Bombesin and G-17 dose responses in duodenal ulcer and controls

Digestive Diseases and Sciences, Vol. 30, No. 11 (November 1985), pp. 1092-1103

Bombesin and G-17 Dose Responses in Duodenal Ulcer and Controls

BASIL I, HIRSCHOWITZ, MD, LEONARD OU TIM, MBBCh, COLIN A. HELMAN, MBBCh, and E. MOLINA, PhD

Gastric acid and pepsin secretion and serum gastrin concentrations were measured in nine patients with uncomplicated duodenal ulcer (DU) and 10 normal controls in the fasting state and in response to graded doses of bombesin, a tetradecapeptide gastrin releaser, and, for reference, synthetic gastrin G-17. Serum gastrin with bombesin stimulation was significantly greater in duodenal ulcer (maximum 467 pg/ml) than in controls (153 pg/ml), while in seven of the D U group tested gastrin levels after a meal were not different from that seen in five of the normal controls. Gastric acid concentrations and outputs were greater in duodenal ulcer with both stimuli. Secretory responses were then related to serum gastrin levels; despite increasing gastrin levels with bombesin stimulation, peak outputs achieved with bombesin were only 50% of G-17 maximum in normals and up to 90% of maximum in duodenal ulcer. Up to the point of peak response to bombesin, acid and pepsin outputs were the same with exogenous and endogenous gastrin, ie, bombesin acted only via G-17. Furthermore, in direct comparison of duodenal ulcer and normals with G-17 infusion, acid and pepsin outputs related to serum gastrin were congruent up to 75% of duodenal ulcer maximum, at which point normals reached their maximum level. These data have shown that duodenal ulcer patients are not more sensitive to either exogenous or endogenous gastrin; we have also shown regulatory defects in duodenal ulcer patients not previously described: (1) an exaggerated release of gastrin with bombesin stimulation, and (2) a defective inhibition of acid and pepsin secretion with higher doses of bombesin.

On the average, patients with duodenal ulcer (DU), compared to normal controls, secrete more acid and pepsin in the fasting (unstimulated) state as well as with all known gastric stimuli. At the same time, many DU patients have basal or stimulated secretion in the normal range. Maximum rates of secretion are related to the secretory cell mass, deter-

Manuscript received September 12, 1984; revised manuscript received January 24, 1985g accepted February 4, 1985.

From the Division of Gastroenterology, University of Ala- bama at Birmingham.

Presented at AGA, Washington, D.C., 1983. Mr. Molina's present address is: Departmen! of Pharmacol-

ogy, University of Parma, 43100 Parma, Italy. Address for reprint requests: Dr. Basil I. Hirschowitz, Divi-

sion of Gastroenterology, University of Alabama at Birmingham, University Station, Birmingham, Alabama 35294.

mined by cell counts (1). While basal secretion is believed to be due largely to vagal cholinergic drive (2), a role for gastrin, which is central to the pathologic hypersecretion of the Zollinger-Ellison syndrome, has not been clearly defined in the pathophysiology of duodenal ulcer. Since gastrin not only stimulates gastric secretion, but is also trophic to the gastric secretory mucosa (3, 4), both the increased basal secretion and the increased maximum, defining a greater secretory cell mass where it exists, prompted a re-examination of gastrin release and action in patients with duodenal ulcer. For this purpose, we used bombesin, a 14- amino acid peptide first isolated from frog skin (5) and more recently found to be represented in antrum of animals (6-8) and man (9) by a bombesin-

1092 Digestive Diseases and Sciences, Vol. 30, No. 11 (November 1985)

0163-2116/85/1100-109254.50/0 �9 1985 Plenum Publishing Corporation

BOMBESiN DOSE RESPONSES IN DU

like peptide named gastrin-releasing-peptide (GRP). Bombesin and mammalian GRP have nine identities in their terminal residues and have identical effects (10). Bombesin releases gastrin in animals (11) and man (12) at very low doses, suggesting a possible physiologic transmitter role for GRP in addition to acetylcholine in the vagal control of gastric secretion (12-16). Bombesin stimulates gastric secretion through the release of gastrin, but this effect is modified by corelease of other peptides, including somatostatin (13, 14).

To understand and quantitate the effect of bombesin on gastric secretion, it was necessary to use a reference infusion of synthetic G-17. In this way, effects on the G-cell and on the peptic and parietal cells could be separately analyzed.

We found that bombesin stimulated acid and pepsin secretion in man only via an increase in circulating G-17 gastrin. We could not confirm an increased sensitivity to endogenous or exogenous gastrin in this group of DU patients. However, compared to normals, DU had a fourfold greater serum gastrin response to bombesin and an apparent defect, previously undescribed, in the suppression of gastric secretion of acid and pepsin at higher doses of bombesin, which resulted in a higher rate of acid and pepsin secretion relative tO reference G-17 in DU than in controls.

MATERIALS AND METHODS

We studied nine patients with endoscopically docu- mented uncomplicated (seven active, two recently healed) duodenal ulcer (DU) (six males, three females, mean age 37.3 -2_ 4 years, weight 73.1 _ 5 kg), and 10

healthy age- and weight-matched controls without ulcer history (five males, five females, mean age 36 - 4.8 years, weight 69.6 _ 6 kg), each of whom gave informed consent for the studies. All antisecretory drugs were withdrawn for at least 36 hrs. In each test, after a 10-hr fast, an Argyle Salem sump nasogastric tube (Nashville Surgical Supply, Anniston, Alabama) was positioned fluoroscopi- cally in the dependent part of the stomach, fasting gastric contents were removed, and secretion was collected in 10-rain consecutive periods at constant 90-120 mm Hg suction. Saliva was expectorated at frequent intervals. In each sample, volume was measured to the nearest 1 ml, and 2.ml aliquots were titrated with 40 mM NaOH to pH 7.0 using a Radiometer autoburette (Radiometer Amer- ica, Westlake, Ohio).

Pepsin concentration was measured by an automated technique (17) using a hemoglobin substrate (Eastman Kodak Co., Rochester, New York) at pH 2 with reference to crystalline pepsinogen (Sigma Chemical Co., St. Lou- is, Missouri) as the standard. Results are reported in milligrams. Blood was drawn at 20-min intervals and the serum separated and stored at -20 ~ C for later measure- ment of serum gastrin concentration by radioimmunoassay (18) using antibody 1296 kindly donated by Dr. John Walsh, University of California, Los Angeles, Cal- ifornia. The sera were assayed in Several different assays with the sera labeled only by name, date, and number. lnterassay variation was 7% and within assay variability 5% (19). Results are given in picograms per milliliter, using synthetic gastrin (15-norleucine-G-!7-I) as both tracer and standard.

Pure synthetic bombesin-14 [gift of Dr. R. deCastiglione, Farmitalia, Milan, Italy (IND No. 12-549)] was made up fresh in saline from sterile freeze-dried stock for each study and given intravenously from a Harvard syringe pump in 40-rain consecutive periods starting after a 40-rain basal secretion period. Four doses of bombesin--30, 100, 300, and 1000 ng/kg/hr (17, 57, 170,570 pmol/kg/hr)---were given. The last dose was followed by a 40-min period without drug. Blood pressure and heart rate were measured every 20 min.

Meal Stimulated Gastrins 250

Serum Gastrin pg/ml 200

150

I00

50 { meal

o I I I I I . , ~ I

--15 0 15 30 45 60 ,,., 90rain. Minutes After Food

Fig 1, Mean serum gastrin before and at frequent intervals after a meal of a cheeseburger and a glass of milk in seven (3F, 4M) of the nine DU subjects and five of the five controls (2F, 3M).

Control (n=5) DU (n=7)

Digestive Diseases and Sciences, Vol. 30, No. 11 (November 1985) 1093

HIRSCHOWITZ ET AL

600 Serum gostrin

50O

40O

30o

200

I00

OU (n = 9)

SEM

�9 '~ p< 0:5

�9 "~ p<.OI

- ~ Control (n=lo)

r ,6o ' 3 0 0 ' ~00 Bombesin ng/kg'hr

Fig 2. Mean serum gastrin (+ SEM) in the fasting state and at the end of successive 40-min infusions of bombesin in nine patients with duodenal ulcer (DU) and in 10 healthy controls.

(

No significant changes in vital Signs were noted in any subject. One DU patient vomited at the end of the study; three in each group had cramps with the highest dose, but none required discontinuation of the study. Serum gastfin was also measured in seven of the DU subjects and five controls before and at intervals for 90 min after a meal of a cheeseburger and a glass of milk.

In all subjects studied, we obtained basal and maximal acid and pepsin secretion as follows. In eight of the 10 controls and seven of the nine duodenal ulcer subjects, dose-responsive gastric secretion and serum gastrin were measured as described above during infusion of synthetic human gastrin G-i7 [ (IND No: 10-872) Research Plus, Bayonne, New Jersey] in consecutive doses Of 50, 100, 200, 1000, and 2000 ng/kg/hr. In 10 of the 19 subjects including the four who did not have G-17 dose responses, basal and maximum acid and pepsin output were also determined using a single subcutaneous dose of pentagastrin 6 ~g/kg. No significant difference in maximum output was found when G-17 dose responses and a Single large dose (6 p,g/kg) of pentagastrin were compared in five DU subjects (794 --+ 50 Vs 830 - 43 ixeq/kg/hr). This finding confirmed the conclusion from the kinetic analysis of the dose response that the dose range of G-17 used was adequate to obtain and calculate maximum responses. The doses of bombesin used gave levels of serum gastrin within the range of the serum levels required to give a full dose response with G-17.

Analysis of Data. For doSe-response analyses, the plateau value of serum gastrin at each dose was related to the dose of bombesin. To allow for equilibration, the output Of acid and pepsin in the last 30 of each 40-min (4 • 10 min) dose period, corrected for body weigh t, was related to (1) dose of bombesin or G-17, and (2) serum gastrin levels measured in the fasting state and during bombesin or G-17 administration. Responses (V) were related to stimuli (D) by an exponential model V = Vmax (l=eC-bD), where V = measured output of acid and pepsin per unit time or level of serum gastrin, D = dose of

concentration of stimulant (bombesin, G-17, or serum gastrin), Vmax = calculated maximum output, and b and c are calculated conStants. The dose of concentration of stimulant equivalent to threshold T = c / b and the dose giving 50% of maximum output if basal = 0, ie, K,, = In 2/b. Ds0, the dose required to raise existing output to 50% = (KIn-T) (19, 20), Dose-response data were also analyzed by fractional linear transformatioh, D/V = aD + b from which b/a = Dso and 1/a = Vi .~ (21). Differences between groups of data were tested by Student's t test; P < 0.05 was taken as significant.

RESULTS

S e r u m Gastrin

Fasting serum gastr in w a s somewha t higher in the D U group than the controls (92 --- 14 vs 52 +- 5:8 pg/ml, P < 0.05). To confirm that we were not

TABLE l. BOMBESIN DOSE RESPONSE*

serum gastrin (pg/ml)f Amount

(ng/kglhr)$

N Fasting Vm~ AVmax 1950 T Km

DU 9 92 • 14w 467 375 38 26 64 C 10 52 • 5.8 153 103 36 34 70

*Data derived from analysis of the mean serum gastrin dose response to infusion of four doses of bombesin in DU and controls. In all cases, r = 0.999.

fVmax = calctilated maximum serum gastrin concentration; AVm,x = maximum increment above fasting level.

*Ds0 = dose of bombesin required to raise the serum gastrin to 50% of maximum from observed basal; T = threshold, the dose equivalent to give the observed basal gastrin level; Km= dose required tO raise the serum gastrin to 50% nf maximum serum gastrin from 0 (Kin = D5o + T) (20).

w

1094 Digestive Diseases and sciences, Vol. 30, No. 11 (November 1985)

2000

I000

ASerum Gastrin pg/rnl

1500

x Cont.

500

BOMBESIN DOSE RESPONSES IN DU

)(

I I I I I

500 I000 Dose of G-17 IV

0 J I I

0 2000 ng/kcj.h.

y=.91x-9.7 r=.999 y=.95x-3

Fig 3. Serum gastrin increases resulting from five successive 40-min infusions of graded doses of gastrin G-17 in seven DU (4M, 3F) and eight (4M, 4F) controls. See text for volume of distribution and metabolic clearance rates.

dealing with an unusual DU population, eg, antral G cell hyperplas ia (22), we determined the gastrin response to a standard meal in seven (3F, 4M) of the nine DU patients. Postprandial gastrin values were

not significantly different be tween the D U group and five (2F, 3M) of the controls (Figure 1), nor did they deviate significantly f rom a large group of DU studied separately (unpublished). Fasting serum

BOMBESIN

ACID 3oo /.tEq/kg. 30min

D.U. �9 -x-%

200

~p<.05 ~-,~ p< .01

I0

CONTROL

o1--/, ,c;o 3bo ,obo B A S A L

BOMBESIN ng/kg.hr Fig 4. Acid output (mean - SEM) corrected for weight in response to successive intravenous graded doses of bombesin in nine patients with duodenal ulcer and in 10 controls.


HIRSCHOWlTZ ET AL

G-17

ACID 30o ffEq/kg3Omin

2OO

,oo S

o // ,do z;o ,obo 2obo BASAL

G-17 ng/kg.hr

Acid Output

100%

80%

60%

4 0 %

20 %

D.U.

x =DU o----O =C

/ /

. r )

CONTROL

0 o / 0 I I I I

I0 50 I00 250 I000 ng/kg.h

G-17 Dose + Colculoted T.

Fig 5. Top: Acid output (mean + s~,M) corrected for weight in seven DU and eight controls given graded doses of G-17. Bottom: Acid output was normalized to 100% maximum in both groups and related to the dose infused corrected by adding the calculated threshold equivalent dose.

gastrin measured on at least two other occasions in each subject studied ruled out hypergastrinemia.

At each dose of bombesin, the patients with DU exhibited a significantly greater (P < 0.01) serum gastrin level than the controls (Figure 2). Serum gastrin levels at high doses did not deviate from that predicted by fractional linear transformation (21) of the initial part of the curve, ie, there was no indication of inhibition of gastrin responses at higher doses of bombesin. Calculated maximum

serum gastrin concentrations in DU (467 pg/ml) and the increase above fasting (375 pg/ml) were three to four times greater than in the controls (153 and 101 pg/ml, respectively). However, the DU patients were not more sensitive to bombesin, with both Ds0 and Km the same as in the controls (Table 1). The values for threshold, ie, the calculated dose equivalent of bombesin required to give the fasting gastrin, was also similar in the two groups.

Serum gastrin levels increased linearly with the



ACID /~_q/ko.:~min

200

I00

0 I0

300

ACID pEq/kg �9 30 min

200

IOO

10

Duodenal Ulcer

Bombesin

6o ,o6o 26oo o Serum Gastrin po/ml 4a

Controls

% of Max G-17

100%

75%

50%

2_5%

%of Max G-17

/ G-17 / / 75% ,L

,, SEM

,,,,, , ~ B 50% ombesin

25%

r6o obo o Serum Gostrin pQ/ml 4b

Fig 6. Acid output (mean + SEM) related to measured (mean + SEM) serum gastrin levels in seven duodenal ulcer subjects (4M, 3F) and in eight controls (4M, 4F), each stimulated with G-17 and with bombesin in separate experiments.

five graded doses of G-17 and were the same in the seven DUs (4M, 3F) and eight controls (4M, 4F) studied with G-17 (Figure 3). From the slope of the line (h serum gastrin, pg/ml, vs dose of G-17 in ng/kg/hr: DU, y = 0.91x - 9.7, r = 0.994; control, y = 0.93x - 3, r = 0.999) (Figure 3), values for volume of distribution (DU 14.2%, control 14.4%) and metabolic clearance rate (DU 14.2 and control 15 ml/kg/min -1) were similar to those found in normal dogs (28).

Responses Related to Dose

Acid responses to bombesin in DU were greater than in controls (Figure 4). In both groups the peak output of acid occurred at the lower rather than the larger doses of bombesin used--in controls 113 +

11 p~eq/kg/30 min at 100 ng/kg/hr and in DU 270 - SE 45 ~eq/kg/30 min at 300 ng/kg/hr. Higher doses elicited a lower response in controls [60 +- SE 9 p~eq/kg/30 rain (P < 0.02)] and in DU [242 +- 46 i~eq/kg/30 min (P > 0.1)] despite a continuing increase in serum gastrin. With G-17, acid output (Fig- ure 5) reached plateau values in DU and controls at a dose of I000 ng/kg/hr. The DU group had a significantly greater acid output in the basal state and with each dose of gastrin than controls. The differences between the two groups (a parallel upward shift of DU responses) was subject to further interpretation when basal secretory rates, as well as the infused dose of G-17, were taken into account for analysis.

To determine whether the DU patients were more sensitive to G-17, the dose equivalent, T = threshold

Digestive Diseases and Sciences, Vol, 30, No. 11 (November 1985) 1097

HIRSCHOWITZ ET AL

1500

Pepsin ug/kg50 rain

I000

500

Duodenal Ulcer L

- " sb J 6 o - - - s 6 o o6o zobo Serum Gastrin pg/ml

% of Max G- 17 G-17 100%

75%

i0%

!5%

/, 0

Pepsin ug/~ -30min

I000

5O0

Controls

~SEM ....... L . L

/ ~G-17 / z

, / ~ B%mbesin

100%

75%

50%

25%

0 s6 ,do 56o ,o6o 2obo Serum Gastrin pg/ml

Fig 7. Mean (+ SEM) pepsin output corrected for body weight related to mean (+ SEM) measured serum gastrin in seven duodenal ulcer and in eight control subjects, respectively, each given graded doses of G-17 and bombesin in separate experiments.

(see ref 20) calculated to be responsible for basal secretion was added to the infused dose, and the acid outputs were normalized to 100% for each group. [Whether basal secretion is due to vagal, gastrin, or histamine activity is irrelevant, since the equivalent can be expressed in terms of the drug being used for dose response studies, in this case, G-17; in ref 20, pentagastrin.] Figure 5 (lower) shows identical curves for DU and controls, indicating the same sensitivity to G-17. This conclusion was further confirmed by calculation o f kinetic parameters, analyzing the data in Figure 5 (top) by the exponential model (see Materials and Methods). By this calculation, V ~ was higher in DU [305 + 2.9 (SE) vs 236 --+ 4.6, P < 0.001]. Ds0, the apparent sensitivity (20), was lower (DU 39 --- 4.9 vs control 60.6 -+ 2.9 ng/kghar, P < 0.001), but threshold (T) was higher (DU 35 -+ 1.0 vs 15 -+ .7, P < 0.001, reflecting the higher basal in DU, viz, 28 vs 14%). The intrinsic sensitivity (20), represented by Km (= Ds0 +

10 was, however, the same (74 vs 75.6 ng/kg/hr). In both cases, the fit of the data to the model was good (r = 0.999 and 0.998, respectively, for DU and control). Kinetic analysis thus confirms the congruent curves between DU and controls (Figure 5, bottom).

Responses Related to Serum Gastrin

Comparing Bombesin to G-17. In order to directly compare secretion due to endogenous gastrin (that released by bombesin) with that due to exogenous gastrin, we plotted observed secretion responses against measured levels of serum gastrin. Basal values were not subtracted from either gastrin or acid and pepsin secretions, since measured values were available for both serum gastrin and gastric secretion in both basal and stimulated states.

In those 15 subjects who had both studies, acid (Figure 6) and pepsin (Figure 7) outputs with G-17 and with bombesin were congruent in the DU



pEqlk .30min 30(

2~

I00

.iJg/kg.3Omin 1500

I000

500

~..~ . . . . . . DU

i i I ~ Control /' / 1

/ i /

so t6o idoo Serum 8astrin pg/ml.

Pepsin-G-17 infusion

/ Control

Acid #Eq/kg3Omin 300

200

I00

Bombesin

,'" DU

,~.J , ~ CONTROLS

_ , , . , I00 50O IO00 2000

Serum Gostrin pg/ml

Pepsin ug/kg.3Omin ~SEM

I000

500

/ /, ~~"-->~- CONTROLS

sb ,6o 560 Ic;o sdo ,06o z o 6 o Serum Gastrln pg/mt Serum Gbstrin pg/ml

Fig 8. Direct comparison between DU and controls of absolute acid and pepsin output per kilogram body weight related to serum gastrin levels in the DU and controls studied with G-17 dose responses (left) and bombesin dose responses (right). Data rearranged from Figures 5 and 6.

patients (4M, 3F) as well as in the control patients (4M, 4F) up to the point of peak response to bombesin. Beyond that point, acid output increased to its logical and predictable maximum with G-17, as calculated from the dose-response data using the fractional linear transformation (21), The calculated maximum output was confirmed by the output With a subcutaneous large dose (6 ~g/kg) of pentagastrin in five DU subjects (see Materials and Methods). Pepsin output with G-17 reached maximum at lower doses in controls than in DU (Figure 7). In the bombesin studies, acid and pepsin output fell despite increasing serum gastrin levels. In controls, the peak output and subsequent output reversal with bombesin for both acid and pepsin occurred at 50 and 56% (P < 0.01 for both) of the G-17 maximum, respectively, while in DU the bombesin peak

occurred at 90 and 80% (differences not significant), respectively; of maximum G-17 output (Figures 6 and 7). In DU, pepsin output did not decliiae from peak with bombesin, but leveled off (Figure 7).

Comparing DU to Controls. When the results with G-17 in DU were directly compared to those in controls, acid and pepsin output curves related to serum gastrin were identical to the 100% point for controls and to about 75% of the DU maximum (P < 0.05) (Figure 8, left). Outputs with G-17 continued to increase in DU, with higher serum gastrin levels (higher doses of G-17), but remained at or near peak levels in controls. Thus these DU patients did not exhibit greater sensitivity to circulating gaStrin (al- ready showm Figure 5), but did have a one third greater maximum response than controls, probably reflecting a greater secretory cell mass. For endoge-


Serum gastrin % of peak

100% o ~

~-.,A o 50% Contro 1

~','~ ~'~-.~ (Bombesin "'-Du j

,0% o-r7

~ (DU, Control)

I0 20 50 40 rain STOP INFUSION Time

Fig 9, Decline of increased, ie, basal subtracted, serum gastrin levels in the 40 min after discontinuing G-17 and bombesin infusions, respectively, in duodenal ulcer (DU) and controls.

nous gastrin (bombesin infusion), peak outputs of both acid and pepsin in DU were more than double (P < 0.001) those of controls (Figure 8, right).

Recovery from Stimulation

Serum gastrin decreased rapidly in both DU patients and the control group after G-17 infusion was stopped (Figure 9), reaching 50% in about 6.5 min. Acid and pepsin outputs, which decreased by half in 20-30 min, fell more slowly than serum gastrin in both DU and control. By contrast, serum gastrin declined more slowly (P < 0.01) after bombesin, with calculated tV2 = 52 min in controls and 27 rain in DU (P < 0.05 vs controls) (Figure 9). The slower decline in serum gastrin after bombesin was reflected in the persistent stimulation of acid and pepsin in both DU and control compared to the fall after G-17. In fact, acid and pepsin Output increased after bombesin was discontinued, especially in DU (Figure 10). The persistent elevation of Serum gastrin and stimulation of acid and pepsin after stopping bombesin was also seen in dogs subjected to the same experiments (24). In both cases we assume that G-cell receptors have a high affinity for bombesin.

DISCUSSION

Our results demonstrate that, as in the case of food (25), stimulation of acid and pepsin secretion by bombesin in man can be accounted for by the increase

HIRSCHOWITZ ET A L

in circulating G-17 gastrin. This is true both in DU and non-DU normal controls and is proven by the congruence of the curves relating acid and pepsin output to serum gastrin levels whether the subjects were given exogenous G-17 or bombesin (endogenous gastrin). At about 50% of maximum acid and pepsin output in controls, and at about 80-90% of maximum in DU, bombesin-stimulated secretion began to deviate from the G-17 reference curve, showing progressive inhibition. This inhibition was first reported by Bertaccini et al (26) in dogs and has been confirmed at 50-70% of maximum in normal man (12, 27) and 50% of maximum in dogs studied by the same technique (24).

The nature of the inhibiting mechanism is un- known. Bombesin releases a number of peptides other than gastrin--pancreatic polypeptide from the pancreas (28); neurotensin, secretin, and CCK from the small gut (29); and somatostatin from the stomach (14, 30-32). Somatostatin has been shown to suppress basal and stimulated release of gastrin (13), and perfusion of isolated rat stomachs with somatostatin antibody during bombesin administration (14) augments the release of gastrin. However, the release of gastrin in our studies here or in normal dogs (24) did not deviate from the expected dose response and therefore did not appear to be suppressed. What has not yet been shown is whether the suppression of acid and pepsin secretion is due to the co-release of somatostatin, most likely acting in paracrine fashion (14), especially if gastrin release is not suppressed at the same time. A recent paper by Richelsen et al (33) showed that bombesin did not release somatostatin from human antral mucosa in vitro. Our findings are consistent with an inhibitory effect of bombesin active against acid and pepsin, but not against gastrin release in both normals and DU. Under the conditions of our study, patients with duodenal ulcer were less sensitive to this inhibitory mechanism of bombesin. If we consider all the peptides released by bombesin (29, 30), we would have to select somatostatin to be the most likely candidate. Somatostatin may well be a physiological regulator of many of the integrated secretory and digestive functions of the upper gastrointestinal tract (32).

We have shown here that the gastrin response to bombesin is three to four times greater in DU than in normal controls. However, kinetic analysis of the bombesin dose response did not show an increased sensitivity in DU to bombesin. Since the gastrin response to bombesin is increased in DU, the subtle role of gastrin in the pathophysiology of secretion

1 100 Digestive Diseases and Sciences, Vol. 30, No. 11 (November 1985)


ACID SECRETION CONTROLS D.U.

ffEq/kg 30mi n p.Eq / kg. 30rain 300[ 300[

/

~ o o ~ ' ~ 2 o o ~ T

STOP IV 'STOP I~/

0 I0 2 40rnin 0 I0 20 30 40ram TIME TIME

PEPSIN SECRETION

CONTROLS mg/kg. 30min

- " ~ B B t STOO 13/

O0 I() 20 3'0 40min TIME

D.U.

mg/kg. 30min

0 " ' in

TIME Fig lg. Acid and pepsin outputs in DU and controls in the 40 min after discontinuing the last dose of G-17 or bombesin (BB). Outputs for each 10-min period adjusted to 30-min rate.

becomes clearer. Because very small increments in circulating gastrin can cause appreciable increases in gastric secretion, and circulating gastrin is the means whereby bombesin (12, and this study) stimulates secretion, the greater secretory response of the stomach in DU to bombesin is explained. More- over, gastrin is gastrotrophic (3, 4) and, over a prolonged period of time, is likely to result in an increase in gastric secretory cell mass, another important abnormality in DU (1).

By using actual measured serum gastrin levels, we were able to examine critically the question of

whether increased secretory responses to exogenous stimuli are due to an abnormal sensitivity of DU patients to such stimuli. In this group of DU, we could not demonstrate for either exogenous or endogenous hormone the reported (25) increased sensitivity to gastrin. Although this result could arise from using the relatively small sample described here, we have also shown (20) in a much larger sample that most DU patients are not intrinsically more sensitive to pentagastrin than nonulcer controls.

The congruence of secretory responses in normal and DU patients to levels of circulating G-17 up to


those which are maximal for normals may reflect the concep t that response is a direct quantal func- t ion o f the number o f molecules of secretagogue present (35), is independent of the total mass of potential ly stimulable secre tory cells, and clearly shows a lack of hypersensi t iv i ty to the stimulus in the D U group. The m ax i m um response, however , would be a direct measure of the number or mass of secre tory cells (1).

Although not necessari ly present in all patients with duodenal ulcer , gastric hypersecre t ion in D U may result f rom several interacting abnormalit ies: (1) An excess ive response of gastrin release to bombes in and, to a lesser extent , to food (34), which we have not shown, probably due to small sample size, o c c u r s in D U patients. (2) The higher levels o f serum gastrin result not only in higher rates of secretion, but, ove r a period of time, may lead to secre tory cell mass hyperplas ia (3, 4), giving a higher max imum output. (3) Patients with duodenal ulcer exhibit defect ive inhibition of gastric se- cret ion, which m a y additionally Contribute to higher sec re t ion rates. When these abnormali t ies a r e added to (4) higher rates of basal secretion, and (5) in some pat ients an increase in apparent sensitivity to stimuli, eg, gastrin (20, 25), the consequences descr ibe the essential abnormal i ty Of gastric secretion in D U (16); viz, for a greater part of each day, grea ter volumes of gastric juice, containing higher concentra t ions of acid and pepsin empty into the duodenal bulb. The essence of effective t reatment for duodenal ulcer depends on correcting this state.

ACKNOWLEDGMENTS

This research was supported by NIH NIAMDDK AM09260 and GCRC MOIRR00032.

The authors appreciate the technical help of Philip Goodwin in performing the gastric secretion studies, of Brenda Bishop in data storage and management, and of the Staff of the Lister Hill Library for verifying and correcting the references.

REFERENCES

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2. Hirschowitz BI, Hetman CA: Effects of fundic vagot0my and cholinergic replacement on pentagastrin dose-responsive gastric acid and pepsin secretion in man. Gut 23:675-682, 1982

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Bombesin and G-17 dose responses in duodenal ulcer and controls