8*t 46-6*t 34.8*(1 0) (1-2) (1-8) (1 0) (1 8) (1 6) (1 6) (4 1) (26) (26)

*Significant change (p<005) as compared with the value before the meal. tSignificant change (p<005) as compared with the valueobtained in placebo treated subjects.

standard meal in loxiglumide treated subjectsreached significantly higher increments than inplacebo treated subjects. Thus, the removal ofthe effects of endogenous cholecystokinin by theantagonism of its type A receptors with loxi-glumide resulted in an increase in gastric acidsecretion and gastrin release under physiologicalpostprandial conditions.The mechanism of the action of cholecysto-

kinin on gastric acid secretion observed previ-ously in dogs9' and in the present report in manhas not been explained but it appears to be ofdualcharacter. One component of this action is astimulatory effect but it is rather weak andprobably involves the B type of cholecystokinin/gastrin receptors.'0 This stimulatory componenthas been well documented under the in vitroconditions when cholecystokinin or its naturalanalog, caerulein, was found to be equipotentwith that of gastrin in the stimulation of acidproduction. Under in vivo conditions, however,the stimulatory component is rather weak asshown in the present study by a small increase inacid secretion in response to iv infusion ofgradeddoses of caerulein. When caerulein was added topentagastrin infusion, a significant inhibition ofgastric secretion was observed indicating thatthe predominant component of the action ofcaerulein is the inhibition of gastrin-stimulatedgastric secretion. The antagonism of type Areceptors with loxiglumide eliminated the inhibi-tory component as evidenced in this study by theconversion of caerulein from partial into the fullgastrin like agonist ofgastric secretion and by thereversal of the inhibitory effect of caerulein onthe pentagastrin induced secretion. Thiseffect of loxiglumide was probably mediated bytype A cholecystokinin receptors probablylocalised on the somatostatin producingcells.70"29 The pretreatment with loxiglumidefailed to affect the pentagastrin induced gastricacid secretion (see Figure 3) indicating thatpentagastrin acts predominantly via the type Bcholecystokinin/gastrin receptors and that loxi-glumide is specific antagonist of the type A butnot the type B receptors. Selective antagonism oftype B cholecystokinin/gastrin receptors wouldbe necessary to conclude that the stimulatoryeffect of cholecystokinin or caerulein on gastricacid secretion is caused by the type B receptors.In dogs, such blockade of type B cholecystokininreceptors with selective antagonist L-365,260completely eliminated the stimulatory effects ofgastrin and cholecystokinin on gastric acid secre-

tion.29 Recent studies in man with the blocker ofthe type B receptors using L-365,260 revealedthat such antagonism inhibited pentagastrininduced gastric acid secretion30 but no attemptswere made to determine whether cholecystokininor caerulein induced gastric acid secretion isaffected by L-365,260.The postprandial stimulation of gastric secre-

tion and gastrin release can also be mimicked byinfusion of gastrin releasing peptide. ' It is ofinterest that despite an excessive gastrin releaseas evidenced by the pronounced increment inplasma gastrin concentration, gastrin releasingpeptide was rather weak stimulant of gastric acidsecretion. The highest observed gastric acidresponse to gastrin releasing peptide reachedonly about 25% of pentagastrin maximum andthis corresponded to about 60% of peptone mealinduced acid output. After the blockade of thetype A cholecystokinin receptors with loxi-glumide, both gastric acid outputs and incre-ments in plasma gastrin showed further signifi-cant increase. These results could be interpretedthat cholecystokinin, that was shown to bereleased by gastrin releasing peptide,2 attenuatesthe stimulatory action of concurrently releasedendogenous gastrin on oxyntic glands so only asmall increase in gastric acid secretion isobserved after administration of gastrin releasingpeptide. After the elimination of the inhibitorycomponent ofcholecystokinin by the blockade oftype A cholecystokinin receptors with loxi-glumide, only the stimulatory action of chole-cystokinin and gastrin persisted and this wasprobably mediated entirely by type Bcholecystokinin/gastrin receptors at the oxynticglands.

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2 Walsh JH. Gastrointestinal hormones. In: Johnson ILR, ed.Physiology of the gastrointestinal tract. New York: RavenPress, 1987: 181-252.

3 Johnson LR, Grossman MI. Analvsis of inhibition of acidsecretion by cholecystokinin in dogs. Am .7 I'hysiol 1970;218: 550-4.

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5 Mayer EA, Elashoff J, Mutt V, Walsh JH. Reassessmentof gastric acid inhibition by cholecystokinin and gastricinhibitory polypeptide in dogs. Gastroenterologv 1982; 83:1047-50.

6 Soll A, Amirian D, Thomas L, Reedy T, Elashoff J. Gastrinreceptors on isolated canine parietal cells. .7 Clin Invest 1984;73: 1434-47.

7 Soll A, Amirian D, Park J, Elashoff J, Yamada r. Cholecysto-kinin potently releases somatostatin from canine fundicmucosal cells in short-term culture. Am.7 Phvsiol 1985; 248:G569-73.

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