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.
[1-13C]