Constant-pressure perfusion of the rat hindlimb shows as well as
adrenergic stimulation of oxygen consumption.
Ye, Ji-Ming, Michael G. Clark, and Eric Q. Colquhoun.
Department of Biochemistry, University of Tasmania, Hobart,
Tasmania, 7001 Australia
APStracts 2:0134E, 1995.
Ye, Ji-Ming, Michael G. Clark, and Eric Q Colquhoun. Constant-pressure
perfusion of the rat hindlimb shows - as well as -adrenergic
stimulation of oxygen consumption. Am. J. Physiol. (Endocrinology and
Metabolism) Isolated rat hindlimbs were perfused at 37 degrees C and
constant physiological pressure (80 0.5 mmHg) while monitoring the
flow rate that was allowed to freely self-adjust. Under these
conditions evidence was obtained for both - and -adrenergic
stimulation of oxygen consumption (O2) in contrast to constant-flow
perfusion which has only convincingly shown -adrenergic stimulation
of O2 in response to adrenergic agents. Addition of norepinephrine
(NE, 1-33 nM) led to an increase in O2 with a maximum of 29% above
the basal value at 3.3 nM even though the flow rate decreased.
Phenylephrine (PE, 3.3-33 nM) and vasopressin (VP, 10-100 pM) also
showed similar, but lesser in magnitude, vasoconstriction-associated
stimulatory effects on O2. Prazosin ( 1-antagonist) completely
reversed the NE-mediated decrease in flow rate and significantly
blocked the increased O2. In contrast, isoproterenol (Iso, 10-1000
nM) increased both flow rate (30%) and O2 (32%). The Iso-stimulated
O2 was not blocked by the 1, 2-antagonist, propranolol (10 M)
although the increased flow was reversed. In the presence of
propranolol (1 or 10 [mu]M), BRL 35135A ( 3-agonist) also stimulated
O2 (18%) without significant change in flow rate. These results lend
further support to the role of 1-adrenoceptor in muscle O2. In
addition there is evidence for the presence of a functional 3
-adrenoceptor as an additional subtype responsible for NE-mediated
thermogenesis in the rat hindlimb.
Received 12 April 1995; accepted in final form 22 June 1995.
APS Manuscript Number E171-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.