Periaqueductal gray (PAG) plays a very important role in pain modulation through endogenous opiate peptides including leucine-enkephalin (L-Ek), methionine-enkephalin (M-Ek), β-endorphin (β-Ep) and dynorphin A(1-13) (DynA(1-13)). Our pervious study has demonstrated that intra-PAG injection of oxytocin (OXT) increases the pain threshold, and local administration of OXT receptor antagonist decreases the pain threshold, in which the antinociceptive role of OXT can be reversed by pre-PAG administration of OXT receptor antagonist. The experiment was designed to investigate the effect of OXT on endogenous opiate peptides in the rat PAG during the pain process. The results showed that (1) the concentrations of OXT, L-Ek, M-Ek and β-Ep, not DynA(1-13) in the PAG perfusion liquid were increased after the pain stimulation; (2) the concentrations of L-Ek, M-Ek and β-Ep, not DynA(1-13) in the PAG perfusion liquid were decreased by the OXT receptor antagonist; (3) the increased pain threshold induced by the OXT was attenuated by naloxone, an opiate receptor antagonist; and (4) the concentrations of L-Ek, M-Ek and β-Ep, not DynA(1-13) in the PAG perfusion liquid were increased by exogenous OXT administration. The data suggested that OXT in the PAG could influence the L-Ek, M-Ek and β-Ep rather than DynA(1-13) to participate in pain modulation, i.e. OXT in the PAG participate in pain modulation by influencing the L-Ek, M-Ek and β-Ep rather than DynA(1-13).
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Oxytocin in the periaqueductal gray participates in pain modulation in the rat by influencing endogenous opiate peptides.
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College of Pharmacy, Xinxiang Medical University, Xixiang, Henan 453003, China.
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State Key Laboratory of New Technology for Pharmaceuticals, Jiangsu Provincial Institute for Novel Pharmaceuticals at Taizhou, Yangtze River Pharmaceutical Group, Taizhou, Jiangsu 225321, China.
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Institute for Pharmaceuticals and Medical Science, Guangdong Bangmin Pharmaceutical Co. Ltd., Jianghai Distract, Jiangmen, Guangdong, 529080 China.
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December 2006
Institute for Pharmaceuticals and Medical Science, Guangdong Bangmin Pharmaceutical Co. Ltd., Jianghai Distract, Jiangmen, Guangdong 529000, China.
Previous study has proven that arginine vasopressin (AVP) enhances periaqueductal gray (PAG) secreting enkephalin and endorphin in vivo in the rat. Present work investigated that AVP effect on PAG secretion and synthesis of enkephalin and endorphin in vitro. Radioimmunoassy results showed that AVP increased leucine-enkephalin (L-Ek), methionine-enkephalin (M-Ek), beta-endorphin (beta-Ep) rather than dynorphin A(1-13) (DynA(1-13)) concentrations in PAG slice culture liquid, and V(2) receptor antagonist: d(CH(2))(5)[D-Ile(2), Ile(4), Ala(9)-NH(2)]AVP decreased L-Ek, M-Ek and beta-Ep, not DynA(1-13) concentrations in PAG slice culture liquid in a dose-dependent manner, but V(1) receptor antagonist: d(CH(2))(5)Tyr(Me)AVP did not change these peptide concentrations in PAG slice culture liquid.
View Article and Find Full Text PDFThrough V2, not V1 receptor relating to endogenous opiate peptides, arginine vasopressin in periaqueductal gray regulates antinociception in the rat.
Regul Pept
December 2006
Institute for Pharmaceutical and Medical Science, Guangdong Bangmin Pharmaceutical Co. Ltd., Jianghai District, Jiangmen, Guangdong 529000, China.
Our previous study has proven that central arginine vasopressin (AVP) plays an important role in antinociception, and pain stimulation raises AVP concentration in the periaqueductal gray (PAG). The nociceptive effect of AVP in PAG was investigated in the rat. The results showed that microinjection of AVP into PAG increased pain threshold, whereas microinjection of V2 receptor antagonist-d(CH2)5[d-Ile2, Ile4, Ala9-NH2]AVP into PAG decreased pain threshold in a dose-dependent manner, but local administration of V1 receptor antagonist-d(CH2)5Tyr(Me)AVP did not change pain threshold; Pain stimulation elevated AVP, Leucine-enkephalin (L-Ek), Methionine-enkephalin (M-Ek) and beta-endorphin (beta-Ep), not dynorphinA(1-13) (DynA(1-13)) concentrations in PAG perfuse liquid; PAG pre-treatment with naloxone, an opiate receptor antagonist or V2 receptor antagonist completely reversed AVP-induced increase in pain threshold, however, PAG pre-treatment with V1 receptor antagonist did not influence this effect of AVP administration.
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