Inhibition of brown fat activity during hypothalamic stimulation in the rat.
Previous work has shown that low-level electrical stimulation of the ventromedial hypothalamus (VMH) in anesthetized 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 [Woods, A. J., and 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 radio-labeled 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.
Woods
A J
AJ
Department of Physiology, St. George's Hospital Medical School, Tooting, London, United Kingdom.
Stock
M J
MJ
D002001:Adipose Tissue, Brown / Q000098:blood supply / Q000502:physiology*; D000818:Animals; D001783:Blood Flow Velocity; D001833:Body Temperature Regulation; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D009638:Norepinephrine / Q000008:administration & dosage; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar; D013373:Substance P / Q000008:administration & dosage; D014661:Vasoconstriction / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000008:administration & dosage
D014662:Vasoconstrictor Agents; D013373:Substance P; D009638:Norepinephrine