2.3. Oral Glucose Tolerance Test (OGTT), and Mixed Meal Tolerance Test (MMTT)

OGTTs and MMTTs are used as standardized means to assess glycemic responses. OGTTs involve administration of only glucose and serve as the standard approach to assess glucose tolerance, including in humans with CF. MMTTs involve administration of carbohydrates, protein, and lipid, and thus may better model the impact of a typical meal. Because both tests employ delivery of enteral nutrients, they also assess gut hormone responses. We have previously standardized methods for OGTTs and MMTTs in ferrets fasted for 4 hours [22]. Briefly, an oral glucose dose of 1.75 g /kg body weight (glucose tolerance beverage, Thermo Scientific) was administered for OGTT. For MMTTs, mixed meals included Elecare (Abbott) and canned food (Fancy Feast). Each mixed meal contained a total of 0.026 g carbohydrate/cm² estimated body surface area. Blood samples were collected by venipuncture during brief isoflurane anesthesia. Other analytes from the OGTT and MMTT data presented in Figure 1, including glucose and insulin, have been previously published [22]. At least one month’s recovery was allowed between tests for ferrets undergoing repeated measures.

Body weight (A) and acyl-ghrelin (B) in CF (CF) and non-CF ferrets aged 2–16 months. Acyl-ghrelin was measured in serum after 4 hours fast in co-reared CF:non-CF ferret pairs, some having measurements made at more than one age (A-D: N=10 ferret pairs; mean ± standard deviation shown by bars). The influence of CF status on acyl-ghrelin levels did not vary with weight (C) or age (D). Acyl-ghrelin levels during mixed meal tolerance tests “MMTT” (E-G), and oral glucose tolerance tests “OGTT” (H-J). Mixed meal (E) and glucose (H) administration occurred at time 0. The respective area under the curve “AUC” (F,I) and incremental area under the curve “iAUC” (G,J) are shown. (E-J: N=4–5 co-reared CF:non-CF ferret pairs aged 2–12 months; mean ± standard deviation shown; H-J data includes 2 repeated measures). Symbols summarizing statistical test results are conserved throughout all figures: * p<0.05 for difference between CF and non-CF; † p<0.05 for change in value compared to time 0; & p<0.05 for mean value differing from zero.