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

Abstract

Background: The endocrine pancreas and hypothalamic-pituitary-adrenal axis (HPAA) are central to energy homeostasis, but information on their dynamics in response to energy challenges in healthy newborn foals is lacking.

Objectives: To evaluate glucagon, insulin, ACTH, and cortisol response to fasting and carbohydrate administration in healthy foals.

Animals: Twenty-two healthy Standardbred foals ≤4 days of age.

Methods: Foals were assigned to fasted (n = 6), IV glucose (IVGT; n = 5), PO glucose (OGT; n = 5), and PO lactose (OLT; n = 6) test groups. Blood samples were collected frequently for 210 minutes. Nursing was allowed from 180 to 210 minutes. Plasma glucagon, ACTH, serum insulin, and cortisol concentrations were measured using immunoassays.

Results: Plasma glucagon concentration decreased relative to baseline at 45, 90, and 180 minutes during the OLT (P = .03), but no differences occurred in other test groups. Nursing stimulated marked increases in plasma glucagon, serum insulin, and glucose concentrations in all test groups (P < .001). Plasma ACTH concentration increased relative to baseline at 180 minutes (P < .05) during fasting and OLT, but no differences occurred in other test groups. Serum cortisol concentration increased relative to baseline during OLT at 180 minutes (P = .04), but no differences occurred in other test groups. Nursing resulted in decreased plasma ACTH and serum cortisol concentrations in all test groups (P < .01).

Conclusions and clinical importance: The endocrine response to enterally and parenterally administered carbohydrates, including the major endocrine response to nursing, suggests that factors in milk other than carbohydrates are strong stimulators (directly or indirectly) of the endocrine pancreas and HPAA.

Keywords: ACTH; cortisol; energy axis; glucagon; neonate.

FIGURE 1

Glucagon concentrations expressed as percent 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 range. * indicates statistical significance (P < .05) from baseline. IVGT, IV glucose test; OGT, PO glucose test; OLT, PO lactose test

FIGURE 2

Glucagon (A), ACTH (B), cortisol (C), and insulin (D) concentrations expressed as percentage change from time point 180 in response to nursing. # indicates statistical significance (P ≤ .05) from baseline

FIGURE 3

ACTH concentrations expressed as percent 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. * indicates statistical significance (P < .05) from baseline. IVGT, IV glucose test; OGT, PO glucose test; OLT, PO lactose test

FIGURE 4

Serum cortisol concentrations expressed as percent 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. * indicates statistical significance (P < .05) from baseline. IVGT, IV glucose test; OGT, PO glucose test; OLT, PO lactose test

FIGURE 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. ¶ indicates statistical significance from baseline (time 0). * indicates statistical significance from time 180 (P < .05)

FIGURE 6

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. * indicates statistical significance (P < .05) from baseline. IVGT, IV glucose test; OGT, PO glucose test; OLT, PO lactose test