Cherrington, A. | bioRxiv Science

bioRxiv2025

Morning Elevation in Insulin Enhances Afternoon Postprandial Insulin Action and Glucose Effectiveness

The second-meal phenomenon refers to the improved glycemic response to a subsequent identical meal. We previously showed that morning (AM) hyperinsulinemia is a key mediator, priming the liver for enhanced net hepatic glucose uptake (NHGU) and glycogen storage during an afternoon (PM) hyperinsulinemic-hyperglycemic clamp. Postprandial NHGU is regulated by three primary mechanisms: insulin action (IA), initiated by hyperinsulinemia; glucose effectiveness (GE), driven by hyperglycemia; and the portal glucose signal (PGS), a neurally-mediated signal activated by glucose delivery into the hepatoportal circulation. It remained unclear, however, which of these mechanisms govern the increase in PM NHGU following AM insulin exposure. To address this, dogs underwent an AM clamp with either a 4-hour hyperinsulinemic prime (Prime, n=8) or basal insulin delivery (No Prime, n=8). After a 1.5-hour rest, both groups underwent a PM hyperglycemic clamp with portal glucose delivery under basal insulin conditions to isolate the effects of an AM insulin prime on PM glucose-mediated hepatic signals (GE/the PGS). Mean PM NHGU was significantly greater in the Prime group (2.2 {+/-} 0.3 mg/kg/min) compared to the No Prime group (0.1 {+/-} 0.3 mg/kg/min, p=0.005), accompanied by augmented net glycolytic and glycogen flux. These findings indicate that morning insulin can enhance glucose-mediated PM NHGU independently of a rise in PM insulin. However, maximal second-meal NHGU also requires elevated PM insulin. Together, this suggests that strategically timed early-day insulin or insulinotropic interventions could potentially improve hepatic responsiveness in settings of impaired postprandial glycemic control, such as insulin resistance or diabetes. Article HighlightsO_LIElevated morning insulin primes the liver for enhanced afternoon net hepatic glucose uptake (NHGU), but it was unclear whether augmentation of insulin action (IA), glucose effectiveness (GE), or the portal glucose signal (PGS) mediates this effect. C_LIO_LIDogs underwent a morning euglycemic clamp with either elevated or basal insulin delivery, followed by an afternoon euinsulinemic-hyperglycemic clamp to isolate the effect of morning insulin priming on afternoon GE/PGS. C_LIO_LIMorning insulin priming enhanced afternoon NHGU via increased glucose-mediated mechanisms, though maximal afternoon NHGU also requires elevated afternoon insulin. C_LIO_LIThese findings identify mechanisms underlying insulin-induced hepatic metabolic memory, providing a framework to inform strategies improving postprandial glucose handling in diabetes. C_LI

physiology↗

bioRxiv2025

Hepatic Metabolic Memory Triggered by AM Exposure to Glucagon Alters Afternoon Glucose Metabolism

The Staub-Traugott effect, or second-meal phenomenon, describes improved glucose disposal after a second identical meal. We previously showed that morning hyperinsulinemia primes the liver to enhance afternoon net hepatic glucose uptake and glycogen storage. However, mixed meals trigger co-secretion of insulin and glucagon, and glucagon is traditionally viewed as opposing insulins hepatic actions. Whether glucagon modifies the persistence of insulins priming effects across sequential metabolic challenges is unknown. Therefore, we investigated whether morning hyperglucagonemia alters the ability of morning hyperinsulinemia to prime subsequent hepatic glucose metabolism. Conscious dogs underwent two pancreatic clamp periods separated by a 1.5h rest period. Endogenous insulin and glucagon were suppressed with somatostatin and replaced intraportally at defined rates. During a 4h morning hyperinsulinemic-euglycemic clamp, dogs received matched insulin prime infusions with either basal glucagon (AM INS; n=8) or elevated glucagon (AM INS+GCG; n=8). After the rest period, both groups underwent a 2.5h afternoon hyperinsulinemic-hyperglycemic clamp under identical hormonal conditions. Afternoon net hepatic glucose uptake, glycogen, glycolytic, and gluconeogenic flux rates were quantified using arteriovenous difference methods and [3-3H]-glucose tracer kinetics. Liver biopsies were collected before and after the afternoon clamp to assess gene transcription and protein regulators of hepatic glucose metabolism. During the afternoon clamp, despite matched insulin, glucagon, and glucose levels, net hepatic glucose uptake was 41% lower in AM INS+GCG (3.6{+/-}0.4 mg/kg/min) than in AM INS (6.1{+/-}0.6 mg/kg/min; p<0.003). This was accompanied by a trend toward incomplete suppression of hepatic glucose production in AM INS+GCG (1.4{+/-}0.4 mg/kg/min), whereas it was fully suppressed in the AM INS group (p=0.06). Direct glycogen synthesis was also 44% lower in AM INS+GCG (1.8{+/-}0.2 vs 3.2{+/-}0.7 mg/kg/min; p<0.015), along with reductions in net glycogen synthesis and glycolytic flux. Morning insulin with basal glucagon increased hepatic glucokinase mRNA and protein before the afternoon clamp, whereas concurrent glucagon prevented this induction. In summary, antecedent morning hyperglucagonemia attenuates insulin-mediated hepatic priming, reducing hepatic glucose flux during a later hyperinsulinemic-hyperglycemic challenge. These findings identify glucagon as a regulator of hepatic metabolic memory alongside insulin and demonstrate that early-day insulin-glucagon dynamics shape the livers response to subsequent challenges, providing mechanistic insight into postprandial glucose regulation and implications for metabolic health and diabetes risk. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/639957v3_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@6d210org.highwire.dtl.DTLVardef@1c93840org.highwire.dtl.DTLVardef@18c0b49org.highwire.dtl.DTLVardef@138ee9f_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗