Different light/dark condition modulation of the daily rhythm of insulin and glucagon in dogs

Abstract

Considering the importance of glucose homeostasis and knowing that the alteration of its regulation is the cause of many dogs’ pathologies, the present study aimed to investigate insulin, glucagon, and glucose daily rhythmicity in dogs subjected to a light/dark cycle (15/9 - L/D) and constant light (L/L). Five Beagle dogs (2 years old, male, 14.00 ± 0.50 kg) were housed in individual boxes, fed at 17:00, with water ad libitum; blood samples were collected every 4 h over 24 h for each photoperiod. A daily rhythmicity of insulin and glucagon was observed. Insulin acrophase was observed in the dark phase of the L/D cycle; glucagon acrophase was observed at the beginning of the light phase of the L/D cycle, for both parameters it was anticipated for about 4 h in the L/L cycle. The glucose oscillation trend remained constant during both photoperiods. Insulin and glucagon were positively correlated both in L/D and L/L cycles, the temporal difference of their oscillation of about 4 h persisted in both photoperiods. These findings contribute to the field of dogs’ circadian physiology and should be taken into consideration during the dogs’ clinical evaluation, particularly for the diagnosis and treatment of blood glucose homeostasis alterations.