Dependent potency of endomorphin-1 and its regulation of ? opioid receptor / 第二军医大学学报

ABSTRACT

Objective:To observe the development of tolerance and dependence to endomorphin 1(EM 1) and its regulation on ? opioid receptor(MOR) in rat brain,providing references for the mechanism of the EM 1 dependence. Methods: Totally 60 SD rats were randomly divided into saline, acute EM 1 treatment and chronic EM 1 treatment groups. For acute EM 1 treatment, rats were injected intracerebroventricularly with 10 ?g/kg EM 1 30 min prior to sacrifice. The chronic group were treated with EM 1 daily administration at 800 and 1500 starting with 10 ?g/kg on day 1 to 50 ?g/kg on day 9. After chronic EM 1 treatment on day 1, 3, 6 and 9, the antinociceptive AD 50 or catatonic ED 50 values were determined by modified Dixon's method. The B max and K d values of 3H DAMGO saturation binding to MOR were measured by Scatchard analysis. The gene expression of MOR was appraised by RT PCR. Results:(1) EM 1 chronic treatment produced a high degree of tolerance to the antinociceptic and catatonic effects on the 3rd day (3.1 fold and 1.9 fold) and the 9th day (28.4 fold and 8.5 fold). The jumping times, weight lost and withdrawal score of rats were significantly higher than that of the control group after 9 d chronic EM 1 treatment. (2) After 9 d of administration with EM 1, the specific binding capacity and mRNA expression of MOR in rat cortex, midbrain and striatum were all decreased compared with those of the control and acute treatment groups, but the K d values were not significantly altered. Conclusion:Endomorphin 1 has the tolerant and dependent potent. For long term chronic treatment, Endomorphin 1 induces downregulation of the binding capacity and mRNA of MOR, which may be related to the dependence development.