Effect of arginine vasopressin on acupuncture analgesia in the rat.

Arginine vasopressin (AVP) has been proven to be involved in the process of pain regulation. This communication was designed to investigate the effect of AVP on acupuncture analgesia in the rat model. The results showed that intraventricular injection (icv) of AVP could enhance acupuncture analgesia in a dose-dependent manner, whereas icv of anti-AVP serum decreased acupuncture analgesia. However, neither intrathecal (ith) nor intravenous injection (iv) of AVP or anti-AVP serum could influence acupuncture analgesia. Electrical acupuncture of "Zusanli" points (St. 36) decreased AVP concentration in the hypothalamic paraventricular nucleus (PVN), and increased AVP concentration in the hypothalamic supraoptic nucleus (SON), periaqueductial gray (PAG), caudate nucleus (CdN) and raphe magnus nucleus (RMN), but did not change AVP concentration in the pituitary, spinal cord and plasma. The effect of AVP on acupuncture analgesia was partly reversed by pretreatment with naloxone, an opiate receptor antagonist. These data suggested that AVP in the brain played a role in the process of acupuncture analgesia in combination with the endogenous opiate peptide system.

Effect of oxytocin on acupuncture analgesia in the rat.

Oxytocin has been demonstrated to be involved in pain modulation. Acupuncture analgesia is a very useful clinical tool for pain relief, which has over 2500-year history in China. The present study investigated the role of oxytocin in acupuncture analgesia in the rat through oxytocin administration and measurement. Central administration of oxytocin (intraventricular injection or intrathecal injection) enhanced acupuncture analgesia, while central administration of anti-oxytocin serum weakened acupuncture analgesia in a dose-dependent manner. However, intravenous injection of oxytocin or anti-oxytocin serum did not influence acupuncture analgesia. Electrical acupuncture of "Zusanli" (St. 36) reduced oxytocin concentration in the hypothalamic supraoptic nucleus, and elevated oxytocin concentration in the hypothalamic suprachiasmatic nucleus, hypothalamic ventromedial nucleus, thalamic ventral nucleus, periaqueductal gray, raphe magnus nucleus, caudate nucleus, thoracic spinal cord and lumbar spinal cord, but did not alter oxytocin concentration in the hypothalamic paraventricular nucleus, anterior pituitary, posterior pituitary and plasma. The data suggested that oxytocin in central nervous system rather than in peripheral organs is involved in acupuncture analgesia.

Only arginine vasopressin, not oxytocin and endogenous opiate peptides, in hypothalamic paraventricular nucleus play a role in acupuncture analgesia in the rat.

Our previous study proved that hypothalamic paraventricular nucleus (PVH) plays an important role in acupuncture analgesia. The effect of acupuncture on the concentrations of arginine vasopressin (AVP), oxytocin (OXT), leucine-enkephaline (L-Ek), beta-endorphin (beta-Ep) and dynorphinA(1-13) (DynA(1-13)) was investigated in rat PVH. Electrical acupuncture of "Zusanli" points (St. 36) 30 min increased the AVP, not OXT, L-Ek, beta-Ep and DynA(1-13) concentrations in PVH tissue using micropunch and radioimmunoassay, which showed a negative relationship between the pain threshold and AVP concentrations in PVH tissue. Electrical acupuncture could elevate the AVP concentrations in PVH perfuse liquid during acupuncture, and then reduce the AVP concentrations in PVH perfuse liquid after acupuncture. But no change in OXT, L-Ek, beta-Ep and DynA(1-13) concentrations was detected in PVH perfuse liquid. Electrical acupuncture decreased the number of AVP, not OXT, L-Ek, beta-Ep and DynA(1-13) immunoreactive cells in PVH using immunocytochemistry. The results suggested that only AVP, not OXT and endogenous opiate peptides in PVH involved acupuncture analgesia in the rat.

Through central arginine vasopressin, not oxytocin and endogenous opiate peptides, glutamate sodium induces hypothalamic paraventricular nucleus enhancing acupuncture analgesia in the rat.

Our previous study proved that the hypothalamic paraventricular nucleus (PVH) plays an important role in acupuncture analgesia. The neuropeptides involving in the PVH regulation of acupuncture analgesia was investigated in the rat. The changes of pain threshold, which was induced by electrical acupuncture of "Zusanli" points (St. 36), were measured as acupuncture analgesia. Microinjection of l-glutamate sodium into the PVH, which only excites the PVH neurons, could dose-dependently enhance the acupuncture analgesia, but microinjection of l-glutamate sodium into the area nearby the PVH did not alter acupuncture analgesia. Removing pituitary did not influence this effect of l-glutamate sodium. Microinjection of l-glutamate sodium into the PVH only increased the arginine vasopressin (AVP), not oxytocin (OXT), leucine enkephaline (L-Ek), beta-endorphine (beta-Ep) and dynorphinA(1-13) (DynA(1-13)) concentrations in the PVH perfuse liquid using radioimmunoassay. Intraventricular injection of anti-arginine vasopressin serum (AAVPS) could completely reverse the effect of microinjection of l-glutamate sodium into the PVH enhancing acupuncture analgesia. Intraventricular injection of naloxone, one opiate peptide antagonist, partly attenuated this effect of l-glutamate sodium, and intraventricular of anti-oxytocin serum (AOXTS) did not change this effect of l-glutamate sodium. The results suggested that l-glutamate sodium induces the PVH enhancing acupuncture analgesia only through AVP, not OXT and endogenous opiate peptides in central nervous system.