1 13c d glucose

At the end of the feeding period, the rats were anesthetized with an intraperitoneal injection of chloral hydrate (8%, 1 mL/200 g BW; Sigma-Aldrich, USA) and placed on a heated pad (37°C). [1-¹³C]D-glucose (750 mM, Cambridge Isotope Laboratories, Inc.) was infused into the tail vein over a total period of 60 min, following a previous 20 steps, time-decreasing exponential rate protocol going from 15–1.23 ml/h during the first 25 min after which the rate was kept unchanged for the last 35 min. This infusion protocol was designed to reach constant [1-¹³C]D-glucose concentrations in the blood and the total amount of glucose administered was 2.19 mmol/h per 200 g BW.

A total of 24 guinea pigs (Dunkin-Hartley), both male and female (obtained from Pipers Farm, NSW, and Australia and Flinders University, Australia respectively) and weighing about 400–800 g were used in the experiments. They were fed ad libitum on standard Guinea pig/rabbit pellets, with fresh carrots and hay roughage, and maintained a 12 h light/dark cycle. All experiments were carried out according to the guidelines of the National Health and Medical Research Council of Australia and were approved by the institutional (UNSW) Animal Care Ethics Committee (ethical approval number: 20/105B, Approval date: 1 July 2020). The study, an exploratory investigation, was not pre-registered.
[1-¹³C]d-glucose, [1,2-¹³C]acetate and sodium [¹³C]formate were purchased from Cambridge Isotope Laboratories Inc (Andover, MA, USA). Histidine, MeAIB (2-(methylamino)isobutyric acid), cycloleucine (1-aminocyclopentanecarboxylic acid), BCH (2-aminobicyclo [2.2.1]heptane-2-carboxylic acid) and GPNA (L-γ-glutamyl-p-nitroanilide) were purchased from Sigma-Aldrich (St Louis, MO, USA). AABA (2-amino-4-bis(aryloxybenzyl)aminobutanoic acid; compound 12) was supplied by Professor Stefan Bröer (Research School of Biology, Australian National University) [56 (link)]. All other reagents were of Analytical Reagent grade.