AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 1 14-R20, Copyright © 1995 by American Physiological Society
Functional assessment of the 5-HT 1A-, 1B-, 2A/2C-, and 3-receptor subtypes on food intake and metabolic rate in rats
S. Bovetto and D. Richard
Department of Physiology, Faculty of Medicine, Laval University, Quebec, Canada.
The 5-hydroxytryptamine (5-HT) agonists
(+/-)-8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT), RU-24969,
(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI),
and 1-phenylbiguanide were administered to male Wistar rats to assess the
respective involvement of the 5-HT 1A-, 1B-, 2A/2C-, and 3-receptor
subtypes in the control of food intake and metabolic rate (VO2). Four
series of experiments were carried out, each series addressing the effects
of four doses (including saline or dose 0) of each of the agonists
selected. The drugs were intraperitoneally injected in spontaneously fed
animals. Injections were performed during the first 15 min of either the
diurnal or the nocturnal phases of the light-dark daily cycle. Food intake
and VO2 measurements were carried out over the 12-h periods ensuing after
the agonist injections. The two highest doses of the 5-HT1A-receptor
agonist 8-OH-DPAT led to a quickly appearing but transient elevation of
diurnal VO2. During the night, VO2 was higher when the rats were treated
with 8-OH-DPAT than when they were treated with saline. There was no
significant effect of 8-OH-DPAT on either diurnal or noctural food intake.
The highest dose of RU-24969 induced a significant increase in diurnal VO2,
whereas all doses of RU-24969 blunted the nocturnal rise in metabolic rate
characteristically observed in rats kept under a daily light-dark cycle.
Importantly, RU-24969 induced marked diurnal and nocturnal
hypophagia.(ABSTRACT TRUNCATED AT 250 WORDS)
