Further studies on the acute dependence produced by morphine in opiate naive rats

Morphine appears to be capable of initiating the opiate dependence process with the first exposure. This can be demonstrated within 3 hrs by the administration of a low dose of naloxone which results in a significant elevation in plasma corticosterone. The response was still evident if the interval between morphine-priming and naloxone was extended to 6, 12, or 24 hours. The magnitude of the hormone elevation varied with the priming dose of morphine or with the dose of naloxone used to precipitate the response. Results are presented suggesting that the stress/withdrawal hormone response may be evident as early as 30 min after morphine-priming. Rats pretreated for eight days with either diazepam, phenobarbital, or amphetamine showed similarities in hormone responses after morphine-priming and naloxone administration when compared to saline-pretreated controls. The exception being the phenobarbital-pretreated group, where the response was attenuated and not observed at the 24 hr interval. These results emphasize the parallels between acute dependence and chronic dependence, suggesting that the same mechanism is involved.