Temporal response characteristics and interplay of energy metabolism-related hormones during fasting in piglets

Fasting-induced dynamic changes in energy metabolism hormones constitute a critical physiological process for maintaining energy homeostasis; however, their dynamic characteristics and coupling relationships during early fasting remain to be further elucidated. In this study, piglets were used as the experimental model, and linear mixed-effects models combined with nonlinear function fitting were employed to systematically investigate the temporal profiles and coupling relationships of glucose (Glu), insulin (INS), leptin (LEP), and ghrelin (GHR) at 6 (FT6), 8 (FT8), 10 (FT10), and 12 (FT12) hours of fasting. The results demonstrated that Glu, INS, and LEP exhibited an initial decrease followed by an increase with prolonged fasting, all reaching their nadirs at FT8 (Glu: 5.60 mmol/L; INS: 7.13 mIU/L; LEP: 2.90 ng/mL). In contrast, GHR showed an opposite trend, peaking at FT8 (1.62 ng/mL). Fasting significantly affected the temporal pattern of Glu (F_3,42 = 4.60, P < 0.01), and the change from FT6 to FT10 differed significantly between groups (P < 0.05). Significant between‑group differences at FT6 were observed for INS and GHR (P < 0.05), with both being lower in the fasting group. Dynamic response modeling of INS and LEP revealed a higher-order nonlinear relationship at FT6 and FT12. Derivative analysis of the fitted curves identified three extrema and two inflection points at FT6, whereas only one extremum and one inflection point were observed at FT12. Collectively, FT8 represents a critical point, while the early FT6 and late FT12 exhibit distinct nonlinear endocrine coupling patterns.