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Fat absorption in dogs with diabetes mellitus or hypothyroidism
Researchin VeterinaryScience1991,50, 346-348
Fat absorption in dogs with diabetes mellitus or hypothyroidism J. W. SIMPSON, A. H. M. VAN DEN BROEK, Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, Summerhall, Edinburgh, EH9 1QH
Quantitative fat absorption was studied in normal dogs and in dogs with hypothyroidism and diabetes mellitns. The serum triglyceride concentrations of diabetic and hypothyroid dogs were significantly higher at each sampling time than those of normal dogs. The fat absorption curve of hypothyroid dogs peaked at 180 minutes and though significantly raised was parallel to that of normal dogs whereas the fat absorption curve of diabetic dogs continued to rise up to 240 minutes. These results provide evidence for impaired plasma clearance of triglyceride in canine diabetes mellitus and hypothyroidism. DISTUR~BANCES of fat metabolism, manifested by hyperlipidaemia, hypercholesterolaemia and hyper"triglyceridaemia have been documented in a variety of canine hormonal imbalances, notably diabetes mellitus, hypothyroidism and hyperadrenocorticism (Scott 1979, Zerbe 1986). Studies of fat absorption in normal dogs and dogs with spontaneous and iatrogenic hyperadrenocorticism demonstrated significant increases in serum triglyceride concentrations and provided putative evidence of impaired plasma triglyceride clearance in dogs with hyperadrenocorticism (Simpson and van den Broek 1990). In view of the disturbances of fat metabolism observed in canine diabetes mellitus and hypothyroidism, similar changes in fat absorption might be anticipated in these conditions. The purpose of this study was to investigate fat absorption in dogs with diabetes mellitus and hypothyroidism in order to determine whether they exhibit changes similar to those found in dogs with hyperadrenocorticism. Materials and methods
Animals Group 1 consisted of 14 clinically normal dogs. These were domestic pets aged between two and 12 years old (mean six years and three months) and comprised five entire males, two entire females and
seven neutered females representing the following breeds: labrador retriever (three), German shepherd dog (four), springer spaniel (two), boxer (one), Irish setter (one), rough collie (one), Yorkshire terrier (one) and one crossbred dog.
Group 2 consisted of nine dogs with confirmed hypothyroidism. These were domestic pets aged between three and 11 years old (mean seven years and five months) and comprised three entire males, one entire female and five neutered females representing the following breeds: Siberian husky (two), doberman pinscher (two), springer spaniel (one), Irish setter (one), flat coated retriever (one), shetland sheepdog (one) and miniature schnauzer (one). Group 3 consisted of five dogs with confirmed diabetes mellitus. These were domestic pets aged between nine and 14 years old (mean 11 years and three months) and comprised one entire male, three entire females and one neutered female. One dog was a crossbreed and one came from each of the following breeds: border collie, cocker spaniel, border terrier and Jack Russell terrier. The diagnosis of diabetes mellitus was confirmed by measurement of plasma glucose levels, glycosuria and response to treatment. Possible involvement of hyperadrenocorticism was eliminated by the adrenocorticotrophin hormone (ACTH)stimulation test (Feldman 1983). Method The fat absorption test described by Simpson and van den Broek (1990) was used. Dogs were fasted for at least 12 hours and then weighed. A 2 ml venous blood sample was collected in an anticoagulant-free vacutainer tube (Becton Dickinson) and the dogs were then fed vegetable oil (3 ml kg-1) up to a maximum of 90 ml. Further venous blood samples were collected hourly for four hours. The serum was separated and the triglyceride concentration determined using a Technicon RAS00 auto-analyser, using a commercial test kit (Technicon).
346
Fat absorption in canine hormonal disorders
347
TABLE 1 : Serum triglyceride concentration Inmol litre- 1) for each group of dogs at each sampling time Time parameter Zero Mean Range SD Number < normal range Number > normal range 60 min Mean Range SD Number < normal range Number > normal range 120 min Mean Range SD Number < normal range Number > normal range 180 rain Mean Range SD Number < normal range Number > normal range 2 4 0 min Mean Range SD Number < normal range Number > normal range
Normal (n = 14)
Hypothyroid (n = 9)
Diabetes mellitus (n = 5)
O. 55 O. 3 8 - 0 . 7 7 0"09
1.62 c 0"39-3-75 1.01 0 7
3.1 a 0.92-9.87 3-8 0 5
O. 8 4 O. 44-1 • 8 9 O" 37
1.95 b 0"47-4"10 1"18 0 3
4.46 b 1.53-11.31 3"95 0 4
I • 33 O. 6 2 - 2 . 2 6 0"49
3- 0 3 b 0"68-6"58 1.75 0 6
7.77 c 1-91-13.99 5"00 0 4
1 - 78 O. 7 2 - 3 . 0 5 O" 69
3"61 a 0.73-9.16 2.44 0 6
10.17 c 4"62-17.57 5.44 0 5
1 - 46 O- 6 7 - 2 . 7 1 0"63
3.02 b 0-67-5.11 1.43 0 6
11.57 c 5'97-20.25 5"67 0 5
Means with superscripts a,b,c differ significantly by P < O ' 0 6 , P < O . 0 1 and P < O . O 0 1 , respectively, from the mean of normal dogs SD Standard deviation Number < normal range = number of dogs w i t h values less than the normal range at that time Number > normal range = number of dogs w i t h values greater than the normal range at that time
Statistics The mean and standard deviations were calculated for each group ateach sampling time. The results were analysed by the Student's t test using separate variance estimates for each group.
dogs at 60 minutes (P <0.01) and at 120, 180 and 240 minutes (P < 0.001) after feeding vegetable oil. The mean serum concentration of triglyceride in the serum of normal dogs and hypothyroid dogs but not diabetic dogs peaked three hours after feeding vegetable oil.
Results
The number of normal, diabetic and hypothyroid dogs in each group together with the mean, standard deviation, range of values, number of dogs outside the normal range at each sampling time and the results of statistical analysis are recorded in Table 1. Significant differences were recorded between the mean serum concentration of triglyceride of hypothyroid and normal dogs at 180 minutes ( P < 0 . 0 5 ) and at 60, 120 and 240 minutes (P<0"01) after feeding vegetable oil and between the mean serum concentration of triglyceride of diabetic and normal
Discussion
The significantly raised c o n c e n t r a t i o n o f triglyceride in the serum of fasted diabetic and hypothyroid dogs may be explained by a decreased rate of plasma clearance of triglyceride due to impaired activity of adipose tissue lipoprotein lipase (DeBowes 1987). This may be aggravated in diabetic dogs by excessive lipolysis resulting from increased hormone sensitive t r i g l y c e r i d e lipase activity which accompanies insulin deficiency (DeBowes 1987). Although the concentration of serum triglyceride at
348
J. W. Simpson, A. H. M. van den Broek
each sampling time was significantly higher in hypothyroid dogs the fat absorption curve paralleled that of normal dogs, with a peak concentration of triglyceride occurring 180 minutes after feeding vegetable oil. However, the fat absorption curve obtained in diabetic dogs continued to rise up to 240 minutes after feeding vegetable oil and in this respect was similar to the fat absorption curve observed in dogs with hyperadrenocorticism (Simpson and van den Broek 1990). This difference in the fat absorption curve of hypothyroid and diabetic dogs may reflect a difference in the degree of impairment of lipoprotein lipase activity induced by deficiencies of thyroid hormones and insulin. However, although none of the diabetic dogs had evidence of hyperadrenocorticism the possibility of increased adrenocortical activity beirig stimulated in these dogs by inability to meet energy requirements by glucose metabolism cannot be ignored and may explain the similarity observed in the fat absorption curves of dogs with diabetes mellitus and hyperadrenocorticism. This also suggests that there may be subclinical hyperadrenocorticism in dogs which the ACTH stimulation test is not sensitive enough to detect. It is clear from this study that further research is required into the mechanisms involved in controlling lipoprotein lipase activity in hormonal diseases of dogs.
Acknowledgements The authors would like to thank the Waltham Centre for Pet Nutrition, Melton Mowbray for their financial support. References DEBOWES, L. J. (1987) Lipid metabolism and hyperlipoproteinaemia in dogs. Compendium o f Continuing Education for the Practicing Veterinarian 9, 727-734 FELDMAN, E. C. (1983) Comparison of ACTH response and dexamethasone suppression as screening tests in canine hyperadrenocorticism. Journal of the American Veterinary Medical Association 182, 506-510 SCOTT, D. W. (1979) Hyperadrenocorticism (hyperadrenocorticoidism, hyperadrenocorticalism, Cushing's disease, Cushing's syndrome). Veterinary Clinics of North America 9, 3-28 SIMPSON, J. W. & VAN DEN BROEK, A. H. M. (1990) Assessment of fat absorption in normal dogs with hyperadrenocorticalism. Research in Veterinary Science 48, 38-41 THODAY, K. L. (1990) The Thyroid Gland. In: Hormones of Small Animal Endocrinology. Ed M. Hutchison. Cheltenham, British Small Animal Veterinary Association. pp 25-58 ZERBE, C. A. (1986) Canine Hyperlipidaemia. In: Current Veterinary Therapy IX. Ed R. W. Kirk. Philadelphia, W. B. Saunders. pp 1045-1053
Received August 13, 1990 Accepted December 5, 1990
Fat absorption in dogs with diabetes mellitus or hypothyroidism J. W. SIMPSON, A. H. M. VAN DEN BROEK, Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, Summerhall, Edinburgh, EH9 1QH
Quantitative fat absorption was studied in normal dogs and in dogs with hypothyroidism and diabetes mellitns. The serum triglyceride concentrations of diabetic and hypothyroid dogs were significantly higher at each sampling time than those of normal dogs. The fat absorption curve of hypothyroid dogs peaked at 180 minutes and though significantly raised was parallel to that of normal dogs whereas the fat absorption curve of diabetic dogs continued to rise up to 240 minutes. These results provide evidence for impaired plasma clearance of triglyceride in canine diabetes mellitus and hypothyroidism. DISTUR~BANCES of fat metabolism, manifested by hyperlipidaemia, hypercholesterolaemia and hyper"triglyceridaemia have been documented in a variety of canine hormonal imbalances, notably diabetes mellitus, hypothyroidism and hyperadrenocorticism (Scott 1979, Zerbe 1986). Studies of fat absorption in normal dogs and dogs with spontaneous and iatrogenic hyperadrenocorticism demonstrated significant increases in serum triglyceride concentrations and provided putative evidence of impaired plasma triglyceride clearance in dogs with hyperadrenocorticism (Simpson and van den Broek 1990). In view of the disturbances of fat metabolism observed in canine diabetes mellitus and hypothyroidism, similar changes in fat absorption might be anticipated in these conditions. The purpose of this study was to investigate fat absorption in dogs with diabetes mellitus and hypothyroidism in order to determine whether they exhibit changes similar to those found in dogs with hyperadrenocorticism. Materials and methods
Animals Group 1 consisted of 14 clinically normal dogs. These were domestic pets aged between two and 12 years old (mean six years and three months) and comprised five entire males, two entire females and
seven neutered females representing the following breeds: labrador retriever (three), German shepherd dog (four), springer spaniel (two), boxer (one), Irish setter (one), rough collie (one), Yorkshire terrier (one) and one crossbred dog.
Group 2 consisted of nine dogs with confirmed hypothyroidism. These were domestic pets aged between three and 11 years old (mean seven years and five months) and comprised three entire males, one entire female and five neutered females representing the following breeds: Siberian husky (two), doberman pinscher (two), springer spaniel (one), Irish setter (one), flat coated retriever (one), shetland sheepdog (one) and miniature schnauzer (one). Group 3 consisted of five dogs with confirmed diabetes mellitus. These were domestic pets aged between nine and 14 years old (mean 11 years and three months) and comprised one entire male, three entire females and one neutered female. One dog was a crossbreed and one came from each of the following breeds: border collie, cocker spaniel, border terrier and Jack Russell terrier. The diagnosis of diabetes mellitus was confirmed by measurement of plasma glucose levels, glycosuria and response to treatment. Possible involvement of hyperadrenocorticism was eliminated by the adrenocorticotrophin hormone (ACTH)stimulation test (Feldman 1983). Method The fat absorption test described by Simpson and van den Broek (1990) was used. Dogs were fasted for at least 12 hours and then weighed. A 2 ml venous blood sample was collected in an anticoagulant-free vacutainer tube (Becton Dickinson) and the dogs were then fed vegetable oil (3 ml kg-1) up to a maximum of 90 ml. Further venous blood samples were collected hourly for four hours. The serum was separated and the triglyceride concentration determined using a Technicon RAS00 auto-analyser, using a commercial test kit (Technicon).
346
Fat absorption in canine hormonal disorders
347
TABLE 1 : Serum triglyceride concentration Inmol litre- 1) for each group of dogs at each sampling time Time parameter Zero Mean Range SD Number < normal range Number > normal range 60 min Mean Range SD Number < normal range Number > normal range 120 min Mean Range SD Number < normal range Number > normal range 180 rain Mean Range SD Number < normal range Number > normal range 2 4 0 min Mean Range SD Number < normal range Number > normal range
Normal (n = 14)
Hypothyroid (n = 9)
Diabetes mellitus (n = 5)
O. 55 O. 3 8 - 0 . 7 7 0"09
1.62 c 0"39-3-75 1.01 0 7
3.1 a 0.92-9.87 3-8 0 5
O. 8 4 O. 44-1 • 8 9 O" 37
1.95 b 0"47-4"10 1"18 0 3
4.46 b 1.53-11.31 3"95 0 4
I • 33 O. 6 2 - 2 . 2 6 0"49
3- 0 3 b 0"68-6"58 1.75 0 6
7.77 c 1-91-13.99 5"00 0 4
1 - 78 O. 7 2 - 3 . 0 5 O" 69
3"61 a 0.73-9.16 2.44 0 6
10.17 c 4"62-17.57 5.44 0 5
1 - 46 O- 6 7 - 2 . 7 1 0"63
3.02 b 0-67-5.11 1.43 0 6
11.57 c 5'97-20.25 5"67 0 5
Means with superscripts a,b,c differ significantly by P < O ' 0 6 , P < O . 0 1 and P < O . O 0 1 , respectively, from the mean of normal dogs SD Standard deviation Number < normal range = number of dogs w i t h values less than the normal range at that time Number > normal range = number of dogs w i t h values greater than the normal range at that time
Statistics The mean and standard deviations were calculated for each group ateach sampling time. The results were analysed by the Student's t test using separate variance estimates for each group.
dogs at 60 minutes (P <0.01) and at 120, 180 and 240 minutes (P < 0.001) after feeding vegetable oil. The mean serum concentration of triglyceride in the serum of normal dogs and hypothyroid dogs but not diabetic dogs peaked three hours after feeding vegetable oil.
Results
The number of normal, diabetic and hypothyroid dogs in each group together with the mean, standard deviation, range of values, number of dogs outside the normal range at each sampling time and the results of statistical analysis are recorded in Table 1. Significant differences were recorded between the mean serum concentration of triglyceride of hypothyroid and normal dogs at 180 minutes ( P < 0 . 0 5 ) and at 60, 120 and 240 minutes (P<0"01) after feeding vegetable oil and between the mean serum concentration of triglyceride of diabetic and normal
Discussion
The significantly raised c o n c e n t r a t i o n o f triglyceride in the serum of fasted diabetic and hypothyroid dogs may be explained by a decreased rate of plasma clearance of triglyceride due to impaired activity of adipose tissue lipoprotein lipase (DeBowes 1987). This may be aggravated in diabetic dogs by excessive lipolysis resulting from increased hormone sensitive t r i g l y c e r i d e lipase activity which accompanies insulin deficiency (DeBowes 1987). Although the concentration of serum triglyceride at
348
J. W. Simpson, A. H. M. van den Broek
each sampling time was significantly higher in hypothyroid dogs the fat absorption curve paralleled that of normal dogs, with a peak concentration of triglyceride occurring 180 minutes after feeding vegetable oil. However, the fat absorption curve obtained in diabetic dogs continued to rise up to 240 minutes after feeding vegetable oil and in this respect was similar to the fat absorption curve observed in dogs with hyperadrenocorticism (Simpson and van den Broek 1990). This difference in the fat absorption curve of hypothyroid and diabetic dogs may reflect a difference in the degree of impairment of lipoprotein lipase activity induced by deficiencies of thyroid hormones and insulin. However, although none of the diabetic dogs had evidence of hyperadrenocorticism the possibility of increased adrenocortical activity beirig stimulated in these dogs by inability to meet energy requirements by glucose metabolism cannot be ignored and may explain the similarity observed in the fat absorption curves of dogs with diabetes mellitus and hyperadrenocorticism. This also suggests that there may be subclinical hyperadrenocorticism in dogs which the ACTH stimulation test is not sensitive enough to detect. It is clear from this study that further research is required into the mechanisms involved in controlling lipoprotein lipase activity in hormonal diseases of dogs.
Acknowledgements The authors would like to thank the Waltham Centre for Pet Nutrition, Melton Mowbray for their financial support. References DEBOWES, L. J. (1987) Lipid metabolism and hyperlipoproteinaemia in dogs. Compendium o f Continuing Education for the Practicing Veterinarian 9, 727-734 FELDMAN, E. C. (1983) Comparison of ACTH response and dexamethasone suppression as screening tests in canine hyperadrenocorticism. Journal of the American Veterinary Medical Association 182, 506-510 SCOTT, D. W. (1979) Hyperadrenocorticism (hyperadrenocorticoidism, hyperadrenocorticalism, Cushing's disease, Cushing's syndrome). Veterinary Clinics of North America 9, 3-28 SIMPSON, J. W. & VAN DEN BROEK, A. H. M. (1990) Assessment of fat absorption in normal dogs with hyperadrenocorticalism. Research in Veterinary Science 48, 38-41 THODAY, K. L. (1990) The Thyroid Gland. In: Hormones of Small Animal Endocrinology. Ed M. Hutchison. Cheltenham, British Small Animal Veterinary Association. pp 25-58 ZERBE, C. A. (1986) Canine Hyperlipidaemia. In: Current Veterinary Therapy IX. Ed R. W. Kirk. Philadelphia, W. B. Saunders. pp 1045-1053
Received August 13, 1990 Accepted December 5, 1990