Bromocriptine administration reduces hyperphagia and adiposity and differentially affects dopamine D2 receptor and transporter binding in leptin-receptor-deficient Zucker rats and rats with diet-induced obesity

Abstract

Background: The dopamine (DA) D(2) receptor (D2R) agonist bromocriptine (BC) decreases body fat in animal and human models and increases lean muscle mass, improves glucose intolerance and insulin resistance, and reduces triglycerides and free fatty acids. We have previously shown a negative correlation between D2R and body weight in obese individuals and in rodents, and that chronic food restriction increases D2R binding in genetically obese rats. The purpose of this study was to assess whether the antiobesity and metabolic effects of BC are related to changes in midbrain DA and D2R activity by measuring D2R and DA transporter (DAT) binding in a genetic (leptin-receptor-deficient) and environmental (diet-induced) rodent obesity model.

Methods: Obese (fa/fa) (leptin-receptor-deficient), lean (FA/FA) Zucker rats and rats with diet-induced obesity (DIO) were treated with 10 mg/kg BC for 4 weeks. Body weight, food intake, locomotor activity and blood glucose levels were measured along with D2R- and DAT-binding levels using in vitro receptor autoradiography.

Results: BC decreased food intake and body fat and increased locomotor activity in both the (fa/fa) and DIO rats. Furthermore, BC increased D2R binding in (fa/fa) but not in DIO rats. Finally, BC increased DAT binding in DIO rats but not in the (fa/fa) rats.

Conclusion: These observations are all consistent with the existence of unique leptin-DA interactions and the hypothesis that there is hyposensitivity of the DA system in obesity.

Fig. 1

Mean + SEM food intake levels before (week 1) and after (week 4) BC treatment. Zucker and DIO rats treated with BC showed significant reductions in food intake at week 4 compared to week 1 (* p<0.05).

Fig. 2

Mean + SEM body weight levels before and after BC treatment. There were no significant differences in body weight in response to BC treatment.

Fig. 3

Mean + SEM dark-phase locomotor activity levels before (week 1) and after (week 4) BC treatment. BC significantly increased locomotor activity in both Zucker and DIO rats (*p < 0.05). All other experimental groups except lean Zucker rats showed significant reductions in locomotor activity between weeks 1 and 4 (*p < 0.05).

Fig. 4

a Mean + SEM D2R binding in Zucker rats. BC treatment caused significant increases in D2R binding in obese rats in all brain regions (*p < 0.05). Obese nontreated rats showed significantly lower D2R binding in all brain regions compared to lean controls (^†p < 0.05). Lean Zucker rats showed greater D2R binding in the ST and NA core compared to BC-treated rats (^p < 0.05). b Mean + SEM DAT binding in DIO rats. Results are presented as a percent from control. BC caused significant decreases in DAT binding in the ST and NA shell (*p < 0.05). Results are presented as a percent from control.