Despite its limited ability to cross the blood-brain barrier, peripherally administered oxytocin (OT) acutely decreases food intake, most likely via the brainstem and hypothalamic mechanisms. Studies performed to date have focused mainly on the effects of subcutaneous or intraperitoneal OT on the consumption of only solid calorie-dense diets (either standard or high-fat), whereas it is unknown whether, similarly to central OT, peripherally administered peptide reduces intake of calorie-dilute and non-caloric palatable solutions. In this project, we established that 0.1 μg/kg intravenous (IV) OT is the lowest anorexigenic dose, decreasing deprivation-induced standard chow intake by ca. 40% in rats and its effect does not stem from aversion. We then used this dose in paradigms in which effects of centrally acting OT ligands on consumption of palatable solutions had been previously reported. We found that IV OT did not change episodic intake of individually presented palatable solutions containing 10% sucrose, 0.1% saccharin, combined 10% sucrose-0.1% saccharin or 4.1%. Intralipid and it failed to affect daily scheduled consumption of a sucrose solution in non-deprived rats. In a two-bottle choice test, IV OT did not shift animals’ preference from sucrose to Intralipid. Finally, OT injected IV prior to the simultaneous presentation chow and a sucrose solution in food-deprived rats significantly decreased chow intake, whereas sugar water consumption remained unchanged. We conclude that IV OT reduces deprivation-induced chow intake without causing aversion, but the dose effective in decreasing energy-driven consumption of high-calorie food fails to affect consumption of palatable calorie-dilute solutions.
Bibliographical noteFunding Information:
The studies were supported by the Royal Society of New Zealand Marsden grant.