Energy metabolic profile of mice after chronic activation of central NPY Y1, Y2, or Y5 receptors.

OBJECTIVE: Neuropeptide Y (NPY), a 36-amino acid peptide with orexigenic properties, is expressed abundantly in the central nervous system and binds to several NPY receptor subtypes. This study examines the roles of the NPY Y1, Y2, and Y5 receptor(s) in energy homeostasis.

RESEARCH METHODS AND PROCEDURES: We administered intracerebroventricular NPY (3 microg/d) or selective peptide agonists for the Y1, Y2, and Y5 receptor subtypes to C57Bl/6 mice for 6 days by mini-osmotic pumps to assess the role of each receptor subtype in NPY-induced obesity. Energy expenditure (EE) and respiratory quotient (RQ) were studied using indirect calorimetry. Adiposity was measured by DXA scanning and fat pad dissection. Insulin sensitivity was tested by whole-blood glucose measurement after an insulin challenge.

RESULTS: Central administration of the selective Y1 agonist, Y5 agonist, or NPY for 6 days in mice significantly increased body weight, adiposity, and RQ, with significant hyperphagia in the Y5 agonist- and NPY-treated groups but not in the Y1 agonist-treated group. The NPY, Y1, or Y5 agonist-treated mice had little change in total EE during ad libitum and pair-feeding conditions. Conversely, selective activation of the Y2 receptor reduced feeding and resulted in a significant, but transient, weight loss.

DISCUSSION: Central activation of both Y1 and Y5 receptors increases RQ and adiposity, whereas only Y5 receptor activation reduces energy expended per energy ingested. Selective activation of Y2 autoreceptors leads to hypophagia and transient weight loss, with little effect on total EE. Our study indicates that all three NPY receptor subtypes may play a role in regulating energy homeostasis in mice.