Naltrexone modulates growth in infant rats.
Naltrexone, a potent opiate antagonist, had both stimulatory and inhibitory effects on somatic growth in preweaning rats depending on dose. Daily injections of 50 mg/kg naltrexone, which blocked morphine-induced analgesia for 24 hr/day, resulted in increased body and organ weights, and acceleration in the appearance of physical characteristics and maturation of spontaneous motor activity. Naltrexone in a dosage of 1 mg/kg, which blocked morphine-induced analgesia for 4 hr/day, had the opposite effects. These results show that naltrexone can modulate growth, and suggest a role for the endorphins and opiate receptors in developmental events.
D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development; D001835:Body Weight / Q000187:drug effects; D004431:Ear, External / Q000187:drug effects; D005123:Eye / Q000187:drug effects; D005260:Female; D006128:Growth / Q000187:drug effects*; D006197:Hair / Q000187:drug effects; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000031:analogs & derivatives*; D009271:Naltrexone / Q000494:pharmacology*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*
D011957:Receptors, Opioid; D009270:Naloxone; D009271:Naltrexone