Opioid and non-opioid components of insulin-induced feeding.

The present study was initiated to clarify the involvement of endogenous opioids in insulin-induced feeding. Naloxone (3 mg/kg) was injected in male Sprague Dawley rats every hour for 2 hours after insulin injection (10 U/kg). Only the first hour food intake was depressed (68% reduction). When naloxone was given only 1 hour after insulin administration, depression of food intake was not noted. When food was withheld for 2 hours after insulin injection, both naloxone and its long acting congener, naltrexone (3 mg/kg) were able to depress only the first hour feeding subsequent to food presentation. These data suggest that insulin-induced feeding can be divided into two pharmacologically distinct phases: the early phase being naloxone-sensitive while the late phase is naloxone-insensitive. Furthermore, the early phase begins with the presentation of food and not with the administration of insulin.