Nahoko Yamazaki1, Hiroshi Umeno2 and Yasushi Kuraishi1,*
1Department of Applied Pharmacology, Faculty of Pharmaceutical
Sciences, Toyama Medical and Pharmaceutical University,
Toyama 930 - 0194, Japan
2Institute for Life Science Research, Asahi Chemical Industry
Co., Ohito, Shizuoka 410 - 2321, Japan
* To whom correspondence should be addressed.
Abstract: We investigated the antinociceptive effect of systemic
injection of calcitonin and its mechanisms of action in rats. Subcutaneous
injection of [Asu1,7]eel calcitonin (ECT, 4 UEkg-1Eday-1)
daily for 7 days suppressed nociceptive hypersensitivity induced by formalin
(and by carrageenan); the effect was gradually increased by the repeated
injections and significant effects were observed after administration for
more than 4 days. The antinociceptive action of ECT (4 UEkg-1Eday-1
for 7 days) was inhibited by intracerebroventricular injection of the serotonergic
neurotoxin 5,7-dihydroxytryptamine and serotoninreceptor antagonists methiothepin,
cyproheptadine and ketanserin; methysergide showed an inhibitory tendency.
Intrathecal injections of 5,7-dihydroxytryptamine, methiothepin, cyproheptadine
and ketanserin were without effects on the ECT action. The results suggest
the involvement of serotonin in the brain, but not in the spinal cord, in
the ECT antinociception. Intracerebroventricular or intrathecal injection
of the catecholaminergic neurotoxin 6-hydroxydopamine and intracerebroventricular
injection of the ¿adrenoceptor antagonist phentolamine were also without
effects on the ECT action. A subcutaneous infusion of the opioid receptor
antagonist naloxone inhibited the antinociceptive action of morphine, but
not that of ECT. Thus, adrenergic and opioidergic systems may not play important
roles in the ECT antinociception. The present results suggest that repeated
systemic injection of ECT produces analgesia and that the brain serotonergic
terminals are involved in this action.
Keywords: Calcitonin analgesia, Nociceptive hypersensitivity, Serotonin,
Noradrenaline, Opioid