The Oral Glucose Tolerance Test in Canine Pancreatic Malabsorption

Br. vet.

J.

(1972),

128,207

THE ORAL GLUCOSE TOLERANCE TEST IN CANINE PANCREATIC MALABSORPTION By F. W. G.

HILL AND

D. E.

KIDDER

Department of Veterinary M edicine, School of Veterinary Science, Langford House, Langford, Somerset

SUMMARY

Sixty-four oral glucose tolerance tests were performed on three groups of healthy dogs and a group with exocrine pancreatic insufficiency. A "diabetic type" tolerance curve resulted in the latter group. The resting plasma glucose levels were significantly higher in the younger healthy dogs. INTRODUCTION

An oral glucose tolerance test (O.G.T.T.) will often reveal a state of mild or sub-clinical diabetes mellitus, when the fasting blood glucose level is within normal limits (Varley, 1963). This occurs in man in some pathological disorders of the pancreas, where there is concurrent exocrine pancreatic insufficiency and the test procedure is recommended for pancreatic function testing (Baron, 1969; Bouchier, 1970). As canine pancreatic insufficiency has been recorded (Holroyd, 1968; Hill, Osborne & Kidder, 1971), we considered that the test might be an aid in establishing the presence of generalized pancreatic disease in dogs. This paper describes the results of a suitable test procedure performed on twenty-nine healthy dogs and sixteen with exocrine pancreatic insufficiency. MATERIALS AND METHODS

Dogs Group I. Young normals. Six healthy mongrels approximately six months old. Group 2. Adult normals. Seven healthy beagles, two to four years old. Group 3. Screened normals. Sixteen clinical cases referred to the Department for investigation for the presence of malabsorption and in which normal digestionabsorption function had been subsequently established by screening tests (Hill, 1970 ). Group 4. Exocrine pancreatic insufficiency. Sixteen dogs in which the diagnosis had been established by a malabsorption screening test procedure (Hill, 1970) and confirmed by the clinical response to test therapy of pancreatic extract supplement in the diet or by the presence of pancreatic disease at subsequent laparotomy or post-mortem examination. The clinical details and pathology of eight of these cases have been recorded elsewhere (Hill, Osborne & Kidder, 197 I).

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The dogs were kennelled individually and received a daily diet of 120 to g meat (Pedigree Chum, Petfoods) and 120 to 250 g biscuit (Terrier Meal, Wilson's) depending upon individual bodyweights. 210

Glucose dose It was necessary to establish a suitable dose of glucose for use in the tests. Such a dose would have to meet the following requirements in healthy dogs: (I) the peak plasma glucose level following the dose should be approximately fifty per cent above the resting level; (2) the plasma glucose level should revert to the resting level approximately two hours following dosing; (3) the concentration of the glucose solution should be such that the plasma glucose level curve contained only a single peak; (4) The volume of water for the glucose solution was not so great as to prevent the dogs consuming the dose quickly. Preliminary tests showed that a glucose dose rate of 2 g/kg bodyweight dissolved in a volume of water to produce a concentration of 12·5 per cent fulfilled these criteria. Technique of dosing and carrying out the test The dogs were weighed accurately and the appropriate glucose dose calculated. Prior to a test they were fasted overnight but water was not restricted until shortly before the test commenced. The procedures were always performed in the morning and great care was taken to avoid undue excitement amongst the dogs over the test period. Glucose test solutions were offered after resting blood samples had been obtained. The dogs in groups I and 2 had previously been trained to drink the solution; the dogs in group 4, being always hungry, also consumed the solution voluntarily. However, with some of the dogs in group 3 it was necessary to administer the test solution via a stomach tube. Subsequently I-ml samples of cephalic venous blood were collected at 15, 30, 60, 90 and 120 minutes into oxalate fluoride tubes (Teklab). The test was performed on the six dogs in group I on three alternate mornings when on each occasion four received a test dose, the remaining two acting as controls, receiving only the appropriate volume of water. The test was performed at least twice on the adult beagles (group 2) and once on the clinical cases (groups 3 and 4). Plasma glucose estimation The glucose oxidase method of Huggett & Nixon ( 1957) was used, the estimation being carried out in the afternoon of the day of the test procedure. RESULTS

The mean results and standard deviations for the tests carried out on the four groups of dogs are recorded in Table I and illustrated as tolerance test curves

ORAL GLUCOSE TOLERANCE TEST IN DOGS

in Fig. 1- 4. The results of control tests carri ed out on group only water, are shown in Fig. 5.

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TABLE 1 ORAL

Dog group

Noo

N oo

of

of tests

dogs 6

12

7

20

3

16

16

4

16

16

2

GLUCOS E

TOLERA NCE

TEST o

MEAN

RESU LTS

AND

STAN DARD

DEVIATI ONS

OF

PLASMA

GLUCOSE

Plasma glucose (mg/ I 00 ml ) mil/utes after dosil/g 0

± 82 °9 ± 8 101 ± 74"9 ±

100°6

15

4"7 5° 8 8 °9 10°2

± 15°8 ± 20 °9 116 08 ± 20 06 162°4 ± 43°9 149°9

124°5

30

± 16 °9 ± 20 °9 137°9 ± 20°7 210 °5 ± 43°9 155"5

134°2

60

± 18 °7 116°3 ± 27° 1 132°5 ± 20°0 220 08 ± 45° 6 128°4

90

± 14°9 95°8 ± IS03 108 °5 ± 14°9 '202 ± 38 °4 108 °4

~ c::

LEVELS

1 20

± 5° 1 ± 7° 1 85"8 ± 8 02 180'9 ± 40°3

[)

Mean rise ill plasma glucose after dosing (mg/lOo ml)

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BRITISH VETERINARY JOURNAL, 128,4

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Fig. 5. Oral glucose tolerance test, group I dogs receiving water only. Mean results and standard deviations.

Resting plasma glucose (mg/ Ioo ml) The levels for the two groups of healthy adults were very close together (82'9 ± 5.8 and 81'1 ± 8'9), with the pancreatic malabsorption cases slightly, but not significantly, lower (74'9 ± 10'2 ) . The resting levels of the young dogs ( 100·6 ± 4'7) were significantly higher (P < 0'001) than those of the adults of group 2 although both groups of dogs were kept under the same conditions and on the same diet. If the six resting levels for the young dogs used as controls are included, the mean resting level (10 1'36 ± 4'4) is still equally significantly higher than that for the adults. Peak rise in plasma glucose after dosing In the three groups of healthy dogs plasma glucose levels reached their highest point thirty minutes after dosing, whereas the peak occurred sixty minutes after dosing in those with pancreatic insufficiency (group 4). Furthermore the actual peak rises in plasma glucose above the resting levels for the first three groups were similar (group 1--54'9; group 2--51'3; and group 3--56'8 mg glucose/ Ioo ml plasma) and these differed markedly from the dogs in group 4 where the peak rise in plasma glucose was 145 mg/ Ioo ml above the resting level (P < 0 '00 1 ) . Degree of return to the resting level after dosing Two hours after dosing, plasma glucose had returned to the resting or predosing levels in all the healthy dogs (Figs. I, 2 and 3) but remained markedly TABLE II DOSE RATES OF GLUCOSE FOR AN O.G.T.T. IN THE DOG

Authors

Goldner & Haerem (1943) Hill & Chaikoff (1956) Kaneko, Moulton, Brody & Perryman ( 1965) Kaneko (1970) Hill & Kidder

Dose

1'5 gJkg bodyweight as a 20 per cent solution. 4 gJkg bodyweight mixed with a few grams of horse meat. 2 gjkg bodyweight as a 50 per cent solution. 4 gJkg bodyweight mixed with a few grams of horse meat. 2 gJkg bodyweight as a 12'5 per cent solution.

ORAL 'GLUCOSE TOLERANCE TEST IN DOGS

21 3

elevated in those with exocrine pancreatic insufficiency (group 4), when the tolerance curve was typically "diabetic" (Fig. 4). The actual range at two hours for healthy dogs was from 67'5 to 104'2 mg glucose/ IOo ml plasma and for cases of pancreatic insufficiency 128·6 to 264 mg glucose/ IOO ml plasma. DISCUSSION

Following the O.G.T.T. the marked difference in the rate of return of plasma glucose to the fasting levels together with the absence of an overlap in the ranges of the two-hour plasma glucose levels between healthy dogs and those with pancreatic insufficiency suggests that the test could be of diagnostic value in the investigation of canine pancreatic disease. It is emphasized in human medical textbooks (e.g. Cantarow & Trumper, 1955) that because of the several factors that may influence the O.G.T.T. curve, the conditions under which the test is performed must be rigidly standardized. The quantity and concentration of the glucose dose are also important, a satisfactory test result being dependent on the rapid entry of the ingested glucose into the lumen of the small intestine (Goldner & Haerem, 1943). The rate at which an orally administered glucose solution reaches the small intestine diminishes with increasing glucose concentration. This has been shown in the rat by Fenton (1945), in man by Hunt (1956, 1963) and in the pig by Reed (1967) and Reed & Kidder (1972). Concentrated solutions cause irregular emptying of the stomach. Reed & Kidder (197 I) showed that a 50 per cent glucose solution used in an O.G.T.T. in pigs caused spasmodic emptying, giving a blood glucose curve with two peaks, but that a 20 per cent solution was satisfactory. In the dog various procedures have been recommended as listed in Table II. In the present work the adequate size of the glucose peaks and the consistently rapid return to fasting levels in the healthy dogs show that the dose of 2 g/kg as a 12'5 per cent solution is suitable for the O.G.T.T. in the dog. The diet before the test can influence the O.G.T.T. result, dogs which have been on a low carbohydrate diet giving a "diabetic" tolerance curve which reverts to normal on inclusion of glucose or fructose in the diet (Hill & Chaikoff, 1956). For this reason Kaneko (1970) recommends placing the dog on a high carbohydrate diet for 3-5 days before the test. Our diet contained adequate carbohydrate, but this was in the form of starch which would have been poorly absorbed by the dogs with pancreatic exocrine insufficiency. It is therefore possible that a low effective carbohydrate intake contributed to the diabetic nature of the response to the oral glucose. Although this affects the interpretation of the test as a measure of islet cell damage in these cases, it does not reduce its value in the differential diagnosis of pancreatic malabsorption. The three groups of adult dogs (including the pancreatic insufficiency group) all had mean resting plasma glucose levels well within the published normal range determined by the same technique (Kidder & Rouse, 1966). As far as can be ascertained, the finding of higher resting plasma glucose levels in young dogs has not been described previously.

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BRITISH VETERINARY JOURNAL, 128,4 ACKNOWLEDGEMENTS

We wish to thank veterinary surgeons in practice who referred cases for examination. One of us (F.W.G.H.) is a Wellcome Research Fellow and the work was supported by a grant from the Wellcome Trust which is gratefully acknowledged . REFEREN CES

BARON,J. H . (1969). Ann. clin. Biochem. 6, 74. BOUCHlER, I. A. D. (1970). Ann. cZin. Biochem. 7, 122. CANTAROW, A. & TRUMPER, M. (1955). Clinical Biochemistry, 5th edn., p. 27. Philadelphia: W. B. Saunders. FENTON, P. F. (1945). Am. J. Physiol. 144,609. GOLDNER, M. G. & HAEREM, A. T. (1943). Proc. Soc. ex!}. Biol.. N.T. 52, 186. HILL, F. W. G. (1970). Vet. Rec. 87, 495. HILL, F. W. G., OSBORNE, A. D. & KIDDER, D. E. (1971). J. compo Path. 81, 321. HILL, R. & CHAIKOFF, I. L. (1956). Proc. Soc. expo BioI. Med. 91, 265. HOLROYD, J . B. (1968). J. small Anim. Fract. 10, 269. HUGGETT, A. ST. G. & NIXON, D. A. (1957). Lancet, ii, 368. HUNT,J. N. (1956). J. Physiol., Lond. 132, 267. HUNT,J. N. (1963) . Gastroenterology, 45,1 49. KANEKO,]. J. (1970). In Clinical Biochemistry of Domestic Animals, ed. Kaneko, J. J. & Cornelius, C. E ., p. 28. New York: Academic Press. KANEjO,]. J., MOULTON, J. E., BRODY, R. S. & PERRYMAN, V. D. (1965). J . Am. vet. med. Ass. 146, 463. KIDDER, D. E. & ROUSE, B. T. (1966). Vet. Rec. 79, 87. REED,J. H. (1967). Ph.D. Thesis, Bristol. REED,J. H. & KIDDER, D. E. (1972) Q. JI expo Physiol 57, 30. REED,]. H. & KIDDER, D. E. (1971) Br. vet. J. 127,318. V ARLEY, H. (1963). Practical Clinical Biochemistry, p. 49. London ; Heineman. (Accepted for publication 25 October 197 I) L'epreuve hyperglycemique par voie bucca1e dans Ie cas de tnauvais absorption pancreatique chez Ie chien (Hill et Kidder) ResUIRe. On a effectue soixante quatre epreuves hyperglycemiques par voie buccale dans trois groupes de chien bien portants et un groupe souffrant d'une insuffisance pancreatique exocrine. Dans ce dernier groupe la courbe de l'epreuve hyperglycemique etait du "type diabetique". Les taux de glucose plasmatique au repos etaient plus eleves de fa~on significative chez les chiens bien portants les plus jeunes. Der orale Glukosetoleranztest bei gestorter pankreatischer Resorption beitn Hunde (Hill und Kidder) ZusaInInenfassung. Vierundsechzig Toleranztests fUr Glukose wurden bei drei Gruppen gesunder Hunde und einer Gruppe mit einer Insuffizienz der Pankreassekretion (nicht der innern) vorgenommen. In dieser letzten Gruppe ergab sich eine Toleranzkurve "diabetischen" Charakters. Die Plasmaglukosekonzentrationen im Ruhestand waren signifikant hoher bei jungen gesunden Hunden. EI test de tolerancia de la glucosa en los caninos con sindrome de tnalabsorcion pancreatico (Hill y Kidder) ResUIRen. Se realizaron sesenta y cuatro pruebas de tolerancia a la glucosa en tres grupos de perros sanos y en otro grupo de perros con insuficiencia del pancreas exocrino. En este Ultimo grupo se obtuvo una curva de tolerancia "de tipo diabetico". Los niveles de glucosa en plasma en los animales no sometidos a ejercicio fueron significativamente mas elevados en los perros sanos mas j6venes.