Journal of Lipid Research, Vol 32, 1489-1499, Copyright © 1991 by Lipid Research, Inc.
Late expression of alpha 2-adrenergic-mediated antilipolysis during differentiation of hamster preadipocytes
JS Saulnier-Blache, M Dauzats, D Daviaud, D Gaillard, G Ailhaud, R Negrel and M Lafontan
INSERM U.317, Institut de Physiologie, Toulouse, France.
In order to study the ontogenesis of the beta- and alpha 2-adrenergic
control of lipolysis during the adipose conversion process, a model based
on preadipocytes isolated from the stromal-vascular fraction of hamster
adipose tissue was developed. When cultured in an ITT (insulin,
transferrin, triiodothyronine) medium supplemented with 2% fetal calf
serum, adipose precursors differentiated into adipose-like cells. On 8-
day-post-confluent differentiating preadipocytes, the rank order of potency
of activation of lipolysis by various beta-adrenergic agonists (BRL37344
greater than norepinephrine = isoproterenol greater than epinephrine
greater than fenoterol) was equivalent to that determined in mature
adipocytes isolated from adult hamster adipose tissue. On 8-
day-post-confluent differentiating preadipocytes, phenylisopropyladenosine
(A1-adenosine agonist) and prostaglandin E1 evoked a strong antilipolytic
response whereas that evoked by UK 14304 and clonidine (alpha 2-adrenergic
agonists) remained undetectable at this step of differentiation. The
activity of UK 14304 and clonidine only appeared on 20- to
25-day-post-confluent differentiating preadipocytes. They induced
dose-dependent antilipolysis with a maximal effect reaching 80-85%
inhibition of adenosine deaminase-stimulated lipolysis. Their action was
blocked by increased concentrations of different alpha 2-adrenergic
antagonists with the following order of potency, RX 821002 greater than
phentolamine much greater than yohimbine. This order of potency was similar
to that determined on mature adipocytes isolated from adult hamsters. Both
the density of the alpha 2-adrenoceptors, identified with the selective
alpha 2-adrenergic radioligand [3H]RX-821002 (19 +/- 1 vs. 30 +/- 1 fmol/mg
protein: P less than 0.01) and the amount of Gi proteins identified by
pertussis toxin-catalyzed ADP-ribosylation (31 +/- 4 vs. 43 +/- 4% of the
amount defined in mature fat cells from adult hamsters: P less than 0.05)
were significantly increased between 8 days and 20-25 days after
confluence, explaining the late emergence of the alpha 2-adrenergic control
of lipolysis during preadipocyte differentiation. In conclusion, the late
emergence of the alpha 2-adrenergic control of lipolysis, which is also
supported by previous data obtained in vivo that demonstrated the age
and/or the fat cell size dependence of alpha 2-adrenoreceptor expression in
mature adipocytes, allows the alpha 2-adrenoceptor to be considered as a
marker of adipocyte hypertrophy.
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