Comparison of trophic effects of norepinephrine, insulin and igf-1
in mouse brown adipocytes.
Desautels, M., B. Bhaumick, and J. I. Ram.
Dept. of Physiology and Dept of Medicine, College of Medicine,
University of Saskatchewan, Saskatoon, Saskatchewan, Canada, S7N
5E5
APStracts 2:0342R, 1995.
The objective of this work was to evaluate if insulin, like
norepinephrine (NE), exerts direct growth effects in brown
adipocytes, as assessed by changes in rates of protein labelling with
[35S]methionine. Mouse brown adipocytes isolated by tissue
collagenase digestion were incubated for up to 24h +/- NE in DME 's
medium with albumin, calf serum and antibiotics. There was a 40% cell
loss and a 50% decrease in cell content of succinate dehydrogenase
(SDH) activity over 24h. Both cell recovery and SDH content
significantly improved in the presence of NE. In addition, NE
increased [35S]methionine incorporation into proteins in both
cytosolic and mitochondrial compartments. These effects of NE were
inhibited by propranolol. Both insulin and IGF-1 receptors were
detected in brown adipocytes, with insulin receptors in much greater
concentration. Increased protein labelling was observed when brown
adipocytes were incubated for 4h with 0.2-5 nM insulin in the absence
of serum. This effect was small (30% stimulation) compared to the
200-350% increase observed with NE, while 5 nM IGF-1 had no effect.
These results indicate direct trophic actions of both NE and insulin
in mouse brown adipocytes with the effects of NE an order of
magnitude greater than those of insulin.
Received 24 April 1995; accepted in final form 29 November 1995.
APS Manuscript Number R250-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 12 December 95