Whereas leptin administration only has a negligible effect on the treatment of obesity, it has been demonstrated that its action can be improved by co-administration of leptin and one of its sensitizers. Considering that oxytocin treatment decreases body weight in obese animals and humans, we investigated the effects of oxytocin and leptin cotreatment. First, lean and diet-induced obese (DIO) mice were treated with oxytocin for 2 weeks and we measured the acute leptin response. Second, DIO mice were treated for 2 weeks with saline, oxytocin (50 μg/day), leptin (20 or 40 µg/day) or oxytocin plus leptin. Oxytocin pre-treatment restored a normal acute leptin response, decreasing food intake and body weight gain. Chronic continuous administration of oxytocin or leptin at 40 µg/day decreased body weight in the presence (leptin) or in the absence (oxytocin) of cumulative differences in food intake. Saline or leptin treatment at 20 µg/day had no impact on body weight. Oxytocin and leptin cotreatments had no additional effects compared with single treatments. These results point to the fact that chronic oxytocin treatment improves the acute, but not the chronic leptin response, suggesting that this treatment could be used to improve the short-term satiety effect of leptin.
Keywords: food intake; leptin; obesity; oxytocin.