Effects of the 5-HT2A antagonist mirtazapine in rat models of thermoregulation.
Thermoregulation is a complex intercommunicative function requiring coordination between core body temperature (CBT), the central nervous system, and peripheral vasculature. In menopausal women, dysregulation of thermoregulatory mechanisms leads to hot flushes and night sweats. A previous study in ovariectomized (OVX) rats has suggested that mirtazapine can alleviate thermoregulatory dysfunction by blocking 5-HT(2A) receptor signaling. This is in opposition to other work in which 5-HT(2A) receptor blockade appeared to exacerbate thermoregulatory dysfunction in OVX rats. Thus, the goals of the present study were to reexamine the effects of mirtazapine on temperature regulation in OVX rat models and explore further the role of 5-HT(2A) receptor blockade. Mirtazapine exhibited potent functional antagonism (EC(50)=0.62 nM) at the cloned human 5-HT(2A) receptor. In the morphine-dependent model of thermoregulatory dysfunction, mirtazapine (10 mg/kg, i.p.) induced an increase in tail-skin temperature (TST) prior to naloxone administration. In the telemetry model, mirtazapine (0.3-3 mg/kg, i.p.) caused an increase in TST. However, at the highest dose tested (10 mg/kg, i.p.), mirtazapine induced a small but significant decrease in TST followed by an increase in TST. To examine this finding further, mirtazapine's effect on CBT was determined. Administration of mirtazapine (1-3 mg/kg, i.p.) resulted in a slight decrease in CBT but at the 10 mg/kg dose a dramatic decrease (-3.6 degrees C) in CBT was observed. These data support the concept that 5-HT(2A) receptors play a role in temperature regulation but that functional blockade of these receptors by mirtazapine is not a likely mechanism for restoring thermoregulatory processes in OVX rats.
Pawlyk
Aaron C
AC
Women's Health and Musculoskeletal Biology, Wyeth Research N3148B, 500 Arcola Rd., Collegeville, PA 19426, USA. pawlyka@wyeth.com
Cosmi
Scott
S
Alfinito
Peter D
PD
Maswood
Navin
N
Deecher
Darlene C
DC
D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D019584:Hot Flashes / Q000517:prevention & control*; D008803:Mianserin / Q000031:analogs & derivatives* / Q000494:pharmacology; D000078785:Mirtazapine; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology*
D044402:Receptor, Serotonin, 5-HT2A; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists; D008803:Mianserin; D000078785:Mirtazapine