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Naltrexone modulates body and brain development in rats: a role for endogenous opioid systems in growth

Title
Naltrexone modulates body and brain development in rats: a role for endogenous opioid systems in growth
Publication Type
Journal Article
Research Type
Animal
Reported as
Date
November 12, 1984
Authors
Zagon IS, McLaughlin PJ.
Institution
Pennsylvania State University
Link
Abstract
Preweaning rats receiving daily injections of 20, 50, or 100 mg/kg Naltrexone, a potent opiate antagonist, had body and brain weights that were increased 16-22% and 6-13%, respectively, from control levels on day 21 (weaning). All of these dosages of Naltrexone blocked the opiate receptor for 24 hr/day as measured in opiate challenge experiments. Dosages of 0.1, 1, and 10 mg/kg Naltrexone, which blocked the opiate receptor for less than 12 hr/day, inhibited growth. Repetitive administration of low dosages (3 mg/kg Naltrexone, 3 times daily), which blocked the receptor 24 hr/day, increased body and brain development by 31% and 10%, respectively, whereas a cumulative dosage of 9 mg/kg Naltrexone given once daily retarded growth. These results show that developmental events are dictated by the duration of opiate receptor blockade and provide compelling evidence that endogenous opioid systems play a crucial role in growth.