AJP - Endocrinology and Metabolism, Vol 259, Issue 1 E80-E88, Copyright © 1990 by American Physiological Society
Selective reduction of alpha 2-adrenergic responsiveness in hamster adipose tissue during prolonged starvation
C. Carpene, J. Galitzky, J. S. Saulnier-Blache and M. Lafontan
Institut National de la Sante et de la Recherche Medicale, U 317, Toulouse, France.
The influence of fasting on the dual adrenergic control of adipose tissue
lipolysis was investigated in hamsters because in this species the
adipocytes exhibit both beta-stimulatory and alpha 2-inhibitory adrenergic
responses. In adipocytes from fed animals, the number of alpha 2-receptors
(identified with [3H]clonidine and [3H]RX 821002) was greater than that of
beta-receptors. As in humans, the alpha 2-adrenoceptor number was greater
in adipocyte membranes from subcutaneous (inguinal and popliteal) than from
internal (perirenal and epididymal) adipose tissues. Despite this
difference in alpha 2-adrenoceptor number, the antilipolytic responses to
the alpha 2-agonists clonidine and UK 14304 were similar in the two
tissues. Food deprivation for a period of 1-6 days induced a net depletion
of both adipose tissues. In 6-day starved animals the number of adipocyte
alpha 2-adrenoceptors and the maximal antilipolytic effect of UK 14304 were
less than 50% of those in fed controls. In contrast, the antilipolytic
responses to phenylisopropyladenosine or prostaglandin E1 remained
unchanged. Starvation induced a decrease in alpha 2-adrenoceptor number and
an increase in beta-adrenergic sensitivity that were greater in adipocytes
from subcutaneous than from internal fad pads. The data suggest that the
adipocyte beta- and alpha 2-adrenoceptors are independently regulated
during starvation. In the adipocyte, the alpha 2-antilipolytic responses
and the alpha 2-adrenoceptor levels are dependent on the extent of the
adipose mass; they are particularly reduced in emaciated hamsters.
