INTRODUCTION: Oxytocin is expressed throughout the small intestine, suggesting a role for oxytocin in postprandial metabolism. Accordingly, single-dose intranasal oxytocin reduces food intake and improves glucose tolerance. We investigated the effects of a continuous intravenous oxytocin infusion on ad libitum food intake, appetite sensations, and postprandial metabolism.
METHODS: In a randomised, placebo-controlled, double-blind, crossover study, overnight fasted participants with obesity underwent two 4.5-hour intravenous infusions of oxytocin (0.2 international units/min) and placebo (saline), respectively, on separate days interposed by a wash-out period of a minimum of seven days. After 60 min of infusion, participants ingested a standardised liquid mixed meal containing 1.5 g paracetamol (for evaluation of gastric emptying). Appetite sensations were assessed by visual analogue scales, and concentrations of plasma glucose as well as glucose and appetite-regulating hormones were measured. After four hours, food intake (primary endpoint) was assessed by an ad libitum meal test.
RESULTS: Twenty-four individuals (12 women, median age 41.5 (interquartile range (IQR) 28.5;55.3) years, body mass index 36.2 (32.1;37.6) kg/m, mean glycated haemoglobin 34 ± standard deviation (SD) 3.5 mmol/mol) completed the study. Ad libitum food intake was similar between oxytocin and saline infusions (mean 714 ± SD 382 vs. 707 ± 385 kcal). Compared with placebo, oxytocin did not affect sensations of appetite nor circulating glucose, insulin, C-peptide, glucagon, glucagon-like peptide 1, glucose-dependent insulinotropic polypeptide, cholecystokinin, or paracetamol. 2
CONCLUSION: In individuals with obesity, 4.5-hour intravenous infusion of oxytocin causing supraphysiological plasma concentrations of ~400 pg/mL has no effect on ad libitum food intake, appetite sensations, plasma glucose levels, circulating concentrations of glucose and appetite-regulating hormones, or gastric emptying.
