Enteroinsular axis response to carbohydrates and fasting in healthy newborn foals

Abstract

BackgroundThe enteroinsular axis (EIA) comprises intestinal factors (incretins) that stimulate insulin release after PO ingestion of nutrients. Glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are the main incretins. The EIA has not been investigated in healthy neonatal foals but should be important because energy demands are high in healthy foals and dysregulation is frequent in sick foals.Objectives and HypothesisTo evaluate the EIA response to carbohydrates or fasting in newborn foals. We hypothesized that incretin secretion would be higher after PO versus IV carbohydrate administration or fasting.AnimalsThirty‐six healthy Standardbred foals ≤4 days of age.MethodsProspective study. Blood was collected before and after a PO glucose test (OGT; 300, 500, 1000 mg/kg), an IV glucose test (IVGT; 300, 500, 1000 mg/kg), a PO lactose test (OLT; 1000 mg/kg), and fasting. Foals were muzzled for 240 minutes. Blood was collected over 210 minutes glucose, insulin, GIP, and GLP‐1 concentrations were measured.ResultsOnly PO lactose caused a significant increase in blood glucose concentration (P < .05). All IV glucose doses induced hyperglycemia and hyperinsulinemia. Concentrations of GIP and GLP‐1 decreased until foals nursed (P < .05), at which time rapid increases in glucose, insulin, GIP, and GLP‐1 concentrations occurred (P < .05).Conclusions and Clinical ImportanceHealthy newborn foals have a functional EIA that is more responsive to milk and lactose than glucose. Non‐carbohydrate factors in mare's milk may be important for EIA activity. Constant exposure of intestinal cells to nutrients to maintain EIA activity could be relevant to management of sick foals. Foals can be fasted for 4 hours without experiencing hypoglycemia.

Glucagon, insulin, adrenocorticotropic hormone, and cortisol in response to carbohydrates and fasting in healthy neonatal foals

“…Minor changes in theses hormones were observed with PO carbohydrate challenges, which were more evident in response to nursing. Our results and those of previous studies from our laboratory 14…”

“…These findings were contrary to our hypothesis, in which an increase in plasma glucagon concentration was expected in response to fasting so as to maintain euglycemia by glycogenolysis and gluconeogenesis. However, based on previous data, 14 knowledge, not previously reported in foals or horses. This finding also is intriguing because it was recently shown that immediately after nursing, healthy foals exhibited hyperglycemia that was followed by hyperinsulinemia.…”

“…IVGT, IV glucose test; OGT, PO glucose test; OLT, PO lactose test F I G U R E 5 Glucagon, insulin, glucose, ACTH, and cortisol concentrations expressed as median percentage change from baseline in fasted foals. Insulin and glucose data previously reported 14. # indicates time point at which foals were allowed free-choice nursing.…”

“…First, the number of foals per group was small, which increases the likelihood of type II statistical error, and could lead to misinterpretation of results. Although type II statistical error is possible, Serum insulin concentrations, reported previously,25 expressed as percentage change from baseline (time 0) in response to fasting (A), PO lactose (B), PO dextrose (C), and IV dextrose (D). Values expressed as medians with ranges.…”

Comparison of insulin sensitivity between healthy neonatal foals and horses using minimal model analysis

“…A 50% dextrose solution (300 mg/ kg) (VetOne, MWI Animal Health, Boise, Idaho, USA) was administered IV (time 0). The dose of dextrose administered was based on previous data from our laboratory [25], as well as preliminary data showing that this dose of dextrose (300 mg/kg) resulted in a tolerable level of hypoglycemia (without clinical signs) in response to insulin (Unpublished data, LDH & HMK). Blood samples were collected at -60, 0, 2, 5, 7, 10, 15,19,22,25,30,35,40,50,60,75,90,120,150, and 180 minutes relative to administration of dextrose.…”