A cholecystokinin-1 receptor agonist (CCK-8) mediates increased permeability of brain barriers to leptin

Background and purpose: Leptin regulates energy expenditure and body weight by acting both on the hypothalamus and on peripheral targets. Central actions of leptin are enhanced by cholecystokinin (CCK). The interaction between leptin and CCK makes physiological sense, as rats lacking CCK1 receptors are resistant to peripheral leptin but not to leptin directly infused into the brain. We have recently reported that CCK enhances leptin effects by increasing the entry of leptin into the CNS. The aim of this work was to further characterize the effect of CCK (10 mu g kg(-1)) on leptin kinetics as well as the CCK receptor subtype involved in the interaction between CCK and leptin. Experimental approach: Experiments were carried out both in free-feeding and in fasted rats receiving a single dose of leptin (100 mg kg(-1); i.p.). Parameters analysed over the next 6 h were plasma and cerebrospinal fluid concentrations of leptin. Key results: We observed that CCK-8 depressed the increase in plasma leptin that followed the i.p. injection and simultaneously increased leptin concentration in the cerebrospinal fluid from 92 +/- 25 to 230 +/- 24 pg mL(-1) (P<0.05). The effect of CCK-8 was totally prevented by the CCK1 receptor antagonist, SR-27,897 (0.3 mg kg(-1), s.c.), but not by the CCK2 receptor antagonist, L-365,260 (1 mg kg(-1)). Conclusions and implications: These results show that CCK plays a role in regulating the access of leptin to the brain and suggest that CCK analogues, acting on CCK1 receptors, might be useful drugs in improving leptin actions within the brain.