Chelation of zinc in the extracellular area of the spinal cord, using ethylenediaminetetraacetic acid disodium-calcium salt or dipicolinic acid, inhibits the antinociceptive effect of capsaicin in adult mice
Aa. Larson et Kf. Kitto, Chelation of zinc in the extracellular area of the spinal cord, using ethylenediaminetetraacetic acid disodium-calcium salt or dipicolinic acid, inhibits the antinociceptive effect of capsaicin in adult mice, J PHARM EXP, 288(2), 1999, pp. 759-765
Citations number
54
Categorie Soggetti
Pharmacology & Toxicology
Journal title
JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Capsaicin depolarizes primary afferent C-fibers releasing substance P (SP)
whose N-terminal metabolites appear to play a role in the development of an
tinociception. Because some effects of SP(1-7) are similar to those of zinc
, we tested the hypothesis that zinc in the extracellular area plays a role
in capsaicin-induced antinociception, as measured using the abdominal stre
tch (writhing) assay. Decreases in zinc were achieved by intrathecal (i.t.)
injection of membrane-impermeable compounds: ethylenediaminetetraacetic ac
id disodium-calcium salt (Ca++ EDTA), a calcium-saturated chelator of dival
ent cations, or dipicolinic acid, a zinc chelator. Ten nanomoles of Ca++ ED
TA had no effect on writhing at either 90 min or 24 h after injection, yet
pretreatment with Ca++ EDTA prevented the development of antinociception 24
h after i.t. injection of either 2.8 nmol of capsaicin or 10 nmol of SP(1-
7). One nanomole of dipicolinic acid injected i.t. also blocked capsaicin-
and SP(1-7)-induced antinociception. When injected 24 h after SP(1-7), Ca+ EDTA failed to reverse antinociception. Acute antinociception produced 30
min after injection of SP(1-7) was also blocked when Ca++ EDTA was injected
24 h, but not 60 min, before SP(1-7). Thus, the optimal time of Gate EDTA-
induced hyperalgesia (90 min), described previously, did not correspond to
that of its inhibitory effect on antinociception (24 h). In contrast, we fo
und that the previously described antinociception after an i.t. injection o
f zinc (90 min) is greatly attenuated by 24 h. Thus, zinc appears to be nec
essary, but may not be sufficient, for the long-term antinociceptive effect
of capsaicin, acting downstream from the action of substance P N-terminal
metabolites.