Inhibition of brown fat activity during hypothalamic stimulation in
the rat.
Woods, Anthony J, and Michael J Stock.
Department of Physiology, St. George's Hospital Medical School,
Tooting, London, SW17 ORE, UK
APStracts 2:0293R, 1995.
Previous work has shown that low-level electrical stimulation of the
ventromedial hypothalamus (VMH) in anaesthetized rats produces a
sustained decrease (Phase 1) in interscapular brown adipose tissue
(IBAT) temperature, followed by a rise (Phase 2) after the stimulus
has stopped [A.J. Woods & M.J. Stock, Am. J. Physiol. 266
(Regulatory, Integrative Comp. Physiol. 35): R328-R337, 1994]. In
this study, rat oxygen consumption was found to decrease (24 %), and
then increase (74 %) during Phase 1 and 2, respectively. The effect
of norepinephrine, [alpha]-adrenoceptor antagonists, Substance P and
neuropeptide Y, with and/or without VMH stimulation, suggested that
vasoconstriction was unlikely to account for the Phase 1 decreases in
thermogenesis and temperature. However, measurement with
radiolabelled microspheres showed that IBAT capillary blood flow was
reduced by 70 % during Phase 1 and this, plus a 50 % decrease in
blood oxygen extraction, indicated that Phase 1 could be due to
vasodilatation of arteriovenous anastomoses. It was postulated that
Phase 1 resulted from release of neuropeptides, such as Substance P,
causing diversion of arterial blood away from IBAT capillaries,
thereby increasing convective heat loss and inhibiting heat
production during Phase 1.
Received 21 March 1995; accepted in final form 18 October 1995.
APS Manuscript Number R190-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 November 95