Diurnal variation in insulin-stimulated systemic glucose and amino acid utilization in pigs fed with identical meals at 12-hour intervals

The diurnal variation in insulin-stimulated systemic glucose and amino acid utilization was investigated in eleven pigs of approximately 40 kg. Pigs were fed isoenergetic/isoproteinic diets (366 kJ/kg BW (0.75) per meal) in two daily rations (06:00 and 18:00 h). After a 3-week habituation period, hyperinsulinemic euglycemic euaminoacidemic clamp studies (by intra-portal insulin, glucose and amino acids infusion and arterial blood sampling) were performed starting at 06:00 or 18:00 h (while skipping the meal), using a cross-over within-animal design. Basal (preclamp) plasma concentrations of insulin, glucose, lactate, individual amino acids and urea were similar in the morning compared to the evening. Insulin-stimulated ( approximately 4-fold increase over basal) systemic glucose utilization was similar (17.6+/-1.4 and 18.9+/-1.8 mg x kg (-1) x min (-1)) but amino acid utilization was 19% greater in the morning VS. the evening (2.37+/-0.21 VS. 1.99+/-0.15 mg x kg (-1) x min (-1), p<0.05), respectively. Insulin-stimulated plasma lactate concentrations remained constant in the morning (0.77+/-0.06 to 0.71+/-0.04 mmol x l (-1)) but declined in the evening (0.89+/-0.09 to 0.65+/-0.06 mmol x l (-1), p<0.05). By contrast, insulin-stimulated plasma urea concentrations declined in the morning (2.48+/-0.11 to 2.03+/-0.10 mmol x l (-1), p<0.005) but remained constant in the evening (2.18+/-0.14 to 2.12+/-0.12 mmol x l (-1)). In conclusion, pigs fed identical meals at 12-hour intervals follow a clear diurnal biorhythm in protein anabolism, with greater insulin-stimulated systemic amino acid utilization and lower plasma urea response in the morning compared to the evening.