Cocaine- and amphetamine-regulated transcript, glucagon-like peptide-1 and corticotrophin releasing factor inhibit feeding via agouti-related protein independent pathways in the rat

Abstract

The melanocortin-4 receptor (MC4-R) appears to be an important downstream mediator of the action of leptin. We examined to what extent the anorectic effects of cocaine- and amphetamine-regulated transcript (CART), glucagon-like peptide-1 (GLP-1) and corticotrophin releasing factor (CRF) might be mediated via MC4-R. α-Melanocyte stimulating hormone (α-MSH), the MC4-R agonist, administered intracerebroventricularly (ICV) at a dose of 1 nmol reduced food intake by approximately half. Agouti-related protein (Agrp) (83–132), a biologically active fragment of the endogenous MC4-R antagonist, administered ICV at a dose of 1 nmol completely blocked the anorectic effect of 1 nmol α-MSH. CART (55–102) (0.2 nmol), GLP-1 (3 nmol) and CRF (0.3 nmol) produced a reduction in feeding of approximately the same magnitude as 1 nmol α-MSH. Agrp (83–132) (1 nmol) administered ICV did not block the anorectic effects of CART (55–102) (1 h food intake, 0.2 nmol CART (55–102), 2.7±0.8 g vs. CART (55–102)+Agrp (83–132), 2.6±0.6 g, P=0.87; saline control 5.4±0.3 g, P<0.001 vs. both groups). Agrp (83–132) also did not block the anorectic effects of GLP-1 or CRF (1 h food intake, 0.3 nmol CRF, 0.7±0.3 g vs. CRF+Agrp (83–132), 0.7±0.3 g, P=0.91; 3 nmol GLP-1, 1.9±0.4 g vs. GLP-1+Agrp (83–132), 1.1±0.5 g, P=0.23; saline control 5.0±0.6 g, P<0.001 vs. all four groups). Thus, as previous data suggests, GLP-1 and CRF do not appear to reduce food intake predominantly via MC4-R, we here demonstrate for the first time that CART, in addition to GLP-1 and CRF primarily acts via Agrp independent pathways.