Endocrine Abstracts

Cannabinoids and ghrelin are potent appetite stimulators. The ghrelin receptor (GHS-R1a), endocannabinoids and the cannabinoid 1 (CB1) receptor are expressed in the hypothalamus. There is evidence that the novel CB1 antagonist, rimonabant, causes weight loss by both central and peripheral effects. The AMP-activated protein kinase (AMPK) is a sensor of cellular energy status and regulates the energy metabolism within the single cell but also at whole body level. We have shown previously that ghrelin and endocannabinoid systems could interact with each other and influence feeding behaviour through AMPK in the hypothalamus. Icv administration of ghrelin provoked an increase in food intake and this effect was reversed by rimonabant. Both icv and ip injections of ghrelin and cannabinoids significantly increased AMPK activity in the hypothalamus. The aim of this study was to confirm the above in vivo data with cell lines in vitro. Therefore, a mouse hypothalamic cell line, N39, expressing both GHS-R and CB1 receptor was treated with ghrelin, BIM-28163 (GHS-R antagonist) and anandamide. Based on time- and dose-response curves, 30 min treatment was performed with ghrelin at 10⁻⁷ M, BIM-28163 at 10⁻⁶ M and anandamide at 10⁻⁵ M. AMPK activity was tested with an AMPK functional assay and with immunoblotting for pAMPK and total AMPK. Both ghrelin and anandamide increased the AMPK activity, 168.6%±28.5 and 180.5%±33 of the control respectively, while BIM-28163 decreased it 47.1%±1.7 compared to ghrelin. These results suggest that ghrelin and cannabinoids activate AMPK in the hypothalamic cell line while the GHS-R antagonist BIM-28163 inhibits the ghrelin-induced AMPK activity. The latter result might be very important because would suggest that the ghrelin effect in the AMPK activity in the hypothalamus might be through the identified GHS-R. These results also confirm our previous in vivo data which showed a relationship between brain ghrelin and endocannabinoid systems and confirm that ghrelin and endocannabinoids stimulate AMPK activity in the hypothalamus.