Summary
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1.
The thermoregulatory effects (including metabolic, vasomotor and respiratory activities) produced by an injection of clonidine (1–3 μg in 0.5 μl) into the preoptic anterior hypothalamus were assessed in conscious rats at ambient temperatures (T a) of 8, 22 and 30°C.
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2.
Intrahypothalamic administration of clonidine caused a dose-dependent fall in rectal temperature at T a 8°C and 22°C. The hypothermia in response to clonidine was due to decreased metabolic heat production and/or cutaneous vasodilation. There was no change in respiratory evaporative heat loss.
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3.
The clonidine-induced hypothermic response was attenuated by pretreatment of the rats with either 5,7-dihydroxytryptamine (10 μg, administered intrahypothalamicly, 14 days before clonidine injection), yohimbine (0.2 μg, administered intrahypothalamicly, 10 min before clonidine injection), cyproheptadine (1 μg, administered intrahypothalamicly, 10 min before clonidine injection), or atropine (0.1 μg, administered intrahypothalamicly, 10 min before clonidine injection).
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4.
The data indicate that clonidine may act on α-adrenoceptors located on a serotonin-acetylcholine pathway within the preoptic anterior hypothalamus to induce hypothermia by promoting a reduction in metabolic heat production and/or an enhancement in dry heat loss in rats.
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Lin, M.T., Shian, L.R. & Leu, S.Y. Clonidine-induced hypothermia: Possible involvement of cholinergic and serotonergic mechanisms. Naunyn-Schmiedeberg's Arch. Pharmacol. 326, 124–128 (1984). https://doi.org/10.1007/BF00517308
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DOI: https://doi.org/10.1007/BF00517308