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Acute Antinociceptive Tolerance and Asymmetric Cross-Tolerance between Endomorphin-1 and Endomorphin-2 Given Intracerebroventricularly in the Mouse

Acute Antinociceptive Tolerance and Asymmetric Cross-Tolerance between Endomorphin-1 and... Abstract Development of tolerance in mice pretreated intracerebroventricularly with μ-opioid receptor agonist endomorphin-1, endomorphin-2, or d -Ala 2 , N -Me-Phe 4 ,Gly-ol 5 -enkephalin (DAMGO) was compared between endomorphin-1- and endomorphin-2-induced antinociception with the tail-flick test. A 2-h pretreatment with endomorphin-1 (30 nmol) produced a 3-fold shift to the right in the dose-response curve for endomorphin-1. Similarly, a 1-h pretreatment with endomorphin-2 (70 nmol) caused a 3.9-fold shift to the right for endomorphin-2. In cross-tolerance experiments, pretreatment with endomorphin-2 (70 nmol) caused a 2.3-fold shift of the dose-response curve for endomorphin-1, whereas pretreatment with endomorphin-1 (30 nmol) caused no change of the endomorphin-2 dose-response curve. Thus, mice acutely tolerant to endomorphin-1 were not cross-tolerant to endomorphin-2, although mice made tolerant to endomorphin-2 were partially cross-tolerant to endomorphin-1; an asymmetric cross-tolerance occurred. Pretreatment with DAMGO 3 h before intracerebroventricular injection of endomorphin-1, endomorphin-2, or DAMGO attenuated markedly the antinociception induced by endomorphin-1 and DAMGO but not endomorphin-2. It is proposed that two separate subtypes of μ-opioid receptors are involved in antinociceptive effects induced by endomorphin-1 and endomorphin-2. One subtype of opioid μ-receptors is stimulated by DAMGO, endomorphin-1, and endomorphin-2, and another subtype of μ-opioidreceptors is stimulated solely by endomorphin-2. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Pharmacology and Experimental Therapeutics Am. Soc for Pharma & Experimental Therapeutics

Acute Antinociceptive Tolerance and Asymmetric Cross-Tolerance between Endomorphin-1 and Endomorphin-2 Given Intracerebroventricularly in the Mouse

Acute Antinociceptive Tolerance and Asymmetric Cross-Tolerance between Endomorphin-1 and Endomorphin-2 Given Intracerebroventricularly in the Mouse

The Journal of Pharmacology and Experimental Therapeutics , Volume 299 (3): 1120 – Dec 1, 2001

Abstract

Abstract Development of tolerance in mice pretreated intracerebroventricularly with μ-opioid receptor agonist endomorphin-1, endomorphin-2, or d -Ala 2 , N -Me-Phe 4 ,Gly-ol 5 -enkephalin (DAMGO) was compared between endomorphin-1- and endomorphin-2-induced antinociception with the tail-flick test. A 2-h pretreatment with endomorphin-1 (30 nmol) produced a 3-fold shift to the right in the dose-response curve for endomorphin-1. Similarly, a 1-h pretreatment with endomorphin-2 (70 nmol) caused a 3.9-fold shift to the right for endomorphin-2. In cross-tolerance experiments, pretreatment with endomorphin-2 (70 nmol) caused a 2.3-fold shift of the dose-response curve for endomorphin-1, whereas pretreatment with endomorphin-1 (30 nmol) caused no change of the endomorphin-2 dose-response curve. Thus, mice acutely tolerant to endomorphin-1 were not cross-tolerant to endomorphin-2, although mice made tolerant to endomorphin-2 were partially cross-tolerant to endomorphin-1; an asymmetric cross-tolerance occurred. Pretreatment with DAMGO 3 h before intracerebroventricular injection of endomorphin-1, endomorphin-2, or DAMGO attenuated markedly the antinociception induced by endomorphin-1 and DAMGO but not endomorphin-2. It is proposed that two separate subtypes of μ-opioid receptors are involved in antinociceptive effects induced by endomorphin-1 and endomorphin-2. One subtype of opioid μ-receptors is stimulated by DAMGO, endomorphin-1, and endomorphin-2, and another subtype of μ-opioidreceptors is stimulated solely by endomorphin-2.

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Publisher
Am. Soc for Pharma & Experimental Therapeutics
Copyright
Copyright © Journal of Pharmacology and Experimental Therapeutics
ISSN
0022-3565
eISSN
1521-0103
Publisher site

Abstract

Abstract Development of tolerance in mice pretreated intracerebroventricularly with μ-opioid receptor agonist endomorphin-1, endomorphin-2, or d -Ala 2 , N -Me-Phe 4 ,Gly-ol 5 -enkephalin (DAMGO) was compared between endomorphin-1- and endomorphin-2-induced antinociception with the tail-flick test. A 2-h pretreatment with endomorphin-1 (30 nmol) produced a 3-fold shift to the right in the dose-response curve for endomorphin-1. Similarly, a 1-h pretreatment with endomorphin-2 (70 nmol) caused a 3.9-fold shift to the right for endomorphin-2. In cross-tolerance experiments, pretreatment with endomorphin-2 (70 nmol) caused a 2.3-fold shift of the dose-response curve for endomorphin-1, whereas pretreatment with endomorphin-1 (30 nmol) caused no change of the endomorphin-2 dose-response curve. Thus, mice acutely tolerant to endomorphin-1 were not cross-tolerant to endomorphin-2, although mice made tolerant to endomorphin-2 were partially cross-tolerant to endomorphin-1; an asymmetric cross-tolerance occurred. Pretreatment with DAMGO 3 h before intracerebroventricular injection of endomorphin-1, endomorphin-2, or DAMGO attenuated markedly the antinociception induced by endomorphin-1 and DAMGO but not endomorphin-2. It is proposed that two separate subtypes of μ-opioid receptors are involved in antinociceptive effects induced by endomorphin-1 and endomorphin-2. One subtype of opioid μ-receptors is stimulated by DAMGO, endomorphin-1, and endomorphin-2, and another subtype of μ-opioidreceptors is stimulated solely by endomorphin-2.

Journal

The Journal of Pharmacology and Experimental TherapeuticsAm. Soc for Pharma & Experimental Therapeutics

Published: Dec 1, 2001

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