Influence of Glucose Dosage on Interpretation of Intravenous Glucose Tolerance Tests in Lean and Obese Cats

Abstract

Intravenous glucose tolerance tests (IVGTTs) are used in cats and other species to assess insulin sensitivity. Several dosages have been reported but the dosage that maximally stimulates insulin secretion in cats has not been determined nor has it been compared in lean and obese animals. IVGTTs were performed in 4 lean and 4 obese spayed female cats with 5 glucose dosages: 0.3 (A), 0.5 (B), 0.8 (C), 1.0 (D). and 1.3 (E) g/kg body weight (BW). Each cat received each dosage in a random design. The glucose disposal rate was significantly different only between lean and obese cats at the highest glucose dosage. The area under the curve for insulin increased significantly among A, B, C, and D in lean and among A, B, and C in obese cats but not between D and E in lean and among C, D, and E in obese cats. Baseline insulin secretion was significantly higher (P = .03) and 1st peak insulin secretion was approximately 50% lower in obese as compared to lean cats (P = .03). Lean but not obese cats reached baseline insulin concentrations at all dosages at 120 minutes. We conclude that the glucose dosage for maximal insulin secretion is 1.0 g/ kg BW in lean and 0.8 g/kg BW in obese cats, supporting routine use of 1 g/kg BW to maximally stimulate insulin secretion regardless of body composition. Obese cats showed an abnormal insulin secretion pattern, indicating a defect in insulin secretion with obesity and insulin resistance.

Feline Models of Type 2 Diabetes Mellitus

“…Significant ground work has been laid for further evaluating diabetes and glucose metabolism in the cat. Normal, obese, and diabetic cats have been evaluated with a variety of physiological tests including the intravenous glucose tolerance test (Appleton et al 2001a;Hoenig et al 2002;Nelson et al 1990;O'Brien et al 1985) and hyperinsulinemic euglycemic clamp (Petrus et al 1998), as well as glucagon and arginine stimulation tests (Kirk et al 1993;Kitamura et al 1999). …”

Effect of glimepiride and nateglinide on serum insulin and glucose concentration in healthy cats

“…Since our laboratory has routinely performed intermediate dose IVGTTs in cats with 0.5 g/kg glucose with satisfactory results, we performed IVGTTs on healthy and diabetic cats using this dose. This is in light of a previous study by Hoenig et al (2002) which has advocated the routine use of high dose (1.0 g/kg) glucose to elicit a maximal insulin response and a monitoring period of 120 min for IVGTT in healthy cats. However, that study did not examine diabetic cats.…”

“…Moreover, since only a 0.5 g/kg dose is used, it is not necessary to conduct the IVGTT for up to 120 minutes since at 90 minutes, serum glucose and insulin concentrations have returned to baseline or close to baseline levels in healthy control cats thus indicating complete disposal of glucose. One thing which we would like to emphasize though is that our laboratory has been extremely successful at observing and detecting two peak/phase insulin secretory response patterns in control and diabetic cats in spite of the fact that many studies employing dosages of <0.8 g glucose /kg body weight in IVGTT have met with little success demonstrating a clear distinction of a 2nd phase in insulin secretion profile (Hoenig et al 2002). As such, since our IVGTTs were performed with a glucose dose of 0.5 g/kg in our IVGTT assays, it should be noted that this may be a limitation of our study.…”

“…As such, the IVGTT proved to be adept at discerning between normal healthy and normoglycemic cats which may implicate its usefulness as a diagnostic test for diabetes under a clinical setting. Hoenig et al (2002) have advocated routine use of a 1.0 g glucose /kg dose to elicit a maximal insulin response and a monitoring period of 120 min when performing IVGTT in healthy cats. However, the traditional use of a 1.0 g glucose/kg dose originates from IVGTT testing in dogs (Greve and Anderson 1973).…”

“…As such, since our IVGTTs were performed with a glucose dose of 0.5 g/kg in our IVGTT assays, it should be noted that this may be a limitation of our study. However, we want to reiterate that our laboratory believes it is more important to evaluate the IVGTT response with respect to the pattern of insulin secretion and glucose disposal rather than with respect to absolute concentrations as has been advocated by Hoenig et al (2002). Understandably though, if one wishes to employ the IVGTT under a clinical setting and wanted to advocate its use as a clinical test to discern between diabetic state (ie.…”